The Card Type Command – Don’t Flop


If you’ve ever found yourself staring at a VWIC2-1MFT-T1/E1 or a NM1-T3/E3 module, you know that you’ve got some configuration work ahead of you.  Whether it be for a PRI circuit to hook up that new VoIP system or a DS3 to get a faster network connection, the T1/T3 circuit still exists in many places today.  However, I’ve seen quite a few people that have been stymied in their efforts to get these humble interface cards connected to a router.  I have even returned a T1/E1 card myself when I thought that it was defective.  Imagine the egg on my face when I discovered that the error was mine.

It turns out that ordering the T1/E1 or T3/E3 module from Cisco requires a little more planning on the installation side of things.  These cards can have a dual identity because the delivery mechanism for these circuits is identical.  In the case of a T1/E1, the delivery mechanism is almost always over an unshielded twisted pair (UTP) cable.  Almost all of the T3/E3 circuits that I’ve installed have been delivered over fiber but terminated via coax cables with BNC connectors.  The magic, then, is in the location.  A T1 circuit is typically delivered in North America, while the E1 circuit is European version.  There are also differences in the specifics of each circuit.  A T1 is 24 channels of 64kbits each.  An E1 is 32 channels of the same size.  This means that a T1 has an effective data rate of 1.544 Mbits while an E1 is a bit faster a 2.048 Mbits.  There are also framing differences and a slightly different signaling structure.  The long and short of it is that T1 and E1 circuits are incompatible with each other.  So how does Cisco manage to ship a module that supports both circuit types?

The key is that you must choose which circuit you are going to support when you install the card.  The card can’t automatically flip back and forth based on circuit detection.  Where the majority of issues come from in my line of work is that the card doesn’t show up as a configurable interface until you force a circuit type.  This is accomplished by using the card type command:

RouterA(config)#card type ?
 e1 E1
 e3 E3
 t1 T1
 t3 T3

Choose your circuit type and away you go!  As soon as you enter the card type, the appropriate serial interface is created.  You will still need to enter the controller interface to set parameters like the framing and line code.  However, the controller interface only shows up when the card type has been set as well.  So unless you’ve done the first step, there isn’t going to be a place to enter any additional commands.


Tom’s Take

Sometimes there are things that seem so elementary that you forget to do them.  Checking a power plug, flipping a light switch, or even remembering to look for little blinking lights.  We don’t think about doing all the easy stuff because we’re concentrating on the hard problems.  After all our hard work, we know it has to be something really messed up otherwise it would be fixed by now.  In the case of T1/E1 cards, I made that mistake.  I forgot to check everything before declaring the card dead on arrival.  Now, I find myself spending a lot of time providing that voice of reason for others when they’re sure that it has to be something else.  The little voice of reason doesn’t always have to be loud, sometimes it just has to say something at the right time.

About these ads

One thought on “The Card Type Command – Don’t Flop

  1. I have been reading your blog for a while and enjoy it very much. There are a group of blogs that I try to check every day. I nearly always learn something new from any one of the blogs I read. In this case, I could have written a book of “me too’s” when relating to this topic. Now, when a junior engineer calls me for assistance I always end up asking what platform BEFORE asking if they have defined the card type, because in the newer ISRs you define all of the parameters you would normally put under the controller, you now define with a service module command under the interface. The 1941 with a CSU/DSU card comes to mind right now where this would be the case. It freaked me out the first few times I tried to configure the card type on it and would type confi t/card ? and get an unrecognized command error. Then i learned you had to do it like I mentioned above.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s