On Transmission Scheduling in a Server-less Video-on-Demand System

Outline

Background Transmission Scheduling Performance Evaluation Summary

PlaybackInternet(N – 1) nodes

STB

STB

STB

STB

Server-less VoD System

Network delay

Packet Loss

Access router

Transmission Scheduling is required

Transmission Scheduling

On Request SchedulingStaggered SchedulingRandomized Scheduling

On Request Scheduling

At receiver side Initiate a video sessionSend requests to all nodes at the same time

At sender sideAdmit requestsReserve a timeslots for each requestFirst come, first serve

On Request Scheduling

ri : request from node i

r1 r2

r1 r2

Node 0

Node 1

Node 9

r1 r2

1 1

1 1

1 1

2

2 2

2 2

On Request Scheduling

Simple algorithm Minimize start-up latency However,

Timeslots assigned by different nodes to the same request are usually close together

Bursty traffic at the receiver sideCongestion and packet loss

Staggered Scheduling

Why not spreading out the transmission in advance?Non-overlapping timeslots for each requestPre-allocation of timeslots

AlgorithmNode i serves node j at timeslot

(i – j – 1) mod N

Staggered Scheduling

1 2 3 4 5 7 8 2 3 4 5 7 86 9 0 1 6 9 0Node 0

Node 1

Node 9

12 3 4 5 7 8 2 3 4 5 7 86 9 0 1 6 9 0

1 2 3 4 5 7 8 2 3 4 5 7 86 9 0 1 6 90

Node i serves node j at timeslot (i – j – 1) mod N

Staggered Scheduling

AssumptionNodes are clock synchronized

Two implicationsPerformance depends on clock

synchronization accuracyAssumptions may not always be feasible

Randomized Scheduling

MotivationEliminate the requirement of synchronizationDecorrelate the transmission time

RandomizedTimeslots to each requestTimeslots in each round

Performance Evaluation

Cluster Size Router Buffer Size Queueing Delay

Simulation Model

Parameters Default Values

Cluster size 500

Video block size 8KB

Video bitrate, Rv 4Mbps

Access network bandwidth 1.1Rv

Router buffer size (per node) 32KB

Mean propagation delay 0.005s

Variance of propagation delay 10-6

Mean router queueing delay 0.005s

Variance of clock jitter 10-6

Cluster Size

00.10.20.30.40.50.60.70.80.9

1

0 100 200 300 400 500 600

Cluster Size (nodes)

Pac

ket L

oss

Rat

e

ORS SS RS

Router Buffer Size

00.10.20.30.40.50.60.70.80.9

1

0 20 40 60 80 100

Router Buffer Size (KB)

Pac

ket L

oss

Rat

e

ORS SS RS

Queueing Delay

00.10.20.30.40.50.60.70.80.9

1

0.0001 0.001 0.01 0.1 1 10

Mean of Queueing Delay (sec.)

Pac

ket L

oss

Rat

e

ORS SS RS

Summary

Transmission scheduling is required to resolve the congestion

Staggered scheduling can achieve near-zero packet loss rate with small net

work delay variation and clock synchronization Randomized scheduling

can achieve consistent performance for any delay variation

Without clock synchronization suitable for serverless system

Current and Future Works

Deterministic scheduling Optimal schedule for any given delay profileUsing QQP

Stochastic scheduling Schedule based on stochastic informationReceiver messaging feedback