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GCR for mesh

GCR for mesh. Authors:. Date: January 2011. 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:

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GCR for mesh

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  1. GCR for mesh Authors: Date: January 2011 Ivan Pustogarov, IITP RAS

  2. 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. Groupcast with Retries in TGaa Ivan Pustogarov, IITP RAS

  3. 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. What can TGaa do for mesh? Ivan Pustogarov, IITP RAS

  4. 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. GCR procedure Mesh BSS Infrastructure BSS Ivan Pustogarov, IITP RAS

  5. Changes to Tgaa: • Introduce new definitions: • Groupcast transmitter: An access point (AP) or a mesh station (mesh STA) that transmits group addressed frames. • Groupcast receiver: A non-access point (non-AP) station (STA) or a mesh STA that receives group addressed frames. • Replace “AP” with “Groupcast transmitter” and “non-AP STA” with “Groupcast receiver” • Concealment scales to mesh networks • 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. Changes to TGs: • Allow using TCLAS and TSPEC elements by mesh STAs to establish a GCR agreement (same is done in TGv for DMS agreement, see normative text) • Mesh STAs shall be taught to wake up according to the GCR schedule (same is done for MCCA and already in TGs draft, see normative text) Changes required Ivan Pustogarov, IITP RAS

  6. Back up slides Ivan Pustogarov, IITP RAS

  7. Two approaches exist in TGs to organize multicast traffic delivery to the intended receivers Multicast approaches in mesh UnreliableMulticast frames are broadcasted NonscalableMulticast frames are converted to unicast frames Ivan Pustogarov, IITP RAS

  8. 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? Example of more efficient multicast approach in mesh Improved Multicast tree approach (minimum one multicast packet transmission in branchpoints). Ivan Pustogarov, IITP RAS

  9. 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 GCR-BlockAck as a building block for efficient multicast in mesh Ivan Pustogarov, IITP RAS

  10. Example of draft change Ivan Pustogarov, IITP RAS

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

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