Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

How to see and set transmit interval (Tc) in QoS

Anybody knows how to see the transmit interval (Tc)? I tried the command "show traffic-shape", but looks like that command only works for frame relay traffic shaping. I configured "police" in ethernet interface, with bandwidth of 320000 bps without specifying the Bc. The router then automatically set the Bc to 1/32 of the CIR, which is 10000 byte. If we follows the CIR=Bc/Tc, then Tc=Bc/CIR, then we got the Tc = 0.25 s. The problem is, from what I've read from cisco documentation, Tc is between 10 ms - 125 ms. This means that the value from the router doesn't conform with the document. How could this happen? I tried this using cisco 7200 series.

4 REPLIES
Cisco Employee

Re: How to see and set transmit interval (Tc) in QoS

Prima,

I think you are confusing traffic shaping with policing. The policer adds more tokens to the bucket based on the formula below. Tc has no meaning in policing.

[(Current_arrival_time - previous_arrival_time) * CIR]/8

If you want to configure shaping, use the "shape average" command. Once you configure this you can run "show policy-map interface" and see the Bc value. From this you can calculate Tc.

On the ISR platform you can pretty much set the Tc to whatever you want. I personally would leave it at the default value for Tc = 4ms in 12.4 code.

New Member

Re: How to see and set transmit interval (Tc) in QoS

Hmm.. okay. Anyway, how to set the Tc in ISR platform? I haven't found the way yet.

Cisco Employee

Re: How to see and set transmit interval (Tc) in QoS

There is no way to directly set the Tc. You need to configure Bc and the CIR to make the Tc you want using the formula below.

Tc = CIR/Bc

policy-map shape-out

class class-default

shape average 320000 Bc_VALUE

Super Bronze

Re: How to see and set transmit interval (Tc) in QoS

If you're using the traffic-shape command, the 2nd and 3rd parameters configure Bc and Be, which will adjust Tc.

2951
Views
0
Helpful
4
Replies