Improving QoS Support in Mobile Ad Hoc Networks

Agenda

Motivations Proposed Framework Packet-level FEC Multipath Routing Simulation Results Conclusions

Motivations

Challenges for improving QoS in MANET Network congestion, buffer overflow

Same as we met in wired networks, but bandwidth is much lower

Radio channel characteristicsMultipath propagation, path loss, interference …

Frequent topology reconfigurationsConstant rerouting & packet dropping due to link/path failures

Motivations

QoS provisioning in MANET requires QoS-based routing protocol, Medium Access Control (MAC) protocol, and resource reservation protocol to work together.

This work focuses on improving QoS performance at the network layer, addressing packet losses due to link and path failures resulting from node mobility. Improve packet delivery ratio Improve end-to-end delay and jitter Maintain low control overhead Reduce bursty packet losses

Proposed Framework

Multi-path routing protocol (MPR) Spatial reutilization of wireless channel Improve packet delivery ratio, end-to-end

delay and jitter, routing overhead Reduce burstiness of packet losses

Packet-level Forward Error Correction scheme Reduce average packet loss rate Avoid retransmission

Observations Packet-level FEC can reduce packet loss, avoid

retransmission and associated delay. But, no significant gains can be attained by

adopting packet-level FEC over single path routing in MANET.

Packet loss tends to be bursty due to frequent path failures A packet interleaving scheme is needed.

Delay -- packets need to be buffered for interleaving before being sent out.

Memory requirements. Multi-path routing can also act as a packet

interleaver.

Correlated Packet Loss in MANET

A 3x4 Packet Interleaver

Input sequence: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] Output sequence: [1, 4, 7, 10, 2, 5, 8, 11, 3, 6, 9, 12] No impact on packet loss rate, but effectively reduces

the average burst length, converting bursty losses to random losses.

Multi-path Illustration

Reed-Solomon Erasure Coding

Multipath Routing Scheme Dynamic Source Routing (DSR) is chosen as the basis

protocol for MPR implementation. Major difference between MPR and DSR:

Route Discovery: Target node replies indiscriminately to all incoming route

requests carrying node-disjoint routes. Intermediate nodes no longer reply to route requests.

Route Maintenance: New route discovery initiated only after all active routes

broke. Packet Distribution:

Round robin packet distribution over multiple routes. Up to 3 node-disjoint paths are concurrently in use.

Simulation Model All modifications were integrated directly into

Qualnet. Random waypoint mobility model. 50 mobile

nodes randomly placed in a terrain of dimension (1500, 1500).

CBR traffic, 5 sessions, from 10, 11, 12, 13, 14 to 25, 26, 27, 28, 29, respectively. Each with 500 data packets of size 512 bytes.

IEEE 802.11 MAC with RTS/CTS. Metrics:

Packet delivery ratio, end-to-end delay and jitter, average routing overhead, burst length of packet loss.

Simulation Results:Comparison among MPR, SPR, MPR-FEC and SPR-FEC

Average Packet Del i very Rati o

00. 2

0. 40. 60. 8

11. 2

5 10 15 20 25 35 45Avg. Node Mobi l i ty Rate

(m/ s)

Pack

et D

eliv

ery

Rati

o

Mul t i -pathSi ngl e-pathMP-FEC(5=4+1)SP-FEC(5=4+1)

Average End- to- End Del ay

0

1

2

3

4

5

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate(m/ s)

Time

(s) Mul t i - path

Si ngl e- pathMP- FEC(5=4+1)SP- FEC(5=4+1)

Simulation Results:Comparison among MPR, SPR, MPR-FEC and SPR-FEC

Average End- to- End J i t ter

0

1

2

3

4

5

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate(m/ s)

Time

(s) Mul t i - path

Si ngl e- pathMP- FEC(5=4+1)SP- FEC(5=4+1)

Simulation Results:Comparison among MPR, SPR, MPR-FEC and SPR-FEC

Avg. DSR Cont rol Overhead

0

100

200

300

400

500

600

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate(m/ s)

Ctrl

Pkt

s pe

r No

de

Mul t i - pathSi ngl e- pathMP- FEC(5=4+1)SP- FEC(5=4+1)

Simulation Results:Comparison among MPR, SPR, MPR-FEC and SPR-FEC

Correlated Packet Loss Histogram (1)

Correl ated Packet Loss Hi stogram (Pause t i me = 0)

05

10152025303540

1 2 3 4 5 6 7 8 9 10+Consecuti ve Pkt Loss

Time

s

Si ngl e-path

Mul ti -path (wi thoutFEC)MP-FEC(5=4+1)

Correlated Packet Loss Histogram (2)

Correl ated Packet Loss Hi stogram (Pause t i me = 60s)

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10+Consecuti ve Pkt Loss

Time

s

Si ngl e-path

Mul ti -path (wi thoutFEC)MP-FEC(5=4+1)

Correlated Packet Loss Histogram (3)

Correl ated Packet Loss Hi stogram (Pause t i me = 120s)

02468

1012141618

1 2 3 4 5 6 7 8 9 10+Consecuti ve Pkt Loss

Time

s

Si ngl e-path

Mul t i -path (wi thoutFEC)MP-FEC(5=4+1)

Effects of Various FEC Redundancy Levels

Avg. Packet Del i very Rat i o

0

0. 2

0. 4

0. 6

0. 8

1

1. 2

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

Pack

et D

eliv

ery

Rati

o

7=4+37=5+27=6+1

Avg. DSR Rout i ng Overhead (RREQ+RREP+RERR)

0

100

200

300

400

500

600

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

DSR

Rout

ing

Over

head

7=4+37=5+27=6+1

Effects of Various FEC Redundancy Levels

Avg. End- to- End Del ay

0

0. 5

1

1. 5

2

2. 5

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

End-

to-E

nd D

elay

(s)

7=4+37=5+27=6+1

Avg. End- to- End J i t ter

0

0. 5

1

1. 5

2

2. 5

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

End-

to-E

nd J

itte

r (s

)

7=4+37=5+27=6+1

Effects of Various FEC Block Sizes

Avg. Packet Del i very Rat i o

0

0. 2

0. 4

0. 6

0. 8

1

1. 2

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

Pack

et D

eliv

ery

Rati

o

5=4+110=8+215=12+3

Avg. DSR Rout i ng Overhead (RREQ+RREP+RERR)

0

50100

150200

250300

350

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

DSR

Rout

ing

Over

head

5=4+110=8+215=12+3

Effects of Various FEC Block Sizes

Avg. End- to- End Del ay

0

0. 51

1. 52

2. 53

3. 5

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

End-

to-E

nd D

elay

(s)

5=4+110=8+215=12+3

Avg. End- to- End J i t ter

0

0. 5

1

1. 5

2

5 10 15 20 25 35 45

Avg. Node Mobi l i ty Rate (m/ s)

End-

to-E

nd J

itte

r (s

)

5=4+110=8+215=12+3

Conclusions

MPR significantly outperforms SPR in all criteria. SPR-FEC performs worse than SPR, due to

inherent packet loss correlation in MANET. MPR reduces most consecutive packet losses to

single packet losses, desirable by real-time video/audio applications.

MPR-FEC further improves packet delivery ratio, but at the cost of higher delay, jitter and control overhead (compared to MPR).

Higher FEC redundancy may not always be good.

Questions?

Thanks!

The End