CS 15-849E: Wireless Networks (Spring 2006)

Ad Hoc Routing

Discussion Leads: Abhijit Deshmukh Sai Vinayak

Srinivasan Seshan

Dave Andersen

Papers“Outdoor Experimental Comparison of

Four Ad Hoc Routing Algorithms”Gray, Dubrovsky, Masone,

Kotz, Fiske, McGrath,

Newport, Liu, Yuan

“A Performance Comparison of

Multi-Hop Wireless Ad Hoc Network Routing Protocols”Broch, Maltz, Johnson, Hu, Jetcheva

“Link-level Measurements from an 802.11b Mesh Network”Aguayo, Bicket, Biswas, Judd, Morris

Outline• Motivation• Outdoor Experimental Comparison

• APRL• ODMRP• AODV• STARA

• Performance Comparison• DSDV• TORA• DSR• AODV

• Link-level Measurements, Mesh Networks• RoofNet• Temporal and Spatial Variation

• Take Aways• Q & A

Motivation

• Infrastructureless Networks• Ad Hoc Routing Algorithms?• Issues coupled with Wireless Ad Hoc?

• Dynamic Nature • Limited Transmission Range• Node as a router• No Maintenance• Tradeoff: Link state maintenance & Messaging complexity

Ad Hoc Network Routing Protocols

AdHoc Routing Algorithms (1)

• APRL

• STARA

• AODV

• ODMRP

Proactive Reactive

APRL STARA AODV ODMRP

APRL

• Proactive Routing

• Periodic Beaconing

• Ping Destination Via Neighbor (PDVN)

• Features• Loopless routing• Any path (not necessarily the shortest)

STARA

• Proactive Scheme

• Periodic broadcast of neighborhood probe packets NP and NP_ACKs

• Probabilistically chooses neighbor thru which to route packet• First uniform, then based on end to end latency

• Sends dummy data packets (DDPS) to update latency information of alternate routes

AODV

• Reactive Scheme

• Route request (RREQ) packet to explore route to destination

• Route response (RREP) along reverse route

• Link failure detection?• Periodic Hello messages• Link layer detection

ODMRP

• Reactive routing protocol

• Route establishment Similar to AODV

• Sender broadcasts JoinQuery

• Interested parties respond with JoinReplies

• Sender piggybacks data packet along with JoinQuery

Outdoor Evaluation-Experimental Setup

• All 4 algos implemented at the user level• Apps use virtual interface, Routing algos use physical

interface• UDP Traffic + Multicast IP• Traffic Generator

• Packet Number + sizes 2 Gaussian Distributions• Delay b/w packet streams 2 Exponential Distributions• Destination Laptops 1 Uniform Distribution

Analysis

• Message Delivery Ratio

• Communication Efficiency

• Hop Count

Analysis (Contd.)

• Zero Hop Failures• Stara-S 88%• APRL 63%• AODV 25%

Final Verdict

• AODV• Good in limited bandwidth or energy resources

• OMDRP• If bandwidth and energy resources are plentiful &

data packets are small and reliability is crucial

• Reactive is better than proactive

• Tradeoff in AD-HOC algorithms• Efficiency vs. Reliability

DSDV (Destination-Sequenced Distance Vector)

• Distance Vector Routing Protocol

• Tag Route with Sequence Number

• Updates• Periodically• Infinite-metric route

• DSDV vs. DSDV-SQ• Change == new metric• Triggered update == New sequence number• Overhead vs. packet delivery ratio

DSDV (Destination-Sequenced Distance Vector)

• Advantages• loop-free fewest-hop path

• Disadvantages• Periodic updates • Maintaining routes in the presence of mobility • Route info. may be expensive and unnecessary

TORA (Temporally Ordered Routing Algorithm)

• Highly adaptive, loop-free distributed algorithm• Link-reversal

• Maintain a mesh• Local Adaptation

• Key Design Concept• localization of control messages to a very small set of

nodes near the occurrence of a topological change.

• Three basic steps• Route creation• Route maintenance• Route erasure

Link Reversal

A FB

C E G

D

G

Any node, other than the destination,

that has no outgoing links reverses all its incoming links.

Node G has no outgoing links

F

E G

Represents a link that was reversed recently

B

E

A B

Link Reversal

A FB

C E G

D

Now all nodes (other than destination D) have an outgoing link

TORA

• QUERY packet propagation

• UPDATE packet• subsequent height increase of neighbors

• CLEAR packet• Incase of a network partition

TORA

• Advantages• Loop free paths • Establish routes quickly, before topology changes • Able to detect network partitions very quickly

• Disadvantages• Temporary oscillations (count to infinity type)• Needs synchronization

DSR (Dynamic Source Routing)

• Source Routing

• On-demand

• Two mechanisms• Route Discovery

• ROUTE REQUEST (propagating , non-propagating)

• Route Maintenance

DSR (Dynamic Source Routing)

Route RequestRoute Reply

DSR (Dynamic Source Routing)

• Advantages• Reactive: only active routes• Route caching : reduce route discovery overhead

• Disadvantages• Packet header size • Collisions between route requests and route reply?

Evaluation

• DSR vs. AODV-LL• Similar shape, yet AODV has greater overhead?

• Propagation of route discovery packets to all nodes

• 2200 route discoveries• DSR: 950 non-propagating + 300 propagating• DSDV-LL : 110,000 ROUTE REQUEST

Evaluation

• TORA• Congestive Collapse

• Positive feedback loop• MAC-layer collisions

Evaluation

• DSDV-SQ• Constant Overhead

• Periodic update with new sequence number

Link Level Measurements in Mesh Networks

• Analyze cause of packet loss

• Neighbor Abstraction• Ability to hear control packets or No Interference• Strong correlation between BER and S/N

• RoofNet pairs communicate• At intermediate loss rates• Temporal Variation• Spatial Variation

Roofnet Node Map

1 kilometer

Typical Rooftop View

A Roofnet Self-Installation Kit

Computer ($340)533 MHz PC, hard disk, CDROM

802.11b card ($155)Engenius Prism 2.5, 200mW

Software (“free”)Our networking software based on Click

Antenna ($65)8dBi, 20 degree vertical

Miscellaneous ($75)Chimney Mount,Lightning Arrestor, etc.

50 ft. Cable ($40)Low loss (3dB/100ft)

Takes a user about 45 minutes to install on a flat roof

Total: $685

RoofNet

Implies failure of Neighbor Abstraction

RoofNet (Spatial Distribution of Loss Rates)

Reasons for Differences ?• Different Antenna Heights• Multi-path fading

RoofNet (Effect of Signal-to-Noise Ratio)

• High S/N == high delivery probabilities

• Range of S/N values > 3 db

RoofNet (Effect of Power Level)

• 10 40 milliwatts doubles delivery

RoofNet (Effect of Multi-Path)

• Significant losses inter-node distance• Reflected signal delayed by a microsecond• Approx 300 meters

Q & A