AAL2 negotiation procedure

Details AAL2 negotiation procedure AAL2 negotiation procedure

1998-08-27

2004-09-07

Vanderpuye, Kenneth (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395100

Reexamination Certificate

active

06788691

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to digital communications networks, and particularly, although not exclusively to an arrangement and method for enabling a plurality of channels to occupy a single asynchronous transfer mode (ATM) connection.
BACKGROUND TO THE INVENTION
The known asynchronous transfer mode (ATM) transmission technique is, a modern telecommunications switching technique which is able to switch connections for a wide range of different data types at a wide range of different bit rates. ATM technology provides a flexible form of transmission which allows various types of service traffic data, eg. voice data, video data, or computer generated data to be multiplexed together onto a common physical means of transmission. Currently, several trends are encouraging the widespread introduction of ATM; for example the availability of high speed, low error rate communication links between switching centers, an availability of technology to digitize video and speech, and pressure to reduce operating costs by integrating previously separate telephony and data network. ATM technology allows speech data, video and inter-computer data to be carried across a single communications network. The information carried in each of these services is reduced to digitized strings of numbers which are transmitted across such a communications network from point to point.
Referring to
FIG. 1
herein, there is illustrated schematically a pair of known interworking functions
101
and
102
connected by an ATM virtual channel connection (ATM VCC)
103
across an ATM network
100
.
FIG. 1
illustrates a pair of interworking functions which may be residing at a pair of distinct telecoms resources eg switches, cross connects, comprising processing means and memory means. It will be understood by those skilled in the art that a plurality of interworking functions may be interconnected over a plurality of ATM VCC. Incoming to first interworking function
101
are, for example, a plurality of digitized voice signals multiplexed together using the E
1
or T
1
mutiplexing systems. First and second interworking functions
101
and
102
are configured to convert data arriving in a plurality of forms and conforming to a plurality of different data standards into a form suitable for transmission over ATM VCC
103
across ATM network
100
. Interworking functions
101
and
102
are also configured to perform conversion of data sets across ATM network
100
back into a plurality of different data standards. Each of these incoming channels may carry data at a bit rate of 64 kilobits per second (kbits/s).
There is a financial cost associated with leasing sufficient bandwidth between interworking functions
101
and
102
to transmit a plurality of uncompressed 64 kbits/s channels down a single ATM virtual circuit
103
. Therefore, it is known to apply a range of different data compression techniques in order to make more efficient use of the available band width. For example, the known G series data compression techniques can be used to compress streams of data having a bit rate of 64 kbits/s down to bit rates of 40 kbits/s or 8 kbits/s. In addition, speech activity detection (SAD) techniques can be used to suppress pauses in speech data allowing other data to be inserted in the gaps. After compression, there may exist a plurality of compressed 8 kbits/s data to be transferred between interworking functions
101
and
102
across ATM virtual channel
103
via ATM network
100
. The plurality of compressed channels of data may represent a plurality of calls between a plurality of users.
Referring to
FIG. 2
herein, there is illustrated schematically first and second interworking functions
101
,
102
represented as a set of functional layers. Each interworking function comprises the following protocol stack of functional layers:
a Service Specific Conversion Sub-layer (SSCS)
201
into which compressed voiced data are input and output;
a Common Part Sub-layer (CPS)
202
;
an ATM Sub-layer
203
; and
a Physical Sub-layer
204
.
The set of functional layers
201
to
204
are well known in the art. Each functional layer within the protocol stack is configured to exchange information with the functional layer above it and the functional layer below it. The exchange of information between functional layers within the protocol stack enables each functional layer to provide a service for the functional layer immediately above it. Each functional layer can be considered to exchange information directly with the same functional layer within a protocol stack residing within a distant interworking function across a virtual channel. The exchange of information between interworking functions
101
and
102
is actually effected by the exchange of information across a physical connection between physical sub-layers
204
and
208
. Compressed voice data which are input into the interworking function
101
by the Service Specific Conversion Sub-layer
201
are transferred across an ATM network to the remote second interworking function
102
which comprises a similar protocol stack to interworking function
101
. The output of Service Specific Conversion Sub-layer
205
of first interworking function
102
is compressed voice data.
Whilst transmission of compressed voice data is shown in one direction in
FIG. 1
, the protocol stacks are bi-directional and transmission can occur in both directions between first and second interworking functions
101
,
102
.
In
FIG. 2
herein there is illustrated a single Service Specific Conversion Sub-layer
201
associated with interworking function
101
. In a real network there may be a plurality of such Service Specific Conversion Sub-layers receiving a plurality of compressed voice data channels. The Common Part Sub-layer
202
is configured to receive a plurality of compressed voice data channels from the plurality of Service Specific Conversion Sub-Layers and multiplex the plurality of compressed voice data channels together. The combination of Service Specific Conversion Sub-layers
201
and Common Part Sub-layer
202
in interworking function
101
are also known in the prior art as ATM Adaption Layer Type
2
(AAL2).
In order to make best use of the available band width over a single ATM VCC it is known to have a plurality of channels carrying a plurality of, for example, compressed voice data channels. In order to be able to carry a plurality of separate streams of digital data across a network using a plurality of ATM AAL2 channels over a single ATM virtual channel connection (VCC), there is a need to be able to identify individual ATM AAL2 channels at both interworking functions.
SUMMARY OF THE INVENTION
Specific embodiments and methods according to the present invention aim to facilitate the establishment of a plurality of ATM AAL2 channels across a single ATM virtual circuit, thereby providing a more efficient use of available band width in communications networks.
According to a first aspect of the present invention there is provided a method of communicating a plurality of AAL2 channels over an ATM virtual channel connection between first and second communications entities, said method comprising the steps of:
maintaining a stored record of a plurality of channel identifiers relating to a plurality of AAL2 channels; and
establishing an AAL2 channel on a virtual channel connection by sending and receiving a plurality of messages over an AAL2 channel between said first and second communication entities,
wherein said messages operate on said stored record of channel identifiers to modify said channel identifiers into an assigned state indicating an AAL2 channel has been assigned to a virtual channel connection, or an unassigned state, indicating an AAL2 channel is unassigned to a virtual channel connection.
The invention includes a method of establishing an AAL2 channel over an ATM virtual channel connection comprising the steps of:
maintaining a stored record of a plurality of channel identifiers relating to a corresponding plurality of AAL2 channels; an

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