Common Mesh TSF Issues Date: 2007-09-12 Authors: September 2007 Month Year doc.: IEEE 802.11-yy/xxxxr0 September 2007 Common Mesh TSF Issues Date: 2007-09-12 Authors: Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company John Doe, Some Company

Month Year doc.: IEEE 802.11-yy/xxxxr0 September 2007 Abstract This presentation discusses the issues and resolutions regarding common mesh TSF. Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company John Doe, Some Company

September 2007 Problem Statement Current draft states that every MP should attempt to maintain a common mesh TSF. In order to “maintain” it, how do we achieve this common mesh TSF in the first place? Distributed network synchronization mechanism. Define a synchronization master and propagate the time base through the mesh network. Neither mechanism scales well in a multi-hop mesh network. Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Issues With Distributed Synchronization September 2007 Issues With Distributed Synchronization No master clock or external reference time. All MPs cooperate to achieve the same time base. IBSS synchronization is not designed for multi-hop environment. Time to convergence could be long Ripple effect of re-synchronization Some part of the network could be out-of-sync. Is the network still functional? Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Issues With Time Base Propagation September 2007 Issues With Time Base Propagation How to choose a synchronization master? It could be elected. A distributed problem again. MPP could be the master. But what if there’re more than one MPP’s or no MPP at all? Issues with NTP-like protocols A hierarchical tree structure has to be formed first. Frequent re-forming the tree will cause network out of sync. How to reliably transmit the correct time information. Propagation delay, mobility, etc. It takes time to propagate the time information. Some part of the network could be out-of-sync. Is the network still functional? Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

September 2007 Resolutions Define a framework to accommodate different synchronization modes, as well as vendor-specific synchronization modes. Vendor could use “out-of-band” mechanisms to achieve common mesh TSF. The “out-of-band” mechanism is out of scope. Define a “Peer link synchronization mode” mode. Instead of maintaining an offset to the common mesh TSF, an MP should maintain an offset for each peer. An offset should be a per-peer or per-link property. No absolute need to have common mesh TSF. Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Synchronization Mode Identifier September 2007 Synchronization Mode Identifier Octets:1 1 4 2 ID Length Version Active Path Selection Protocol Identifier Metric Identifier Congestion Control Mode Identifier Channel Precedence Synchronization Mode Identifier Mesh Capability Mesh Configuration element Synchronization mode identifier values OUI Value Meaning 00-0F-AC Peer-link synchronization mode 1-255 Reserved for future use Vendor OUI 0-255 Vendor specific An MP should request synchronization from a peer MP only if the peer MP supports synchronization and has a matching synchronization mode identifier. Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Peer Link Synchronization Mode September 2007 Peer Link Synchronization Mode MP1 MP2 MP3 An MP should maintains an offset to each of neighbors. Neighbor Table of MP2 Neighbor MPs Offset MP1 Offset1 MP3 Offset3 Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Peer Link Synchronization Mode, cont. September 2007 Peer Link Synchronization Mode, cont. MP1 Mesh Beacons of MP1 MP2 Mesh Beacons of MP2 Offset1 Mesh Beacons of MP3 Offset3 MP3 Slide 9 Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

Peer Link Synchronization Mode, cont. September 2007 Peer Link Synchronization Mode, cont. It does NOT impact power save. In current draft, an MP wakes up at TBTT of every neighbor, regardless of which time base to use. An MP can achieve it by keeping track of offset of every neighbor. MDA works too. An MP needs to advertise MDAOP times and neighbor MDAOP interfering times in terms of its own time base. An MP receiving such times should translate them into its own time base by applying the offset. Slide 10 Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

September 2007 Summary Define a synchronization mode identifier to accommodate different synchronization mode. Define peer link synchronization mode. Vendor-specific synchronization mode is allowed. Power save and MDA still work without common mesh TSF. Zhen Xie, Atheros, et al. Zhen Xie, Atheros, et al.John Doe, Some Company

September 2007 Straw Poll #1 Should “Synchronization Mode Identifier” be included in the draft to allow different synchronization modes? Zhen Xie, Atheros, et al.

September 2007 Straw Poll #2 Is there any interest to investigate in the direction of “Peer Link Synchronization Mode”? Slide 13 Zhen Xie, Atheros, et al.

September 2007 Straw Poll #3 For simplicity, should references to “common mesh TSF” be removed from the draft, unless there’s a proven “in-band” algorithm to achieve such a common mesh TSF? Slide 14 Zhen Xie, Atheros, et al.