Architectural Considerations for IEEE 802.11s May 2007 doc.: IEEE 802.11-07/xxxxr0 May 2007 Architectural Considerations for IEEE 802.11s Date: 2007-05-10 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@ok-brit.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>. Michael Bahr, Siemens AG Michael Bahr, Siemens AG

May 2007 doc.: IEEE 802.11-07/xxxxr0 May 2007 Abstract This presentation discusses issues with respect to architectural assumptions of IEEE 802.11s networks and mesh points. For several aspects, the underlying assumptions are a little bit uncertain and it can come to ambiguities easily. Michael Bahr, Siemens AG Michael Bahr, Siemens AG

Overview Architectural topics of this presentation Mesh Discovery May 2007 Overview Architectural topics of this presentation Mesh Discovery Peer Link vs. Physical Link Extensible Path Selection Framework Michael Bahr, Siemens AG

Mesh Membership of MPs When is an MP a member of an IEEE 802.11s mesh? May 2007 Mesh Membership of MPs When is an MP a member of an IEEE 802.11s mesh? if there is a physical link between the mesh and the MP? if the MP has an active profile? if it performed the initial MSA authentication with a peer MP? What is with the first MP of a mesh? Michael Bahr, Siemens AG

Mesh Membership – Physical Link May 2007 Mesh Membership – Physical Link physical link (in radio range) Michael Bahr, Siemens AG

Mesh Membership – Physical Link May 2007 Mesh Membership – Physical Link every MP can talk with any other MP as long as they are in range all MPs are a single big mesh  want some „administra-tive“ differentiation between meshes Michael Bahr, Siemens AG

Mesh Membership – Mesh Profile May 2007 Mesh Membership – Mesh Profile Michael Bahr, Siemens AG

Mesh Membership – Mesh Profile May 2007 Mesh Membership – Mesh Profile MPs know to which mesh they belong (Mesh ID) still, every MP can send frames to any other MP as long as they are in range if two different meshes have the same active path selection protocol and path selection metric, they behave as a single big mesh (paths are found over both meshes)  want some means to ensure forwarding of frames only to MPs of the same mesh Michael Bahr, Siemens AG

Mesh Membership – Peer Links and MSA Security Associations May 2007 Mesh Membership – Peer Links and MSA Security Associations Michael Bahr, Siemens AG

Mesh Membership – Peer Links and MSA Security Associations May 2007 Mesh Membership – Peer Links and MSA Security Associations MPs know to which mesh they belong (Mesh ID) every MP can send frames to any other MP it has a peer link with security association every MP knows which frames to discard, because they are not from a peer MP with security association if two different meshes have the same active path selection protocol and path selection metric, they behave as two different meshes: paths are only found in the same mesh no frames can be forwarded between MPs of different meshes  peer link establishment / MSA authentication gives a list of MPs that are allowed to communicate with the local MP Michael Bahr, Siemens AG

Requirements for IEEE 802.11s communication over a link May 2007 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 IEEE 802.11 Link is implicitly defined DATA-ACK handshake  if received ACK, link has been available and communication has been successful Michael Bahr, Siemens AG

Relation of HWMP to Links May 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. Michael Bahr, Siemens AG

Peer Link Establishment May 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 Michael Bahr, Siemens AG

Peer Link vs. Physical Link May 2007 Peer Link vs. Physical Link necessary for secure (MSA) authentication security association has long lifetime 30 minutes, hours, one day, several days lifetime depends on external events revocation of keys timeout of security association 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. Michael Bahr, Siemens AG

Mesh Boot up first MP chooses active mesh profile subsequent MPs May 2007 Mesh Boot up first MP chooses active mesh profile subsequent MPs choose active mesh profile if not in range of another MP with active mesh profile establish peer link if in range of MP with active mesh profile Michael Bahr, Siemens AG

May 2007 Mobile MP – First Round Mobile MP sets up peer links with all MPs it comes in range 8 peer link setups = 88+ messages path maintenance by path selection protocol (HWMP: PERR, PREQ, PREP) Michael Bahr, Siemens AG

Mobile MP – Second Round (1) May 2007 Mobile MP – Second Round (1) if Peer Link corresponds to physical Link: peer link is closed if physical link is lost 8 peer link setups = 88+ frames 8 peer link closes = 16 frames delay due to peer link protocol (state machine processing, timers) before link is available again path maintenance by path selection protocol (HWMP: PERR, PREQ, PREP) might be not successful due to peer link setup delay Michael Bahr, Siemens AG

Mobile MP – Second Round (2) May 2007 Mobile MP – Second Round (2) if Peer Link does not corresponds to physical Link: peer link corresponds to physical link during peer link establishment peer link is kept open if physical link is lost only packets: path maintenance by path selection protocol (HWMP: PERR, PREQ, PREP) can start immediately since there is no delay due to peer link setup Michael Bahr, Siemens AG

Dependency Models between Peer Link – Physical Link May 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 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 Michael Bahr, Siemens AG

Extensibility Framework May 2007 Extensibility Framework MP Arbitrary Path Selection Protocol Arbitrary Path Selection Metric Functionality and Mechanisms independent of the active path selection protocol / metric (e.g. beaconing, peer link establishment, security) general mechanisms should contain all functionality that is common to all path selection protocols / metrics general mechanisms should not contain functionality which is realized differently in different path selection protocols / metrics Michael Bahr, Siemens AG

May 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) Michael Bahr, Siemens AG

Proposal: Logical Peer Link Concept May 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 Michael Bahr, Siemens AG

Advantages of Logical Peer Link Concept May 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 Michael Bahr, Siemens AG

Necessary Changes to IEEE 802.11s Draft D1.03 May 2007 Necessary Changes to IEEE 802.11s Draft D1.03 Revise Definitions neighbor MP 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 peer link / mesh link / physical link Check draft for consistency assumed that only a few changes necessary current draft is not specific on the relationship between peer link and physical link in most places Michael Bahr, Siemens AG

May 2007 Straw Poll Should 802.11s go into the direction of such a logical peer link concept? yes: no: abstain: Michael Bahr, Siemens AG