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I am working on network simulation where my network should be as close from real-world conditions as possible. I am coding a function that calculates the latency and bandwidth of between switch A and switch B every minute. Isn't it more reasonable and accurate to capture the current TCP throughput instead of the bandwidth? Throughput formula as I remember is: TCP window size/ RTT but I don't know how to find TCP window size here (Assuming switch A and B are intermediate switches along a path from the sender to the receiver)?

Thank you so much in advance. Appreciate any response.

  • The bandwidth and latency between two connected switches isn't going to change. The two switches will connect to each other with a fixed bandwidth and latency. Also, switches know nothing about upper-layer protocols, such as TCP. There are things, e.g. IP SLA, to constantly monitor things like latency, jitter, etc. between two points on a network. – Ron Maupin Jan 21 '17 at 0:56
  • @RonMaupin I agree with you that bandwidth will not change. However, latency might change due to traffic conditions, is that right? – Don Jan 21 '17 at 2:31
  • Not with switching, which will simply drop excessive traffic with wire-speed switching. Routing and queuing can introduce latency. – Ron Maupin Jan 21 '17 at 2:44
  • @RonMaupin Thank you. I just now learn that latency appears from L3 and above. This means Nodal delay, i.e. Nodal delay = d_proc + d_queu+ d_tran + d_prog , calculates type of delays appear from L3 and above, correct? – Don Jan 21 '17 at 3:05
  • switches still have queues and absolutely do exercise varying performance based on traffic conditions and congestion – rnxrx Jan 21 '17 at 7:12
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Several factors determine actual throughput, for example, datagram size (see IMIX) and datagram processing (fast switching, process switching, etc). Terms such as packet per second, pps, and bits per second, bps, are distinct and are typically seen in performance literature.

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  • "fast switching, process switching, etc" are routing terms, not for switches. – Ron Maupin Jan 21 '17 at 4:50
  • "Cisco routers and multilayer switches support the following three primary modes of packet switching: Process switching, Fast switching (route caching), Cisco Express Forwarding (topology-based switching)" - Cisco Press – Ronnie Royston Jan 21 '17 at 18:41

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