BRI vs. PRI

[polm]

PRI technology is somewhat simpler that BRI, which is considered multipoint, meaning it has the capability to have multiple ISN devices connected to the same B Channel. As a result, in multipoint networks there is arbitration at Layer 1 and Layer 2, allowing multiple devices to access the network without collisions or interruptions between devices that need to share the ISDN nework.

I am confused about this. Multiple IDSN BRI devices can share a B channel ?

 

[ScottMac]

I believe they are putting it in the context of a SWITCHED circuit (one B channel can be connected to one of many destinations, depending on the number dialed).

Because it is essentially a dial-up service, there is a layer one, layer two, layer three negotiation.

This can be seen on a Cisco router (verify operation) by looking at the following:

(Layer 1): show isdn status - look for "multiple_frame_established:" if there, layer one is up OK
(Layer 2): debug isdn q921 - look for a dialog of "SABME" messages: if there, layer two is up OK
(Layer 3): debug isdn q933 - you'll see the actual dialog between the interface and the switch (Inbound call, voice/data, DN, calling number, etc)

PRIs are usually not used as an aggregated data channel (if used for data, each B channel usually goes to a modem or voice line). For straight-up data, a T1 is much more common.

So, again, I believe their meaning of "multipoint" refers to circuit-switched data (one-to-(one-of-many)).

You CAN have "nailed up" BRIs (individually or multi-linked), but they are not that common outside of IDSL.

Good Luck

Scott