high clockrates with a low speed interface

[dbolte]

Hello,

I have a 3640 router which has a 8 ports sync/async module (nm-8-a/s) installed. This router is directly connected (back-to-back) via serial 2/0 with V35 cables to an high speed serial interface (WIC-1T) in a 1751 router. DCE cable is connected to 1751. The WIC-1T should have a maximum througput of 2 Mbits or more. The nm-8-a/s has a maximum througput of 128 Kbits. At this moment we have a clockrate of 256000 configured on the Serial0/0 (WIC-1T) of the Cisco 1751. This is working.

I heard that it is possible to increase the clockrate of one serial interface on the nm-8-a/s when you do not use the other serial interfaces on that router. In this situation none of other interfaces on the nm-8-a/s are used.

Is it necessary to configure something on the Serial2/0 of the nm-8-a/s module in the Cisco 3640? The clock rate of 256000 is configured on the Cisco 1751.

Can anyone help me?

Thanks in advance.

[dnagarajachary]

The clock rate command which you give under the serial interface has nothing to do with the actual bandwidth of the link.

You can specify the maximum clock rate, supported by the IOS. This clock rate is used by the routing protocols to calculate the metrics.

You can specify the maximum clock rate on all serial interfaces provided, the interface is having a DCE cable attached to it.

-Deepu

[dbolte]

Sorry, but as far as I know the clock rate has everything to do with the actual bandwidth of the link. The bandwidth command itself is used in the routing protocols and to calculate the load.

The clockrate is important.

I have increased the clock rate to 512000 on the cisco 1751. This router has the DCE cable attached to it. I t works but it seems to me that the quality has something to do with the load on the line. I lose packets when to load is getting higher. When I increase the clock rate to 1.000.000 the link goes down.

Dirk Bolte

[dnagarajachary]

I am very sorry that i confused the clock rate command with the bandwidth command.

As you have said , bandwidth command is used by the routing protocols.

The clock rate is important .

An excerpt from Cisco document is

The fastest speeds might not work if your cable is too long, and that speeds faster than 148,000 bits per second are too fast for EIA/TIA-232 signaling. It is recommended that you only use the synchronous serial EIA/TIA-232 signal at speeds up to 64,000 bits per second. To permit a faster speed, use EIA/TIA-449 or V.35.

Hope this would help

-Deepu

[dbolte]

My cable is a V35 cable an shopuld be able to handle a minimum of 2 megabits per second. The lenght of the two cables together is 6 meters (2 standard Cisco cables)

I still do not understand why the maximum speed is 512000 bits per second

[olorunloba]

Well, I think the interface still can not do more than 128k, and you are only trying to drive it beyond. Was the info from cisco, please clarify. You might be able to decieve the router to increase the clockrate of the interface beyond its nominal, but I believe that the engineering of the interface will still limits the throughput to about 128. Your best option will be to use another WIC-1T or 2T on the 3600.

[dbolte]

Thanks,

I am going to try to use the WIC-2T. The problem is that it is not our router and very difficult to arrange change on that.

Thank for your information.