Mobile IP 2

Background
• With new applications developing at a rapid
pace, and advancements in Mobile
Computing technology, the number of users
replacing their desktop PCs with super-
portable laptops is on the up.

Topics covered
• Simple overview : Mobile IP
• Tunneling
• TCP Comparison
• Route Optimization
• Mobile IP in IPv6

Design Goals : Mobile IP
• Make size and frequency of routing updates
as small as possible.
• Software level : Simplicity in
implementation
• Allow mobile nodes to operate with on one
IP address, instead of a spool of addresses.

Terminology
• Mobile Node
• Home Address, Home Link, and Home
Agent.
• Care-of Address, Foreign Link, and Foreign
Agent.

Components : Mobile IP
• Agent Discovery : Provides information
about home and foreign agents to the
mobile node.
• Registration : Mobile node requests services
from its foreign agent.
• Mobile IP defines the rules for routing any
type of packet - unicast, multicast, and
broadcast.

Overview of Operation

• When a mobile host moves out of its home
site, it contacts the closest foreign agent.
• Registration takes place.
• Previous foreign(local) agent if any are
notified regarding the change.
• Communication starts. (also known as
triangle routing).

Figure 1 :CN sending data to MN at home

Correspondent node

bulk data

acknowledgements

Home agent Foreign agent

bulk
adv
acknowledgements
Scenario A:
Mobile node No tunnelling
No fragmentation
No dogleg route

Figure 2:MN sending data to CN from home

Correspondent node

acknowledgements

bulk data


acknowledgements
adv
Scenario B:
bulk
No tunnelling
Mobile node No fragmentation
No dogleg route

Figure 3:CN sending data to MN through Foreign Agent

Correspondent node

bulk data acknowledgements

tunnelled bulk data


bulk data
Scenario C: adv
MTU is 1500 bytes acknowledgements
Tunnelling of bulk data
Fragmentation Mobile node
Dogleg route

Figure 4:MN sending data to CN via Foreign Agent

Correspondent node

acknowledgements bulk data

tunnelled acknowledgements

Foreign agent
Home agent

acknowledgements
Scenario D: adv
No tunnelling of data bulk data
Tunnelling of acks
No fragmentation Mobile node
Dogleg route

TCP Performance in Mobile-IP

• Factors affecting TCP performance
– Tunneling overhead
– Dogleg route overhead
– Fragmentation overhead
– Handover overhead

Scenario 1:
Correspondent node

bulk data

acknowledgements


bulk
adv
acknowledgements
Scenario A:
Mobile node No tunnelling
No fragmentation
No dogleg route

Fig. 1 - Mobile node is receiving bulk data from the
correspondent node while the mobile node is at home. MTU
is 1500 bytes

Scenario 2:
Correspondent node

acknowledgements

bulk data


acknowledgements
adv
Scenario B:
bulk
No tunnelling
Mobile node No fragmentation
No dogleg route

Fig. 2 - Mobile node is sending bulk data to the
correspondent node while the mobile node is at home. MTU
is 1500 bytes

Scenario 3:
Correspondent node


tunnelled bulk data


bulk data
Scenario C: adv
MTU is 1500 bytes acknowledgements
Fragmentation Mobile node
Dogleg route

correspondent node while the mobile node is at a foreign
network. MTU is 1500 bytes

Scenario 4:
Correspondent node

acknowledgements bulk data

tunnelled acknowledgements

Foreign agent
Home agent

acknowledgements
Scenario D: adv
No tunnelling of data bulk data
Tunnelling of acks
No fragmentation Mobile node
Dogleg route

Fig. 4 - Mobile node is sending bulk data to the

Scenario 5:
Correspondent node


tunnelled bulk data


bulk data

adv
acknowledgements
Scenario E:
MTU is 1450 bytes Mobile node
No fragmentation
Dogleg route


Comparisons: Differences in Setup

Scenario : Sender of the Location of MTU (in
file mobile node bytes)
A CN At home 1500
B MN At home 1500
C CN At foreign 1500
D MN At foreign 1500
E CN At foreign 1450
Table 1 - Differences in setup between the five different scenario

Comparisons: Presence of tunneling, fragmentation
and dogleg route

Scenario : Tunnelling Fragmentation Dogleg route
overhead overhead overhead
present? present? present?
A No No No
B No No No
C Yes Yes Yes
D Yes No No
E Yes No Yes

Test Details

• MTU in scenario 5 was reduced solely to
prevent fragmentation.
• Comparison using FTP file transfer, 30.2
MB file ≈ 241.6 Mbits
• Repeated 20 times
• Throughput = file size / mean transfer time
• % throughput = throughput / maximum
capacity of link

Comparisons: Mean transfer time and standard
deviation for FTP file transfer

Scenario : Mean transfer Standard Throughput
time (s) deviation (s) (Mbit/s)
A 41.21 1.81 5.86
B 43.30 1.04 5.58
C 78.22 1.43 3.09
D 46.17 1.14 5.23
E 75.62 1.33 3.19

Evaluations
• File transfer takes 90% more time to complete, with all 3
overheads.
• Encapsulation and Decapsulation of bulk data or
acknowledgments takes the same time
• The longer route results in a higher delay before the
packets reach the mobile node
• Link usage will increase if the IP packet and its
encapsulated form both use the same link while being
routed to the destination
• The tunneling overhead causes the file transfer to take
about 7% more time to complete

Evaluations
• Fragmentation overhead causes the file transfer to take
about 6% more time to complete
• The dogleg route overhead obtained using this method
causes the file transfer to take about 80% more time to
complete
• The handover overhead will depend on the TCP handover
latency, the frequency of handoffs, the duration of the TCP
connection and the agent advertisement interval
• The TCP handover latency is about 60% more than the
MIP network handover latency

Evaluations

• The handover overhead is about 13%.
• Two ways of reducing the handover overhead:
– reduce the retransmission timer value
– reduce the agent advertisement interval.
• Tradeoff: bandwidth consumption

Route Optimization and
Authentication

• The paper describes the Internet Mobile
Host Protocol with the following features:
– route optimization
– authentication of management packets
– performance and operational
transparency to the user.

IMHP Architecture Entities

• Mobile host
– unique home address
• Local Agent
– helps mobile host register, provides care-
off address
– maintains a visitor list
• lists all the mobile hosts
• needs to be refreshed


• Cache Agent
– Maintains the location cache
– using cache entry the data packet is
“tunneled” to the mobile host.
• Done by including a small IMHP header
• adds 8 or 12 bytes of overhead to each
packet


• Home Agent
– maintains a home list
– special case: home agent maintains a
visitor entry for mobile host
– must also be a cache agent for its mobile
hosts

Authentication
• Basically required to authenticate
binding and management packets.
• MH to HA : by including an
authenticator based on a shared secret
• General Authentication: node sends a
request for binding with random
number and gets reply with the same
number.

Authentication
• Use of route flag in management packet to
enforce normal IP routing of packet.
• Local agent authenticates visitor list entries
from the home agent.
• All entries into lists are timer based.

Optimization
• special tunnel packet - destination of
tunnel is same as destination of packet.
• Specified as a set of forwarding rules
for the IMHP entities.

Rules for forwarding
• Node receives tunneled packet with its
own destination address.
• Node receives a non-tunneled packet
with its own destination address

Rules: Home Agent
• HA receives an IMHP management
packet with route flag set.
• HA receives a special tunnel packet.
• HA receives packet for one of its
mobile hosts
– HA has a visitor entry for the host.
– HA does not have a visitor entry.

Rules: Home Agent
• HA never tunnels a packet back to a
node that has just tunneled the packet
to it.

Rules: Other Agents
• Receives special tunnel packet with route
flag set.
• LA receives a tunneled packet for host in
visitor list.
• LA receives a regular packet for host in
visitor list
• CA receives a packet and has an entry in its
location cache.

Rules: Other Agents

• Receives packet that was tunneled directly
to this node, and the agent is unable to
forward it further.
– Solution : special tunnel

Bindings

• Binding notifications:
– MH notifies HA and previous LA about
“change of address”.
– Any node can notify any other node
about wrong binding information stored
by it.
– Notification Back-off

IMHP : Other Issues

• restrictions on advertising bindings - use of
private flag.
• MH in Popup Mode
– requires facilities such as DHCP
– acts as its own local agent.
– Binding should be kept private
• Performance of MH at home should be like
a stationary host.

Mobility Support in IPv6
• IPv6:
– 128 bit address space
– link local addresses
• Extension headers : Destination
Options header, hop-by-hop header,
routing header and an authentication
header.

Overview of Mobile IPv6
• All packets carrying information must be
authenticated.
• Avoid “remote redirection” attacks
• Allows MH to allow more than one care-of
addresses at a time, but registers only one of
its bindings.
• Allows CH to dynamically learn the MH’s
binding. In this case it uses the Routing
header but does not encapsulate.

Overview of Mobile IPv6

• Reasonable to expect all the IPv6 nodes to
have caching capabilities.
• Implementation of the Binding Updates and
Binding Acknowledgments - the key to
reliability and optimization.

Binding Update Option

• Provides optimization and performance in
IPv6
• Used by mobile host to:
– notify home agent of its primary care-of
address
– notify correspondent nodes of its current
binding
• Binding Updates should always be
authenticated.

Binding Update Format

• Lifetime:time duration for which the
binding remains valid.
• Identification: To ensure in order
processing of updates.
• Care-of address: Holds the current care of
address

Binding Update Format

• Flags:
– H: Destination requested to serve as home
agent.
– A: Acknowledgment expected
– L:Link Local address present
• Updates could be retransmitted if there is no
acknowledgment.

Binding Acknowledgment Format

• Code: indicates whether binding update
was accepted or rejected.
– < 128 update accepted
– >= 128 update rejected
• Lifetime: during for which node will retain
the binding.
• Refresh: time interval for sending updates
• Identification: Same number as the update.

Sending Updates

• First update sent to home agent to register
the new care-of address.
– From another foreign network
– From the home network
• Can be included in a regular packet or sent
alone.
• Only the mobile node can send its own
binding updates.

Movement detection

• Neighbor Discovery protocol including
Router Discovery and Neighbor
Unreachability Detection to create list
• Selects the default router from the list
• configures its care-off address

Unreachability

• detecting unreachability
– using the Neighbor Unreachability detection
– using the higher layers
– using the lower layers.
– When not receiving packets

Smooth Handoffs

• Using overlapping cells - accept packets at
multiple addresses for a short while.
• Router Assisted - Previous router can
forward packets to new local router.

• Renumbering the home network

CH & HA Operations

• Sending packet to MH
• Handling ICMP error messages
• Home agent discovery

More information on Mobile IP

• National University of Singapore
• Carnegie Mellon University
• Columbia University

• Presentation based on the reading
list sent out earlier.

All diagrams and tables have been included
from the reading list research papers.

Mobile IP

Prashant Bhargava
CS 599 : Wireless Communications
and Mobile Computing
602 08 8857

Mobile IP 2

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