MXPA01010495A - Telecommunications network congestion - Google Patents

Abstract

A method of routing signalling information at a signalling point of a telecommunications network. A Global Title Routing Case (GTRC) table is provided for mapping Global Titles to GTRCs, where each GTRC is allocated a primary and secondary destination signalling point. At least one peak time period is predefined, and said primary and secondary destination signalling points are swapped for a fraction of said GTRCs during said peak period to allow for load sharing during this period. For a signalling transfer request received at the signalling point, the Global Title associated with the request is mapped to a GTRC using the GTRC table, and the destination signalling point is determined in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC and signalling point availability, and, in the case of said fraction of GTRCs, the time at which the request is received.

Description

TELECOMU NETWORK CONGESTION ICATIONS FIELD OF THE INVENTION The present invention relates to congestion in a telecommunications network and more particularly to lightning congestion during the routing of signaling information between the signaling points of a telecommunications network.

Background of the Invention In a modern telecommunications network, a considerable amount of signaling information is continuously being exchanged between the signaling points of the network. Examples of signaling points are network switches, databases, etc. The current signaling information that is exchanged may be associated with a specific telephone call, for example, in connection with an establishment or call termination, or it may be related to the network administration functions. Complex protocols have been created to deal with the exchange of signaling information. In particular, the Signaling System no. 7 (SS7) defines (subject to certain national / regional variations) an integrated platform of protocol parts (or levels) capable of dealing with requests for modern network signaling.

Figure 1 schematically illustrates the "structure" of the SS7 (it will be appreciated that parts of the SS7 are generally implemented by software running on computer processors). Above the stack of SS7 sits the user and the application parts which are the entities that make use of and provide the signaling information. For example, an ISDN User Part (ISUP) controls the establishment and control of exchange connections for subscriber calls while a Mobile Application Part (MAP) handles database requests in a mobile network (e.g. to determine the current location of a mobile subscriber). At the bottom of SS7 is the Message Transfer Part (MTP) which in fact comprises three different levels. Level 1 defines the physical, electrical and functional characteristics of a digital signaling link. Level 1 of MTP has a number of different possible forms that includes the European standard E.l (channels 2048 kb / s and 32 64 kb / s). MTP level 2 takes care of the exact end-to-end transmission of messages through a chosen signaling link, while level 3 MTP handles the routing of signaling messages between neighboring signaling links based on the information received of the highest SS7 levels that have to do with the final destination of a signaling message. MTP level 3 handles the re-routing inter alia of messages away from failed or congested signaling links. Routing by MTP level 3 is carried out based on a destination signaling point and subsystem number (SSN) provided to the MTP with a higher SS7 layer. In particular, for the Transaction Capability Application TCAP (which handles the database requests for the MAP, INAP, etc.), a Signaling Connection and Control Part (SCCP) generates the destination signaling point and the subsystem number that uses a process called "Global Interpretation of Titles". The SCCP typically performs a Global Interpretation of Titles in a Global Title (GT), which can be an Intelligent Dialing Service (IN) service number for example, an 800 number, a subscriber identification number or the like, using a Global Title Routing Box (GTRC) table. This table contains a mapping between GT series and GTRCs (a GTRC is typically one of an ordered series of numbers). An interpretation of additional GTRC is then performed to map the determined GTRC to an associated primary destination signaling point (and subsystem number) '. The destination signaling point is referred in some cases as a "Destination Point Code" (DPC).

A Global Title Routing box defines, by means of the destination signaling point, the route by which the signaling information is transmitted. Especially during peak call times, certain routes can be congested with large volumes of signaling traffic. In fact, it is often the case that when a call is initiated, the primary destination signaling point generated by the GT and GTRC interpretations associated with the call are available. In such a situation (and following the diffusion of a congestion message from a signaling point given to the neighboring signaling points), a secondary destination signaling point, defined as a backup for the primary destination signaling point, It is used to route signaling information. This load compaction procedure is described in Recommendation ITU-T Q.714 (Chapter 5). The load sharing mechanisms use primary and secondary signaling points that are also described in US5,583,976 and O98 / 51096. It will be appreciated that the secondary signaling destination point handles the overflow signaling information whose primary destination signaling point is unable to handle. It will also be appreciated that when the overflow occurs, the processor (s) at the primary destination signaling point will be operating at maximum capacity while those at the secondary destination signaling point may be functioning well below that maximum capacity. It may also happen that the subsequent secondary destination signaling point is congested, requiring the transfer of information and signaling back to the primary destination signaling point (if the primary signaling point remains congested, an additional exchange back to the secondary point may occur, and so on). This back-and-forth switching between the primary and secondary destination signaling points may result in loss of signaling information.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to solve or at least mitigate the disadvantages described in the preceding paragraph. In particular, it is an object of the present invention to avoid or mitigate the congestion associated with the signaling traffic routed by the Connecting and Signaling Control Part. It is a further object of the present invention to provide means by which possible congestion at a signaling point can be predicted, thereby allowing signaling traffic to deviate away from that signaling point before congestion occurs. These and other objects are achieved in a first aspect of the invention by defining the peak periods during which heavy signaling traffic is expected. During these peak periods, a proportion of the Global Titles normally assigned to a given destination signaling point are automatically re-assigned to an alternative destination signaling point. The peak periods are defined on the basis of the history of the congestion notification messages issued by the given signaling point. According to a first aspect of the present invention, a method is provided for routing the signaling information at a signaling point of a telecommunications network, the method comprising: providing a GTRC Global Routing Box table that maps the Global Titles to GTRCs; assign to a set of GTRCs a primary destination signaling point, and a secondary one, a secondary destination signaling point which is used to route the signaling information when a primary destination signaling point is not available; define at least one period of time in the base of a record of congestion notification messages issued by the primary destination signaling point; exchange the primary and secondary destination signaling points with a set fraction of GTRCs for the duration of at least one period of; for a signaling transfer request at the signaling point, map the Global Title associated with the request to a GTRC using the GTRC table; and determining a destination signaling point to be used by the request depending on the primary and secondary destination signaling points assigned to the mapped GTRC and the signaling point availability. By carefully selecting the period (s) to correspond to the known peak signaling traffic periods, embodiments of the present invention automatically divert traffic away from the primary destination signaling point without having to wait until the point congestion actually occurs. of primary destination signage. The resulting load sharing reduces the risk of congestion at the primary and secondary destination signaling points. This results in a more opl use of processor power at the destination signaling points and also reduces the need to transfer signaling traffic from a congested route to a backup path. In addition, because the maximum volume of signaling traffic through a given signaling point will likely be reduced, the maximum processing power specified for the point (ie, its "dimension") can be reduced, resulting in considerable cost savings . It will be understood that the term "Global Titles" encompasses, but is not limited to, called and called shared telephone numbers, subscriber identity number, mobile identification number, and the like. The GTRC table can map the GTRC Global Titles using a series of Global Titles, that is, where the Global Titles are grouped in series and each series is mapped to a corresponding GTRC. Preferably, the destination signaling points are Destination Point Codes (DPC) or the like, whose DPCs identify designated signaling points to receive the signaling information. Preferably, at least one period of is defined during each period of 24 hours of operation. More preferably, the first period or periods correspond to a relatively high period of use.

Preferably, the congestion notification messages are broadcast by the signaling points in the network, when the points become congested. These messages are monitored at other points in the network to create a congestion record for the sending signaling points. At the base of these registers, a signaling point defines the period (s). The congestion notification messages can contain a level of congestion that can be additionally used by a receiving signaling point to define the time period (s). Preferably, the method of the present invention is employed in a Signaling Connection and Control Part.

(SCCP) of a Signaling System network no. 7 (SS7). Congestion notification messages can be Congested messages from the SCCP / Subsystem (SSC). Preferably, the time period (s) are dynamically defined so that they can be moved, or their duration changed, to reflect the patterns of change in network traffic. This process can be automatic, or semi-automatic. The time period (s) may be further defined using inquiry messages sent from the signaling point to the primary destination signaling point, where the primary destination signaling point responds to give a receipt of the inquiry upon returning a reply message to the destination. signaling point. Based on the delay between the transmission of the query and the reception of the response, the signaling point is able to estimate the level of congestion at the primary destination point and on the signaling link of intervention. If such queries are sent at regular intervals, the signaling point is able to complement the information obtained from the congestion notification messages. In a network that uses SCCP, the query message is known as Subsystem Testing (SST) while the response message is known as Subsystem Allowance (SSA). According to a second aspect of the present invention, an apparatus is provided for routing the signaling information to a signaling point of a telecommunications network, the apparatus comprising: first memory means for storing a GTRC table of Global Routing of Titles that maps the Global Titles to GTRCs; second memory medium for storing a set of GTRCs, a primary and a secondary destination signaling point, a secondary destination signaling point that is used to route the signaling information when a primary destination signaling point is not available; first means of signal processing for exchanging the primary and secondary destination signaling points for a fraction of GTRCs for the duration of a time period defined in the base of a record of congestion identification messages issued by the signaling point of primary destination; and second signal processor means accommodated to receive a signaling transfer request, map the Global Title associated with the request of a GTRC used in the GTRC table, and to determine a destination signaling point to be used by the request in dependence. of the primary and secondary destination signaling points assigned to the mapped GTRC and to the availability of signaling point. Preferably, the apparatus comprises intelligent processing means accommodated to respond to the signaling traffic levels of change over time, adapting the duration and position of the time period. According to a third aspect of the present invention, an SCCP Signaling Connection and Control Part is provided for use in a signaling system of Signaling System no. 7, the SCCP comprises: a GTRC Global Routing Box table that maps Global Titles to GTRCs; a first primary and a secondary destination signaling point assigned to a set of GTRC, a secondary destination signaling point is used to route the signaling information when a primary destination signaling point is not available; a definition of at least a period of time, the definition is made on the basis of a register of congestion notification messages issued by the primary destination signaling point, accommodated means for exchanging the primary and secondary destination signaling points for a fraction of the set of GTRCs for the duration of the time period; means for mapping a Global Title, associated with a signaling transfer request received at the signaling point, to a GTRC using the GTRC Table; and means for determining the destination signaling point that is used for the request depending on the primary and secondary destination signaling points assigned to the mapped GTRC and the availability of a signaling point. According to a fourth aspect of the present invention there is provided, a method for determining the congestion of a destination signaling point of a telecommunications network, the method comprising: sending a request message by echo from a signaling point to a destination signaling point; in response to receiving the echo request message at the destination signaling point, returning a response message to the signaling point; and determining at the signaling point the delay between the sending of the echo request message and the reception of the response message, wherein the delay provides an indication of the level of congestion at the destination signaling point. Preferably, the destination signaling point is one of a destination signaling point set invited by emission by the signaling point. This set can correspond to those points of destination signaling in the network where congestion will probably occur. Where the signaling point and the destination signaling point (s) use SCCP, the echo request message may be a SCCP Status Test / subsystem (SST) message while the response message may be a status message from the SCCP / subsystem (SST). Subsystem Allowed (SSA). It is noted that this proposal represents a new use for the SSC and SSA messages that are normally used to determine the operational status of a remote network node.

Modes of the present invention can use a certain degree of echo response to assign dynamics and / or reassign signaling traffic to destination signaling points, for example, signaling traffic can be commed from a primary destination signaling point up to a point of secondary destination signaling if the primary destination signaling is observed to be congesting. In other embodiments of the invention, the echo response delays, or congestion levels derived therefrom, for a destination signaling point are recorded during the time period and, using this record, the periods of peak signaling traffic are define During such peak periods, the signaling traffic can be automatically transferred from the destination signaling point to some other secondary destination signaling point. These periods can be redefined dynamically if the pattern of signaling traffic within the network (and as represented in the congestion registers) changes. The embodiments of the fourth aspect of the invention may comprise the steps of: providing a Global Routing Box of Titles (GTRC) that maps the Global Titles to GTRCs; assign to each GTRC a primary and a secondary destination signaling point; exchange the primary and secondary destination signaling points for a fraction of GTRCs when the primary destination signaling point is approaching congestion or is predicted to be close to congestion; for a signage request in signaling, map the Global Title, associated with the request to a GTRC using the GTRC Table; and determining the destination signaling point to be used by the request in dependence on the primary and secondary destination signaling points assigned to the mapped GTRC. According to a fifth aspect of the present invention there is provided an apparatus for determining congestion at a destination signaling point of a telecommunications network, the apparatus comprising: transmission means for sending a request message by echo from a point of signage to a destination signaling point; automatic response means for returning a response message to the signaling point in response to the echo request message request; and processing means at the signaling point to determine the delay between sending the request message by echo and receiving the response message, wherein the delay provides an indication of the level of congestion at the destination signaling point.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention and to be able to show how in the same way it can be carried out in effect reference now it will be done, by way of example, to the attached drawings, in which: Figure 1 schematically shows the protocol levels of a Signaling System signaling network no. 7; Figure 2 schematically illustrates a mobile telecommunications network comprising a number of signaling points; Figure 3 is a flow diagram illustrating a method of assigning DPC in the network of Figure 2; and Figure 4 is a flow chart illustrating an alternate DPC allocation method in the network of Figure 2.

Detailed Description of Certain Modalities A protocol stack of Signaling System no. 7 (SS7) with reference to Figure 1. In particular, the Control Signaling Connection Part (SCCP) has been described including its role in transforming Global Titles (GTs) into Destination Point Codes (DPCs) by means of Boxes Global Title Routing (GTRCs). Figure 2 illustrates a mobile telecommunications network comprising a Mobile Gateway Switching Center 1 (GMSC) which provides a gateway inside and outside the mobile network for "foreign" networks. GMSC 1 connects directly to a pair of Mobile Switching Centers (MSCs) 2,3. One of these MSCs 2 is directly connected to a Local Location Register 4 (HLR), while the other of the MSCs 3 indirectly connects to HLR 4 through a third MSC 5. Each of the MSCs, GMSC, and HLR can be considered a Signaling Point (SP) to indicate the traffic that is transmitted over the network between the homologated application or user parts (for example, ISUPs, TCAPs, etc.). Each of the SPs of the network of Figure 2 comprises a computer / processor programmed to implement the SS7 protocol of Figure 1. In particular, the SCCP is implemented in each SP for the purpose of routing the SCCP messages on the signaling network. As already described above, on the basis of a GT associated with an SCCP message, the SCCP determines the Destination Point Code (DPC) associated with the destination SPC (or a next "hop" SPC in the case where the signaling information is sent to the destination SPC through one or more intermediate SPs). When considering the case where GMSC 1 wishes to request information about the status (current location, etc.) of a mobile subscriber, a database request should be sent from GNSC 1 to HLR 4. From Figure 2, it will be appreciated that the most direct (and therefore primary) route for the associated signaling information is through the MSC 2, through a secondary route it is through MSCs 3 and 5. A first database 6 (a "database of GT interpretation ") associated with GMSC 1 contains a table that maps the GT series to respective GTRCs. Thus, for example, all so-called shared numbers that begin with digits 123 or 124 are mapped to GTRC 1, all so-called shared numbers that begin with digits 125 are mapped to GTRC 2, and all so-called shared numbers that are begin with the digits 126 are mapped to GTRC 3. A second database 7 (a database of "interpretation of GTRC") maps GTRCs to the respective primary and secondary DPCs, for example GTRC 1 and 2 are mapped to DPC 1 -2-3 (using network cluster member notation) as primary DPC and DPC 1-2-4 as secondary DPC, while GTRC 3 maps to DPC 1-1-1 as primary DPC and DPC 2-2- 2 as a secondary DPC. The GT interpretation and interpretation GTRC databases are illustrated respectively in Tables 1 and 2 below. Each signaling point in the network is continuously monitoring the signaling traffic it is driving. In the event that a point becomes congested, it diffuses a congestion notification message known to the neighboring points as a Congested Message from the SCCP / Subsystem (SSC). In conventional systems, receiving such a message at a signaling point may cause a temporary reconfiguration of the GTRC interpretation database to occur, so that for certain GTRCs (ie, those having the congested signaling point as its primary DPC), the primary and secondary DPCs are exchanged. However, in the system described herein, in addition to this process, the SSC messages received at a signaling point are recorded in a congestion registration database 8. In this way, each signaling point is able to build a record of congestion levels occurring at neighboring points over a period of time. Based on these records, a signaling point (or network operator) is able to identify each neighboring signaling point, periods of peak usage (for a given day) during which that point can be expected to be congested. For example, the operator can define periods 9am to 10am and 1pm to 2pm as periods of peak traffic for a given neighbor signaling point. Outside these periods, the computer running the SCCP maintains the GTRC interpretation database 6 in a given state, with each GTRC being mapped to the primary and secondary DPCs. When signaling traffic is slow, it will be expected that primary DPCs can handle traffic without congestion. However, if the congestion really occurs, then the secondary DPC can be used to handle any overflow of signaling traffic. When a peak user period is entered, the computer performs an automatic reconfiguration in the GTRC interpretation database, so that for certain GTRCs, the primary and secondary DPCs are exchanged. For example, and with reference to Table 1 above, the primary and secondary DPCs assigned to GTRC 1 and 3 may remain unchanged during the peak period, while for GTRC 2 the normal primary and secondary DPCs are exchanged, so that the DPC primary becomes DPC 1-2-4 and the secondary DPC becomes 1-2-3. Considering the example of Figure 2, outside the peak periods, SCCP messages that have GTs that fall within one of the 123xxx, 124xxx, or 125xxx series will preferably be routed through the primary route, that is, through the MSC 2. However, during peak periods, SCCP messages that have GTs falling within the 125xxx series will preferably be transferred through the old secondary route, that is, through MSCs 3 and 5, while the SCCP messages that have GTs falling within of the 123xxx or 124xxx series will continue to be transferred through the primary route. Figure 3 illustrates this route assignment process by means of the flow chart. The route assignment process described above will generally result in a more even distribution or sharing of signaling traffic between the signaling routes, since it avoids the need to occupy a given route to its capacity before a reassignment occurs. In a modification to the modality described in the above, the congestion registration database 8 may comprise derived information using echo messages / response reply (referred to as Subsystem Status Test (SST), and Permitted Subsystem Status ( SSA)), where the delay in receiving a replica is a measurement of congestion at the remote signaling point and congestion in the network. The use of SST and SSA messages to determine the level of congestion at a signaling point can be applied more generally, for example, where periods of peak and low signaling traffic are not necessarily defined. For example, a signaling point can invite by emission to the neighboring signaling points, or at least those that are likely to be congested, at regular intervals using SST messages. The issuing invitation signaling point may react dynamically to receive an SSA message from a guest signaling point per issue, and a subsequent determination that the issuing guest signaling point is approaching congestion) to reconfigure the base of data 7 of interpretation of GTRC. This process is illustrated in the flow diagram of Figure 4. It will be appreciated by the person skilled in the art that various modifications can be made to the embodiment described in the foregoing without departing from the scope of the present invention. For example, the invention is not limited to the SPs of mobile networks but can be applied to any signaling network that the SCCP employs. It will also be appreciated that, where the volume of signaling traffic warrants it, a GTRC can be mapped to a primary DPC and a plurality of secondary DPCs, ie, two or more. Alternatively, or in addition, several GTRCs have the same primary DPC, they may have different secondary DPCs such that during the signaling traffic of the peak periods they may deviate from the primary DPC to two or more secondary DPCs. Table 1 Table 2

Claims (19)

1. A method for routing signaling information at a signaling point of a telecommunications network, the method comprises: providing a GTRC Global Routing Box table that maps Global Titles to GTRCs; assigning to a GTRC set a primary and a secondary destination signaling point, a secondary destination signaling point that is used to route the signaling information when a primary destination signaling point is not available; defining at least one period of time based on a record of congestion notification messages issued by the primary destination signaling point; exchange the primary and secondary destination signaling points for a fraction of the set of GTRCs for the duration of the time period; for a signaling transfer request at the signaling point, map the Global Title associated with the request to a GTRC using the GTRC table; and determining a destination signaling point to be used by the request depending on the primary and secondary destination signaling points assigned to the mapped GTRC and the signaling point availability. The method according to claim 1, wherein the Global Titles are shared telephone call numbers, so-called shared telephone numbers, subscriber identity numbers, or mobile identification numbers. 3. The method according to claim 1 or 2, wherein the GTRC table maps the Global Titles to GTRCs using series of Global Title. The method according to any of the preceding claims, wherein the destination signaling points are Destination Point Codes, DPC, whose DPCs identify signaling designation points to receive the signaling information. 5. The method according to any of the preceding claims, wherein the first period (s) corresponds to a relatively high period of use. The method according to any of the preceding claims, and comprising: spreading congestion notification messages from a destination signaling point when this point becomes congested; monitor the messages at the signaling point to create a congestion log for the sending of the destination signaling point; and define the period (s) based on the record. The method according to claim 6, wherein the congestion notification messages contain a level of congestion that is additionally used by the reception signaling point to define the time period (s). The method according to claim 6 or 7, wherein the signaling point and the destination signaling points each comprise a Signaling Connection and Control Part (SCCP) of a Signaling System network no. 7 SS7, and the congestion notification messages are SSC, SCCP / Congested Subsystem messages. The method according to any of the preceding claims, wherein the time period (s) are dynamically defined so that they can be moved, or their duration changed to reflect the patterns of change in network traffic. 10. Apparatus for routing signaling information at a signaling point of a telecommunications network, the apparatus comprising: first memory means for storing a Global Routing Box of GTRC Titles that maps the Global Titles to GTRCs; second memory means for storing a set of GTRC, a primary and secondary destination signaling point, a secondary destination signaling point which is used to route the signaling information when a primary destination signaling point is not available; the first means of signal processing for exchanging the primary and secondary destination signaling points with a fraction of GTRCs for the duration of a defined period of time based on a record of congestion notification messages issued by the signaling point of primary destination; second signal processor means accommodated to receive a request for signaling transfer, mapping the Global Title associated with the request to a GTRC using the GTRC table; and to determine a destination signaling point to be used by the request in dependence on the primary and secondary destination signaling points assigned to the mapped GTRC and to the availability of signaling point. Apparatus according to claim 10 and comprising intelligent processing means accommodated to respond to signaling traffic levels of change over time, adapting the duration and precision of the time period. 1

2. A Signal Connection and Control Part (SCCP) for use in a signaling network of Signaling System no. 7, the SCCP comprising: a GTRC Global Routing Box table that maps the Global Titles to GTRCs; a primary destination signaling point, and a secondary destination assigned to a set of GTRCs, a secondary destination signaling point that is used to route the signaling information when a primary destination signaling point is not available; a definition of at least one period of time, the definition is made on the basis of a record of congestion notification messages issued by the primary destination signaling point; means accommodated to exchange the primary and secondary destination signaling points for a set fraction of GTRCs for the duration of the time period; means for mapping a Global Title associated with a signaling transfer request received at a signaling point, although GTRC using the GTRC table; and means for determining a destination signaling point to be used by the request depending on the primary and secondary destination signaling points assigned to the mapped GTRC and the signaling point availability. 1

3. A method for determining congestion at a destination signaling point of a telecommunications network, the method comprising: sending a request message by echo from a signaling point to a destination signaling point; in response to receiving the echo request message at the destination signaling point, returning the signaling point a response message; and determining at the signaling point the delay between the sending of the echo request message and the reception of the response message, wherein the delay provides an indication of the level of congestion at the destination signaling point and on the signaling link of intervention. 1

4. The method according to claim 13, wherein the destination signaling point is one of a set of destination signaling points invited or issued by the signaling point, the set corresponding to those destination signaling points in the network where congestion will likely occur. The method according to claim 13 or 14, wherein the signaling point and the destination signaling point (s) use SCCP, and the echo message is a SCCP Status Test message / SST subsystem and the response message is a SSA Permitted Subsystem Status message. 16. The method according to any of claims 13 or 15, and comprising using a predetermined echo response delay to dynamically allocate and / or reassign the signaling traffic to the destination signaling points. The method according to any of claims 13 or 15, wherein the echo response delays, or congestion levels derived therefrom, for a destination signaling point are recorded for a period of time and using In this record, peak signaling traffic periods are defined during which signaling traffic is automatically transferred from the destination signaling point to some other secondary destination signaling points. The method according to any of claims 13 or 17, and comprising the steps of: providing a GTRC Global Routing Box table that maps the Global Titles to GTRCs; assign to each GTRC a primary and a secondary destination signaling point; exchange the primary and secondary destination points for a fraction of the GTRCs when the primary destination signaling point is approaching congestion or is predicted to be approaching congestion; for a signaling transfer request at the signaling point, map the Global Title associated with the request to a GTRC using the GTRC table; and determining the destination signaling point to be used by the request in dependence on the primary and secondary destination signaling points assigned to the mapped GTRC. 19. Apparatus for determining congestion at a destination signaling point of a telecommunications network, the apparatus comprising: transmission means for sending a request message by echo from a signaling point to a destination signaling point; automatic response means for returning a response message to the signaling point upon receipt of an echo request message; and processing means at the signaling point to determine the delay between the sending of the request message by echo and the reception of the response message, wherein the delay provides an indication of the level of congestion at the destination signaling point on the Intervention signaling link