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Mobile IP
Performance Issues in Practice
Introduction

What is Mobile IP?
– Mobile IP is a technology that allows a "mobile
node" (MN) to change its point of attachment
to the Internet while communicating with the
"correspondent node" (CN) using IP.

Portable IP verses Mobile IP
= Laptop verses Mobile Phone
Key Issues
Why need Mobile IP?
 Implementation of Mobile IP
 Mobile IPv4
 IP Routing
 IP QoS

So, why Mobile IP?



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In original IP routing, mobility of hosts was not
considered to be an issue.
Routing methods built for static networks
Hosts were unlikely to move from one subnet to
another.
Mobile IP defines protocols and procedures by
which packets can be routed to a mobile node,
regardless of its current point-of-attachment to the
Internet, and without changing its IP address.
Mobility: Vocabulary
Permanent address: remains
constant (e.g., 128.119.40.186)
visited network: network
in which mobile currently
resides (e.g., 79.129.13/24)
Care-of-address: address
in visited network.
(e.g., 79.129.13.2)
wide area
network
correspondent hosts:
wants to communicate
with mobile device
foreign agent: entity in
visited network that
performs mobility
functions on behalf of
mobile agent.
Mobility via Indirect Routing
foreign agent
receives packets,
forwards to mobile
home agent intercepts
packets, forwards to
foreign agent
home
network
visited
network
3
wide area
network
correspondent
addresses packets
using home
(“permanent”)
address of mobile
1
2
4
mobile unit
replies directly
to correspondent
Packet Formation
Data sent by a node to a Mobile IP
HA IP
Header with
Mobile IP
Header
Data
New Data Packet from Home Agent to MN
Mobile IP v4 – Registration Request Header
Mobile IP v4 – Registration Reply Header
Mobile IP v4 – UDP Packet Header
IP Routing

Two most popular protocols:
– Distance Vector Protocol
– Link State Protocol
Distance Vector Protocol




In DVP, each node contains a routing table with a
list of shortest paths to the other nodes in the
network
At start, each node has knowledge of its own
address and is able to transmit on all links
connecting to neighboring nodes
If distance to the node is shorter than the distance
in the routing table, the distance table is updated
with the new value
When transmission of distance vector no longer
causes an update of the tables, the protocol
converges and the topology of the network has
been fixed
Link State Routing Protocols
All nodes maintain a distributed map of the
network
 Maps are updated quickly, when network
topology changes using….??
 LSP use Shortest Path First algorithm
(Dijkstra’s Algorithm)
 Considered better than Distance Vector
Protocols. Why ??

Why these protocols Fail in Mobile IP
Cellular Systems and Internet networks
supporting mobile users depend on a fixed
infrastructure
 Base station can always reach all mobile
nodes in the cell without routing, via a
broadcast
 But, Mobile Networks have a special case of
Ad-Hoc Networks

Routing in Ad-Hoc Networks

In Ad-hoc networks,
– A fixed infrastructure is missing and topologies
change quickly
– A destination node might be out of range of a
source node transmitting packets
– Each node must be able to forward data to
other nodes
So why do they fail in Ad-Hoc networks




Dynamic routing algorithms assume network
topology does not change during transmission
they would react too slowly or generate too much
traffic to update the tables – their updating
frequency of about 30 sec is too long for ad-hoc
networks
Routing algorithms depend on symmetric links in
which routing information colleted for one
direction can be used for other direction – in adhoc networks, links can be asymmetric
Interference amongst close nodes that
simultaneously forward transmissions
QoS Issues

Most popular techniques:
– IntServ and RSVP
– DiffServ
– MPLS



IntServ maintains per-flow states in each node
DiffServ approach discriminates amongst
datagrams in different classes, not flows
MPLS forces traffic into specific labeled switched
paths (LSPs) using routers called as labeledswitching routers (LSRs)
Performance considerations

The RSVP method does not fit into Mobile
IP QoS architecture
Resv
S
R1
R2
R3
Path
RSVP Operation
R
Failure of RSVP

Processing overheads and memory
consumption directly proportional to the
number of separate RSVP reservations

Also, states reservation is not possible over
the tunnel between Home Agent and Foreign
Agent… why ??
Solution – RSVP over IP Tunnels
This mechanism enables reservations across
all IP-within-IP tunnels
 The tunnels are of three types:

– Type 1: no QoS guarantees (best effort tunnel)
– Type 2: no resource allocation to individual data
flows, but QoS guarantees to aggregate flows
– Type 3: resource allocation for individual end to
end flows
RSVP over IP Tunnels (contd)
M3
M1
R1
Intermediate
Router
Intermediate
Router
R2
M2
IP TUNNEL
M4
Mobility Management in Real Time
Services


Makes use of the “mobility notification method”
Working
– sender delivers a PATH message to MN
– When mobile node not connected to HN, HN captures the
RSVP message and replies to sender with a PathChange
message containing the COA of MN and its own address
(MOBILITY_NOTIFICATION Object)
– Source receives PathChange message, caches it and sends new
PATH message to mobile node, tunneling it to COA