Streaming digital video over wireless link PROGRESS project EES.5653 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Agenda General issues with streaming over a wireless link Streaming MPEG video - link layer approach Briefly - transport layer approach Future work 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Video over wireless link Typical scenario: video transmission from set-top box to the (mutiple) screens wireless 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Simplified sender/receiver communication video source video sink sender buffer receiver buffer - Latency or playback delay. - What the jitter is. - Why do we need buffers? The bigger the buffers – the higher the latency, the less the jitter. If we want lower latency (par example conferencing), we want smaller buffers. (In case of RT video – conferencing) The bigger the buffers – the less probability of data loss - So, we have a dillema – we need to find how to minimize latency and still provide data delivery. - Explain why it’s not meaningful to use the sender buffer bigger than the receiver buffer. - Explain that the size of the receiver buffer is oftern limited and that for sake of lower latency we may want smaller buffers - With smaller buffers more data will get lost That’s why we need to consider sending first of all what is most important. If we need to drop data, then we drop pieces which influence our quality leas wireless interface (sender) wireless inerface (receiver) 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Video over wireless link Wireless link properties: High jitter vs high losses because of interferences on physical level jitter comes up to 0.25s with default settings on CISCO 350 WiFi card Low troughput (< 5Mbps for 802.11b) can be higher with 802.11a/g, but never as high as wire/optical Variable throughput Typical perceived quality issues: Artefacts “Hick-ups” 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

IP (Internet Protocol) Layers we look at OSI stack: application layer MPEG en-/decoder MPEG-packetizer transport layer TCP, UDP/RTP network layer IP (Internet Protocol) packet scheduler link layer 802.11 driver physical layer 802.11 WLAN 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Link layer approach Sender Application/ encoder TCP/IP stack MAC-level retries video stream driver/scheduler buffer IP packets TCP/IP stack Explain here what the MAC retries means, how it influences the fullness of the scheduler buffer, how the jitter occurs. Retries parameter lets us specify the trade-off between reliability of the wireless link and it’s throughput 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

I BBPBBPBB(I) MPEG encoding GOP (group-of-pictures): Frame types: I, P, B Typical GOP structure and dependences: I BBPBBPBB(I) So, losing B frames is less undesirable than P frames. Same with P and I accordingly. Importance of a frame decreases in following order: I, P, B 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Importance of I and P frames Missing of I/P frames causes a lot of artefacts: A complete stream only missing B frames has no artefacts in worst case you only get then 8.3 fps instead of 25 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Example of an mpeg stream 5Mpbs stream (LOTR) B-frames make up more than a half of the whole bitrate (i.e. >2.5Mbps) 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Scheduling of frames (I) Packetizing Assign prioritites to packets according to frame types: P(B) = 1 P(P) = 2 P(I) = 3 Scheduling Packets with higher priorities should get a better chance to be sent Involved layers application layer transport layer network layer 802.11 driver link layer IP (Internet Protocol) TCP, UDP/RTP MPEG en-/decoder packet scheduler physical layer 802.11 WLAN MPEG-packetizer 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Scheduling of frames (II) Scheduling algorithm incoming frame buffered frame sent frame Fi Fb Fs if P(Fi) > P(Fs) and P(Fb) > P(Fs) Fs := Fb, Fb := Fi (discard Fs) else if P(Fi) >= P(Fb) Fb := Fi (discard Fb) Fi := 0 (discard Fi) 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Advantages of link layer approach We only need to modify the sending part it will work with any terminals supporting RTP reception it can be used for broadcasting it is very reactive against fast network fluctuations 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Transport layer approach If... we don’t have direct access to the wireless interface we don’t want to modify it we want more reliability, than UDP/RTP does or we want to combine link layer and transport layer approaches Then we would like to look at the tranport layer Our main interest: Transport Control Protocol (TCP) Can we make it suitable for real-time? Can we make it suitable for wireless? 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Further work Link-layer & transport-layer creating math. model evaluation of the approach gathering statistics evaluation of perceived quality 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653

Questions? 18-Sep-18 Sergei N. Kozlov, s.n.kozlov@tue.nl TU/e Informatica, System Architecture and Networking PROGRESS project EES.5653