This table shows the effect of copy
share with different latencies dela s . Notice that althou h we didn t
estrict the bandwidth at all our connection is 100Mb s b the time we
each 150ms London to California t e round tri s the maximum
bandwi th used is ust 1.5Me abits er second. This is a case where
buying bandwidth can t speed this transfer up.
f ou think we are overstatin the case we know of several ro ects
ncludin a document retrieval ro ect our Word document exam le is a
sim le document retrieval rocess that failed utterl in the WAN althou h
it had successfully passed several LAN- ased tests. It sim l
slow as to be unusable.
Table 2: Test of Data Transfer Times for a 62mb file using NetBIOS
In all Cases Using a 100 Megabit connection
Throw More Bandwidth at the Problem
We all know about bandwidth at home you probably started with dial-
connections to access the inte
were proving too slow, moved to broadband ADSL or cable Problem solved.
So why not buy more bandwidth? Beyond a certain point i does not matter
how much bandwidth you have as the transfer is limited by the nee to et
n acknowled ement back from the receivin end ever time ou send a
certain amount of data.
So how do you test application performance over the
Clearly, testing in the LAN is an essential first step. After all, if an
application will not work over the internal network, it s very unlikely to
perform over the WAN. However, as discussed, it does not follow that an
application that performs in the LAN will necessarily perform well or in
extremis even work at all in non-LAN environments.
OK, so now you re (hopefully!) convinced of the importance of testing in
the WAN. However, a request to conduct testing of a new and untried
application in your live WAN environment carrying business-critical data is
likely to be declined.
A possible alternative is to confine your testing over the live WAN to out-
of-office hours. The problem is that most live networks are actually busy
(or even busier) at night as the company performs network back-ups etc.
It is also going to be impractical to get the right people in place at the
required locations in order to conduct the initial test and subsequent