Mobile Network Layer

Introduction
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In this protocols and mechanisms developed for
the network layer to support mobility.
It provides protocol enhancement that allows
transparent routing of IP datagrams to mobile
nodes in the internet.
Mobile IP – Adds mobility support to the
internet network layer protocol IP.
RFC 2002 is a reference document for the
complete detail about the mobile IP.

Goals, Assumptions and
Requirements
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Receving of IP datagram after leaving your home network.

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Now nodes needs a so-called topologically correct address.
Quick Solution
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Assign new IP address when enter into new location.
● Increase problem with higher layer protocols like TCP , as
they rely on IP layer.
● Routers are built for fast forwarding but not for fast update
of routing table.
Quick solution not working.

Entities and Terminology

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Mobile Nodes – a host or router that changes its point of attachment from one
network or subnetwork to another.
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Home Agent – a router on a mobile node's home network which tunnels
datagrams for delivery to the mobile node when it is away from home.
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Mobile node change its location without changing its IP address.

Also, maintain current location information for the mobile node.

Foreign Agent – router on a mobile node's visited network which provides routing
services to the mobile node while registered.
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It detunnel and deliver the datagram to the mobile node that were tunneled by
the mobile node's home agent

Entities and Terminology(Cont.)
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Correspondent Node (CN) – partner through which MN is connected. It can be
a fixed or mobile node.
Home network – it is subnet the MN belongs to.
Foreign network – it is a current subnet the MN visits and which is not a home
network.
Care-of Address – it defines the current location of the MN from an IP point of
view.
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All the packets sent to the MN are delivered to the COA,not directly to the IP
address of the MN

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Marks the tunnel endpoint (i.e address where packets exit the tunnel)

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Location of COA:●

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Foreign agent COA – COA could be located at the FA, i.e COA is an IP
address of the FA.
Co-located COA – if the MN temporarily acquired an additional IP
address which acts a COA.This address is topologically correct , and the
tunnel endpoint is at MN.

IP packet delivery

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CN wants to send an IP packet to the MN.
Internet , not having info on the current location of MN, routes the packet to the
router(Home Agent) responsible for the home network of MN.

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HA now intercept the packet(to find current location)

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Not found in home n/w then encapsulated and tunnelled to the COA.

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A new header put in front of the old header showing the (FA) COA as the new
destination.
FA now decapsulates the packets (remove additional header)
Last, MN sends the packets as usual with its own fixed IP address as source and
CN's address as the destination.

Agent Discovery
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One initial problem of an MN after moving is
how to find a foreign agent ?.
Two types of methods:
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Agent advertisement – in this HA and FA
advertise their presence.
Agent solicitation – the mobile node send agent
solicitations messages.

Agent Advertisement
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FA and HA advertise their presence
periodically using special agent
advertisement message.
ICMP messages are used with some mobility
extensions.
Upper part represent ICMP while lower part
represent extention needed for mobility.

Agent Advertisement Packet
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ICMP part
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Code – 0 or 16

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#addresses – no. of addresses advertised
with this packet

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Lifetime – length of time this advr. is valid

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Type – 9

Preference – most eager router to get new
node

Extension part – for mobility
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Type – 16

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Length – depends on no. of COAs provided
with the msg.

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Seq. No

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Reg. Lifetime – max. lifetime in sec. a node
can request during reg.

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R – reg. , B – busy , H – HA , F – FA ,
M & G – method of encapsulation , V version

Agent Solicitation
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No agent advertisement

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Mobile node must send agent solicitations.

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Sould not flood the network

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MN can send three solicitations msgs. , one
per sec. , as soon as enter in new network.
Discovery of new agent can be done
anytime.

Registration
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Objective – is to inform the HA of the current
location for correct forwarding of packets
After receving COA address the MN has to
register with the HA.
Registration can be done in two ways:–
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Registration of mobile node via the FA
Or , directly with the HA

Registration (COA is the FA)

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If the COA is at the FA then,
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MN sends its registration request containing the
COA to the FA which then forward the request to the
HA.
Now HA will do the mobility binding containing the
mobile node's home IP adress with the current
COA.

Registration (COA is co-locted)
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If the COA is co-located.
MN send the request directly to the
HA and vice versa.
Also , a registration procedure for MNs
returning to their home network.

Registration request

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UDP packets are used for registration requests.
IP source address is the MN interface address and IP destination address is
the FA or HA address.
Type – 1 , S – an MN wants the HA to retain prior mobility binding
B – MN want to receive broadcast packets received by HA in home n/w

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M & G – minimal or generic routing encapsulation.

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Destnation port – 434

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UDP is used because of low overheads and better performance.

Registration Reply

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Type – 3

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code – result of the registration request

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lifetime – validity of the registration ,

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Home IP address

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Home Agent address

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64-bit identification used to match the registration request with reply

Tunneling & Encpsulation

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It is mechanisms used for forwrding packets between the HA and
COA.
Packets entering a tunnel are forwarded inside the tunnel and leave the
tunnel unchanged.
It can be achieved by using encapsulation.
Encapsulation is the mechanism of taking a packet consisting of
packet header and data and putting it into the data part of a new
packet.
The reverse of encapsulation is decapsulation.

Encapsulation Methods
IP-in-IP encapsulation
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Ver – IP protocol version no.

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IHL – internet header length

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TOS – type of services (copied from
inner header)
Length – complete encapsulated
packet length.
IP id. , flags , frag. offset – used
for fragments
TTL -time to live

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IP-in-IP – upper layer protocol

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IP checksum – error detection

IP-in-IP encapsulation packet format

Minimal Routing Encapsulation

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In IP-in-IP several fields re redundant

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Minimal encapsulation will remove these redundancy

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Type – 55

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If S bit is set , the original sender address of the CN is
included.

Generic Routing Encapsulation
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Minimal and IP-in-IP only works for IP while
generic routing also supports other
network layer protocols

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GRE header starts with several flags

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C – checksum is present

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R – offset and routing info present

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K – key field , used for the aunthentication

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S – sequence number present

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s – strict source source routing is used
rsv. - is used to distinguishes GRE from IPin-IP and minimal encapsulation
Protocol – the protocol of the packet
following the GRE.

Optimization
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Mobile IP is having inefficient behavior which is
known to be as a triangular routing
HA

To optimize the route is to inform the CN of the
current location of the MN.
And , CN will cache it in a binding chache.

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The entity to inform the CN of the location is the
HA.
Optimized mobile IP protocol needs four
additional messages :–

Binding request

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Binding update

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Binding acknowledgement

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Binding warning

CN

COA/MN
3

Optimized mobile IP
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CN request current location from HA using
binding request.
HA return the COA address using binding
update.

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Now CN directly send to FA old.

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Tunnel is formed between CN nd FA old.
MN now change its location

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Register with FA new
This info is forwarded to HA to update its
location.
FA new will inform FA old about the new
registration.
Still CN send data to FA old which forward the
data to FA new.

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FA old will send the binding warning to CN.

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then , CN sends binding request to HA

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and get the updated FA of the MN.

DHCP
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Dynamic Host Configuration Protocol

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Self Study

Mobile Ad-hoc networks
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Till now mobility of the nodes is supported by the at least some
infrastructure.(home agent, tunnel etc.)
Their are situations where their no infrastructure.
Mobiles nodes in an ad-hoc scenario comprise routing and end
system functionality.
Under those conditions we use multi-hop ad-hoc network when
describing ad-hoc networking.
Use of such network
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Instant infrastructure
Disaster relief
Remote areas

Routing
Differences between wired n/w and ad-hoc n/w
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Asymmetric link – signal quality uneven in both direction
of the link.
Redundant links – wired n/w have few redundant links
while ad-hoc will have many redundant links.
Interference – it is very high in case of wireless ad-hoc
n/w
Dynamic topology – change in topology is very frequent
which affects the routing table and routing methods.

DSDV Routing
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Destination Sequence Distance Vector is an enhancement
to ditance vector routing for ad-hoc network.
Distance Vector – exchange distance vector to its
neighbors for all destination.

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Problem with DV is the cout-to-infinity.

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DSDV adds two things to the DV
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Sequence No. - each routing adv. comes with a seq. no. Seq. no.
help to apply the advertisement in correct order.
Damping – Transient change in topology that re of short
duration should not destabilize the routing mechanisms.

DSDV Routing
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If the sequence number of one node in the
newly received same as the corresponding
sequence number in the routing table , then
the metric will be compared and the route
with the smallest metric will be used.

DSR
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Dynamic Source Routing
Problem associated with DSDV

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Previous routing exchange routing information with all nodes ,
although currently their may be no data to exchange.

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Cause unnecessary traffic and consumes more battery power.

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DSR , divides the task into two :–
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Route discovery – a node only discover route to a destination
want to send somthing to this destination.
Route maintenance – if a node is continuously sending packet
via a route, it has to make sure that the route is held upright.

DSR eliminates all periodic routing updates.

DSR
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If the node receive a route request:If the node has already received the request (which is
identified using the unique identifier) , it drops the request
packet.
– If node recognizes its own address as the destination , the
request has reached its target.
– Otherwise, the node appends its own address to a list of
traversed hops in the packets and broadcast this update
request.
Destination may receive several list containing different paths
from the initiator.It could return the best path, the first path or
several path.
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Mobile Network Layer

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