GB2351415A

GB2351415A - Continuity checking in a telecommunications network

Info

Publication number: GB2351415A
Application number: GB9914656A
Authority: GB
Inventors: Mark Hollis; Stephen Terrill; Christian Groves; Leslie Graf; Juan Noguera
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1999-06-22
Filing date: 1999-06-22
Publication date: 2000-12-27
Also published as: GB9914656D0

Abstract

A method of performing a continuity check between two signalling points in a telecommunications network, where the Call Control signalling protocol is independent of the underlying transport mechanism. The method comprises sending a continuity check message from an originating signalling point to a peer signalling point at the Call Control level, and, following receipt of the continuity check message at the peer signalling point, establishing a bi-directional call path between the two signalling points at the Bearer level. Following the establishment of the call path, a check signal is transmitted over the call path from the originating signalling point to the peer signalling point and is looped back to the originating signalling point where its correct receipt is confirmed.

Description

1 2351415 CONTINUITY CHECKING IN A TELECOMMUNICATIONS NETWORK

Field of the Invention

The present invention relates to continuity checking in a telecommunications network and in particular to continuity checking in a network in which the Call Control protocol is independent of the underlying bearer transport technology.

Backaround to the invention

Telecommunications networks currently rely to a large extent upon the Signalling System no.7 (SS7) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks. Typically, one or more application and user parts at a given signalling point will make use of SS7 to communicate with peer application and user parts at some other signalling point. Examples of user parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of application paxts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS7 protocol stack includes Message Transfer Parts MTPI, MTP2, and MTP3 which handle the formatting of signalling messages for transport over the physical layer as well as various routing ftinctions.

There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) bearer transport mechanisms in telecommunications networks to carry user data, for example, voice traffic. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Internet Protocol (IP) networks to transport user information between network nodes. IP networks have the advantage that they make efficient use of transmission resources by using packet switching and are relatively low in cost due to the widespread use of the technology (as opposed to specialised telecommunication I 2 technology). There is also interest in using other transport mechanisms including AAL 1 /2/5, FR etc.

The standard ISUP which deals with the setting-up and control of call connections in a telecommunications network is closely linked to the standard bearer transport mechanism and does not readily lend itself to use with other non-standard transport technologies such as IP and AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a protocol for the control of calls, which is independent of the underlying transport mechanism. This can be viewed as separating out from the protocol, bearer control functions which relate merely to establishing the parameters (including the start and end points) of the "Pipe" via which user plane data is transported between nodes, and which are specific to the bearer transport mechanism. The new protocol, referred to as Transport Independent Call Control (TICC), retains call control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data. Figure la illustrates the conventional integrated Call Control and Bearer Control structure of ISUP whilst Figure lb illustrates the proposed new separated structure.

Currently, ISUP provides two mechanisms for confirming the integrity of a call connection between two network nodes. A first of these mechanisms is referred to as "per call continuity check", whilst the second is referred to as "continuity check test call".

The ISUP per call continuity check procedure is initiated by including a continuity check request indicator in the Initial Address Message (IAM) which is sent from the originating node to a neighbouring peer node. The node initiating the continuity check "inserts" a transceiver into the call transmission path, which generates a continuity check tone when the IAM is sent forward. Upon receiving the IAM containing a continuity check request indicator, the peer node causes the speech path to be looped back so that the continuity check tone is returned to the originating node. When the transceiver in the originating node detects the continuity check tone, the continuity j 3 check is considered successful and the transceiver is removed. A Continuity (COT) message indicating a successful continuity check is sent forward from the originating node to the peer node. When the COT message is received in the peer node, the looping of the speech path is removed and the call establishment continues. This process is illustrated in Figure 2.

A continuity check test call is initiated manually by an operator. The node originating the test sends a Continuity Check Request message (CCR) to a peer node and connects a transceiver into the call path. The transceiver inserts a continuity check tone into the speech path. The peer node receiving the CCR will loop back the speech path so that the continuity check tone is returned to the originating node. When the transceiver in the originating node detects the continuity check tone, the continuity check is considered successful and the transceiver is removed and a Release message (REL) is sent forward to the peer node. When the REL message is received in the peer node, the looping of the speech path is removed and a Release Complete message (RLC) is returned to indicate the end of the procedure. This process is illustrated in Figure 3.

SummM of the Present Invention.

The inventors of the present invention have recognised that when the Call and Bearer functions are separated, the existing Continuity Check procedures as used in ISUP will no longer fimction correctly. This is because the bearer path (i.e. speech path) is not established until after the IAM has been sent. In the case of an ATM,/IP transport mechanism, bearer connections are established by the Bearer Control Function (BCF) and not by the Initial Address Message carried by call control signalling. Thus, upon sending the IAM there is no speech path immediately available for transmitting a check tone or the like.

According to a first aspect of the present invention there is provided a method of performing a continuity check between two signalling points in a telecommunications network, where the Call Control signalling protocol is independent of the underlying bearer transport mechanism, the method comprising:

4 sending a continuity check message from an originating signalling point to a peer signalling point at the Call Control level; following receipt of the continuity check message at the peer signalling point, establishing a bi-directional call path between the two signalling points at the Bearer level; following the establishment of the call path, transmitting a check signal over the call path from the oniginating signalling point to the peer signalling point and looping the signal back to the originating signalling point; and confirming the correct return of the transmitted check signal to the oniginating signalling point.

By initiating transmission of the test signal only after establishment of the call path at the bearer level, the problems inherent in the conventional ISUP continuity test mechanisms are overcome.

In certain embodiments of the present invention, the continuity check message is sent in an Initial Address Message (IAM) which initiates a call connection, e.g. between local telephone exchanges of a calling and a called party. Upon receipt of an IAM at the Call Control level, a signalling point notifies the Bearer Control level to establish a call path with the Bearer level at the originating signalling point. In the event that the path is successfully established, a Bearer connect message is returned to the originating signalling point at the Bearer level. The Bearer connect message triggers transmission of the check signal from the oni ginating signalling point.

In other embodiments of the present invention a continuity check message is sent independently of a call between subscribers. The check message itself causes the receiving signalling point to notify the Bearer Control level to establish a call path with the Bearer level at the originating signalling point. Again, in the event that the path is successfully established, a Bearer connect message is returned to the originating signalling point at the Bearer level and the Bearer connect message triggers transmission of the check signal from the originating signalling point.

According to a second aspect of the present invention there is provided a signalling point of a telecommunications network arranged in use to perform a continuity check between itself and a peer signalling point, where the Call Control signalling protocol is independent of the underlying bearer transport mechanism, the signalling point comprising: means for generating a continuity check message and for sending the message from to said peer signalling point at the Call Control level; means for establishing a bi-directional call path between with the peer signalling point at the Bearer level following receipt of the continuity check message at the peer signalling point; a transceiver for transmitting a check signal over the call path from the originating signalling point to the peer signalling point following the establishment of the call path, and for receiving the signal back from the peer signalling point; and processing means for confirming the correct return of the transmitted check signal to the originating signalling point.

Brief Description of the Drawings

Figure la shows in block diagram form the architecture of a conventional telecommunications network; Figure lb shows in block diagram form a network architecture in which the Call Control protocol is independent of the transport mechanism; Figure 2 illustrates a first continuity check mechanism used in the network of Figure I a; Figure 3 illustrates a second continuity check mechanism used in the network of Figure la; Figure 4 illustrates a first continuity check mechanism used in the network of Figure lb; and Figure 5 illustrates a second continuity check mechanism used in the network of Figure lb; Detailed Description of Certain Embodiments

6 The proposed separation of the Call Control (CC) protocol and the Bearer Control (BC) protocol in future teleconimunications standards, such as the Universal Mobile Telecommunications Standard (UMTS) has been described above with reference to Figures I a and I b. Furthermore, the per call continuity check and continuity check test call mechanisms used in ISUP (having the architecture of Figure la) to test the continuity of a call path have been described with reference to Figures 2 and 3.

A per call continuity check mechanism suitable for use with a network having the architecture of Figure lb will now be described with reference to Figure 4 which illustrates the transfer of signalling messages between signalling points of a network at the CC level and at the BC level. The signalling messages are sent at the CC level between peer signalling points Node A and Node C and an intermediate signalling point Node B. At the BC level, signalling messages are sent between signalling points via a transport mechanism which may have one or more routing nodes.

Assume that a subscriber sends a call initiation request to Node A. Node A must establish a call path between itself and the signalling point (Node Q which is the local exchange of the called party. Assume further that Node A requires to test the integrity of the call path between itself and the intermediate signalling point Node B. Node A will indicate the requirement for a continuity check by setting the continuity check indicator in the IAM. The call control signalling then proceeds to allow the bearer connection to be established. This call control signalling may include for example a capability negotiation mechanism in order to negotiate the codec to be used for the connection. The initiating Node A will connect a transceiver to the speech circuit when the bearer connection is successfully established. The node that receives the IAM with the request for a continuity check, i.e. Node B, will cause the speech path to be looped back to Node A when the bearer connection is established. The procedure then continues as specified in the ISUP recommendation Q.764.

Figure 5 illustrates the signalling associated with a continuity check test call mechanism suitable for use in a network having the architecture of Figure lb. The node initiating the continuity check test call, i.e. Node A, will request a continuity check with a I 7 neighbouring signalling point Node B using a Continuity Check Request (CCR) message. The CC level signalling may need to signal back from Node B to Node A the valid BC address before the outgoing exchange can establish a bearer connection. Once the bearer connection is successfully established, the Node A will insert a transceiver into the connection and start sending the check signal, e.g. an inband tone. Node B receiving the CCR will loop the bearer connection when it is established. The procedure then continues as specified in the ISUP recommendation.

It will be appreciated that various modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, it will be appreciated that the names given to various messages and parameters may differ in ftirther standards from those used above whilst the fimction of the message or parameter remains substantially unchanged. It will also be appreciated that connections at the BC level may be established either in the forward direction, i.e. from the originating signalling point to the peer signalling point, or in the backward direction from the peer signalling point to the originating signalling point.

I

Claims

CLAIMS:

I. A method of performing a continuity check between two signalling points in a telecommunications network, where the Call Control signalling protocol is independent of the underlying transport mechanism, the method comprising: sending a continuity check message from an originating signalling point to a peer signalling point at the Call Control level; following receipt of the continuity check message at the peer signalling point, establishing a bi-directional call path between the two signalling points at the Bearer level; following the establishment of the call path, transmitting a check signal over the call path from the originating signalling point to the peer signalling point and looping the signal back to the originating signalling point; and confirming the correct return of the transmitted check signal to the originating signalling point.
2. A method according to claim 1, wherein the continuity check message is sent in an Initial Address Message (IAM) which initiates a call connection.
3. A method according to claim 2, wherein, upon receipt of an IAM at the Call Control level, a signalling point notifies the Bearer Control level to establish a call path with the Bearer level at the originating signalling point and, in the event that the path is successfully established, a Bearer connect message is returned to the oniginating signalling point at the Bearer level and the Bearer connect message triggers transmission of the check signal from the originating signalling point.
4. A method according to claim 1, wherein a continuity check message is sent independently of a call between subscribers.
5. A method according to claim 4, wherein the check message itself causes the receiving signalling point to notify the Bearer Control level to establish a call path with the Bearer level at the originating signalling point, and, in the event that the path is 9 successfully established, a Bearer connect message is returned to the originating signalling point at the Bearer level and the Bearer connect message triggers transmission of the check signal from the originating signalling point.
6. A signalling point of a telecommunications network arranged in use to perform a continuity check between itself and a peer signalling point, where the Call Control signalling protocol is independent of the underlying transport mechanism, the signalling point comprising: means for'generating a continuity check message and for sending the message from to said peer signalling point at the Call Control level; means for establishing a bi-directional call path between with the peer signalling point at the Bearer level following receipt of the continuity check message at the peer signalling point; a transceiver for transmitting a check signal over the call path from the originating signalling point to the peer signalling point following the establishment of the call path, and for receiving the signal back from the peer signalling point; and processing means for confirming the correct return of the transmitted check signal to the originating signalling point.