routing in ad-hoc networks

Routing in Ad-hoc Networks 19th CEENet WorkshopBudapest, 2004

Routing in Ad-hoc Networks

9th CEENet Workshop on Network TechnologyNATO ANW

Iskra Djonova Popova ([email protected])


Contents:

Ad-hoc Networks Problems with Routing Destination Sequenced Distance Vector (DSDV) (Clusterhead Gateway Switch Routing (CGSR) Dynamic Source Routing (DSR) Location Aided Routing (LAR) Classification of the Routing Protocols Standardization and Future Work


Ad-hoc Networks

Two types of wireless network: Infrastructured

the mobile node can move while communicating the base stations are fixed as the node goes out of the range of a base station, it gets

into the range of another base station Infrastructureless or ad-hoc

the mobile node can move while communicating there are no fixed base stations all the nodes in the network need to act as routers

In Latin “ad-hoc” literally means “for this purpose only”. Then an ad-hoc network can be regarded as “spontaneous network”


Infrastructured network

PDA

Pen computer

Radio tower

Laptop computer

Radio tower

Infrastructure(Wired line)

Desktop computer

Laptop computer

Ad-hoc Networks


Infrastructurless (ad-hoc) network or MANET (Mobile Ad-hoc NETwork)

Ad-hoc Networks

PDA

Pen computer

Laptop computer

Laptop computer

PDA


Single hop – nodes are in their reach area and can communicate directly

Multi hop – some nodes are far and cannot communicate directly. The traffic has to be forwarded by other intermediate nodes.

Classification of ad-hoc networks

Ad-hoc Networks


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 Each host is an independent router Hosts use wireless RF transceivers as network

interface Number of nodes 10 to 100 or at most 1000

Ad-hoc Networks


Why we need ad-hoc networks? 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)

Do not need backbone infrastructure support Are easy to deploy Useful when infrastructure is absent, destroyed or

impractical

Ad-hoc Networks


Ad-hoc Networks

Example applications of ad hoc networks: emergency search-and-rescue operations, meetings or conventions in which persons

wish to quickly share information, data acquisition operations in inhospitable

terrain, local area networks in the future.


Ad-hoc Networks

Mobile Ad Hoc Networking is a multi-layer problem !

Physical/Link Layer

Network Layer

Transport Layer

Application Layer

- Routing- Addressing- Location Management

- Power Control- Multiuser Detection- Channel Access

- TCP- Quality of Service

- Security- Service Discovery- Location-dependent Application


Is it possible to use standard routing protocols? Distance-vector protocols

Slow convergence due to “Count to Infinity” Problem Creates loops during node failure, network partition or

congestion

Link state protocols Use flooding technique and create excessive traffic

and control overhead Require a lot of processor power and therefore high

power consumption

Problems with Routing


Problems with Routing

Limitations of the Wireless Network packet loss due to transmission errors variable capacity links frequent disconnections/partitions limited communication bandwidth Broadcast nature of the communications

Limitations Imposed by Mobility dynamically changing topologies/routes lack of mobility awareness by system/applications

Limitations of the Mobile Computer short battery lifetime limited capacities


DSDV

DSDV (Destination Sequenced Distance Vector) Each node sends and responds to

routing control message the same way No hierarchical structure Avoids the resource costs involved in

maintaining high-level structure Scalability may become an issue in larger

networks


Basic Routing Protocol known also as Distributed Bellman-Ford or RIP

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

Bi-directional links are required!

DSDV


Traditional Distance vector tables

CDest. Next Metric …

A A 1B B 0C C 2

Dest. Next Metric …A A 0B B 1C B 3

1 2

Dest. Next Metric …A B 3B B 2C C 0

BA

DSDV


(A, 1)(B, 0)(C, 1)

(A, 1)(B, 0)(C, 1)

Distance Vector Updates

CDest. Next Metric …

A A 1B B 0C C 1

Dest. Next Metric …A A 0B B 1C B 3 2

1 1

Dest. Next Metric …A B 3 2B B 1C C 0

BA

B broadcasts the new routing information to his neighbors

Routing table is updated

DSDV


(D, 0)

(A, 2)(B, 1)(C, 0)(D, 1)

(A, 1)(B, 0)(C, 1)(D, 2)

Distance Vector – New Node joins the network

C1 1

BA D1

broadcasts to update tables of C, B, A with new entry for D

Dest. Next Metric …A B 2B B 1C C 0D D 1

Dest. Next Metric …A A 1B B 0C C 1D C 2

Dest. Next Metric …A A 0B B 1C B 2D B 3

DSDV


Distance Vector – Broken link

C1 1

BA D1

Dest.c

Next Metric …

… … …D C 2

Dest. Next Metric …… … …D B 3


Dest. Next Metric …… … …D D

DSDV


(D, 2)(D, 2)

Distance Vector - Loops

C1 1

BA D1


Dest. Next Metric …… … …D C 2


DSDV


(D,2)

(D,4)

(D,3)

(D,5)

(D,2)

(D,4)

Distance vector - Count to Infinity

C1 1

BA D1

Dest. Next Metric …… … …D B 3, 5, …

Dest. Next Metric …… … …D B 3, 5, …

Dest.c

Next Metric …

… … …D C 2, 4, 6…

DSDV


Traditional Distance Vector are not suited for ad-hoc networks! Loops

Bandwidth reduction in network Unnecessary work for loop nodes

Count to Infinity Very slow adaptation to topology changes.

Solution -> Introduce destination sequence numbers

DSDV


DSDV keeps the simplicity of traditional Distance Vector Protocols

DSDV need to guarantee loop freeness New Table Entry for Destination Sequence Number

DSDV need to allow fast reaction to topology changes Make immediate route advertisement on significant

changes in routing table but wait with advertising of unstable routes

(damping fluctuations)

DSDV


Features introduced in DSDV Sequence number originated from destination.

Ensures loop freeness. Install Time when entry was made (used to

delete stale entries from table. Stable Data Pointer to a table holding information

on how stable a route is. Used to damp fluctuations in network.

Destination Next Metric Seq. Nr Install Time Stable DataA A 0 A-550 001000 Ptr_AB B 1 B-102 001200 Ptr_BC B 3 C-588 001200 Ptr_CD B 4 D-312 001200 Ptr_D

DSDV


Advertise to each neighbor own routing information Destination Address Metric = Number of Hops to Destination Destination Sequence Number Other info (e.g. hardware addresses)

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 Advertisement


Update information is compared to own routing table1. Select route with higher destination sequence

number (This ensure to use always newest information from destination)

2. Select the route with better metric when sequence numbers are equal.

DSDV – Route Selection


DSDV Tables

CDest. Next Metric Seq

A A 1 A-550B B 0 B-100C C 2 C-588

Dest. Next Metric SeqA A 0 A-550B B 1 B-100C B 2 C-586

Dest. Next Metric Seq.A B 1 A-550B B 2 B-100C C 0 C-588

BA

DSDV


(A, 1, A-550)(B, 0, B-102)(C, 1, C-588)

(A, 1, A-550)(B, 0, B-102)(C, 1, C-588)

DSDV Route Advertisement

CBA

B increases Seq.Nr from 100 -> 102B broadcasts routing information to Neighbors A, C including destination sequence numbers

Dest. Next Metric SeqA A 0 A-550B B 1 B-102C B 2 C-588

Dest. Next Metric SeqA A 1 A-550B B 0 B-102C C 1 C-588

Dest. Next Metric Seq.A B 2 A-550B B 1 B-102C C 0 C-588

DSDV


DSDV Respond to topology changes Immediate advertisements

Information on new routes, broken Links, metric change is immediately propagated to neighbors.

Full/Incremental Update: Full Update: Send all routing information from own

table. Incremental Update: Send only entries that has

changed. (Make it fit into one single packet)

DSDV


(D, 0, D-000)

When new node joins the network

CBA DDest. Next Metric Seq.

A A 0 A-550B B 1 B-104C B 2 C-590

Dest. Next Metric Seq.A A 1 A-550B B 0 B-104C C 1 C-590

Dest. Next Metric Seq.A B 2 A-550B B 1 B-104C C 0 C-590D D 1 D-000

1. D broadcast for first timeSend Sequence number D-000.

2. Insert entry for D with sequence number D-000.Then immediately broadcast own table.

DSDV


(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)

(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)

(New node (cont.)

CBA DDest. Next Metric Seq.

A A 1 A-550B B 0 B-102C C 1 C-592D C 2 D-000

Dest. Next Metric Seq.A A 0 A-550B B 1 B-104C B 2 C-590

Dest. Next Metric Seq.A B 2 A-550B B 1 B-102C C 0 C-592D D 1 D-000

………………

3. C increases its sequence number to C-592 then broadcasts its new table.

4. B gets this new information and updates its table…….

DSDV


(D, 2, D-100)(D, 2, D-100)

No loops, no count to infinity

CBA D1

Dest.c

Next Metric Seq.

… … …D C 2 D-100

Dest. Next Metric Seq.… … …

D B 3 D-100


D D D-101

1. Node C detects broken Link:-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)

2. B does its broadcast-> no affect on C (C knows that B has stale information because C has higher seq. number for destination D) -> no loop -> no count to infinity

DSDV


(D, , D-101)(D, , D-101)

Immediate Advertisement

CBA DDest.

cNext Metric Seq.

… … …D C 3 D-100

Dest. Next Metric Seq.… … …D B 4 D-100

Dest. Next Metric Seq.… … …D B 1 D-100


D D 1 D-100

D D D-101

1. Node C detects broken link:-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)

3. Immediate propagation

B to A:(update information has higher Seq. Nr. -> replace table entry)

2. Immediate propagationC to B:(update information has higher Seq. Nr. -> replace table entry)

Dest.c

Next Metric Seq.

… … … ...D C 2 D-100D C D-101

Dest. Next Metric Seq.… … … ...

D B 3 D-100

D B D-101

DSDV


Problem of Fluctuations Entry for D in A: [D, Q, 14, D-100]

D makes broadcast with Seq. Nr. D-102 A receives from P Update (D, 15, D-102)

-> Entry for D in A: [D, P, 15, D-102] A must propagate this route immediately.

A receives from Q Update (D, 14, D-102)-> Entry for D in A: [D, Q, 14, D-102]A must propagate this route immediately.

This can happen every time D or any other node does its broadcast and lead to unnecessary route advertisements in the network, so called fluctuations.

A

D

QP

10 Hops11 Hops

(D,0,D-102)

DSDV


Advantages Simple (almost like Distance Vector) Loop free through destination seq. numbers No latency caused by route discovery

Disadvantages No sleeping nodes Bi-directional links required Overhead: most routing information never used Scalability is a major problem

DSDV


CGSR

CSGR (Clusterhead Gateway Switch Routing) Similar to DSDV Based on concept of

clusters and cluster heads

Routing is done via the cluster heads and gateways


CGSR Problems with CGSR

More time is spend in selection of cluster heads and gateways

If the mobile node uses CDMA/TDMA then it can take some time to get permission to send packets


DSR

DSR (Dynamic Source Routing) Similar to the source routing in traditional

networks A node maintains route cache containing the

routes it knows Includes route discovery on request and route

maintenance when needed


DSR Route discovery

The source sends a broadcast packet which contains source address, destination address, request id and path.

If the host receiving this packet, saw this packet before, discards it.

Otherwise, it looks up its route caches to look for a route to destination. If a route is not found, it appends its address into the packet and rebroadcasts it.

If the route is found, it sends a reply packet to the source node.

The route will be eventually found when the request packet reaches the destination


Source

DSRRREQ (Route request)

4

3

6

5

1

2

RREQ(1,5,{1,2,4})

Route cache

(3,5) > {3,6,5}...

Route cache...

Route cache...

RREQ(1,5,{1})

RREQ(1,5,{1,2})

RREQ(1,5,{1,2})

Route cache...

Route cache...

(source, destination, path)

Destination


DSR

How to send a reply packet? If the destination has a route to the source in its

cache, use it Else if symmetric links are supported, use the

reverse of the route record Else, if symmetric links are not supported, the

destination initiate route discovery to source


DSR

4

3

6

5

1

2

Routecache

(3,1) > {3,2,1}(3,2) > {3,2}(3,5) > {3,6,5}...

Routecache...

Routecache

(5,1) > {5,4,2,1}(5,2) > {5,4,2}(5,4) > {5,4}...

Routecache

(2,1) > {2,1}(2,4) > {2,4}...Routecache

(1,5) > {1,2,4,5},{1,2,3,6,5}

...

RREP(5,1,{1,2,4,5})

RREP(5,1,{1,2,4,5})

RREP(5,1,{1,2,4,5}) RREP(3,1,{1,2,3,6,5})

RREP (Route reply)Source, destination, source route)

Source

Destination


DSR

Route maintenance Whenever a node transmits a data packet, a

route reply or a route error, it must verify that the next hop correctly receives the packet.

If not, the node must send a route error to the node responsible for generating this route header.

The source restarts the route discovery


DSR

Advantages Do not exchange routing update periodically, so

overhead transmission is greatly reduced Can refer to cache for the new route when link

fails. Disadvantages

Scalability problem: High route discovery latency for large network.

High mobility problem: although the packet dropped may not be substantional, the overhead traffic will increase a lot.


LAR

LAR (Location Aided Routing) Modified flooding algorithm Exploits location information to limit

the scope of the route request flood Location information being obtained

from a GPS unit


The expected zone is defined as the region that is expected to hold the current location of the destination

X

rX = last known location of node D, at time t0

r = (t1 - t0) * estimate of D’s speed

LAR


The route request is limited to the Request zone.

The request zone is the smallest rectangular region that contains the expected zone and the location of the sending node.

LAR


X

r

1

S

2

request zone

network space

LAR

expected zone


Only nodes within the request zone forward route request

The request zone is explicitly specified in the route request

If route discovery using the smaller request zone fails to find a route, the source node initiates another route discovery (after a timeout ) using a larger zone

LAR


Implicit request zone Node x forwards a route request received from y if

x is deemed closer to the expected zone when compared to y.

This is an attempt to bring the route request physically closer to the destination node after each forwarding

LAR


Proactive (table driven) Require each node to maintain one or more tables to store

routing information Each node responds to changes in network topology by

propagating updates throughout the network in order to maintain a consistent network view

DSDV, OLSR (Optimized Link State Protocol)

Reactive protocols (source initiated) Creates routes only when desired by the source node Once a route has been established, it is maintained by a

route maintenance procedure until either the destination becomes inaccessible along every path from the source or until the route is no longer desired

DSR, AODV (Ad-hoc On-demand Distance Vector)

Classification of the Routing Protocols


Proactive Approach Reactive Approach

Route Latency

LowerA route is kept at all times

HigherA route is never kept when not used

Routing Overhead

HigherA frequent dissemination of topology information is required

LowerFewer control packets in general

Various simulation studies have shown that reactive protocols perform better in mobile ad hoc networks than proactive ones. However, no single protocol works well in all environments. Which approach achieves a better trade-off depends on the traffic

and mobility patterns.



Other classification Pro active protocols

DSDV, STAR, WRP, ...

Reactive protocols AODV, DSR, TORA, ...

Hierarchical/Clustering protocols CGSR, ZRP, CBR, FSR, LANMAR, ...

Position aware protocols GPSR, LAR, GRA, ABR, ...



Standardization effort led by IETF Mobile Ad-hoc Networks (MANET) task group http://www.ietf.org/html.charters/manet-charter.html

Other protocols being researched utilize geographic , nodes provided with GPS info. Hybrid schemes that combine reactive and pro

active type of protocols

Standardization and Future Work


Standardization and Future Work

Leading protocols chosen by MANET DSR: Dynamic Source Routing AODV: Ad-hoc On-demand Distance Vector

Routing

Both are “on demand” protocols: route information discovered only as needed

routing in ad-hoc networks

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