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ISDN PRI (E1)

Discussion in 'Network+' started by supernova, Nov 18, 2008.

  1. supernova

    supernova Gigabyte Poster

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    I am not actually doing the N+ but i know its a part of the N+ and some of you may have experiance from work as well.

    I just read that a E1 PRI has 30 B channels and 1 Delta 30B+D ... thats fine

    However i am sure when i had a PRI installed years ago for phones via a PBX it was 32 channels and 2 were control

    Anyone?

    Or was that extra channel something to do with the backup power battery
     
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  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Every PRI that I've seen was either co-ax, Twisted Pair (i.e. ethernet-like) or fibre.

    I've *never* seen it wired as a 32 way cable!

    Are you sure you aren't thinking of the 32 channels that a PRI is divided up into?

    30 are use for voice/data, 1 for signalling, and 1 for link control.

    Harry.
     
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  3. supernova

    supernova Gigabyte Poster

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    Thanks Harry

    Yes sorry i mean channels, not physical and what they are eventually broken out into. (corrected original)

    anyway, signalling must be the d channel so the remainder must be link controller?

    I wonder why the link controller wasn't mentioned ?

    30B+D is how the standard is written and described as 31 channels
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Yes - the D channel in PRI is usualy ch 16.

    No idea - ask them.

    Er - what standard are you referring to here? G.704 is the usual one, and defines variations depending on use.

    Harry.
     
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  5. r.h.lee

    r.h.lee Gigabyte Poster

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    AndiC,

    I think you're getting confused between ISDN and leased line.

    For ISDN, from Customer Premises to Central Office, for ISDN PRI in Europe, there's 30 channels of which 1 channel is used for signalling, so effectively ISDN PRI = 29B+1D.

    For E1, from Customer Premises to Central Office, for E1 in Europe, there's 32 channels. So I don't think it was an ISDN PRI that you installed to the PBX. PBX - Central Office is usually an E1 link and not an ISDN PRI link.

    The way I remember the difference between ISDN and leased line is who calls who. For ISDN, it's the customer who "dials up" the temporary uplink. For E1/T1, it's the central office that called the customer premises equipment and stays permanently up as long as the customer keeps paying the bills. Did this help clarify the difference?

    Source:
    1. Internetworking Technology Handbook - Dial-Up Technologies - http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Dial_up.html#wp1020586
     
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  6. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Sorry - but this isn't quite right. And the Cisco page referenced doesn't really help here!

    In Europe an E1 is 2048kbps, divided up into 32 64kbps channels. 30 of these are 'bearer' ('B') channels, one is the signaling channel, and one is a link status channel. So PRI in europe is 30B+1D.

    Some info is given here.


    The article you quote talks about PRI and CAS, but in Europe CAS is now nearly obsolete - we have hundreds of PRIs here, but none use CAS.

    In the UK most leased lines are provided using DSL technology rather than fractional E1s which at one time was common.

    Harry.
     
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  7. supernova

    supernova Gigabyte Poster

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    Hi

    Problem solved

    I believe some telecoms companies non-bt do provide 32 channel PRI's, especially GSM providers and I believe we did have a direct connection with a mobile provider because we deployed devices with GSM in them.

    I'll have to call a co worker from the time.
     
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  8. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    I'd be interested to hear what it was.

    Normaly a 32 channel PRI is used as a second link along with a 'main' PRI. I know in SS7 you can use the signalling on one E1 to control other E1s, so the signalling channel could be used as a bearer. I *believe* ( but can't find the reference) that this can be done with ISDN as well.

    Harry.
     
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