1

If a network has a throughput bottleneck, does it matter whether the slow link comes before or after?

For example:

example

c wants to send something to h.

the bottleneck is on h's side. What throughput speed will the red arrow have? 200 or 100?

The question is about throughput only. Meaning we neglect the router's buffer and processing (little queuing delay, processing delay and also transmission delay).

  • It really depends on the bottleneck. Network congestion is usually directional, so it will have a bottleneck only in one direction. – Ron Maupin Oct 23 '16 at 16:57
  • the bottleneck is a throughput bottleneck. (meaning it's a bandwidth bottleneck if I understand right) – Mina Michael Oct 23 '16 at 17:00
  • That is almost always caused by network congestion, and that is almost always only in one direction. – Ron Maupin Oct 23 '16 at 17:01
4

If a network has a throughput bottleneck, does it matter whether the slow link comes before or after?

No it doesn't, Only matters when destination is before or after that bottleneck link.

What throughput speed will the red arrow have? 200 or 100?

Yes it will be bottle necked at 100mbps. So bottleneck throughput speed would be of the lowest throughput link between h and c. So this bottleneck throughput will be applicable when the packet is sent from h to c also.

Hope this helps!

1

It does not matter where the slow link is in the path from source to the destination, but the bandwidth of the entire path is dependent on the bandwidth of the slowest link.

Bandwidth will be 100Mbps for the entire path.

0

If C sends packets as fast as he can both links will be filled, but only half the packets will reach H, the other half will be dropped by the router.

On the other hand if C runs a protocol like TCP then his TCP/IP stack will estimate the availble bandwidth for the full path and the data rate through the two links will be very similar.

  • 1
    This is only true when TCP SACK is available, I've seen Win XP without SACK over a rate-limited WAN and it's not pretty. In that case a file transfer from C to H will incur packet loss, retransmissions and back off to slow start, but a file transfer from H to C will be clocked at the line rate and have no packet loss of its own. Both cases will be affected by other traffic if the medium is shared. – marctxk Oct 25 '16 at 12:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.