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

Clock Rate on 2501 Routers-can you help ?

Hi everyone!

This is my first post here as a minuscule CCNA!

I am from a Transmission background and know the full make up of an E1 Frame as far as TS0 & TS 16 and the 30 data channels.

I have x2 2501 connected back to back.

One is DCE and one is DTE.

I am basically trying to see the relationship between bandwidth and clock rate.

When I issue the set clock rate on the DCE I get the following options:-

ROUTER_TESTLAB(config-if)#clock rate ?

Speed (bits per second)

1200

2400

4800

9600

19200

38400

56000

64000

72000

125000

148000

250000

500000

800000

1000000

1300000

2000000

4000000

<300-8000000> Choose clockrate from list above

Why doesn’t it go up in logical steps of 64k or even 56K (T1)?

For instance I have a customer who says he has a 640k link set up between two sites.

I would logically assume this to be 10 timeslots i.e. 10 x 64 =640Kbs

On my router I don’t have the option to set this specific rate as I can either set 500000 or 800000 !

Can anyone possibly explain the relationship of why these figures go up in the way that they do especially to 4000 000

4 REPLIES
Cisco Employee

Re: Clock Rate on 2501 Routers-can you help ?

The reason why the 2500 series has this set of available clockrate settings is due to the hardware. The chipset for the serial interfaces can only do these values.

If you need values other than what is listed, then a CSU/DSU will be required.

New Member

Re: Clock Rate on 2501 Routers-can you help ?

Hi tblancha

I guessed it was a HW limitation so thanks for the confirmation.

Please bear with me.

I have a customer who launches a GUI format PC which has 640K BW allocated to it.

Now I am assuming as he is being so precise about the 640 K that he must have a channelised E1 Unit and has assigned the specific rate to the that serial interface.

The Problem:-

He says it takes 15 Minutes to launch the application across his routers to his server!

I am trying to simulate what he is trying to achieve by connecting 2 routers back to back.

I only have qty=2 of 2501

As I cant select specific n*64k (B1 Channels) I thought the only way I can achieve this is to maybe set up a Point 2 Point Frame Relay link and change the CIR rates.

Does this sound logical to you?

To that I have created a Frame Relay link but I can’t see any command where I can specify CIR thus limiting the bandwidth.

Any help/advice is truly appreciated.

Br

Jimmy

Cisco Employee

Re: Clock Rate on 2501 Routers-can you help ?

I would say it depends on what is in use already. Is the customer using FR or HDLC --- IP or IPX or SNA? If it is a layer3 protocol, is route-cache or CEF enabled?

I think you would be better off getting sniffer trace on the actual hardware in place than replicating it.

Have you stress tested the wan with a BERT or with varying size and pattern pings?

New Member

Re: Clock Rate on 2501 Routers-can you help ?

Hi Tblancha

You said:-

I would say it depends on what is in use already. Is the customer using FR or HDLC --- IP or IPX or SNA? If it is a layer3 protocol, is route-cache or CEF enabled?

The customer is visiting me tomorrow so I can get all the information from him!

I think you would be better off getting sniffer trace on the actual hardware in place than replicating it.

Have you stress tested the wan with a BERT or with varying size and pattern pings?

I SAY:-

No what I have done is just set up a point 2 point link using HDLC across my routers and used the clock rate command to change the throughput of the serial link.

I used a program called Check to complete this which is very useful.

I also believe he has serious problems as I dropped the clock rate to 64k and my application was still launching ok and he was telling me that he has a 15 minute wait across a 640 k link which feeds into an aggregate pipe of 2048 Kbs.

Thanks again for the information.

I shall quiz him about this.

Br

Jimmy

255
Views
0
Helpful
4
Replies
CreatePlease to create content