Learning PRI and T1, any help?

Asterisk Asterisk Support
1

Hello, first off Ive read the faq on here and im on page 100 of the Oreilly book on Asterisk.

Ive done some basic configuring on our existinng Mitel PBX at work, but not hardware and phone lines really.

I have tried to read up on it, but seems I keep getting the wrong idea in my head.
I figured out PRI and BRI are both versions of ISDN or T1 (whats the differennce between ISDN and T1)
PRI has like 23 channels and 1 data channel, BRI has like 4 or something I forget.

What does a PRI connection look like? Is it a RJ45 connenctor coming in from the telco? How many wires does it run off?

thanks for any help, im working hard to learn this stuff

2

as i understand this (not an ISDN/PRI expert so could be wrong on some of this)

ISDN (Integrated Services Digital Network) is the type of link that is used.

BRI is Basic Rate Interface, 2 B (bearer) channels and one D (data) channel. This is the usual ISDN variant for homes and small business and is popular in Europe. It never really cought on in the USA- probably because it was difficult to order, expensive, not widely supported, and by the time anybody noticed that it existed, DSL and cable modems took up its market share. I know, I used to have ISDN at my house. I had to explain it three times to the telco before they let me order it :smile: (this was many years ago…). ISDN in the USA was once jokingly interpreted as “I Still Don’t Needit…”

Each B-chan can support 64kbit/sec of data or one voice call. The D channel is used to setup/teardown calls and provide out-of-band signalling. Channels can be dynamically allocated to data or voice and reassigned as needed.

PRI (primary rate interface) is the business version. The american version (T-1) has 23 B channels and one D channel for 24 total. This results in a combined total of 1.544mbit/sec. As before, channels can be dynamically reassigned between voice and data as needed.

It will almost certainly be an RJ45 connection, using one or two pairs (not sure on that one…)

3

Thank you.

So the PRI version of ISDN is just another name for T1 then?

Only other thing im having trouble with is the fact that it has 24 channels, but not 24 wires i dont think.

So, say you have a PBX with a T1 card in it. And you get a DATA T1 from the telco. The telco puts a T1 box up on the wall, they put ours next to our PBX. Thier is 2 pair going into thier T1 box, then out of the T1 box to us is a Cat5 cable that plugs into our T1 Modem/Router.
So where are the 24 channels coming into play? Does that mean they are dedicating 24 channels (1.5mg) to our 2 pairs of wire? Where are these 24 channels located, at the telco or maybe before thier T1 box (thier is another box of thiers before thier T1 box, im guessing maybe they got 24 wires going into it…?

Thanks! Im excited to understand this.

4

Your cable TV connection at home is on one cable yet you have many, many channels. The same is true on a PRI or T1.

5

Ok that makes more sense.
BRI, PRI, E1, all these run on just 2 pair of wire. Even though they range from 64kbps-upperMBPS…

That is all I will worry about then. 2 pair of wire, the Telco can worry bout the rest.

NOW, that answers my Data T1 questions, what about Voice T1 lines?
I know a voice T1 is just for pstn lines right? no data…
Does that mean you get 23 phone lines (phone numbers also) (or maybe its 12 not 23)…
What if you only need 8 lines tho, does the telco usually only carge you for the 8 lines of the T1?

thanks!

6

depends on the service agreement you have.

T1 can be mixed between voice and data. If you don’t need a whole T1 you can get a fractional T1, which only turns on X channels.

I believe the T1 can work like that (each channel is a line) but the more useful way of doing it is to be trunked- when a call comes in the D-chan tells * what number was called and stuff, and a free B-chan is chosen to carry the call…

7

Is a fractional T1 also called a frame relay?

So you could get half data/and half voice lines?

So for a PRI ISDN (T1) you could do 750kbs for data, and 750kbs for phone lines?

8

There is also a piece of hardware called a CSU/DSU that will allow you to segment the voice and data channels.

9

On the back of our Cisco T1 modem where the T1 plugs in (RJ45), it says T1/CSU/DSU

Got any more info on that hardware? Like where it connects physically? (before T1 modem or after…)

thanks

10

Hi

This should help alumnus.caltech.edu/~dank/isdn/isdn_ai.html

Personaly I did a course on ISDN with cable and Wireless many years ago and as such have a certificate saying im certified to work on their lines :wink: . It was the most mind numbing course I ever did, a week of 1 and 0s from morning to night.

11

Woa guys… be very careful here…

A PRI and T-1 are not synonymous for each other.

T-1s are common in the US as a digital carrier line. They come in two flavors, T-1 PRI and T-1 Channelized. You can not mix the two and they are two different beasts.

Channelized T-1s are usually terminated at a device called a channel bank. They are called channelized because each 64K channel is one line with one phone number. These are similar to bringing in 24 plain old telephone lines only multiplexed over two copper pairs or a fiber. You can break them out with the channel bank into 24 analog lines, v.35 serial data, a fractional DS1, or any combinaiton of the above.

A PRI T-1, as was mentioned earlier has 23 voice channels and a control channel. Thus calls are just sent on the next available channel. Unlike the Channelized T-1, if a call is placed to one of your phone numbers it could come in any one of the 23 voice channels (assuming all 23 are for voice) and the control channel will send the last for digits of the number the caller dialed. This is more commonly known as DID (directed inward dialing), often used to give each extension of a PBX its own real phone number without having a dedicated line for each. PRI T-1s can also be broken out into analog, but you need special intelegent hardware to do this (like a cisco router w/ fxo card). It is often easier to have a PBX break out analog lines by having a dedicated setup in the dialplan by number to analog fxo ports on the PBX.

A fractional T-1 is not frame realy… that is a technology all itself… it also comes in a 64K variant like Channelized and PRI T-1s, but they have nothing really in common.

And yes, a T-1 PRI is in essance a larger version of the consumer ISDN.

Also, you can on either a channelized or PRI T-1 set it up for partial data and partial voice. It all depends on what pricing package your telco can provide and if your hardware supports it. While I have not done a channelized T-1 on asterisk, I believe that their T-1 cards support either channelized or PRI by jumper.

I can go into more detail about what you would want to ask for if you would like… Right now I am negotiating a contract for one of my clients for 2 T-1s, one full channelized for data and a fractional 12 channel PRI for voice. Our package comes with 100 DID numbers which can be used however we see fit (since all the logic is done in the PBX or dialplan).

-Cheers, Peter.

12

Here’s some of what I didn’t know and had to figure out when I installed my first PRI. All are relatively trivial, but would have been nice to know. Hope they are helpful. They are only in the order in which I thought of them, not based on any level of importance.

  1. AT&T bills for the PRI and the digital circuit (T1) separately. I actually receive two bills, one for each.

  2. A T1 is simply a digital circuit that links you to the central office and your exchange carrier. Depending upon what hardware (switch type) is available, your carrier will make a list of services/provisioning types available to you. pbrunnen listed a number of them.

  3. The local exchange carrier (LEC) is responsible for “setting a loop”. This loop is the final leg between your site and the nearest CO. The loop itself is between the CO and a Network Interface Unit (NIU) which is usually an Adtran device that you can plug an RJ45 into, two wires hanging off the back of it lead to the MPOE. The LEC may extend the DEMARC past the NIU into your phone closet, always for a fee. You may go with a number of carriers for your service but the LEC will always be the company that owns the copper in your area.

  4. You are prohibited by law from playing with any wiring between the DEMARC and the CO per PUC guidelines. DEMARC points are often what’s called a “customer convenience block” which is just little plastic box with an RJ45 jack, though they can be right at the NIU. Never monkey with the other side of the DEMARC unless it’s requested you do so by the LEC.

  5. The local loop gets you to a central office where the carriers may have to set “cross connects” between their backbones. Cross-connects between backbones get your signal to where it can be provisioned. In one case, I have an NIU in the SF Bay area that is provisioned in Virginia for data. There are a number of cross-connnected T3s it traverses before getting there.

  6. When your loop has been set and all cross-connects have been made, your line is provisioned and a “turn-up” is scheduled. A turn-up is simply when you get on the phone with your carrier and ensure your switch/card is talking to their switch and the two are happy with one another. After a successful turn-up, your line is released for use by the carrier and you are on your own. Remember, the D-Channel won’t come up until Asterisk is running so be prepared. Simply running ztcfg won’t cut it.

  7. You have a send pair and a receive pair in your T1. Connecting send to receive is called a “loopback”. Adtran has diagrams as to how one is made. Have one handy when you’re on the line with your carrier. You’ll hear terms like “up-up” (loop is up and D-Chan is up) or “all ones” which means you’re good to go. “Alarm state” or “red alarm” mean you’re dead in the water.

  8. PRI circuits can be provisioned a number of ways, but in the few times I’ve ordered one, I’ve always used these parameters:

ISDN Compliance: NI-1
DID digits: 4 digit
Signaling: WINK
Pulse Type: DTMF
Line Coding: B8ZS
Framing: ESF
  1. I use Sangoma cards. For the above provisioning, my zaptel.conf looks like:
loadzone = us
defaultzone = us

#span definitions
span = 1,1,0,esf,b8zs

#channel definitions
#span 1
bchan = 1-23
dchan = 24

  1. Asterisk and the hardware available to use with it is usually more forgiving and versatile than some mainstream PBXs. Read the manuals and be sure the provisioning you order is compatible, sometimes it can take days to re-provision a circuit.

  2. You’ll find most people you talk to at the carrier are just as ignorant as you are about the different ways a T1 can be set up. Ask them what they have available and what they’d recommend. Sometimes you’ll get a kind/knowledgable soul to tell you lots of things about how/what to order.

Have fun!

13

Beautiflly posted kheston! Those are all excellent points!

Per kheston’s comment about people at the carrier not knowing… Yea… You will most likely speak with (interface with… hehehe) sales people who really only know what is on the pricing sheets in front of them.

Try asking them to get an Engineer involved early on in your decision making meetings. They will know exactly what they have available and what they can do. Plus you can ensure that the Sales agent did his/her job and got the details right. That can save you money and headaches if something does not get “communicated” properly.

(IMO… Never go with Choice One, now called One Communincations. They have botched up provisioning so many times I just refuse to deal with them. I have a customer who went with them, order a PRI and after setting up a cutover we found that they ended up provisioning a DSL circuit. OMG…)

14

this is great information, alot of the post 2 above this above my head, but still worth reading lol

thanks i feel smarter now

15

Cool. :smile:

Was there something in particular that we could clarify?
I know it is a lot to absorb at once…

16

[quote=“kheston”]Here’s some of what I didn’t know and had to figure out when I installed my first PRI. All are relatively trivial, but would have been nice to know. Hope they are helpful. They are only in the order in which I thought of them, not based on any level of importance.

  1. AT&T bills for the PRI and the digital circuit (T1) separately. I actually receive two bills, one for each.

  2. A T1 is simply a digital circuit that links you to the central office and your exchange carrier. Depending upon what hardware (switch type) is available, your carrier will make a list of services/provisioning types available to you. pbrunnen listed a number of them.
    So T1 is the digital circuit, and PRI is the package that runs on the T1 digital circuit?

  3. The local exchange carrier (LEC) is responsible for “setting a loop”. This loop is the final leg between your site and the nearest CO. The loop itself is between the CO and a Network Interface Unit (NIU) which is usually an Adtran device that you can plug an RJ45 into, two wires hanging off the back of it lead to the MPOE. The LEC may extend the DEMARC past the NIU into your phone closet, always for a fee. You may go with a number of carriers for your service but the LEC will always be the company that owns the copper in your area.
    What is the MPOE? something power over ethernet? What is DEMARC?
    I understand that LEC is our service provider, Sprint/Embarq. What/Who is the CO refering to?

  4. You are prohibited by law from playing with any wiring between the DEMARC and the CO per PUC guidelines. DEMARC points are often what’s called a “customer convenience block” which is just little plastic box with an RJ45 jack, though they can be right at the NIU. Never monkey with the other side of the DEMARC unless it’s requested you do so by the LEC.

  5. The local loop gets you to a central office where the carriers may have to set “cross connects” between their backbones. Cross-connects between backbones get your signal to where it can be provisioned. In one case, I have an NIU in the SF Bay area that is provisioned in Virginia for data. There are a number of cross-connnected T3s it traverses before getting there.
    What do u mean provisioned?

  6. When your loop has been set and all cross-connects have been made, your line is provisioned and a “turn-up” is scheduled. A turn-up is simply when you get on the phone with your carrier and ensure your switch/card is talking to their switch and the two are happy with one another. After a successful turn-up, your line is released for use by the carrier and you are on your own. Remember, the D-Channel won’t come up until Asterisk is running so be prepared. Simply running ztcfg won’t cut it.

  7. You have a send pair and a receive pair in your T1. Connecting send to receive is called a “loopback”. Adtran has diagrams as to how one is made. Have one handy when you’re on the line with your carrier. You’ll hear terms like “up-up” (loop is up and D-Chan is up) or “all ones” which means you’re good to go. “Alarm state” or “red alarm” mean you’re dead in the water.

  8. PRI circuits can be provisioned a number of ways, but in the few times I’ve ordered one, I’ve always used these parameters:

ISDN Compliance: NI-1
DID digits: 4 digit
Signaling: WINK
Pulse Type: DTMF
Line Coding: B8ZS
Framing: ESF
  1. I use Sangoma cards. For the above provisioning, my zaptel.conf looks like:
loadzone = us
defaultzone = us

#span definitions
span = 1,1,0,esf,b8zs

#channel definitions
#span 1
bchan = 1-23
dchan = 24

  1. Asterisk and the hardware available to use with it is usually more forgiving and versatile than some mainstream PBXs. Read the manuals and be sure the provisioning you order is compatible, sometimes it can take days to re-provision a circuit.

  2. You’ll find most people you talk to at the carrier are just as ignorant as you are about the different ways a T1 can be set up. Ask them what they have available and what they’d recommend. Sometimes you’ll get a kind/knowledgable soul to tell you lots of things about how/what to order.

Have fun![/quote]

17

[quote=“pbrunnen”]Woa guys… be very careful here…

A PRI and T-1 are not synonymous for each other.

T-1s are common in the US as a digital carrier line. They come in two flavors, T-1 PRI and T-1 Channelized. You can not mix the two and they are two different beasts.

Channelized T-1s are usually terminated at a device called a channel bank. They are called channelized because each 64K channel is one line with one phone number. These are similar to bringing in 24 plain old telephone lines only multiplexed over two copper pairs or a fiber. You can break them out with the channel bank into 24 analog lines, v.35 serial data, a fractional DS1, or any combinaiton of the above.

A PRI T-1, as was mentioned earlier has 23 voice channels and a control channel. Thus calls are just sent on the next available channel. Unlike the Channelized T-1, if a call is placed to one of your phone numbers it could come in any one of the 23 voice channels (assuming all 23 are for voice) and the control channel will send the last for digits of the number the caller dialed. This is more commonly known as DID (directed inward dialing), often used to give each extension of a PBX its own real phone number without having a dedicated line for each. PRI T-1s can also be broken out into analog, but you need special intelegent hardware to do this (like a cisco router w/ fxo card). It is often easier to have a PBX break out analog lines by having a dedicated setup in the dialplan by number to analog fxo ports on the PBX.

A fractional T-1 is not frame realy… that is a technology all itself… it also comes in a 64K variant like Channelized and PRI T-1s, but they have nothing really in common.
what is a frame relay then?

And yes, a T-1 PRI is in essance a larger version of the consumer ISDN.
consumer ISDN is T-1 BRI right?

Also, you can on either a channelized or PRI T-1 set it up for partial data and partial voice. It all depends on what pricing package your telco can provide and if your hardware supports it. While I have not done a channelized T-1 on asterisk, I believe that their T-1 cards support either channelized or PRI by jumper.

I can go into more detail about what you would want to ask for if you would like… Right now I am negotiating a contract for one of my clients for 2 T-1s, one full channelized for data and a fractional 12 channel PRI for voice. Our package comes with 100 DID numbers which can be used however we see fit (since all the logic is done in the PBX or dialplan).
so you will have 100 phone numbers, but only can use 12 at a time on the the fractional Voice T1?

-Cheers, Peter.[/quote]

18

So T1 is the digital circuit, and PRI is the package that runs on the T1 digital circuit?
More like a PRI is one way to ‘setup’ a T1.

What is the MPOE? something power over ethernet?
MPOE is ‘minimum point of entry’. That is the short possible distance where the telecom wires cross from public land onto private propery.

What is DEMARC?
The DEMARC is ‘demarkation point’. This is the line between what wires belong to you (or the building where you rent) and the telecom company. This is often a set of 66 blocks setup by the phone company where you connect your internal lines.

I understand that LEC is our service provider, Sprint/Embarq.
Yes. To be even more specific, the company who owns the wires (often who you call for home phone service) is the ILEC (incumbent local exchange carriers) also sometimes called RBOC (regional bell operating companies) from before the monopoly breakup in the 80s. CLECS are ‘competitive local exchange carriers’, they provide service but need to use the wires of the ILEC.

What/Who is the CO refering to?
CO is ‘central office’. This is where the ILEC’s wires converge locally to the switching facility. Often these are seen as little brick buildings with heavy air-conditioning on the side. This is where your local exchange xxx-123-nnnn is handled.

What do u mean provisioned?
Provisioned basically means ‘setup’ or prepared.

what is a frame relay then?
Well, frame relay is a packet switching technology. Basically you data is broken into chunks called frames. The frames are added to a loop at the CO along with other customers frames. I say this is a different beast because frame relay is a logical technology that runs on may different types of physical topologies. For instance, you can use frame relay over a PRI T1.

consumer ISDN is T-1 BRI right?
Yes. It is just not called T-1; it is just refered to as BRI.

so you will have 100 phone numbers, but only can use 12 at a time on the the fractional Voice T1?
Yes. But only on a PRI T1 where you pay for 12 channels. You can have up to 23 voice channels.

*Lets assume moving forward that we have 12 channels provisioned on a fractional T1.

If you have a Channelized T1, each channel has a phone number.
For example, Channel 5 is 123-4567. If you call 123-4567, channel 5 will ‘ring’ reguardless if Channels 1 through 4 or 6 through 12 are busy or not.

If you have a PRI T1, you have a pool of phone numbers. When you call a number in that pool, the first available channel will ‘ring’ and the D channel will signal what phone number was called. This way you can handle calls differently based on what number was called without needing to increase you costs by having more dedicated channels.

-Cheers, Peter.