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T1 configuration

i am bit confuse about the concept that.....what sthe differenc between PRI and T1....or they r both what sthe difference between chanlized and unchnalized T1......i was configuring my router having PRI card.....some how i created Tunnel 1.....i dont know whats that an dwhy it was created as i was trying to config T1.....kindly help me out as i am bit new in this field....thanks in advance


Re: T1 configuration

Although both T1 and PRI use the same low-level signaling (i.e., ESF/B8ZS), that's pretty much where the similarity stops.

ISDN uses a control language over the assigned "D" channel to handle the coordination of the traffic over the remaining 23 "B" (Bearer) channels.

If you do a "DEBUG ISDN Q921" you'll see the layer two ISDN managment traffic: if you do a "DEBUG ISDN Q931" command, you'll see the layer 3 ISDN management traffic (call setup, call progression, call ending) ... the ISDN L2/L3 is not part of the Ethernet & TCP/IP L2/L3 ... consider it a sub-layer.

A T1 at the same level, does not have that kind of coordinating protocol. A T1 (channelized) usually relay on a few "robbed bits" (RBS - "Robbed Bit Signaling" Also CAS - "Channel Associated Signaling") to indicate phone off-hook, inbound ring, and perhaps some other info, depending on the endpoint systems.

For a pure data application, the T1 bandwidth is unchannelized and is pretty much a raw bit stream used with an encapsulation like HDLC, PPP, or Frame-Relay.

To use more than one channel on a PRI for data, the channels must be aggregated using protocols like BONDING or MLPPP.

Here's a link to isco's Internetworking Guide online:

It does a pretty good job of covering the high-level details on all of the technologies and protocols.

Good Luck


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