Bandwidth

Why is it called Bandwidth?

• Bits transmitted at a particular bandwidth can be seen as having some width
• One bit transmitted at 1 Mbps can be seen as being 1 microsecond wide

Delay and Bandwidth

• Can think of the channel between a pair of processes as a hollow pipe
  • Latency (delay) is length of the pipe
  • Bandwidth is the width of the pipe
• Scenario:
  • Delay of 50 ms
  • Bandwidth of 45 Mbps
  • $(50\times 10^{-3}\mathrm{s})\cdot (45\times 10^{6}b/s)=2.25\times 10^6\mathrm{bits}=280\mathrm{KB}$
• Relative importance of bandwidth and latency depends on application
  • For large file transfer, bandwidth is crucial
  • For small messages (HTTP, NFS), latency is crucial
  • Variance in latency (jitter) can also affect some applications, e.g. audio/video conferencing

Bandwidth vs Throughput

Bandwidth vs Throughput

• Bandwidth is the capacity at a particular point
• Throughput is the reality, the rate at which data is actually transmitted

When data is being transmitted between two links, the throughput is whatever the smaller bandwidth is (the bandwidth of the bottleneck link)

TODO check if this understanding of throughput is right

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