The Kurose & Ross book uses \"store-and-forward delay\" as a synonym for the tra

Question

The Kurose & Ross book uses "store-and-forward delay" as a synonym for the transmission delay of a packet over a network link.

As a newcomer to computer networks, it isn't immediately obvious to me how these two terms are synonymous. My current understanding is that if not for the store-and-forward behavior of packet switches, the transmission delay of a link would be negligible as it would be pipelined with the propagation delay of the previous link; i.e. as the bits propagate across Link A, they are transmitted and stream into Link B. However, due to store-and-forward, no bits are transmitted onto Link B before all the bits have crossed Link A, and hence, we need to add the transmission delay of Link B.

Is this correct?

Explanation / Answer

I haven't read that book, so I may be off the mark.

Usually the transmission delay on a direct link is negligible compared with the processing delay at the endpoints and at each hop. In concrete scenarios, going via a geosynchronous satellite is the only way you have significant transmission delays on a link (about 0.2s to go up and down).

So when you have a network link that consists of a chain of direct links with a router at each hop, the total transmission delay is the sum of the store-and-forward delays on the routers. Strictly speaking, it's that plus the total length of the link divided by the speed of light (if the signal propagates at light speed), but that second part is usually negligible.

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