CN1326643A - Signalling in telecommunications system - Google Patents

Abstract

A method of transmitting signaling data between a pair of telecommunications switches (1,3) using ISUP signaling over a packet-switched data network, the method comprising communicating over the data network using the H.323 protocol, wherein the signaling data is transmitted by a Q.931 protocol transmission, which is extended to prepare for the transmission of ISUP network deletion indication messages.

Description

Signaling in Telecommunications Systems

Field of the invention:

The present invention relates to signaling in telecommunication systems and in particular to the transmission of signaling data over packet-switched networks.

Background technique:

Traditional telecommunications networks that carry voice and other user information typically rely on dedicated telecommunications network infrastructure and transport protocols. However, with the recent explosion of digital data transmission, particularly driven by the use of intranets and the Internet, there is a tendency in the telecommunications industry to use more common infrastructure and transport protocols. This trend is primarily driven by the desire to interoperate between telecommunication networks and other data networks, followed by cost and performance advantages that general data network systems offer over traditional telecommunication systems.

In 1996, the International Telecommunication Union (ITU) established standards for the transmission of multimedia data over Local Area Networks (LANs) and "Internetworks" consisting of multiple interconnected LANs. This standard is called H.323, and the 1998 revision is called the second edition of H.323. The main and fundamental part of H.323 is the specification for the transmission of digitized and compressed audio data. However, H.323 also specifies optional provisions for the transmission of video and other data forms.

H.323 makes it necessary to use the ITU standard Q.931 for establishing a call negotiation between two H.323 terminals in order to establish a channel between them through which the terminals can send user and signaling data. In addition, Q.931 is required for certain call hold and termination functions.

Probably the most advanced telecommunications network protocol is known as the International Standard Digital Network (ISDN). In the link between a subscriber and that subscriber's local exchange (the subscriber's "access point"), ISDN uses a signaling protocol known as Digital Subscriber Signaling System No. 1 (DSS1), while using a signaling protocol known as ISDN A further protocol of the user part (ISUP) transfers signaling data within the network, ie inter-switching signaling. Even in networks where ISDN access networks are not used, for example the access network is the Public Switched Telephone Network (PSTN), ISUP is typically used for internal switching signalling.

In the current competitive telecommunications market, it is critical for telecommunications operators to provide a wide and variable range of value-added services and to minimize service costs to end users. In this regard, existing telecommunication network protocols, and ISUP in particular, have been developed to provide for the transfer of much information and parameters regarding such services between the various nodes (or signaling points) of the network.

Because the Q.931 signaling protocol is mainly based on the DSS1 protocol, the intercommunication between ISUP and H.323 is basically satisfactory. It is thus possible to replace the middle part of the ISUP network with an H.323 network (or rather a TCP/IP network using the H.323 protocol). For example, a connection between two telephone exchanges such as exchanges can be made via an H.323 network.

Summary of the invention:

The inventors of the present invention found that the existing Q.931-based signaling protocol used by H.323 cannot adapt to certain information generated within the ISUP-based network. More specifically, it was found that existing Q.931-based signaling protocols cannot be adapted to the network that can be generated in telecommunications network switches in the event that the switch does not support user-to-user signaling information contained in received Q.931 messages Delete instruction message. This deficiency in the Q.931 based signaling protocol means that in the switch from which the signaling message originates from user to user, for example, there is no way to inform the receiving switch that the signaling message has been deleted. In some cases this will result in the caller being overcharged.

It is an object of the present invention to overcome or at least alleviate the above-mentioned drawbacks of existing telecommunication signaling systems. It is a further object of the present invention to provide a telecommunications system using a packet switched network for transporting user voice and data information and signaling data, wherein a network deletion indication message can be sent across the network between a pair of switches.

According to a first aspect of the present invention there is provided a method of communicating signaling data over a packet-switched data network between a pair of telecommunications switches using ISUP signaling, the method comprising communicating over the data network using the H.323 protocol, wherein the signaling data By transmission based on the Q.931 protocol, the protocol is extended to prepare for the transmission of ISUP network deletion indication messages.

Preferably, the extended Q.931 protocol used by the present invention is arranged to be implemented within the H.323 protocol stack. Preferably, said connection or part of the connection formed between the two users is provided through a TCP/IP-based network. This network can be a LAN, an internetwork, the Internet, or a combination of two or more of these. In these examples, the H.323 protocol stack is provided through the TCP/IP protocol stack.

According to a second aspect of the present invention, there is provided an apparatus for transmitting signaling data over a packet-switched data network between a pair of telecommunication exchanges using ISUP signaling, the apparatus comprising means for communicating over the data network using the H.323 protocol, wherein the signaling Let the data be transmitted by a protocol based on Q.931, which is extended to prepare for the transmission of network deletion indication messages.

Graphic description:

For a better understanding of the invention and to show how it may be practiced, reference will be made to the accompanying drawings by way of example, in which:

Figure 1 schematically illustrates a telecommunication network for transporting user and signaling data between network switches over an IP network; and

FIG. 2 is a flow chart showing a transport network deletion indication message in the network of FIG. 1 .

Some examples detail:

In the telecommunications network of Figure 1, a first telephone exchange 1 is coupled to user terminals 2 via an ISDN access network (ie using the DSS1 signaling protocol), while a second exchange 3 is coupled to user terminals 4 via a PSTN access network. Signaling between switches within the network is transmitted using the ISUP protocol, which requires the provision of the PSTN switch 3 at the PSTN/ISUP interface 5 . In the case of a call between two user terminals 2, 4, the call is established from the terminal 2, which is called the "calling party" and the other terminal 4, the "called party". It will be appreciated that the terminals 2, 4 are connected to the respective access switches 1, 2 via intermediate routing nodes such as multiplexers/demultiplexers.

The following description is based on the disclosure of the ITU H.323 standard, which must use the Q.931-based standard for establishing and maintaining a call connection between two H.323-enabled terminals. In the example shown in FIG. 1 , switches 1 , 3 of two telecommunication networks communicate via respective H.323 enabled terminals 6 , 7 which in turn communicate with each other via an IP-based network 8 . In the H.323 terminals 6, 7, the H.323 protocol stack is located on top of the TCP/IP protocol layer, so that H.323 data can be transmitted between switches through the IP network 8 . Therefore, at each switch there is a protocol stack consisting of ISUP over Q.931 over TCP/IP.

Consider the case where the calling party 2 wishes to send certain user-to-user signaling information to the called party 4 during call setup, and this can be facilitated for the calling party 2 by an ISDN access network. This information may include, for example, call forwarding information, call waiting information or similar information. The information is encapsulated at the access switches 1,6 into suitable Q.931 messages and sent over the H.323 network 8 to the terminating switches 3,5,7. It is now assumed that the terminating exchange 3 cannot use the received user-to-user signaling information. In this case, the terminal switch 3 must generate a network deletion indication message, encapsulate it in a Q.931 message, and send the obtained Q.931 message back to the original switch through the IP network 8 .

The Q.931 standard defines the notification (NOTIFY) message with the following structure, wherein the reference item indicates the corresponding information unit reference item in the Q.931 standard, and the direction indicates the direction in which a unit can be transmitted by the NOTIFY message (n=network, u= H.323 users), and the length indicates the unit length in octets: information unit reference item (clause) direction type length protocol discriminator 4.2 two-way m 1 call reference 4.3 two-way m 2 information type 4.4 two-way m 1 load capacity 4.5 n → u o 2-12 notification instructions 4.5 two-way m 3 show 4.5 n → u o ≥2

Among the six message units, the notification indication unit is defined in the existing Q.931 standard as having three meaningful values or states, which are: Bit 7654321 0 0 0 0 0 0 00 0 0 0 0 0 10 0 0 0 0 1 0 User termination User recovery load service change

All other values are currently reserved.

An extension to the Q.931 protocol is proposed here to prepare for network deletion indication messages. This message is assigned to any reserved value of the notification indication unit.

FIG. 2 is a flowchart showing the steps involved in the network delete indication message relayed from PSTN switch 3 to ISDN switch 1. In FIG.

Those skilled in the art will appreciate that various modifications can be made to the above-described embodiments without departing from the scope of the present invention. For example, although the above embodiments describe the content included in the network deletion indication message in the Q.931 notification message, other messages may be used for the currently existing reserved value. The switches between which the network delete indication message is sent may be coupled via one or more intermediate switches with the IP network extending through only an intermediate portion of the signaling connection, for example between two intermediate switches. In this case, the Network Delete Indication message can be generated at the terminating or originating switch or an intermediate switch. The network delete indication message can be sent directly to the IP network through the switch that generated the message, or it can be sent to an intermediate switch first, such as through the Signaling System No. 7 (SS7) signaling network.

Claims (5)

1. A method for transmitting signaling data between a pair of telecommunication switches using ISUP signaling through a packet-switched data network, the method comprising using the H.323 protocol communication through the data network, wherein the signaling data is transmitted by a Q.931-based Protocol transport, which is extended to provide for the transport of ISUP network deletion indication messages. 2. A method according to claim 1, wherein the extended Q.931 protocol is arranged to be used within the H.323 protocol stack. 3. A method according to claim 2, wherein the connection or part of the connection formed between the user parties is provided over a TCP/IP network. 4. The method of claim 3, wherein the H.323 protocol stack is provided by the TCP/IP protocol stack. 5. A device for transmitting signaling data between a pair of telecommunication switches using ISUP signaling through a packet-switched data network, the device includes a device for communicating with the H.323 protocol through the data network, wherein the signaling data is transmitted by the Q-based .931 protocol, which has been extended to prepare for the transmission of ISUP Network Delete Indication messages.

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