Lecture 9 10 .mobile ad-hoc routing protocols

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

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.
A
B A
B
2

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

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

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

Traditional routing algorithm
 InWired network
1. Static :
2. Dynamic
a) DistanceVector
b) Link State
 DistanceVector (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 infinity
6

7
 Example of DV: 0
5
1
2
4
3Destination Next Hop Distance
0 2 3
1 2 2
… … …
Routing table at node 5 :

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.
1
2
4
3 5
8

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

10
 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.

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}

12
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

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

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

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

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
16

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

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.
18

Ad Hoc Routing Protocol
 Routing protocols category :
(a)Table-driven,
(b) Source-initiated on-demand-driven.
19

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)
20

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.
21

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 DistanceVector (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 forWireless
Networks,”ACM Mobile Networks andApp. 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, MobileWireless Networks with Fading
Channel,” Proc. IEEE SICON ’97,Apr. 1997, pp. 197-211.

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.
 MainAdvantage 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.
24

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

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.
26

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.
27

DSDV (Cont…)
When X receives information fromY about a route to Z
 Let destination sequence number for Z at X be S(X), S(Y) is sent
fromY
 If S(X) > S(Y),then X ignores the routing information received fromY
 If S(X) = S(Y),and cost of going throughY is smaller than the route known
to X, then X setsY as the next hop to Z
 If S(X) < S(Y),then X setsY as the next hop to Z, and S(X) is updated to
equal S(Y)
X Y Z
28

DSDV (Cont…)
Destination Next Hop
Number of
Hops
Sequence
Number
InstallTime
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

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,
32

2. Wireless Routing Protocol (WRP)
S. Murthy and J. J. Garcia-Luna-Aceves,“An Efficient Routing Protocol
forWireless Networks,”ACM Mobile Networks andApp. 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.
 InWRP, routing nodes communicate the distance and second-to-last
hop information for each destination in the wireless network.
 Belong to the class of path findingAlgorithm;
 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.
33

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
34

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.
35

36
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
I
B
(0, J)
(2, K)
(2, K)
(1, K)
X1
1
10
1
5
10
(, K)
(10, B)
(10, I)
(11, B)

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.
38

3. Cluster Switch Gateway Routing
(CSGR)
C.-C. Chiang, “Routing in Clustered Multihop, MobileWireless 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

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.
40

(CSGR)
 CSGR uses Destination Sequenced DistanceVector (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 and41

(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.
42

(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.
43

44
CGSR
 Example:
Routing from node 1 to node 8
Node
Cluster head
Gateway1
2
3
4
5
6
8
7

45
1
3
2
4 7
10
5
6
8
9
11
12
Cluster Head
Internal Node
Gateway Node
Routing in CGSR from node 1 to node 12
CGSR (Cont’d)

46
CGSR(cont.)
(5 hops)
(3 hops)
 Example:
Routing from node 1 to node 11

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

Lecture 9 10 .mobile ad-hoc routing protocols

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