A Staggered-Push Parallel Server Architecture - Scalable Continuous Media Streaming Systems - page 222

and

N S
m

N ( n

N full ( n , m ) = − m , N S − m , − 1) . (12.7)

12.4 Traffic Overlapping
If server clock jitter is greater than zero, then transmissions from two or more servers destined
to the same client will overlap and multiply the transmission rate in the overlapping interval
(Figure 12.7). This could cause congestion at the network and the client, resulting in the packet
being dropped.
To avoid traffic overlapping, we can sacrifice some server and network bandwidth, and
transmit video data at a rate higher than R V , say R ORT (Figure 12.8). We call this scheme over-
rate transmission (ORT) for obvious reasons. The transmission window will then be reduced
to a time interval of

Q
R ORT

T w = (12.8)

We can guarantee that there will be no transmission overlapping by ensuring that

T w + τ< T F (12.9)

Rearranging, we can then obtain the minimum transmission rate needed to avoid traffic over-
lapping:

QR V

R ORT >

(12.10)

Q − R V τ

Server 0

Server 1

Total

overlapping

Figure 12.7 Traffic overlapping due to server clock jitter

Server 0

Server 1

Total

Figure 12.8 Preventing traffic overlap by over-rate transmission