It's more application performance that I want to investigate. I've got a client / server application and I want to introduce network delay between the client and the server to see what the impact will be.
You can make a small network among the router and the server using a switch an the port conected to the server you can put a rate limit, add this you can connect other machine to generate a lot of traffic whit a traffic generator, this will cause a big load in the channel that results in latency
Latency is just the time a packet takes to travel across the network. This is usually travel time + the time it takes the network devices to process the packet. Assuming you don't have spare wan circuits that you could route the packets through before returning it to your lab, the best way to create latency would be to increase the processing time for the packets. You could for example use a second server to generate extra traffic and then shape the interface to a low value. This would delay the packets but not drop them. You are limited by the interface queue sizes so you may end up dropping traffic before you introduce enough delay to the target flow, but it's worth a shot. You could also drive up the processor usage in the routers. Configuring them to process switch everything and then configuring multiple routing protocols with very low hello timers and multiple neighbors. Do you have any spare 2500's?
We use a PC with two network cards running Monowall ( http://m0n0.ch/wall/ ) You simply need to create a pipe and set the latency you desire and traffic passing between interfaces will be delayed by that amount.
You need a network emulator / virtual test network. Take a look at the NE-ONE Network Emulator which allows you to configure bandwidth, latency, packet loss, packet reordering, packet duplication, packet fragmentation, network congestion and many more impairments so that you can create real-world network conditions in the lab. Different impairments can be configured for the up and downlink so you could have a really good uplink but a really bad downlink, great for seeing how the app handles TCP queuing because the acks don't come back in a timely manner and the overall latency therefore increases!
There's an overview video here https://www.youtube.com/watch?v=DwtqlE7LcrQ, specifically aimed at game developers, but it shows what it's about. NE-ONE is configured using a web browser so it's really easy to get installed and configured - you don't need to be a network guru :-)
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