Mobile Ad hoc NETwork (MANET)

Outline

MANET overview Applications of MANET Issues in MANET MAC Protocols for MANET Routing Protocols for MANET Open issues and future directions

Infrastructure networks (single hop)

Cellular networks IEEE 802.11

Mobile Ad Hoc Networks Formed by wireless

autonomous hosts Without (necessarily)

using a pre-existing infrastructure

Routes between hosts may potentially contain multiple hops

Host mobility cause route changes

Shared wireless channel

Mobile Ad Hoc Networks

MH3

MH2

MH4

MH1

MH5

MH6

MH7Symmetric link

Asymmetric link

Why Ad Hoc Networks ? Ease of deployment

Speed of deployment

Decreased dependence on infrastructure

User flexibility

Application areas Military environments

Battle field: sensors, soldiers, vehicles Emergency operations

search-and-rescue policing and fire fighting

Civilian environments conference halls sports stadiums, Library, etc.

Personal area networking laptop, PDA, cell phone, ear phone, wrist watch

Challenges & Issues Medium Access Control

Distributed Operation Synchronization Hidden & Exposed terminal problem Access delay and Fairness Real Time Traffic support Low bandwidth Ease of snooping on wireless transmissions

Routing Mobility-induced route changes/packet losses High BER Location-dependent contention Looping Distributed Routing

Challenges & Issues Transport Layer Protocols

UDP – Highly Unreliable, may result into increasing congestion

TCP – Frequent path breaks, stale routing information, high error rate, frequent network partitions.

Energy Management Battery energy management Transmission Power management Processor and device power management

Security Denial of Service attack (DoS) Resource Consumption

Energy Depletion Buffer Overflow

Compromised Nodes Interference

Challenges & Issues Deployment Constraints

Environment Area of Coverage

Asymmetric Capabilities transmission ranges battery life processing capacity Speed/pattern of movement

MAC Protocols Goals

Operation should be distributed Support QoS for Real Time data Minimize Access Delay Fairness Scalable Power Control Mechnism Adaptive Rate Control Synchronization

MAC ProtocolsClassification of MAC Protocols Contention-Based Contention-Based with Reservation Contention-Based with Scheduling

Why is Routing in MANET Different? Host mobility

link failure/repair due to mobility different characteristics than those due to other

causes Rate of link failure/repair may be high when

nodes move fast Distributed Environment New performance criteria may be used

Route stability despite mobility Packet delivery ratio Routing Overhead

Routing Protocols in MANET Goals

Fully Distributed Adaptive to frequent topology changes Route computation and maintenance must

involve minimum number of nodes Routing state must be localized Must be loop free and free from stale route Converge must be quick Efficient resource utilization like BW, comp

power, battery, memory Provide QoS

Ad hoc Routing Protocols Proactive protocols (Table Driven)

(Eg.DSDV)

Reactive protocols (On-Demand)(Eg. AODV, DSR)

Hybrid protocols (ZRP, CEDAR)

Which approach achieves a better trade-off depends on the traffic and mobility patterns

Proactive Protocols Each node maintains a table having consistent,

up-to-date routing information from each node to every other node.

Respond to changes by propagating updates to throughout the network

Variations are on basis of number of tables required and the way updates are propagated.

Features: Traditional distributed shortest path routing protocols link-state or distance-vector protocol

Examples Destination-Sequenced Distance-Vector (DSDV) Clusterhead Gateway Switch Routing (CGSR) The Wireless Routing Protocol (WRP)

Reactive Protocols Creates route only when desired by the source node Source initiates a route discovery process within the

network Once a route has been established, it is maintained by

some form of route maintenance procedure Features:

Maintain routes only if needed Flooding of control message higher latency and lower overhead Source routing/hop-by-hop routing

Examples Ad hoc On Demand Distance Vector Protocol (AODV) Dynamic Source Routing Protocol (DSR) Temporally-Ordered Routing Algorithm (TORA) Associativity-Based Routing (ABR) Signal Stability Routing (SSR)

Hybrid Protocols

Hybrid routing protocols are proposed to combine the merits of both proactive and reactive routing protocols and overcome their shortcomings.

Features: Constrained link state maintenance Route established on-demand

Examples Zone Routing Protocol (ZRP) Core-Extraction Distributed Adhoc Routing (CEDAR)

DSDV Destination Sequenced Distance Vector

routing protocol Proactive Each node maintains its own sequences

number Updates (increments) at each change in

neighborhood information Used for loop freedom

Each node maintains routing table with entry for each node in the network

DSDV --- Routing Table at MN4

Dest Nexthop Metric DestSequenceMN1 MN2 2 406MN2 MN2 1 128MN3 MN2 2 564MN4 MN4 0 710MN5 MN6 2 392MN6 MN6 1 076MN7 MN6 2 128MN8 MN6 3 050

DSDV routing updates Each node periodically transmits updates

Includes its own sequences number, routing table updates

Nodes also send routing table updates for important link changes

When two routes to a destination received from two different neighbors Choose the one with greatest destination

sequence number If equal, choose the smaller metric (hop

count)

DSDV --- full dump

Full Dumps Carry all routing table information Transmitted relatively infrequently

Incremental updates Carry only information changed since

last full dump Fits within one network protocol data

unit If can’t, send full dump

DSDV --- link additions

When A joins network Node A transmits routing table: <A, 101, 0> Node B receives transmission, inserts <A, 101, A, 1> Node B propagates new route to neighbors <A, 101,

1> Neighbors update their routing tables: <A, 101, B, 2>

and continue propagation of information

DSDV --- link breaks

Link between B and D breaks Node B notices break

Update hop count for D and E to be infinity Increments sequence number for D and E

Node B sends updates with new route information <D, 203, infinite> <E, 156, infinite>

DSDV --- Summary Routes maintained through periodic and event

triggered routing table exchanges Incremental dumps and settling time used to

reduce control overhead Lower route request latency, but higher

overhead Perform best in network with low to moderate

mobility, few nodes and many data sessions Problems:

Not efficient for large ad-hoc networks Nodes need to maintain a complete list of routes.

Clusterhead Gateway Switch Routing (CGSR) Similar to DSDV except addressing being

employed and network organization Node are grouped into clusters. Clusterhead

selection algo (Least Cluster Change) is employed to elect a clusterhead

Gateways are used to relay packets between clusterheads.

Each node maintains cluster member table which stores destination cluster head for each node.

Also they maintain routing table, like DSDV to find next hop

CGSR---Routing

Routing from Node 1 to Node 8

CGSR--- Summary Easy to implement scheduling Better utilization of resources

Problems: Increase in path length Instability at high mobility

The Wireless Routing Protocol (WRP) Each node maintains 4 tables:

Distance table Routing table Link-cost table Message retransmission list (MRL)

DT contains matrix where each element contains distance and penultimate node reported by neighbor of a particular destination

MRL contains sequence no of update message, retransmission counter, ack required flag for each neighbor, list of update sent in update message

AODV The Ad-hoc On-Demand Distance Vector

Algorithm Reactive Pure on-demand route acquisition system Route discovery cycle used for route finding Maintenance of active routing Sequence number used for loop prevention and

route freshness criteria Descendant of DSDV Provides unicast and multicast communication

AODV --- Goal Quick adaptation under dynamic

link conditions Lower transmission latency Consume less network bandwidth

(less broadcast) Loop-free property Scalable to large network

AODV --- unicast route discovery

RREQ (route request) is broadcast Sequence Number:

Source SN: freshness on reverse route to source Destination SN: freshness on route to destination

RREQ message <bcast_id, dest_ip, dest_seqno, src_seqno,

hop_count> While forwarding, intermediate nodes record address of

neighbor from where first copy of RREQ is received, thus creating reverse path.

AODV --- unicast route discovery

RREP (route reply) is unicast back From destination if necessary From intermediate node if that node has a

recent route Intermediate node forwarding RREP stores this

info in their routing cache to set up a path to destination

Route timer is maintained with each entry. If idle for some time delete that route

As RREP is always forwarded over path of RREQ, it always expects symmetric links.

AODV --- route discovery (1)

1. Node S needs a route to D2. Create a route request (RREQ)

Enters D’s IP address, sequence number, S’s IP address, sequence number

Broadcasts RREQ to neighbors

AODV --- route discovery (2)

3. Node A receives RREQ Makes reverse route entry for S

Dest = S, nexthop = S, hopcount = 1 It has no route to D, so it broadcasts RREQ

4. Node C receives RREQ Makes reverse route entry for S

Dest = S, nexthop = A, hopcount = 2 It has route to D && seq# for route D > seq# in RREQ

Creates a route reply (RREP) Enters D’s IP address, sequence number, S’s IP address,

hopcount Unicasts RREP to A

AODV --- route discovery (3)

5. Node A receives RREP Unicasts RREP to S Makes forward route entry to D

Dest = D, nexthop = C hopcount = 2

6. Node S receives RREP Makes forward route entry to D

Dest = D, nexthop = A hopcount = 3 Sends data packets on route to D

AODV --- route maintenance (1)

Link between C and D breaks Node C invalidates route to D in routing table Node C creates route error (RERR) message

Lists all destinations which are now unreachable Sends to upstream neighbors

Node A receives RERR Checks whether C is its next hop on route to D Deletes route to D, and forwards RERR to S

AODV --- route maintenance (2)

Node S receives RERR Checks whether A is its next hop on route

to D Deletes route to D Rediscovers route if still needed

AODV --- Optimizations Expanding ring search

Prevents flooding of network during route discovery

Control Time to Live of RREQ Local repair

Repair breaks in active routes locally instead of notifying source

If first repair attempt is unsuccessful, send RERR to source

AODV --- Summary Reactive / On-demand Sequence numbers used for route

freshness and loop prevention Route discovery cycle Maintains only active routes Optimization can be used to reduce

overhead and increase scalability

Dynamic Source Routing (DSR) Two Phases

Route discovery Route maintenance

Before transmitting, a node consults its route cache. If unexpired route available, use that route else begin route discovery by broadcasting route request pkt.

RREQ contains add of Dest, Source Add, unique ID

Dynamic Source Routing (DSR) Node receiving the pkt checks, if it knows the

route to destination. If it does not then adds its own address to record route and forward the pkt to next neighbor.

RREP is generated by destination or any intermediate node knowing path to destination.

Responding node can use path to initiator for RREP if available else if symmetric links are supported, reverse path in record route.

If symmetric links are not supported, initiate RREQ with RREP being piggybacked

DSR

Dynamic Source Routing (DSR) Route Maintenance – Whenever a link

breakage is noticed, route error pkt is generated and broadcated and route containing that hop is deleted.

Apart from error pkt, ack is used to check correct operation of links (typically passive ack)

Associativity Based Routing (ABR) Route selection based stability of a route Stability is measured based count of beacons If a beacon is not received for some interval,

count is set to zero for a link A link is stable is it is leading to a stable

neighbor and same way unstable link

Associativity Based Routing (ABR) RREQ is flooded Intermediate nodes forwards RREQ by appending

its address and beacon count in it. When it reaches destination, dest waits for

TRouteSelectTime to receive more RREQ from different paths

Select route with maximum proportion of stable links

If two routes with same proportion of stable links, then choose shorter one.

But more priority is given to stability than length

Associativity Based Routing (ABR) Route Maintenance If a link is down, neighbor node detects the

breakage of link and initiates local recovery by broadcasting route repair pkt called Local Query(LQ) broadcast with limited TTL (Ex 2)

Advantages & Disadvantages Routes are stable so less chance of link failure Cons: Path may be longer Repetition of LQ

Hybrid Protocols Proactive protocol:

Pro-actively updates network state and maintains route regardless of whether any data traffic exists or not

Reactive protocol: Only determines route to a

destination if there is some data to be sent to the destination

Zone Routing Protocol(ZRP) Uses best features of reactive and proactive Uses proactive routing within a zone and reactive

outside the zone Intra Zone Routing Protocol (IARP) and Inter Zone

Routing Protocol (IERP) A routing zone of a given node is subset of nw

within which all nodes are reachable within less than or equal to zone radius hops

Interior nodes and peripheral nodes Each nodes maintains info abt all nodes in the

zone by periodic route update pkt (IARP)

Zone Routing Protocol(ZRP) When a pkt from s is to be transmitted to d S checks whether d is in its routing zone, if yes it

uses proactive routing table If no it broadcasts RREQ to all peripheral nodes If they know they respond with RREP else they also

forward to their peripherals until the destination is reached

All forwarding (RREQ) nodes appends their address to the RREQ to deliver RREP on that path

Broken link is handled by local repair and a path update message is sent to source

CEDAR Core-Extraction Distributed Ad Hoc Routing Dominator Set

Each node is in dominator sets or is the neighbor of one dominator node

Minimum Dominator Set and the links which length is no greater than 3 construct the core

Minimum Dominator Set and Core

Core Extraction Core extraction

Establishment & maintenance of a routing infrastructure called “core”

Finding core (Minimum Connected Dominating Sets) is NP-complete

Each node picks one core node as its dominator Dominator node is chosen based on degree of the

outgoing link Periodical Link state propagation

propagation of the link-state of stable high-bandwidth links in the core

Route Computation Route computation

route computation at the core nodes using all pair shortest path algorithm

S D

CEDAR --- Route Discovery

Node S informs its dominator core node A

Node A finds a route in the core network to the core node B which is the dominator for destination D

Core nodes on the above route between A and B then build a route from S to D using locally available link state information

CEDAR --- Summary Advantages

Route discovery/maintenance duties limited to a small number of core nodes

Link state propagation is a function of link stability/quality

Disadvantages Core nodes have to handle additional traffic,

associated with route discovery and maintenance

Hard to converge under high mobility

Special Constraints

Routing with special constrains Power Security QoS

Open issues and future directions

Power-Aware Routing: criteria

Define optimization criteria as a function of energy consumption. Examples:

Minimize energy consumed per packet

Minimize time to network partition due to energy depletion

Maximize duration before a node fails due to energy depletion

Power-Aware Routing: approach Assign a weight to each link

Weight of a link may be a function of energy consumed when transmitting a

packet on that link residual energy level

Prefer a route with the smallest aggregate weight

Security Issues in Mobile Ad Hoc Networks: What’s New ? Ad hoc network based on peer cooperation

Can you trust your peer? Wireless medium is easy to snoop on

Trace the path of active routes Easier for intruders to insert themselves into

the network Everybody is a “router” inject erroneous routing information divert network traffic, or make routing inefficient

Open Problems Address assignment problem

Stationary or auto-configuration? Improving interaction between protocol

layers Some routing protocol need feed back from MAC

to detect link status Position information from higher layer

Integration with Internet Existing ad hoc routing with infrastructure nodes Different network perspectives

Open ProblemsScalability

Short-range Throughput per node decreases at a rate 1/ , where N is the number of nodes This cannot be fixed except by physical layer improvements, such as directional antennas

Quality of service Need to provide best-effort service only for Voice, live video and file transfer

Client server model shift There is no server, but demand for basic services still exists. Address allocation, name resolution, authentication and service location are just examples of very basic services which are needed

Security Lack of any centralized network management or certification authority Networks are particularly prone to malicious behavior

Interoperation with the Internet Networks require some Internet connection Interface between the two are very different

Energy conservation Lifetime of a single battery and the whole network.

Node cooperation Why anyone should relay other people’s data

Interoperation What happens when two autonomous ad hoc networks move into same area