An Adaptive Congestion Control Mechanism for Video MulticastPresentation Transcript
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],[SF97],[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.
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
compare our scheme with the existing multicast congestion 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 limited number of receivers
low overhead incurred in network
higher average goodput for receivers
good fairness competing with traditional TCP-like congestion control mechanisms
Equation Based Congestion Control:
basically the equation based congestion control is based on the following equation:
So we propose the receiver send feedback to sender including the RTT and loss rate p it estimates so that the sender can calculate the estimated acceptable rate.
Dynamic receiver grouping:
Transmission rate to each receiver is calculated by sender and the sender need to optimally partition receivers to groups with a specific transmission rate for each group.
Algorithm to find the optimal partition of receivers should achieve the goals of reducing the number of groups and maximize total goodput.
Receiver interference problem:
Adjusted equation based control: adjust the equation let higher layer receiver to be more sensitive to loss and RTT.
Employ “deaf” period for lower layer receivers: after a new higher layer receiver being added, allow lower layer receivers to be “deaf” to loss and RTT for a while.
receivers make estimation of RTT and loss rate p based on different transmission rate:
Advantage: no need for sender to be aware of where the bottleneck is.
Disadvantage: the lower layer receivers still suffer for a short time, though less influenced.
Notify affected receivers to be “deaf” for a period of time to let the newly added high layer receiver quiet down.
Advantage: Lower layer receivers will not be affected at all.
Sender needs to be aware of where the bottleneck is and who are behind the bottleneck.
Necessary adjustment of rate may be delayed by the “deaf” period.
One additional notation of receiver interference:
Since we transmit different layer in different XCAST group, that means we can use different flows to transmit different layers.
With the help of current DiffServ Architecture, we can easily isolate those flows so that different layers will have much less impact on each others.
Potential bandwidth finding:
May need to build tractable list of receivers in each layer. (need to discuss)
probing packets for each destination are sent out periodically.
The branching records are kept in the probing packets and are sent back to sender.
Sender uses those branching records to build up the sink tree.
Only need max(RTT) of all the receivers to build that sink tree.
As long as we get such information, it is easy to find potential bandwidth in bottleneck. So it’s safe to add this new receiver for high layer.
This technique is kind of congestion avoidance technique, not congestion control.
Prove the effectiveness of the architecture in future Internet providing DiffServ services for QoS requirements
explore impact of combining XCAST and resource allocation in this architecture.
explore impact of QoS routing and its impact on this architecture.
[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.