Telephonic communications – Plural exchange network or interconnection – Interexchange signalling
Reexamination Certificate
1999-03-12
2002-08-13
Matar, Ahmad F. (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
Interexchange signalling
C379S229000, C379S211010, C370S328000
Reexamination Certificate
active
06434229
ABSTRACT:
This invention relates to a channel associated signalling (CAS) compatible telecommunications node and software platform therefor.
BACKGROUND OF THE INVENTION
There are two common digital communications formats; firstly T
1
which is a 24 channel format utilised in the US and Japan and secondly E
1
which is a 30 channel format utilised in the rest of the world. The T
1
standard is set by the American National Standards Institute (ANSI) and runs at a clock rate of 1.544 Mbits/s. The E
1
standard is set by CEPT (the conference of European postal and telecommunications administrations) and operates at a clock rate of 2.048 Mbits/s. In T
1
channels signalling is carried within each of the 24 time slots whereas in E
1
channels signalling is carried within time slot
16
.
Channel Associated Signalling (CAS)
CAS is a signalling protocol, the fundamentals of which will be explained in this section, with reference to
FIG. 1
, although many national variations apply. CAS protocols are approved by a number of standards bodies including ITU (International Telecommunications Union) and ETSI (European Telecommunications Standards Institute).
As mentioned above in the E
1
format a connection is split in time into 32 individual time slots in which time slot “0” is used for frame signalling information and channel
16
is used for line signalling information. Register signalling is also incorporated on individual time slices as bearer information within the frame, or as pulsed charges in channel
16
. Time slot or channel
16
is divided into sub-channels, each of which relate to the correspondingly numbered channel within the frame. Line signalling information regarding each of the channels within the frame is transmitted in channel
16
within the corresponding sub-channel. Each of these sub-channels transmits four bits of information, which for historic reasons are termed A, B, C and D bits.
These digital bits are utilised to indicate to the receiving node information such as:
The line is idle;
Trunk seizure is requested;
Trunk seizure is accepted;
Connection signal;
Clear signal;
Released signal;
In each of the different national GAS protocols different binary codes may be used to signify each of these requests, e.g. an “idle line” signal may be “00100” in one national CAS and “0101” in another national CAS, for example.
National CAS protocols may also differ in that a line signal may be continuous in some and pulsed in others. Also, register signals may be compelled that is a request is required in some systems and not in others. In some CAS systems a timer is set when a signal such as a request for a line is sent and a fault is determined when a response (either negative or positive) is not received within a predetermined time.
A very simplified process of making a telephone call utilising a compelled CAS protocol as discussed above is illustrated in the flow diagram of FIG.
2
. This diagram is included to give an indication of the process through which a CAS protocol is used to make a call. However, it should be noted that this is a considerably simplified version and a host of information which is available through CAS such as billing information, metering information, call party status, for example, is not indicated.
With reference to
FIG. 2
for a simple CAS protocol, when a channel, for example, channel
1
in a frame is not being utilised to make a call a line signal “Idle” signal is transmitted in the corresponding sub-channel
1
(block
40
). If a first node (node A) wishes to utilise channel
1
it will send a “Seize (SZG)” signal in said sub-channel
1
(block
42
). On receipt of this “Seize” signal at a connected node (node B) if the use of this channel is acceptable to node B, node B will send a “Seize acknowledge (SZA)” signal (block
44
). On receipt of said “Seize acknowledge” signal node A will transmit a first digit of the telephone number of the telephone to which ultimately node A wishes to make a connection (block
46
). This is the first register signalling signal which is sent on the channel
1
as opposed to the sub-channel
1
within channel
16
. On receipt of said first digit of a telephone number node B will send a request for the next digit of a telephone number (block
48
).
These requests and telephone digits are transmitted until node A sends the final digit of a telephone number (block
50
) at which point node B may connect the line to the telephone. in question and send a “Connect Call Charge” signal to node A (block
52
). After the telephone in question is placed off-hook an answer signal may be sent by node B to node A (block
54
) and voice communication on channel
1
of the time frame may be established between the two nodes (block
56
). This will continue until the phone is placed on-hook again at which point node A will send a “Clear Forward” signal to node B (block
58
) upon receipt of which node B will send a “Release Guard” signal to node A (block
60
). At this point both nodes will continue to retransmit the original idle signal (block
40
).
In
FIG. 2
, the indication as to whether or not signals are commonly line signals or register signals is indicated by the letter L or R to the left of the blocks. Line signalling is commonly utilised for control information whereas register signalling is typically utilised for call information. Different systems may be used although a common one is a dual tone multi-frequency system transmitted along the individual time frames.
As was discussed above, the binary line signal codes or tones for each of these signals may be different in different national CAS protocols and the duration for which they are transmitted may be different. The time interval before a reply or response is expected may be different and the overall waveform used in each signal may be different.
In known systems the operation of a node in compliance with the national CAS standard is determined by hard coding the operation of the node which requires a massive amount of rewriting of software in order to adjust a node for operation in compliance with a different national standard. For example, in order to provide a digital switch for use in a country utilising a CAS protocol for the first time, may take six or more months of intense software development as well as a vast amount of finance and manpower. Therefore, it is a huge commercial problem for telecommunications companies wishing to sell a client a switch for a new country if software has to be rewritten so that the switch will operate in that country. To date no solution to this problem has been found. Also, as there are so many legacy switches and PBXs in the field all operating on different national CAS protocols, CAS signalling can not be completely superseded by other protocols such as CSS
7
or PRI.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a CAS software platform which allows flexible relatively fast and relatively low cost CAS development.
It is a further object of the present invention to provide a CAS software platform which allows easy extension for new functionality.
It is a further object of the present invention to provide a telecommunications node and a system comprising said nodes with the aforementioned CAS software platform characteristics.
According to a first aspect of the present invention there is provided a Channel Associated Signalling (CAS) compatible telecommunications node, comprising an operating program in which CAS signalling information is separated from functional behaviour information which defines the behaviour of the node, such that adjustment of the operation of the node can be achieved through datafill.
Preferably, the CAS signalling information and the functional behaviour information are stored in mapped look-up tables in which specific signalling information is mapped to corresponding node behaviour information.
Most preferably, the CAS signalling information includes line signalling information and register signalling information. Preferably, the CAS signalling information also inclu
Bradd Patrick David
McDonald Brent Allan
Knowlin Thjuan P.
Lee, Mann, Smith, McWilliam Sweeney & Ohlson
Matar Ahmad F.
Nortel Networks Limited
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