Basic question

Unanswered Question
May 9th, 2010

Hi,

Whether there is any formula or method that we can calculate the bandwidth of link based on delay(ms) in ping request ?

d:\> ping 10.1.1.2

Reply from 10.1.1.2: bytes=32 time=302ms TTL=46

Note :  Current the link 10 % usage.

I have this problem too.
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Peter Paluch Mon, 05/10/2010 - 01:59

Hello,

Using pings to determine the available bandwidth is very unreliable. While it is true that it holds: amount of transferred data = bandwidth x time from which the bandwidth can be computed given the total size of the ping packet and the transfer time, the time given by the ping command is usually the total round trip time that consists of the time necessary for the ECHO REQUEST packet to traverse from source to destination, the time until the destination processes it and sends an ECHO REPLY packet, and the time necessary for this reply to get back. Replying to ping packets is usually a low-priority process on the destination device and may, under circumstances, take several milliseconds. Also, different queueing and processing delays contribute to the overall round-trip time. Therefore, even if approximating the one-way delay as RTT/2, it is a very imprecise approximation and the gathered data may fluctuate wildly. Even if the bandwidth is computed this way, it has a property of an immediate available bandwidth in the moment of the ping, however, because of bursty nature of network traffic, such measurement is not a representative of the average bandwidth that should not vary over time.

The available bandwidth should be measured over a certain period of time using a particular data flow. A simple file download may give you a decent approximation of the available bandwidth, however, it is best to use a flow in which there is no upper-layer flow control - such as UDP, for example (the flow control mechanisms generally prevent congestion at the price of slightly lower bandwidth utilization).

To sum it up - I would personally suggest not to try to infer the bandwidth using pings.

Best regards,

Peter

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