November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 1

Improving Multicast ReliabilityDate: 2008-11-11

Name Company Address Phone email

Alex Ashley NDS Ltd One London Road, Staines, Middlesex, UK

+44 1784 848770 aashley@nds.com

Raja Banerjea Marvell Semiconductor 5488 Marvell Lane, Santa Clara, CA 95054

408.222.3713 rajab@marvell.com

Darwin Engwer Nortel Networks 4655 Great America Pkwy, Santa Clara CA 95054

+1-408-495-2588 dengwer at nortel.com

Subbu Ponnuswamy

Aruba Networks 1322 Crossman Ave, Sunnyvale CA

408-754-1213 subbu@arubanetworks.com

Emily Qi Intel Corporation 2111 NE 25th Ave, Hillsboro OR

503-264-7799 Emily.h.qi@intel.com

Ganesh Venkatesan

Intel Corporation JF3-381, 2111NE 25th Ave, Hillsboro, OR 97124

+1 503 334 6720 ganesh.venkatesan@intel.com

Authors:

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 2

Multicast Reliability

– The reliability of multicast delivery in 802.11 WLANs is notoriously low.

– The reliability of multicast delivery can be dramatically improved by sending multicast MSDUs from an AP to the associated STAs using the Directed Multicast Service (DMS).

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 3

Directed Multicast Service Benefits• Increases the reliability of multicast/broadcast MSDU delivery

– Multicast MSDUs are sent as unicast (when channel bandwidth is available)– Unicast is more reliable than multicast– Allows multicast MSDUs to be fragmented, further increasing reliability of delivery

• Today, multicast MSDUs cannot be fragmented

• Improves Network Discovery Operations– Especially for low duty cycle service advertisement protocols

• Improves security of multicast MSDUs– Multicasts sent via unicast can be protected using the client’s negotiated Pairwise cipher

with the AP– Today, multicast is protected by the lowest common (or open) authentication

• Reduces non-AP STA Power Consumption– Sleeping non-AP STAs can retrieve queued multicast frames along with other

individually addressed MSDUs on their own schedule, potentially reducing power consumption at the non-AP STA

– Sleeping STA doesn’t need to wake up at every DTIM or FBMS interval to receive multicast frames

– Sleeping STA only needs to wake up to check the AID TIM bit at a desirable interval (e.g. listen interval)

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 4

Directed Multicast Service (DMS) Overview

• AP advertises Directed Multicast Service (DMS) Capability

• Non-AP STA sends a request to specify traffic classes (i.e. multicast address) for the directed multicast traffic delivery

• AP may accept or reject the traffic class specified by the non-AP STA

• If the service is accepted by the AP, – AP shall transmit the requested group addressed (multicast) traffic as

individual addressed (unicast) traffic to the requesting STA in an A-MSDU frame format. The AP may still transmit the group addressed traffic for other STAs within the multicast group in the BSS as normal.

– The requesting STA shall discard group addressed frames received fro mthe AP that match a multicast address entry list.

– Other STAs will process group addressed traffic as normal.

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

DMS Request and Response frames

Slide 5

Category Action Dialog Token Request Type (“Add” or

“Remove”)

DMS Descriptor List

Octets: 1 1 1 1 variable

DMSID Length TCLAS Elements (optional)

TCLAS Processing Element (optional)

Octets: 1 1 variable 3

DMS

Descriptor

Category Action Dialog Token DMS Status List

Octets: 1 1 1 1

DMSID DMS Status

Octets: 1 1

DMS Status

•DMS Request frame:

•DMS Response frame:

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

A-MSDU is used for Directed Multicast

• Original destination address (DA) is transmitted in A-MSDU subframe header (the DA field)

• The DA and SA fields of the A-MSDU subframe header contain the values passed in the MA-UNITDATA.request and MA-UNITDATA.indication primitives. (e.g. DA=multicast address)

• RA (Address 1) in the MAC header is set to the requesting non-AP STA address

• Support of A-MSDU processing is mandatory according to the IEEE 802.11n draft specification.

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 7

Questions

• 1. Is DMS Scalable?

• 2. How does DMS relate to TGaa’s work?

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 8

Question 1: Is Directed Multicast scalable?

• Considerations:– DMS improves the reliability of multicast delivery to the same level

as unicast, at the cost of wireless medium (WM) bandwidth.– If a large number of non-AP STAs are using DMS the channel

capacity could be exceeded.• Solutions:

– Limit the DMS service for use by less than x associated STAs.– Enable this feature environments with less than x associated STAs,

for example, the home environment.– Allow the AP to disable/reject DMS service when too many STAs

are associated.– Allow the AP to disable/reject DMS service when there is

insufficient available channel bandwidth to support the current multicast traffic load without unicast traffic effects.

– DMS is an optional feature.

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

Question 2: How does DMS relate to TGaa work?

• Considerations:– DMS may overlap with TGaa efforts

– TGaa scope: “Improved link reliability and low jitter characteristics for multicast/broadcast audio/video streams.”

• DMS should be considered in TGv: – DMS extends the existing multicast enhancements in TGv and addresses a TGv

objective [Req 2120] – Including DMS in TGv can benefit low bandwidth applications sooner– Including DMS in TGv will also benefit TGaa– DMS is not intended as a general solution to the multicast stream delivery problem

(although in an environment of an AP with a single associated STA, DMS is a reasonable, simple approach)

• Straw poll taken in the May 2008 TGv/TGaa joint meeting:– Directed multicast proposal (11-08-0049)should be considered in:

• TGv:25; TGaa:8; abstain: 8

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

References

• IEEE Std. 802.11-2007

• 802.11n Draft 7.0

• 11-08-0049-03

• 11-08-0050-03

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

Backup Slides

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission Slide 12

Existing Multicast Enhancements in TGv

• FBMS – Flexible Broadcast/Multicast Service – Enables flexible delivery interval for broadcast/multicast at STA’s

request (at multiples of the DTIM intervals)

– Enables group addressed frames to be transmitted at higher data rates, reducing the amount of basic rate traffic sent over the wireless medium.

• Multicast Diagnostics Reporting– STA provides the AP an indication of the number of dropped group

addressed frames in order to enable reliable service

DMS extends existing multicast enhancements in TGv, naturally fits in TGv

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

802.11aa Requirements• Reliable Multicast is a complex problem, and different

applications may require different solutions.

• DMS provides the same level of reliability as unicast for all traffic classes, at the cost of bandwidth– Directed multicast can be used while streaming a multicast Standard

Definition (SD) stream to 2 or 3 STAs, it does not scale well for High Definition (HD) video streaming.

• 802.11aa targets multicast robustness (reliability is a part of robustness) for HD video streaming (high bandwidth) applications– 802.11n is sufficient for Standard Definition video streaming

• DMS targets low bandwidth applications, which is not the target of 802.11aa

DMS and 802.11aa target different application spaces

November 2008

Darwin Engwer, Nortel Networks

doc.: IEEE 802.11-08/1378r0

Submission

DMS should be considered in TGv

• DMS addresses TGv objective [Req 2120]; complements TGv FBMS – FBMS provides power saving for TGv devices. However, the legacy device (non-

TGv device) within the BSS will experience unexpected multicast delivery delays.

– DMS provides power saving for TGv devices without introducing latency on the legacy (non-TGv) device. However, its usage is limited to a small number of associated STAs due to bandwidth requirements.

• Including DMS in TGv can benefit low bandwidth applications sooner– TGv is in the process of initial ballots, expected sponsor ballot in 2009

– TGaa is at the stage of calling for proposals, expected sponsor ballot Nov 2010

• Including DMS in TGv will also benefit TGaa– All features specified in the existing 802.11-2007 standard and draft amendments

(e.g. TGv DMS) can be utilized by later amendments (e.g. TGaa)