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Anue goes to the movies: The Three Stooges
Posted on Wednesday 2 May 2007
AKA Can the WAN whack your app? Soitenly!
Your application runs just fine on the LAN. You enable remote access and
it slows to a crawl. Your local wise guy says, what do you expect, after
all, the LAN is running on 100 Mbps or 1 Gbps Ethernet, but your WAN connection
is a broadband service running 8 Mbps or so. So you increase the budget
to add some bandwidth and see little or no improvement. The wise guy loses
credibility, the users lose productivity and you lose sleep.
When it comes to application performance and transaction response time,
it pays to remember that the LAN and WAN differ in more ways than one.
There are actually Three Stooges lurking in the WAN: delay, loss and bandwidth.
Individually they can cause problems. Collectively they can cause havoc.
When you have to resolve an issue, it’s important to know which
Stooge is causing the problem.
Round trip time, also known as two-way delay, has a significant effect
on throughput, especially when stateful protocols like TCP are involved.
In one test, a file transfer from California to Asia with 400 ms of two-way
delay could only achieve a 50 Kbps transfer rate, even though there was
2 Mbps of available bandwidth. When 1% packet loss was introduced, the
transfer rate dropped to 20 Kbps. Increasing bandwidth can resolve some
problems, but not this one. That’s focusing on the wrong Stooge.
Network emulation allows you to discover
which Stooge is actually whacking your app so you can fix it the first
time.
Fixing the problem is good. Avoiding it is even better. Network emulation
allows you to test transaction response time and application performance
under a variety of realistic network conditions, discover the primary
contributors to poor performance, devise fixes to address them and then
verify the fixes, all before deployment.
Beating the Stooges translates into reduced risk for your project, lower
operating cost as you right-size your network, shorter development and
QA schedules as you catch the issues early in the cycle, which means less
time to deployment. A properly engineered and configured application means
increased productivity for your organization, fewer tech support calls
and improved user satisfaction, all of which establish a better competitive
edge for your company.
Things your mother told you
Posted on Wednesday 18 April 2007
Your mother always knows. The older you get, the more you realize
how true it is.
You’re probably thinking your mother doesn’t know anything
about networks. Telecommunications networks, that is. She probably had
her own network that allowed her to know exactly what you had done before
you even got home, so when you walked in the door she could say . . .
Is there something you want to tell me?
. . . and the next thing you know, you’re spilling your guts. You
never knew how she does it, but it always seemed to work. She could give
lessons to Homeland Security.
Sometimes maybe she would interfere and insist you do something you thought
was totally unnecessary, like change your shirt or take a sweater with
you or get a sandwich or something and you would roll your eyes and she
would say . . .
You’ll thank me later
. . . and you’d realize later she was right, but you’d never
admit it.
So, now somebody comes along and says you need to test your application
under real-world conditions with a network emulator and you’re thinking
that you already threw all kinds of traffic at it and stress-tested it
and got all the kinks worked out and you really don’t need to bother
with a network emulator because it’s going to mess up your schedule
and besides, what could go wrong? Right?
Just remember what your mother said.
It’s for your own good
That’s right. What could go wrong? Plenty! The effect of delay across
the WAN is multiplied when session-oriented protocols like TCP are involved.
If your application is too chatty, dropped packets and retransmissions
can bring it to a grinding halt faster than you can make up your bed.
If buffer sizes aren’t big enough to handle reorder problems, they
turn into dropped packet problems.
The truth is that if your solution hasn’t been tested under real-world
network conditions, you have no idea how it’s really going to act,
and that’s not a good thing. In fact, it’s a really, really
bad thing. It can mean a failed launch, delayed schedules, productivity
loss, finger pointing, loss of confidence in your department. Bad stuff,
Maynard.
On the other hand, if you test under real-world conditions using network
emulation, your application will be ready for prime time and anything
the network can throw at it. Which is good, because when it comes time
for the rollout, you don’t want it to crash and burn and then hear
your manager say . . .
It looks like a tornado came through here
Listen to your mother. Even if she doesn’t know anything about networks.
Since 1997, Gillaspy Associates has built
a solid reputation for developing strong relationships with our customers
by providing quality solutions and ongoing support.
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