At a lower level a PRI is a channelized T1 with ESF framing and B8ZF
encoding. This gives you 24 x 64kbps channels.
Channels 1 to 23 are "B channels" which are used to carry data, or
digitized voice. What is carried and how many "B Channels" are used in
a call is controlled by the "D Channel".
The 24th channel is known as the "D channel". It is used to communicate
ISDN signalling (Q.931) between the ISDN switch and the ISDN
endstation. The signalling does things like call-setup, call-release, &
signals optional parameters like BONDING (muxing) modes, caller ID info,
etc.
Note: Cisco numbers the channels 0 to 23; so channel 23 is the D
channel.
The D Channel is used to negotiate call parameters. Type of data,
Bonding mode (muxing), number of B channels being used for the call, who
is calling (for caller-id) etc. The call parameter negotiations must
first be completed before the B channels are asigned to be used.
To answer your question is it "just ISDN with a bigger pipe": YES
Does it create/accept and assign B channels dynamically: YES
Can individual B channels be used for different calls and/or differnet
types of data: YES
Does PRIs and BRIs use the same signaling (Q.931): YES
Do the PRIs dial: YES (they have ISDN phone numbers just like BRIs)
Basically you can use PRIs for higher speed connections (greater than
128Kbps), and they are reall handy when you are setting up a dial-in
platform. One circuit/cable and you can handle up to 23 calls...
Hope it helps
DaveC
Chris Wornell wrote:
>
> Hello,
>
> For some reason, PRI has racked my brain ever since I learned about it.
> >From what I understand, its basically a line with 23 64kb B channels and 1
> 64kb D channel. The thing I'm confused about is I always see it mentioned
> with ISDN. Is it really just an ISDN line with a bigger pipe? Is there
any
> sort of dialing required when using it? Does it use the same protocols as
> ISDN? Can you use each channel for either voice or data dynamically like
> BRI? Any information would be helpful.
>
> Thank you,
>
> Chris Wornell
> CCNA, CCDA
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