Fault-Tolerant Algorithms for the Concurrent-Push Architecture - Scalable Continuous Media Streaming Systems - page 203

support fault tolerance and the total client buffer requirement is given by

2 τ + τ + Q S

f + − f − − f + − f − + T E T L

B SSS

FEC =

+ + (11.19)

T avg T avg

11.5 Analysis of Progressive Redundancy Transmission
Unlike FEC, PRT requires additional buffers to sustain continuous video playback during
system reconfiguration. Incorporating this requirement, we derive the corresponding buffer
requirement for block striping and sub-schedule striping in the following sections.

11.5.1 Buffer Requirement under Block Striping
A client operating under PRT will simultaneously receive ( N S − K ) instead of N S video

blocks. Therefore, a group of video blocks comprises only ( N S − K ) video blocks. Unlike

FEC, derivations for the buffer requirements depend on whether the failure occurs before
or after video playback starts. For the case where the failure occurs before video playback
starts, the playback schedule will be delayed because playback cannot start until the required
number of buffers are prefilled. The buffer requirements are found to be (see Appendix A.3
for derivations)

1

f + − f − −

+ τ +

T E

y Before = (11.20)

( N S − K ) T avg

and

1

+ τ +

f + − f − + T L +

D F

z Before =

(11.21)

( N S − K ) T avg

For the case where the failure occurs after video playback starts, the playback schedule will
not be affected. The buffer requirements are found to be

1

f + − f − −

+ τ +

T E + D F

y After = (11.22)

( N S − K ) T avg

and

1

f + − f − +

+ τ +

T L

z After = (11.23)

( N S − K ) T avg

Hence, the client buffer requirement is either

l Before = y Before + z Before (11.24)

or

l After = y After + z After (11.25)