1. 802.1 Audio Video Bridging and 802.11 Overview
Month Year
doc.: IEEE yy/xxxxr0
May 2007
802.1 Audio Video Bridging and Overview
Date:
Authors: Myron Hattig, Michael Johas Teener, Kevin B. Stanton
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M. Hattig, M Johas Teener, K. Stanton
John Doe, Some Company

2. Introduction Goal of presentation Process:
Provide active mechanism for long-term, on-going discussion between and
Process:
Present to and discuss with both and groups.
Gather input from both groups when it appears aspects of both specifications overlap or somehow inter-relate to each other .
Determine best path for resolving those issues (e.g. specify mapping of one protocol to another).
First Step (and focus of this presentation):
Relating Quality of Service to AVB
Present to in May Meeting. Update presentation based on feedback.
Present to 802.1AVB in May Meeting. Update presentation based on feedback.
Joint /802.1 session in July Meeting.
Potential Future Step:
Relating Logical Link Discovery Protocol (LLDP) to u Generic Advertisement Services (GAS).

3. Agenda IEEE 802.1 AVB 802.11 Quality of Service Basics
Applying AVB to Standards

4. IEEE 802.1 Audio Video Task Group
Formed late 2005 to provide the specifications that will allow time-synchronized low latency streaming services through 802 networks
Based on current work:
802.1Q - bridges/switches.
Ethernet MAC/PHY
MAC/PHY
Three current projects:
P802.1AS: Time Synchronization
P802.1Qat: Stream Reservation
P802.1Qav: Forwarding and Queuing for Time-Sensitive Streams
Expect technical closure in 2007, final draft standards in 2008

5. 802.1 AVB Target Topology & Connectivity
Home Networks with limited number of segments intended market.

6. Traffic Class? 802.1Q introduced 8 different traffic classes
Highest (6 & 7) reserved for network management
low utilization, for emergencies
Next two for streaming (4 & 5)
AV bridging:
Class 5 is for lowest latency streaming (2ms through 7 hops)
Class 4 is for moderate latency streaming
Class 5 is roughly 250 usec per bridge hop for 100baseTX, near 125 usec for 1G or better: interactive audio/video
Class 4 is roughly 1ms per bridge hop, longer for wireless, MoCA, power line: voice over IP, movies

7. Admission controls (p802.1Qat - added to 802.1Q)
Priorities and shaping work only if the network resources are available along the entire path from the talker to the listener(s).
For AV streams it is the listener’s responsibility to guarantee the path is available and to reserve the resources.
Done via 802.1ak “Multiple Multicast Registration Protocol” and the new SRP (“Stream Registration Protocol”)
Registers streams as multicast addresses using MMRP
Reserves resources for streams as bandwidth/traffic class
Streaming priority mechanism can reliably deliver data with a deterministic low latency and low jitter
but only if the network resources (bandwidth, in particular) are available along the entire path from the talker to the listener(s).
For AV streams it is the listener’s responsibility to guarantee the path is available and to reserve the resources.
Done via 802.1ak “Multiple Multicast Registration Protocol” and the new SRP (“Stream Registration Protocol”)
Registers streams as multicast addresses using MMRP
Reserves resources for streams as bandwidth/traffic class
Specifics for “bandwidth” include at least max packet size and number of packets per traffic class measurement intervals
Perhaps other information useful for stream management such as path availability, egress port MAC addresses, etc.

8. Admission Control (1) (registration)
With MMRP registration, the talker and intermediate bridges know where are potential listeners and how to get to them

9. Admission Control (2) (successful reservation)
When a registration reaches the talker for that stream, it triggers a reservation back towards the registering listener.
Reservation signaling triggers admission control operations in intermediate bridges. It also locks resources and updates filtering database if the admission control is successful.
In this example, admission control is successful along the whole path. Reservation signaling serves as the end-to-end explicit ACK signaling to listener.

10. Admission Control (3) (failed reservation)
In this example, admission control fails at B2. The SI (Status Indication) flag of the reservation signaling will be set to FAIL.
The reservation is still forwarded to the listener. However, down-stream bridges (i.e., B1, B2) will not lock resources for the reservation whose SI is set to FAIL.
Listener is noted of the failure since a reservation with FAIL SI serves as an end-to-end explicit NACK

11. Precise synchronization (P802.1AS)
All AV devices participate in a “native IEEE 802 layer 2 profile” of IEEE 1588v2
This precise synchronization has three purposes:
allow multiple streams to be synchronized (e.g. networked speakers),
provide a common time base for sampling data streams at a source device and presenting those streams at the destination device with the same relative timing, and
to enable traffic shaping.
Traffic shaping results in more deterministic performance if is synchronized with it’s peers
Multiple stream synchronization is useful for lip-sync, and particularly for multiple speaker systems

12. AVB (1588) Grand Master clock
There is a single device within an AVB cloud that provides a master timing signal.
All other devices (“ordinary clocks”) synchronize their clocks with this master.

13. Master clock selection
Selection of the master is largely arbitrary, but can be overridden if the network is used in an environment that already has a “house clock”.
Professional A/V studios
Homes with provider time-synchronization service
Carrier networks
Selection algorithm and clock attributes are the same as IEEE 1588
Typically, fully automatic and transparent to the end user
Note that all AV devices that can source data will be master-capable

14. 802.11 Quality of Service Basics
Agenda
IEEE AVB
Quality of Service Basics
Applying AVB to Standards

15. General 802.11 MAC Layer Operation
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
STA only transmit when the channel is idle
STA can start to transmit immediately if channel is idle for distributed Inter-frame spacing (DIFS) period.
Short Inter-Frame Spacing (SIFS) for ACK
Network Allocation Vector (NAV) in RTS/CTS reserves medium time.
If busy, STA starts a binary backoff mechanism as follows:
Selects a random # between the contention window min and max.
Uses random # to calculate back off time.
Backoff timer decreases only when the channel is idle, otherwise frozen
STA waits DIFS each time the channel is idle
STA is authorized to transmit when then backoff timer expires
DIFS
Source
(Tx)
Data
Each STA maintains an internal timer called Network Allocation Vector which indicates when the channel is busy
SIFS = short inter-frame spacing
SIFS
ACK
Destination
(Rx)
DIFS
Contention Window
Other
NAV
Backoff
Defer access = NAV+DIFS

16. Enhanced Distributed Channel Access (EDCA)AP
AC3 (Voice)
AC2 (video)
AC2 (video)
AC2 (video)
STA3
AC0 (Best Effort)
STA1
STA2
EDCA is Prioritized Transmission of packets (similar to 802.1Q).
Access Category (AC) is set of EDCA parameters used by STA to contend
for the channel to transmit MSDU within a certain priority.

17. EDCA Access Categories (AC)
AIFS - Arbitration Inter-Frame Spacing
CWMIN - Contention Window – Min Time
CWMAX - Contention Window – Max Time AC
CWmin
CWmax
AIFS
Best Effort 2
Back Ground 1
Video
[CWmin +1]/2 ─ 1
Voice 3
[CWmin +1]/4 ─ 1
AIFS = Arbitration inter-frame spacing (period). CWmin =31, CWmax =1203
Slot time is determined from the PHY layer

18. EDCA Queuing Examine 802.1Q Tags to determine AC of Packet Low
Priority
High
Priority
AC0
AC1
AC2
AC3
Rationale: Eight kinds of applications do not transmit at the same time
Backoff
(AIFSN0)
(CWmin0)
(CWmax0)
Backoff
(AIFSN1)
(CWmin1)
(CWmax1)
Backoff
(AIFSN2)
(CWmin2)
(CWmax2)
Backoff
(AIFSN3)
(CWmin3)
(CWmax3)
Scheduler/Transmit Selection (resolves virtual collisions by granting TXOP to highest priority)
Transmission Attempt

19. Inter-Frame Spacing Earliest transmission for high-priority AC
DIFS = 50 microseconds for b, PIFS = 30 microsecond
NAV Network Allocation Vector
Short Inter-Frame Spacing – CTS/RTS
PCF Inter-Frame Spacing – PIFS
DCF Inter-Frame Spacing – DIFS
AC Inter-Frame Spacing - AIFS

20. EDCA + Admission Control
Admitted
flows AP
Rejected
Video stream
TSPEC (AC3)
AC2 (video)
AC3 (Voice)
TSPEC (AC2)
AC2 (video)
AC2 (video)
AC1
STA1
STA3
STA2
Capability Negotiation of Admission Control per AC occurs during association.
If STA and AP support Admission Control on an AC, then STA will request bandwidth from AP prior to sending packet with the AC.
STA request is in the form of ADDTS request with a TSPEC. TSPEC can be for upstream, downstream, or bi-directional traffic.
AP has proprietary algorithm to accept/deny ADDTS request based on medium time consumed.

21. TSPEC Main Parameters User priority (UP): 0 (lowest) to 7 (highest).
Maximum MSDU size (M): maximum size of the packets (octets).
Maximum Burst Size (MBS): maximum size of the data burst that can be transmitted at the peak data rate (octets)
Minimum PHY rate (R): physical bit rate assumed by the scheduler for transmit time and admission control calculations (b/s).
Peak data rate (PR): maximum bit rate allowed for transfer of the packets.
Mean data rate (ρ): average bit rate for transfer of the packets (bs).
Delay bound (D): maximum delay allowed to transport a packet across the wireless interface (including queuing delay, in ms).
Nominal MSDU size (L): nominal size of the packets (octets).
Maximum Service Interval (MSI): interval required by TS in this TSPEC between the start of two successive TXOPs.

22. Applying 802.1 AVB to 802.11 Standards
Agenda
IEEE AVB
Quality of Service Basics
Applying AVB to Standards

23. Applying 802.1 AVB to 802.11 Standards
Audio/Video Bridging in the home between Ethernet and starts to make sense with n throughput rates (e.g. 100Mbps).
Non-Focus of applying these to is:
P802.1Qav: Forwarding and Queuing for Time-Sensitive Streams is meant to guarantee latency per hop and bandwidth per class.
is a lossy network; can’t guarantee latency per hop or bandwidth per class.
Currently no work planned related P802.1Qav. .
Current focus:
Priority Mapping
P802.1Qat defined Stream Reservation Protocol (SRP) can be related to EDCA with Admission Control.
P802.1AS defined Precision Synchronization maps directly to part of v Draft (name section).

24. AC values mapping to Traffic Class values
802.1Q introduced 8 different traffic classes
Highest (6 & 7) reserved for network management
low utilization, for emergencies
Next two for streaming (4 & 5)
Lowest four for “best effort”
AV bridging using 802.1Q values of:
Class 5 is for lowest latency streaming (2ms through 7 hops)
Class 4 is for moderate latency streaming
Class 5 and 4 map well to AC_VI, Video Access Category User Priority should be set to 5 and 4 as well.
Any issues with this mapping?
Should voice be included?
Is this mapping Static or Dynamic in AP/STA?
Where is this mapping specified? ? 802.1AVB? A SIG like DLNA?
Class 5 is roughly 250 usec per bridge hop for 100baseTX, near 125 usec for 1G or better: interactive audio/video
Class 4 is roughly 1ms per bridge hop, longer for wireless, MoCA, power line: voice over IP, movies

25. Stream Reservation Protocol (SRP) and 802.11e Admission Control
Any combination of links may be Today, a bridge in the diagram may be STA or AP. Some day it may be a device within a Wi-Fi Mesh network; however, Mesh does not include Admission Control today, so SRP would not work over Mesh Networks.
If bridge is AP propagating reservation, AP looks at current load to propagate reservation or decline request. No protocol. OR, should AP always propagate the reservation then simply allow the STA to always make the ADDTS request?
If bridge is STA propagating reservation, STA sends ADDTS with appropriate TSPEC to AP. ADDTS response from AP determines if reservation is propagated or not.
Next steps:
Should AP (that is a bridge) always pass reservation propagation to STA so STA can send ADDTS. Or should AP internally allocate medium time (or not) if the AP can support the bandwidth requested by the stream reservation?
Define exact translation of SRP packet to packets or 802.1AVB spec?
Define exact translation of TSPEC to 802.1AVB stream identifier and stream definition or 802.1AVB spec?
Understand implications of Multicast over wrt MMRP, SRP, and Stream Identification.
When a registration reaches the talker for that stream, it triggers a reservation back towards the registering listener.
Reservation signaling triggers admission control operations in intermediate bridges. It also locks resources and updates filtering database if the admission control is successful.
In this example, admission control is successful along the whole path. Reservation signaling serves as the end-to-end explicit ACK signaling to listener.

26. Multiple MACs supported by 802.1AS
802.1AS architecture
Changes exist in v D0.11
Multiple MACs supported by 802.1AS