Multiple Sender Distributed Video Streaming Nguyen, Zakhor IEEE Transactions on Multimedia April 2004

Agenda  Motivation  Proposed Approach  Rate Allocation Algorithm  Packet Partition Algorithm  Experimental Results  Conclusion

Motivation  Addresses the problem of video streaming over best effort, packet- switched networks.  Streaming of video requires high bit rates.  Packet loss and delay due to network congestion.

Aim of the proposed approach  Increase throughput in order to meet the high bit rate demands.  Reduce the probability of packet loss.

Proposed approach  Simultaneous video streaming from multiple senders to a single receiver.  Employs a receiver driven protocol  The distributed streaming protocol consists of a Rate Allocation Algorithm (RAA) and a Packet Partition Algorithm (PPA)

Assumption  The bandwidth bottleneck is not at the last hop.

Rate Allocation Algorithm (RAA)  Run at the receiver.  Determines the optimal sending rate for each sender.  Uses information about available network bandwidth, channel characteristics.  Receiver can also redistribute rates among existing senders.

Packet Partition Algorithm (PPA)  Run at the senders.  Ensures that every packet is sent by one and only one sender.

The distributed streaming framework

RAA : A closer look  Goal of RAA is to “determine how to split the total video rate among M senders in order to minimize the probability of packet loss.”  Used in conjunction with Forward Error Correction (FEC).

FEC  Used at the receiver side for recovering lost packets.  A FEC block consists of a number of packets.  N packets in a block, K data packets, N-K redundant packets.  For recovery, any K packets in a block must be received.

RAA (contd.)  RAA used with FEC reduces packet loss as compared to single route streaming.

RAA (contd.)  Notations: N : Total no. of packets in FEC block K: No. of data packets in FEC block N A : Number of packets sent by sender A in a FEC block N B : Number of packets sent by sender B in a FEC block

Rate Allocation Formula  We seek to minimize the probability of irrecoverable loss given by N A + N B j C(K,N 0,N 1 )= ∑ ∑ P(A,i, N A )P(B,j-i,N B ) j =N–K+1 i=0

Packet Partition Algorithm (PPA)  Goal of the PPA is to “determine which packets should be sent by which senders in order to prevent duplicate packets and minimize start up delay.”

Minimization of start-up delay in PPA  In Kazaa, senders send contiguous blocks of data. Duplication of packets cannot occur.  In PPA, senders send interleaved packets. Reduces start-up delay, but packets may be duplicated.

Avoiding Packet Duplication in PPA  Each sender independently arrives at the same decision as to which packet to send next.  All senders use the same information to choose the next packet to send.  This information is sent to all senders by the receiver.

How PPA works  The receiver sends identical control packets to all senders.  The control packet contains RTT of all senders. Sending rate for all senders. Starting sequence number.

How PPA works (contd.)  Each of the senders uses the information in the control packet to compute the estimated arrival time for packet k  The time difference between the arrival and playback time of packet k is then computed.  The sender that maximizes this time difference is chosen to send packet k

Illustration of how PPA works

Choosing the starting sequence no.

Irrecoverable loss probability for various FEC levels as a function of bad times

Optimal sending rate for route A as a function of bad times for route B

Irrecoverable loss probability ratio as a function of average bad time of route B

Irrecoverable probability as a function of sending rate of sender A

Number of lost packets per FEC block for a single sender

No. of lost packets per FEC block for two senders

Throughput of two senders

Sequence No. difference of two consecutive received packets

Conclusion  Inaccuracy in parameter estimation can skew the results.  Cannot protect against packet loss in case of coinciding congestion intervals on different routes.