An Adaptive Congestion Control Mechanism for Video Multicast

Yi Pan

Yuji Imai

Necessity of Congestion Control of Video Multicast

• Users are now getting more and more interested in video data transmission.

• Video data consumes a lot of network resource and users want to find a way to transmit satisfactory video stream without severely interfering current data streams.

• Adaptive congestion control of video multicast will help to achieve this goal.

Current Research Related to Video Multicast Congestion

Control• TCP-friendly congestion control ([SF00],[S

F97],[SCH98])– current usage is only under unicast connections– proved fairness with traditional TCP traffic– existing protocol can be used to implement the

congestion control (RTP/RTCP)

• Multi-layer encoded multimedia ([SAMM], [BTW])– adaptive to heterogeneity of bandwidth in video

multicast.– the promising solution to encode video for

multi-receivers

• Multi-layer multicast congestion control ([INFO98], [RLM])– under classical multicast model– need the assistance of intermediate nodes

Fundamental Problems in Multilayer Video Multicast

• Multicast branch pruning problem:– Behind a bottleneck, leaving of the only

receiver subscribing to a layer should immediately alleviate the congestion at the bottleneck while in Internet Standard Multicast (ISM), it will take long time.

• Receiver interfering problem:– Behind a bottleneck, a receiver who adds to a

new layer may cause congestion at the bottleneck. That may cause other receivers react by lowering their subscribing level which is not desirable feature of the video multicast.

• Finding of potential bandwidth:– Behind a single bottleneck, when there are

receivers subscribing to different layers of video stream, a receiver adding to a new layer may not need extra bandwidth at the bottleneck, which means there is potential bandwidth exists at the bottleneck.

• Multicast group managing problem:– the problem is with the number of the multicast

group needed for multi-layer video multicast.• Fixed number of multicast group may have some

“empty” groups which waste network resource.

• Adaptive number of multicast group will take long time to establish/delete a new multicast group under ISM architecture.

Goals of Video Multicast Congestion Control

• Quick convergence of video congestion control

• Adaptiveness of video congestion control to receivers in various situations.

• Fairness of congestion control of video transmission competing with other traditional methods (TCP-like)

• Those issues are stated in [SF00],[INFO98],[SCH98].

Our Proposal of Adaptive Congestion Control over XCAST• Combination of good techniques:

– there exists unicast congestion control which fixes the “too sensitive” feature of TCP.

– multi-layer encoded video stream satisfies heterogeneous receiver connections

– XCAST solves the problem of joining/leaving overhead in intermediate routers

– Sender-driven multicast congestion control has benefits of fine-tuned, quick convergence,etc.

Our Solution

• Sender-driven congestion control for multi-layer encoded video stream.– Receiver make estimation of its available

bandwidth and send the feedback to sender.– Sender adjusts the number of layers and the rate

of each layer based on the feedback messages.– Make the receivers in the same layer as an

XCAST group.• With XCAST, it’s now possible to use multiple

dynamic flows to transmit multiple layers in sender-driven scheme.

• Integrate Traffic Control to congestion control for video transmission.– Equation-based Congestion Control

• Receiver reports estimated Round Trip Time and estimated loss rate p.

• Sender calculates transmit rates based on a certain equation, group receivers in different layers, and send out video stream

– FEC congestion control• using FEC encoding to let receivers recover the loss

• Employ XCAST to solve fundamental problems with multicast video transmission.– XCAST groups are explicit and branch pruning

can be done within a round trip time (as long as the “quit” message arrives the sender)

– We can employ intelligent aggregation algorithms to make optimal grouping of receivers in dynamic number of layers

– XCAST does not need the assistance of intermediate nodes

Simulation and Expected Results

• Simulation Scenario:– compare our scheme with the existing multicast con

gestion control in:• convergence time for congestion control• fairness between different users• adaptive to different connections• overhead of congestion control• average goodput for receivers• fairness when competing with other flows using TCP-like

congestion control

• Expected results are:– quick convergence time for congestion control– adaptive to heterogeneous connections under li

mited number of receivers– low overhead incurred in network– higher average goodput for receivers– good fairness competing with traditional TCP-li

ke congestion control mechanisms

Reference List

• [SF00] S. Floyd, M. Handley, J. Padhye, J. Widmer, “Equation-Based Congestion Control for Unicast Applications”, SIGCOMM 2000

• [SF97] J. Mahdavi, S. Floyd, “TCP-Friendly Unicast Rate-Based Flow Control”, Jan 1997

• [SCH98] D. Sisalem, H. Schulzrinne, “The Loss-Delay Based Adjustment Algorithm: A TCP-Friendly Adaptation Scheme”, Proc. of NOSSDAV'98, July, Cambridge, UK

• [SAMM] B. Vickers, C. Albuquerque, T.Suda, “Source Adaptive Multi-Layered Multicast Algorithms for Real-time Video Distribution”, IEEE ToN, 1999

• [INFO98] L. Vicisano, J. Crowcroft, “TCP-like Congestion Control for Layered Multicast Data Transfer” Proc. of IEEE INFOCOM'98.

• [BTW] J.C. Bolot, T. Turletti, I.Wakeman, “Scalable Feedback Control for Multicast Video Distribution in the Internet”, Proc. of ACM SIGCOMM, pp58-67, Aug. 1994.

• [RLM] S. McCanne, V. Jacobson, M. Vetterli, “Receiver-Driven Layered Multicast”, Proc. of ACM SIGCOMM, pp117-130, Aug. 1996.