[ns] goodput calculation

Michael Welzl michael at tk.uni-linz.ac.at
Sun Jun 17 23:22:02 PDT 2001


Hi,


> thanks for the reply. but i am still confused regarding 
> goodput calculation.
> 
> is this definition of goodput correct.
> 
> goodput = (max no of pkts recvd by the rx in sequence)
>           / (total number of pkts sent by the sender 
> including retransmissions)

I think the reason for all the issues Lloyd brought up is that
there is no such thing as a "correct definition of goodput".
But I would say that goodput should always be related to a
bandwidth measurement - bytes / interval. That is suggested by
the similarities betweeen the names "throughput" and "goodput".

So, I would rather change your definition to:
goodput = (max no of pkts recvd by the rx in sequence)*packetsize
           / measurement interval

(for a fixed packetsize, that is).

This definition should conform with how Lloyd defines goodput as
he is interested in how much is actually handed to the application.
Which is a sensible way to define goodput.

Still, it is not always defined like that - that depends on the
context. For instance, papers which do not consider retransmissions
may define goodput as "throughput seen by the receiver" as opposed
to "throughput used by the sender".
Come to think of it, the only actual difference is at which network
layer your "receiver" is located.

Cheers,
Michael




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