GCR for mesh Date: January 2011 Authors: January 2011 July 2010 Ivan Pustogarov, IITP RAS Ivan Pustogarov, IITP RAS

Groupcast with Retries in TGaa January 2011 Groupcast with Retries in TGaa Groupcast with Retries (GCR) is a flexible service defined in TGaa draft to improve the delivery of group addressed frames while optimizing for a range of criteria. GCR defines two retransmission policies for group addressed frames: GCR-Unsolicited-Retry When using the GCR-Unsolicited-Retry delivery method for a group address, the AP retransmits an MSDU one or more times to increase the probability of correct reception at STAs that are listening to this group address. GCR-Block-Ack The GCR-Block-Ack delivery method extends the block acknowledgement mechanism to group addressed frames. Ivan Pustogarov, IITP RAS

What can TGaa do for mesh? January 2011 What can TGaa do for mesh? According to PAR, TGaa is indented to improve audio and video streaming, including multicast/broadcast audio and video streams TGaa PAR does not specify directly the type of BSS, however the current TGaa draft is written with Infrastructure BSS in mind (AP and non-AP STAs are mentioned everywhere in the text) Audio/video applications for mesh are of the same (very high) importance as for infrastructure BSS Some TGaa mechanisms may be adapted for usage in a mesh: in particular GCR mechanism, especially given that little effort shall be done. Ivan Pustogarov, IITP RAS

GCR procedure January 2011 Mesh BSS Infrastructure BSS TCLAS information element (it carries the group address) and the schedule are included into GCR agreement exchange GCR group addressed MSDUs shall be sent in an A-MSDU frame format with the RA set to the GCR Concealment address. Concealment address prevents group addressed frames transmitted via GCR from being passed up the MAC-SAP of GCR-incapable STAs. Ivan Pustogarov, IITP RAS

Changes required in TGaa January 2011 Changes required in TGaa GCR text: GCR transmitter/receiver STAs: Option 1: introduce new definitions and replace “AP” with “Groupcast transmitter” and “non-AP STA” with “Groupcast receiver” Option 2: replace “AP” with “AP or mesh STA” and “non-AP STA” with “non-AP STA or mesh STA”, adding “transmitting/receiving” mesh STA” where needed How many concealment addresses? An option is to make the concealment address the same for all STAs in a mesh and distribute it in an information element like Mesh ID… … however it is not necessary. The concealment address may be chosen by each groupcast transmitter locally and stored by a groupcast receiver within a GCR agreement instance. Mesh STA: Allow using TCLAS and TSPEC elements by mesh STAs to establish a GCR agreement (is already done in TGv for DMS agreemen) Mesh STAs shall wake up according to the GCR schedule (same is done for MCCA in TGs draft, see normative text) Ivan Pustogarov, IITP RAS

January 2011 Back up slides Ivan Pustogarov, IITP RAS

Multicast approaches in mesh January 2011 Multicast approaches in mesh Two approaches exist in TGs to organize multicast traffic delivery to the intended receivers Unreliable Multicast frames are broadcasted Nonscalable Multicast frames are converted to unicast frames Ivan Pustogarov, IITP RAS

Example of more efficient multicast approach in mesh January 2011 Example of more efficient multicast approach in mesh Multicast tree approach can be used to decrease total number of retransmissions : We exploit broadcast nature of the medium and use one-hop multicast in branch points. NOTE: Branch points determine the next stations in the route according to a proprietary tree setup mechanism Do we have appropriate tools to implement such an approach? Improved Multicast tree approach (minimum one multicast packet transmission in branchpoints). Ivan Pustogarov, IITP RAS

GCR-BlockAck as a building block for efficient multicast in mesh January 2011 GCR-BlockAck as a building block for efficient multicast in mesh In the example of multicast tree approach: Group addressed MCCA reservation can be used to protect one-hop multicast traffic from collisions with packets sent by stations in the two-hop neighborhood, BUT: Currently no ARQ-like mechanism exists to react on multicast transmission errors. Hence: groupcast audio/video quality may degrade significantly due to packet losses. Group addressed topology control frames may be lost which leads to broken routes. One solution is to use GCR-BlockAck Ivan Pustogarov, IITP RAS

Example of draft change January 2011 Example of draft change Ivan Pustogarov, IITP RAS

The proposal is partially sponsored by EU FP7 project “Flavia”. January 2011 The proposal is partially sponsored by EU FP7 project “Flavia”. Ivan Pustogarov, IITP RAS