A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols

Josh BrochDavid A. Maltz

David B. JohnsonYih-Chun Hu

Jorjeta Jetchevahttp://www.monarch.cmu.edu/ (subsequently moved to rice univ.)

Presented at MobiCom ‘98

Presented by Chris Dion

Agenda

• Introduction• Simulation Environment• Routing Protocols Studied• Methodology• Simulation Results• Observations• Related Work/Conclusions

Ad Hoc Networks

• Each mobile node operates as a router as well as a host.

• May have Multi-hop paths through the network.

• Examples include students using laptops, soldiers relaying information, disaster relief personnel coordinating efforts.

What can we measure?

• As of this paper (1998), little was known about performance of ad-hoc protocols

• 4 protocols will be studied and compared against

• Ns-2 simulator was extended to realistically simulate ad hoc networks

How do we simulate moving networks?

1. Accurately modeling radio waves• Use 1/r2 (r = distance between antennas) and 1/r4 for

distances outside ‘reference’

2. Medium Access Control• Use Distributed Coordination Function (DCF)

3. Address Resolution• Uses RFC 826 ARP

4. Packet Buffering• 50 Packet TX buffer, drop-tail

4 Protocols to Simulate

• DSDV (Destination-Sequenced Distance Vector)

• TORA (Temporally-Ordered Routing Algorithm)

• DSR (Dynamic Source Routing)• AODV (Ad Hoc On-Demand Distance

Vector)– Some improvements were made to all protocols

Destination-Sequenced Distance Vector (DSDV)

• Presented SIGCOMM ’94 by Perkins and Bhagwat

• Each node contains a routing table for each hop with sequence number and metric

• Each node advertises a monotonically increasing even sequence number

• Lowest sequence number is the more favorable route.

• Guaranteed Loop-freedom

DSDV Example

Updated Forwarding Table:

Temporally-Ordered Routing Algorithm (TORA)

• Presented INFOCOM ’97 by Park and Carson

• Designed to Minimize overhead and discover routes on demand

• Think about it as water flowing through tubes on its way to a destination

• Node broadcasts a Query packet, recipient broadcasts an Update packet

• Uses IMEP as transport

Route Creation Example

Link Failure without reaction

Re-establishing routes

Dynamic Source Routing (DSR)

• Published in Mobile Computing, ’96 by Johnson and Maltz (sound familiar?)

• Uses source rather then hop-by-hop routing, each packet contains list of nodes for packet to pass through.

• No need for up-to-date routing information, more importantly eliminates need for periodic route advertisement

DSR (cont)

• Route Discovery– Flood route request message – Request answered with route reply by:

• Destination• Optimized if some other node that knows the way

• Route Maintenance– If 2 nodes listed next to each other in route move out

of range• Return route error message to sender• Sender can either use another route in its cache or invoke

Route Discovery Again.

Ad Hoc On-Demand Distance Vector (AODV)

• Presented as Internet-Draft (Currently on Version 12), Perkins and Royer, 1997

• Takes the basic on-demand mechanism of Route Discovery and Maintenance from DSR, plus hop-by-hop routing, etc from DSDV

• Hello messages are passed between routes every second, Failure to receive 3 consecutive means link is taken down

AODV Example

Route Request

Route Reply

Test Methodology

• All tests based on:– 50 wireless nodes– Rectangular flat place, 1500m x 300m– 900 seconds of simulated run time– 7 Different Pause Times, which is how long each

node remains stationary:• 0,30,60,120,300,600, and 900 (no motion)

– 10 movement patterns for each pause time, 70 total– 20 m/s Max node speed (10 avg.), also used 1m/s

Packet Size/Amount/rate

• Rate is equivalent to the number of sources, decided to be fixed at 4 pps at each of 3 different # of sources (10,20,30)

• Note about Packet size:– At 1024 byte packets congestion became an issue– Used 64 byte packets to more accurately measure

network performance• Had simulator measure distances between

sender and destination nodes (shortest distance), and labeled packet with information

What do we measure?• Packet delivery ratio: Application layer packets

originated at source to received packets– Characterizes completeness and correctness of the

routing protocol• Routing overhead: Total # of packets sent during

transmission– Scalability

• Path optimality: Difference between number of hops a packet took and the shortest path measured– Measures the ability to efficiently use network resources.

Packet Delivery vs. Pause time (20 sessions)

Routing OH vs. pause time (20 sessions)

Path Optimality

Change of Speed (20m/s -> 1ms)

Additional Observations

• OH Bytes vs. Packets?– DSR clearly wins in ‘bytes for the buck’, but

does it matter?• DSDV vs. DSDV-SQ

– Sends triggered update for each new seq. number

– DSDV requires that they only be sent when a new metric is received for a destination

• Link breakages are not detected as quickly

Conclusions?

• Detailed packet-level simulation of 4 recent routing protocols

• DSDV performs predictably, not good when mobility increases

• TORA uses large amounts of OH, delivered packets well

• DSR was good at all speeds and rates!• AODV does almost as good, but more OH

makes it more expensive then DSR

Some Examples of Newer Protocols since this paper

• Periodic based updates (DSDV-like)– Fisheye, 1999– GSR (Global State Routing), 1998

• On demand based updates– ABR (Associativity-Based Routing)– ZRP (Zone Routing Protocol)– PAR (Power-Aware Routing)