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The serialization delay is the amount of time it takes to forward bits out of an interface. A 1 gigabit per second interface can send 1 billion bits per second. One billion bits per second equates to roughly 125 megabytes per second.

Therefore, a 24 megabyte buffer can hold 0.19 seconds of gigabit traffic. For fun, the same buffer would hold only –.019 seconds of traffic at 10 megabits.

Can you explain how the author derived at his conclusion:

24 megabyte buffer can hold 0.19 seconds of gigabit traffic

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Well, that appears to be simple math:

24 MB / 125 MBps = .192 seconds

What is confusing about that?


For fun, the same buffer would hold only –.019 seconds of traffic at 10 megabits.

That is the part that doesn't make sense because 10 Mbps is 100 times slower than 1 Gbps, therefore it should be 100 times longer to transmit the same amount of traffic, not 10 times faster.


Also, understand that this does not take into account the protocol overhead. Ethernet has a 7 byte Preamble, a one byte Start of Frame Delimiter, 14 byte Frame Header, 4 byte Frame Check Sequence, and a 12 byte Inter-Packet Gap. That's 38 bytes of overhead for each ethernet packet, which is about 2.5% overhead on top of the maximum 1500 bytes of data, which includes other protocol overhead.

That's just for the ethernet. IPv4 would have a 20 byte header (IPv6 is 40 bytes), and then there is UDP (8 bytes) or TCP (20 bytes), plus maybe an application-layer protocol.

  • Is it possible the author was referring to 10Gb instead of 10Mb? – dcrearer Jun 4 '18 at 16:53
  • Possibly, but the scenario just isn't realistic. You would need more information about the protocols used in order to calculate the amount of time necessary to transmit the buffer. – Ron Maupin Jun 4 '18 at 16:56

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