Unframed isochronous shaping method to reduce delay and...

Details Unframed isochronous shaping method to reduce delay and... Unframed isochronous shaping method to reduce delay and...

1997-10-27

2001-02-27

Nguyen, Chau (Department: 2772)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

C370S395430

Reexamination Certificate

active

06195333

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
The present invention is generally related to telecommunications apparatus, and more particularly to virtual circuits in telecommunications apparatus.
Voice carrying connection standards such as T
1
and T
3
multiplexed digital channels are well known. A T
1
connection carries 24 standard voice channels and a T
3
connection carries 28 T
1
connections. T
1
and T
3
connections can also carry video signals and computer data. T
1
and T
3
are synchronous systems in which each individual voice connection has periodic time slots within which to transmit voice carrying data. Asynchronous systems, such as Asynchronous Transfer Mode (“ATM”) networks, are also known. ATM networks can carry different types of data such as voice, video and computer data. However, while ATM systems are capable of transmitting voice data, the voice data is transmitted asynchronously.
Under some circumstances it is desirable to integrate synchronous networks and ATM networks. For example, voice data could be received by a first ATM switch from a “circuit” in a first synchronous network, propagated asynchronously to a second ATM switch through a “virtual circuit,” and subsequently transmitted over a circuit in another synchronous network. In order to prevent gaps from occurring in the second synchronous network the second ATM switch must maintain a sufficient reserve of voice data units in a “playout buffer” to fill each time slot allocated to the voice connection in the second synchronous network with voice data. However, if the voice data units must be transmitted through many ATM switches, the amount of memory required to maintain a sufficient reserve of voice data units in the playout buffer can become prohibitively large. More particularly, as the number of intermediate ATM switches increases, the effect on variable transmission delay at each subsequent downstream ATM switch in the virtual circuit is cumulative.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, flow shaping is performed at each asynchronous device in a virtual circuit. More particularly, the flow of data units through the virtual circuit is controlled at each asynchronous device such that the variable transmission delay remains substantially constant throughout the virtual circuit.
Flow shaping at each switch in the virtual circuit facilitates use of Asynchronous Transfer Mode (“ATM”) networks in association with synchronous networks. Flow shaping causes variable transmission delay to remain substantially constant throughout the virtual circuit. Further, because variable transmission delay remains substantially constant throughout the virtual circuit, the size of the playout buffer in the furthest downstream ATM switch need not be adjusted depending on the number of intermediate ATM switches in the virtual circuit. Hence, an ATM virtual circuit having an arbitrarily large number of intermediate ATM switch “hops” can be initiated without increasing the playout buffer size in the furthest downstream ATM switch.


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