Network support for Multimedia

Dimensioning Best Effort Networks:

Approach: Deploy enough link capacity so that congestion does not occur, and multimedia traffic flows without delay or loss

• low complexity of network mechanisms
• Challenge: How much bandwidth is enough?

Providing multiple classes of service:

The earlier approach is a “one-size-fits-all” approach.

Alternative: provide multiple classes of services

• Partition traffic into classes

• Network treats different classes of traffic differently

• Packet marking needed for router to distinguish between different classes, and new router policy to treat packets accordingly.

• Traffic Policing: Force a source to adhere to bandwidth allocations.

Policing Mechanism:

Goal: Limit traffic to not exceed declared parameters

Three commonly used criteria:

1. Average rate: How many packets can be sent per unit time
2. Peak rate: What is the max rate at which the flow can send packets
3. Burst Size: Max. number of packets sent consecutively

Token Bucket:

Limit input to specified burst size and average rate.

How?

• Bucket can hold b tokens
• Tokens are generated at rate r tokens/sec
• Over interval of length t: $\text{\#packets admitted} \le rt + b$

Differentiate Services:

• Want qualitative service classes

Scalability: simple functions in network core; relatively complex functions at edge