Filter
Top Products
7-8 DATA CONNECTIVITY — AN OVERVIEW
_ ___________________________________________________________________________________________________________________________
_ ___________________________________________________________________________________________________________________________
_ ___________________________________________________________________________________________________________________________
Channel Assignment — Dial-up vs. Dedicated Connections
The assignment of a communications stream to a path or channel through a circuit switch is made
dynamically or on a permanent basis.
• The dynamic assignment of a communications stream to a channel is provided when the user dials the
telephone number of the destination. The resulting connection is sometimes called a dial-up
connection.
• When the originating DTE cannot dial a destination, an internal switch channel can be permanently
assigned to the connection. The permanent assignment of a communications stream to a channel is
achieved through a feature called the dedicated switched connection on the System 85 (R2V3 and
R2V4*) and Generic 2 communications system. On the System 75 and Generic 1 communications
system, permanent assignments are provided through the permanent switched connection feature.
Connections that result from these features are sometimes called nailed-up connections.
Permanent and dedicated switch connections can be used for connections that normally require special
wiring. One application is in the connection of packet switches through a dedicated channel on the System
75, System 85, and Generic 1 and 2. See chapter 9 to determine how these connections are configured.
Channel Information — Bearer vs. Signaling Channels
Channels on a communication link can pass data created at the originating DTE, or signaling data created
by the switch or DCE.
On DS1 links administered for 24th-channel signaling, the switch creates and inserts signaling information
on the 24th channel. All other channels pass DTE/DCE-created information.
On PRI links, the switch uses the D-channel to pass both signaling and caller information. The D-channel’s
ability to carry information is used in telemarketing gateway applications to give a host information on an
incoming call. It is also used in the lookahead interflow application to tell a switch of an upcoming ACD
call. (See chapter 8 for more details on the telemarketing gateway applications.)
Note: Although the Generic 2 communications system provides a BRI port, which interfaces with the
ISDN-BRI standard of two B-channels and one D-channel, it cannot handle X.25 packets transported over
the D-channel.
Transmission Mode Changes and Modem Pools
Data is carried over communications channel as analog or digital signals. The type of signal used depends
upon the type of facilities available. The transmission mode of digital data that must travel over analog
facitilies must change to analog before those facilities can carry it. Similarly, analog data destined for a
digital port must be changed to digital.
__________________
* Only the System 85 R2V4 can send data over a dedicated switched connection.