1. 1 Simple Efficient Extensible Mesh (SEE-Mesh) Proposal IEEE 802.11-05/0562r0 June 2005 This proposal can be obtained from http://www.802wirelessworld.com/.http://www.802wirelessworld.com/

2. 2 Current 802.11s Proposals Table from: “Proposals for TGs”, IEEE 802.11-05/0597r8

3. 3 Outline 1.General Description 2.Mesh Topology Discovery and Formation Neighbor Discovery Channel Selection Link Establishment Local Link State Measurement 3.Mesh Path Selection and Forwarding Path Selection Metrics Path Selection Protocol Data Message Forwarding 4.Interworking Support

4. 4 1.General Description Device Classes Mesh Point (MP) Mesh Access Point (MAP): MP+AP Simple Station (STA) Mesh Portal (MPP): MP+Bridge MP MAP STA MPP Bridge/ Router

5. 5 2.Mesh Topology Discovery and Formation MP Boot Sequence 1)Neighbor discovery 2)Channel selection 3)Link establishment 4)Local link state measurement 5)Path selection initialization 6)AP initialization (optional – if MAP) described in this section described in the next section

6. 6 Each device supports one or more profiles. Each profile consists of A Mesh ID: like SSID, e.g., “NCTU Mesh” A path selection protocol identifier: AODV, OLSR A path selection metric identifier: airtime cost The neighbor state is one of { Neighbor, Candidate_peer, Association_pending, Subordinate_link_down, Superordinate_link_down, Subordinate_link_up, Superordinate_link_up }

7. 7 Neighbor Discovery The following is executed for each profile in the order of user’s preference. The first match is selected. Passive (listen beacon) or Active (probe request) Scanning Beacon/Probe Response frame contains: (1) Mesh ID (2) Active Protocol ID (3) Active Metric ID (4) Peer Capacity: # of additional peer that can accommodate If (1) ~ (3) are the same,  State := Neighbor If, in addition, (4) > 0,  State := Candidate_peer Example: max_peer_capacity = 3 C is a candidate_peer N is not C N A beacon pc=1 beacon pc=0

8. 8 Channel Selection Two channel selection modes: Simple unification mode (a) or advanced mode (b)(c). Simple Channel Unification Protocol: 1. Use the channel in the 1 st profile if no neighbor is found. 2. Use channel precedence indicator (CPI, a random number) to coalesce disjoint graphs and support channel switching for dynamic channel selection. beyond the scope of the proposal Figure from: “802.11 TGs Simple Efficient Extensible Mesh (SEE-Mesh) Proposal”, IEEE 802.11-05/0562r0

9. 9 Example: A 1. MP A is turned on. No neighbor is found. It switches on channel 1 and initiates a CPI = 5. B 2. MP B is turned on. No neighbor is found. It switches on channel 2 and initiates a CPI = 8. D 4. MP D is turned on. Find neighbor MP A and MP B. Because MP B has the higher CPI, MP C switches on channel 2 as MP B. C 3. MP C is turned on. Find neighbor MP A. It switches on channel 1 as MP A and sets CPI to the same as MP A. 6 6. MP C receives the channel cluster switch announcement and knows that it needs to switch to channel 2. It also forwards the channel cluster switch announcement. 7. When the timer expires, MP A and MP C switch to channel 2 simultaneously. 5 5. MP A discovers a higher CPI on channel 2. It sets a channel switch wait timer and broadcasts a channel cluster switch announcement.

10. 10 Link Establishment A MP selects from its candidate_peers to establish peer links with based on measurement of signal quality, until the maximum number of peers is established. Use association request and association reply frame to establish the link, and use directionality field (a random number) to break two concurrent associations. Example: AB State of B = candidate_peer State of A = candidate_peer assoc req (dir=5) State of B = association_pending assoc req (dir=3) State of A = association_pending assoc rep (accept) State of B = subordinate_link_down State of A = superordinate_link_down assoc rep (reject) If dir recv <=dir send then reject

11. 11 Local Link State Measurement The superordinate node is responsible for measuring the link quality. And then it sends a local link state announcement frame to the subordinate node. The measuring parameters may be: r :current bit rate in use (modulation mode) e pt :packet error rate at the current bit rate Example: AB State of B = subordinate_link_down State of A = superordinate_link_down superordinatesubordinate measuring local link state ann. (r, e pt ) State of B = subordinate_link_up State of A = superordinate_link_up after the measurement

12. 12 3.Mesh Path Selection and Forwarding The framework enables flexible implementation of path selection protocols and metrics. But the following default mandatory protocol and metric must be supported for all implementations. Path Selection Metrics Airtime Cost Path Selection Protocols Radio Metric AODV Radio Aware OLSR (optional)

13. 13 Path Selection Metric – Airtime Cost Airtime cost reflects the amount of channel resources (time) consumed by transmitting the frame. ParameterValue (802.11a) Value (802.11b) Description O ca 75  s 335  s Channel access overhead OpOp 110  s 364  s Protocol overhead BtBt 8224 Number of bits in test frame 48Mb/s, 12%PER 48Mb/s, 6%PER 12Mb/s, 15%PER 36Mb/s, 5%PER 54Mb/s, 8%PER 54Mb/s, 2%PER D S 405  s 891  s 1024  s 435  s 367  s 344  s D S (75+110+ 8224/48)* (1/0.88) = 404.6 us (75+110+ 8224/48)* (1/0.88) = 404.6 us

14. 14 Path Selection Protocol – RMAODV R adio M etric A d hoc O n- D emand D istance V ector Summary of features beyond AODV: Identify best-metric path with arbitrary path metrics Reduce flooding when maintaining multiple paths  Aggregate multiple RREQs in same message Modification to RREQ/RREP processing/forwarding rules  Forward RREQ with better metric  No route caching Optional periodic path maintenance  Allows proactive maintenance of routes to popular destinations (e.g. MPP)

15. 15 Example: 4 8 10 4 3 3 CD A S B RREQ(m=0) m=3, prev=S m=8, prev=S m=10 prev=S Initiate RREQ m=10, prev=S 4 8 10 4 3 3 CD A S B RREQ(m=10) m=3, prev=S m=8, prev=S m=13, prev=A Forward RREQ Destination replies RREP 4 8 10 4 3 3 CD A S B RREP(m=13) m=3, prev=S m=8, prev=S m=10, prev=S, next=D m=13, prev=A next=A Forward RREQ 4 8 10 4 3 3 CD A S B RREQ(m=3) m=3, prev=S m=8, prev=S m=7, prev=B, next=D m=13, prev=A next=A

16. 16 Example (cont.): Forward RREQ with better metric 4 8 10 4 3 3 CD A S B RREQ(m=7) m=3, prev=S m=8, prev=S m=7, prev=B, next=D m=10, prev=A next=A Reply RREP with better metric 4 8 10 4 3 3 CD A S B RREP(m=10) m=3, prev=S, next=A m=8, prev=S m=7, prev=B, next=D m=10, prev=A next=B Forward RREQ. But the destination do not reply because the metric is no better. 4 8 10 4 3 3 CD A S B RREQ(m=8) m=3, prev=S, next=A m=8, prev=S m=7, prev=B, next=D m=10, prev=A next=B

17. 17 Data Message Forwarding MSDU Ordering Mesh E2E Sequence Number Use a buffer to re-order the frame Use a timer to avoid indefinitely waiting Eliminates possibility of infinite loops Mesh TTL Frame Ctrl Dur Addr 1 Addr 2 Addr 3 Seq Ctrl Addr 4 QoS Ctrl Mesh Ctrl BodyFCS MAC Header Mesh E2E Seq Mesh TTL 2 2 6 6 6 2 6 2 3 4 07823 new field

18. 18 Translation between four-address frames and three-address frames ToDS 1 1 0 FromDS 1 0 1 Addr1 RA BSSID DA Addr2 TA SA BSSID Addr3 DA SA Addr4 SA N/A Frames in Mesh Frames to AP in BSS Frames from AP in BSS MP MAP STA Four-address frames Three-address frames

19. 19 The Mesh is considered a broadcast LAN. 4.Interworking Support H C F E A B D G X Y MPPs are expected to support: Transparent forwarding (broadcast LAN) Bridge learning (overhearing of packets) Support for bridge-to-bridge communications (e.g. allowing MPPs to participate in Spanning Tree Protocol)

20. 20 Key Decisions in Packet Forwarding Determine if the destination is inside or outside the Mesh: first ask all MPPs For the destination inside the Mesh, Use Mesh path selection For the destination outside the Mesh, Forward to all MPPs, until the right MPP is found Identify the right MPP and deliver packets via unicast Is the destination inside or outside the Mesh? Which MPP(s) should forward the packet? What is the path to the destination? inside outside

21. 21 Example: When A wants to send data to X, A multicast a portal update request message to all MPPs. C G A H B X Y A Forwarding table of G A Forwarding table of H G and H have no information of X in their forwarding tables. So their do not respond. When X replies (e.g. TCP-ACK), G and A learn that information. C G A H B X Y XA Forwarding table of G A Forwarding table of H C G A H B X Y Forwarding table of G Forwarding table of H When a timeout expires, A floods the data packet to all MPPs. MPPs forward it to the whole LAN. C G A H B X Y A Forwarding table of G A Forwarding table of H

22. 22 Example (cont.): When B wants to send data to X, B multicast a portal update request message to all MPPs. C G A H B X Y XA Forwarding table of G A Forwarding table of H Because G knows where X is, it replies a portal update response message to B. C G A H B X Y XA,B Forwarding table of G A,B Forwarding table of H So B can send the data packet to X via G. C G A H B X Y XA,B Forwarding table of G A,B Forwarding table of H

23. 23 Example (cont.): When C wants to send data to A, C multicast a portal update request message to all MPPs. C G A H B X Y XA,B Forwarding table of G A,B Forwarding table of H G and H know A is in the Mesh, they reply portal update response messages to C. C G A H B X Y XA,B,C Forwarding table of G A,B,C Forwarding table of H Since C knows A is in the Mesh, it initiates a RREQ to find the path. C G A H B X Y XA,B,C Forwarding table of G A,B,C Forwarding table of H

24. 24 Conclusion The SEE-Mesh proposal provides a simple, efficient and extensible solution for wireless mesh networks. It just specifies a framework which provides all the common features of the target applications. It is flexible to extend for future enhancements. Channel selection modes Path selection protocols Path selection metrics