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IEEE 802.11s Mesh Networking Amendment 2011-03-14

This tutorial introduces the IEEE 802.11s mesh networking amendment, covering topics such as architecture, peering, security, power saving, and more.

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IEEE 802.11s Mesh Networking Amendment 2011-03-14

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  1. The IEEE 802.11s Mesh Networking Amendment2011-03-14 – IEEE 802 plenary meeting – Singapore IEEE doc. 11-11-0380-00 Dan Harkins Dee Denteneer Guenael Strutt Guido R. Hiertz Kazuyuki Sakoda Jarkko Kneckt Michael Bahr ARUBA NETWORKS PHILIPS PHILIPS SONY POWERWAVE TECHNOLOGIES NOKIA SIEMENS AG

  2. Outline • Motivation • Introduction to 802.11s • Usage scenarios • 802.11s architecture • The Mesh BSS • Mesh Discovering • Peering • Security • Multi hopping • Path selection (reactive) • Power save • Radio resource management • MBSS connected to external STAs • Wrap up • Conclusion

  3. L P P M M M M Motivation for the tutorial STA STA AP STA AP STA STA STA STA

  4. Why a tutorial? M P P L M M M 2nd recirculation Sponsor Ballot completed March 5 with 95% approval rate Timeline targets approval to forward to ExCom by July 2011 STA STA AP STA AP STA STA STA STA

  5. M M M L P L M P M M M P P M Outline of the tutorial • What’s new in 802.11s? • Design principles • Topologies of increasing complexity Lightweight, low power nodes Wireless backhaul STA STA AP STA Interworking AP STA STA STA STA Infrastructure networks STA range extension Mesh network Peer-to-peer island STA STA AP STA AP STA STA STA STA

  6. L P P M M M M Introduction to Mesh STA STA AP STA AP STA STA STA STA

  7. Benefit #1: it’s wireless! Can form larger scale wireless network without adding wired backhaul Networked devices go where wires cannot M M M M P M P M M L M AP AP AP AP STA STA AP STA AP STA STA STA STA

  8. Network grows as devices are added Coverage is expanded with minimal configuration M M M M M M M M P M M M P M M M M M L Benefit #2: it’s self-forming! STA STA AP STA AP STA STA STA STA

  9. Resilient to single point of failure Network continues to operate during maintenance M M M M M M M M M M M M Benefit #3: it’s self-healing! Out of service Out of service

  10. Can deploy, extend, modify, and pullout the wireless network easily with minimal cost/overhead Mesh stations can be client devices True ad hoc networking with relaxed range restriction No (re-)configuration delays because there is no need to define a master station or cluster “Infrastructure” mesh stations can be deployed, upgraded, replaced or removed regardless of role Benefit #4: it has no hierarchy!

  11. L P P M M M M Usage Scenarios STA STA AP STA AP STA STA STA STA

  12. IEEE 802.11s Mesh Usage Scenarios 1 3 5 L M M M P M P Siemens-Pressebild / Siemens Press Picture 2 STA STA AP STA AP STA STA STA STA Residential / Home Office Industrial / M2M 4 6 Smart Metering/ Smart Grid Campus/Community/Public Access Public Safety/Emergency pictures (1)(2)(3)(4)IEEE doc 11-04/0662r16, (5) Siemens Press Picture, (6) IEEE doc 11-09-1313r5

  13. Backhaul Mesh • Campus/ Community/Public Access • Office • Industrial • Smart Metering/Smart Grid 2 3 5 6

  14. Client Mesh • Home Networks • Emergency/Public Safety • Industrial/M2M • Smart Metering/Smart Grid 1 4 5 6

  15. P P M M M M L STA STA AP STA AP STA STA STA STA Mixed (backhaul & client) Mesh • Home Networks • Office • Emergency/Public Safety 1 3 4

  16. L P P M M M M The 802.11s architectureExtensions required for multi-hop communications STA STA AP STA AP STA STA STA STA

  17. What has changed on the inside? L M M M M P P 802.11 STA 802.11 Mesh STA New Mesh Functions 3 Association Peering Management 802.1X 802.1X Needed serious improvements (IBSS replacement, safe disassociation, instance management etc.) SAE SAE 2 2 Addressing Addressing + Mesh Ctrl Same frame format EDCA EDCA MCCA EDCA reusable 1 PHY PHY No H/W change • MCCA provides much-needed determinism • SAE provides much-needed 802.11-based security • New mesh functions include routing, power management, synchronization … STA STA AP STA AP STA STA STA STA

  18. P P M M M M L Nothing has changed from the outside Transparent forwarding to/from any 802 STA STA STA AP STA AP STA STA STA STA

  19. The Mesh BSS Mesh Discovery Peering Mesh Security

  20. Mesh discovery When a STA boots up, it first locates neighbor mesh STAs Reuse traditional mechanism in 802.11 Passive scan (use beacon frames) Active scan (use Probe request/response) M M M M L M P P M M M M Is there anybody out there? I am here! I am here! I am here! STA STA AP STA AP STA STA STA STA

  21. Mesh discovery (cont’d) The “Mesh profile” uniquely identifies the network “Mesh ID” (Information Element in mgmt. frames): Octet string identification of the network, similar to SSID Other active attribute identifiers:the active protocol set Supplemental information: “Connected to gate” “Number of mesh peerings” L M M M M P P Mesh Profile of STA-A Mesh Profile of STA-B STA STA AP STA AP STA STA STA STA

  22. Mesh Peering A distributed, non-hierarchical, and non-exclusive agreement to communicate Each mesh STA manages its own peerings with other mesh STAs Peering Establishing Protocol A true peer-to-peer protocol Each side offers and agrees to parameters that define the terms of the peering and govern communication Two modes for secured peering (AMPE) or unsecured peering (MPM) P P M M M L M STA STA AP STA AP STA STA STA STA

  23. How is peering done Capability check via profile matching A peering has attributes that must be agreed upon Each side must make an offer of attributes to use for a potential peering Each side must confirm the agreed-upon attributes that define the peering After each side has offered and confirmed agreement, the peering is established Each side can initiate a peering and both sides can initiate the peering simultaneously P P M M M L M STA STA AP STA AP STA STA STA STA

  24. How Peering is Done L M M M P P M Initiator Responder offer offer confirm confirm STA STA AP STA AP STA STA STA STA

  25. How Peering is Done L M M M P P M Initiator Responder offer offer confirm confirm STA STA AP STA AP STA STA STA STA

  26. How Peering is Done L M M M P P M Initiator Initiator offer offer confirm confirm STA STA AP STA AP STA STA STA STA

  27. L M P P M M M Mesh Security– Simultaneous Authentication of Equals (SAE) • Distributed • No centralized server • Robust security • Misuse-resistant • A standard RSN authentication method for all of 802.11 • Can be as a drop-in replacement to WPA(2)-PSK in BSS, IBSS, and PBSS networks • Fixes well-known security problem! • Peer-to-Peer • Non-hierarchical, mutual authentication • Uses only a password • Resistant to attack • Can use short, easy-to-remember, weak passwords • Sharing a password among mesh points does not lessen security STA STA AP STA AP STA STA STA STA

  28. How SAE is performed • AKM advertising support for SAE in RSN IE in beacons and probe responses • SAE is after discovery but before peering or association • Uses 802.11 authentication frames • Simple two message exchange • Same type of exchange used for peering • Each side first commits to a guess of the password • Each side then confirms its guess and verifies the peer’s guess • Successful termination results in a PMK • Unsuccessful termination does not leak any information about the password

  29. Establishing Secure Peerings • Discovery • Identifies peer • SAE • Derives shared key • AMPE • Establish peering • Subsequent traffic is protected

  30. Mesh Peering: A Better Approach to Peer-to-peer networking Better than Bluetooth Easy-to-use, ad-hoc, auto-discovery Secure peering with short key High speed data transfer between peers Secure, direct, link establishment No pre-provisioning or “protected set-up” necessary Link is directly established between the peers without need for role determination The right tool for the right job No need to implement functionality of multiple roles (e.g. STA and AP) Security is integrated into link establishment P P M M M L M STA STA AP STA AP STA STA STA STA

  31. Multi-hopping in the Mesh BSS Path selection (reactive) Power save Radio resource management Wireless Mesh network = multi-hop topology ≠ master-slave topology

  32. Path Selection Determines paths from source mesh STA to destination mesh STA in an MBSS, possibly over multiple hops Paths are stored in forwarding information HWMP, the Hybrid Wireless Mesh Protocol, is the mandatory default path selection protocol Path selection extensibility framework for use of other path selection protocols Active path selection protocol indicated by path selection protocol identifier in Mesh Configuration IE HWMP can be always configured for interoperability P P M M M L M STA STA AP STA AP STA STA STA STA

  33. Hybrid Wireless Mesh Protocol (HWMP)Default Routing protocol in 802.11s Reactive path selection as basic path selection mechanism (always available) path is only established if needed (on-demand) no path selection control traffic if no data is sent on-demand path discovery mechanism works with arbitrary path selection metrics Proactive path selection tree to designated mesh STAs (can be configured at root mesh STAs) described later P P M M M L M STA STA AP STA AP STA STA STA STA

  34. Path Discovery in HWMPPath Request (PREQ) P L M M M M P PREQ reverse path PREP forward path O A T B E F D C O – Path Originator T – Path Target STA STA AP STA AP STA STA STA STA

  35. L P P M M M M Forwarding info @ “D“ after PREQ STA STA AP STA AP STA STA STA STA

  36. Path Discovery in HWMPPath Reply (PREP) L M M M M P P PREQ reverse path PREP forward path O A T B E F D C O – Path Originator T – Path Target STA STA AP STA AP STA STA STA STA

  37. M L M M M P P Forwarding Info @ “D” after PREP loop prevention recipient for forwarding PERR forwarding, loop prevention best quality path timeout of unused forwarding information STA STA AP STA AP STA STA STA STA

  38. P L M M M M P PREQ PREQ PREQ PREP PREP PREP The Simplest Path Discovery O T … easily extensible T O STA STA AP STA AP STA STA STA STA

  39. M L M P P M M Further Features of HWMP • Path repair • If path gets disrupted, Path Error (PERR) is generated at link break and propagated towards source mesh STA • Source mesh STA set ups new path to destination mesh STA • PERR used for indication of different error conditions • Non-forwarding mesh STA • Is only mesh source or mesh destination but does not forward frames for other mesh STAs • Participates in HWMP, but does not propagate HWMP control messages • Increases the risk of disconnected MBSS STA STA AP STA AP STA STA STA STA

  40. Frame format Mesh Control field provides address extension (six addresses), TTL, & Sequence Number Mesh Control field is encrypted as part of data M M M L P P M So… What do we do with this forwarding information? STA STA AP STA AP STA STA STA STA

  41. Multi-hopping in the Mesh BSS Power save in the Mesh BSS Wireless Mesh network = multi-hop topology ≠ master-slave topology

  42. Power save Optimized power consumption for the whole network Any device may operate in power save Power constrained devices limit forwarding and minimize power consumption Instant power-up Relaxed transition to sleep Deep & light sleep Good responsiveness of the network P P M M M L M STA STA AP STA AP STA STA STA STA

  43. M L P P M M M Interaction between power save and forwarding • Frames are buffered for Power save mesh STAs • Power saving mesh STAs can limit participation in forwarding: • Mesh STA may limit the amount of peerings • Mesh STA may operate in non-forwarding mode • Only create paths for own traffic • Link metrics may account for power constraints STA STA AP STA AP STA STA STA STA

  44. Power save and peerings Each mesh peering consists of two mesh power modes: Local mesh power mode, a promise to the peer Peer mesh power mode, a promise by the peer Power modes of different mesh peerings are independent from each other Mesh STA may operate in Doze state (radio off) only if no peering requires operation in Awake state (radio on) P P M M M L M STA STA AP STA AP STA STA STA STA

  45. Mesh power modes Mesh STAs communicate their mesh power mode for each link: Active mode Mesh STA available at any time Light sleep mode Monitoring peer STA beacons Responsible to fetch buffered data Deep sleep mode Not monitoring peer STA beacons Not responsible for fetching buffered data P P M M M L M STA STA AP STA AP STA STA STA STA

  46. Link-specific mesh power modes Mesh power mode can be set dynamically “per link” M4 M3 M2 M1 P M5 M M M M L P Weak link Active mode Light sleep mode Deep sleep mode Safe link STA STA AP STA AP STA STA STA STA

  47. Power save details Going to active mode is safe Transmissions cannot be missed, i.e. signaling is done with group- and individually-addressed frames Going to power save is less safe Transmissions may be missed if peer is assumed to be available, i.e. individually-addressed frames are used The service periods maintain power saving devices available during the individually addressed data transmission P P M M M L M STA STA AP STA AP STA STA STA STA

  48. Multi-hopping in the Mesh BSS Topics in radio resource management Wireless Mesh network = multi-hop topology ≠ master-slave topology

  49. Radio resource management Main challenges: Hidden node problem mitigation Distributed management Minimize and localize the effect of topology dynamics Some topics from 802.11s radio resource management Robust neighbor discovery Distributed resource reservation Synchronization P P M M M L M STA STA AP STA AP STA STA STA STA

  50. Hidden node problem MBCA  mitigates beacon collisions in 2 hop range MCCA  enables distributed reservation access L M M M P M P Interference STA2 STA4 STA1 STA3 STA STA AP STA AP STA STA STA STA

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