1. Relationship between peer link and physical link
November 2007
doc.: IEEE /2572r2
November 2007
Relationship between peer link and physical link
Date:
Authors:
M. Bahr, Siemens AG
M. Bahr, Siemens AG

2. November 2007
doc.: IEEE /2572r2
November 2007
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
M. Bahr, Siemens AG

3. Proposal: Logical Peer Link Concept
November 2007
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
November 2007
Visualization
first cut
needs refinement
for information only
M. Bahr, Siemens AG

5. Changes to IEEE 802.11s Draft D1.07
November 2007
Changes to IEEE s 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
November 2007
Changes to IEEE s Draft D1.07
M. Bahr, Siemens AG

7. Changes to IEEE 802.11s Draft D1.07
November 2007
Changes to IEEE s 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. November 2007
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 November 2007
M. Bahr, Siemens AG

10. Requirements for IEEE 802.11s communication over a link
November 2007
Requirements for IEEE s 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 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
November 2007
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
November 2007
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. Peer Link vs. Physical Link
November 2007
Peer Link vs. Physical Link
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/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. Dependency Models between Peer Link – Physical Link
November 2007
Dependency Models between Peer Link – Physical Link
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 s
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
M. Bahr, Siemens AG

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

19. November 2007
References
11-07/0861r0 „ Architectural Considerations for IEEE s”
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