Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

DS3 bandwidth question

We have just upgraded a Remote site that had a Frame T1 1544/512 to the Hub Site to a Frame DS3 with a port speed of 45M and a 6M of CIR.

My initial thought was that they will be atleast 10x faster on DS3 but they are only 4x faster.

Question is, is it the provider issue or am i missing something in the calculation of the bandwidth or something to look in the frame relay traffic shapping configurations. Could someone explain that. thanks.


Re: DS3 bandwidth question

What do you mean faster?

If you mean the time it takes to transfer a single large file via a tcp based protocol then it is more complex than a simple bandwidth.

The latncy due to distance is more of limiting factor on high speeed lines than the bandwidth.

Your best measure of thoughput is to use a tool that can send UDP based packets to avoid the issue of tcp window size. IPERF is a simple one to test with but is a line mode command.

Your other thing may be that you were able to burst to the full t1 on your old circuit and your new one you are not able to burst much above the 6m cir. It will depend if the provider put a artifical limit on you or if you were just lucky and the provider network was underutilized and your frames did not get discarded.


Re: DS3 bandwidth question

A lot depends on how you are testing it, and the length of the end-to-end span.

It's almost impossible, for example, for a single FTP session to fill the 45M pipe. The latency of the TCP ACKs keeps the actual throughput fairly low.

If you ran several FTP session from multiple endpoints, you might be able to get a better idea of capacity.

Something like QCheck (from IXIA, it's free) might also give you a better performance check.

Good Luck


Re: DS3 bandwidth question


besides measurement issues, which the previous posts mention, I noticed: 4x 1.5Mbps = 6 Mbps = current CIR.

So how does the contract you have look like? CIR = max data rate allowed? Then 4x the speed would be exactly what is to be expected, because the SP will implement some shaper to limit the traffic speed to 6 Mbps.

In case you are allowed tu burst up to 45 Mbps for extended periods of time, this will still only work, if enough capacity is free in the SP network.

In any case I would not assume that you regularly get 15 Mbps or above.

In case you get only 2 Mbps (are you refering to 4x 512 or 4x 1544 ??) then it might be:

1) a measurement issue - see other posts

2) a configuration error within the SP network

3) an overload situation within the SP network (they all do overbook FR, right!?)

4) a configuration error on your equipment

For 1) make sure you measure the right thing. If you can proove you get less than you pay for and it is not 4), then contact your SP and let him check his side.

Regards, Martin

Regards, Martin

New Member

Re: DS3 bandwidth question

Thanks for all your responses,

I agree the 4 x 1.5Mbps= 6Mbps which is the current CIR that we have, and we are allowed to burst to 45Mbps as well as the port speed. As I monitor the traffic for that site in NET QOS tool which shows to be the utilization reaching up to 15 Mbps and i think thats their highest level of utilization as of today.

I will be getting with the provider to find out if there is anything on thier end that needs to be looked.

So if i were to increase the cir from the present 6M to lets say 10M. would that make a difference?

Re: DS3 bandwidth question


yes 10 Mbps would make a difference. What I do not understand is: what are you concerned about? I mean, which applications do not perform well, which users are complaining?

And if nothing is broken, why do you want to fix something? ;-)

Regards, Martin

New Member

Re: DS3 bandwidth question


Yes you are absolutely correct about nothing is broken,But here is the customers perspective, His concern is that he had a Frame T1 previously which was 1.5M and now they have a DS3 45M. so why the difference is not 40 times faster.

I have explained to him the upgrade plays a big role in controlling congestion and latency.

Re: DS3 bandwidth question


they do have a 45 Meg - and NOT. He is interested in application speed, not OSI layer1 speed. He ordered 6 Mbps CIR and this is what he gets. So just an explanation problem.

Tell him he bought a Ferrari, but advised the technician (ISP) to limit him to first two gears ... ;-)

And by the way starting with 3rd gear it costs more money ... :-)

Regards, Martin

New Member

Re: DS3 bandwidth question

I like that:). all clear my friend. Thanks for your help. Appreciate it.

CreatePlease to create content