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Unit – IIMobile Network Layer
Dr.T.V.PadmavathyProfessor
Department of ECERMKEC
Wireless Networks
Introduction - Which Technology
05/03/2023 Unit - II Mobile Network Layer 2
Introduction - Which Technology ?
Cellular Technologies
Wireless LAN Technology
Short range Technologies
Long Range Technologies
05/03/2023 Unit - II Mobile Network Layer 3
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
05/03/2023 Unit - II Mobile Network Layer 4
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
05/03/2023 Unit - II Mobile Network Layer 5
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
05/03/2023 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
05/03/2023 Unit - II Mobile Network Layer 7
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!!
05/03/2023 Unit - II Mobile Network Layer 8
A B C
Mobile Ad hoc Network Example
05/03/2023 Unit - II Mobile Network Layer 9
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 capacities05/03/2023 10Unit - II Mobile Network Layer
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
05/03/2023 Unit - II Mobile Network Layer 11
05/03/2023 Unit - II Mobile Network Layer 12
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
05/03/2023 Unit - II Mobile Network Layer 13
05/03/2023 Unit - II Mobile Network Layer 14
Ad hoc Network Architecture
physical
Data link
network
transport
application
physical
Data link
network
transport
application
physical
Data link
network
transport
application
Swireless link
Source DestinationIntermediate nodewireless 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
05/03/2023 15Unit - II Mobile Network Layer
Why Routing?
Routing Classification
05/03/2023 16Unit - II Mobile Network Layer
Ad hoc Routing Protocols
Topology Based Position Based
Table Driven Hybrid Source Initiated On-Demand Driven
Location Services
Forwarding Strategy
05/03/2023 Unit - II Mobile Network Layer 17
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
05/03/2023 Unit - II Mobile Network Layer 18
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
05/03/2023 19Unit - II Mobile Network Layer
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)
05/03/2023 20Unit - II Mobile Network Layer
Reactive Routing Protocols
05/03/2023 21Unit - II Mobile Network Layer
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)
05/03/2023 Unit - II Mobile Network Layer 22
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
05/03/2023 23Unit - II Mobile Network Layer
Route Discovery in DSR
B
A
S EF
H
J
D
C
G
IK
Represents a node that has received RREQ for D from S
M
N
L
05/03/2023 Unit - II Mobile Network Layer 24
Route Discovery in DSR
B
A
S EF
H
J
D
C
G
IK
Represents transmission of RREQ
Broadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ
[S][S]
05/03/2023 Unit - II Mobile Network Layer 25
Route Discovery in DSR
B
A
S EF
H
J
D
C
G
IK
Node H receives packet RREQ from two neighbors: Potential Collision
M
N
L
[S,E]
[S,C][S,B][S,B]
[S,C]
05/03/2023 Unit - II Mobile Network Layer 26
Route Discovery in DSR
B
A
S EF
H
J
D
C
G
IK
• 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]
05/03/2023 Unit - II Mobile Network Layer 27
Route Discovery in DSR
• 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 EF
H
J
D
C
G
IK
M
N
L
[S,C,G,K]
[S,E,F,J]
Unit - II Mobile Network Layer05/03/2023 28
Route Discovery in DSR
B
A
S EF
H
J
D
C
G
IK
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 Layer05/03/2023 29
Route Discovery in DSR
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
05/03/2023 Unit - II Mobile Network Layer 30
Route Reply in DSR
B
A
S EF
H
J
D
C
G
IK
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message
05/03/2023 Unit - II Mobile Network Layer 31
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.05/03/2023 Unit - II Mobile Network Layer 32
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
05/03/2023 Unit - II Mobile Network Layer 33
Data Delivery in DSR
B
A
S EF
H
J
D
C
G
IK
M
N
L
DATA [S,E,F,J,D]
Packet header size grows with route length
05/03/2023 Unit - II Mobile Network Layer 34
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
05/03/2023 Unit - II Mobile Network Layer 35
BA
S EF
HJ
D
CG
IK
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
05/03/2023 Unit - II Mobile Network Layer 36
BA
S EF
HJ
D
CG
IK
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
05/03/2023 Unit - II Mobile Network Layer 37
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
05/03/2023 38Unit - II Mobile Network Layer
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
05/03/2023 39Unit - II Mobile Network Layer
05/03/2023 Unit - II Mobile Network Layer 40
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)
05/03/2023 Unit - II Mobile Network Layer 41
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 topology05/03/2023 42Unit - II Mobile Network Layer
Distance Vector (Tables)
05/03/2023 Unit - II Mobile Network Layer 43
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 ∞ ∞ 1E 1 ∞ ∞ ∞ 0 ∞ ∞F 1 ∞ ∞ ∞ ∞ 0 1G ∞ ∞ ∞ 1 ∞ 1 0
Routing Tables
• information, routing table at A is -->
05/03/2023 Unit - II Mobile Network Layer 44
D
G
A
F
E
B
C
Cost Next HopB 1 BC 1 CD ∞ -E 1 EF 1 FG ∞ -
Evolution of the Table
05/03/2023 Unit - II Mobile Network Layer 45
Cost Next Hop
B 1 BC 1 CD 2 CE 1 EF 1 FG 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
05/03/2023 Unit - II Mobile Network Layer 46
A B C D E F G
A 0 1 1 2 1 1 2B 1 0 1 2 2 2 3C 1 1 0 1 2 2 2D 2 2 1 0 3 2 1E 1 2 2 3 0 2 3F 1 2 2 2 2 0 1G 2 3 2 1 3 1 0
D
G
A
F
E
B
C
Distance-Vector (Disadvantages)
05/03/2023 Unit - II Mobile Network Layer 47
A
E
B
C
D
Link 1 Link 6
Link 2Link 4
Link 3Link 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.
Distance-Vector (Disadvantages)
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.
05/03/2023Unit - 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
Distance-Vector (Disadvantages)
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
05/03/2023 Unit - II Mobile Network Layer 49
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
05/03/2023 50Unit - II Mobile Network Layer
Destination Sequenced Distance Vector Routing (DSDV)
Protocol Overview
Route Advertisements
Routing Table Entry Structure
05/03/2023 51Unit - II Mobile Network Layer
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
05/03/2023 52Unit - II Mobile Network Layer
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)
05/03/2023 53Unit - II Mobile Network Layer
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
= 05/03/2023 54Unit - II Mobile Network Layer
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.
05/03/2023 Unit - II Mobile Network Layer 55
Example of DSDV in operation
05/03/2023 Unit - II Mobile Network Layer 56
MH3
MH6
MH2
MH1MH7
MH4
MH8
MH5
Destination Next Hop Metric Seq. NoMH4 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)
05/03/2023 57Unit - II Mobile Network Layer
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”
05/03/2023 58Unit - II Mobile Network Layer
Destination Sequenced Distance Vector Routing (DSDV)
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
05/03/2023 59Unit - II Mobile Network Layer
Thank You
05/03/2023 60Unit - II Mobile Network Layer