It is desirable for authorities such as the police and intelligence services to be able to monitor communications between criminals, terrorists or other that are involved in criminal activities. It is important to be able to conduct this surveillance without detection.

In the next generation of packet based networks it will be difficult to enable surveillance without detection. In such networks so-called soft switches will establish communication paths without the bearer path touching the s'witch'because the call control and bearer traffic are separated.

A further complication is caused by access nodes and gateway nodes in the network originating from different vendors.

Call transfer can result in a yet further complication in that a call connection can result in the call being routed outside of the service provider's network.

Prior art figure 1 shows a proposed softswitch based Voice over Packe VoP network in which network devices used to provide the bearer transport are different to those devices used to provide the call control functions. In this network the softswitch is used to provide a bearer network for a call from the various network devices. The switch does not however receive the call contents, that is to say, it itself does not form part of the bearer network. The problem therefore arises how a call may be intercepted without alerting the person being monitored.

According to the invention there is provided method for intercepting at least part of the content of a call over a telecommunications network which method comprising: determining at least one network device through which the at least part of the content will pass which can act as an intercept access point; selecting the at least one network device to act as an intercept access point ; instructing the intercept access point to intercept the at least part of the content and to convey the intercepted content to collection node of the telecommunications network.

By selection of a network device already used for a connection to act as the intercept access point (IAP) detection of the monitoring of the call by the subscriber is prevented.

The collection node will be one accessible by a monitoring authority such as a police or security service or other agency.

A specific embodiment of the. invention will now be described, by way of example only, with reference to the drawings in which: Figure 1 shows a prior art softswitch acket based communications network; Figure 2 shows a communications network operating in accordance with the invention ; Figure 3 shows part of the communications network of figure 2 in more detail;

Figure 4 is a flow chart of a call intercept operation in accordance with the invention; and Figure 5 shows an alternative preferred embodiment of the invention in which the network device selected to be used as the intercept access point is a border network element.

As is shown in figure 1, a prior art communications network 1 comprises subscriber equipment 2, a number of softswitches 3, a packet network 4, a trunk gateway 5, a public switched telephony network 6, a number of STPs 7, a SIP proxy server 8 and an access gateway 9. The subscriber equipment 2 includes telephones, sip phones and Integrated access devices IADs. The softswitches 3 utilise the indicated protocols to control the call connections. It should be noted that the call itself does not route through the softswitch but the bearer path is set-up by the softswitch. The softswitch does not have access to the call contents but it can identify network devices in the bearer path which will have access to the contents and which can be used as Intercept Access Points.

In the method of the invention, the softswitch is used to identify a network device in the bearer path that may be utilised to gain access to the call contents. The device or devices may be an access gateway, a router, an Asynchronous Transfer Mode ATM switch, a Network Address Translation NAT Server, a firewall server, a border gateway, a media server or other device that has access to the in-band call contents.

Thus, as is shown in figure 2, where like components bear the same reference numerals as figure, the softswitch 3 identifies network- devices 10,11 and access gateway 9 as being devices that, for communications involving users of equipment 2, may be used to intercept call content. The network devices may be an access gateway, a border gateway, an edge router, an edge ATM switch, a NAT server or other device.

The device is then instructed by the softswitch 3 to intercept particular calls in accordance with a set of interception criteria, for example with reference to certain destination addresses. The device then sends a copy of the contents of packets to a legal authority via a delivery function, the packet network 4 and the PSTN 6. The devices could be configured with an interface for this or the existing control interface used. The network devices used for the intercept are termed Intercept Access Points (IAPs).

The criteria for use in the interception of a call are termed the IAP Classifier and the CCC Classifier.

The IAP Classifier is used to identify the call contents which are to be intercepted. The information within the IAP Classifier includes the end point identifier of the subject, the IP address of the subject and the port number associated with the call.

The CCC Classifier is used to identify the destination for the destination for the intercepted contents. That is to say, the legal or other monitoring authority. The information within the classifier includes the IP address of the delivery function, and the CCC Identity.

Figure 3 shows in a schematic way the control by the softswitch 3 of the network device, the delivery function 14 and a collection function 15 at a legal authority. The softswitch 3 has control links 12 and 13 to the IAP 10,11 and the delivery function 14. The call content transport takes place via a d interface 16 between the IAP 10,11 and the delivery-s function 14. The call content transport between the delivery function 14 and the collection function 15 takes place via an e interface 17.

As is shown in figure 4, a first step 40 is for the establishment of a collection function. The next step 41 requires a delivery function to be established. Then in step 42, the softswitch 3 applies selection criterion to select a network device to act as an intercept access point IAP. In

step 43, the call intercept categories are sent to the IAP. In step 44, the IAP applies the categories and intercepts a call. In step 45, the intercepted call contents are sent to a delivery function and in step 46 the contents are sent by the delivery function to the collection function.

As will be appreciated by those familiar with communications networks, a feature of such networks is that the bearer path may change as a call connection is transferred or re-routed to different network nodes. This may be necessary because of loading on the network or faults developing or indeed as the result of a call transfer. As a result of this process the chosen IAP may no longer be involved in the call. Thus, in an enhancement of the method a real time interface is provided to the IAP such that in the event of the route changing the softswitch 3 is able to select a new network device to act as IAP. For this reason, devices will be chosen in preference to others to act as IAP since certain nodes are more likely than others to be involved in the calls originating from the subscriber.

The preferred devices to be used for the Intercept Access Points are Border Network Elements (BNE) and Media Servers (MS). The reason for this preference is that providers of IP based voice networks are faced with certain problems. Firewalls and NAT functions make it difficult to access subscribers from the network side because their private IP addresses are invalid in the public network domain. Security threats to the network and, in particular, denial of service attacks require a robust defence mechanism. Further, a quality of service QoS for voice traffic must not be detrimentally affected. Using the BNE or media server alleviates these problems since the device is positioned on the network side of the VoP infrastructure. Furthermore, all the voice traffic of a subscriber under surveillance must pass through these devices. The BNE creates a copy of the contents of the traversing traffic and sends the copy to the media server which forwards it to the monitoring authority.

Figure 5 shows the preferred embodiment. In this embodiment the softswitch 53 is a hiQ9200 switch and this establishes a bearer path from intercept subject 51 to an associate 52 of the subject. The establishment of the bearer path involves a protocol MGCP on control paths 55 and 56 to packet access devices 57 and 58.

The softswitch 53 determines to use a border network element 59 as the intercept access point (IAP) in conjunction with a delivery platform comprising media server (MS) 60. The MS 60 is instructed by the softswitch 53 via a protocol MGCP to deliver packets from the BNE to the monitoring authorities 61,62.

The BNE is instructed to act as the IAP, as before via a real time interface, and intercepts and copies contents of packets received from the packet access devices 57 and 58. The copied contents are sent to the MS 60 and thence to the monitoring authorities 61 and 62.

In alternative embodiments other network nodes may be used as the IAP for example the media server.