Ad-hoc Routing

Michalis MichaelidesDept. of Electrical and Computer Engineering

University of Cyprus

ECE 654 – Computer Networks Seminar

November 12, 2004

Presentation Overview

Motivation Ad-hoc Networks Ad-Hoc Routing Challenges Ad-Hoc Routing protocols DSR- Dynamic Source Routing AODV- Ad-Hoc on Demand Distance Vector DSR vs. AODV comparison Sensor Networks Conclusions

References

Josh Broch, David Johnson, and David Maltz. The Dynamic Source Routing protocol for mobile ad hoc networks. Internet draft (work in progress), Internet Engineering Task Force, October 1999.

Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta Jetcheva. A performance comparison of multi-hop wireless ad hoc network routing protocols. In Proc. ACM/IEEE MobiCom, pages 85–97, October 1998.

David B. Johnson. Routing in ad hoc networks of mobile hosts. In Proc. of the IEEE Workshop on Mobile Computing Systems and Applications, pages 158–163, December 1994.

Charles Perkins, Elizabeth Royer, and Samir R. Das. Ad hoc On demand Distance Vecor (AODV) routing. Internet draft (work in progress), Internet Engineering Task Force, October 1999.

Charles E. Perkins and Pravin Bhagwat. Highly dynamic Destination-Sequenced Distance-Vector routing (DSDV) for mobile computers. In Proc. ACM SIGCOMM Conference (SIGCOMM ’94), pages 234–244, August 1993.

E. M. Royer and C-K. Toh. "A review of current routing protocols for ad-hoc mobile wireless networks."  IEEE Personal Communications, April 1999.

D. Braginsky, D. Estrin, Rumor Routing Algorithm For Sensor Networks. WSNA 2002 Karp, B., and Kung. H. T.  "GPSR: Greedy Perimeter Stateless Routing for Wireless Networks."

In Proceedings of the 6th Annual International Conference on Mobile Computing and Networking (MobiCom 2000), 243-254, 2000.

W. R. Heinzelman, A. Chandrakasan, and H. Balakrishnan, "Energy-efficient communication protocol for wireless micro-sensor networks" In Proc. IEEE Hawaii Int. Con. on System Sciences, pages 4-7, January 2000.

J. E. Wieselthier, G. D. Nguyen, and A. Ephremides, "On the construction of energy-efficient broadcast and multicast trees in wireless networks" In Proceedings of IEEE INFOCOM, pages 585-594, March 2000.

Motivation

Mobile hosts such as notebook computers featuring powerful CPUs, large main memories and disk space, multimedia capabilities and colour displays are now quite common in everyday business and personal life.

At the same time network connectivity options for use with mobile hosts have increased dramatically, including support for a growing number of wireless networking products based on radio and infrared.

Natural desire and ability to share information between mobile users: Employees in a conference room Friends in an airport terminal Search and rescue teams Military data acquisition operations in inhospitable terrain

Ad-hoc Networks

A collection of wireless mobile hosts dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration.

Due to the limited transmission range of wireless network interfaces, multiple network “hops” may be needed for one node to exchange data with another across the network.

Need a dynamic routing protocol that can efficiently find routes between two nodes.

Ad-hoc Routing

Source

Destination

Ad-hoc Routing Challenges

Correct and efficient route establishment between a pair of nodes so that messages may be delivered in a timely manner.

Keep up with high degree of node mobility. Conserve power- power aware routing Wireless medium challenges:

Links may not be bi-directional High error rates (Hidden Terminal Problem) Redundant paths Limited BW Multicast

Ad-hoc routing protocols history

DARPA (Defence Advanced Research Projects) packet radio networks in early 1970s was the first attempt.

Since then numerous protocols have been developed: Table-driven

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

DSDV, CGSR, WRP Substantial traffic and power consumption caused by periodic updates but

routes are always available. Source-initiated On-Demand

When a node requires a route to destination it initiates a route discovery process within the network.

AODV, DSR, TORA, ABR, SSR… MANET (Mobile ad hoc networking) has been formed within the

IETF (Internet Engineering Task Force) to develop a routing framework for IP-based protocols in ad hoc networks.

2 primary candidates: DSR and AODV

Dynamic Source Routing (DSR)

Source routing - The sender knows the complete hop-by-hop route to the destination.

Route cache - Nodes may learn and cache multiple routes to any destination.

Composed of 2 mechanisms: Route Discovery Route Maintenance

Requires no periodic packets of any kind at any level within the network- purely on demand.

Allows uni-directional links. Supports internetworking between different types of

wireless networks and mobile IP.

Route Discovery

RREQ (Route Request packet) Is broadcast when node S needs do send a packet to

D and does not already know a route. Each RREQ includes source and destination address,

unique request id and complete route record of all intermediate nodes.

RREP (Route Reply packet) If a node receives an RREQ for which it is either the

destination or it has a route to the destination in its route cache it responds with a RREP.

DSR

N1

N2

N5

N6

N4

N8

N3

N7Source

Destination

RREQ

RREP

N1

N1

N1-N3

N1-N2

N1-N3-N4N1-N3-N4

N1-N3-N4

N1-N3-N4-N6

N1-N2-N5

N1-N3-N4-N7

N1-N2-N5-N8

N1-N2-N5-N8

N1-N2-N5-N8

Route Maintenance

Hop-by-hop acknowledgement Link-level acknowledgement IEEE 802.11 Passive acknowledgement (Overhearing) DSR specific acknowledgement

RERR (Route Error packet) Informs the source of any broken link. Source removes any routes containing broken link from route cache.

Additional Optimizations

Packet Salvaging An intermediate node can use an alternate route from its own cache in case of a

failed link. Gratuitous route repair

A source node receiving an RERR packet piggybacks the RERR in the following RREQ.

Helps clean up cashes of other nodes in network. Promiscuous listening

When a node overhears packet checks to see whether it could be routed via itself to gain a shorter route and sends a gratuitous RREP to source.

Learn different routes without participating in routing process.

Ad-hoc On-Demand Distance Vector Routing (AODV)

Discovers routes on-demand. Uses traditional routing tables, one entry per destination

that are dynamically established at each intermediate node.

Use ‘hello’ messages for local connectivity management. Sequence numbers maintained at each destination to

determine freshness of routing information and to prevent rooting loops.

Timer-based states in each node regarding utilization of individual routing table entries.

Expanding ring search optimization.

Path Discovery

Every node maintains two separate counters: Node sequence number – Maintain freshness information of route Broadcast id – Incremented for every new RREQ

RREQ (Route Request packet) <Source and destination address ,source and destination sequence

number, broadcast id, hop count> Each node that cannot satisfy the RREQ rebroadcasts to its own

neighbours after increasing hop count. Each node keeps expiration timers to remove old RREQ and routes

from its cache. RREP (Route Reply packet)

Unicast back to the neighbour from which it received the first RREQ. <Source and destination address, destination sequence number, hop

count, lifetime>

AODV

N1

N2

N5

N6

N4

N8

N3

N7Source

Destination

RREQ

RREP

Path Maintenance

Detecting link failures Periodic ‘hello’ messages Link Layer acknowledgements (LLACKS) Attempts to forward packet to next hop fail

RERR (Route Error packet) Created when next-hop link breaks. Propagated to all predecessors until all sources using

the failed link are informed. Sources restart discovery process if they still need the

route to destination.

DSR vs. AODV

Source routing More routing overhead No periodic routing

advertisements Route caching

More routing information Fast recovery from failure More RREP

Supports uni-directional links Only broadcast No mechanism to expire stale

routes or prefer ‘fresher’ routes RERR backtracks the data

packet

Dynamic routing tables Only next-hop information Periodic “hello” messages for

local connectivity One entry per destination

Limited routing information New RREQ for every failure More RREQ

Only bi-directional links Multicast capability Expiration timers remove stale

routes and sequence numbers RERR informs all predecessor

nodes of link failure

DSR-AODV performance comparison

Simulation model ns-2 model for simulating multihop wireless networks Virtual carrier sense with RTS/CTS to reduce hidden terminal problem. 802.11 Link layer acknowledgements for each packet transmission. Send buffer with FIFO and routing packets getting higher priority than

data packets. Continuous bit rate (CBR) sources and destinations randomly spread in

rectangular field. Nodes move with randomly chosen speed, pause and then move again. Vary number of sources, node mobility, traffic load

Performance metrics Packet delivery fraction (Throughput)

Ratio of packets delivered to destination to those generated by the CBR Routing load

Routing packets transmitted per data packet delivered Path optimality or Delay (QoS)

DSR-AODV performance comparison simulation results

DSR authors DSR has the lowest routing overhead. Both DSR and AODV exhibit similar good

performance compared to DSDV,TORA.

AODV authors DSR outperforms AODV in less stressful situations-

small number of nodes and lower mobility. AODV outperforms DSR in more stressful situations.

DSR consistently generates less routing load than AODV.

Sensor Networks

Sensor networks are a special class of Ad-Hoc Networks

DIFFERENCES Number of nodes- scalability Densely deployed Prone to failure (power outage) Topology may change frequently Limited power, computational capability and memory Broadcasting vs. point-to-point Sensor nodes may not have global identification ID

because of the large amount of overhead and large number of sensors

What are sensor networks?

Sink

Internet or Satellite network

Internet or Satellite network

Task Manager Node

sensor field

sensor nodes

Ad-hoc routing for sensor networks

Geographic routing GPSR (Greedy perimeter stateless routing) uses positions of immediate

neighbours and a packet’s destination to make greedy forwarding decisions.

Outperforms DSR and demonstrates scalability on densely deployed networks.

Probability routing Gossip- Each node forwards a message with some probability to reduce

overhead of routing protocol. Adding gossiping to AODV results in significant performance

improvement. Minimum Energy

LEACH (Low Energy Adaptive Clustering Hierarchy)- Clustering based protocol that uses randomization to distribute energy dissipation.

BIP (Broadcast Incremental Power)- Uses Wireless Multicast Advantage

Conclusions

Mobile Ad hoc Networks are becoming part of our everyday lives.

DSR and AODV both provide simple on-demand routing solutions for ad-hoc networks.

They fail however to scale to large networks with limited energy resources so further enhancements are possible using position, probability, clustering, power management…