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TCP bandwidth question

Hi,

We have a 4mb Frame relay connection to one of our sites. We did some tests to confirm the bandwidth. All shaping/throttling of traffic was turned off and it was done after hours where no other users were using the link.

Sending TCP packets the line maxed out at about 2MB however sending UDP packets the full 4MB was utilised. With TCP we could never get above 2.5 MB max. We monitored the usage using MRTG.

Can someone please explain why this happened?

1 ACCEPTED SOLUTION

Accepted Solutions
Blue

Re: TCP bandwidth question

TCP must acknowledge the data sent, so the latency of the connection plays a bigger role. UDP can just blast the packets out without being concerned about the receiver's ability to handle them.

What application did you use to test TCP over the link? What is the latency between the 2 sites? You can try using a bigger window size, which will allow the sending side to send more packets between acks. Did you try multiple streams? TTCP is useful for testing bandwidth if your routers support it.

Please rate helpful posts.

2 REPLIES
Blue

Re: TCP bandwidth question

TCP must acknowledge the data sent, so the latency of the connection plays a bigger role. UDP can just blast the packets out without being concerned about the receiver's ability to handle them.

What application did you use to test TCP over the link? What is the latency between the 2 sites? You can try using a bigger window size, which will allow the sending side to send more packets between acks. Did you try multiple streams? TTCP is useful for testing bandwidth if your routers support it.

Please rate helpful posts.

Silver

Re: TCP bandwidth question

In order to size the TCP windowing for your devices you need to know the bandwidth of the link (4Mb) and the RTT. response time for a ping. Multiply these togther to get the window size. Then tune your devices to this window size and see what happens. Also what application were you using for your TCP testing???

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