HP 200 Series Services And Applications page 214

Improving Network Availability
Switched Circuit Types
V.25 bis Adapter
V.25 bis is a CCITT data-communications standard that defines a set of
commands exchanged between a DTE and a DCE. These commands control
setting up and tearing down switched communications services. V.25 bis is
similar in concept to the Hayes AT command set used in PC-to-modem
communications. Unlike the AT commands, V.25 bis commands are used on
a synchronous interface. Many ISDN terminal adapters and Switched 56
DSUs/CSUs now support V.25 bis. In addition, V.25 bis is available on some
high-speed analog modems (when set up for synchronous operation).
HP routers support V.25 bis, plus extensions to V.25 bis that have been
defined by Cisco Systems, Inc., and Ascend Communications, Inc. The V.25
bis extensions are primarily used to control parameters used with inverse
multiplexers such as the Ascend Multiband.
The use of V.25 bis adapters provides a superset of the capabilities described
previously for manual adapters. Additional capabilities provided include:
Bilateral communication initiation and establishment. Each side of
the switched connection can dial the other party and establish
communication. V.25 bis supports connecting when "data is available
or on incoming calls", rather than when "data is available" as is the
case using manual adapters.
Enhanced security. A router may be set up to accept calls only from
a predefined list of originating phone numbers (on adapters that
return incoming numbers).
A circuit-switched port can be configured to dial several different
numbers. In the event that the first number dialed encounters a
problem (such as a busy condition), another number can be dialed.
Interface for parametric control of devices such as the Ascend
Multiband inverse multiplexer for bandwidth-on-demand
applications.
Pooled circuit switching (IP only). This feature allows a circuit-
switched port to receive or originate calls to a maximum of 16
different networks or subnetworks. Circuit-switched ports may be
pooled such that up to three ports can be used as interfaces to a
maximum of 16 (sub)networks.
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