Configuring WIC-1DSU-T1-V2 on back to back routers

[jekood001]

Hi there,

   Can some give me detail instructions on how to configure two WIC-1DSU-T1-V2 in two different 2811 routers. I will be using a T1 crossover cable but I'm not sure if I need to configure the following entries for the serial interface:

Interface serial 0/0
service-module t1 clock source internal
service-module t1 timeslots 1-24 speed 64
service-module t1 framing esf
service-module t1 linecode b8zs
ip address 10.1.1.1 255.255.255.0
encapsulation pppfair-que
no shut

Can someone break down what each line means in the configuration above? Thank you so much in advance!

[Edison Ortiz · Accepted solution]

On a back-to-back configuration, one router will provide the clocking, the DTE end - while the other router will follow the clock, the DCE end.

Per your configuration, both devices will use their internal clocking. I recommend having one set to line (DCE) and the other to internal (DTE).

service-module t1 clock source internal
service-module t1 timeslots 1-24 speed 64
service-module t1 framing esf
service-module t1 linecode b8zs
ip address 10.1.1.1 255.255.255.0
encapsulation pppfair-que

First line means to use the internal clocking from the router. Usually seen at the DTE side

Second line means to use 24 channels at 64Kbps each. That gives you a T1.

Third line and Fourth line, framing specified by the telco and linecode. Standard config in USA

Regards,

Edison

[jekood001]

Thanks so much for your response Edison!

Since this is just a back to back connection with a T1 crossover do I still need lines

3 and 4, since this is normally designated by the TELCO?

Also I would like to limit my connection speed to only 512K. can this be accomplished by setting line two  to the following:

service-module t1 timeslots 1-8 speed 64

Thanks for the information again!

[Hitesh Vinzoda · Accepted solution]

Hi,

Your config should be as below:

Set one CSU/DSU to clock source internal, and the other CSU/DSU to clock source line. The linecode, framing, data-coding, and timeslots must be set the same on both CSU/DSUs.

service-module t1 timeslots 1-8 speed 64

you can use the above command, implies that you are using fractional T1..

Hope this helps

Hitesh Vinzoda

Pls rate useful posts.

[huangedmc]

I'm also trying to set up a back to back connection between two 2800's, and have some additional questions:

It seems one side's supposed to be configured as the clock source, and the other side to follow it.

However, when I leave everything as default (clock source line), the link is up/up, and I can ping across the cross-over T1 link between the two routers.

Why is it working when the connection isn't yet configured properly?

R2#sh service-module s0/2/0
Interface Serial0/2/0
...

Framing is ESF, Line Code is B8ZS, Current clock source is line,
Fraction has 24 timeslots (64 Kbits/sec each), Net bandwidth is 1536 Kbits/sec.

===

R5#sh service-module s0/2/0
...
Framing is ESF, Line Code is B8ZS, Current clock source is line,
Fraction has 24 timeslots (64 Kbits/sec each), Net bandwidth is 1536 Kbits/sec.

R5#ping 150.100.25.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 150.100.25.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

====

I've seen on some older routers where the clock & framing, etc are configured under "controller t1".

When would you configure these settings under controller, and when would you do it under service-module?

====

Also, why are the T1's generally believed to have 1.544M of bandwidth, when it's actually 1.536M? (24 * 64K)

====

How does the router know which side is DCE, and which side is DTE?
It looks like it's pre-determined...how do I change it?

R2(config)#int s0/2/0
R2(config-if)#service-module t1 clock source internal
R2(config-if)#clock rate 128000
This command applies only to DCE interfaces

[burkj]

R2(config-if)#service-module t1 clock source internal -- This command is a DTE side configuration, this sets the router to provide clocking

It would probably stay up with your configuration, but you would see a lot of CRC errors if you did a show interface s0/2/0

The 'controller t1' configuration is for a different type of interface card, like a VWIC or HWIC for T1 - the WIC-1DSU configures as a service module

[fracjackmac]

I realize this is an old post, but it was referenced in the answer to a recent question regarding the configuration of a back-to-back T1 connection.

My interest here was in providing a bit of extra information that was asked for by huangedmc in his follow-on question, specifically: ** Also, why are the T1's generally believed to have 1.544M of bandwidth, when it's actually 1.536M? (24 * 64K) **

This is a great question and deserves an answer that is found within this wikipedia article on Digital Signal 1 -- "A total of 1.536 Mbit/s of bandwidth is achieved by sampling each of the twenty-four 8-bit DS0s 8000 times per second. This sampling is referred to as 8-kHz sampling (See Pulse-code modulation). An additional 8 kbit/s of overhead is obtained from the placement of one framing bit, for a total of 1.544 Mbit/s"

In other words, the additional 8 kbps needed to get from 1536 kbps to 1544 kbps is framing overhead unrelated to the data that is being carried.  It allows the two ends of the T1 to determine where a T1 frame (physical layer) starts and stops.

   ---   fjm