Doc.: IEEE 802.11-05/0904r2 Submission Highlights of the CCC MMAC Mathilde Benveniste, Avaya Labs...

doc.: IEEE 802.11-05/0904r2

Submission

Highlights of the CCC MMAC

Mathilde Benveniste, Avaya Labs [email protected]

Jeffrey Zhifeng Tao, Polytechnic University

[email protected]

References: IEEE 802.11-05-707r0, 877r0, 880r0

September 2005

Avaya Labs, Polytechnic University

Slide 2

doc.: IEEE 802.11-05/0904r2

Submission

Highlights of the CCC MMAC

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Date: 2005-09-16

Name Company Address Phone email Mathilde Benveniste

Avaya Labs 233 Mt Airy Road Basking Ridge, NJ 07920

973 7616105 [email protected]

Jeffrey Z. Tao Polytechnic University

Electrical and Computer Engineering Department Polytechnic University Brooklyn, NY 11201

917-977-0908 [email protected]

Authors:

September 2005


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Introduction

CCC is a MMAC proposal• CCC provides a way for mesh points to access their

assigned/selected channels in order to forward received frames to next hop

• Topology Discovery/Link Establishment/Routing are determined independently

• CCC is compatible with all of the proposals for Topology Discovery/Link Establishment/Routing

September 2005


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Overview

• The CCC protocol uses a common control channel ‘framework’

• Several optional features available – They let CCC offer capabilities competitive with any other protocol

• The CCC framework is the simplest mesh MAC presented to TGs to date

September 2005


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What is the CCC framework

• Reservations are made through RTS/CTS, exchanged on control channel, for transmission of data on one of several channels– Mesh traffic can be sent on control channel

– Reserving a channel other than the control channel for mesh traffic must be indicated on the RTS/CTS

– The extended RTS/CTS called MRTS/MCTS

– Transmission of data is based on EDCA

• A NAV is maintained for each usable channel– The duration field on the MRTS/MCTS is used to update the NAV for the

channel reserved

September 2005


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Definitions/Frames

Definition• MTXOP (mesh transmit opportunity): a sequence of frames transmitted

between a pair of MPs following a single contention/reservation for the channel (similar to 11e TXOP)

FRAMES• MRTS (mesh RTS): an expanded RTS used to reserve a MT channel

• MCTS (mesh CTS): an expanded CTS used by a MP to respond to a MRTS

• MACK (mesh Ack): a group Ack transmitted on the control channel (optional)

September 2005


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• MPs reserve time on MT channels by exchanging MRTS/MCTS on the control channel

• Control channel can serve mesh traffic channels of diverse PHYs (11a/g/n)

Reservations on control channel

MC

TS

MC

TS

time

Reserve MT channel 1

MR

TS

MR

TS

MR

TS


MR

TSReserve MT channel 1


MTXOP

MTXOP

MTXOP MTXOP

MC

TS

MC

TS

MT 2

Frequency

MT 1

CC

MT 3

CC: control channelMT: mesh traffic channel

September 2005


Slide 8

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Submission

Why CCC is the simplest MMAC

• CCC for single-radio MPs is simply EDCA – Can be used in homes to extend the reach of a BSS

– Can use existing silicon

• Add 1 receiver (or full radio) + MRTS/MCTS for full CCC– Gain multi-channel throughput

– Additional radios per MP for high-rate links

(needed in large – e.g. corporate/municipal – meshes, especially near portal)

• Like EDCA, CCC does not require synchronization– CCC is the simplest asynchronous MMAC presented

– Other common control channel protocols require synchronization

September 2005


Slide 9

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Other advantages of CCC MMAC

• Best channel utilization– No requirement to release channel at regular pre-specified times

• Multi-radio MPs without adjacent channel interference (ACI) – Some other approaches can introduce ACI when using multiple radios

• Minimal end-to-end delay/jitter – enables VoIP– Some other protocols (especially, single-radio multi-channel) add

substantial delay/jitter per hop

• Can do multicast/broadcast– Not clear how it is done with other protocols

• Can co-exist with independent WLANs– Mesh traffic channels are accessed through EDCA

September 2005


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Best channel utilization

September 2005


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Submission

Channel Utilization

MRTS/MCTS MTXOP

P

CC

MT 1

MT 2

MT 3

MT 4

CCW CCW CCW

Traffic channels sit idle• idle time increases with # of channels

Single-radio multi-channel MMAC CCC MMAC

CCC MMAC more efficient!

September 2005


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Mesh delay/jitter is minimal for CCC:provides QoS

September 2005


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QoS considerations

• QoS sensitive applications – such as VoIP – have limited tolerance for delay

• Delay on wireless access to the DS should be a small fraction of total tolerable delay

• The delay experienced on each hop of a wireless mesh should be even smaller – Not more than a few milli-seconds per hop

September 2005


Slide 14

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Delay with a periodic MMAC

Delay P experienced at each additional hop!

E-to-E Delay

P

R R R

TimeP P

P

R R

TimeP P

P

R R R

TimeP P

Reservationinterval

A-B

B-C

C-D

A

B

C

D

MP B cannot forward received traffic immediately: Must wait

for reservation interval

R

September 2005


Slide 15

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Delay with CCC MMAC

E-to-E Delay

Time

Time

TimeA-B

B-C

C-D

A

B

C

D

Delay with CCC is minimal!

September 2005


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CCC preserves capacity without adjacent channel interference

September 2005


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Adjacent channel interference is a problem for any MMAC

What is it?• Adjacent channel interference (ACI) is caused by energy on channels that are

close in the RF spectrum [Ref: Doc 05-916r0]– Greater channel separations needed when the receiver and transmitter are on same

device – i.e. on a multi-radio MP

Its impact on a mesh• A multi-radio MP cannot use any combination of channels

– It cannot transmit and receive at once on adjacent channels– This eliminates reuse in 2.4 Ghz band, and reduces reuse in 5 Ghz bands by at least half– Without special antennas and/or special MMAC, at most one channel can be used by a

multi-radio MP from each band

September 2005


Slide 18

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Multi-radio mesh points

• For large meshes, multi-radio MPs are needed closer to the portal of the mesh

– Load increases geometrically with the number of hops as paths converge toward the portal

Load =x

Load =3x

Portal

Load =7xLoad =15x

Load =31x

September 2005


Slide 19

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How CCC can prevent capacity lossand avoid ACI

Control channel in different band• MRTS/MCTS don’t cause ACI to mesh traffic

Mesh-ACK (optional)• Group ACK on control channel

Only CCC offers this capability!• Forwarding MP has a receiver on the control channel to hear the M-ACK

Mesh traffic in one direction• A multi-radio MP can use any channel in a band for mesh traffic if

1. acknowledgments are not sent on the same channel as mesh traffic

2. traffic on adjacent channels flows in same direction

Band I Band II

RF spectrum

MT channelsCC

September 2005


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Performance EvaluationRef: Doc 05-877r2

September 2005


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Simulation Settings

OPNET Modeler

• 8 traffic streams– Constant payload size: 1500 bytes– Exponential frame inter-arrival

• Physical layer rates– DATA/ACK @ 24Mbps and 54Mbps– MRTS/MCTS @ 6Mbps

• Access parameters– CWmin 32; CWmax 1024; AIFS DIFS

• TXOP sizes– 10 and 15 frames

September 2005


Slide 22

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Submission

0

50

100

150

200

250

300

350

1 2 3 4 5

Goo

dput

(M

bps)

PHY rate: 24Mbps PHY rate: 54Mbps

EDCF(1 MT)

CCC(2 MTs)

CCC(4 MTs)

CCC(6 MTs)

CCC(8 MTs)

Max Goodput -- 15 frames/TXOP

Control channel at 6 Mbps; 8 traffic streams

Goodput increases linearly with the number of data channels

The control channel is not a bottleneck

September 2005


Slide 23

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Max Goodput -- 10 frames/TXOP

0

50

100

150

200

250

300

1 2 3 4 5

Goo

dput

(M

bps)

PHY rate: 24Mbps PHY rate: 54Mbps

EDCF(1 MT)

CCC(2 MTs)

CCC(4 MTs)

CCC(6 MTs)

CCC(8 MTs)

Control channel at 6 Mbps; 8 traffic streams

Shorter TXOP increased control traffic by 50%

Goodput still increases linearly with the number of data channels

The control channel is not a bottleneck

September 2005


Slide 24

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Data PHY rate: 24MbpsLoad: 19 Mbps

Average Queueing Delay

Control channel at 6 Mbps; 8 traffic streams; 10 frames/TXOP

Goodput increases with longer TXOPs

EDCA cannot meet QoS delay requirements on a large mesh 60 ms of delay for EDCA

reduced to 3.5 ms by CCC

September 2005


Slide 25

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Data PHY rate: 24MbpsLoad: 19 Mbps

Queueing Delay CDF

Control channel at 6 Mbps; 8 traffic streams; 10 frames/TXOP

EDCA causes high jitter

CCC gives low jitter

CCC can provide good QoS

September 2005


Slide 26

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Other issues addressedRef: Doc 05-880r0 (Table 1), 05-707r0

• CCC provides optional features to address multiple issues– Hidden terminal

– Exposed node

– Allows mesh and BSS traffic to share radio/channel

– Congestion avoidance

– Superior prioritization

– Bounded jitter

– Power Control

September 2005


Slide 27

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Submission

Conclusions

• The CCC protocol is the simplest MMAC presented to date– For single-radio MPs, CCC is simply EDCA

• Applies to meshes with mix of single and multi-radio MPs

• CCC offers improved multi-channel MMAC performance– Surpasses EDCA: higher goodput and lower delay/jitter

• The control channel is not a bottleneck, even at 6 Mbps

• High channel utilization -- dynamic channel assignment

• Multi-radio MPs without adjacent channel interference or capacity loss • Delay/jitter is minimal – enables VoIP

• Can do multicast/broadcast

• Options available to address many other concerns

Doc.: IEEE 802.11-05/0904r2 Submission Highlights of the CCC MMAC Mathilde Benveniste, Avaya Labs...

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