Efficient Server Design for Hybrid Multicast Streaming - Scalable Continuous Media Streaming Systems - page 362

T R T R

static channel 1
static channel 2
static channel 3

Micro-round

Time

A macro-round

Static round

All static channels start
transmit at the same time

Transmission

Static round Dynamic round Static round

… …

Data Retrieval

Data for all the
requests in a groups

Data from
outer zones

Data from
inner zones

Micro-round

Figure 20.5 Scheduling disk retrieval and network transmission of WSGP

Data in cache

NQ ( 2N S +N D )

Buffer
requirement NQ ( N S +N D )

NQ ( N S +2N D /G D )

NQ ( N S +N D /G D )

NN S Q

Dynamic round
Static round

Dynamic round

Static round

Time

: Transmissions

Figure 20.6 Data in cache at different temporal positions in a service round

This scheduler, however, has a subtle problem. We found that the server buffer requirement is
dominated by the memory used to cache data for the static channels, which involved continuous
retrievals for two large data blocks, and this increases the buffer requirement significantly. To
reduce the buffer requirement, we sub-divide the static round into G S micro-rounds of equal
durations, where G S equals to the number of videos. In each static micro-round, static channels
belonging to the same video are scheduled and data are transmitted at the end of the static