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ISDN Configuration Guide G-1
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This appendix contains supplemental ISDN configuration information.
This section covers the following topics:
■ “Definitions” on page G-1
■ “Dynamic B-channel usage” on page G-1
Definitions
The following terms are used in this appendix:
Directory number: The actual phone number associated with the ISDN line you order. Depending on the type of
switch protocol used on your line, there may be one directory number for both B-channels, or one for each
B-channel.
If you encounter other unfamiliar terms, check the glossary.
Dynamic B-channel usage
If the B-Channel Usage item in a connection profile’s PPP/MP Options screen is set to Dynamic or 2 B,
Pre-emptible, one or both B channels may be in use at any time during a call made with that connection profile.
Use of the second B-channel depends on traffic volume.
In addition, one of the B-channels may be relinquished if there is an incoming call, or if a second outgoing
connection is made using another connection profile.
The ability to allow incoming calls when both B-channels are in use depends on the type of switch protocol on
the local ISDN line, and how that line is provisioned (configured). Some types of switch protocols never allow
incoming calls when both B-channels are in use. Switch protocols that do allow incoming calls must have the
additional call offering (ACO) parameter turned on for data. ACO for data is off by default.
To find out if your switch protocol supports ACO, or to turn ACO on, contact your ISDN service provider.
Other incoming call restrictions
A B-channel will not be relinquished to admit an incoming call if a connection profile has B-Channel Usage set
to 2 B-Channels.
A B-channel will not be relinquished to admit an incoming call when there are two separate concurrent calls.
Incoming calls are automatically allowed in when there is at least one B-channel free.