Question : Problem: Telnet Application Issues

Hi There,

I am a network engineer for a company that runs a proprietary order processing application hosted on HP Unix server that clients connect to using a telnet based application. Clients connected to this from various locations over WAN connections through our MPLS network.

The server is to be moved to a new location, much further in proximity to the sites than where it is now (basically another continent). A test server has been set up for cliens to test the connections.

All the clients are now reporting a slow response from the application. The problem mainly seems to be that keyboard strokes can take a short while to appear on the screen rather than instantaneously. Sometmes the characters don't appear for a few keystrokes then appear quickly in a bunch.

Network utilisation at all the locations appears to be fine 30-40% on average. And there are no other reported problems from users. The only difference I can see is tha latency to the server has risen from an average of 55-70 ms to 150-200 ms.

The application people are claiming there is no issue on there side, as well as the server people.

The test server is actually a much higher specification then the production one.

I'm just wondeting if anyone has had similar problems with telnet applications over WAN connections? How sensitive is telnet to a 100ms increase in latency? Any ideas on what could be causing this or how we can further troubleshoot?

Answer : Problem: Telnet Application Issues

Boy are you going to have fun.

By default telnet works like this.  When you press a key on your computer, your computer sends a signal to the telnet server and the telnet server sends back what character to display.

So with the servers in location #1, it took 55-70 ms for this to happen.  With the servers in location #2 it is now taking a minimum of 150-200ms.  The busier the link, the longer it will take.  With even a high if 70 ms, in the first situation you could get 14-15 characters a second typed in.  In the second situation with a low of 150 ms, you could only get about 6-7 characters.

Instead of looking at it as you added 100ms look at it as you have doubled the time it take to talk to the remote side, so you are cutting the amount of work you can get though in half.

What you can try and do is see if the telnet client and server can be configured to use local echo and local buffering.

That is the local computer will decide what characters to display and buffer them up until the user presses enter.  Then it will send all of the data/commands entered to the server to be processed and the results sent back.