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New Member

T3 circuit performance

I am wrestling with a T3 circuit performance issue. The service provider is measuring 13Mbps btwn their router and mine. I have a Cisco 3725 router on my end. Does anybody have any ideas why we are not seeing closer to the 45Mbps capacity of that circuit?

Below is a partial config:

controller T3 1/0

clock source line

description ISP_A


interface Serial1/0

mtu 4470

bandwidth 44210

ip address

ip access-group 101 in

no ip redirects

no ip unreachables

dsu bandwidth 44210

ACL 101 does antispoofing and denies telnet and echo.




Re: T3 circuit performance

How exactly are you testing? Is CEF enabled? What is the CPU usage of the 3725 during the test? A 3725 using CEF can handle a full T3 easily without ACLs, but should be able to do so with ACLs as well, so it's probably not a router performance issue. Are there any incrementing errrors on the serial interface (show int s1/0) while the test is running?

You may want to look over RFC1323, which deals with TCP performance issues over WAN links: Depending on how "long" the link is between you and your ISP, the latency could be such that TCP extensions like window scaling are needed to max out the circuit with a single flow.

New Member

Re: T3 circuit performance

Thank you for your response.

The service provider is running some sort of test from their end. CPU utilization is 2%, errors are very low. CEF is not enabled.


Re: T3 circuit performance

I don't know how they could run a bandwidth test without your cooperation, unless they have access to your router and they're using TTCP.

You can do some tests on your own. One option is starting a bunch of simultaneous downloads from one or more fast servers ( comes to mind), and see what aggregate throughput you get.

New Member

Re: T3 circuit performance

Thanks again for the response. The SP said they ran some application - I can't recall what it was. They said they were getting 13Mbps from their router to ours.

We have tinkered with downloading files and testing the download speeds, but this becomes tedious and time consuming.



New Member

Re: T3 circuit performance

Are you sure that you have 45Mbps of traffic to push through the pipe? You can always run MRTG on your end of the link to measure bandwidth.


Re: T3 circuit performance

why don't you give ttcp a try

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