Browse Prior Art Database

Flowing Voice Data Over Unsynchronized Clocks

IP.com Disclosure Number: IPCOM000118224D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Bowater, R: AUTHOR [+2]

Abstract

Digital telephony trunks synchronously clock many channels of voice data over Time Division Multiplexed (TDM) buses. Each frame of data is clocked every 125 microseconds.

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This is the abbreviated version, containing approximately 52% of the total text.

Flowing Voice Data Over Unsynchronized Clocks

      Digital telephony trunks synchronously clock many channels of
voice data over Time Division Multiplexed (TDM) buses.  Each frame of
data is clocked every 125 microseconds.

      There is a common requirement for Computer Telephony
Integration (CTI) systems to flow data from different digital trunks
with different clocks onto a common TDM bus with its own clock.

      Relative to the common TDM bus clock, the digital trunk clocks
are not necessarily phase synchronized and are only approximately
frequency synchronized.  Thus, the digital trunk clocks will randomly
jitter and possibly slowly drift relative to the TDM bus clock.

      The scheme described provides a mechanism for flowing data from
one data bus having one clock to another having a different clock
while minimizing the corruption of the data and correcting for
detected clock drift without introducing significant latency into the
flow of data from one data bus to the other.

      The solution involves the introduction of circular buffers
into the system.  Each buffer consists of eight slots.  Each slot is
capable of holding all of the digital samples for one frame of a 8kHz
clock---that is, 125 microseconds worth of digitally sampled data.
The process interfacing to the digital telephony trunk accesses a
slot of the buffer on each 125 microsecond frame of the trunk's
clock, moving in a circular manner around the buffer.  The process
interfacing to the  TDM bus would, on each 125 microsecond frame of
the TDM data bus clock,  access the buffer in exactly the same way.
The system is initialized so that the trunk process accesses a slot
as far away as possible from  the slot being accessed by the TDM
process.  The slots in the buffer are sequentially numbered from 0 to
7.  Thus, the trun...