[Asterisk-Users] Difference between E1 and PRI

[Scott Stingel]

Alistair-

Good writeup!   Question regarding Q.SIG:  Can it be used to solve the 
problem of signaling a remote switch to "take a call back" and extend it 
to another channel instead?   This, as you know, is always a challenge 
when using IVR in a call centre environment, when one wants to extend an 
IVR call to a live operator without holding up channels in the IVR.

Regards,
Scott Stingel
Emerging Voice Technology, Inc.
www.evtmedia.com


Alistair Cunningham wrote:

> Eric,
>
> E1 is a physical layer protocol, like ethernet. It defines a 2Mbps 
> pipe, which can be used for data, or can be split into 32 64Kbps 
> telephone channels, or a mixture. If used for telephone channels, 30 
> of these channels can carry one telephone conversation each, and 2 
> carry signalling and timing information.
>
> T1 is similar to E1. It is used in North America. It is 1.544Mbps, and 
> can carry 24 telephone channels, each of which can carry a telephone 
> conversation (but see below).
>
> There are a number of protocols which can run on top of E1. Some of 
> these are called CAS, Channel Associated Signalling. Examples are FXS 
> loop start and E&M wink start. They provide information such as the 
> number that was called, and what state the call is in. They're limited 
> in what information they can carry, and are slow to set up.
>
> A more modern protocol which overcomes these problems is ISDN. On E1, 
> EuroISDN is the standard. On T1, there are different standards from 
> different providers. DMS100, DMS250, NI1, and NI2 are common examples. 
> ISDN uses one channel (called the D channel) for signalling call 
> information. On E1, this is one of the 2 signalling channels, leaving 
> 30 channels for voice (called B channels). On T1, there aren't any 
> spare signalling channels, so one of the voice channels is used, 
> leaving 23 B channels for voice.
>
> A PRI (Primary Rate ISDN) is simply an E1 or T1 with ISDN on top of 
> it. ISDN gives fast, reliable call setup and hangup detection, and 
> detailed information about the call. In the UK, PRI is also called 
> ISDN30.
>
> An important extension to ISDN is Q.SIG, which provides extra 
> signalling information that is used when connecting PBX systems.
>
> An alternative to PRI is BRI (Basic Rate ISDN), which is a cheaper 
> system for small offices. It has 2 64Kbps B channels for voice, and 1 
> 16Kbps D channel for signalling. It is sold as an alternative to 
> analogue telephone lines. IN the UK, it is also called ISDN2e.
>
> I hope this answers your question! My company offers commercial 
> support and installation services for PRI and Asterisk if you need 
> help for specific scenarios.
>
> This email may form the basis of a future Integrics Tip. See:
>
> http://integrics.com/tips/
>
> Alistair Cunningham,
> Integrics Ltd,
> Telephony, Database, Unix consulting worldwide
> +44 (0)7870 699 479
> http://integrics.com/
>
>
> Eric Bishop wrote:
>
>> Hi all,
>>
>> I have seen the term E1 and PRI used interchangably when referring to
>> a voice service with 30B channels and 1 D channel. Are they just
>> different terms for the same thing or is there some technical
>> difference. Even Newton's telco dictonary seemed a bit fuzzy on this
>> topic. I have seen it said the PRi is a protocol that runs on top of
>> E1. Is this true?
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