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

2. 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

3. 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

4. GCR procedure January 2011 Mesh BSS Infrastructure BSS
TCLAS information element carries the group address
TSPEC information element carries the schedule
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

5. Changes required January 2011 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”
Allow using TCLAS and TSPEC elements by mesh STAs to establish a GCR agreement (same is done in TGv for DMS agreement)
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.
Mesh STAs shall be taught to wake up according to the GCR schedule carried in TSPEC (same is done for MCCA and already in TGs draft)
Ivan Pustogarov, IITP RAS

6. January 2011
Back up slides
Ivan Pustogarov, IITP RAS

7. 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

8. 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

9. 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

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