> 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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