Browse Prior Art Database

Distributed ISDN Call Control from Comm Port AT Dial Strings

IP.com Disclosure Number: IPCOM000123329D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 56K

Publishing Venue

IBM

Related People

Chandler, R: AUTHOR [+5]

Abstract

A controllerless, DSP-based modem performs communications functions autonomously, transmitting data received over its UART-like port to a PC's internal bus by compressing it (V.42bis), packetizing it (V.42), modulating it (e.g., V.32bis), and transmitting it. Receive data takes the reverse path. However the DSP on such a modem does not handle call control autonomously. Besides the standard comm-port (UART) interface that the modem makes visible to applications, the modem has private pipes (interrupt, bus master DMA, mailboxes) to routines running in the host PC for support, including an AT command parser. When an AT command is received by the DSP's comm-port interface, it is sent to the AT parser for interpretation.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 57% of the total text.

Distributed ISDN Call Control from Comm Port AT Dial Strings

   A controllerless, DSP-based modem performs communications
functions autonomously, transmitting data received over its
UART-like port to a PC's internal bus by compressing it (V.42bis),
packetizing it (V.42), modulating it (e.g., V.32bis), and
transmitting it.  Receive data takes the reverse path.  However the
DSP on such a modem does not handle call control autonomously.
Besides the standard comm-port (UART) interface that the modem makes
visible to applications, the modem has private pipes (interrupt, bus
master DMA, mailboxes) to routines running in the host PC for
support, including an AT command parser.  When an AT command is
received by the DSP's comm-port interface, it is sent to the AT
parser for interpretation.  The support code converts that to the
appropriate off-hook and tone generation commands, which are sent to
the DSP.  Call progress tones from the network are interpreted by the
DSP and indications are passed to the host PC.  In addition to the
UART interface, a more efficient Media Control Interface may be used
by applications (e.g., for fax).

   Described below are the extensions to this technique
required for a DSP-based ISDN adapter with modem capability. Goals
are to perform protocol processing on the host PC and to minimize
impact on the modem function.  This is accomplished by creating a DSP
task (ISDN BIOS) which duplicates the function performed by the prior
analog task, interc...