Computer Networks · free preview
Network Software and Performance
The Internet's success rests on software, nearly every protocol runs on general-purpose computers behind the socket interface, which separates a protocol's services from the syntax that invokes them, and performance reasoning rests on two metrics, bandwidth and latency, whose product is the volume of the pipe, how many bits can be in flight, which explains why high-speed links remain delay-bound and why effective throughput depends on transfer size.
1. Software all the way down
Software all the way down
2. Bandwidth and latency
Bandwidth and latency
3. The pipe and its volume
The pipe and its volume
4. What applications ask, and what changed
What applications ask, and what changed
5. Services versus syntax
The socket interface separates two concerns. Which statement captures the separation correctly?
6. Decomposing latency
A 1500 byte packet crosses a 4000 kilometer fiber link at 10 gigabits per second, with no queueing and light in fiber at meters per second. Which component dominates the one-way latency?
7. The volume of the pipe
What does the delay-bandwidth product of a channel tell a protocol designer?
8. High speed, same light
A 1 megabyte file crosses a path with a 100 millisecond RTT. Why does upgrading from 1 megabit per second to 1 gigabit per second change the transfer so dramatically while the RTT is unchanged?
9. Effective throughput
A user fetches a 1 megabyte file over a 1 gigabit per second link with a 100 millisecond RTT, and the transfer time is RTT plus size over bandwidth. What effective throughput results?
10. Why video states a burst bound
Why is a video application's average bandwidth need alone insufficient for engineering the network?
11. The universal API
What is the name of the network programming interface, born with Berkeley Unix and now supported on virtually every operating system, whose central abstraction is the point where a process attaches to the network?
12. The pipe's volume
The product of delay and bandwidth is the volume of the pipe. For a channel with 50 milliseconds of one-way latency and 45 megabits per second of bandwidth, how many bits can be in flight at once? Answer as a whole number of bits.
13. The third delay component
Latency decomposes into propagation delay and transmission delay, plus a third component caused by packets waiting in switch memories under statistical multiplexing. Name it.
14. The transfer time formula
For a request-response transfer, the total time is the round-trip time plus the data size divided by what link property?
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