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Network Performance Issues

Sub-topic outline:

• Performance Problems

• System Design for Better Performance

Performance Problems

• Some performance problems which may arise in the operation of a network:

1. Congestion
2. Structural resource imbalance – eg. fast high-speed line connected to a slow host
3. Synchronous overload – eg. bad TCP segment broadcast to many receivers – results in "storm" of error replies.
4. Incorrect system tuning – eg. not setting enough memory for processing received packets, segments, etc.
5. Incorrect time outs – for frames awaiting acknowledgments

Analyzing Performance

• Bandwidth-delay product – multiplying the bandwidth (data rate in bps) with the roundtrip time (in sec).

• Measures the capacity (in bits) of a connection from the sender to receiver and back.

• Receiver’s window should be as large as the bandwidth-delay product.

System Design for Better Performance

• Some important design criteria (for systems and for networks) learnt from experience:

1. CPU speed is more important than network speed
2. Reduce packet count.
3. Minimize context switches – eg. kernel mode to user mode.
4. Minimize copying from uffer to buffer.
5. Buying more bandwidth doesn’t reduce delay at nodes.
6. Avoiding congestion is better than recovering from it.
7. Avoid Timeouts

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