Multiple Sender Distributed Video Streaming

1
Multiple Sender Distributed Video Streaming

• Nguyen, Zakhor
• IEEE Transactions on Multimedia
• April 2004

2
Agenda

• Motivation
• Proposed Approach
• Rate Allocation Algorithm
• Packet Partition Algorithm
• Experimental Results
• Conclusion

3
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.

4
Aim of the proposed approach

• Increase throughput in order to meet the high bit
  rate demands.
• Reduce the probability of packet loss.

5
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)

6
Assumption

• The bandwidth bottleneck is not at the last hop.

7
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.

8
Packet Partition Algorithm (PPA)

• Run at the senders.
• Ensures that every packet is sent by one and only
  one sender.

9
The distributed streaming framework
10
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).

11
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.

12
RAA (contd.)

• RAA used with FEC reduces packet loss as compared
  to single route streaming.

13
RAA (contd.)

• Notations
• N Total no. of packets in FEC block
• K No. of data packets in FEC block
• NA Number of packets sent by sender A in a FEC
  block
• NB Number of packets sent by sender B in a
  FEC block

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Rate Allocation Formula

• We seek to minimize the probability of
  irrecoverable loss given by
• NA NB j
• C(K,N0,N1) ? ? P(A,i, NA)P(B,j-i,NB)
• j NK1 i0

15
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.

16
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.

17
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.

18
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.

19
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

20
Illustration of how PPA works
21
Choosing the starting sequence no.
22
Irrecoverable loss probability for various FEC
levels as a function of bad times
23
Optimal sending rate for route A as a function of
bad times for route B
24
Irrecoverable loss probability ratio as a
function of average bad time of route B
25
Irrecoverable probability as a function of
sending rate of sender A
26
Number of lost packets per FEC block for a single
sender
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No. of lost packets per FEC block for two senders
28
Throughput of two senders
29
Sequence No. difference of two consecutive
received packets
30
Conclusion

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