T1 or ISDN PRI

[tlsmith1000]

Our company is using 3 ISDN BRI lines for VC now but we wish to get a bridge to enable voice conferencing and video conferencing. The bridge we are looking at can use multiple ISDN PRI lines which I understand but it also states that a T1 can be connected.

I always thought that a T1 was used as a point to point connection. Can it be used like an ISDN PRI? We're only just expanding this system and I'm rather new at the phone company end of things.

[George]

tlsmith,

the short answer to your question is no. A T1 is dedicated point to point H.323 connectivity. An ISDN PRI is basically a channelized T1, which is where your difference lies. ISDN H.320 connectivity cannot be directly supported over a normal T1. They say a T1 can be connected meaning it has the ability to terminate a T1 for IP H.323 calls.

George

[tlsmith1000]

That's what I thought but I didn't want to sound stupid. I guess this means I can not only ad ISDN PRI for connection to the world but T1 for connection to a dedicated business partner.

[dndtech]

People confuse T-1 and PRI due to the fact that they are both 1.544Mbs pipes. The D channel establishes, maintains and terminates the ISDN connection. Since the management is done on a separate channel (D), the entire B channel bandwidth is available for data transfer. Basic breakdown is:

T-1 - North America, Japan and Korea
- 1.544 MBs = 24 X 64Kbs channels
- These is raw bandwidth – Signaling is performed within each channel.

ISDN PRI – Primary Rate Interface
- 1.544Mbs = 24 X 64Kbs channels
- This is further broken down into 23B + 1D channel
- B = Bearer or the channels that transport your data (voice, video etc.)
- D = Demand or signaling channel

ISDN BRI – Basic Rate Interface
- 144Kbs = 2 X 64Kbs + 1 X 16Kbs
- Referred to as 2B + D
- B = Bearer or the channels that transport your data (voice, video etc.)
- D = Demand or signaling channel

I can expand on this if there is interest.

For tlsmith – Your bridge requires ISDN PRI. The D channel MUST be present to manage the calls. The literature you are perusing is referring to a T-1, but, I suggest, really means ISDN PRI. Hope this helps.

FYI – The remainder of the globe generally uses E-1 or 30B +D based on 2.048Mbs pipe.

[Entropy3XD]

tlsmith1000,

Never worry about sounding stupid around here. None of us were born with this knowledge (at least not me). We are all here to share the wisdom, so never hesitate to ask, no matter how silly you think the question may be.

[jaron]

good explaination dndtech ... i know this got me stumped early on in my VC career ... the nice thing about this industry is that you can learn something new every day and this forum can only but help :)

[tlsmith1000]

Thanks everybody! I've only used this forum for two days and already it's proved usefull.

The bridge we are looking at is a Compunetix audioVirtuoso and what confused me was looking at the Network Interface specs where it listed one of the types as "T1/E1 PRI". The way it's stated made it sound like they were the same thing.

ISDN is what we need, and it's also what I (slightly) understand. Now I can't wait to get it in here and see what all I can make it do!

Thaks again for the help. Hopefully I'l be able to contribute to you. We currently have 2 Polycom ViewStation FX, 1 iPower 9000 and a dozen ViaVideos. All connections are either ISDN straight to the unit or in the case of the ViaVideos through a Cisco IPVC 3520 with 3 BRI lines. If anybody needs help with any of these let me know and I'll do my best. The hardware is what I really understand.

[tjulian]

Industry standardly uses the T1/E1 PRI designation to mean it works with both the North American and European Standard PRIs. You would've thought someone could have found a different way of stating that in the beginning, hih? :)

As a sidenote, did you guys know that Networking classes are now teaching that there is no basic difference in a T1 and a PRI? Are they crazy?

[dndtech]

I had a discussion this morning and discovered that you in fact can use a raw T-1 to link between MCU's. I'm not sure if this is manufacturer dependant (ie Tbg to Tbg / Poly to Poly) and will test different combinations over the next few weeks to clarify. It must be a dedicated pipe between the two MCU's, which would be just like a private network, even of you use a commercial carrier.

An ISDN connection (D channel) is mandatory when dialing to the "outside" world. Remember the D Channel initiates, maintains and terminates an ISDN call through the public network.

Cheers.

tlsmith - The only stupid question is the one that's not asked. ;)

[Pnutley]

Couldn't help but chime in here being an old telecom geek.

Here's the deal, and here is where the confusion comes in.

A T1 is a 1.544 Mbps pipe, that's all you know when someone says T1 (the problem is that many people say T1 when they shouldn't, more on this shortly).

A PRI is a T1 line formatted for 23B and 1D (since the signaling is done out of band, each of the 23 B channels can use the entire 64Kbps available).

A DS1 is a T1 line formatted for 24 channels of 56 Kbps each and using robbed bit signaling (when you signal in-band you steal away from the 64 Kbps available, which leaves only 56 Kbps per channel in a DS1)

A "raw" T1 shoots data through the pipe at 1.544 Mbps - this is usually used for point to point high speed (relatively) comminications.


SOOOOOO - a PRI and DS1 are BOTH T1s, I think the confusion is that for whatever reason many people refer to a DS1 (24 56Kbps channels) as just a T1 - which is not an accurate description.

Hope I didn't confuse things even more ....... ;)

[dndtech]

And further more, since pnutley has gone deeper.... :o

- Each of those 64Kbs/56Kbs channels is often referred to as a DS0 (within the T1 pipe)
- A single D Channel can manage up to 20 PRI, but the general rule of thumb is to add an additional D Channel for every 8 PRI. However, with critical circuits, a second D Channel is usually added on the second PRI as a back up. In other words:

- 1st PRI = 23B + 1D
- 2nd PRI = 23B + 1D
- 3-8 PRI = 24B

The PRI #1 D Chnl is "boss" (primary D) with the PRI #2 D Chnl (backup D) sitting in the weeds waiting for work. In the event you have a PRI #1 D Chnl failure, this configuration will ensure your comms stay up using the PRI #2 D Chnl. An alarm will indicate the PRI #1 D Chnl has failed and can be repaired without service loss. Of course, if you lose the entire PRI #1, all comms on that pipe will die, but the remainder will operate normally using PRI #2 D Chnl.

Large users, like us, have DS3 connections. A DS3 is qty 28 T1's in a single pipe. This is often referred as 45Mbs, but is actually 43.232 Mbs (1.544 X 28) We use these to feed our bridge sites which contain a host of product from Avaya, Polycom and Tandberg.

In Canada, the price point from the big carriers makes a DS3 cost effective at about the 16 T1 mark. The price point to jump to a PRI is about 13 DS0's.

Now are you confused? Further queries are welcome. If a VC tech can talk this lingo to their bandwidth provider (usually a Telco), the service level seems to improve. Go figure. Cheers.

[Joe Vallender]

Wouldn't it be easier to say the T1/E1 is the physical circuit and PRI is the service riding on the circuit? The devices on either end of the circuit determine what service is used.

[dndtech]

Nope. That's where confusion starts.

A T1 is simply 24 (DS0 or 64Kb) channels of raw bandwidth for a total pipe of 1.544Mbs. Any signalling is performed within the individual channel.

An ISDN PRI is also 24 (DS0 or 64Kb) channels and the total pipe is also 1.544Mbs. But signalling is managed by one of the DSO channels, leaving the remaining channels for data transfer. This is the ISDN capability.

You cannot simply order a T1 and expect it to function like ISDN. It must be configured as such. A further explanation of ISDN and why it is used is available here:

http://computer.howstuffworks.com/framed.h.../isdnintro.html (http://computer.howstuffworks.com/framed.htm?parent=question372.htm&url=http://www.jet.net/isdn/isdnintro.html)

E1 services are indentical in technology except they are based on 30 DS0 (64Kb) with total pipe of 2.048Mbs.

[Entropy3XD]

Originally posted by dndtech@May 14 2004, 06:29 PM
Nope. That's where confusion starts.

A T1 is simply 24 (DS0 or 64Kb) channels of raw bandwidth for a total pipe of 1.544Mbs. Any signalling is performed within the individual channel.

An ISDN PRI is also 24 (DS0 or 64Kb) channels and the total pipe is also 1.544Mbs. But signalling is managed by one of the DSO channels, leaving the remaining channels for data transfer. This is the ISDN capability.

You cannot simply order a T1 and expect it to function like ISDN. It must be configured as such. A further explanation of ISDN and why it is used is available here:

http://computer.howstuffworks.com/framed.h.../isdnintro.html (http://computer.howstuffworks.com/framed.htm?parent=question372.htm&url=http://www.jet.net/isdn/isdnintro.html)

E1 services are indentical in technology except they are based on 30 DS0 (64Kb) with total pipe of 2.048Mbs.
dndtech,

Great Link!!! Thank you.

[Syed-Ali]

Dear all ,
with respect to Pakistani market.

We have ISDN BRIs but with very low quality .
I face a lot of times. the network Errors while conducting the Demossss

[StandByVideo]

I was glad to see Pnutley post.
There actually was life back before IP, and there is a lot of the world for which "T1" still means a bunch of phone lines into the back of a PBX on a single pair.
Seams like you can get real T1 from just about anybody these days.

Clearly the local phone company will still, (what day is it?), sell you T1 meaning that you can have 50 people in a small biz sharing a PBX and dialing out on telephones over 24 available lines.

The 3000 odd CLECS and value - added resellers out there will sell you T1 or Fractional T1 of some flavor.

Then you can get T1 from the long distance carriers, (this is relatively new), and really cheap. Everything becomes a long distance call, even a block away.

Then you can get T1 between Chicago and Toledo which means 24 channels that are accessible only to those folks.
We used to call that a lease line or a span.

Then of course we have the Internet.

T1 in IP speak means how fast can your connection, (shared with a bunch of other folks), go and if the answer is 1.5 meg down, it is a T1

We used to call that frame relay.

Doesn't make it any easier, but it is important to recognize that T1 used to refer to a chunck of expensive bandwidth that was for your exclusive use, PRI still means that, the other definitions sort of depends on who you are talking to.

[fivedos]

George,

FYI...We have both PolyCom and Tandberg systems, and we have a few Tandberg MCU. They work great. Much sharper if you go straight from Tandberg to Tandberg, but still good either way.

[bmoores]

Does anyone have experince in folding back PRI channels back to a PBX when not in use for VTC from an Adtran 55O?

[senthil]

hi
we have a Codian gateway with 2 PRI line. We are providing support E1/PRI any gateway facility.If any one having problem of using PRI's in India drop me a mail.Also if any one wants to make test call in ISDN or IP send me mail.

Senthil.

[trapehzoid]

hi
we have a Codian gateway with 2 PRI line. We are providing support E1/PRI any gateway facility.If any one having problem of using PRI's in India drop me a mail.Also if any one wants to make test call in ISDN or IP send me mail.

Senthil.

how do you like your codian gw? I haven't looked at that one up close. Does it offer any sort of graphical IVR for incoming calls like the MCU does?

[senthil]

hi
Trapehzoid we have the codian gateway connected with codian MCU.
The MCU is giving graphical IVR for incoming calls.If you wants to test that just send me mail I will you our PRI number to you for test.

senthil