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New Member

how to interpret the bandwidth numbers

We have a 2610 router that is connected to an ISP through a T1 Frame Relay. The bandwidth on the T1 circuit is 1.5 Mg/sec. When I do the "sh int" on the serial interface that is connected to the ISP, I get the following:

"5 minute input rate 1342000 bits/sec.".

Yet, when I attempted to FTP a file, I was getting about 100 bits/sec. Does the 1342000 represent the aggregate number? - otherwise how do I account for this descepency?

Thanks.

2 REPLIES
Cisco Employee

Re: how to interpret the bandwidth numbers

Are you going by the throughput reported by your FTP application? If so, the discrepancy is likely due to the application only reporting the throughput of data (the file you copied) and does not include the overhead of TCP and IP headers that are wrapped around your data as it is transferred. If you are sharing the T1 bw with any other traffic (and possibly hitting congestion at times) then TCP (the transport protocol that carries FTP) will back off its transmit window size until it no longer has to retransmit packets. The application will use the total time it takes to transfer the file when it calculates throughput. A way to see all this for yourself would be to capture the ftp session with a sniffer and study the transfer (see how much overhead is there, what the transmit window is, if any retransmissions are seen, etc).

New Member

Re: how to interpret the bandwidth numbers

I just want to make sure that I understand this response.

From the application layer, FTP is simply measuring the total data that it sees (data less headers and tails) and the total time taken to transfer said data, including re-trx due to collisions and resizing.

From the routers perspective it is measuring the entire data unit, with headers and tails, and is measuring the raw data hitting the interface, whether it needs re-trx or not.

Is this the case?

Thanks!

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