AT&T MERLIN LEGEND Release 4.0 Feature Reference page 166

Feature Reference
each T1 trunk. For more information see the Primary Rate Interface and T1
feature.
Basic Rate Interface
The ISDN (Integrated Services Digital Network) NI-1 Basic Rate Interface (BRI)
is a standard access arrangement that can be used to connect the system to a
network providing voice and digital data services. BRI is supported in
Release 4.0 and later systems only. BRI supports two 64-kbps data connections
(known as B-channels) for up to 128 kbps data throughput. For more information
see the Basic Rate Interface feature.
2B Data
The use of two data channels (B-channels) allows BRI devices (such as desktop
video system) to be connected to an MLX port and use full 128 kbps
connections using ISDN NI-1 BRI or ISDN PRI B-channels or 112 kbps if
T1 Switched 56 is used.
NOTE:
For more information about 2B Data see the Data and Video Reference .
Devices that are to be used for 2B Data must be connected to MLX ports that
have the associated adjunct extension programmed as 2B Data capable.
Devices that do not support 2B Data should not be connected to ports
programmed for 2B Data.
The MLX extension numbers used to add 2B Data capability must correspond to
the MFM/Terminal Adapter adjunct extension number for the MLX telephone. By
default, these adjunct extensions are numbered beginning with the digit 7. If the
MLX extension is 20, its corresponding adjunct extension would be 720.
Once an MLX port is properly programmed, a 2B Data capable device properly
connected to that port should operate at the same data rate (up to 128 kpbs) as
an NI-1 BRI line connected directly to a central office.
NOTE:
Users can use any combination of PRI, NI-1 BRI and T1 to obtain a 2B Data
connection. Data transfer speeds are slower on T1 Switched 56 lines (56 kbps
on each line).
Considerations and Constraints
If using desktop video systems in passive bus configuration with an MLX
telephone, and the connected MLX telephone is using one of the B-channels for
any reason, and a 2B data video connection is received by the desktop video
system, the desktop video system can only receive the call as a 1B Data call.
166
Digital Data Calls