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I was reading a textbook which says:

The transmission delay the amount of time required to push (that is, transmit) all of the packet’s bits into the link.

Does it mean that transmission delay is determined by router? if you have a stronger/higher capacity router which pushs bits into the link faster, then the transmission delay is lower?

but the book also says:

Denote the length of the packet by L bits, and denote the transmission rate of the link from router A to router B by R bits/sec. For example, for a 10 Mbps Ethernet link, the rate is R = 10 Mbps; for a 100 Mbps Ethernet link, the rate is R = 100 Mbps. The transmission delay is L/R

Then we can see that transmission rate seems to be determined only by the link's rate. But isn't it contracting to "the amount of time required to push bits into a link"?

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Does it mean that transmission delay is determined by router?

The delay is determined by the media characteristics. Remember that most media is serial -- that is, one bit is sent at a time*. A 10Mbps link means that you can transmit 10 million bits per second, or 1 bit every 100 ns. So a 100 byte message would take

100 bytes * 8 bits * 100 ns = 80 µs (microseconds)

To be sent on the link.

(* Note that this is a simplified example. In real life, encoding methods and phase changes are used to increase the amount of information sent per bit.)

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    I think it is 800 bits / 10 x 10^6 bits/s = 0.00008s = 80us
    – Elias Bats
    Jul 22, 2020 at 11:06

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