Note: Descriptions are shown in the official language in which they were submitted.
RCV. VON : EPA-MUENCFRTT1 ~)8 :18- 8- U : 11:16 : 358 8 8866°"0-~.~.-:
.~.4.g gg ..~~,.~.. . ~~ . ,. ..
'c~8-08-2000 EP 009906168
lA
SIGNADLING IN A T~LgCO~NICATIONS SY8TEi3
Field of the Invention
The present invention relates to signalling in a
telecommunications system and in particular, though not
necessarily, to 'the transmission of signalling data over
an H.323 network.
Hackaround to the Invention
Traditional telecommunications networks are known as
Public Switched Telephone Networks (PSTNs) and use a
variety of transmission and signalling protocols to
communicate between subscribers and network nodes. Far
example, in the United Kingdom inter-exchange signalling
is conveyed using the NLTP protocol whilst certain other
countries use the TUP-protocol.
Recently, a new type of telecommunications network has
been introduced and is known as the Integrated Services
Digital Network (ISDN). ISDN may be implemented between
network nodes and between subscribers and their local
exchanges. In the link between a subscriber and that
subscribers local exchange (the subscriber "access
point"), ISDN uses a signalling protocol known as
Digital Subscriber Signalling System No.i (DSS1), whilst
a further protocol known as ISDN User Part tISUP) is
used to convey signalling data within the network, i.e.
inter-node signalling. In a typical scenario, a call
connection may pass through one or more PSTN parts and
one or more ISDN parts.
In the current competitive telecommunications market, it
is vital for a telecom operator to provide a wide and
varied range of basic, supplementary, and added value
CA 02341169 2001-02-19 - AM EN D E D S H E ET
R~-v vnrt a t: n s -.~ 0~ :18- 8- U : I 1:1? : 358 9 68fi68~ +~9 89 ?"~u'" ~
°c ~ ,~ a
8-08-2000 E P 009906168
2A
services, as well ae to minimise the cost of services to
the end users. As such, existing telecommunications
networks, and in particular ISUP, have evolved to
provide for the transfer of many messages and parameters
relating to such services between the various nodes for
signalling points) of the networks.
Conventional telecommunication networks are designed
such that the calling party (A-subscriber, A-user, A-
party, A-number, A-address etc.) is normally responsible
and therefore charged for the cost of a call and~or
connection time, while the called party (B-subscriber,
B-user, B-party, B-number, B-address etc.) does not have
to pay anything for the received calls and/or the
connection time of the received call. The charging may
be arranged to occur beforehand (so called pre-paid
calling arrangements) or afterwards (e.g. by means of a
telephone bill).
Telephone calls are usually charged according to their
duration. Other charging criteria may be used by network
operators such as the distance between the subscribers,
etc. So as to enable reliable charging, an ongoing call
is monitored and required charging information sent to a
Call Charging Point (CCP) of the calling party which may
be implemented for example in the A-subscriber's local
exchange. So-called pulse metering and toll-ticketing
(TT) are referred to herein as possibilities for
implementing the charging. At the end of a call, i.e.
3o when the call is released, the call charging point will
be notified accordingly and the call charge accumulation
will be terminated.
Conventional telecommunications networks for conveying
voice and other user information have in general relied
upon dedicated telecommunications network infrastructure
and transmission protocols (i.e. PSTN and ISDN).
CA 02341169 2001-02-19 AM E N D E D S H E ET
RCV. VON : Ef'A-MI.fETICIi~I OS :18- 8- 0 : 11:1? : 358 9 68668 +~4~9 89
7~~.~~ : ~e ~
i 8-08-2000 EP 009906168
3A
However, with the recent explosive growth in digital
data transmission, driven in particular by the use of
intranets and the World Wide Web, there has been a move
towards the use of more generic infrastructure and
transmission protocols in the telecommunications
industry. Tbis move is driven primarily by the desire
for interoperability between telecommunications networks
and other data networks, and secondarily by the cost
advantages which general data network systems offer over
1o conventional. telecommunications systems. One application
of the above-mentioned matter is disclosed in the patent
application EP-A-0 841 831.
In 1996, the International Telecommunications Union
(ITV) defined a standard for the transmission of
multimedia data over Local Area Networks (LANs) as well
as "internetworke" composed of multiple interconnected
LANs. This standard is knows as H.323, whilst the 1998
revision is known as H.323 Version 2. A.fundamental and
2o essential component of H.323 ie the provision for the
transmission of digitised and compressed voice data.
However, H.323 also makes optional provision for the
transmission of video and other data forms. H.323 has
already been implemented in multimedia products such as
Microsoft Netmeetingz". There currently exists a demand
to introduce H.323 as a means of communicating betweea
signalling points of a telecommunications network. This
may lead to a situation where H.323 must co-exist with
ISDN and PSTN. A typical scenario might involve a
3o calling party and a called part both being connected to
respective PSTN access networks (using for example NUP
or TTJp) , with part of the intermediate signalling link
being provided by an ISDN network (using ISUP) and a
part being provided by an H.323 network. '
CA 02341169 2001-02-19 AM EN D E D S H E ET
RCV. VON:~p4-M(:W iC'~1 OS :18- 8- 0 : 11:18 : 368 9 68668444-. +49 89
?~~a.4.~.~:~e R
i 8-08-2000 E P 009906168
4A
H.323 makes mandatory the use of the ITU standard H.225
which is based on DSS1 (sometimes referred to as Q.931)
signalling for the negotiation of a call set-up between
two ~i.323 nodes, to establish a channel therebetween
over which the terminals may send user and signalling
data. In addition, DSS1 is mandatory for certain call
maintenance and termination functions.
Summary of the Present Invention
is
The inventors of the present invention 1=~ave discovered
that the existing DSS1 based signalling protocol
employed by H.323 is not able to accommodate certain
signalling information which may be generated within a
telecommunications system and for which provision is
made in the existing PSTN and ISUP standards. It has
further been recognised that this incompatibility
hinders the introduction of H.323 in telecommunications
networks.
In current PSTN networks (where the connection between
the calling party and called party is purely PSTN) a
calling party (A-subscriber) terminates a call by
hanging-up his telephone, i.e. by going "on-hook". This
results in a Clear-Forward Signal (CFS) being sent from
the A-subscriber s local PSTN exchange to the
appropriate Call Charging Point (CCP). The call is
terminated immediately and charge accumulation stopped.
The mechanism for terminating a call in response to an
on-hook by a called party (B-subscriber) is however
somewhat different. On-hook by the B-subscriber ie
detected at his local PSTN exchange. Detection of a B
subscriber on-hook is signalled back to the CCP by
sending a Clear Hack (CLB) ~signai from the B-subsciber~s
local exchange to the CCP.
CA 02341169 2001-02-19 AM EN D E D S H E ET
RCV. VON:1PA-MUENCHEN 06 : 18- 8- 0 : 11: 18 : 388 9 f~8668444-~ +49 89
~'»arc~.~ o
18-08-2000 E P 009906168
5A
Receipt of a CLB signal at the CCP does not immediately
result in the termination of the call. Rather, receipt
causes the initiation of a timer at the CCP. In the
event that the B-subscriber goes °off-hook~~ before the
expiry of the timer (typically the timer runs for 9~
seconds or thereabouts), the B-subscriber s local
exchange sends a REANSWER signal to the CCP. This causes
the cancellation of the timer at the CCP. If no REANSWER
signal is received by the CCP before expiry of the
i0 timer, the CCP causes the connection to be cleared and
charge accumulation is stopped. This facility is
provided to allow, for example, the 8-subscriber to on-
hook on one extension and to subsequently off-hook on
another extension without terminating the call.
Where an intervening portion of the signalling
connection between the A and 8 subscribers is provided
by ISUP signalling, the CLB and REANSWER signals are
carried by appropriate ISUP messages. In particular, the
2o CLB signal is carried by an ISUP SUSPEND message (with
an indication that the suspension request is network
initiated) whilst the REANSWER signal is carried by an
ISUP RES''JME message (again with an indication that the
suspension request is network initiated).
The inventors of the present invention have noted
however, that whilst ISUP caters for a B-subscriber
timer initiation and reanswer as described above, H.323
(H.225) does not. This means that in telecommunications
3o networks which rely upon H.323 for carrying signalling
information aver at least part of a connection, the,H-
subscriber cannot suspend a call in the expected manner.
It is an object of tre present invention to overcome or
at least mitigate the above noted disadvantages of
existing H.323 (H.2251 signalling systems.
CA 02341169 2001-02-19 AM E N D E D SH E ET
RCV. VOAi:EPA-MUETlCHEN 06 :18- 8- 4 : 11:19 : 358 9 686Ei84A4-. +49 89
'MO~~~~x~n
18-08-2000 EP 009906168
6A
It is a second object of the present invention to
provide an improtred solution for call charging
procedures in telecommunication networks using an access
protocol or an access based protocol for signalling.
It is a third object of the present invention to ease
network architecture planning without the need to
redesign the basics of the present protocol signalling,
especially having regard to IP networks and other router
1o based networks.
It is a fourth object of the present invention to avoid
the need to relocate call charging points of a network.
According to a ffret aspect of the present invention
there is provided a method of communicating signalling
information between a pair of telecommunication networks
employing ISUP or PSTN signalling, via a data network,
the method comprisizrg using the H.323 protocol to
2o communicate over the data network where signalling data
is carried by a DSS1 based protocol extended to provide
for the transmission of ISUP/PSTN information which
cannot be carried by DSSl.
The term "extended" is used here to define that the DSS1
based protocol is changed to accommodate new messages
and/or message fields. ISUP/PSTN information not already
catered for in DSS1 is not merely transmitted over the
data network by encapsulating them within "carrier"
3a messages.
In one embodiment of the present invention, the method
is used for initiating a timer procedure at a call
charging point of one of the ISUP/PSTN networks. The
method comprises the further steps of detecting an on-
hook state of a called party, and signalling a timer
CA 02341169 2001-02-19 AM EN D E D SH E ET
RCV. VON : EPA-hIUENChIF~ U6 :18- 8- U : 11: 19 : 358 8 68668444-. +49 89
?~a~~ - ~ ~ ~
18-08-2000 E P 009906168
7A
initiation request from the called party access point to
the call charging point by means of an extension to the
DSS1 based protocol. A subsequent off-hook state of tre
called party may result in signalling a REP~ISWER
indication to the call charging point whereupon the
timer is cancelled.
Preferably, the on-hook state is detected at the access
point of the called party, and the timer initiation
to request is signalled by means of the extension of the
DSSl based protocol from the access point of the called
party to the call charging point, the call charging
point of the calling party being integrated or linked to
the access point of the calling party.
20
More preferably, the timer initiation signal is a clear
back signal (CLB) which causes an immediate
initialisation cf the call suspension timer which upon
expiry will clear the call.
The DSSl based protocol may be extended to include an
extension for signalling REANSWER signal (RES) to the
charging point of the calling party for cancelling the
call suspension timer.
Preferably, said data network which uses H.323 is a
packet switched data network. More preferably, the
network is an IP network. This network may be a i~AN, an
internetwork, the Internet, or a combination of two or
3o more of these. In these cases, the H.323 protocol stack
is provided over an IP protocol stack.
According to a second aspect of the present invention
there is provided a method of passing a Clear Back (CLB)
3S and/or REANSWER message from a PSTN access point to a
call charging paint via a network which uses a DSS1
based signalling protocol, the method comprising
CA 02341169 2001-02-19 AM E N D E D S H E ET
R~r wnm.~os .u,»;y(pJ 05 :18- 8- 0 : 11:19 : 358 9 68668444-~ +49 89
.~~~~'~~~'......
18-08-2000 EP 009906168
8A
defiaing call clearback and reanswer parameters and
including one or other of the parameters as a
Notification Indicator information element of a NOTIFY
message of the DSS1 based protocol, for transmission
over said network, in response to generation of a Clear
Back or REANSWBR message at the PSTN access point.
Preferably, the Notification Indicator information
element is available for transmission front a called
party access point to the charging centre or calling
party access point in response to an off-hook operation
at the called paxty, wherein the element conveys an off-
hook notification value. Preferably, in response to an
on-hook operation by the called party, the Notification
Indicator information element conveys an on-hook
notification value.
Preferably, the method comprises polling the called
party from the called party access point to detect an
on-hook operation.
Preferably, said DSS1 based signalling protocol is used
by an H.323 network to establish and control connections
over said network.
According to a third aspect of the present invention
there is provided apparatus for communicating signalling
data between a pair of telecommunication networks
employing ISUP or PSTDT signalling, via a data network.
3o the apparatus comprising means for using H.323 protocol
to communicate over the data network where signalling
data is carried by a DS81 based protocol extended to
provide for the transmission of ISUP/PSTN messages which
cannot be carried by DSS1.
According to a fourth aspect of the present invention
there is provided a method of communicating signalling
CA 02341169 2001-02-19 AM E N D E D SH E ET
RCV. VON : EPA-MUEIVCHEN 05 :18- 8- 0 : 11 : 20 : 358 9 886684~44~ +49 g~J-
?a~ac ~ ~, ~a
18-08-2000 E P 009906168
9A
data between a pair of telecommunication networks
employing ISUP or PSTDT signalling, via a data network,
the method comprising using H.323 protocol to
communicate over the data network, wherein signalling
data is carried by a Q.76x based protocol substituted in
the H.323 protocol for DSS1.
Brief Description of the Drawings
to For a better understanding of the present invention and
in order to show how the same may be carried into effect
reference will now be made, by Way of example, to the
accompanying drawings, in which:
Figure 1 illustrates schematically a
telecommunications network in which user and signalling
data is carried between exchanges of the network via an
IP network;
Figure Z illustrates a flow of signalling
information in the network of Figure 1; and
2o Figure 3 is a flow diagram illustrating the
transmission of on-hook and off-hook signalling
information in the network of Figure 1.
Detailed Descrit~tion of Certain Embodiments
The following description builds upon the disclosures of
the ITU H.323 standard which makes mandatory the use of
a DSS1 based standard for establishing and maintaining a
call connection between two H.323 enabled nodes. In the
example illustrated in Figure 1, two PSTN exchanges 1, 2
of a telecommunications network communicate with
respective ISUP gateway exchanges 3,4 using the TUP
signalling protocol. The ISt3P exchanges in turn
communicate with respective H.323 gateway ;codes 5,6
using the ISUP interface. The gateway nodes 5,6
communicate with one another over a packet switched data
network 7 (in this case an IP network). More
CA 02341169 2001-02-19 AM EN D E D S H E ET
RCV. VON : EPA-MUFf~K.~l 06 : 18- 8- 0 : 11: 20 : 3S8 9 6866844-~ +49 8~1 23~
: ~e 7 e.
i 8-08-2000 E P 009906168
l0A
particularly, the H.323 protocol layer is located above
the TCP/IP layers ir_ the protocol stacks of the two
gateway nodes 5,6.
The exchanges 1,2 provide PSTN access points to the
telecommunications network for respective subscriber
terminals 8,9. In the case of a call between the two
terminals 8,9, the terminal 8 from which the call is
established is referred to as the A-subscriber whilst
1o the other terminal 9 is referred to as the B-subscriber.
It will be appreciated that the exchanges 1,2 may be
located in the network of a single operator or may be
located in networks of different operators. It will also
be appreciated that the terminals 8,9 may be connected
to respective access exchanges 1,2 via intermediate
routing nodes.
In order to allow signalling messages to pass seamlessly
between the exchanges 1,2, the H.323 gateway nodes 5,6
2o make use of an extended version of the DSS1 protocol
specified by H.323. More particularly, the DSSl protocol
is extended to enable certain PSTN (and associated ISUP)
parameters to be transmitted over the TCP/IP network 7.
T'he exchange 1 acts as a collector of information
relevant to call charging, for a call initiated from the
A-subscriber 8. More particularly, the exchange 1 gasses
information such as call initiation and termination
signals, and calling and called party locations, to a
3o Call Charging Point for Toll Ticketing arrangement) 10
which calculates a toll ticket for a given call on the
basis of the ir_formation received from the exchange 1
and certain predefined tariff information (including
subscriber specific tariff information).
The basic DSS1 standard defines a NOTIFY message having
the following structure, where the Reference indicates
CA 02341169 2001-02-19 AM EN D E D S H E ET
x~ar an. ~ . co. y~~ 0s : 18- 8- 0 : 11- 20 : 368 9 68668444-~ +49 89 ~ ~~~ ~
. ..~ . ...
18-08-2000 E P 009906168
11A
the corresponding Information element reference in the
DSS1 standard, Direction indicates the directionts) in
which an element may be carried by the NOTIFY message fn
= network, a - H.323 user), and Length indicates the
length of the element in octets:
Information Reference Direction Type Length
element (subclause)
Protocol 4.2 Both M 1
discriminator
Call reference 4.3 Both M 2
Message type 4.4 Hoth M 1
Bearer 4.5 - n ~ a 0 2-12
capability
Notification 4.5 Both M 3
indicator
Display 4.5 -. n ~ a O Z2
Of the six message elements, the Notification Indicator
element is defined in the existing DSS1 standard as
1o having two meaningful values or states. These are:
Bites
7 6 5 4 3 2 li
0 0 0 0 0 0 0 User suspended
0 0 0 0 0 0 1 Qser resumed
All other values are currently reserved.
Tn~hat is proposed here is an extension to the DSS1
protocol to provide a Notification Indicator element
able to convey the detection of an off-hook and an on
_. hook operation at the B-subscriber. These two operations
are assigned to any two of the reserved values of the
Notification Indicator element.
CA 02341169 2001-02-19 AM E N D E D S H E ET
RCV. VON:EPA-ML~E~iCFIE."V 05 :18- 8- 0 : 11:21 : 358 9 68668 +49 89
23994465:i~16
18-08-2000 EP 009906168
12A
Consider for example that a call is in progress between
the terminals 8,9 and that the B-subscriber 9 terminates
the call by hanging-up tB-subscriber Initiated Call
Clearing, B-ICC). In order to initiate the call
suspension timer, the Call Charging Point 10 must
receive a CLB signal. The exchange 2 polls the called
party terminal 9 to detect the on-hook operation, and
upon detection generates a CLB signal. The exchange 2
passes the CLB signal to the ISUP gateway exchange 4
which generates a corresponding SUSPEND signal which is
forwarded to the H.323 gateway node 6. The gateway node
6 generates a NOTIFY message in which the Notification
Indicator element has a value corresponding to the CLB
signal. The gateway node 6 subsequently transmits the
NOTIFY message over the IP network 7 to the initiating
side gateway H.323 node 5. This gateway node 5 generates
an ISUP SUSPEND message and passes it to the ISCTP
gateway exchange 3 which generates a CL8 signal which is
passed to the PSTN exchange 1. The CLB signal is
2o forwarded to the CCP 10 which initialises the suspension
timer in response.
In the event that the B-subscriber "reanewers" his
telephone within some predefined time period (e.g. 90
seconds) following the earlier hang-up, this is also
detected by the exchange 2 and a call RERNSWER message
is generated and passed to the ISUP gateway exchange 4.
The gateway exchange 4 generates an ISUP RESUME signal
and passes it to the H.323 gateway node 6. Again, a
NOTIFY message is generated at the gateway node 6, the
message including as a Notification Indicator element a
value corresponding to a REANSWER message. This is
relayed to the originating side H.323 gateway node 5,
converted into an T_SUP REST message and passed to the
ISUP gateway exchange 3. A TUP REANSWBR message ie
formed and passed to the PSTN exchange 1. The REANSWER
message is passed to the CCP 10 which, in response,
CA 02341169 2001-02-19 AM EN D E D S H E ET
RCV. VON ~ EPA-MLI~TIC~:v US : 18- 8- 0 : 11 :21 : 368 9 686681~4~4~ +49 89 ~~
Y 8-08-2000 E P 009906168
13A
terminates the suspension timer so that the call is not
subsequently terminated. The suspension and reanawer
signalling flow is illustrated in Figure 2.
Figure 3 is a flow chart illustrating the steps involved
in the setting up of a call between the two terminals
8,9 and the subsequent termination of the call by the B-
subacriber 9.
It will be appreciated by the person of skill in the art
that various modifications may be made to the above
described embodiment without departing from the scope of
the present invention. For example, as an alternative to
extending the existing DSS1 protocol, comprehensive
interworking between ISUP and Ii.323 may be achieved by
substituting the DSS1 protocol for the Q.763 protocol
which is the protocol used by ISUP. Thus, complete
interworking is assured.
CA 02341169 2001-02-19 AM EN D E D SH E ET
