Multi-Channel Basic Input/Output Interface for Integrated Services Digital Network
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Davis, GT: AUTHOR [+3]
A method for interfacing multiple tasks to the time-division multiplexed channels within an Integrated Services Digital Network (ISDN) physical interface is disclosed. Individual channels are separated into separate input and output circular buffers, and where necessary sample rate conversion is provided to match the requirements of the task.
Multi-Channel Basic Input/Output Interface for Integrated
A method for
interfacing multiple tasks to the time-division
multiplexed channels within an Integrated Services Digital Network
(ISDN) physical interface is disclosed. Individual channels are
separated into separate input and output circular buffers, and where
necessary sample rate conversion is provided to match the
requirements of the task.
Digital Signal Processor (DSP), available from
IBM** Microelectronics Division, supports multimedia environments
which include telephony, audio, and video processing. A
operating system makes it possible to have multiple such tasks active
concurrently. The Mwave communications subsystem, in order to
support standard analog modems, uses a simple Basic Input/Output
Services (BIOS) task to interface between various application tasks
running in the DSP and the circular buffers used by the hardware to
connect with external analog codec chips which generate the
real-world signals required by the telephone network. In an ISDN
adapter, multiple sub-channels must be multiplexed into a single
circular buffer. (Two 64 Kbps "B" channels, one ISDN Call control
"D" channel, and miscellaneous. Physical layer control functions all
have to be combined in a time-division multiplexed fashion). When
analog signals are being passed through a "B" channel, a conversion
must take place between the logarithmic coding standard used within
the ISDN network and linear sampled data required by various DSP
algorithms. An additional complication is the requirement to
samples at 9600 Hz instead of the ISDN standard sample rate of 8000
Hz. Modem algorithms typically require this sample rate conversion
which is accomplished in an Interpolator/Decimator process.
All of these
functions have been incorporated in an ISDN BIOS
task illustrated in the Figure. The ISDN BIOS task uses several
standard Mwave data structures to communicate with other adapter
tasks running in the system:
General Purpose Connector (GPC) A GPC is circular buffer used to
data streams between adapter tasks. A task's output GPC resides
the task's data segment.
Inter-Task Control Block (ITCB) An ITCB allows an adapter task to
share a block of data with another adapter task. A task's
primary ITCB resides in that task's data segment. A task's
secondary ITCB resides in another task's data segment.
System Control Blocks (CTL) A system control block, hereafter
referred to as a control block, allows an adapter task to
share a block of data with a system task. The control
block resides in the adapter task's data segment.
BIOS task in a conventional analog modem subsystem
provides a connection between hardware-driven circular buffers
(interfacing to an analog codec chip) and the GPC buffers which
connect to the modem tasks. T...