Relationship between peer link and physical link

1. Relationship between peer link and physical link Authors: Date: 2007-09-19 M. Bahr, Siemens AG

2. Abstract Background information on the resolution for comments CID 418 and 465 is given. These comments are concerned with the relationship between peer links and physical links. The resolution proposes a logical peer link concept as described in 11-07/0861r0, where the logical peer link is used for mesh discovery, mesh membership, and security setup, but the physical link and the management of the connectivity is left to the path selection protocol. The changes to the draft are minimal and are given in document 11-07/2569r2. M. Bahr, Siemens AG

3. Proposal: Logical Peer Link Concept • a peer link between two MPs means: • logical link • the two MPs are allowed to communicate (transmit frames to each other) • peer link is necessity for mesh membership • the two MPs have exchanged the necessary security material • after establishment, a physical link is not required • peer link is closed through timeout or revocation of security material, explicit close, not closed if physical link is lost • cf. to backup slides and 11-07/0861r0 for more information M. Bahr, Siemens AG

4. Visualization • first cut • needs refinement • for information only M. Bahr, Siemens AG

5. Changes to IEEE 802.11s Draft D1.07 • Revised definitions • neighbor MP • MPs in direct communication range • not all neighbor MPs are peer MPs • peer MP • not all peer MPs are neighbor MPs • peer MPs – link between MPs established through peer link management protocol • neighbor peer MP • peer MPs in direct communication link • peer link • established with mesh peer link management protocol • not necessarily in direct communication range • mesh link • peer link AND physical link (i.e. peer MPs are in direct communication range) M. Bahr, Siemens AG

6. Changes to IEEE 802.11s Draft D1.07 M. Bahr, Siemens AG

7. Changes to IEEE 802.11s Draft D1.07 • make changes to use peer link, mesh link, peer MP, neighbor MP, neighbor peer MP in the right context throughout the document where appropriate • change constants of mesh peer link establishment protocol starting with MESH_LINK_... to PEER_LINK_... • removed strong coupling of logical peer link and physical link connectivity in introductory clause of mesh discovery (clause 11A.1.1) Revised definitions • proposed changes to normative text in 11-07/2569r2 • changes are minimal M. Bahr, Siemens AG

8. Motion • Move to adopt the changes proposed in 11-07/2569r2 as resolution to comments CID 418 and 465 and to instruct the editor to incorporate them into the draft. • yes: no: abstain: M. Bahr, Siemens AG

9. Some slides from 11-07/0861r0 Backup Material M. Bahr, Siemens AG

10. Requirements for IEEE 802.11s communication over a link Sending a frame • to what neighbor (MAC address)? • next hop provided by path selection protocol • am I allowed to send to that neighbor? • information provided by peer link establishment and initial MSA authentication • secure communication? • key material provided by MSA authentication over peer link • IEEE 802.11 Link is implicitly defined • DATA-ACK handshake  if received ACK, link has been available and communication has been successful M. Bahr, Siemens AG

11. Relation of HWMP to Links • HWMP refers to (allowed) physical links • HWMP does not need explicit state information on links • HWMP discovers links on-demand through probing during path discovery (PREQ, PREP)* • receiver of PREQ, PREP needs to associate a metric value to last hop • airtime link metric, hop count • path discovery is only done over links that are allowed* • derived from peer link establishment / MSA security association • „link close“ is done/detected by • path timeout, missing ACK • delete next hop information *In practice, the mesh will provide the set of links that are allowed, and the path selection protocol will work on that subset of links. M. Bahr, Siemens AG

12. Peer Link Establishment • only MPs can setup a peer link • passive / active scanning (beacons, probe request) • 1 or 2 messages • peer link management protocol for peer link establishment • 4 messages for setting up the peer link • (2 messages for closing the peer link) • peer link establishment is needed for secure setup of key material (MSA authentication) • Initial MSA authentication • EAP authentication (2+ messages) • 4-way handshake (4 messages) • group keys  11+ messages, message exchanges takes time M. Bahr, Siemens AG

13. necessary for secure (MSA) authentication and mesh membership security association has long lifetime 30 minutes, hours, one day, several days lifetime depends on external events revocation of keys timeout of security association necessary for communication Physical Link has wide range of lifetimes short, long, in some cases even very long lifetime depends on dynamics of wireless topology mobility fluctuations of radio environment Peer Link vs. Physical Link Peer link/security association and physical link have lifetimes on different time scales, and lifetimes vary independently and unpredicably in case of physical link. M. Bahr, Siemens AG

14. Peer Link requires existing Physical Link Peer Link is closed if Physical Link is lost incurs overhead in terms of packets, delay to mobile MPs maybe additional overhead for testing the physical link longer processing of events decreases the level of mobility to be supported by 802.11s Peer Link does not require existing Physical Link existing physical link required for peer link establishment established Peer Link is not closed if Physical Link is lost Peer Link is required for sending frames to peer MP no overhead in terms of packets, delay to mobile MPs due to repeated peer link establishment path selection protocols can deploy their own, optimized path maintenance procedures higher level of mobility can be supported Dependency Models betweenPeer Link – Physical Link M. Bahr, Siemens AG

15. Interface between general functionality and path selection protocols / metrics path selection protocols have different, optimized methods for detecting physical links • HWMP: on-demand link discovery with PREQ, PREP; implicit link through DATA-ACK • RA-OLSR: Hello messages with willingness, MPR state • additional specific state variables associated with link (forwarding willingness, MPR state in RA-OLSR) M. Bahr, Siemens AG

16. Proposal: Logical Peer Link Concept • a peer link between two MPs means: • logical link • the two MPs are allowed to communicate (transmit frames to each other) • peer link is necessity for mesh membership • the two MPs have exchanged the necessary security material • after establishment, a physical link is not required • peer link is closed through timeout or revocation of security material, explicit close, not closed if physical link is lost M. Bahr, Siemens AG

17. Advantages of Logical Peer Link Concept • clear and secure mechanism for determining MPs with which a node can communicate • discovery/maintenance of physical link left to specialized path selection protocol / path selection metric • use of optimized and enriched mechanisms for physical link discovery/maintenance possible • no repetition of same functionality for physical link discovery/maintenance in general peer link management and specific path selection protocol (e.g. periodic testing for availability of physical link) • no overhead in terms of frames and delay due to repeated peer link establishment for mobile nodes • no inconsistencies between (physical) link state of peer link and in path selection protocol M. Bahr, Siemens AG

18. Straw Poll in Montreal May 2007 • Should 802.11s go into the direction of such a logical peer link concept? • yes: 13 no: 1 abstain: 10 M. Bahr, Siemens AG

19. References • 11-07/0861r0 „ Architectural Considerations for IEEE 802.11s” • 11-07/2569r0 “Text changes for relationship between peer link and physical link“ • IEEE P802.11s™/D1.06: Draft STANDARD Amendment <number>: Mesh Networking M. Bahr, Siemens AG