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TABLE OF CONTENTS
L IS T O F T A B L E S .............................................................................. ................ .. v i
LIST OF FIGURES .................. .............................. ...... .............. .. vii
A B STR A C T ................. .............................................................................................. ix
1 IN TR OD U CTION ....................................... ................ .. ........ ..
2 R E L A T E D W O R K .............................................................................. .. ........ 5
N network Layer Handoff M anagem ent ................................................................5
M obile IP ............................................................ . 6
A g ent D iscov ery ............................................... .. ...... .. ...... ........ ...... 8
R eg istratio n ....................................................................... 10
T unneling ........................................ 12
H ierarchical M IP .................... ................. ...................................... 15
C cellular IP ................................................................. ..... ............. 16
R outing ..................................... .............. ..................... 17
Handoff ................................. ............................... ......... 17
Paging ......................................... 19
HAW AII ........................................... ..................... ........ 20
W irele ss L A N ............................................................................................... 2 4
Technology Overview................................ ...... .......... 24
The IEEE 802.11 Established Standards ........................................... 25
Standard 802 .11.................................................... 26
Standard 802.11b......................... ...............28
Standard 802.11a......................... ...............29
Standard 802.11g................................. ........................31
Pending Specifications W within the 802.11 Suite ................... ............. 33
The IEEE 802.11 Wireless LAN Architecture ......... ............. .. .........33
W wireless LA N Station ......................................................... ............... 34
B asic Service Set (B SS) ............... .............. ...... ...... ...................34
Independent Basic Service Set (IBSS)........................................ 34
Infrastructure Basic Service Set(BSS) .................................................. 35
Extended Service Set (ESS) .......................................... ...............35
Wireless LAN Handoff Management......................................................35
Wireless LAN Handoff Management Frames ................. .................. 35
IEEE 802.11 H andoff Procedure ...................... ..........................................37
Techniques to Reduce IEEE 802.11 Handoff Time.................................39
Low Latency Handoff Mechanisms for MIP over 802.11 Network .............. 41
L2 Triggers....................................................................... 42
P re-R eg istratio n .............................................................. .. .......... .... .4 2
Post-Registration .................. ............................ ......... .. ...... .... 43
L location Tracking ............ .... ...................................................... ...... .... ... .. 44
O their R elated W ork ..................................... ...... ....................... 46
3 PERFORMANCE OF MIP OVER WLAN AT DIFFERENT SPEEDS.............49
M IP over W wireless LAN Handoff Procedure .................................................49
R A M ON Testbed .................. ..................................... .. ........ .... 50
H ardw are A rchitecture.............................................................. ............... 51
Softw are A architecture ............................................................................ 52
Perform ance Evaluation ................................... ............................................ 53
Emulation Scenario and Result.................. .............................................. 53
Experim ental Result Analysis................................................ .................. 57
4 QUANTITATIVE ANALYSIS OF THE MIP OVER WIRELESS LAN HANDOFF
LATENCY ...................................................................... .... ......... ................... 63
L ayer 2 H andoff L atency ........................................................................ ... ... 63
Layer2 M movement Detection Phase............... .............................................64
Layer2 AP Searching Phase................................ .......... .... ............... 65
Layer2 R association Phase ........................................ ....... ............... 66
L ayer 3 H andoff L atency............................ ............................. ............... 66
Agent Discovery ....... .... ...................... .................... .. 66
Registration .......... ......... .... .................... ................. 68
Layer 4 Handoff Latency...................... ........... ................... 69
Quantitative Analysis of the Handoff Latency ............. .................................. 70
5 SPEED ADAPTIVE MIP AND ITS PERFORMANCE EVALUATION..........73
Traditional MIP over WLAN Handoff Procedure .............................................73
Algorithm of Speed Adaptive M IP ............... ............................................. 77
Implementation of Speed Adaptive M IP................................. ...... ...............82
H om e A g ent .............. ....... .............................................. 82
Mobile Node ...... ......... ......... .......... ........84
Foreign Agent ...... ............... ..... ...............86
Evaluation of Speed Adaptive Extension for MIP ....................................87
6 SUMMARY AND FUTURE WORKS..................................... 90
LIST O F REFEREN CE S ......... .................... ......... .................................... 91
BIOGRAPHICAL SKETCH ........... ..... ............... ............... 97
LIST OF TABLES
2-1 Characteristics specified by the 802.11 standard............................................. 28
2-2 Characteristics specified by the 802.1 lb standard...........................................29
2-3 Characteristics specified by the 802.lla standard.....................................................31
2-4 Characteristics specified by the 802.1 1g standard...........................................32
2-5 Comparison of characteristics specified within the IEEE 802.11 suite....................33
3-1 Average throughput at different speeds and AP distances.......................................58
4-1 Handoff latency distribution of MIP over WLAN .................................................71
5-1 Average throughput for speed-adaptive MIP ................................... .................89
LIST OF FIGURES
2-1 M acro and M icro m obility ........................................ ................................. 6
2-2 Three functional entities of M IP ........................................................................ .. 8
2-3 IP in IP encapsulation and minimal encapsulation..................... ...............13
2-6 802.11 wireless LAN handoff procedure .........................................................39
3-1 RAM ON testbed architecture........................................................ ............. 51
3-2 D ynam ic M IP sam ple scenario........................................... ........................... 53
3-3 Time-sequence graph at speed 20m/s and AP distance 1000m.............................54
3-4 Throughput graph at speed 20m/s and AP distance 1000m............................... 54
3-5 Time-sequence graph at speed 80m/s and AP distance 1000m .............................55
3-6 Throughput graph at speed 80m/s and AP distance 1000m................................ 55
3-7 Time-sequence graph at speed 10m/s and AP distance 500m.............................56
3-8 Throughput graph at speed 10m/s and AP distance 500m.....................................56
3-9 Time-sequence graph at speed 40m/s and AP distance 500m.............................57
3-10 Throughput graph at speed 40m/s and AP distance 500m. ..................................57
3-11 Average throughputs vs speeds. ........................................ ......................... 59
3-12 Time-sequence graph at AP distance 1000m with speed 20m/s without handoff...60
3-13 Time-sequence graph at AP distance 1000m with speed 80m/s without handoff...60
3-14 Average throughput vs handoff rate..................................................62
4-1 Handoff procedure with message exchange............................................................67
4-2 LCS handoff latency for M IP ...................................................... ...................67
4-3 ECS handoff latency for M IP ...................................................... ...................68
4-4 Handoff procedure with handoff latency distribution.....................................72
5-1 Traditional M IP Handoff Procedure.................................................................... 74
5-2 FA Set size vs handoff rate...................................................................... 79
5-3 Normal vendor/organization specific extension............................. ...............80
5-4 SA -M IP handoff procedure ......................................................... .............. 81
5-5 Function flowchart of registration in HA ...................................... ....... ............ 84
5-6 R registration request m message form at ............................ .................. .....................85
5-7 Registration request message extension format ................................ ............... 85
5-8 Function flowchart of sending registration request........................................86
5-9 Function flowchart for FA handling registration request ........................................87
5-10 Time-sequence graph at speed 60m/s and AP distance 1000m .............................88
5-11 Time-sequence graph at speed 80m/s and AP distance 1000m .............................88
5-12 Average throughput vs. handoff rate.............................. ...............89
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
A SPEED ADAPTIVE MOBILE INTERNET PROTOCOL
OVER WIRELESS LOCAL AREA NETWORK
Chair: Abdelsalam (Sumi) Helal
Major Department: Computer and Information Sciences and Engineering.
This dissertation presents two novel contributions in the area of mobile network
communication. The first is the performance/moving speed relationship of Mobile Internet
Protocol(MIP) over Wireless Local Area Network(LAN). In this dissertation, the rapid
mobility of MIP over Wireless LAN is emulated on a testbed. The performance of MIP
over Wireless LAN at different moving speeds is evaluated. The result shows that current
MIP protocol is not suitable for rapid moving environments. This dissertation analyzes the
emulation results and depicts the relationship between the performance and the moving
speed of the mobile devices. This relationship is used in a novel protocol, which is the
second contribution, to improve the performance of MIP over Wireless LAN in rapid
moving environments. The second contribution is the Speed Adaptive Mobile IP. In the
Speed Adaptive Mobile IP, Mobile Node's registration message is extended by speed
extension. With the speed information popularized in the mobile IP network, the behavior
of the Speed Adaptive Mobile IP will automatically adapt to the speed of the Mobile Node
so that the performance of the Speed Adaptive Mobile IP won't decline dramatically in a
rapid moving environment. At the same time, the Speed Adaptive Mobile IP only uses
reasonable resources that are enough for seamless handoff The emulation result shows
that the Speed Adaptive MIP greatly improves the performance of MIP over Wireless
LAN in rapid-moving environments.
The population living on the world wide internet is exploding. According to the
analysis of Internet usage across more than 50 countries, the latest report from Computer
Industry Almanac(CIA) Inc.'s shows that as of the end of March 2004, there are 945
millions of internet users world wide. The report also indicates 1.12 billion Internet users
projected for the end of 2005, and 1.46 billion for 2007. A significant number will be using
wireless devices such as Web-enabled cell phones and PDAs to go online. In America,
27.9% of 193 millions of internet users are using wireless internet. At the end of 2007,
46.3% of 263 millions will be wireless internet users.
Throughout history, the economic wealth of people or a nation has been closely tied
to efficient methods of transportation. The transportation speed is becoming faster and
faster. A person can drive a car on high way at speed of 70mph. Some high speed trains
such as France TGV, Japanese bullet, German maglev can travel at speeds of over
300km/hour(186mph). Could those people surf the internet, communicate with families
and enjoy an online movie while traveling at high speeds? Could the current network
infrastructure support rapid mobility?
While TCP/IP successfully overcomes the barriers of time and distance in a wired
network, mobile IP is a promising technology to eliminate the barrier of location for the
increasing wireless internet usage. Third generation (3G) services combine high speed
mobile access with IP-based services. With access to any service anywhere, anytime, from
one terminal, the old boundaries between communication, information sharing, media
distribution will disappear. 3G enables users to transmit voice, data, and even moving
images whenever and wherever. But, 3G networks are not based on only one standard, but
a set of radio technology standards such as cdma2000, EDGE and WCDMA. Mobile IP
[Perk02] can be the common macro mobility management framework to merge all these
technologies in order to allow mobile users to roam between different access networks.
These radio technologies only need to handle Micro mobility issues such as radio specific
mobility enhancements. Mobile IP is different from other efforts for doing mobility
management in the sense that it is independent to any specific access technology[Mobi03].
Wireless local area networks (WLAN) have experienced incredible growth over
recent years. WLANs provide wireless users with an always-on, wireless connection to
each other, to local area networks (LAN), to wide area networks (WAN), and to the
Internet. The major benefit of WLANs over wired network is its flexibility and mobility
[Kapp02]. There are currently two major WLAN standards, and both operate using radio
frequency (RF) technology. The two standards have heretofore been colloquially referred
to as 802.1 lb and 802.1 la. 802.1 lb operates in the radio frequency (RF) band between 2.4
and 2.485GHz while 802.1 la operates between 5.15-5.35GHz and 5.725-5.825GHz. The
performance of both 802.1 lb and 802.1 la decreases as your distance from the antenna
increases. This degradation is neither linear nor granular. Instead, each wireless
specification has a handful of pre-defined bandwidth levels at which it can operate
(802.1 lb has four, while 802.1 la has seven). Take 802.1 lb as an example. Within a closed
office, the bandwidth will drop from 11, 5.5, 2 to Imbps when the distance increases from
25, 35, 40 to 50 meters. For outdoors, the bandwidth will drop from 11, 5.5, 2 to Imbps
when the distance increases from 160, 270, 400 to 550 meters. So if you want to keep a
high throughput, you have to reduce the distance between access points. For example, to
keep 5.5mbps when outdoors, the distance between two access points should be no more
than 500 meters. The smaller the cell the higher the bandwidth you get.
The use of current cellular/PCS high data rate services for data networking is not
economically feasible due to high usage costs. The success of WLAN lies in the following
factors. First, WLAN uses license-free band. 802.1 lb and 802.1 Ig use Industrial,
Scientific, and Medical (ISM) 2.4GHz radio band while 802.1 la operates in the 5 GHz
National Information Infrastructure (UNII) radio band. Second, WLAN offers reasonably
high available data rates. 802.1 lb can transmit data up to 11 Mbps while 802.1 Ig and
802.1 la can provide data rate up to 54Mbps. Finally, there are lots of commercially
available WLAN products around the world. Even though WLAN has been designed and
used for mostly indoor applications, the possible use of WLAN technologies for high
mobility outdoor applications, such as, telemetry, traffic surveillance, rescue operations,
and outdoor data networking can provide reasonably high data rates at minimal operational
costs. For outdoor applications WLANs provide support for link-layer handoff, which is
used to switch a mobile node (MN) from one access point (AP) to another. For WLANs
connected by an IP backbone, Mobile IP[Perk02] is the protocol for location management
and network-layer handoff. These attractions led us to investigate the performance of MIP
over WLAN in outdoor rapid moving environments.
In this dissertation, Chapter 2 introduces related research in the area of mobile
network protocols, wireless LAN standards, layer 3 and layer 2 handoff mechanisms and
location tracking technologies. Chapter 3 introduces a protocol evaluation testbed,
RAMON. The performance of MIP over wireless LAN and its relationship to speed are
shown in Chapter 3 as well. Chapter 4 breaks down the handoff procedure of MIP over
wireless LAN and presents a quantitative analysis of the handoff latency. A speed adaptive
MIP protocol is proposed in Chapter 5 and the performance for this protocol is evaluated.
Chapter 6 summarizes the dissertation and presents future works.
Mobile computing and networking try to provide users confident accesses to the
Internet anytime, anywhere. One big challenge for mobile computing and networking is
how to manage global and seamless roaming among various access technologies. Mobility
management contains two components: location management and handoff management
[Akyi99]. In wireless network, there are two kinds of roaming, interdomain and
intradomain roaming. Interdomain roaming, also called macromobility, refers to roaming
among different domain of systems. Intradomain roaming, also called micromobility,
refers to roaming among different cells in the same domain or system. In this chapter we
will introduce network layer handoff management of macro/micro mobility, wireless LAN
protocol standards and technologies to reduce handoff latency for wireless LAN and
Mobile IP network. At the end of this chapter, some research works on location tracking
will be introduced.
Network Layer Handoff Management
Macro Mobility protocols aim to handle global moving of users. An example is
mobile IP[RFC3344]. Micro-mobility protocols are used to handle local moving (e.g.,
within a domain) of mobile hosts without interaction with the Mobile IP enabled internet.
Hierarchical MIP, Cellular IP, IntraDomain Mobility Protocol(IDMP), HAWAII are
examples of micro mobility protocols. Figure 2-1 shows the macro and micro mobility.
Macro mobility -SA
cro mobility Micro mobility.
Figure 2-1 Macro and Micro mobility
IP mobility support for IPv4 is specified in RFC3344. The Mobile IP protocols
support transparency above the IP layer, including maintenance of active TCP connections
and UDP port bindings. It allows a node to continue using its 'permanent' home address no
matter where the node physically attached to. Therefore, ongoing network connections to
the node can be maintained even as the mobile host is moving around the internet.
Mobile IP defines three functional entities where its mobility protocols must be
implemented: Mobile Node(MN), Home Agent(HA) and Foreign Agent(FA).
MN is a movable device whose software enables network roaming capabilities.
FA is a router that may function as the point of attachment for the MN when it roams
to a foreign network, delivering packets from the HA to the MN. Mobile IP works by
allowing the MN to be associated with two IP addresses: a home address and a dynamic,
Care-of Address(CoA). Home address is fixed IP address the MN gets from its home
network. The CoA is the termination point of the tunnel toward the MN when it is on a
foreign network. CoA changes at each new point of attachment to the Internet.
HA is a router on the home network serving as the anchor point for communication
with the MN; it tunnels packets from a device on the Internet, called a Correspondent
Node(CN), to the roaming MN. (A tunnel is established between the HA and a reachable
point for the MN in the foreign network.). The HA maintains an association between the
home IP address of the MN and its CoA, which is the current location of the MN on the
foreign or visited network. The MN's movement is invisible to the CN.
Figure 2-2 shows the three functional entities and routing of datagrams transmitted
from a MN away from home. When a MN moves, it finds an agent on its local network by
the Agent Discovery process. It listens for Agent Advertisement messages sent out by FAs
or HAs. If it doesn't hear these messages it can sent Agent Solicitation message to ask for
it. From the Agent Advertisement message, the MN determines whether it is on its home
network or a foreign one. The MN works like any fixed node when it's on its home
network. When the MN moves away from its home network, it obtains a CoA on the
foreign network. The MN registers each new CoA with its HA while away from home.
This may be done either directly between the MN and the HA, or indirectly using the FA as
a conduit. The packets from CN are tunneled by HA to FA then to the CoA. The packets
from MN to CN are either directly routed to the CN or reverse-tunneled from FA to HA
then to the CN.
Figure 2-2 Three functional entities of MIP
MIP has three main processes, Agent discovery, registration and tunneling.
The Mobile IP agent discovery process makes use of ICMP Router Advertisement
Protocol(RFC 1256) and add one or more MIP extensions. HAs and FAs periodically
broadcast a router advertisement ICMP messages with an advertisement extension. The
router advertisement portion of the message includes the IP address of the router. The
advertisement extension includes additional information such as lift time, care-of-address,
etc. A MN listens for these agent advertisement messages. If a MN needs to get a care-of
address and does not want to wait for that long time, the MN can broadcast or multicast an
agent solicitation(also an ICMP message) and then listens for the agent advertisement
messages. Another important rule of agent discovery process is movement detection. This
can be done in two ways. One way is to make use of Lifetime field in the agent
advertisement message. When a MN receives an agent advertisement from a FA that it is
currently using or that it is now going to register to, it records the lifetime field as a timer.
If the timer expires before the agent receives another advertisement from the agent, then
the node assumes that it has lost contact with that agent. In this situation, the MN may
choose to wait for another advertisement or to send an agent solicitation. Another way is to
use network prefix. The MN checks whether any newly received agent advertisement is on
the same network as the current care-of address of the node. If it is not, the MN assumes
that it has moved and uses the new advertisement.
The MN can also get a collocated care-of-address acquired from a Dynamic Host
Configuration Protocol (DHCP) server. In this case, the MN acts as its own FA.
The agent advertisement extension consists of the following fields:
0 1 2 3
01 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901
I Type I Length I sequence Number I
| Registration Lifetime IRIB|HIFMIGI|rTTI reserved I
| zero or more Care-of Addresses |
Type: 16, indicates that this is an agent advertisement.
Length: (6 + 4N), where N is the number of care-of addresses advertised.
Sequence number: The count of agent advertisement messages sent since the
agent was initialized.
Lifetime: The longest lifetime, in seconds, that this agent is willing to accept a
registration request from a mobile node.
R: Registration required. Registration with this foreign agent (or another foreign
agent on this link) is required even when using a co-located care-of address.
B: Busy. The foreign agent will not accept registrations from additional mobile
H: This agent offers services as a home agent on this network.
F: This agent offers services as a foreign agent on this network.
M: This agent can receive tunneled IP datagrams that use minimal encapsulation.
G: This agent can receive tunneled IP datagrams that use Generic Routing
r: Set as zero; ignored on reception.
T: Foreign agent supports reverse tunneling.
Care-of Address(es): The care-of address or addresses supported by this agent
When a MN realizes that it is on a foreign network and has acquired a
care-of-address, it needs to notify the HA by sending a registration request message so that
the HA can forward IP packets between MN and CN. There are two kinds of registration
messages, registration request and registration reply, both sent to User Datagram Protocol
(UDP) port 434. The MN sends the request to the FA, which then relays the request to the
home agent. If the MN is using a collocated care-of-address, the MN sends its request
directly to the HA, using collocated care-of-address as the source IP address of the request.
The registration request message consists of the following fields:
0 1 2 3
01 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901
I Type ISIBIDIMIGI|rTI|I Lifetime
| Home Address
I Home Agent I
I care-of Address |
+ Identification +
Type: 1, indicates that this is a registration request.
S: Simultaneous bindings. When set, the mobile node is requesting that the home
agent retain its prior mobility bindings. The home agent will forward multiple
copies of the IP datagram, one to each care-of address currently registered for this
B: Broadcast datagrams. Indicates that the mobile node would like to receive
copies of broadcast datagrams that it receives if it were attached to its home
D: Decapsulation by mobile node. The mobile node is using a collocated care-of
address and will decapsulate its own tunneled IP datagrams.
M: Indicates that the home agent should use minimal encapsulation.
G: Indicates that the home agent should use GRE encapsulation.
R: Sent as zero; ignored on reception.
T: Reverse Tunneling requested.
X: Set as zero; ignored on reception.
Lifetime: The number of seconds before the registration is considered expired. A
value of zero is a request for deregistration.
Home address: The home IP address of the mobile node.
Home agent: The IP address of the mobile node home agent.
Care-of address: The IP address for the end of the tunnel. The home agent
should forward IP datagrams that it receives with the mobile node home address
to this destination address.
Identification: A 64-bit number generated by the mobile node, used for matching
registration requests to registration replies and for security purposes.
Extensions: authentication extension must be included, and other optional
The registration reply message consists of the following fields:
0 1 2 3
01 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901
S Type I code | Lifetime |
| Home Address |
| Home Agent
+ Identifi cation +
Type: 3, indicates that this is a registration reply.
Code: Indicates result of the registration request. 0 for registration accepted, 77
for invalid care-of address, etc.
Lifetime: If the code field indicates that the registration was accepted, the
number of seconds before the registration is considered expired. A value of zero
indicates that the mobile node has been deregistered.
Home address: The home IP address of the mobile node.
Home agent: The IP address of the mobile node home agent.
Identification: A 64-bit number used for matching registration requests to
Extensions: authentication extension must be included, and other optional
The identification field of the registration request and reply messages and the
authentication extension are used to protect replay attack. The Identification value enables
the mobile node to match a reply to a request. Two methods are described in RFC 3344:
timestamps mandatory ) and noncess" (optional).
An authentication extension consists the following fields:
Type: Used to designate the type of this authentication extension. 32 for MN-HA,
33 for MN-FA, 34 for FA-HA.
Length: 4 plus the number of bytes in the authenticator.
Security parameter index (SPI): An index that identifies a security context
between a pair of nodes. This security context is configured so that the two nodes
share a secret key and parameters relevant to this association (for example,
Authenticator: The value used to authenticate the message. The default
authentication algorithm uses HMAC-MD5[RFC2104] to compute a 128-bit
"message digest" of the registration message.
After a successful registration, the home agent must be able to intercept datagrams
destined to the mobile node and tunnel them to the mobile node's care-of-address. The
tunneling can be done by one of several different encapsulation algorithms, IP in IP
encapsulation [RFC2003], Minimal encapsulation [RFC2004] and GRE encapsulation
[RFC 1701]. By default, home agents and foreign agents must support tunneling datagrams
using IP in IP encapsulation. Any mobile node that uses a collocated care-of address must
support IP in IP encapsulation. In IP-within-IP encapsulation, the original entire IP
datagram becomes the payload in a new IP datagram. The original IP header is unchanged
except to reduce Time To Live (TTL) by 1. The outer IP header is a full IP header. Two
fields are copied from the inner IP header: The version number, 4, which is the protocol
identifier for IPv4, and the type of service field. Figure 2-3 is the IP in IP encapsulation and
minimal encapsulation format.
u mi I nuimal foihgl IP hn te b -rtwen the origina lIP-------
a hea erIs'- .'- Ow t oM form a new out e I
c 'B R IfIl -- ---
Figure 2-3 IP in IP encapsulation and minimal encapsulation
Minimal encapsulation results in less overhead but is little complicated than IP in IP
encapsulation. It can only be used if the MN, HA, and FA all agree to use it. With minimal
and the original IP payload. The original IP header is modified to form a new outer IP
header. The minimal forwarding IP header includes the following fields:
Protocol: Copied from the protocol field in the original IP header. It identifies the
protocol type of the original IP payload.
S: If 0, the original source address is not present, and the length of this header is 8
octets. If 1, the original source address is present, and the length of this header is
Header checksum: Computed over all the fields of this header.
Original destination address: Copied from the Destination Address field in the
original IP header.
Original source address: Copied from the Source Address field in the original IP
header. This field is present only if the S bit is 1. The field is not present if the
encapsulator is the source of the datagram.
The new outer IP header is modified from the original IP header. The modified field
are as following.
Total length: Incremented by the size of the minimal forwarding header (8 or
Protocol: 55, indicts the following header is minimal IP encapsulation header.
Header checksum: recomputed over all the fields of this header.
Source address: The IP address of the encapsulator, typically the home agent.
Destination address: The IP address of the end of the tunnel, the care-of address.
Mobile IP is a macro mobility management protocol. MIP-based mechanisms use a
flat hierarchy, whereby every change in the MN's point of attachment requires a global
binding update. Frequent global binding updates can not only incur high latency, thereby
making rapid handoffs impossible, but also significantly increase the overall signaling
overhead, especially when the number of MNs increases. Various solutions have been
proposed to solve this problem. All these solutions implicitly or explicitly use a concept of
micro-mobility regions where registrations with the home agent are not necessary if the
MN is moving within these regions. Only if the MN moves between micro-mobility
regions, registrations with the HA would be required. Micro-mobility management
protocols are designed to reduce the high handoff latency of Mobile IP by handling
mobility within micro-mobility regions.
The micro-mobility protocols can be categorized in two types: Hierarchical
Tunneling and Mobile-Specific Routing [Camp02]. Hierarchical tunneling schemes rely
on a tree-like structure of FAs. In Hierarchical tunneling schemes HA delivers
encapsulated traffic to the root FA. Each FA on the tree decapsulates and then
re-encapsulates data packets while they forward the data down the FA tree towards the
MN's point of attachment. As the MN moves between two FAs, location updates are made
at the optimal point in the tree, which is the common root of the two FAs. Hierarchical
Mobile IP[Soli02]) is an example of Hierarchical tunneling scheme.
Mobile-Specific Routing schemes avoid the overhead introduced by decapsulation
and re-encapsulation in hierarchical tunneling schemes. These proposals use mobile
specific routes to forward packets toward a MN's point of attachment. Examples of
micro-mobility protocols that use mobile-specific routing include Cellular IP and
The Hierarchical Mobile IP (HMIP)
employs a hierarchy of FAs to locally handle
Mobile IP registration. In this protocol MNs
send mobile IP registration request messages FA
to update their respective location,
information. The Registration messages -
F F At
establish tunnels between neighboring FAs /
along the path from the mobile host to a
gateway foreign agent(GFA). Packets Figure 2-4 Hierarchical MIP
addressed to mobile hosts travel through these tunnels from the GFA to MN. Figure 3-4
illustrates the operation of Hierarchical Mobile IP. The red dash arrow is a regional
registration, which only need to reach a local entity, GFA. The blue real arrow is a normal
registration, which have to traverse the whole network to the HA. For the purposes of
managing hierarchical tunneling the location register is maintained in a distributed form by
a set of Mobility Agents (MA), i.e. GFAs. Each MA reads the original destination address
of the incoming packets and searches its visitor list for a corresponding entry. The entry
contains the address of the next MA one level lower in the hierarchy. Such entries are
created and maintained by registration messages transmitted by MNs. [Soli02]
The Cellular IP (CIP) protocol[Cam99] from Columbia University and Ericsson
supports fast handoff and paging techniques. Cellular IP inherits features found in cellular
networks, such as, seamless mobility, passive connectivity and paging, for mobile IP hosts.
It uses Mobile IP to provide interconnectivity between a set of Cellular IP access networks,
which in turn provide a cellular internetworking environment. The Cellular IP access
networks will be connected to the Internet via gateway routers. In that case, host mobility
between gateways(i.e., Cellular IP access networks) will be managed by Mobile IP, while
mobility within access networks will be handled by Cellular IP. MNs attached to the
network use the IP address of the gateway as their Mobile IP care-of address. The data
packets from CN to MN will be first routed to MN's HA and then tunneled to the gateway.
The gateway "detunnels" packets and forwards them toward base stations. Inside the
Cellular IP network, data packets are routed directly to the MN. Data packets from MN to
CN are first routed in the cellular IP network to the gateway and from there on to the
HA[CampOO]. The following presents an overview of the Cellular IP routing, handoff and
In Cellular IP, location management and handoff support are integrated with routing.
To minimize control messaging, regular data packets transmitted by mobile hosts are used
to refresh host location information. Uplink packets are routed from MN to the gateway
on a hop-by-hop basis. The path taken by these packets is cached in base stations, which is
call route cache. Cellular IP uses mobile originated data packets to maintain reverse path.
This path is used to route downlink packets addressed to a mobile host. When the mobile
host has no data to transmit then it periodically sends empty IP packets to the gateway to
maintain its downlink routing state. The loss of downlink packets when a mobile host
moves between access points is reduced by customized handoff procedures. Cellular IP
supports two types of handoff scheme, hard handoff and semi-soft handoff
The Cellular IP hard handoff algorithm is based on simple approach that trades off
some packet loss in exchange for minimizing handoff signaling. Hard handoff causes
packet losses proportional to the round-trip time and to the downlink packet rate. Mobile
hosts listen to beacons transmitted by base stations and initiate handoff based on signal
strength measurements. To perform a handoff, a mobile host tunes its radio to a new base
station and sends a route-update packet. The route-update message creates routing cache
mappings on route to the gateway hence configures the downlink route to the new base
Cellular IP semi-soft handoff exploits the notion that some mobile hosts can
simultaneously receive packets from the new and old base stations during handoff During
semi-soft handoff a mobile host may be in contact with either the old and new Base
Stations and receives packets from them. Packets intended to the mobile host are sent to
both Base Stations, so when the mobile host eventually moves to the new location it can
continue to receive packets without interruption. To initiate semi-soft handoff, the moving
mobile host transmits a route-update packet to the new Base Station and continues to listen
to the old one. The S flag is set in this route-update packet to indicate semi-soft handoff
Semi-soft route-update packets create new mappings in the Route and Paging Cache
similarly to regular route-update packets. When the semi-soft route-update packet reaches
the crossover node where the old and new path meet, the new mapping is added to the
cache instead of replacing the old one. Packets sent to the mobile host are transmitted to
both Downlink neighbors. When the mobile host eventually makes the move then the
packets will already be underway to the new Base Station and the handoff can be
performed with minimal packet loss. After migration the mobile host sends a route-update
packet to the new Base Station with the S bit cleared. This route-update packet will remove
all mappings in the Route Cache except for the ones pointing to the new Base Station. The
semi-soft handoff is then complete. If the path to the new Base Station is longer than that to
the old Base Station or if it takes non-negligible time to switch to the new Base Station,
then some packets may not reach the mobile host. To overcome the problem, packets sent
to the new Base Station can be delayed during semi-soft handoff. This way a few packets
may be delivered twice to the mobile host, but in many cases this results in better
performance than a few packets lost. Introduction of packet delay can be best performed in
the Cellular IP node that has multiple mappings for the mobile host as a result of a
semi-soft route-update packet. Packets that belong to flows that require low delay, but can
tolerate occasional losses, should not be delayed.
Semi-soft handoff minimizes packet loss providing improved TCP and UDP
performances over hard handoff. Distinguishing idle and active mobile hosts reduces
power consumption at the terminal side. The location of idle hosts is tracked only
approximately by Cellular IP. Therefore, mobile hosts do not have to update their location
after each handoff This extends battery life and reduces air interface traffic. When packets
need to be sent to an idle mobile host, the host is paged using a limited scope broadcast. A
mobile host becomes active upon reception of a paging packet and starts updating its
location until it moves to an idle state again.
If a mobile host has not received data packets for a system specific time
active-state-timeout, it becomes idle. The idle mobile hosts allow their soft-state routing
cache mappings to be time out. Idle hosts transmit empty IP packets(paging-update
packets) at regular intervals(paging-update-time) to the gateway. Paging-update packets
are sent to the base station that offers the best signal quality. Paging-update packets are
also routed on a hop-by-hop basis to the gateway. Base stations may optionally maintain
paging cache. A paging cache has the same format and operation as a routing cache except
for two differences. First, paging cache mappings have a longer timeout period called
paging-timeout. Second, paging cache mappings are updated by any packet sent by mobile
hosts including route-update packets and paging-update packets. This results in idle
mobile hosts having mappings in paging caches but not in routing caches. If the base
station has no paging cache, it will forward the packet to all its interfaces except for the one
the packet came through. Paging cache is used to avoid broadcast search procedures found
in cellular systems. Base stations that have paging cache will only forward the paging
packet if the destination has a valid paging cache mapping and only to the mapped
The Handoff Aware Wireless Internet Infrastructure (HAWAII)
protocol [Ramj99][Ramj02] proposes a separate routing protocol to handle intra-domain
mobility. All issues related to mobility management within one domain are handled by a
gateway called a domain root router. A MN entering a new foreign agent domain is
assigned a collocated care-of address. The MN retains its care-off address unchanged
while moving within the foreign domain, thus the HAs does not need to be involved unless
the MN moves to a new domain. In this case, packets for the MN are intercepted by its HA
first. The HA tunnels the packets to the domain root router serving the MN. The domain
root router routes the packets to the MN using the host-based routing entries. When the
MN moves between different subnets of the same domain, only the route from the domain
root router to the BS serving the MN is modified, and the remaining path remains the same.
Thus, during an intra-domain handoff, the global signaling message load and handoff
latency are reduced.
HAWAII path setup messages
There are three types of HAWAII path setup messages: powerup, path refresh, and
path update. On power up a mobile host sends a Mobile IP registration request message to
the corresponding base station. The base station then sends a HAWAII path setup
power-up message to the domain root router which is processed in a hop-by-hop manner.
This has the effect of establishing host specific routes for that mobile host in the domain
root router and any intermediate routers on the path towards the mobile host. The domain
root router finally acknowledges this path setup power-up message to the base station
which finally notifies the mobile host with a Mobile IP registration reply.
If a router knows multiple paths to the domain root router, it can use any of them but
it always has to use the same route for a specific host. The routing entries in the routers are
soft-state, i.e. they have to be refreshed periodically by path setup refresh messages, which
are sent independently by each network node and which can be aggregated. This increases
the robustness of the protocol to router and link failures. The mobile host infrequently
sends periodic path refresh messages to its base station to maintain the host based entries.
The base station and the intermediate routers, in turn, send periodic aggregate hop-by-hop
refresh messages towards the domain root router. Path setup messages are sent to only
selected routers in the domain, resulting in very little overhead associated with maintaining
While the mobile host moves within a domain, maintaining end-to-end connectivity
to the mobile host requires special techniques for managing user mobility. HAWAII uses
path setup update messages to establish and update host-based routing entries for the
mobile hosts in selective routers in the domain so that packets arriving at the domain root
router can reach the mobile host with limited disruption. The choice of when, how, and
which routers are updated constitutes a particular path setup scheme.
HAWAII Path Setup Schemes
The HAWAII handoff procedures are only activated when the mobile host's next
hop IP node is changed during the handoff [Ramj02] assumes base stations have IP
routing functionality and uses a tree-based topology for clarity, but the schemes will also
provide for non-tree-based topologies.
[Ramj99] defines two schemes for implementing Handoff procedures within the
domain, the forwarding and the non-forwarding scheme. The cross-over router is defined
as the router closest to the mobile host that is at the intersection of two paths, one between
the domain root router and the old base station, and the second between the old base station
and the new base station.
Non-forwarding path update scheme
The non-forwarding path set-up is a two way Update handshake process. It is
initiated by the Mobile Station sending an Update to the new Base Station. The path setup
Update message consists of the Mobile Station IP address, the old and new Base Station
address, and some other informations. The following is the algorithm:
Step 1: Update the Cache with the combination of the IP address of the Mobile
Station and the port on which the Update was received. This builds an element in a
"reverse" chain in the direction from the current node towards the new Base Station. If the
current node is the old Base Station, it sends an acknowledgement to the Mobile Station
directly via the air interface. This completes the procedure and the old Base station will not
receive further datagrams for the Mobile Station. The path from the gateway to the new
Base Station will be refreshed, the rest (from the Crossover router to the old Base Station)
will not and times out shortly.
Step 2: (recipient is not the old Base Station) The node extracts the forwarding port
for the old Base Station from the routing table, and forwards the Update. Step 1 is then
Forwarding path update scheme
The forwarding path set-up is initiated by the Mobile Station. Its also a two way
Update handshake process. The Mobile Station sends the old Base Station an Update
message, which consists of the Mobile Station IP address, the old and new Base Station
addresses, and some other informations. The following is the algorithm:
Step 1: If the node receiving the Update is the new Base Station, it sends an
acknowledgement to the Mobile Station directly via the air interface, and updates the
Cache with the IP address and port number for the Mobile Station. This completes the
procedure, leaving two Soft-state paths. One leading from the old to the new Base Station,
and the other from the gateway, via the Crossover router, to the new Base Station. The
second path will be refreshed while the first will time out shortly.
Step 2: (recipient is not the new Base Station) The node extracts the forwarding port
for the new Base Station from the routing table, and updates the Cache with the IP address
of the Mobile Station and this port number. Step 1 is then revisited. The Forwarding path
set-up scheme packets in transit towards the old router are then forwarded from the Old
Base Station to the new Base Station until the flow is diverted at the Crossover router.
The non-forwarding scheme is optimized for networks where the Mobile Station can
listen/transmit to multiple base stations simultaneously, as in the case of Code Division
Multiple Access (CDMA) networks. The forwarding scheme is optimized for networks
where the Mobile Station can listen/transmit to only one base station, as in the case of a
Time Division Multiple Access (TDMA) network. Both schemes ensure no BSS internal
loss of in transit datagrams during handoff.
Over recent years, the market for wireless communications has experienced
incredible growth. Wireless technologies have quickly found a significant place and
popularity in business and the computer industry. Their major motivation and benefit is
increased flexibility and mobility. Unlike a wired LAN, which requires a wire to access the
network, a Wireless LAN connects computers and other components to the network via an
Access Point (AP). Wireless LANs offer several fundamental benefits including user
mobility, rapid installation, flexibility and scalability. However, there are some primary
The speed of wireless networks is constrained by the available bandwidth.
Radio waves can suffer from a number of propagation problems that may
interrupt the radio link, such as multi-path interference and shadows.
On Wire LAN, sniffing is much easier because the radio transmissions are
designed to be processed by any receiver within range. Security is still a prime
The IEEE 802.11 Working Group was formed in September of 1990. Their goal was
to create a wireless LAN specification that will operate in one of the Industrial, Scientific,
and Medical frequency(ISM) ranges. The first 802.11 standard was released in 1997. The
latest version is the 1999 edition. The official name of 802.11 is IEEE Standards for
Information Technology -- Telecommunications and Information Exchange between
Systems -- Local and Metropolitan Area Network -- Specific Requirements -- Part 11:
Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.
The 802.11 protocols address the Medium Access Control (MAC) and Physical (PHY)
layers independently. The MAC layer handles moving data between the link layer and the
physical medium. Figure 2-5 shows how the OSI model match up to the 802.11 standards.
The 802.11 Established Standards
The 802.11 suite has the four established standards: 802.11, 802.1 lb, 802.1 la and
802.1 Ig. The IEEE is continuing to work on new standards that will extend the physical
layer options, improve security, and add quality of service (QoS) features. In the following
several sections, we will brief introduce these four standards .
ISO/OSI esson IEEE 802.11
Network Logical Link Control
Data Link Medium Access (MAC)
Physical Physical (PHY)
Figure 2-5 OSI model vs. IEEE802.11 standard
802.11 was the first IEEE standard used for wireless data networking applications
with maximum data transfer rates at 2 Mbps in the 2.4 GHz radio band. Within 802.11, two
different modulation schemes are supported that can be used to transmit data signals.
The first modulation scheme is frequency-hopping spread spectrum(FHSS). This
transmission technique is used in WLAN transmissions where the data signal is modulated
with a narrowband carrier signal that "hops" in a random sequence from frequency to
frequency as a function of time over a wide band of frequencies. This technique reduces
the chances of interference.
The other modulation scheme is direct-sequence spread spectrum (DSSS). In this
method of transmission, the signal does not hop from one frequency to another but is
passed through a spreading function and distributed over the entire band at once. DSSS
usually provides slightly higher data rates and shorter delays than FHSS, because the
transmitter and receiver don't have to spend time returning. DSSS avoids interference by
configuring the spreading function in the receiver to concentrate the desired signal but
spread out and dilutes any interfering signal. A data signal at the sending station is
combined with a higher data rate bit sequence, or chipping code, that divides the user data
according to a spreading ratio. The chipping code, a redundant bit pattern for each bit that
is transmitted, increases the signal's resistance to interference. If one or more bits in the
pattern are damaged during transmission, the original data can be recovered due to the
redundancy of the transmission.
Although the 802.11 standard supports both modulation schemes, the two types of
spread spectrum technologies are not compatible. The number of channels used by 802.11
compliant products depends on the modulation scheme used. More specifically,
FHSS-based products use 79 channels of the Unlicensed National Information
Infrastructure (UNII) band, whereas DSSS-based products use either 3 non-overlapping
channels or 6 overlapping channels of the Industrial, Scientific, and Medical (ISM) radio
band. Some of the common characteristics specified by the 802.11 standard are listed in
Table 2-1 Characteristics specified by the 802.11 standard
Characteristic 802.11 Description
Application Wireless data networking
Data Rate 1-2 Mbps
Typical Operating Frequency Band ISM band: 2.4 to 2.4835 GHz.
Modulation Mechanism FHSS or DSSS, CRC-16 in header
Channels available 79 channels with FHSS; 3 or 6 channels with DSSS
Coverage 40m to 400m
Mobility Roaming between APs by mobile IP
Security 128-bit WEP
Link Layer Carrier Sense Multiple Access With Collision Avoidance
(CSMA/CA) with request to send (RTS)/clear to send (CTS)
IEEE 802.1 lb[80211b] is the first enhancement 802.11 standard to be ratified in
1999. 802.1 lb uses the same radio signaling frequency(2.4GHz) as the original 802.11
standard. The 802.1 lb standard specifies operation on three channels in the 2.4-2.4835
GHz spectrum. 802.1 lb can transmit data up to 11 Mbps but will scale down to 1 Mbps
based on conditions.
802.1 lb uses DSSS modulation scheme to transmit data signals through the 11
available channels(3 non-overlapping). This unlicensed portion of the radio band shares
space with many low-power signals from home electronics, including microwave ovens,
cordless telephones, Bluetooth-enabled devices, and garage-door openers. 802.1 lb
compliant products have a range of up to 400 meters in ideal conditions and will be
compatible with the products that meet the new 802.1 Ig standard when it is finalized.
Some of the key characteristics specified by the 802.1 lb standard are shown in Table 2-2.
Table 2-2 Characteristics specified by the 802.1 lb standard
Characteristics 802.11b Description
Application Wireless data networking
Data Rate (Mbps) 1, 2, 5.5, 11
Typical Operating Frequency Band ISM band: 2.4 to 2.4835 GHz
Channels available 11 (3 non-overlapping)
Modulation Mechanism DSSS
Coverage (m) 40 to 400
Mobility Roaming between APs by mobile IP devices
Security 128 bit WEP
Link Layer CSMA/CA with RTS/CTS
Pros of 802.1 lb lowest cost; signal range is best and is not easily obstructed.
Cons of 802.1 lb Speed and channel restriction are significant limitations of
802.1 lb compliant networks. Interference within one's own 802.1 lb network becomes
more likely as the number of users and APs increase. Similarly, interference is more likely
as 802.1 lb compliant networks are deployed near each other. 802.1 lb products share the
bandwidth with other low-power signals, and thus, problems may arise when the
technology is used near some electronic devices such as microwave ovens,
Bluetooth-enabled devices, and cordless telephones.
802.1 la[8021 la], a High-speed Physical Layer in the 5 GHz band standard for
WLANs, was completed in September 1999. It is offered in the 5 GHz radio (UNII) band,
and operates on 8 channels; however, the available radio spectrum in some countries
permits the use of 12 channels. The additional number of channels used in the higher
spectrum yields less interference from neighboring APs. The Federal Communications
Commission (FCC) has divided the total of 300 megahertz (MHz) frequencies used by
802.1 la WLANs into 3 distinct 100 MHz domains, each with a different legal maximum
power output. The "low" band operates in the 5.15-5.25 GHz range and has a maximum
output power of 50 milliwatts (mW). The "middle" band is located in the 5.25-5.35 GHz
range, with a maximum of 250 mW. The "high" band uses the 5.725-5.825 GHz range,
with a maximum of 1 Watt. Because of the high power output, most devices transmitting
in the high band are building-to-building bridge products. The low and medium bands are
more suited to in-building wireless products.
802.1 la transfers data at rates of up to 54 Mbps in the available radio spectrum,
which is up to five times faster than 802.1 lb compliant networks. More commonly,
however, 802.1 la compliant networks communications are at the 6 Mbps, 12 Mbps, or
24 Mbps data rates. As the distance between the user and the AP increases, the data rate
802.1 la compliant networks use Orthogonal Frequency Division Multiplexing
(OFDM) modulation to provide these data rates. OFDM is a type of digital modulation in
which a signal is divided into separate channels at different frequencies. Table 2-3 show
the major characteristics of 802.1 la standard.
Pros of 802.11a speed as 5 times as 802.1 lb; supports more simultaneous users;
regulated frequencies prevent signal interference from other devices
Cons of 802.11a shorter range signal that is more easily obstructed; shorter range
costs more APs to cover the same area as an 802.1 lb network; consume more power than
802.1 lb products.
Table 2-3 Characteristics specified by the 802.1 la standard
Characteristic 802.11 a Description
Application Wireless data Networking
Data Rate (Mbps) 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. Rates of 6, 12, and
24 Mbps are mandatory for all products.
UNIIband: 5.15-5.25 GHz, 5.25-5.35 GHz, and
Typical Operating Frequency Band
Channels Available 12 non-overlapping
Modulation Mechanism OFDM- Orthogonal Frequency Division Multiplexing
Coverage (m) < 100
Mobility Roaming between APs by mobile IP devices
Security 128-bit WEP, 64-bit WEP, 152-bit WEP
Link Layer CSMA/CA with RTS/CTS
802.1 la was ratified after 802.1 lb was already penetrating the market, so even
though it offers higher speed and frequency, it may not be worth the switch for users who
have already invested in 802.1 lb technology. Because 802.1 la and 802.1 lb utilize
different frequencies, the two technologies are incompatible with each other. Some
vendors offer hybrid 802.1 la/b network gear, but these products simply implement the two
standards side by side.
IEEE 802.1 Ig was ratified as a standard in Jun. 2003. It operates in the same 2.4
GHz range as 802.1 lb but offers the same speed up to 54 Mbps as 802.1 la does. This
standard features increased data transmission rates while maintaining interoperability with
802.1 lb compliant products. The standard uses the same modulation scheme OFDM as
802.1 la to achieve data rates from 22 Mbps to up to 54 Mbps; however, 802.1 g products
will be backward compatible with 802.1 lb products that use the modulation scheme
DSSS. The backward compatibility feature allows an 802.1 lb compliant client adapter
card to interact directly with an 802.1 Ig compliant AP. Communications between 802.1 Ig
and 802.1 lb devices are limited to data rates up to 11 Mbps. The common characteristics
specified by the 802.1 Ig standard are shown in Table 2-4.
Table 2-4 Characteristics specified by the 802.1 Ig standard
Characteristics 802.11 g Description
Application Broadband Wireless LAN Access
Data Rate (Mbps) 6, 9, 12, 18, 24, 36, 48, 54
Typical Operating Frequency Band ISM band: 2.4 to 2.4835 GHz
Channels available 3 non-overlapping
Modulation Mechanism OFDM/DSSS
Coverage (m) 20 to 400
Mobility Roaming between APs by mobile IP devices
Security 128 bit WEP
Link Layer CSMA/CA with RTS/CTS
Pros of 802.11g fast speed as up to 54mbps; supports more simultaneous users;
signal range is better than 802.11 a and is not easily obstructed
Cons of 802.11g costs more than 802.1 lb; just like 802.1 la, appliances may
interfere on the unregulated signal frequency when the technology is used near some
electronic devices such as microwave ovens, Bluetooth-enabled devices, and cordless
Table 2-5 provides a comparison of the primary 802.11 standards.
Table 2-5 Comparison of characteristics specified within the IEEE 802.11 suite
Characteristics 802.11 802.11a 802.11b 802.11g
UNII 5 15-5 25 GHz,
Spectrum Band ISM 2 4 to 2 4835 GHz 5 25-5 35 GHz, and ISM 2 4 to 2 4835 GHz ISM 2 4 to 2 4835 GHz
5 725-5 825 GHz
Modulation Scheme FHSS or DSSS OFDM DSSS OFDM or DSSS
Number of Channels 79 channels with FHSS,
12 3 3
(non-overlapping) 3 or 6 channels with DSSS
Optimum Data Rates
2 54 11 54
Range (meters) 400 100 400 400
Date established July 1997 September 1999 July 1999 June 2003
Compatibility 80211 only 802 lla 802 lb 802 llb/g
North America, Europe, North America, Europe,
Operability North America, Europe, Asia NorthAmerica, Europe, Asia
Pending Specifications Within the 802.11 Suite
IEEE 802.1 la, lb, 1 Ig are major standard of wireless networking. There are
various other standards which were developed to improve the transmission of data and
promote the effective communication. The following are current standards which enhance
and expand the functionality of the overall 802.11 protocol.[STD802]
IEEE 802.11c: Defines wireless bridge operations
IEEE 802.11d: Defines standards for companies developing wireless products in
IEEE 802.11e: Defines enhancements to the 802.11MAC for QoS.
IEEE 802.11f: Defines Inter Access Point Protocol (IAPP)
IEEE 802.11i: Improved encryption
IEEE 802.11j: 802.11 extension used in Japan.
IEEE 802.11n: New standard expected to be completed in 2005 that is expected
to support up to 100Mbps.
The IEEE 802.11 Wireless LAN Architecture
The 802.11 architecture is comprised of several components and services that
interact to provide station mobility transparent to the higher layers of the network stack.
The major components and services in Wireless LAN are as followings [Jain03].
Wireless LAN Station
The wireless LAN station (STA) is the most basic component of the wireless
network. A station is any device that implements the MAC and PHY functionality of the
802.11 protocol. Typically the 802.11 functions are implemented in the hardware and
software of a network interface card (NIC). A station could be a laptop PC, PDA, or an
Access Point. Stations may be mobile, portable, or stationary and all stations support the
802.11 station services of authentication, de-authentication, privacy, and data delivery.
Basic Service Set (BSS)
802.11 defines the Basic Service Set (BSS) as the basic building block of an 802.11
wireless LAN. The BSS consists of a group of stations.
The Topologies could be Independent Basic Service Set (IBSS), Infrastructure Basic
Service Set(BSS) or Extended Service Set (ESS)
Independent Basic Service Set (IBSS)
The most basic wireless LAN topology is a set of stations, which have recognized
each other and are connected via the wireless media in a peer-to-peer fashion. This form of
network topology is referred to as an Independent Basic Service Set (IBSS) or an Ad-hoc
network. In an IBSS, the mobile stations communicate directly with each other. Every
mobile station may not be able to communicate with every other station due to the range
limitations. There are no relay functions in an IBSS therefore all stations need to be within
range of each other and communicate directly.
Infrastructure Basic Service Set(BSS)
An Infrastructure Basic Service Set is a BSS with a component called an Access
Point (AP). The access point provides a local relay function for the BSS. All stations in the
BSS communicate with the access point and no longer communicate directly. All frames
are relayed between stations by the access point. This local relay function effectively
doubles the range of the IBSS.
Extended Service Set (ESS)
An extended service set is a set of infrastructure BSS's, where the access points
communicate among themselves to forward traffic from one BSS to another to facilitate
movement of stations between BSSs.
Wireless LAN Handoff Management
Wireless LAN Handoff Management Frames
The 802.11 standard defines various frame types that stations (NICs and APs) use
for communications, as well as managing and controlling the wireless link. Every frame
has a control field that depicts the 802.11 protocol version, frame type, and various
indicators for WEP is on/off, power management is on/off, etc. In addition all frames
contain MAC addresses of the source and destination station, a frame sequence number,
frame body and frame check sequence (for error detection). 802.11 control frames assist in
the delivery of data frames between stations. Data frames carry protocols and data from
higher layers within the frame body such as RTS, CTS, ACK. Management frames enable
stations to establish and maintain communications. Here we only introduce the
management frames which relative directly to handoff management. [JimO 1]
Authentication frame: 802.11 authentication is a process whereby the access
point either accepts or rejects the identity of a radio NIC. The NIC begins the
process by sending an authentication frame containing its identity to the access
point. With open system authentication (the default), the radio NIC sends only
one authentication frame, and the access point responds with an authentication
frame as a response indicating acceptance (or rejection). With the optional shared
key authentication, the radio NIC sends an initial authentication frame, and the
access point responds with an authentication frame containing challenge text. The
radio NIC must send an encrypted version of the challenge text, using its wired
equivalent privacy (WEP) key, in an authentication frame back to the access point.
The access point ensures that the radio NIC has the correct WEP key (which is
the basis for authentication) by seeing whether the challenge text recovered after
decryption is the same that was sent previously. Based on the results of this
comparison, the access point replies to the radio NIC with an authentication
frame signifying the result of authentication.
Deauthentication frame: A station sends a deauthentication frame to another
station if it wishes to terminate secure communications.
Association request frame: 802.11 association enables the access point to
allocate resources for and synchronize with a radio NIC. A NIC begins the
association process by sending an association request to an access point. This
frame carries information about the NIC (e.g., supported data rates) and the SSID
of the network it wishes to associate with. After receiving the association request,
the access point considers associating with the NIC, and (if accepted) reserves
memory space and establishes an association ID for the NIC.
Association response frame: An access point sends an association response
frame containing an acceptance or rejection notice to the radio NIC requesting
association. If the access point accepts the radio NIC, the frame includes
information regarding the association, such as association ID and supported data
rates. If the outcome of the association is positive, the radio NIC can utilize the
access point to communicate with other NICs on the network and systems on the
distribution (i.e., Ethernet) side of the access point.
Reassociation request frame: If a radio NIC roams away from the currently
associated access point and finds another access point having a stronger beacon
signal, the radio NIC will send a reassociation frame to the new access point. The
new access point then coordinates the forwarding of data frames that may still be
in the buffer of the previous access point waiting for transmission to the radio
Reassociation response frame: An access point sends a reassociation response
frame containing an acceptance or rejection notice to the radio NIC requesting
reassociation. Similar to the association process, the frame includes information
regarding the association, such as association ID and supported data rates.
Disassociation frame: A station sends a disassociation frame to another station if
it wishes to terminate the association. For example, a radio NIC that is shut down
gracefully can send a disassociation frame to alert the access point that the NIC is
powering off. The access point can then relinquish memory allocations and
remove the radio NIC from the association table.
Beacon frame: The access point periodically sends a beacon frame to announce
its presence and relay information, such as timestamp, SSID, and other
parameters regarding the access point to radio NICs that are within range. Radio
NICs continually scan all 802.11 radio channels and listen to beacons as the basis
for choosing which access point is best to associate with.
Probe request frame: A station sends a probe request frame when it needs to
obtain information from another station. For example, a radio NIC would send a
probe request to determine which access points are within range.
Probe response frame: A station will respond with a probe response frame,
containing capability information, supported data rates, etc., when after it receives
a probe request frame.
IEEE 802.11 Handoff Procedure
An IEEE 802.11 Handoff occurs when a STA moves out of the range of one AP, and
enters another BSS. During the handoff, management frames are exchanged between the
station (STA) and the AP. Also the APs involved may exchange certain context
information (credentials) related to that STA via Inter Access Point Protocol(IAPP).
The handoff procedure can be divided to two steps[Mish03] [Shin04], discovery and
Discovery: this step involves the handoff initiation phase and the scanning phase.
When the STA is moving away from the current AP, the signal strength and the
signal-to-noise ratio of the signal may degrade and initiate the scanning phase. Scanning is
to try to find a new available AP to associate with. There are two can of scanning mode:
passive or active. In passive scanning mode, the STA listens to each channel of the
wireless medium for beacon frames broadcasted by AP. Using the information obtained
from beacon frames the STA can elect to join an AP. In active scanning, apart from
listening to the beacon frames, the STA send probe request frames on each channel and
listens to probe responses from the APs. The basic procedure of the active scanning
includes the following steps , as summarize by[Shin04] :
Using the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
channel access mechanism gain control of wireless medium.
broadcast a probe request frame.
Start a probe timer.
Listen to the channel for probe responses.
If no response has been received by minChannelTime, scan next channel.
If one or more responses are received by minChannelTime, stop accepting probe
responses at maxChannelTime and process all received responses.
Repeat the above steps to scan next channel. After all channels have been scanned,
all information received from probe responses are processed so that the STA can
select one AP to associate.
Reauthentication: The reauthentication process involves authentication and
reassociation to the new AP. The STA sends a authentication request to the new AP,
informing the AP of its identity. The new AP sends back an authentication response,
indicating acceptance or rejection. After successful authentication, the STA sends a
reassociation request to the new AP and waits for a reassociation response containing an
acceptance or rejection notice.
Figure 2-6, taken from [Shin04], shows the IEEE 802.11 handoff process.
Probe request (broadcast)
Authentication st New A
Probe delay E
Probe request (broadcast) A
Authentication request New AP
Authentication delay Authentication response
Association delay Reassociation response
Figure 2-6 802.11 wireless LAN handoff procedure
Techniques to Reduce IEEE 802.11 Handoff Time
A lot of researches have been done to analyze and reduce the handoff latency of
wireless LAN. [Mish03] conducts experiments to accurately measure the handoff latency
in an in-building wireless network. The measurements are done on two co-existing
wireless networks, and using three wireless NICs from different vendors. It analyzes the
handoff latencies by breaking down the whole process into discovery and reauthentication
phases to assess the contribution of each phase to the handoff latency. The experiment
results show that the discovery phase (scanning time) is the most time consuming part of
the handoff process, taking over 90% of the total handoff latency. The variations in the
probe-wait time account for the large variations in the overall handoff latency. The
reauthentication phase contributes only a few milliseconds.
[Mish04] use of an efficient data structure, neighbor graphs, which dynamically
captures the mobility topology of a wireless network as a means for pre-positioning the
station's context ensuring that the station's context always remains one hop ahead. This
caching mechanism is based on the IAPP protocol in order to exchange the client context
information between neighboring APs. The cache in the AP is built using the information
contained in an IAPP Move-Notify message or in the reassociation request sent to the AP
by the client. By exchanging the client context information with the old AP, the new AP
does not require the client to send its context information in order to reassociate, hence
reducing the reassociation delay.Its experimental and simulation results show that the use
of neighbor graphs cache reduces the layer 2 handoff latency due to reassociation by an
order of magnitude from 15.37ms to 1.69ms.
[Kim04] propose a selective scanning algorithm which depends on the use of
neighbor graphs. This approach requires changes in the network infrastructure and use of
IAPP. The scanning delay is defined as the duration taken from the first Probe Request
message to the last Probe Response message. This definition does not take into
consideration the time needed by the client to process the received probe responses.
[Shin04] also propose a selective scanning algorithm and a caching mechanism. This
caching data structure is maintained at the client side and no changes are required in the
existing network infrastructure or the IEEE 802.11 standard. All the required changes are
done on the client side wireless card driver. And [Shin04] considers the time required for
processing the probe responses received by the client. This processing time represents a
significant part of the scanning delay especially when the number of probe responses
received increased significantly.
Sangheon Pack and Yanghee Choi in [Par02] and [Park02] proposed a fast handoff
scheme using the pre-authentication method based on IEEE 802. lx model. In their
proposal, when a mobile host handoff, it performs authentication procedures not only for
the current AP but for a set of multiple APs. Multiple APs are selected using a Frequent
Handoff Region (FHR) selection algorithm considering users' mobility patterns and their
service classes. The FHR is a set of adjacent APs. It is determined by the APs' locations
and users' movement patterns. Namely, the FHR consists of APs with which mobile hosts
are likely to communicate to in the near future. Since a mobile host is authenticated for
FHR in advance, the handoff latency due to the reauthentication can be minimized.
Low Latency Handoff Mechanisms for MIP over 802.11 Network.
The HMIP, Cellular IP (CIP)[Cam99] and (HAWAII) [Ramj02] protocol we talked
in Section 2 of this chapter are handoff management protocols without considering
underlying layers. This clean separation between Layer 2 and Layer 3 protocol stack
allows those protocols to run on most layer technologies. The disadvantage of this clean
separation is lower performance. In MIP over wireless LAN network, the MN may only
keep connectivity with one AP, hereby one FA. So the MN can only start the registration
process after completion of the L2 handoff [Malk02] proposed two mobility protocols,
pre-registration and post-registration, that aim at low latency Layer 3 handoff based on
Layer 2 information or called Layer2 trigger. In pre-registration, MN may communicate
with the new FA while still being connected with the old FA. In post-registration, the data
can be delivered to the MN at the new FA before the registration process has completed.
Here we briefly depict these two method summarize by [Blon04].
A L2 trigger is a signal related to the L2 handoff process. There are there kind of L2
triggers mentioned in [Malk02]: anticipation trigger- an early notice of an upcoming
change in the L2 point of attachment of the MN. Line Down trigger (L2-LD)- indicates
that the L2 link between the MN and the old AP is lost. Line Up trigger (L2-LU)- indicates
that the L2 link between the MN and the old AP is established. A trigger initiated at the old
FA is referred as a source trigger and a trigger initiated at the new FA is referred as a target
Pre-Registration allows the old FA and new FA to utilize information from layer 2
(the L2 "trigger") to set up a kind of "pre-registration" prior to receiving a formal
Registration Request from the Mobile Node.. The network assists the MN in performing an
L3 handoff before the L2 handoff is completed. Both the MN (mobile-initiated) and the
FAs (network-initiated) can initiate a handoff
A mobile-initiated handoff occurs when the L2 anticipation trigger is received at the
MN informing it that it will shortly move to the nFA. The L2 trigger contains information
such as the nFA's IP address identifier.
A network-initiated handoff can be initiated by a source trigger at the oFA
(source-initiated handoff) or by a target trigger at the nFA (target-initiated handoff). A
source-initiated handoff is initiated at the oFA by a received L2 trigger that informs the
oFA of a MN's upcoming movement from oFA to nFA. A target-initiated handoff is
initiated at the nFA by a received L2 trigger that informs the nFA of a MN's upcoming
movement from oFA to nFA.
The Post-Registration handoff method is based on a network-initiated model of a
handoff. The Post-Registration occurs after the L2 handoff has been completed. This
approach uses a bi-directional edge tunnel (BET) to perform a low latency change in the
L2 point of attachment of the MN without requiring any involvement of it.
A handoff occurs when the MN moves from the oFA, where the MN performed a
Mobile IP registration, to the nFA. The MN delays its registration with the nFA, while
maintaining connectivity using the BET between the oFA and nFA. There are two
different Post Registration handoff schemes, Source and Target Trigger Post Registration,
depends on what kind of L2 is using. An FA becomes aware that a handoff is about to
occur at L2 through the use of an L2 trigger. Two types of triggers can be received: a
source trigger at the oFA and a target trigger at the nFA.
The FA receiving the trigger sends a Handoff Request (HRqst) to the other FA. The
FA receiving the HRqst sends a Handoff Reply (HRply) to the first FA. This establishes a
BET. The L2-LD (Link Down) trigger at the oFA and at the MN signals that the MN is not
connected anymore with the oFA. When the oFA receives the L2-LD trigger, it begins
forwarding the MN packets through the forwarding tunnel to the nFA. When the nFA
receives the L2-LU (Link Up) trigger, it begins delivering packets tunneled from the oFA
to the MN and forwards packets from the MN. When the MN receives the L2-LU, it
decides to initiate the Mobile IP Registration process with the nFA by soliciting an Agent
Advertisement or continues using the BET. Once the Registration process is complete
(through the exchange of a Regional Registration Request and a Regional Registration
Reply with the GFA), the nFA replaces the role of oFA.
The ability to determine a user's location in an existing 802.11 wireless network can
provide many useful services for wireless users. Such services include: location sensitive
content delivery, such as being able to send documents to a vicinal printer; creation of
real-time roadmap, asset tracking (locating a valuable device), etc. Some location
mechanisms use additional devices such as GPS, some not.
The Global Positioning System (GPS) is a worldwide radio-navigation system
consists of a constellation of 24 satellites and their ground stations. GPS uses these
"man-made stars" as reference points to calculate positions accurate to a matter of meters.
In fact, with advanced forms of GPS the accuracy can be better than a centimeter[Trim04].
A GPS device, through triangulation of multiple signals received and determination of
propagation (how long it took the signal to go from the satellite to the GPS device), is able
to accurately determine a user's location to within a meter. The problem with GPS is that
the device must have a clear line of sight between itself and the satellite. This means the
technology is unusable in heavily forested areas, urban environments with tall buildings
and indoor environments.
Some works has been done to use the popular 802.11 network infrastructure to
determine the user location without using any extra hardware. Generally, suck kind of
system needs to measure the signal quantity as a function of distance and one or more
reference point such as the APs in the wireless LAN. The signal strength decays
logarithmically with distance in an open space. But in indoors, the wireless channel is very
noisy and the radio frequency (RF) signal can suffer from reflection, diffraction, and
multipath effect [Yous03], which makes the signal strength a complex function of
distance. To overcome this problem, WLAN location determination systems may
constructs radio-maps during offline by sampling the signal at selected locations in the
area of interest and tabulate the complex function. When the system need to determine the
location, the vector of samples received from each access point is compared to the
radio-map and the "nearest" match is returned as the estimated user's location.
[Yous04] divided the radio map-based techniques into two broad categories:
deterministic techniques and probabilistic techniques. Deterministic techniques, such as
RADAR system in [Bahl00] and Location Information Privacy Model in [Smai01],
represent the signal strength of an access point at a location by a scalar value, for example,
the mean value, to estimate the user location. Probabilistic techniques measure the signal
quantity as a function of distance from the APs and store information them into a radio
map and use probabilistic techniques to estimate users location. [CastOl] [Ladd02]
[Roos02] [You04] [You03] are all using probabilistic techniques.
RADAR, An In-Building RF-based User Location and Tracking System, was
developed in Microsoft Research. In RADAR, the signal strength is measured when
transmitting beacon packet between the mobile host and AP. They take sample of radio
signals and build up a radio map for the area interested during offline phase. RADAR uses
3 APs as reference point of its location, which is called triangulation. During location
phase, it match the real time signal strength with the radio map and determines the user's
location. The match is done by linear search.
Horus system from the University of Maryland is an RF-based location
determination system [You04] [You03]. It is implemented in the context of 802.11
wireless LANs. The system uses the stored radio map to find the location that has the
maximum probability given the received signal strength vector. In [Yous04], they also
proved formally that probabilistic techniques give more accuracy than deterministic
Other Related Work
IEEE802.11 standard was originally devised to replicate in a wireless fashion the
structures of the wired LANs. Only recently the idea of utilizing IEEE802.11 technology
for high mobility scenarios has been taken into account and the range of WLAN based
applications has been enriched. In [Mani03], Pierpaolo Bergamo from UCLA and Don
Whiteman from NASA, experimentally studied the behavior of an IEEE802.11 wireless
network when the nodes are characterized by mobility up to the speed of 240 km/h. The
authors studied the survivability and the performance of a connection under various
aggressive mobility conditions. These studies may be adapted for data telemetry from
mobile airborne nodes to fixed networks or between airborne nodes. In [Sing02], authors
assessed the performance of WLANs in different vehicular traffic and mobility scenarios.
The network throughput and the quality of the wireless communication channel,
measured on IEEE 802.1 lb compliant equipment, are observed to degrade with
increasingly stressful communication scenarios. [Amic02] presents a project using a
WiFi-like network for military telemetry applications. For military telemetry, aircraft
and/or cars equipped with IEEE802.11 enabled devices will communicate with a fixed
backbone infrastructure. The authors of [Amic] focused on aspects like frequency
selection and network security. In [Thor], authors developed their own frequency
hopping transceiver working at 900 MHz for telemetry purposes. In [Bamb], authors
assured through analytical considerations that these kinds of transceivers can guarantee
an impressive tolerance to rapid moving environments.
A review on recent research on MIP shows a great amount of efforts contributed to
reducing MIP handoff latency. Malki [Malk02] proposed two mobility protocols, pre-
and post-registration, using L2 trigger. In pre- registration, MN may communicate with
both oFA and nFA. In post-registration, data are cached in nFA before the registration is
completed. Fast-handover [Kood02] for Mobile IPv6 network combines the about two
methods. But they all depend on L2 information. S-MIP[Hsie03], uses MN location and
movement patterns to 'instruct' the MN when and how handoff should be carried out.
[Wijn04] also uses MN's movement model to predict handoff. But all these efforts didn't
consider the speed factor of MN, which may cause problems when the MN moving
PERFORMANCE OF MIP OVER WLAN AT DIFFERENT SPEEDS
MIP over Wireless LAN Handoff Procedure
MIP over wireless LAN provides more flexibility and mobility to mobile IP
network. Unlike a traditional wired mobile IP network, which requires a wire to connect a
computer to the network, wireless LAN users can access IP network from nearly anywhere
without losing connectivity.
Mobile IP is designed independently for all
Layer 2 technologies, so it can run on any layer 2
infrastructures. But such kind of independency
FA1 FA 2 also costs more overhead. Figure 3-1 is the handoff
procedure of MIP over two wireless LAN. When a
S--1 MN moves from wireless LAN1 to wireless
Figure 3-1 MIP handoff LAN2, it performs a layer 802.1 lb handoff
between Access Point 1 (AP1) and Access Point 2(AP2). After the layer handoff, the MN
begins a layer3 handoff, which is MIP handoff. Suppose there is a communication, for
example a TCP stream, between MN and CN. After the layer and layer3 handoff, it will
require a significant time interval to recover the communication. This time internal is
called layer4 handoff latency, which is also a part of the whole handoff cost. Equation 1
gives the life-cycle of MIP over wireless LAN handoff procedure:
thandoff= tL2handoff + tL3handoff + tL4handoff (Equation 1)
Where thandoff is the total handoff latency of MIP over wireless LAN, tL2handoff,
tL3handoff, tL4handoff are the handoff cost of Layer2, Layer3 and Layer4 separately.
In the following section, we introduce an emulation testbed, RAMON, which is used
to evaluation the performance of MIP over WLAN and to analyze the handoff latency of
the MIP handoff procedure.
In order to evaluate the performance of MIP over WLAN, we build up a MIP
emulator RAMON[Hern02]. RAMON is a Rapid Mobile Network emulator. It's a testbed
combining software and hardware components to produce a realistic experimentation
environment that can test the behavior and performance of actual mobile systems. The
testbed provides the wireless and wired infrastructure to allow experimental testing of
wireless and wired mobile network protocols. Figure 3-2 is the architecture of RAMON.
RAMON consists of a Pentium II pc as Emulator, a circuit board as Controller, three
JFW Industries Attenuators with Antennas, three Cisco 350 Access Points, three FAs, a
HA and one or more MNs. All the FAs, HA and MN, which are the major entities of MIP,
are running Linux kernel 2.4.20 and are installed with HUT dynamic MIP implementation
version 0.8.1. The Attenuators are program controllable devices. The Emulator
manipulates the Attenuators by the Controller to control the signal strength coming out
from the Access Points. By increasing or decreasing the signal strength of one AP, we can
emulate the MN moving towards to or away from the AP. By varying the increasing or
decreasing speed of the signal strength, we can emulate the speed change of the MN. The
emulation program running on the emulator can dynamically change the IP addresses for
each AP and FA so that every physical AP(and FA) in Figure. 3-2 can emulator multiple
logical AP(and FA) in Figure 3-3.
Figure 3-1 RAMON testbed architecture
The hardware architecture of RAMON includes
*two PCs-one is emulator, one is home agent
o The emulator has four Ethernet cards. IP addresses are
EthO: 192.168.1.2 mask 255.255.255.0
Ethl: 192.168.2.2 mask 255.255.255.0
Eth2: 192.168.3.2 mask 255.255.255.0
Eth3: 192.168.4.2 mask 255.255.255.0
o The HA has two Ethernet cards. IP address are
EthO: 10.3.3.14 mask 255.255.255.0
Ethl: 192.168.4.2 mask 255.255.255.0
3 IBM ThinkPad laptops-as 3 foreign agents
o FA1 : eth0: 192.168.1.1 mask 255.255.255.0
o FA2 : eth0: 192.168.2.1 mask 255.255.255.0
o FA3 : eth0: 192.168.3.1 mask 255.255.255.0
3 CISCO AIRONET 350 Aps, IP addresses are
o API: 192.168.1.3
o AP2: 192.168.2.3
o AP3: 192.168.3.3
o The backup configuration files of these 3 APs are saved in the
3 Omnidirectional 3dbi Cushcraft Antennas
one control board-control the attenuator to emulate the signal fading
3 JFW Industries 50p-1230 Attenuators
one Laptop-- as mobile host
o MN eth0: 192.168.4.5
o Linux Kernel 2.4.7-10.
o Modules IPIP
o Script emulator to create Virtual interfaces and routing table
o Emulation object file to run the emulation
o Dynamics HUT mobile IP home agent package: dynhad.
o Modules IPIP
o Dynamics HUT mobile IP foreign agent package: dynfad.
o Modules IPIP
o Script FA1, FA2, FA3. simulate the action of foreign agents.
o DynX. 1 dynfad.conf configure files.
o Dynamics HUT mobile IP foreign agent package: dynmnd.
o Dynmnconfl dynmnd.conf configure file.
o Tcpdump to capture data
o Ethereal tool for analysis.
Emulation Scenario and Result
Using RAMON, we emulate HUT dynamic MIP in the following scenario in Figure
FA FA2 FA3 FA4 FA5 FA6 FA7 FA8
Figure 3-2 Dynamic MIP sample scenario
In this scenario, a rapid moving MN will travel trough 8 APs. Each AP is wired to a
FA. The distance between every two APs is d= 250m, 500m or 1000m. The moving speed
of MN is V, varying from 10m/s to 80m/s. In our experiments, we used ftp to transfer a
large file from the CN to the MN. During the ftp transfer, we tracked down TCP sequence
numbers by using the tool tcpdump. We analyze the tcpdump data by using ethereal. Here
we only give the experiment results for d = 500m and 1000m, v = 10m/s to 80m/s. Figure
3-4 and figure 3-5 are the time-sequence graph and throughput graph at speed 20m/s and
AP distance 1000m. Figure 3-6 and 3-7 shows the time-sequence graph and throughput
graph at speed 80m/s and AP distance 1000m. Figure 3-8 to figure 3-11 are those graphs at
speed 10m/s, AP distance 500m and speed 40m/s, AP distance 500m.
number[B] Time/Sequence Graph
80000000 -- -
50 100 150 200 250 300 350 400
Figure 3-3 Time-sequence graph at speed 20m/s and AP distance 1000m
. . .. .... ..rn ss T g.s ~ B= w i-s s a .... .. .. ...... .. ...~"
-. "- =. .--= "
i i i' 9
!*L *- l. -
, S .
*1, ~1 j
50 3 10 150 200 250 300 350 400 450
Figure 3-4 Throughput graph at speed 20m/s and AP distance 1000m
I '" 1'' 1 I I 1 I" I 1 ''" 1 ''" '1''" I '"
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 s0 85 90 95 100 105 110
Figure 3-5 Time-sequence graph at speed 80m/s and AP distance 1000m.
S .. .. 1
ii I i V* vI.
.. ~ M
Figure 3-6 Throughput graph at speed 80m/s and AP distance 1000m.
5 10 15 20 25 30 35
40 45 50 55 60 65 70 75 80 85
90 95 100 105 110
I I2II I I I I I I I
Figure 3-7 Time-sequence graph at speed 10m/s and AP distance 500m.
Figure 3-8 Throughput graph at speed 10m/s and AP distance 500m
, '', I. ka;~ ... POO....RI .
5 10 15 20 2 3 35 o d 5 0 5- 60 65 70 75 W 85 5 19 10 Io
5 I0 15 a0 fi 30 35 do 45 50 55 Wo 65 70 75 W0 85 so 95 1 0 1 10
Figure 3-9 Time-sequence graph at speed 40m/s and AP distance 500m.
..... .... .
r .... .. ... -. -". --
.... .... : ;.
Figure 3-10 Throughput graph at speed 40m/s and AP distance 500m.
Experimental Result Analysis
To compare the performance of MIP/ WLAN at different speeds and different AP
distances, we list the experiment data in table 3-1. In the table, the bytes transferred are the
total bytes transferred from when the MN enters the first cell to when it moves out of the
last cell. The average throughput is calculated by dividing bytes transferred by travel time.
The total handoff time is the summary of the handoff latency of 7 times handoffs. The
effective time is the time for effectively transferring data, which equals to the travel time
minus the total handoff time.
Table 3-1 shows the average throughput drops when the MN's speed goes up. At the
same speed of 20m/s, the average throughputs are 196.97kB/s for d=1000m and
167.172kB/s for d=500m. At the speed of 40m/s, the average throughputs are 167.512kB/s
for d=1000m and 93.877kB/s for d=500m. The table shows that if we double the speed and
at the same time double the AP distance, the average throughput shows no suggestive
difference. For example, at the speed of 40m/s and AP distance 1000m the average
throughputs is 167.512kB/s. At the speed of 20m/s and AP distance500m the average
throughputs is 167.172kB/s.
Table 3-1 Average Throughput at Different Speeds and AP Distances.
Speed AP Bytes Travel Average Total Effective PMaxavg Handoff
(m/s) distance transferred Ti throughput handoff Etimes (kB/s) Rate
(m) (kB) Tme (s) (kB/s) times) te(s) (FAs/s)
20 1000 78000 396 196.970 58 338 232.5 0.02
40 1000 33000 197 167.512 57 140 234.31 0.04
60 1000 16700 130.5 127.969 56 74.5 234.07 0.06
80 1000 9200 98.5 94.359 57 41.5 232.673 0.08
10 500 78500 397 197.733 58 339 233.01 0.02
20 500 33100 198 167.172 56 142 234.4 0.04
30 500 16600 129 128.682 56 73 232.86 0.06
40 500 9200 98 93.877 58 40 232.8 0.08
The analysis of table 1 also shows: (1). The total handofftime doesn't change with
speed. (2). Effective-time/total-travel-time ratio drops when the speed goes up. This is the
reason why higher speed has lower throughput.
Figure 3-12, the average throughput vs. speed graph, gives a more obvious view of
D 180- 180-
80 80 -
0 20 40 60 80 0 10 20 30 40
Speed v(m/s) d= 1000m Speed v (m/s) d = 500m
Figure 3-11 Average throughputs vs speeds.
In order to figure out the relationship between the performance of MIP over wireless
LAN and the moving speed, we measured the throughputs of MIP over wireless LAN at
different moving speeds and AP distances when there are no handoffs. We call this
throughput, PMaxavg, the maximum average throughput without handoff Here we only give
the time-sequence graph at AP distance 1000m with speed 20m/s(left) and 80m/s(right).
From figure 3-13, we get PMaxavg = 93000kB / 400s = 232.5 kB/s. From the right graph of
figure 3-14, we get PMaxavg = 23500kB / 101s = 232.673 kB/s. The PMaxavg at different
moving speeds and AP distances are listed in table 1.
Figure 3-12 Time-sequence graph at AP distance 1000m with speed 20m/s without
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 00 95 90 95 100 105 110
Figure 3-13 Time-sequence graph at AP distance 1000m with speed 80m/s without
Let Pavg Average throughput
Pmaxavg Average throughput without handoff
Travel Total travel time
Teffective Total effective time for ftp transmission
Thandoff Total handoff time while traveling
Khandoff- The number of handoffs while traveling
thandoff Average handoff time among 7 times of handoff
Then, Pavg = (Pmaxavg / Ttravel ) x Teffetive
= Pmaxavg (Ttravel Thandoff )/ Ttravel
= Pmaxavg (1 Thandoff/ Ttravel)
= Pmaxavg( 1 Khandoff x thandoff / Ttravle)
= Pmaxavg( 1 (Khandoff/ Ttravle ) x thandoff ))
Since thandoff doesn't change, The change of Pavg is caused by Khandoff/Ttravel ratio.
We define MN handoff rate as rh = v/d, which is the ratio of the MN's speed and the
cell size(AP distance). It means that how many APs or FAs the MN hands over in one
second. rh is also equal to Khandoff/ Ttravel.
The relationship between the performance of MIP/WLAN and the moving speed is
presented in Equation 2:
Pavg = Pmaxavg( 1 rh x thandoff )) Equation 2
Where Pavg is the average throughput for the MN; PMaxavg is the average throughput
without handoff. thandoff is the average handoff time for each handoff procedure.
Since thandoff doesn't change, the change of Pavg is caused by handoff rate rh. At
handoff rate 0.02 FAs/s, the average throughput is 197.35 kB/s. When the handoff rate
goes up to 0.08 FAs/s, the average throughput drops to 94.118 kB/s. The graphs in Figure
3-12 can be combined into graph in Figure 3-15.
0 0.02 0.04 0.06 0.08
Handoff rate FA/s
Figure 3-14 Average throughput vs handoff rate
This chapter shows that the performance of MIP over WLAN is depends on the
MN's handoff rate. In Chapter 5, we will propose an idea of how to make use of this
throughput/handoff-rate relationship to improve the performance of MIP over wireless
LAN in rapid moving environment. In the following chapter, we will take a deep view of
the handoff latency by breaking down the handoff procedure of MIP over wireless LAN.
QUANTITATIVE ANALYSIS OF THE MIP OVER WIRELESS LAN HANDOFF
Equation 1 in Chapter 3 shows that the life-cycle of MIP over wireless LAN handoff
is the summary of Layer2, Layer3 and Layer4 handoff latency. In the following sections,
we analyze the handoff characters of each layer and provide a quantitative analysis of the
MIP over wireless LAN handoff latency.
Layer 2 Handoff Latency
In the case of IEEE 802.1 lb WLAN, Layer2 handoff is the change of APs. It causes
an interruption of data frame transmission. Buffering and routing update make the handoff
time for uplink and downlink traffic different. Some researches have been done to even
this difference[El-Ho00][Ren99]. In our experiments, we only concern the downlink
handoff time. In [Vela04], Hector Velayos splitting the Layer2 handoff time into three
sequential phases: detection, search and execution. In our experiment, we also split it into
three parts and name them as: movement detection, AP searching and reassociation.
The Layer2 handoff involves three participating entities, the station(here is the MN),
an old AP(oAP) and a new AP(nAP). The oAP is the access point which the station had
layer connectivity prior to the handoff, while the nAP is the access point to which the
station gets layer connectivity after the handoff The handoff process among 2 APs also
includes information exchanges. This information typically consists of the station's
credentials and accounting information. The message exchange between APs can be done
by Inter Access Point Prototcol(IAPP)[1 1F03] or via a proprietary protocol. The following
is a detail analysis of three phases of Layer 2 handoff.
Layer2 Movement Detection Phase
In oAP's coverage, the station keeps frame transmission. There are three reasons for
frames lose: collision, radio signal fading, or oAP is out of range. The station first assumes
the lost frame is cause by collision. In 802.1 lb standard, collision is handled by Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. CSMA/CA is a
basic protocol used to avoid signal collision and canceling. It works by requesting
authorization to transmit for a specific amount of time prior to sending information. When
collision happens, the sending device broadcasts a Request To Send (RTS) frame with
information on the length of its signal. If the receiving device permits it at that moment, it
broadcasts a Clear To Send (CTS) frame. Once the CTS is transmitted, the sending
machine transmits its information. Any other sending device in the area that "hears" the
CTS realize another device will be transmitting and allow that signal to go out
uncontested. If the station tried to retransmit several times and still unsuccessful, then it
assumes signal fading. This time the station sends out probe requests to probe the link.
After several probe requests and without any response, the station assumes oFA is out of
range and begin AP searching phase. In figure 10, from TCP point of view, when MN
receives the last TCP package, it responses with TCP ACKnowledgement. After several
unsuccessful transmission of TCP ACK, the MN assumes the oAP is out of range and
starts a new AP searching phase.
Layer2 AP Searching Phase
After the station assumes oAP is out of range, it tries to find new potential APs to
associate to. This is done by 802.1 lb MAC layer function: SCAN. There are two methods
of scanning, active and passive. In passive scanning, the station listen to each channel for
beacon frames(broadcasted periodically by APs every 10ms). The station takes note of the
corresponding signal strengths while scanning. The beacons contain information about the
AP, including service set identifier (SSID), supported data rates, etc. The station can use
this information along with the signal strength to compare APs and decide upon which one
to chose. In active scanning, the station broadcasts a probe request frame and waits for
response. The time to wait for responses depends on the channel status. If the channel is
idle during MinChannelTime, the station can receive prove response form the AP on that
channel. If there is any traffic during this time, the station will wait for MaxChannelTime
to allow the data in the channel be transmitted and wait for AP's response. After gathers
several response from APs in range, the station will compare and choose one to associate
to. Active scanning enables a station to receive immediate response from APs, without
waiting for beacon frames. However, it imposes additional overhead on the network. In
our experiment, only after got 3 probe responses from an AP, the station regards that AP is
stably in range. This is a default configuration of Orinoco Wireless card.
Layer2 Reassociation Phase
After choose one AP in phase 2, the station sends out a reassociation request to nAP.
If the nAP can get the credentials and other state information from oAP through IAPP,
there is no Authentication message exchange between the station and nAP. Or else, the
station will send out authentication request to the nAP and wait for response. After
authentication, nAP reassociates the station and sends reassociation response back.
The above three phases complete Layer2 handoff. The layer handoff latency can be
expressed in Equation 3.
tL2handoff = tL2detection + tL2seraching + tL2reassociation (Equation 3)
Where tL2detection tL2seraching and tL2reassociation are the time costs for Layer2 movement
detection, Layer2 AP searching and Layer2 reassociation. Figure 4-1 shows these three
phases in green arrows and are indexed as L2.
Layer 3 Handoff Latency
Only after the layer 2 link has been established, could the Layer 3 handoff starts,
because the MN can only communicate with the FA on the same link. The Layer 3 handoff
involves 2 phases, agent discovery and registration.
The well know agent discovery algorithms are Lazy Cell Switching(LCS) and Eager
*.... Data package
L3 HO signal
L2 HO signal
[L2 mnaement de-
L2 L2 AP searching
MIP agent discovt
L4 TCP retmnsmissio
m isls 44m." p PP
I .on... .:ia .
........... ..... .,. ...... .
ie 41 Hanofocede wih mese exnge
Figure 4-1 Handoff procedure with message exchange
oEA unreachable uEA aeent
detection vJ discovery,
oEA out Handoff aE New point of
of range' initiated discovered' attachment
Figure 4-2 LCS handoff latency for MIP
The LCS method is a reactive handoff initiation strategy. In LCS the MN keeps
receiving Agent Advertisement messages from the oFA and refreshes the lifetime of the
CoA and stays in the original network until it moves and loses contact with oFA for the
duration of three advertisement(FA broadcast Agent Advertisement message every 1
second), which means oFA becomes unreachable. A handoff will be initiated if a nFA is
discovered after this moment. If the nFA hasn't been discovered before the oFA becomes
unreachable, the handoff latency will be much higher. An advantage of the LCS is to
reduce the frequency of handoff when the MN hangs around among several FA. As to MIP
over WLAN, because the MN can only keep physical link with one FA, the new agent
can't be discovered before the old agent becomes out of range. Figure 4-2 is the LCS
handoff latency plot for MIP.
ECS is a proactive initiation strategy. It dictates an immediate MIP handoff as soon
as a new agent is discovered. ECS is effective for the moving patterns that the MN rarely
change its moving direction. Figure 4-3 is the ECS handoff latency plot for MIP.
oEA unreachable uEA agent
detection r disc very&
New point of
dEA out uEA iscvered attachment
of range Handoff initiated established
Figure 4-3 ECS handoff latency for MIP
When a MN realizes that it is on a foreign network and has acquired a
care-of-address from the nFA, it needs to notify the HA so that the HA can forward IP
packets between MN and CN. This is done by registration. The registration process
involves four steps.
* The MN sends a registration request to nFA.
* The nFA relays this request to the GFA or HA.
* The HA either accepts or denies the request and sends a registration reply to nFA. If it
accepts the request, it will build a tunnel downward to nFA(if FA decapsulation is
* The nFA relays this reply to the MN. If the registration reply is positive, it will build
a tunnel upward to HA or GFA.
If the MN is using a collocated care-of-address, it will register directly with the HA,
which is not the case in this paper.
The layer3 handoff latency can be splitted into Equation 4[Fiko01]. Figure 4-1
shows these two phases in red arrows and are indexed as L3.
tL3handoff = tmipagentdicovery + tmlpreglstratlon (Equation 4)
Layer 4 Handoff Latency
TCP is a connection-oriented, end-to-end reliable protocol designed to support error
recovery and flow control. Reliability is insured by a sliding-window acknowledgement
and retransmission mechanism. All data sent by TCP must be acknowledged by the
receiver. TCP maintains a variable-sized window of data that is unacknowledged for a
given time. If the window is full, no data will be sent until an acknowledgement is
received. TCP maintains a Retransmission Time Out (RTO) timer. If no ACK has been
received when the RTO timer expired, TCP assumes that the data has lost and retransmits
all of the data in the window. The retransmission follows the exponential back-off
algorithm. According to this algorithm TCP doubles the timeout value on unsuccessful
successive retransmissions[Hsie03]. In our case, during the Layer2 and layer3 handoff, the
TCP doubles the retransmission timeout value several times. So even after the layer and
layer3 handoff is over, TCP still have to wait for RTO to timeout to recover the
retransmission. In figure 4-1, the dash blue arrows depict the TCP retransmission interval
has been doubled. This latency is cost by TCP exponential back-off algorithm. So we call
it TCP back-off delay ttcp-back-off.
We define tL4hadoff= ttcp-back-off (Equation 5)
Quantitative Analysis of the Handoff Latency
According Equation 1, 2, 3 and 4, the handoff latency distribution for MIP over
WLAN is show in Equation 6.
thandoff tL2detection + tL2seraching + tL2reassociation + tmipagentdicovery + tmipregistration + ttcp-back-off (
We used RAMON introduced in Section 3 to emulate the same scenario as in Section
3. We did 20 times experiments to get the average handoff latency. The experimental result
of the handoff latencies of MIP over wireless LANis listed in table 4-1. Table 4-1 gives 20
times of experiment data. Each row is one experiment. Each column is the time latency for
that handoff phase. The data in the last column are the total handoff latencies for every
experiment. The number in the bottom right cell is the average handoff latency.
Table 4-1 Handoff latency distribution of MIP over WLAN
tency L2 L2AP L2 MIP MIP TCP Handoff
movement searching reassociati agent registration backoff latency
xp t detection on discover
1 1.033 0.061 0.005 2.996 0.073 5.058 9.226
2 1.064 0.044 0.009 1.945 0.042 6.01 9.511
3 1.133 0.063 0.006 3.023 0.052 5.345 9.622
4 1.032 0.100 0.008 2.563 0.050 5.323 9.076
5 1.044 0.065 0.003 2.756 0.052 5.125 9.045
6 1.131 0.057 0.004 2.578 0.043 5.004 8.817
7 1.009 0.056 0.010 2.436 0.060 5.625 9.196
8 1.120 0.060 0.006 3.001 0.704 5.002 9.893
9 1.023 0.059 0.026 2.213 0.054 4.998 8.373
10 1.039 0.076 0.005 3.008 0.053 5.006 9.187
11 1.100 0.045 0.030 2.770 0.041 5.728 9.714
12 1.013 0.049 0.010 2.545 0.042 4.768 8.427
13 1.021 0.051 0.009 3.001 0.065 5.202 8.896
14 1.006 0.043 0.017 2.600 0.046 5.312 9.024
15 1.104 0.069 0.006 2.598 0.047 4.544 8.368
16 1.003 0.064 0.013 2.674 0.062 4.806 8.622
17 1.110 0.054 0.010 2.783 0.054 5.705 9.716
18 1.100 0.064 0.006 3.012 0.057 5.602 9.841
19 1.302 0.056 0.009 2.349 0.070 5.71 9.496
20 1.098 0.044 0.004 2.404 0.062 5.172 8.784
Avg 1.074 0.059 0.010 2.660 0.086 5.253 9.142
Avg 1.143 2.746 5.253 9.142
We redraw figure 4-1 with handoff latency distribution in figure 4-4.
....**** Data package
L3 HO signal
L2 HO signal ....- :::
S.......... ...... .. .
7 : :: M *. .I *** .... .
1.074 L2mor ement detection t .... ..... ...
Probe ....... ..
L2delay 0.059 L2 AP seiching Probere .po: .e ......
1.14 ... .
2.660 MIP agent dismcery ..*
L3 delay I
2.746 ReijtaiRaiet __ ,
0.086 MIPregistration Rpi : yrat rniRy
L4delay 5.253 TCPretransion s
L .a..... j... ... .... -.. ..
Handoff delay : 9 142 :::...........c. d ....-...
111m mmmmmmmmm1 mmmmmm m 4,''I
Figure 4-4 Handoff procedure with handoff latency distribution
SPEED ADAPTIVE MIP AND ITS PERFORMANCE EVALUATION
From above analysis of handoff latency distribution, we can see the largest part is
TCP back-off latency ttcp-back-off. Because of TCP exponential back-off algorithm, if we
reduce the L2 and L3 latency, ttcp-back-off will be reduce exponentially. In this chapter, we
deal with L3 latency first. L2 and L4 latency will be considered in future works.
Traditional MIP over WLAN Handoff Procedure
The physical coverage of an IEEE 802.11-base wireless LAN is limited. To increase
the coverage of a wireless network, one can deploy multiple wireless LAN cells or
segments in an overlapped fashion where each cell is associated with an AP. AP serves as
a layer-2 bridge between the high-speed wired network and the wireless LAN. As MNs
move in and out of these overlapped cells, they can associate with the corresponding APs
according to beacon signal strengths. In IEEE 802.1 lb-based networks, the intelligence to
measure signal strength and switch among network segments is built into the wireless
LAN NIC(Network Interface Card), which exposes various status and control information
to the software device driver. To enable cellular-like networking structure, wireless LAN
NIC need to be configured to run in the access point mode, which is also known as the
infrastructure mode. Mobile IP provides MNs the ability to roam across wireless IP
subnets without loss of network-layer connectivity. Any network application executing on
a mobile host with mobile IP support can continue to run regardless of any change in the
mobile node's point of attachment. With mobile IP, mobile nodes do not need to
reconfigure their IP addresses while migrating from home subnets to foreign subnets. A
generic wired and wireless network topology with which mobile IP operates is shown in
API 2 AP3 AP4
5 6 7 8
Figure 5-1 Traditional MIP Handoff Procedure
In this topology, there are one HA and several FAs running on the wired network.
The MN is communicating with CN through the wireless link with AP1. The FAs
periodically broadcast mobile IP advertisements on the wireless LANs(message 1, 2, 3 and
4 in figure 5-1). Because there no wireless link between the MN and AP2, AP3 and AP4,
the mobile IP advertisements messages 2, 3 and 4 can not be transferred to the MN. The
mobile IP advertisements messages 1 can reach the MN. Since MN already registered on
FA1, message 1 will be discarded by the MN. Whenever the MN migrates from one subnet
to another (foreign) subnet, it first needs to establish wireless connection with the
corresponding AP then starts receiving mobile IP advertisements from the corresponding
When an IEEE 802.1 lb-based wireless network is configured in infrastructure
mode, the MN is associated with the AP, which is API in figure 5-1, of the wireless LAN
cell in which it currently resides. Each AP periodically broadcast beacon frames every
10ms in passive scanning mode((message 5, 6, 7 and 8 in figure 5-1). The beacons contain
information about the AP, including service set identifier (SSID), supported data rates, etc.
The station can use this information along with the signal strength to compare APs and
decide upon which one to chose. If the MN chooses AP2, it initiates a link-layer handoff
from API to AP2. The MN sends a reassocation request message to AP2(message 9 in
figure 5-1). If the nAP can get the credentials and other state information of the MN from
API through IAPP, there is no Authentication message exchange between the MN and
AP2. Or else, AP2 will send out authentication request to the MN and wait for response.
After authentication, AP2 reassociates the MN and response with a reassociation response
message(message 10). In all known IEEE 802.1 lb cards, this link-layer handoff logic is
built into the firmware of the NIC, and does not generate any interrupts to notify the
higher-layer software. If the new wireless LAN cell belongs to the same IP subnet as the
old wireless LAN cell(like AP3 and AP4 belongs to the same subnet to FA3), then to the IP
layer and above on the mobile node there is no change in connectivity and the network
applications continue without any disruptions. However, if the new wireless LAN cell
belongs to a different IP subnet, then the MN can no longer communicate with CN until a
network layer handoff is completed. In this case, the MN would eventually receive an
advertisement from the FA2 through AP2(message 2 in figure 5-1). The mobile IP
software running on the MN intercepts these advertisements and sends a registration
request to FA2(message 11). This registration request is forwarded by FA2 to the
HA(message 12). After the authentication(not show in figure 5-1) a registration reply is
sent to the FA2(message 13) and is relayed to the MN(message 14). The mobile IP handoff
is over and an IP-over-IP tunnel is established between the HA and FA2. From this point
onwards, the HA, acts as a proxy for the MN, forwards all packets to FA2 over the tunnel.
FA2 de-encapsulates the packets and forwards them to the MN. Similarly, all packets that
the MN transmits to the CN are first received by FA2 and are tunneled over to the HA,
which further routes them to the CN. This process is known as bidirectional tunneling.
The above process of switching from FA1 to FA2 as the MN moves across adjacent
wireless cells is called mobile IP handoff. After the moves to a new wireless LAN cell but
before the associated mobile IP handoff completes, the mobile node is essentially cut off
from the wired network. For a rapid moving MN, this mobile IP handoff latency greatly
deduces the network performance. In extreme cases, the MN may even not be able to
accomplish mobile IP handoff. For example, assume a rapid moving MN moves at speed
V(m/s), the wireless LAN cell size is D(m) and the mobile IP handoff latency is T(s). If V
x T > D, the MN can never register to the wired network. Therefore, it is critical to reduce
the mobile IP handoff latency in rapid moving environments.
Algorithm of Speed Adaptive MIP
In Chapter 3, we define MN handoff rate as rh = v / d. It means MN move through
how many APs or FAs per second. Chapter 3 also shows that the performance of MIP over
WLAN is depends on the MN handoff rate among FAs. Figure 3-13 shows when the
handoff rate is 0.02 FA/s, the average throughput is above 90kBytes/s. When the handoff
rate rises to 0.08 FA/s, the average throughput drops to around 50kBytes/s. This means
lower handoff rate has higher throughput. rh is also equal to the ratio of Khandoff/Ttravel. We
rewrite the handoff rate rh = v / d in Equation 7.
rh = Khandoff/ Ttravel. (Equation 7)
Where Khandoff is the number of handoffs occurred during the MN traveling. Travel is
MN's total travel time. In order to reduce handoff rate without changing total travel time,
we can reduce the number of handoffs. The optimal is Khandoff = 0
Let N be total FA numbers on the way MN traveling. Let's assume somehow M is
the number of FAs with whom the MN can communicate without L3 latency. The optimal
is M=N. But it costs too many resources, especially when the number of active MNs is
large. Also we don't know how long will the MN travel at the beginning.
We call M the size of the FA Set with whom the MN can communicate without L3
handoff latency. From IP level of view, M is the number of FAs that MN has registered to
and can communicate with at that moment.
Now the question is:
How to decide FA set size M
How to guarantee MN can communicate with a FA set almost like to do with a
The first problem SA-MIP needs to deal with is to decide FA set size M. In SA-MIP
algorithm, M is decided by the following Equation.
M = handoff r +1 (Equation 8)
where t .. is the handoff time for every handoff procedure, and rh is the handoff
rate. Here we use the experimental average handoff time 9.142s for t .. rh is dynamic.
For example, at speed 40m/s, AP distance 500m, M = 9.142 x 40/500 1 + 1 = 2. At speed
80m/s, AP distance 500m, M = 3.
The second problem is how to guarantee MN can communicate with a FA set just
like it can do with one FA. Our solution is to let MN pre-register M potential FAs along the
way MN traveling, at the same time multicast IP packets to those FAs in this FA set. So
MN won't feel any handoff latency from the IP level of view.
In Speed Apative MIP(SA-MIP), the set of FAs that MN can talk to without L3
latency is extended from one point at low moving speed to a line at high moving speed.
The length of the line dynamically changes with the MN handoff rate as in figure 5-2. The
behavior of SA-MIP will automatically adapt to the handoff rate of the MN so that the
performance of SA-MIP won't decline dramatically in rapid moving environments. At the
same time SA-MIP only cost reasonable resource that is as much as enough for seamless
M=l M=2 M=3 M=4
rh= 0 0rh < 0.109 0.109
Figure 5-2 FA Set size vs handoff rate
Speed detection and location tracking is an interesting topic on mobile computing.
[BahlOO][Yous03] are all making use of signal strength information to locate and track
wireless users. [Erge02] uses GPS to inform mobile users about the prospective future
location and to improve performance of the ad hoc routing. In this paper, we assume the
MN has GPS system to detect its location. When the MN moves at speed v, ifv <
30m/s(67. 10miles/h), it performs a normal registration. If 30m/s < v < 40m/s(89.4miles/h),
it initializes registration after receiving two successive agent advertisements. If v>
40m/s(89.4miles/h), we assume the MN won't change it's direction largely in a short
distance. It initializes registration once it gets a new agent advertisement.
MN's registration message is extended by speed extension. According to Mobile IP
Vendor/Organization-Specific Extensions[RFC3115]. Two Vendor/Organization Specific
Extensions are allowed for MIP, Critical (CVSE) and Normal (NVSE)
Vendor/Organization Specific Extensions. The basic difference is when the CVSE is
encountered but not recognized, the message containing the extension must be silently
discarded, whereas when a NVSE is encountered but not recognized, the extension should
be ignored, but the rest of the Extensions and message data must still be processed. We use
the NVSE extension.
The following is the NVSE format.
0 1 2 3
01 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901 2 3 4 5 6 7 8 901
| Type | Length | Reserved I
I vendor/Org-ID |
I vendor-NVSE-Type | vendor-NVSE-Value ...
Figure 5-3 Normal vendor/organization specific extension
In figure 5-3, the type here is 134 for NVSE extension. Length is the size in bytes of
the extension, not including the type and length bytes. The verdor/org-ID is assigned in
RFC 1700. We pick up a large unassigned number 5205. Vendor-NVSE-Type Indicates
the particular type of Vendor-NVSE-Extension. The administration of the
Vendor-NVSE-Types is done by the Vendor. Vendor-NVSE-Value here is a floating point
number for handoff rate.
Figure 5-4 shows the SA-MIP handoff procedure and message exchange.
Whenever the MN needs to handoff to a new FA set, after it gets that many times of
agent advertisements which is determined by speed(step 1 in figure 5-4), it sends a
registration request with up-to-date handoff rate information to the very first FA in a new
FA set(step 2). The first FA relays the registration request to upper FA or HA(step 3).
Meanwhile, it decapsulates the speed extension, refill the MIP header and authentication
extension and then forward it to other FAs(M-1 FAs) in this FA set(step 4). Assume the
handoff rate is below 0.109. The FA set size at this time is 2. These other FAs relay the
registration request to upper FA or HA as well, just like the request comes from the
MN(step 5). When the GFA or HA received these registration requests, it builds up tunnels
downwards to each FA and responses with registration reply(step 6 and 7). When the FA
received the registration reply, it builds up tunnel upwards to the GFA or HA.
FA1 4 12i FA3 FA4
Figure 5-4 SA-MIP handoff procedure
Whenever the MN setups the Link-layer contact with the FA, the later forwards the
registration reply to the former(step 9 or 10). The MN gets the care-of-address from agent
advertisement message(step 10 or 9) or registration reply message(step 9 or 10), and
begins data communication. At the same time, it sends registration request to the new FA
with up-to-date speed information (step 11). This new FA decapsulates the registration
request message and sets up a new FA set. Assume the handoff rate is between 0.109 and
0.218. The FA set size is 3 at this time. The new FA(FA2) refill the MIP header and
authentication extension and then forward it to other FAs(FA3 and FA4 in the figure) in
this FA set and repeats the above process. In Figure 5-4, the FA set size M changes from 2
to 3 when the MN handoff rate changes from 0.08 to 0.11.
Implementation of Speed Adaptive MIP
Mobile IP has three main entities, HA, FA and MN. HUT dynamic MIP
implementation version 0.8.1, originally developed at Helsinki University of Technology
(HUT), is a scalable, dynamical, and hierarchical Mobile IP software for Linux operating
system. The SA-MIP is developed on HUT dynamic MIP implementation version 0.8.1.
The HA implementation of SA-MIP is almost the same as HUT dynamic MIP except
the Registration Request validation check function. The following describes the basic
functionalities of HA.
The HA is responsible for encapsulating and forwarding packets to its MNs when
they are away from their Home Network. It also decapsulates and forwards tunneled
packets originating from its Mobile Nodes. The HA communicates with FAs and MNs
using Berkeley IP sockets. The HA listens to ICMP agent solicitation messages from MNs
on a "packet" socket. ICMP agent advertisement messages are sent in reply to these
messages on the same socket. The HA also listens to Registration Requests on a UDP
socket (port 434 by default) originating from FAs or MNs. If Registration Requests is
validate a mobility binding for the requested Mobile Node will be established or, if one
already exists, updated. The request is then answered with an corresponding Registration
When received of a Registration Request Message the HA performs a Registration
Request validation check process. It first looks up the shared secret for the corresponding
MN. The shared secret is used to check the MAC of the request message. If a Mobility
Binding for the MN exists, then the timestamp in the request is checked to be greater than
the one in the Mobility Binding. If either of these checks fails the HA responds to the
sender with a Registration Reply indicating registration failure. If the checks succeed the
HA determines the smaller lifetime value of the one in the request and the HA's
pre-configured maximum value. It then generates a Session Key and creates a Mobility
Binding consisting of the MN's address, its highest FA, the identification timestamp and
the Session Key. The HA then responds with a Registration Reply indicating registration
success. The message includes the same timestamp as the request, the lifetime value, a
MAC, the Session Key encrypted with the shared secret and the Session Key encrypted
with the highest FA's public key. The HA configures a tunnel between itself and the
highest FA and works as a proxy for the registered MN. If the lifetime in the request is set
to zero, the HA interprets this as a deregistration from the MN. On deregistration the HA
purges the tunnel configuration and stops the proxy ARP functionality for the MN's
address. If the FA differs in a reregistration, a Registration Reply with a lifetime set to
zero is sent to the previous FA to indicate that the old tunnel should be torn down.
In order to focus on performance issues of mobile IP, we ignore the security check
part. When the HA checks the validation of the Registration Requests, the MN-HA
authentication check is comment out. Figure 5-5 is the function flowchart of Registration
Main loop() ] Handle_reg_msg()
Figure 5-5 Function flowchart of registration in HA
In addition to the basic function of HUT dynamic MIP's MN, the MN of SA-MIP
needs to transfer moving speed information to FAs. This is done by extending the
Registration Request message with speed extension. The Registration function in HUT
dynamic MIP implementation is the method by which MN requests forwarding services
when visiting a foreign network, informs their HA of their current CoA, renews a
registration which is due to expire, and/or deregisters when they return home.
The Registration Request message has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
S Type = 1 ISI|BIDIDM|G|r Tx Lifetime
+ Identification +
Optional Non-Auth Extensions for HA ...
Type =32 Length SPI
: MN-HA Authenticator ( variable length
Optional Non-Auth Extensions for FA .........
Optional MN-FA Authentication Extension...
Figure 5-6 Registration request message format
The Registration Request message header consists of the fields from Type to
Identification. The sendregistration () function in the MN implementation first fills out
the Registration Request header with corresponding data then fills out the extension.
Figure 5-7 is the Registration Request Message extension format.
0 1 2 3
01 2 34 5 6 7 8 01 2 34 5 6 7 01 2 3 4 5 6 7 8 9 1
S Type | Length | Reserved
S vendor-NVSE-Type | vendor-NVSE-Value ...
Figure 5-7 Registration request message extension format
The speed extension is as following.
struct speed_ext mn_speed; // speed_ext struct for SA-MIP
if(speedChanged) //compare the handoff rate send last time with current one.
mn_speed = (struct speed_ext *) pos;
if (left < sizeof(struct speed_ext)) //left is the message size after Registration
mn_speed ->type = VENDOREXT_TYPE2;
mn_speed ->length = sizeof(struct speed_ext) 2;
mn_speed ->reserved = 0;
mn_speed ->vendorid = htonl(VENDORIDDYNAMICS);
mn_speed ->sub_type = 25
mn_speed -> mn_spd = handoff_Rate;
pos += sizeof(struct speed_ext);
left -= sizeof(struct speedext);
Figure 5-8 show the function flowchart of sending Registration Request
Figure 5-8 Function flowchart of sending registration request
Whenever the FA received a Registration Request from the MN, it decapsulates the
message, checks the speed extension. If the handoff rate is non-zero, this FA calculates the
FA set size M. It fills out the Registration Request header with new CoA and new MD5
MN-HA authentication. This new Registration Request message is sent to next M-1 FAs,
which in turn forward the Registration Request one level up or the HA.
Figure 5-9 is the function flowchart for FA handling Registration Request.
Figure 5-9 Function flowchart for FA handling registration request.
Evaluation of Speed Adaptive Extension for MIP
We evaluate the performance of SA-MIP over WLAN under the same scenario as in
Section 3. Figure 5-10 amd 5-11 are the time-sequence graph at speed 60m/s(rh = 0.06)and
80m/s(rh = 0.08) and AP distance 1000m. The average throughput at different speed is
listed in table 5-1
nrtM l 1
9O l -
1 OD )0 -
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
S 10 2 u 25 30 35 I4 46 SO Sq C 6t 0 65 M s 90 9a 100 It s 110 11s 1a IS I V 13 140 145 150
Figure 5-10 Time-sequence graph at speed 60m/s and AP distance 1000m
S'I "+ "I" "I I '"I "I' 'I""I" "I" "I"' I"I "I'" 'I'"'I'" I" "I "I"" I" I '"I '"I'"
5 10 15 20 25 30 3 40 45 50 5 W 65 70 75 80 8 90 5 10 105 10
Figure 5-11 Time-sequence graph at speed 80m/s and AP distance 1000m
Table 5-1 Average throughput for speed-adaptive MIP
Speed AP Bytes Travel Arg Handoff
(m/s) distance transferred Time(s) throughput Rate
(m) (kB) (kB/s) (FAs/s)
20 1000 85000 399 213.03 0.02
40 1000 37500 198 189.39 0.04
60 1000 19400 130 149.23 0.06
80 1000 11600 99 117.17 0.08
10 500 84400 398 212.06 0.02
20 500 37400 198 188.89 0.04
30 500 19500 131 148.55 0.06
40 500 11500 98 117.34 0.08
Figure 5-12 is the average throughput vs. handoff rate before and after the speed
adaptive MIP is installed. After installing SA-MIP, at handoff rate 0.02 FA/s, the average
throughput is improved by (212.54 197.35)/ 197.35 = 7.69%. At handoff rate 0.04, 0.06
and 0.08 FA/s, the average throughput is improved by 13.02%, 15.97% and 24.73%
(212.55- 197.35) /197.35
(189.14- 167.34) /167.34
' (148.89 128.32) /128.32
(117.25- 94.12) /94.12 =
0 0.02 0.04 0.06 0.08
Handoff rate FA/s
Figure 5-12 Average throughput vs. handoff rate
SUMMARY AND FUTURE WORKS
In this dissertation, in order to evaluate the rapid mobility of MIP in a laboratory
environment, we build up the performance evaluation testbed on Wireless LAN. The
emulation experiments showed that MIP is not suitable for rapid moving environments.
We depicted the relationship between the performance and the handoff rate of MN and
quantitatively analyzed the handoff latencies of the MIP over wireless LAN. A Speed
Adaptive MIP is proposed and evaluated. The emulation showed that the SA-MIP can
improve the performance from 8% to 25% when the handoff rate changes from 0.02 FA/s
to 0.08 FA/s. Compared to the mechanisms of Malki[Malk02] and Koodli's
mechnism[Kood02], SA-MIP combines the pre- and post-registration methods, but keeps
indenpendency from L2 infrastructure. Compared to Hsieh[Hsi03] and Wijngaert's
mechnism[Wijn04], SA-MIP not only predicts its next move but also involves next M
number of FAs according to MN's moving speed.
In our work so far, SA-MIP only deal with L3 handoff latency. But there is still
physical link break from the Layer 2 handoff And also we noticed that even in SA-MIP,
the biggest part of handoff latency was still the layer4 TCP back-off-latency. In future
works, the speed adaptive scheme should be applied to layer 2 and layer 4 handoff