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Enhancing Video Transport Stream Quality with Intra-flow DiffServ

This proposal explores implementing intra-flow DiffServ to adapt video frames based on channel conditions for improved link reliability and transport stream prioritization.

danielriddle
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Enhancing Video Transport Stream Quality with Intra-flow DiffServ

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  1. Requirements and Implementations for Intra-flow/Intra-AC DiffServ Authors: Date: 2008-5-13 Jun Li, Thomson Inc..

  2. Abstract One of the goals of VTS is to enable link layer adaptation on differentiated frames in a video stream according to channel conditions. This requires an intra-flow/intra-AC differentiated service (intra-Flow DiffServ), which is not supported in 802.11e QoS amendments. This proposal discusses the requirements on link layer intra-flow DiffServ and presents solutions accordingly. Jun Li, Thomson Inc..

  3. Outlines • Why we need intra-flow/intra-AC DiffServ? • Approach • Possible Differentiation Fields • Solution 1: Modify QoS control field • Solution 2: Add a 2-type new field before Frame body • Compatibility to 802.11e • Management frame modifications for supporting intra-flow DiffServ Jun Li, Thomson Inc..

  4. Why we need intra-flow/intra-AC DiffServ? VTS PAR scope proposed the following MAC enhancement Graceful degradation of audio video streams when there is insufficient channel capacity, by enabling packet discarding without any requirement for deep packet inspection. Intra-Access Category prioritization of transport streams by modifying EDCA timing and parameter selection without any requirement for deep packet inspection. Improved link reliability and low jitter characteristics for multicast/broadcast audio video streams Differentiated frames have different importance in a video transport stream, e.g., Video content dependent MAC frames, e.g. SVC base layer or enhance layer; I,P,B frames in MPEG-2 or H.264 Region of interest based encoding Channel coding frames, e.g. FEC and/or ARQ Jun Li, Thomson Inc..

  5. Approach Basic idea: define new information fields in MAC frame to realize frame differentiation without requiring deep frame inspection. Information required: VTS flag For distinguishing the VTS MAC frames against legacy frames VTS stream identification (VTS-SID) For a pair of source and destination addresses, multiple streams may be served. Need to differentiate one stream from another, so that intra-flow (aka. intra-stream) differentiation can be done for each stream In case of intra-AC (Access Category of EDCA), VTS-SID may not be required VTS stream intra-flow differentiation fields Used for frame differentiation within one video flow, e.g., I,P,B frames in MPEG-2 video flow; video, audio, FEC packets in one video flow Provide the frame dropping criteria when there is insufficient channel capacity Jun Li, Thomson Inc..

  6. Possible Differentiation Fields Priority Corresponding to content dependent frames for intra-flow or intra-AC Dropping precedence How to drop – consecutive or not Frame category Video/Audio FEC Jun Li, Thomson Inc..

  7. Solution 1: Modify QoS control field • The TID subfield (4 bits) identifies the TC or TS to which the corresponding MSDU, or fragment thereof, in the Frame Body field belongs. • The EOSP subfield (1 bit) is used by the HC to indicate the end of the current service period (SP). • The Ack Policy subfield (2 bits) identifies the acknowledgement policy. 00=normal Ack, 10=No Ack, 01= No explicit acknowledgment. 11= Block Ack • Bit 7 flag indicates it is a VTS frame with intra-flow/ intra-Access Category (AC) information included. When the flag is set, intra-flow/intra-Access Category field is contained in bits 8-15. When the flag is not set, other information is contained in bits 8-15. Jun Li, Thomson Inc..

  8. Example 1: Intra-AC only (solution 1 Contd.) Drop precedence subfield (1 bit) indicates how the frame is dropped. When the flag is set, this frame will be discarded for graceful degradation when there is insufficient channel capacity. Intra-AC Priority subfield (2 bits) indicates the priority of the frame in the transport stream. B8 B9 B10 B11 B15 Intra-AC Priority Drop Precedence Reserved intra-flow/intra-AC information Jun Li, Thomson Inc..

  9. Example 2: Intra-Flow DiffServ (solution 1 Contd.) Drop Precedence subfield (1 bit) indicates the Precedence that this frame is discarded for graceful degradation when there is insufficient channel capacity. When the flag is set, this frame will be dropped first when there is insufficient channel capacity. Intra-Flow Priority subfield (2 bits) indicates the priority of the frame in the transport stream VTS-SID (3 bits) indicates the stream ID which identifies a given video stream, i.e. frames with the same ID belong to same stream. Frame category (1 bit) indicates FEC channel coding. When the bit is set, the frame is an FEC frame, otherwise it is a source video frame. This field can be optional. B8 B9 B10 B11 B13 B14 B15 Intra-Flow Priority Drop Precedence Frame category VTS-SID Reserved intra-flow/intra-AC information Jun Li, Thomson Inc..

  10. Example 3: Intra-Flow DiffServ (solution 1 Contd.) When TID = 8-15, it can be directly used as VTS-SID. A TSPEC management frame must be used to specify parameters of the stream. In this case, a VTS frame needs to make sure Access policy = 01 (EDCA) and UP (user priority) = AC (access category), in order to compatible with EDCA. B0 B4 B8 B9 B10 B11 B13 B14 B15 VTS-SID (TID) Intra-Flow Priority Drop Precedence Reserved Frame category Reserved intra-flow/intra-AC information TS Info TSPEC element Bits: B0 B7 B8 B9 B11 B13 B18 B21 B22 B23 UP Reserved Access policy = 01 TS Info field Jun Li, Thomson Inc..

  11. Solution 2: Add a 2-type new field before Frame body A 2-byte field, VTS control field, is defined and added before the frame body in the data frame. Priority, Dropping criteria, Frame category fields are defined as same as in solution 1. The bit 7 in QoS control field (see the following figure) shall be set to 1, based on which the VTS MAC frame can be distinguished by a VTS station. Octets:2 2 6 6 6 2 6 2 2 2302 4 VTS control Frame Control Bits: B0 Duration/ ID B3 B4 B5 B6 Sequence control B7 B8 QoS Control VTS control information B15 Frame Body B11 B12 Address 1 Address 2 Address 3 Address 4 FCS VTS Flag =1 TID QoS control field in MAC frame Bits: B0 B3 B4 B5 B6 B7 B8 B14 B15 B11 B12 B13 Reserved Priority Dropping criteria Frame category Reserved VTS-SID Jun Li, Thomson Inc..

  12. Compatibility to 802.11e No compatibility to HCCA It is not required that a VTS device support HCCA function Backward compatibility to EDCA VTS devices can process EDCA frames produced by legacy devices. If all EDCA functions are supported, it is fully compatible. Forward compatibility to EDCA Legacy 802.11e device can process VTS frames as normal EDCA frames. However, a frame generated by VTS device may not contain information of QAP PS buffer status, a possible optional function for EDCA Solution 1 is backward & forward compatible, solution 2 is backward compatible only. Jun Li, Thomson Inc..

  13. Management frame modifications for supporting intra-flow DiffServ Following management frames need to be modified Beacon frame Association request / Reassociation request Association response / Reassociation response Following information elements / fields contained in the above frames need to be extended QoS capability information element QoS info field Jun Li, Thomson Inc..

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