Highlights of the CCC MMAC Mathilde Benveniste, Avaya Labs Research benveniste@ieee.org Jeffrey Zhifeng Tao, Polytechnic University jefftao@photon.poly.edu References: IEEE 802.11-05-707r0, 877r0, 880r0

Highlights of the CCC MMAC September 2005 Highlights of the CCC MMAC Date: 2005-09-16 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Avaya Labs, Polytechnic University

September 2005 Introduction 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 Avaya Labs, Polytechnic University

What is the CCC framework September 2005 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 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 Avaya Labs, Polytechnic University

Reservations on control channel September 2005 Reservations on control channel 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) Reserve MT channel 2 Reserve MT channel 1 MRTS MCTS MRTS MCTS MRTS MCTS MRTS MCTS Reserve MT channel 1 Reserve MT channel 3 CC 2437 GHz MT 1 MTXOP MTXOP 5220 GHz MT 2 MTXOP 5260 GHz MT 3 MTXOP 5300 GHz time CC: control channel MT: mesh traffic channel Frequency Avaya Labs, Polytechnic University

Why CCC is the simplest MMAC September 2005 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 + 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; their performance suffers with clock drift Avaya Labs, Polytechnic University

Other advantages of CCC MMAC September 2005 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 End-to-end delay/jitter is minimal – 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 Avaya Labs, Polytechnic University

Best channel utilization September 2005 Best channel utilization Avaya Labs, Polytechnic University

Channel Utilization September 2005 Traffic channels sit idle Single-radio multi-channel MMAC CCC MMAC CCC MMAC more efficient! CCW CCW CCW CC MT 1 MT 2 MT 3 MT 4 P Traffic channels sit idle idle time increases with # of channels MRTS/MCTS MTXOP Avaya Labs, Polytechnic University

Mesh delay/jitter is minimal for CCC: provides QoS September 2005 Mesh delay/jitter is minimal for CCC: provides QoS Avaya Labs, Polytechnic University

September 2005 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 Avaya Labs, Polytechnic University

Delay with a periodic MMAC September 2005 Delay with a periodic MMAC Reservation interval MP B cannot forward received traffic immediately: Must wait for reservation interval A R R R P P P A-B Time B R R R P P P B-C Time C R R R P P P C-D Time E-to-E Delay D Delay P experienced at each additional hop! Avaya Labs, Polytechnic University

Delay with CCC MMAC September 2005 Delay with CCC is minimal! A A-B Time B B-C Time C C-D Time E-to-E Delay D Delay with CCC is minimal! Avaya Labs, Polytechnic University

CCC preserves capacity without adjacent channel interference September 2005 CCC preserves capacity without adjacent channel interference Avaya Labs, Polytechnic University

Adjacent channel interference is a problem for any MMAC September 2005 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 Multi-radio MPs are a ‘must’ near portal of large mesh Load increases geometrically with the number of hops as paths converge to the portal Avaya Labs, Polytechnic University

How CCC can prevent capacity loss and avoid ACI September 2005 How CCC can prevent capacity loss and avoid ACI Mesh traffic in one direction A multi-radio MP can use any channel in a band for mesh traffic if acknowledgments are not sent on the same channel as mesh traffic traffic on adjacent channels flows in same direction 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 2.4 Ghz 5 Ghz RF spectrum MT channels CC Avaya Labs, Polytechnic University

Performance Evaluation Ref: Doc 05-877r0 September 2005 Performance Evaluation Ref: Doc 05-877r0 Avaya Labs, Polytechnic University

Simulation Settings September 2005 8 independent traffic streams Constant payload size: 1500 bytes Exponential frame inter-arrival Physical layer rates DATA/ACK @ 24Mbps and 54Mbps MRTS/MCTS @ 6Mbps TXOP sizes 10 and 15 frames OPNET Modeler Avaya Labs, Polytechnic University

Max Goodput -- 15 frames/TXOP September 2005 Max Goodput -- 15 frames/TXOP EDCF (1 MT) CCC (2 MTs) (4 MTs) (6 MTs) (8 MTs) Goodput increases linearly with the number of data channels The control channel is not a bottleneck Control channel at 6 Mbps; 8 traffic streams Avaya Labs, Polytechnic University

Max Goodput -- 10 frames/TXOP September 2005 Max Goodput -- 10 frames/TXOP EDCF (1 MT) CCC (2 MTs) (4 MTs) (6 MTs) (8 MTs) Shorter TXOP increased control traffic by 50% Goodput still increases linearly with the number of data channels The control channel is not a bottleneck Control channel at 6 Mbps; 8 traffic streams Avaya Labs, Polytechnic University

Average Queueing Delay September 2005 Average Queueing Delay Data PHY rate: 24Mbps Load: 19 Mbps Goodput increases with longer TXOPs EDCA cannot meet QoS delay requirements on a large mesh CCC can provide good QoS 60 ms of delay for EDCA reduced to 3.5 ms by CCC Control channel at 6 Mbps; 8 traffic streams; 10 frames/TXOP Avaya Labs, Polytechnic University

Other issues addressed Ref: Doc 05-880r0, Table 1 1 Summary description of CCC features   September 2005 Other issues addressed Ref: Doc 05-880r0, Table 1 CCC provides optional features to address multiple issues Hidden terminal Exposed node Co-existence with independent WLANs Congestion Prioritization Delay/Jitter Power Control Avaya Labs, Polytechnic University

Conclusions The CCC protocol is the simplest MMAC presented to date September 2005 Conclusions The CCC protocol is the simplest MMAC presented to date For single-radio MPs, CCC is simply EDCA CCC offers improved multi-channel MMAC performance Surpasses EDCA: higher goodput and lower delay The control channel is not a bottleneck, even at 6 Mbps High channel utilization Avoids adjacent channel interference without losing capacity Delay/jitter is minimal – enables VoIP Can do multicast/broadcast Options available to address many other concerns Avaya Labs, Polytechnic University