Video streaming over Vajda Tamás

Transcription

1 Video sreaming over Vajda Tamás

2 Video No all bis are creaed equal Group of Picures (GoP) Video Sequence Slice Macroblock Picure (Frame) Inra (I) frames, Prediced (P) Frames or Bidirecional (B) Frames. Block (8x8 pixels) MPEG-2 ypically uses one I-frame followed by 15 P/B frames o make up a GOP.

3 Transpor Sream Variable lengh I Frame P Frame B Frame PES Header P Frame Payload SPH TS Header TS Payload... SPH TS Header TS Payload Fixed lengh MAC header IP header UDP header RTP header Payload

4 From video frames o packes Video frames ypically span muliple packes TS header may conain PCR criical for keeping audio/video in sync if los, qualiy suffers dramaically The effec of packe loss is differen depending upon is conens

5 Packe loss If one packe is los his will affec oher correcly received packes Therefore he propagaion effecs of a packe loss can be significan Single packe error ypically corresponds o he loss of a small frame (P/B) or he loss of a par of a big frame Burs packe loss significan degradaion

6 Limiaions in curren mechanisms Limied prioriizaion Lack of iner-layer communicaion Limied se of QoS parameers Limied capabiliy o dynamically weak QoS parameers Lack of conen-specific mehods 6

7 Muliple Prioriy Levels Iner-sream and Inra-Sream prioriies Real-ime video has differen QoSrequiremens compared o sored media. Curren sandard has provision for video access caegory and provides one service o all kinds of video including real-ime video, sored media ec 7

8 Conen Aware Techniques Some video frames are more imporan han ohers (I > P > B frames) Curren MAC/PHY layers don differeniae among differen frames Possible conen-specific mehods MAC Layer Frame based rery limis, fragmenaion size, QoS parameers As a resul of PHY/MAC communicaion: Frame based FEC coding, modulaion scheme, n specific feaures such as STBC, Beamforming ec. 8

9 Curren Mechanisms Disribued medium access (EDCA) prioriizaion Cenralized medium access (HCCA) admission conrol and bandwidh reservaion Dynamic channel selecion (802.11h) RRM(Radio resource managemen) (802.11k/v) (802.11n) PHY echniques for improved robusness 9

10 IEEE e Wireless LAN for Qualiy of Service 1. DCF Access Poin has frames for Saion Beacon Beacon Busy Backoff Frame 1 Backoff Frame 2 Access Poin DIFS DIFS Ack Ack Wireless Saion Beacon Inerval. Typical value = 100 ms

11 2. EDCA < EDCA TXOP limi Beacon Beacon Busy Backoff Frame 1 Frame 2 Backoff Access Poin AIFS AIFS Ack Ack Wireless Saion TXOP Bursing (Reduces Backoff Overhead)

12 3. EDCA wih No ACK < EDCA TXOP limi < EDCA TXOP limi Wireless Saion Busy Backoff Frame 1 Frame 2 Frame 3 AIFS Backoff Frame 1 Frame 2 Frame 3 AIFS Access Poin

13 4. HCCA UPLINK TXOP Polled TXOP limi DOWNLINK TXOP Downlink TXOP limi Beacon Busy Poll + Daa Ack Ack Daa Daa Access Poin PIFS PIFS Daa + Ack Daa Ack Wireless Saion Piggybacking (Reduces Poll and Ack Overheads) November 2003 Javier del Prado e al. Philips Slide 13

14 4. HCCA wih NO ACK UPLINK TXOP Polled TXOP limi DOWNLINK TXOP Downlink TXOP limi Beacon Busy Poll + Daa Daa Daa Daa Access Poin PIFS PIFS Daa Daa Daa Wireless Saion

15 IEEE h -

16 Cross Layer opimizaion- Auomaic Rae Conrol Adjusing he ransmission Rae Each Rae corresponds o differen modulaion scheme wih is own rade-off beween he saions Close Loop: RBAR (Receiver-Based AuorRae Conrol) OAR (Oppurinisic Auo_rae Conrol) Open Loop SNR (Signal-o-Noise Raio) ARF (Auomaic Rae Fallback) AMRF (Adapive Muli Rae Rery)

17 EherCAT EherCAT uses sandard frames: IEEE alernaively via UDP/IP (if IP rouing is needed) no shorened frames MTU: max bye 48 bi 48 bi 16 bi 16 bi 32 bi desinaion source Eher ype header CRC Embedded in sandard Eherne frame w. EherType 88A4h 1..n EherCAT commands Eherne H. IP header UDP H. header Or: via UDP/IP wih UDP por 88A4h 160 bi 64 bi CRC 11 bi 1 bi 4 bi lengh res. ype

18 EherCAT sandard TCP/IP sack Eherne applicaion TCP UDP real-ime applicaion IP acyclic daa mailbox process daa EherCAT MAC / DLL Eherne PHY Eherne PHY fully ransparen for TCP/IP all inerne echnologies available: HTTP, FTP, wihou resricing he real-ime capabiliies

19 Possible areas of work MAC-level echniques Selecive Repeiion o miigae packe loss Smar packe drop Finer prioriizaion among sreams and wihin one sream Conen-specific mehods QoS policy (esablishing, monioring, adapaion) Iner-Layer communicaion (Verical ineracion) PHY-MAC MAC-higher layers 19