1. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 1 ComNets MAC Partial Proposal for IEEE 802.11s 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, 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 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.stuart.kerry@philips.compatcom@ieee.org NameCompanyEmail Rui ZhaoComNets, RWTH Aachen Universityrui@comnets.rwth-aachen.de Bernhard WalkeComNets, RWTH Aachen Universitywalke@comnets.rwth-aachen.de Michael EinhausComNets, RWTH Aachen Universityein@comnets.rwth-aachen.de Date: 2005-06-15 Authors:

2. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 2 Outline General Description Mesh Distributed Coordination Function (MDCF) –Media Access Control Protocol (MACP) –Radio Link Control (RLCP) Compatible Issues

3. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 3 General Description Requirements of MAC for ESS mesh networks –Support of efficient multi-hop operation –Support of QoS delivery –Efficient handling of heavily loaded situations Conclusion –Minor amendments on DCF/PCF/EDCF/HCCA/ might hardly meet the task requirements –Building up of a WDS on multi-radio platform

4. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 4 Our Solution A multi-hop network is formed between Mesh APs on a frequency channel using MDCF BSS networks are formed on another frequency channel using DCF/PCF/EDCA/HCCA

5. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 5 Data Link Layer Model of Mesh APs MDCF –TDMA/TDD –Perfect hidden station solution –QoS guarantee –Fair share of bandwidth between peer-to-peer connections –Multi-hop forwarding in different time slots in a TDMA frame –Long time reserved traffic channels between highly loaded mesh APs –High channel utilization

6. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 6 MAC Services in Mesh APs HCF (EDCA/HCCA) MDCF –MACP –RLCP Relay –Frame formats conversion between HCF and MDCF –Frame filtering based on layer 2 fields

7. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 7 Overview of MDCF MACP: –Prioritized wireless media access –Synchronization –Transport of MACP protocol data units (MPDUs) over TDMA channels –Calming down hidden station –Multiplexing MPDUs onto traffic channels –Priority handling of packet data flows –TDMA channel in Time division duplex (TDD) operation –Error checking RLCP: –Link management –Error control & Flow control –Radio resource control –Segmentation and reassembly –Association control

8. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 8 Media Access Control Protocol (MACP) Unless otherwise stated, all the following time related parameters are example values assuming the IEEE 802.11a PHY TDMA frame and energy signals Prioritized access Link setup and TCH reservation Transmission and on-demand-TDD Calming down hidden station Packet multiplex Multi-hop operation Broadcast and multicast TCH control Synchronization

9. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 9 TDMA Frame and Energy Signals ACH- Access Channel TCH- Traffic Channels ECH- Echo Channel Energy signal (in-band busy tone) –Access-E-Signal (AES) –Busy-E-Signal (BES) Single Value Busy-E-Signal (SVB) Double Value Busy-E-Signal (DVB)

10. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 10 Access Channel (ACH) Prioritization Phase (PP) –m binary Access-E-Signal –Contention related Contention Phase (CP) –m binary Access-E-Signal –High successful probability of an access channel –Fairness access Transmission Phase (TP) –Request packet –Beacons –Broadcast/multicast packets

11. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 11 Access Mechanism (1) Mesh APs generate a number from [0, 2 m -1] –Accounting for QoS and multi-hop requirements Check number bit by bit –If 1, sends –If 0, listens –If mesh AP hears, it defer its contention Winners of PP contend again in CP –A number from [0, 2 n -1] Final winner sends packet in TP

12. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 12 Access Mechanism (2) Contention levels Access CategoryTraffic Type Multi-hop ForwardingContention Level AC_BeaconControl-7 AC_VO_MULTIVoiceyes6 AC_VOVoiceno5 AC_VI_MULTIVideoyes4 AC_VIVideono3 AC_BE_MULTIBackgroundyes2 AC_BEBackgroundno1 AC_BKBest Effort-0 Fairness access –Number used in CP in association with contention loss time of a link. The bigger lose time, the bigger number would be.

13. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 13 Link Setup and TCH Reservation

14. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 14 Transmission and On-demand-TDD Frame ControlQoS ControlFrame BodyFCS Octets: 1 1 0 – 1024 4 MACP Header Type 1 Data MPDU With an overhead of 6 octets per Data frame

15. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 15 Calming down Hidden Stations Transmission range –where data packets can be decoded Carrier sensing range –transmission of packets can be sensed but not decoded. Two times larger than transmission range in this context. Transmission power –Transmission Power for AESes is 1.5 times larger than for others including data packets, BESes. Spatial reuse distance –Sum of transmission range and carrier sense range of data packets

16. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 16 Packet Multiplex Expedited Forwarding (EF) Per Hop Behavior (PHB) in DiffServ protocol in deployed in every mesh AP to multiplex data packets onto any reserved TCH. Increase traffic channel utilization and reduce overall contentions in a network. TCH(s) can be long time reserved between highly loaded stations.

17. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 17 Multi-hop Operation A multi-hop connection consists of multiple one-hop connections in tandem that each is independently controlled. Hop-to-hop forwarding of a multi-hop transmission may take place in parallel in different TCHs of a TDMA frame, achieving low end-to-end packet delay.

18. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 18 Broadcast/Multicast TCH(s) reserved by originator –Broadcast/Multicast on reserved TCH(s). Partner transmits BESes No TCH(s) reserved by originator –Select a one-hop neighbor and then reserve TCH(s) with it. Later Broadcast/Multicast on reserved TCH(s). –Broadcast/Multicast on the TP of ACH by contending Broadcast/Multicast transmission will not cause or get interference by other unicast transmission. Broadcast/Multicast in an entire mesh network needs the support of high level protocol.

19. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 19 TCH Control Release of a TCH –Hang-on release No packet in buffer Expiration of hang-on time –Dependent on traffic type –Longer value -> low delay –Expiration of Valid transmission time (VTT) Dependent on traffic type –Forced release by RLCP An example of hang-on release, where hang-on time is 2 TDMA frames.

20. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 20 Adaptation of TCH(s) for a Link A TCH may be released by above mentioned reasons A station may request more TCH(s) –Maximum allowed number of TCH associated with traffic type  Efficient radio use even for bursty real-time traffic An example of adaptation of TCHs. –Hang on time= 1 TDMA frame –MAX TCHs=3 TCHs

21. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 21 Synchronization MDCF timing synchronization function (MTSF) –Fully distributed algorithm performed by all mesh APs. –No need to maintain a local time. Instead, record the starting time of last TDMA frame. –Each mesh AP attempts to transmit beacons if it does receive a valid one in time. –Beacon recipients adjust the starting instant of next TDMA frame by analyzing beacon. Mesh APs –Type 1, which is allowed to send first beacon. –Type 2, others.  In a multi-hop MDCF network, only one mesh AP can be Type 1 mesh AP.

22. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 22 Maintaining Synchronization Beacon –Contains no time information but channel information where it was transmitted. –Can be transmitted on a reserved TCH in case transmitter has TCH in use, otherwise in TP of ACH by contending. Beacon generation –Initiate a MTSF timer randomly from MeshBeaconPeriod range. –Selection of channel for transmission, either ACH or TCH, after expiration of timer. –Cancel pending beacon transmission if a beacon arrives before selection of a channel –Construction of beacon after winning ACH contention or selecting a TCH for transmission. Beacon reception –Valid beacon if TDMA frame structure of beacon sender agrees with that of beacon recipient –Invalid beacon

23. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 23 MTSF Finite State Machine CLOSED – inactive SCAN - scanning for a beacon SYNC – synchronized with neighbors INT – interfered by two unsynchronized stations

24. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 24 On Reception of a Valid Beacon (1) Reasons leading to time skews –Determinism Access delay Various process delays –Non-determinism Clock skews owing to different drift rates of oscillators Propagation delay ST Li n – the starting instant of the n th TDMA frame at the mesh AP i ST Ri n – the starting instant of the n th TDMA frame of beacon sending mesh AP derived at mesh AP i ΔST RLi n – the time difference of ST Li n and ST Ri n at the n th TDMA frame in mesh AP i

25. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 25 On Reception of a Valid Beacon (2) P TDMA – the time period of a TDMA frame T i n – the local time when receiving the last bit of a beacon frame at the n th TDMA frame in the mesh AP i P ACH – the duration of an ACH P PP – the duration of the PP in an ACH P CP – the duration of the CP in an ACH P TCH – the duration of a TCH S B – the length of the Beacon frame in bits PHY B – PHY data rate used to transmit beacons D pro – the amount of process delays including the computation times at the transmitting and the receiving mesh APs, and initialization times of antenna and transceivers iTCH – the numbered TCH slot that a mesh AP received a beacon When no beacon arrives (n>1) Received beacon in ACH Received beacon in TCH

26. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 26 On Reception of a Valid Beacon (3) t ij – propagation delay between the mesh AP i and the mesh AP ΔX ij – the clock skew caused by different drift rates of crystal oscillator between the sender i and the receiver j in a beacon interval d i – a variable used to represent the compensated drift rate of the mesh AP i; di in units of ppm (parts per million) If ΔST RLi n > max(t ij ), then di= di +10 ppm Else if ΔST RLi n > 2*max(t ij )/3, then di= di +5 ppm Else if ΔST RLi n < - 2*max(t ij )/3, then di= di -5 ppm Else if ΔST RLi n < - *max(t ij ), then di= di -10 ppm

27. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 27 Synchronization in Multi-hop Scenario When reception of more than 2 beacons in a nominal interval, A STA –in an overlapped area –Transmits beacons more frequently A Bigger contention number used in CP of ACH Smaller beacon generation period 12 3 STA 1 is in an overlapped area

28. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 28 Radio Link Control Protocol (RLCP) Service modes –Unacknowledged mode (UM) Connectionless unicast, multicast and broadcast applications Segmentation/Reassembly –Acknowledged mode (AM) Reliable unicast applications Segmentation/Reassembly Selective Repeat Automatic request (SR-ARQ) –Error control –Flow control

29. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 29 Allocation of Service Entities A service entity –Destination ID –Virtual Link ID unique between a transmission pair –Service mode Allocation of a service entity –Same QoS level traffic flows intended for a same direct destination –A traffic flow with special packet delay requirement Des:STA2 Link ID: 1 AM STA 1 STA 2 STA 3 Des:STA1 Link ID: 1 AM Des:STA3 Link ID: 3 UM Des:STA2 Link ID: 3 UM RLCP

30. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 30 RLCP Transmission Processes

31. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 31 Radio Resource Control Call Admission Control (CAC) –Request side Traffic channel utilization Proposed PHY mode for use Proposed channel for use Traffic description: peak/mean rate, delay/jitter, drop rate Forwarding hops –Requested side Traffic channel utilization Estimated traffic load from maintaining virtual links Adaptation of TCHs for use –Forced release of TCHs –Request more TCH for use An example of CAC algorithm is given in the Word document.

32. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 32 Compatible Issues Physical layer (PHY) –IEEE 802.11a/b/g PHY –Driver modification Security –IEEE 802.11i security mechanism Mesh topology discovery –Routing discovery in routing protocol Routing –Accepted manet routing protocol –Extensible mesh routing protocol

33. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 33 Simulation Results ModulationBit rate [Mbps] Bytes per TCH Sensitivity at receiver (dbm) BPSK ½627-85 BPSK ¾940.5-83 QPSK ½1254-81 QPSK ¾1881-79 16QAM ½24108-75 16QAM ¾36162-73 64QAM ¾54243-68 Parameter settings in the TDMA frame Energy signals in PP (ACH)4 Energy signals in CP (ACH)8 Length of TP in an ACH28 μs Length of a TCH45 μs Length of an ECH6 μs TCHs/ECHs in a TDMA frame16 Length of a TDMA frame916 μs Key parameters for different PHY modes.Parameter settings in a TDMA frame. PHY layer: IEEE 802.11a PHY.

34. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 34 TCP Performance over MDCF Networks (1) 123456 111213141516 212223242526 515253545556 Grid topology: each station is 100 meters away. TCP –Version: Reno –Source: STA 1/11/21/31/41/51 –Sink: STA 6/16/26/36/46/56 important settings in the PHY, MACP, RLCP and TCP Transmission power80 mW PHY mode for AESes and BeaconsBPSK ½ PHY mode for data packets16QAM ½ RLC PDU size100 bytes RLC Poll period20 PDUs Header of a MAC frame8 bytes Tx/Re Window size in SR-ARQ100 PDUs TCP VersionReno TCP PDU size1500 bytes TCP Sink PDU size40 bytes

35. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 35 TCP Performance over MDCF Networks (2) Change pattern of TCP connections

36. June 2005doc.: IEEE 802.11-05/0594r0 Submission R. Zhao, B. Walke, M. Einhaus. Slide 36 Results The throughput trace of each TCP connection and their aggregate value over the grid topology. The active connections are specified last page. The average throughput of a TCP connection is sampled each 1.2 s.