Common ISDN standards cheatsheet.  See www.boson.com for updates.
	Copyright (c) 1999 by Boson Software
	Written by dave@boson.com

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OSI  LAYER-3  ISDN  BRI:  Between the TE (router/workstation) and the ET (telco switch)
Layer 3 services include call setup, call tear-down, and data transfer.
The single 16k D channel uses Q.931
The ISDN device must have the correct telco switch type, SPID, and DN configured.

OSI  LAYER-2  ISDN  BRI:  Between the TE (router/workstation) and the ET (telco switch)
Layer 2 services include TEI assignment and layer 3 signaling negotiation.
The single 16k D channel uses LAPD as per Q.921
The dual 64k B channels use PPP or HDLC

TE1: Terminal Equipment type 1:
Native (digital) ISDN devices.  In Europe, this can be part of your native S-Bus.

TE2: Terminal Equipment type 2:
Older style analog equipment, or devices that can be handled by a TA.
In the USA, this represents the POTS ports on your U-Interface device.

TA: Terminal Adaptor:
Literally adapts other kinds of equipment, like async or ethernet, to ISDN.

NT1: Network Termination type 1:
Beginning of the Customer Premise Equipment, not physically at the telco.
Outside the USA, the telco provides the NT1, and an "S/T" interface is provided.
Inside the USA, the customer must purchase the NT1, and a "U" interface is provided.

NT2: Network Termination type 2:
Typically integrated into a single "S/T" interface, providing S-Bus connectivity.
This connecting point could be further broken down by a large telephone switch.

LT: Line Termination:
This is the physical connection into your local telco's network.

ET: Exchange Termination:
This is the local telco's logical connection from your ISDN into the "Cloud."
Typically, this is physically represented by a very large phone switch.

Some people get the TE1 and TA confused.  For example, you purchase an ISDN "modem" for
your computer that uses dialup networking - your computer is now a TE1.  But, if you
purchase an ISDN "router" that your local LAN uses for networking - your computer is
now a TE2 and the router is a TA.  The NT1 is probably just the physical connector.

R: The TA interface that provides Plain Old Telephone Service (POTS).

S: The S-Bus allows native ISDN S-Bus devices to speak native digital ISDN.

T: The physical wire between the NT1 and NT2, which are usually one and the same.

U: ANSI (American-only) standard for combining the NT1, NT2, and TA into a single
local and physical chipset or device, for cost savings.  This means that the telco
must provide a totally different 2-wire ISDN BRI physical interface to your premise,
instead of the 4-wire international standard.

V, LT, ET: Typically refered to as the telco "cloud", using large phone switches.


