ISDN Glossary
-------------

Q.  I'm lost in a sea of strange terms about ISDN.  Can you help?

A.  New technologies always come with acronyms and expressions that can be
daunting.  Here's a list of terms that are used in Northwest Nexus FAQs,
by telephone companies, and by equipment manufacturers.


Analog Call Pre-Emption
-----------------------
For terminal adapters that include POTS jacks, a feature that "borrows"
the second B-channel for an analog call even if that B-channel is in use
for a data connection, then "returns" it to the data connection when the
analog call is ended.  Some adapters support this feature only for
outgoing calls; others support it for incoming calls as well.  Lets you
use both channels for the highest bandwidth data connection, but still
make and receive analog telephone calls without disconnecting the data
connection.


Analog Device
-------------
A phone, fax, modem, or answering machine that communicates over a POTS
line.


Analog Device Port
------------------
An RJ-11 jack for connecting a phone, fax, modem, or answering machine
to an terminal adapter.


Async-to-Sync PPP Conversion
----------------------------
Used in ISDN terminal adapters to convert asynchronous PPP protocol from
serial port to synchronous PPP used by most ISP's ISDN routers.


AT&T Custom
-----------
Extended set of ISDN services, implemented in software for AT&T 5ESS
switches.


B-Channel
---------
See "Bearer Channel."


BACP
----
See "Bandwidth Allocation Control Protocol."


Bandwidth Allocation Control Protocol
-------------------------------------
A proposed IETF standard to provide Dynamic Bandwidth Allocation.


"Bearer" Channel
----------------
The basic building block of ISDN service. Specifically, an ISDN
data-transmission channel of 64-Kbps capacity, used for the "content" of
an ISDN call.  Compare with "Delta" channel.


BONDING
-------
Acronym for a channel aggregation protocol developed by the Bandwidth ON
Demand Interactivity Group.  Combines bandwidth of B-channels for higher
transmission speeds.  Best suited for videoconferencing applications. 
Obsolete for packet-based communications; superceded by multichannel PPP
(MP).


Basic Rate Interface
--------------------
The version of ISDN service most likely to be supplied for residences
and small business.  It consists of two B-channels and one D-channel.


BRI
---
See "Basic Rate Interface."


Central Office
--------------
The telephone company location that contains the telephone switching
computers and at which local loops and trunks terminate.


Channel Aggregation
-------------------
Connection that combines the capacity of two or more ISDN B-channels.
See "Multichannel PPP" and "BONDING."


C.O.
----
See "Central Office."


Cause Code
----------
A number returned by the telephone company switch software that
indicates status or the nature of an problem with establishing a
connection.  Cause codes are the ISDN equivalent of busy signals or
"intercept" messages in conventional telephone service, but are capable
of a far greater range of indications, as befits a more complex and more
capable form of telephone service.  Most ISDN adapters are capable of
storing the cause code that applies to the most recent ISDN call, and
cause codes are reported to the Northwest Nexus side of the connection
as well.  These codes are often useful in debugging connection problems
or verifying proper operation.  Example:  Cause Code 16 means that one
of the parties to the call has "hung up" normally.


D-Channel
--------- 
"Delta" channel; channel (of 16-Kbps capacity in the BRI), primarily
used for communicating between the phone company switch and an ISDN
adapter. In special applications, can also used for packet-switched data
transmission using the X.25 protocol.


Demarcation Point
-----------------
Also called the "demarc," this is the point, often located outside your
residence or business, where the telephone company terminates its wiring
for telephone and ISDN service.  You own, and are responsible for the
installation and maintenance, of the wiring from the demarc to the
telephone jacks into which you plug your telephone or ISDN adapter.


Digital Subscriber Loop
-----------------------
The copper wires between the customer premises and the local central
office.


Dynamic Bandwidth Allocation
----------------------------
The process of determining current traffic loads over a channel, and
automatically increasing or decreasing the bandwidth of the connection
to optimize overall utilization efficiency. In English, a method that
lets an ISDN adapter use a second channel when the volume of data to be
transmitted is high.

Some manufacturers use this same term to refer to a feature that allows
an ISDN adapter to free one of the B-channels in a multichannel
connection to answer an incoming call, and to return the B-channel to
the multichannel connection when the interrupting call is completed.


Directory Number
----------------
The phone number (or numbers) associated with a ISDN line.  Can be
associated by the terminal adapter with a particular B-channel or POTS
port.


DN
--
See "Directory Number."

ISDN
----
Integrated Services Digital Network.


Loop Qualification
------------------
The process performed by the telephone company to ensure that the
digital subscriber loop is of the proper length and is free of bridge
taps and loading coils and therefore suitable for carrying ISDN signals.
This process often takes one to two weeks. 


MP+
---
Proprietary protocol extension developed by Ascend Communications that
adds dialing, control, and DBA ("rubber bandwidth") features to MPP. 
BACP is Internet standard under development to provide same features.


MPP
---
See "Multichannel PPP."


Multichannel PPP
----------------
Also "Multilink PPP," or "ML-PPP."  A standardized channel aggregation
protocol; an extension of Point-to-Point Protocol (PPP). Abbreviated as
"MP" or "MPP," depending on who's claiming credit for inventing it. 
Sometimes called "rubber bandwidth."  Defined in RFC 1717.


National ISDN-1
---------------
Standard set of ISDN services, implemented in software available for all
common switches.


NI-1
----
See "National ISDN-1."  Not to be confused with "NT-1."


NT-1
----
Network Terminator; it converts the two-wire configuration of ISDN to
the four- or six-wire configuration used by ISDN devices.  Most ISDN
adapters sold in the United States include an internal NT-1, making the
purchase and installation of a separate, external NT-1 unnecessary.


Plain Old Telephone Service
---------------------------
The telephone lines installed in 95% of homes and all businesses today.


POTS
----
See "Plain Old Telephone Service."


PRI
---
See "Primary Rate Interface."


Primary Rate Interface
----------------------
"Industrial-strength" ISDN service, consisting of a D-channel and either
23 or 31 B-channels. Delivered via a T-1 circuit, and used by ISPs for
providing ISDN service.


PSTN
----
See "Public Switched Telephone Network."


Public Switched Telephone Network
---------------------------------
The network of switches, trunks, and local loops used to provide
telephone service worldwide.


Service Profile Identifier
--------------------------
A unique number assigned by the phone company to a particular ISDN
adapter (or to each B-channel, depending on local practice); analogous
to the Ethernet address assigned to a particular network adapter card.


SPID
----
See "Service Profile Identifier."


S/T Interface
-------------
The four-wire "bus" upon which ISDN devices with S/T interfaces, such as
ISDN telephones, are interconnected.  Most ISDN adapters in the United
States do not use an S/T interface.


STAC Compression
----------------
Semi-standard method for compressing data for increasing transmission
rates over ISDN connection.  Often implemented in hardware.


Switch
------
Multiport mainframe computer used by phone service providers to connect
callers to circuits.  Three different switches, the products of three
manufacturers, are in common use in North America: AT&T 5ESS, Northern
Telecom DMS 100, Siemens EWSD.  In Washington state, only the first two
switches are in use for ISDN service.


Tariff
------
Documents filed by a regulated telephone company with a state public
utility commission or the Federal Communications Commission (FCC). 
Tariffs describe the details of services, equipment, and pricing
publicaly offered by a telephone company. The bane of ISDN; most ISDN
tariffs are impossibly baroque and complex, and make ordering ISDN
service difficult.


Terminal Adapter
----------------
A device that connects to an ISDN BRI line and provides a data
connection for a computer or network.  ISDN adapters used with Northwest
Nexus Dial-Up ISDN generally have a serial-port interface for a single
computer.  ISDN adapters used with Northwest Nexus Dedicated ISDN
generally have an Ethernet 10baseT or 10base2 connector; some also
include asynchronous or synchronous serial connectors as well.  Many
ISDN adapters used with Dedicated ISDN also include a TCP/IP router.


U-Interface
-----------
The two-wire connection from the telephone company switch to which one
connects ISDN adapters that have an internal NT-1.  Most ISDN adapters
available in the United States today have a U-interface jack and
internal NT-1.


V.120
-----
A protocol for asynchronous communications between ISDN adapters.  Not
used by most ISPs for Internet connections, but useful for establishing
ISDN-modem-to-ISDN-modem connections.


Q:  I'm still interested:  what do I do next?

A.  Obtain and review "Selecting an ISDN Terminal Adapter" (if you
have chosen Dial-Up ISDN service) or "Selecting an ISDN Router" if you
have chosen Dedicated ISDN service.  The complete set of ISDN FAQs
includes the following titles:

	ISDN for Home or Business:  An Introduction and Brief Orientation
    (ISDN basics)
  ISDN Glossary
    (the FAQ you are reading)
	Establishing ISDN Service with Northwest Nexus
		(how to order, install ISDN service)
	Selecting an ISDN Terminal Adapter
		(how to select, overview on install and setup)
	Selecting an ISDN Router
		(how to select, overview on install and setup)
	Configuring Your ISDN Terminal Adapter
	Configuring Your ISDN Router
		(specifics on adapter configuration and software setup)
	Debugging ISDN 
	  (general debugging tips)


Q.  Are there Web sites I should visit to learn more about ISDN?

A.  Microsoft has an excellent Web site that deals with all aspects of
ISDN, from obtaining service to choosing hardware to configuring 
(Windows) software.  Worth reading even if you don't intend to use
any flavor of Windows:

     http://www.microsoft.com/windows/getisdn 
     
GTE and U S WEST both maintain excellent ISDN resource and information
sites:

  U S WEST
    http://www.uswest.com/atwork/interprise/isdn
    
  GTE
    http://www.gte.com/isdn
    
A netizen name Dan Kegel has propelled himself from an unknown graduate
student to a worldwide authority on ISDN by collecting all the ISDN
information he could find and assembling the most comprehensive, detailed,
and exhaustive ISDN Web site in the world:
  
  Dan Kegel's ISDN Site
    http://alumni.caltech.edu/dank/isdn/


Q:  How can I stay up to date on ISDN developments at Northwest Nexus?

You can keep abreast of ISDN at Northwest Nexus by subscribing to one of
our ISDN mailing lists, or by participating in our ISDN newsgroup.

Our ISDN mailing lists are low-traffic, one-way e-mail lists that
contain ISDN-related and news, announcements, and tips.

If you're a Northwest Nexus customer, you may join the isdn-interest
list.  If you're not yet a customer, subscribe to isdn-announce.  Both
lists get news of our latest ISDN products and offerings.

To subscribe, send an e-mail message to majordomo@halcyon.com

In the body of the message, include these two lines:

	subscribe isdn-interest
	end

or

	subscribe isdn-announce
	end


Northwest Nexus also maintains a newsgroup for our users to discuss ISDN issues,
share tips, and troubleshoot problems.  Use your browser or a newsreader and
subscribe to

	halcyon.isdn
	


[1Apr97/MJT]