lecture 9 10 .mobile ad-hoc routing protocols

47
Chandra Prakash Assistant Professor LPU 1 Mobile Ad-Hoc Routing Protocols Lecture (9-10)

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Page 1: Lecture 9 10 .mobile ad-hoc routing protocols

Chandra Prakash

Assistant Professor

LPU

1

Mobile Ad-Hoc Routing Protocols

Lecture (9-10)

Page 2: Lecture 9 10 .mobile ad-hoc routing protocols

Mobile Ad Hoc Networks (MANET)

Host movement frequent

Topology change frequent

No cellular infrastructure. Multi-hop wireless links.

Data must be routed via intermediate nodes.

AB A

B

2

Page 3: Lecture 9 10 .mobile ad-hoc routing protocols

The Routing Problem

S

D

D´S´

The routing problem is to find a route from S to D when some or all of the

nodes are mobile.

The MAC protocol is concerned with per-link communications, not end-

to-end. While Routing Protocol deal with end-to-end communication.3

Page 4: Lecture 9 10 .mobile ad-hoc routing protocols

Ad-hoc Routing Protocol

A standard, that controls how nodes decide which way

to route packets between computing devices in a mobile ad hoc

network .

In ad-hoc networks, nodes are not familiar with the topology of their

networks; instead, they have to discover it.

The basic idea is that a new node may announce its presence and should

listen for announcements broadcast by its neighbours.

Each node learns about nodes nearby and how to reach them, and may

announce that it, too, can reach them.

4

Page 5: Lecture 9 10 .mobile ad-hoc routing protocols

MAC Vs Routing Protocols

The MAC protocol is concerned with per-link

communications, not end-to-end.

While Routing Protocol deal with end-to-end

communication.

5

Page 6: Lecture 9 10 .mobile ad-hoc routing protocols

Traditional routing algorithm In Wired network

1. Static :

2. Dynamic a) Distance Vector

b) Link State

Distance Vector (DV)

Each node maintains a table giving the distance from itself to all possible destination.

Periodically broadcasts update packets to each of the neighbors.

Bellman-Ford algorithm

Finding the shortest path to determine the correct next hop of its neighbors.

When presented a packet for forwarding to some destination, each router simply forwards the packet to the correct next hop router.

Problem: route looping & count to infinity6

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Traditional routing algorithm

Example of DV: 0

5

1

2

4

3Destination Next Hop Distance

0 2 3

1 2 2

… … …

Routing table at node 5 :

Page 8: Lecture 9 10 .mobile ad-hoc routing protocols

Distributed Bellman-Ford Algorithm

We consider only the number

of hops as the cost for sending

a message from a source to a

destination.

Suppose node 1 wants to

send a message to node 4.

Since the shortest path

between 1 and 4 passes

through 2, 1 will send the

message to 2.

12

4

3 5

8

Page 9: Lecture 9 10 .mobile ad-hoc routing protocols

Problems with Distributed Bellman-

Ford Algorithm

All routing decisions are taken in a completely distributed

fashion. Each node uses its local information for

routing messages.

However, the local information may be old and

invalid. Local information may not be updated promptly.

This gives rise to loops. A message may loop around a

cycle for a long time.

9

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10

Traditional routing algorithm

Link State (LS)

Each node maintains a view of the network topology with a cost

for each link.

Each node periodically broadcasts the cost of its outing links to

all other nodes.

Using a shortest-path algorithm to choose its next hop for each

destination.

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11

Traditional routing algorithm(4/4)

Example of LS:

•At node 5, based on the link state packet,

topology table is constructed:

0 1 2 3 4 5

0 1 1 0 0 0 0

1 1 1 1 1 0 0

2 0 1 1 0 1 1

3 0 1 0 1 1 0

4 0 0 1 1 1 1

5 0 0 1 0 1 1

0

5

1

2

4

3

{1}

{2,4}

{0,2,3}

{1,4,5}

•Dijkstra’s Algorithm can then be used

for the shortest path

{2,3,5}

{1,4}

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Problems of traditional routing algorithms Dynamic of the topology

frequent changes of connections, connection quality, participants

Limited performance of mobile systems

periodic updates of routing tables need energy without contributing to the transmission of user data, sleep modes difficult to realize

limited bandwidth of the system is reduced even more due to the exchange of routing information

Asymmetric links

connection in wireless network may be not symmetric

Page 13: Lecture 9 10 .mobile ad-hoc routing protocols

Limitation of Wireless Network

Deals with the typical limitations of Ad-hoc networks, which

include

Resource poor devices

Limited bandwidth

high error rates

Continually changing topology

Battery power

Most constraining is battery power

13

Page 14: Lecture 9 10 .mobile ad-hoc routing protocols

Goal of Routing Protocol

1. Minimal control overhead:

Control messaging consumes bandwidth, processing resources and battery

power to both transmit and receive a message.

Should not send more than the minimum no of control message they

need for operation.

While transmitting is roughly twice as power consuming as

receiving. Thus need to reduce control messaging

2. Minimal processing overhead

Algo that are computationally complex require more processing

cycles, thus consume more resources.

Protocol should be lightweight and use a minimum of

processing resources from the mobile devices 14

Page 15: Lecture 9 10 .mobile ad-hoc routing protocols

Goal of Routing Protocol

3. Multihop routing capability

Transmission range of mobile node is limited.

Routing protocol must be able to discover Multihop routes between

source and destination so that communication between those node is

possible who are not in direct transmission range of each other.

4.Dynamic topology maintenance

Once route is established , link may be break due to movement of

nodes.

A viable routing path must be maintained even while the

intermediate nodes, or even the source or destination nodes are

moving.

If link breaks, it must be handled quickly with a minimum of

associated overhead. 15

Page 16: Lecture 9 10 .mobile ad-hoc routing protocols

Goal of Routing Protocol

5. Loop prevention

When a routing loop exits , data and control packets may traverse

the path multiple times until either the path or fixed and the loop is

eliminated or until he time to live (TTL) of the packet reaches zero.

As bandwidth is scarce and packet processing and forwarding is

expensive, routing loops are extremely wasteful of resources.

Loops should be avoided all the times

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Page 17: Lecture 9 10 .mobile ad-hoc routing protocols

Formation of Loops

Network given above

Node A is transmitting data to node C via node B.

If the link between nodes B and C goes down and B has not yet informed

node A about the breakage, node A transmits the data to node B assuming that

the link A-B-C is operational and of lowest cost.

Node B knows of the broken link and tries to reach node C via node A, thus

sending the original data back to node A.

Furthermore, node A receives the data that it originated back from

node B and consults its routing table.

Node A's routing table will say that it can reach node C via node B (because it

still has not been informed of the break) thus sending its data back to

node B creating an infinite loop.17

Page 18: Lecture 9 10 .mobile ad-hoc routing protocols

Routing Protocol : Assumptions

1. All nodes are homogenous resources and capabilities.

2. Same transmission range of nodes.

3. Bi-directional links

4. Protocol are designed for moderately sized networks of 10

to 100 nodes.

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Page 19: Lecture 9 10 .mobile ad-hoc routing protocols

Ad Hoc Routing Protocol Routing protocols category :

(a) Table-driven,

(b) Source-initiated on-demand-driven.

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Page 20: Lecture 9 10 .mobile ad-hoc routing protocols

Routing Protocols

Table Driven / Proactive protocols Traditional distributed shortest-path protocols Maintain routes between every host pair at all times Based on periodic updates; High routing overhead Example: DSDV (destination sequenced distance vector)

On-Demand Driven/ Reactive protocols Determine route if and only when needed Source initiates route discovery Example: DSR (dynamic source routing)

Hybrid protocols Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol)

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Page 21: Lecture 9 10 .mobile ad-hoc routing protocols

Table Driven / Proactive protocols

Proactive protocols are based on periodic exchange of control

messages and maintaining routing tables.

Derived from traditional distance vector and link state protocol used in

wireline internet.

Each node maintains complete information about the network

topology locally.

This information is collected through proactive exchange of partial routing tables stored at each node. Since each node knows the complete topology, a node can immediately find the best route to a destination.

Limitation :

Generates large volume of control messages and this may take up a large part of the available bandwidth.

The control messages may consume almost the entire bandwidth with a large number of nodes and increased mobility.

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Page 22: Lecture 9 10 .mobile ad-hoc routing protocols

Table Driven / Proactive protocols Maintains fresh lists of destinations & their routes by

periodically distributing routing tables throughout the network

Attempts to maintain consistent, up-to-date routing information from each node to every other node in the network.

Require each node to maintain one or more tables to store routing information.

They respond to changes in network topology by propagating route updates throughout the network to maintain a consistent network view.

These Protocols are differ in the number of necessary routing-related tables and the methods require to broadcast the changes in network structure.

Some examples of proactive protocols are :

Destination Sequenced Distance Vector (DSDV)

WRP

CGSR22

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Table-Driven Routing Protocols

Destination-Sequenced Distance-Vector Routing (DSDV) C. E. Perkins and P. Bhagwat, “Highly Dynamic Destination-Sequenced Distance-Vector

Routing (DSDV) for Mobile Computer,” Comp. Commun. Rev., Oct. 1994, pp. 234-244.

Wireless Routing Protocol (WRP) S. Murthy and J. J. Garcia-Luna-Aceves, “An Efficient Routing Protocol for Wireless

Networks,”ACM Mobile Networks and App. J., Special Issue on Routing in Mobile Communication Networks, Oct. 1996, pp. 183-197.

Clusterhead Gateway Switch Routing (CGSR) C.-C. Chiang, “Routing in Clustered Multihop, Mobile Wireless Networks with Fading

Channel,” Proc. IEEE SICON ’97, Apr. 1997, pp. 197-211.

Page 24: Lecture 9 10 .mobile ad-hoc routing protocols

1. Destination Sequenced Distance Vector

(DSDV)

C. E. Perkins and P. Bhagwat, “Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computer,” Comp. Commun. Rev., Oct. 1994, pp. 234-244.

Table-driven routing protocol

Expansion of distance vector based on Classical distributed Bellman-Ford routing mechanism include freedom from loops in routing tables.

Main Advantage of using this protocol is that it avoid the routing loops in a mobile network of routers.

Each node maintains a routing table of the possible destinations within the non-partitioned network and the number of routing hops / radio hops (Hand Over Point) to each destination are recorded.

Routing information is always made readily available, regardless of whether the source node requires a route or not.

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Page 25: Lecture 9 10 .mobile ad-hoc routing protocols

Destination Sequenced Distance Vector

DSDV(Cont…)

A sequence numbering system is used to allow mobile hosts to distinguish stale routes from new ones.

Routing table updates are sent periodically throughout the network to maintain table consistency.

It generates a lot of control traffic in the network, rendering an inefficient utilization of network resources.

To minimize the routing updates, variable sized update packets are used depending on the number of topological changes.

DSDV uses two types of route update packets. Full Dump update Packet Incremental update Packet

25

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DSDV(Cont…)

Full dump update Packet:

Packet carries all available routing information and can require

multiple network protocol data units (NPDUs).

Take multiple NPDU’s

During periods of occasional movement, these packets are transmitted

infrequently.

Incremental packets update Packet :

Fitted into a single NPDU.

are used to relay only information that has changed since the last full

dump.

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DSDV (Cont…)

New route broadcasts will contain

Address of the destination node

Number of hops to reach the destination

Unique Sequence number : The sequence numbers are generally even if a link is present; else, an odd

number is used.

The number is generated by the destination, and the emitter needs to send

out the next update with this number.

The route labeled with the most recent sequence number (in

increasing order) is always used.

In the event that two updates have the same sequence number, the

route with the smaller hop count is used.

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DSDV (Cont…)

When X receives information from Y about a route to Z

Let destination sequence number for Z at X be S(X), S(Y) is sent

from Y

If S(X) > S(Y), then X ignores the routing information received from Y

If S(X) = S(Y), and cost of going through Y is smaller than the route known

to X, then X sets Y as the next hop to Z

If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to

equal S(Y)

X Y Z

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Page 29: Lecture 9 10 .mobile ad-hoc routing protocols

DSDV (Cont…)

Destination Next HopNumber of

Hops

Sequence

NumberInstall Time

A A 0 A 46 001000

B B 1 B 36 001200

C B 2 C 28 001500

For example the routing table of Node A in this network is

29

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30

DSDV

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31

DSDV

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DSDV Overview

Advantages Much less delay involved in the route setup process.

Incremental updates with sequence no tag makes existing wired network

protocol adaptable to ad-hoc network.

Disadvantage Generates a lot of control traffic in the network, rendering an inefficient

utilization of network resources.

Small network with high mobility or a large network with low mobility can

completely chock the available bandwidth.

In order to obtain information about a particular destination node., a node has

to wait for a table update message initiated by the destination node,

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Page 33: Lecture 9 10 .mobile ad-hoc routing protocols

2. Wireless Routing Protocol (WRP)

S. Murthy and J. J. Garcia-Luna-Aceves, “An Efficient Routing Protocol for Wireless Networks,” ACM Mobile Networks and App. J., Special Issue on Routing in Mobile Communication Networks, Oct. 1996, pp. 183-197.

Similar to DSDV, inherits the properties of the distributed Bellman-Ford algorithm.

It achieves loop freedom.

In WRP, routing nodes communicate the distance and second-to-last hop information for each destination in the wireless network.

Belong to the class of path finding Algorithm; uses the length and predecessor to destination in the shortest path.

Eliminates the “count to Infinity” Problem by forcing nodes to do consistency check of the predecessors

It provides faster route convergence when a link failure event occurs.

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Page 34: Lecture 9 10 .mobile ad-hoc routing protocols

WRP (Cont…)

If a node is not sending packets,

It must send a HELLO message within a specified time period to ensure

connectivity

Otherwise, the lack of messages from the node can indicate the failure of

that wireless link and this may cause a false alarm.

When a mobile receives a HELLO message from a new node, that new node

information is added to the mobile's routing table, and the mobile sends the

new node a copy of its routing table information.

Differs from DSDV in table maintenance and in the update procedures.

DSDV maintains only one topology table,

WRP uses a set of tables to maintain more accurate information

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Page 35: Lecture 9 10 .mobile ad-hoc routing protocols

WRP (Cont…)WRP must maintain four tables, namely:

(a) Distance table : Contain network view of the neighbors of a node.

indicates the number of hops between a node and its destination

(b) Routing table: indicates the next-hop node

(c) Link-cost table: Link-cost table reflects the delay associated with a particular link.

The LCT contains the cost (e.g., the number of hops to reach the destination) of relaying messages through each link.

The cost of a broken link is infinity.

(d) Message Retransmission List (MRL) table.The MRL contains

The sequence number of the update message,

A retransmission counter,

An acknowledgment required flag vector,

A list of the updates sent in the update message.

The MRL records which updates in an update message need to be retransmitted and which neighbors should acknowledge the retransmission.

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WRP (cont.) An Update message is sent after processing updates from neighbors or a

change in link to a neighbor is detected.

After receiving an update message free of errors, a node is required to send a positive acknowledgment (ACK).

If a node is not sending messages, it must send a hello message within a specified time period to ensure connectivity.

Example:

J

K

IB

(0, J)

(2, K)

(2, K)

(1, K)

X11

10

1

5

10

(, K)

(10, B)

(10, I)

(11, B)

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WRP Overview

Advantages Same as that of DSDV,

It has faster convergence and involves fewer table updates.

Disadvantage WRP requires large memory storage and resources in maintaining its tables.

Complexity of maintenance of multiple tables demands a larger memory and greater

processing power from nodes in the ad hoc wireless network.

At high mobility, the control overhead involved in updating table entries is almost the

same as that of DSDV

Not suitable for highly dynamic and also for a very large ad hoc wireless network.

The protocol is not suitable for large mobile ad hoc networks as it suffers from limited

scalability.

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3. Cluster Switch Gateway Routing

(CSGR)

C.-C. Chiang, “Routing in Clustered Multihop, Mobile Wireless Networks with Fading Channel,” Proc. IEEE SICON ’97, Apr. 1997, pp. 197-211.

Table-driven-based routing protocol

Uses a hierarchical network topology while previous protocol employ flat topologies

Mobile nodes are grouped into clusters. These grouping may be based on a no of criteria, but most commonly they are based on either location, or functionality.

The cluster boundaries are based on transmission range of the cluster leaders known as cluster head(CH).

Cluster Head Process control packets on behalf on their member nodes, thus form a routing

backbone within the network

allows some form of control and coordination among a group of ad hoc hosts

Clustering provides a framework for code separation (among clusters), channel access, routing, and bandwidth allocation.

Different cluster Heads could operate on different spreading codes on a CDA system. 39

Page 40: Lecture 9 10 .mobile ad-hoc routing protocols

Cluster Switch Gateway Routing

(CSGR)

To elect a cluster head, a distributed cluster head selection algorithm is used.

When a cluster head moves away, another new cluster head must be selected.

Problem occur If a cluster head is changing frequently and nodes will be spending a lot of time converging to a cluster head instead of forwarding data toward their intended destinations.

To avoid invoking cluster head reselection every time the cluster membership changes, a least cluster change (LCC) algorithm is introduced.

Using the LCC algorithm, cluster heads only change

when two cluster heads come into contact

when a node moves out of the range of all other cluster heads.

Tie is broken either using the lowest ID or highest connectivity algorithms.

A token based scheduling is used within a cluster for sharing the bandwidth among the members of the cluster.

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Page 41: Lecture 9 10 .mobile ad-hoc routing protocols

Cluster Switch Gateway Routing

(CSGR) CSGR uses Destination Sequenced Distance Vector (DSDV) as the underlying

routing scheme.

It modifies DSDV by using a hierarchical cluster-head-to-gateway routing approach to

route traffic from source to destination.

Routing is performed over clusterheads and not individual nodes.

Gateway nodes

Nodes that are within communication range of two or more cluster heads.

Gateway nodes serve as bridge nodes between two or more clusters.

Expected to be able to listen to multiple spreading codes that are currently

operation in the cluster in which the node exits as a member.

Performance is influenced by token scheduling and

code scheduling that are handled at CH and

gateways

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Cluster Switch Gateway Routing

(CSGR)

CSGR assumes that all communication passes through Cluster-Head

A packet sent by a node is first routed to its cluster head, and then the

packet is routed from a cluster head to a gateway to another

cluster head, and so on until the cluster head of the destination node

is reached.

The packet is then

transmitted to the

destination.

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Page 43: Lecture 9 10 .mobile ad-hoc routing protocols

Cluster Switch Gateway Routing

(CSGR)

Each node keep two table Cluster member table It stores the destination cluster head for each mobile node in the network. Being broadcasted by each node periodically using DSDV manner. Nodes receiving this update will refresh their cluster member tables.

Routing table Being used to determine the next hop in order to reach the destination.

On receiving a packet, a node will consult its cluster member and routing tables to determine the nearest cluster head along the route to the destination.

The node then checks its routing table to determine the next hop node to use reach the cluster head.

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CGSR

Example:

Routing from node 1 to node 8

Node

Cluster head

Gateway1

2

3

4

5

6

8

7

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45

1

3

2

4 710

5

6

89

11

12

Cluster Head

Internal Node

Gateway Node

Routing in CGSR from node 1 to node 12

CGSR (Cont’d)

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46

CGSR(cont.)

(5 hops)

(3 hops)

Example:

Routing from node 1 to node 11

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47

Comparisons of the characteristics of

table-driven routing protocol

Table driven DSDV WRP CGSR

Routing philosophy Flat Flat Hierarchical

Loop-free Yes Yes, but not

instantaneous

Yes

No. of required tables 2 4 2

Frequency of update

transmissions

Periodically and as

needed

Periodically and as

needed

Periodically

Updates transmitted to Neighbors Neighbors Neighbors and

cluster head

Utilize hello message Yes Yes No

Critical nodes No No Cluster head