convert analog DID to a PRI? 1

[bthom73]

Hi, I'm trying to figure out the least expensive way of converting an analog DID trunk coming from the phone company to a PRI that I can feed into our ISDN switch. I realize that the analog DID trunk only equates out to one B-channel + one D-channel for signaling but that is fine, the other 22 channels can go unused/unmapped. I'm not too familiar with Cisco gear but figured maybe two MC3810s back to back or a 2610 with the proper add-ons (VIC-2DID + ?). I also need to make sure that the dialed phone number is preserved within the signaling (DID->D-channel). Any low end hardware suggestions would be greatly appreciated. Thanks for any info, Brian.

 

[jneiberger]

Why would you convert a line that costs you very little to go with a line that costs several hundred per month, only to highly underutilize the new service? I'm having trouble figuring out how that makes sense.

 

[bthom73]

We have an old analog DID trunk that's currently used for incoming faxes and it has 280 phone numbers assigned to it. It actually gets very little use, maybe four or five faxes a day but it's the phone numbers that are important.

We also have a campus wide ISDN network and the switch in my building has a few PRI ports to spare. I'd like to run that analog DID trunk into the ISDN switch so that we can use the analog DID trunk (and those 280 phone numbers) for more than just the one fax server that it's currently plugged into. Converting the fax server over to ISDN isn't a problem but dealing with that analog DID trunk is turning out to be sort of tricky...

 

[jneiberger]

So, really all you want to do is repoint those DIDs to a PRI, right? That should be very simple. Just call up your provider and place an order with them. We've done this exact thing many times with no problems. I've never had to do it with that many numbers, though.

 

[bthom73]

Not exactly, although we might end up doing that eventually.

For now I'd like to "create" a PRI out of that analog DID trunk. Obviously 22 of the 23 B-channels would be inactive but that's ok for now since the line doesn't get much use. Eventually if we need more channels we can upgrade it to a true PRI from the phone company.

 

[jneiberger]

Let me make sure I have this straight. It sounds like you want some sort of gateway that would accept an analog DID trunk on one side and convert that to a PRI on the other. Is that right?

 

[bthom73]

Correct. Converting in the other direction is pretty easy using an Adtran Atlas or similar (PRI in->analog DID out) but it seems that switch/router equipment able to act as the customer side of an analog DID trunk is a little harder to come by.

Looks like the VIC-2DID card might be half of the equation but I'm not familiar enough with Cisco gear to know whether there's a way to get from there to a PRI interface while also preserving the dialed phone number. Theoretically the gateway would take the DTMF analog DID number and convert that to D-channel data (where the dialed phone number normally appears on a PRI).

 

[bthom73]

Also looks like the MC3810 might possible work, and they're available pretty cheap. At least it has a voice T1 port and it looks like the FXS port might double as the customer end of an analog DID trunk. Not sure if the firmware does what I'm describing though...

 

[bthom73]

Looks like I might have spoke too soon regarding DID on the MC3810. From what I can find in the Cisco docs, it doesn't look like the "signal did" command is supported on the MC3810 FXS card.

Would it be possible to use a 2600-series router with a VIC-2DID card as the input side and a MC3810 with a voice PRI as the output side?

Thanks for any info.

-Brian

 

[jneiberger]

Can't the 2600 support a PRI interface?

 

[bthom73]

You're correct, there does appear to be a voice-capable PRI interface for the 2600 series but Cisco's part numbers are really confusing me and I'm not sure if a 2600 can handle both the DID and the PRI at the same time. A MC3810 including a voice-capable PRI port sells for about $100.

I've read some info about the NM-HDA (analog) and NM-HDV (digital) carrier cards and it looks like the DSP functionaility is on those carrier cards. Also looks like there's an AIM module "AIM-VOICE-30" that can be used instead of the DSP on either of the above carrier cards. There's also a much more affordable NM-2V carrier card available for "low density" applications, which seems more appropriate for my situation since I'm only dealing with one voice call at a time, but there's no "VIC" available for a voice PRI. There only a "VWIC" (VWIC-1MFT-T1) which I'm not sure can be installed in the NM-2V carrier and whether or not I would also need the AIM-VOICE-30 DSP. Seems like a somewhat expensive experiment even at eBay prices... I'm hoping someone with more experience than I might be able to relate some of these parts to my application before I go out shopping.

Thanks,
Brian

 

[jneiberger]

You might want to try asking these questions on the Cisco CallManager forum instead of the Cisco Router forum. Those guys would probably have some better ideas. I'm pretty new to Cisco voice stuff.

 

[VoIPGuyNSC]

I don't know exactly how to accomplish this, but it most certainly will not be with FXS card (DID). These are Foreign Exchange Station ports and are used to connect to analog devices such as Modems, Faxes and analog phones. At the very least you would need FXO (Foreign Exchange Office) ports to connect to the PSTN.

That being said, though, I don't know of any IOS commands to accomplish this natively with CCME. You might be able to accomplish it with CCM, with some creative route patterns and translation patterns, but that would be no where near an elegant solution and would most certainly be defeating the purpose of the whole exercise.

John Lever
Telecommunications
Richland School District Two

 

[jneiberger]

Actually, the FXS/DID card is the one he'd need. It seems odd that the FXO card, which is what you use to connect to the PSTN, can't do DID and that you need an FXS card to do it. It has something to do with who's providing power to the line, or something like that.

It seems to me that you could use an FXS/DID card to terminate the DID trunk and then use CCME to route the incoming call over the PRI. It should be fairly simple, but I'm not familiar at all with CCME.

 

[VoIPGuyNSC]

Then I guess I'm misunderstanding which caller-id is trying to be preserved:

http://www.cisco.com/en/US/tech/tk652/tk653/technologies_configuration_example09186a00800a9a49.shtml

John Lever
Telecommunications
Richland School District Two

 

[jneiberger]

You're probably understanding that part of it correctly. You just need to keep in mind that the hardware that supports FXS ports also supports incoming DID trunks, which I realize seems odd. The hardware that supports FXO ports cannot support DID. As I mentioned before, I think it has something to do with how the hardware handles power on the line.

A DID is still a central office connection, even if it is terminating on an FXS/DID module. An FXS/DID port can be either an FXS port or a DID port, but they are obviously not the same thing.

 

[bthom73]

As mentioned, analog DID is somewhat backwards compared to analog POTS. The voltage is supplied by the customer instead of by the phone company, which is why when a FXS or FXO card is used for DID, the labels seem to be flipped.

The concept of DID is also quite different from Caller-ID. Caller-ID uses FSK signaling to indicates the source phone number of the person who's calling. DID uses DTMF tones (usually just the last several digits) to indicate the destination phone number that was called. In our case we have 280 phone numbers assigned to the one phone line (DID trunk) and those phone numbers eventually get mapped into email addresses so that professors receive their faxes as email attachments.

So, it's the dialed number that I'm trying to preserve. I'm sure the VIC-2DID card keeps track of it or the card wouldn't really have a purpose, but my lack of Cisco knowledge still has me stumped. I'll keep reading the docs...

 

[jneiberger]

I'm sure this will be an easy thing to accomplish with the VIC and some other module that supports PRI. I wonder...can a voice IOS handle a PRI on its own or do you need to get CME? It would be really cool if you didn't need to even buy CME, but I'd bet that PRI is too complex for just the IOS to handle.

 

[bthom73]

This guide is probably the best one I've found so far:

http://www.adnetman.com/cisco-router-guide.pdf

The PRI card is on page 157 and the DID card is on page 164 along with background requirements for both.

Just hardware wise though it seems to be a $1000+ experiment even at eBay prices to get a 2600 to handle both a DID trunk and a PRI.

The Cisco MC3810 can definitely handle the PRI and they're cheap. It also takes the "high density" factors associated with the 2600 out of the picture. Just need to figure out if I can get the 2600 to send the call to the MC3810 (including the dialed number info).

The all-in-one 2600 is a cleaner solution though. It's hard to tell if the reason the NM-HDV card or AIM-VOICE-30 card is required for the PRI has to do with handling the larger number of concurrent calls that the PRI is capable of. It would be cool if the VWIC-1MFT-T1 card could work with the smaller DSP on the NM-2V if only a few channels are required (as in my case where I only need one channel).

 

[VoIPGuyNSC]

Folks, don't mind me. My brain apparently turned to mush today. I was confusing called-number with calling-number. I need to stick to the CCM forum. <grin>

John Lever
Telecommunications
Richland School District Two