Irwin, or anyone else
I appreciate your answer. In the same order of idea, is there any formula
for the latency on a serial interface depending on the load. Serialization
delay 8*packet_size/speed_of_link is only applicable for a low average usage
of the bandwidth, is it?
thanks
Laurent
>From: Irwin Lazar <[EMAIL PROTECTED]>
>Reply-To: Irwin Lazar <[EMAIL PROTECTED]>
>To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
>Subject: RE: How to determine bandwidth requirements for an application ?
>Date: Tue, 7 Nov 2000 09:12:34 -0700
>
> > Hello,
> > can anyone give a hint or advice `?
> >
> > We have to determine how much line bandwidth is needed to run some
> > application over WAN.
> > That is, we were asked: "Here is a client application X. We
> > plan to install
> > 75 machines running X at remote office. Is 128K line enough
> > for this or do
> > we need 1M line ?" - something like this.
> >
> > The question is: which approaches exist for this problem ?
>
>This is kind of long, but here is a column I wrote on the topic a few
>months
>ago:
>I'd also recommend getting a copy of "Wide-Area Data Network Performance
>Engineering"
>by Robert G. Cole, Ravi Ramaswamy, which directly addresses this topic.
>
>Irwin
>
>----------
>The bandwidth size that is required for any given
>connection is a function of the following three factors,
>number of users, requirements of specific
>applications, and how the application is used. For
>example, a site with five users that all access a highly
>interactive application for twelve hours per day may
>require more bandwidth than a site in which a dozen
>users sporadically access a client-server application
>in which most of the processing is performed by the
>remote server.
>
>In addition, another concern in the bandwidth selection
>process is delay. Certain applications such as voice
>and video may require a low level of delay (latency) as
>well as a low variability in delay (jitter). These
>requirements may add significant complexity to the
>design process.
>
>The first step in sizing bandwidth is to determine the
>requirements for the specific applications that will be
>deployed. During this step, a sniffer is useful in tracing
>application sessions to determine the average packet
>size and the average number of packets for a given
>transaction. Once you have these values, the next
>step is to factor in the number of users, the required
>latency, and the amount of time that typically exists
>between transactions.
>
>Once you have obtained these values, you can use
>the following formula (created by Ravi Ramaswamy of
>AT&T Solutions) to determine bandwidth requirements:
>
> 8 x N x K x M / (K x P + T)
>
>Where:
> N = number of active users at a location (the number of users that
>will simultaneously use an application)
> T = User think time (how much time typically exists between
>inquiries)
> K = number of packets per transaction in any given direction
> M = number of bytes per packet in any one direction
> P = one-way network latency
>
>Note that this calculation must be performed for both
>directions of the connection. The required bandwidth
>is then the maximum bandwidth estimated by this
>formula (unless you are deploying a technology such
>as Frame Relay which allows for different bandwidth
>allocations for each direction of the connection).
>
>Note also that this formula only applies to
>client-server type applications in which there is a
>substantial amount of two-way traffic. For additional
>information on bandwidth sizing, please see
>"Optimizing Client-Server Application Performance on
>the WAN" in the November 1999 issue of "Network
>Magazine."
>
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