Northern UTA220/UTA220k - Manual (Page 40)

4-6
UTA220/UTA220k
ISDN
The TEI is used to identify the terminal device. In most
applications, the network switch automatically assigns a TEI
to the TA when the connection is established; otherwise, you
must enter the TEI before connecting to the network.
If your switch permits it, the UTA220 allows you to use one
SPID and one TEI on simultaneous calls. AT&T switches
allow two calls per SPID. With this support you can configure
two or more ports to share a DN.
Note: To use this feature, configure each port with the same
SPID and DN, enable one port’s TEI, and disable the TEI on
the remaining port(s).
The UTA220 also allows you to use multiple DNs on the same
SPID if your switch supports it. NT switches support up to four
DNs per SPID.
Note: To use this feature, configure both ports with the same
SPID and different DNs, then enable one port’s TEI and disable
the other’s.
ISDN CHANNELS
As previously mentioned, there are three channels available on
the ISDN Basic Rate Interface: two 64 Kbps B-channels and
one 16 Kbps D-channel. The B-channels are the primary means
of carrying user information, whether voice or data. Voice data
must be sent on a B-channel. The B-channel also provides the
most efficient path for data communications, since it has four
times the data capacity of the D-channel.
The D-channel is the control channel between the TA and the
network switch. It is used mainly for exchanging signaling
messages with the switch, to perform functions like setting up
and releasing calls.
Note: The UTA220 supports only data calls.
B-Channel Data Service
When a B-channel data call is placed, the switch allocates a
free B-channel between the TA and the remote DCE (e.g., the
TA at the other end of the ISDN link). This B-channel acts like
a bit-pipe between two network users, operating
synchronously at 64 Kbps. In most cases, the ISDN network
does not know about the format of the data sent on the
B-channels.
There are several ways to use the B-channel to pass data. In
the “clear channel” mode, data from the DTE goes directly
onto the B-channel. However, to use this mode, your DTE must
also operate synchronously at 56 or 64 kbps.