Wn ppt (1)

Unit – II
Mobile Network Layer
Dr.T.V.Padmavathy
Professor
Department of ECE
RMKEC
Wireless Networks

Introduction - Which Technology
1/3/2017 Unit - II Mobile Network Layer 2

Introduction - Which Technology ?
 Cellular Technologies
 Wireless LAN Technology
 Short range Technologies
 Long Range Technologies

 Packet Radio NETwork (PRNET) by DARPA -1972
 Survivable Packet Radio Networks (SURAN) – 1980s
 MANET- IETF -1990’s
 IEEE released 802.11 PHY and MAC standard – 1995
History

Introduction
 In this protocols and mechanisms to support mobility.
 Allows transparent routing of IP datagrams to mobile nodes
 Mobile IP – Adds mobility support to the internet

 Setting up of fixed access points and backbone infrastructure is not
always viable
 Infrastructure may not be present in a disaster area or war zone
 Infrastructure may not be practical for short-range radios;
Bluetooth (range ~ 10m)
 Ad hoc networks:
 Does not depend on pre-existing infrastructure
 Easy to deploy
 Useful when infrastructure is absent
1/3/2017 6Unit - II Mobile Network Layer
Why an Ad Hoc Networks ?

Problems in Infrastructure based & Ad Hoc
Infrastructure based Network
 Access Point placement depends on wired network availability
 Obstructions make it difficult to provide total coverage of an area
 Each Access Point has limited range
Ad Hoc Network
 Communication is only possible between nodes which are directly in
range of each other

Problems in Infrastructure based & Ad Hoc
 If nodes move out of range of the access point (Infrastructure Mode)
 OR nodes are not in direct range of each other (Ad Hoc Mode)
Then communication is not possible!!
A B C

Mobile Ad hoc Network Example
Communication between nodes may be in single/multi-hop
 Each of the nodes acts as a host as well as a router

Challenges in Mobile Environments
Limitations of the Wireless Network
 packet loss due to transmission errors - transport problem
 frequent disconnections/partitions
 limited communication bandwidth
Limitations Imposed by Mobility
 dynamically changing topologies/routes - routing problem
 short battery lifetime - energy efficiency problem
 limited capacities

Typical Applications
 Military environments
• soldiers, tanks, planes
 Emergency operations
• search-and-rescue
 Personal area networking
• cell phone, laptop, etc.
 Civilian environments
• meeting rooms, sports stadiums,
hospitals
 Education
• virtual classrooms, conferences
 Sensor networks
• homes, environmental applications

Classes of Wireless Ad Hoc Networks
Three distinct classes
 Mobile Ad Hoc Networks (MANET)
 possibly highly mobile nodes
 power constrained
 Wireless Ad Hoc Sensor/Device Networks
 relatively immobile
 severely power constrained nodes
 Wireless Ad Hoc Backbone Networks
 rapidly deployable wireless infrastructure
 largely immobile nodes

Characteristics of an Ad-hoc Network
 Collection of mobile nodes forming a temporary network
 Network topology changes frequently and unpredictably
 No centralized administration or standard support services
 Host is also function as router

Ad hoc Network Architecture
physical
Data link
network
transport
application
physical
Data link
network
transport
application
physical
Data link
network
transport
application
S
wireless link
Source DestinationIntermediate node
wireless link
I D

Common objective:
Route packets along the optimal path
 Routing protocols adapt to changing network conditions and by
definition offers multi-hop paths
 Routing protocols differ in route table
• construction
• maintenance
• update
 Next-hop routing protocols can be categorized as:
• Link-state
• Distance-vector
Why Routing?

Routing Classification
Ad hoc Routing
Protocols
Topology Based Position Based
Table Driven Hybrid Source Initiated On-Demand
Driven
Location
Services
Forwarding
Strategy

CGSR DSDV WRP AODV DSR TORA SSRABRZRP
Ad hoc Routing
Protocols
Topology Based Position Based
Table Driven Hybrid Source Initiated On-Demand
Driven
Location
Services
Forwarding
Strategy
Ad Hoc Routing Protocols Overview

Why traditional routing protocols are not suitable for
MANET networks ?
 Hidden Terminal Problem
 Exposed node problem

Routing Protocols
Proactive Protocols
 Determine routes independent of traffic pattern
Traditional (link-state, distance-vector) routing protocols are proactive
Reactive Protocols
 Determine a route only if needed
Hybrid protocols
 Adaptive; Combination of proactive and reactive

Protocol Trade-offs
Proactive protocols
• Always maintain routes
• Little or no delay for route determination
• Consume bandwidth to keep routes up-to-date
• Maintain routes which may never be used
Reactive protocols
• Lower overhead since routes are determined on demand
• Significant delay in route determination
• Employ flooding (global search)

Reactive Routing Protocols

Characteristics of Reactive Routing Protocols
 Determine route if and when needed
 Less control packet overhead
 Source initiates route discovery process
 More route discovery delay
 Example:
• Dynamic Source Routing (DSR)
• Ad hoc On-Demand Distance Vector Routing (AODV)

Dynamic Source Routing (DSR) [Johnson’96]
 Two major phases:
• Route Discovery,
• Route Maintenance.
 Node S initiates a route discovery
 Source node S floods Route Request (RREQ)
 Each node appends own identifier when forwarding RREQ

Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Represents a node that has received RREQ for D from S
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Broadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ
[S]
[S]

B
A
S E
F
H
J
D
C
G
I
K
Node H receives packet RREQ from two neighbors: Potential Collision
M
N
L
[S,E]
[S,C][S,B]
[S,B]
[S,C]

B
A
S E
F
H
J
D
C
G
I
K
• Node C receives RREQ from G and H, but does not forward it again,
because node C has already forwarded RREQ
M
N
L
[S,C,G]
[S,E,F]

• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their transmissions may
collide
B
A
S E
F
H
J
D
C
G
I
K
M
N
L
[S,C,G,K]
[S,E,F,J]
Unit - II Mobile Network Layer1/3/2017 28

B
A
S E
F
H
J
D
C
G
I
K
Node D does not forward RREQ, because node D is the intended target of the
route discovery
M
N
L
[S,E,F,J,M]
Unit - II Mobile Network Layer1/3/2017 29

 Destination D on receiving the first RREQ, sends a Route Reply
(RREP)
 RREP is sent on a route obtained by reversing the route appended
to received RREQ
 RREP includes the route from S to D on which RREQ was received
by node D

Route Reply in DSR
B
A
S E
F
H
J
D
C
G
I
K
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message

Route Reply in DSR
Route Reply can be sent by reversing the route in Route Request
(RREQ) only if links are guaranteed to be bi-directional
• To ensure this, RREQ should be forwarded only if it received on a
link that is known to be bi-directional
 If unidirectional (asymmetric) links are allowed, then RREP may
need a route discovery for S from node D
• Unless node D already knows a route to node S
• If a route discovery is initiated by D for a route to S, then the Route
Reply is piggybacked on the Route Request from D.

Dynamic Source Routing (DSR)
 Node S on receiving RREP, caches the route included in the RREP
 When node S sends a data packet to D, the entire route is included
in the packet header
• hence the name source routing
 Intermediate nodes use the source route included in a packet to
determine to whom a packet should be forwarded

Data Delivery in DSR
B
A
S E
F
H
J
D
C
G
I
K
M
N
L
DATA [S,E,F,J,D]
Packet header size grows with route length

DSR Optimization: Route Caching
 Each node caches a new route
 When node S finds route [S,E,F,J,D]
to node D, node S also learns route
[S,E,F] to node F
 When node K receives Route
Request [S,C,G] destined for node,
node K learns route [K,G,C,S] to node
S
 When node F forwards Route Reply
RREP [S,E,F,J,D], node F learns
route [F,J,D] to node D
B
A
S E
F
H
J
D
C
G
I
K
M
N
L
DATA [S,E,F,J,D]

DSR Optimization: Route Caching
 When node E forwards Data
[S,E,F,J,D] it learns route [E,F,J,D]
to node D
 A node may also learn a route
when it overhears Data packets
B
A
S E
F
H
J
D
C
G
I
K
M
N
L
DATA [S,E,F,J,D]

Use of Route Caching
 When node S learns that a route to node D is broken, it uses another
route from its local cache
 Use of route cache
• can speed up route discovery
• can reduce propagation of route requests

Dynamic Source Routing: Advantages
 Routes maintained only between nodes who need to communicate
• reduces overhead of route maintenance
 Route caching can further reduce route discovery overhead
 A single route discovery may yield many routes to the destination,
due to intermediate nodes replying from local caches

Dynamic Source Routing: Disadvantages
 Packet header size grows
 Flood of route requests may potentially reach all nodes in the
network
 Potential collisions between route requests propagated by
neighboring nodes
• insertion of random delays before forwarding RREQ
 Increased contention if too many route replies come back due to
nodes replying using their local cache
• Route Reply Storm problem

Proactive Routing Protocols

Characteristics of Proactive Routing Protocols
 Distributed, shortest-path protocols
 Maintain routes between every host pair at all times
 Based on Periodic updates of routing table
 High routing overhead and consumes more bandwidth
 Example: Destination Sequence Distance Vector (DSDV)

Distance-Vector [Ford+ 1962]
 known also as Distributed Bellman-Ford or RIP (Routing Information
Protocol)
The Meaning of Distance Vector:
 A router using distance vector routing protocols knows 2 things:
• Distance to final destination
• Vector, or direction, traffic should be directed
 Every node maintains a routing table
• all available destinations
• the next node to reach to destination
• the number of hops to reach the destination
 Periodically send table to all neighbors to maintain topology

Distance Vector (Tables)
D
G
A
F
E
B
C
A B C D E F G
A 0 1 1 ∞ 1 1 ∞
B 1 0 1 ∞ ∞ ∞ ∞
C 1 1 0 1 ∞ ∞ ∞
D ∞ ∞ 1 0 ∞ ∞ 1
E 1 ∞ ∞ ∞ 0 ∞ ∞
F 1 ∞ ∞ ∞ ∞ 0 1
G ∞ ∞ ∞ 1 ∞ 1 0

Routing Tables
• information, routing table at A
is -->
D
G
A
F
E
B
C
Cost Next Hop
B 1 B
C 1 C
D ∞ -
E 1 E
F 1 F
G ∞ -

Evolution of the Table
Cost Next Hop
B 1 B
C 1 C
D 2 C
E 1 E
F 1 F
G 2 F
D
G
A
F
E
B
C
Each node sends a message to neighbors with a list of distances.
F --> A with G is at a distance 1
C --> A with D at distance 1.

Final Distance Matrix
A B C D E F G
A 0 1 1 2 1 1 2
B 1 0 1 2 2 2 3
C 1 1 0 1 2 2 2
D 2 2 1 0 3 2 1
E 1 2 2 3 0 2 3
F 1 2 2 2 2 0 1
G 2 3 2 1 3 1 0
D
G
A
F
E
B
C

Distance-Vector (Disadvantages)
A
E
B
C
D
Link 1 Link 6
Link 2
Link 4
Link 3
Link 5
Destination Link Hop
A Link 4 2
B Link 4 2
C Link 4 1
D Local 0
E Link 6 1
Initially nothing in routing table.
 When it receives an update from C and E, it notes that these nodes
are one hop away.
 Subsequent route updates allow D to form its routing table.

 Link 2 is broken, Node A routes
packets to C, D, and E through
Node B.
 Node B detects that Link 3 is
broken.
 It sets the distance to nodes C, D
and E to be infinity.
 Node B thinks it can route
packets to C, D, and E via Node
A.
1/3/2017
Unit - II Mobile Network Layer
48
Link 6
A
E
B
C
D
Link 1
Link 2 Link 4
Link 3 Link 5
Broken
Broken
Network partitions into two
isolated islands

 Node A thinks it can route packets to C, D, and E, via Node B.
 A routing loop is formed – Counting to Infinity problem.
 New Solution -> DSDV Protocol

Destination Sequenced Distance Vector Routing (DSDV)
[Perkins+ 1994]
 Basic Routing Protocol
 Based on Bellman ford routing algorithm with some improvement
 Each node maintains a list of all destinations and number of hops
to each destination.
 Each entry is marked with a sequence number.
 Periodically send table to all neighbors to maintain topology

 Protocol Overview
 Route Advertisements
 Routing Table Entry Structure

Protocol Overview
 Each Routing Table List all destinations and number of hops to each
node
 Each Route is tagged with a sequence number originated by
destination
 Updates are transmitted periodically and when there is any
significant topology change
 Routing information is transmitted by broadcast

Route Table Entry Structure
 Destination’s Address
 Number of hops required to reach the destination
 Destination Sequence Number
 Sequence number originated from destination. Ensures
loop freeness.
 Install Time when entry was made (used to delete stale entries from
table)

DSDV (Route Advertisements)
Advertise to each neighbor own routing information
 Destination Address
 Metric = Number of Hops to Destination
 Destination Sequence Number
Rules to set sequence number information
 On each advertisement increase own destination sequence
number (use only even numbers)
 If a node is no more reachable (timeout) increase sequence
number of this node by 1 (odd sequence number) and set metric
= 

DSDV (Route Selection)
Update information is compared to own routing table
 Select route with higher destination sequence number (This
ensure to use always newest information from destination)
 Select the route with better metric when sequence numbers are
equal.

Example of DSDV in operation
MH3
MH6
MH2
MH1
MH7
MH4
MH8
MH5
Destination Next Hop Metric Seq. No
MH4 MH4
0 S406_MH4
MH1 MH2
2 S128_MH1
MH2 MH2
1 S564_MH2
MH3 MH2
2 S710_MH3
MH5 MH6
2 S392_MH5
MH6 MH6
1 S076_MH6
MH7 MH6
2 S128_MH7
MH8 MH6
3 S050_MH8

DSDV (Disadvantages)
A
E
B
C
D
Link 1
Link 2 Link 4
Link 3 Link 5
Broken
Broken
Network partitions into two
isolated islands
Node A’s update is state
 Sequence number indicated for nodes
C,D, and E is lower than the sequence
number maintained at B.
Looping avoided

Responding to Topology Changes
 Broken links indicated by 
 Any route through a hop with a broken link is also assigned 
  routes are immediately broadcast
 Sequence number of Destination is incremented and information is
broadcast
 Nodes with same or higher sequence number broadcast their metric
information
 Data broadcast by “full dump” and “incremental”

Advantages
 Simple (almost like Distance Vector)
 Loop free through destination seq. numbers
 No latency caused by route discovery
Disadvantages
 Overhead: most routing information never used

Thank You

Wn ppt (1)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Wn ppt (1)

Similar to Wn ppt (1) (20)

Recently uploaded

Recently uploaded (20)

Wn ppt (1)