Abstract:
A communications system for conveying traffic of first and second types comprising: a first network entity being arranged to receive a request from a calling party to establish a communication channel for traffic to a called party identified in the request, the first network entity having means for determining a type of traffic identified in the request and for routing the request to the called party if the request is for traffic of a first type, and means for redirecting the request if the request is for traffic of a second type; and a second network entity arranged to receive the redirected request and having means for routing the request to the called party whereby a channel for traffic of the second type can be established via the second network entity.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     The present invention relates to video traffic in a communications system, particularly but not exclusively to a system supporting packet switched and circuit switched wireless networks.  
       SUMMARY OF THE INVENTION  
       [0002]     Communications systems providing wireless communication for user equipment are known. An example of a wireless system is the public land mobile network (PLMN). PLMNs are commonly based on cellular technology. In cellular systems, a base transceiver station (BTS) or some other access entity services mobile user equipment (UE) via a wireless interface between these entities. A communication on the wireless interface between the user equipment and element of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities.  
         [0003]     One or more gateway nodes may be provided for connecting the cellular access network to other networks, for example to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks. In such arrangements, a mobile communications network provides an access network enabling a user with wireless user equipment to access external networks, hosts or services being offered by specific service providers.  
         [0004]     A network which is commonly implemented is the IP multimedia call network subsystem (IMS). The IMS includes various network entities for the provision of multimedia services. IMS services are intended to offer, amongst other services, IP based packet data communication sessions between mobile user equipment. The IMS domain commonly supports a session initiation protocol (SIP) as developed by the Internet Engineering Task Force (IETF). Session initiation protocol (SIP) is an application layer packet based protocol for creating, modifying and terminating sessions with one or more participants (end points). A user connected to an SIP communications system may communicate with various entities of the communications system based on standardised SIP messages. These messages are laid down according to RFC (Request for Comments)  822 .  
         [0005]     A gateway node which is available for accessing the existing cellular access network is the H.324M-gateway. 3G-324M-video telephony is one of the new emerging services in the third generation (3G) communications system. The 3G-324M protocol operates over an established circuit switched connection between two communicating terminals, and allows multimedia communication over circuit switched networks. It has been adopted by the third generation partnership project (3GPP) and is based on the International Telecommunications Union (ITU) H.324M specification for multimedia conferencing over CS networks. One of the possibilities it offers is to make a video call between two 3G terminals. Such video calls are termed herein circuit switched video calls because they are provided in real time across a circuit switched network.  
         [0006]     Another gateway node which is available is a SIP gateway node which allows video calls to be made between SIP terminals and 3G-324M terminals. The SIP gateway acts as a mediator between the two domains.  
         [0007]     At the moment, 3G terminals can make a video call to an SIP terminal using the existing communications architecture, including the H.324M gateway and the SIP gateway. However, it is not possible for an SIP terminal to make a video call to a 3G terminal. In an existing communications system, when an SIP terminal seeks to make a video call to a 3G terminal, a request is dispatched towards a network entity in the 3G network in the form of a mobile switching centre (MSC) server. The MSC server recognises the type of call (speech or video), and if it is a speech call routes it to the 3G terminal over the radio access network (RAN) infrastructure. However, if the call type is recognised as a video call, it is teared down at the MSC server because there is no means to provide interworking between the SIP packet based video session and circuit switched H.324M based video calls.  
         [0008]     It is an aim of the present invention to allow such calls to be implemented without affecting the existing SIP IETF standard protocols and in such a manner as to be compatible with existing 3GPP standards.  
         [0009]     According to one aspect of the present invention there is provided a communications system for conveying traffic of first and second types comprising: a first network entity being arranged to receive a request from a calling party to establish a communication channel for traffic to a called party identified in the request, the first network entity having means for determining a type of traffic identified in the request and for routing the request to the called party if the request is for traffic of a first type, and means for redirecting the request if the request is for traffic of a second type; and a second network entity arranged to receive the redirected request and having means for routing the request to the called party whereby a channel for traffic of the second type can be established via the second network entity.  
         [0010]     Another aspect provides a method of conveying traffic of first and second types in a communications system, the method comprising: receiving a request from a calling party to establish a communications channel for traffic to a called party identified in the request; determining a type of traffic identified in the request; routing the request to the called party via a first route if the request is for traffic of a first type; and routing the request to the called party via a second route if the request is for traffic of a second type, the second route including at least one network entity for handling traffic of the second type.  
         [0011]     A further aspect provides a network entity in a communications system being arranged to receive a request from a calling party to establish a communication channel for traffic to a called party identified in the request, the first network entity comprising means for determining a type of traffic identified in the request; means for routing the request to the called party if the request is for traffic of a first type; and means for redirecting the request if the request if for traffic of a second type. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     For a better understanding of the present invention and 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:  
         [0013]      FIG. 1  is a schematic diagram of a network architecture;  
         [0014]      FIG. 2  illustrates the sequence of steps in establishing a video call;  
         [0015]      FIGS. 3A and 3B  show formats of SIP messages; and  
         [0016]      FIG. 4  is a schematic block diagram of functional components of the MSS. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  illustrates schematically a network architecture within which an embodiment of the present invention can be implemented. The architecture does not illustrate all of the intermediate gateways and elements of a communications system, but describes the important entities for implementing an embodiment of the invention. A wireless network  2  is shown connected to an IP (internet protocol) multimedia call network subsystem (IMS)  4 . The wireless network  2  and the IP multimedia call network subsystem  4  are connected to an H.323 domain  6 . The wireless network  2  in the illustrated embodiment is a wideband code division multiplexed access (W-CDMA) network but is illustrated herein as one example of a circuit switched (CS) wireless network. The IMS  4  is illustrated herein as an example of a packet switched (PS) network. It will readily be appreciated that the invention can be implemented with other circuit switched and packet switched networks.  
         [0018]     The wireless network  2  is shown including a single terminal in the form of user equipment  8  which is labelled 3G-UE to denote that it is a user equipment operating according to the third generation wireless standard. It is connected to a mobile switching centre (MSC) server system MSS  10  in the circuit switched network  2 .  
         [0019]     The IP multimedia call network subsystem (IMS)  4  is shown to include a single terminal in the form of user equipment  12  which is labelled herein SIP-UE to show that it implements a session initiation protocol (SIP). In line with SIP terminology, the terminals are sometimes referred to herein as endpoints. User equipment or users that run certain applications on the user equipment are registered with an SIP backbone so that an invitation to a particular session can be correctly delivered to these end points. The SIP terminal  12  is connected to a connection processing server CPS  14 . The connection processing server  14  communicates with a domain name server DNS  16  whose function is to provide address resolution. That is, the address in the ReqURI is converted to the real IP-address by making a DNS query. The IMS  4  is connected to the H.323 domain  6  via an SIP gateway (SIP-GW)  18  which performs protocol conversion between SIP protocol and H.323 protocol suite. This is connected to an H.324M gateway  20  in the H.323 domain which itself is connected to the MSC server system  10  in the radio network  2 .  
         [0020]     It will be appreciated that the user equipment can take any appropriate form, in particular a mobile phone, personal computer (PC), personal digital assistant (PDA), etc. The user equipment includes transmitter and receiver circuitry for establishing wireless channels for communication with the relevant network, and processor means for establishing calls according to protocols supported in the terminals.  
         [0021]      FIG. 2  illustrates the sequence of events which occurs when the SIP user equipment  12  seeks to establish a video call with the 3G-user equipment  8 . In the following, reference is made to standard SIP messages which can be found in RFC 822. They are identified in the following by their name and Standards number. As is well known, SIP messages are divided into requests and responses, each having a preset protocol. The only request which is discussed in the following is an Invite request. Various responses are discussed, each identified by their particular number and name.  
         [0022]     According to step  1 , an invite message Invite  1  is established from the SIP terminal  12  to the connection processing server  14  in accordance with established SIP protocol. An invite message is initiated by the calling party and is used to ask parties to join a call. As shown in  FIG. 3A , the message format includes a start line  300 , one or more header fields  302 , an empty line  304  and an optional message body  306 . In implementation, each line ends with a carriage return line feed. The header fields include an FDP_A field which identifies the type of call, in this case that it is a video and audio call and a ReqURI field which holds an E.164 number identifying the called party. The ReqURI field thus holds a universal resource identifier in accordance with the E.164 standard. E.164 is an international numbering plan defined by ITU-T Recommendation E.164. Recommendation E.164 provides the number structure and functionality for numbers used for International public telecommunication. All telephone numbers can be called if a number is dialled of up to fifteen digits, made up of a one to three digit country code (CC), followed by the subscriber number (SN). The first few digits of the subscriber number can be a so-called National Destination Code (NDC), which can identify the type of telephone number being called. All country codes are assigned by ITU in Recommendation E.164. For instance a mobile number in Finland +358405001574 is an E.164 number where 358 is country code (CC) for Finland, 40 is the National Destination Code (NDC) and 5001574 is the subscriber number (SN).  
         [0023]     In accordance with step  2 , the CPS  14  returns a response  100 , a “trying” message which indicates that a request has been initiated by the calling party but the called party has not yet been located.  
         [0024]     According to step  3 , a DNS query is dispatched to the DNS  16  to provide address resolution. The DNS provides the real IP address needed to send an Invite to the correct physical destination.  
         [0025]     The CPS  14  issues an Invite message to the MSS  10  which once again includes the SDP_A field identifying that this is a video and audio call, and the ReqURI field identifying the E.164 address of the calling party. The MSS  10  returns a Trying message as indicated at step  5 .  
         [0026]     MSS  10  then proceeds to analyse the invite message Invite  1 . As shown in  FIG. 4 , the MSS includes a determining entity  40  which determines the type of call, that is whether it is speech or video. A routing entity  42  is connected to the output of the determining entity  40  and if it is determined that it is a speech call, the routing entity  42  routes the call directly to the called 3G terminal  8  in accordance with known practice. If it identifies that the Invite request corresponds to a video call type, a redirect entity  44  in the MSS  10  adds a prefix  46  to the E.164 address held in the ReqURI field and the contact URI field is set to the prefixed E.164 address which is allocated to the Invite message by the MSS  10 . The prefix can be a simple number like  50  that identifies the SIP gateway. The MSS  10  formulates an SIP message  302  (Moved Temporarily to the Calling Party) which is illustrated in  FIG. 3B . This message indicates that the called party is temporarily unavailable, and an alternate location should be included in the header. The SIP message  302  currently exists for call redirection purposes. It includes a contact URI field for holding the alternate location, so the prefixed E.164 address is held there.  
         [0027]     As indicated in step  8 , the connection processing server  14  returns the SIP message  302  to the calling party  12 . In accordance with normal redirect procedure, a calling party  12  now issues a new Invite message Invite  2  as shown in step  9  with the SDP_A field set to video and audio, and the ReqURI field now holding the new contact location, namely the prefix and the E.164 address (see  FIG. 3C ).  
         [0028]     An SIP  100  message Trying is returned from the CPS  14  as shown in step  10 . At the same time the CPS  14  sets up a query to the DNS  16  as shown in step  11 . Assuming that the address resolution for the prefixed address is satisfactory, the CPS establishes an Invite message including the prefix E.164 address to the SIP gateway  18 . The SIP gateway  18  returns an SIP  100  message trying to the CPS  14  as shown in step  13 , and also performs a conversion from the SIP protocol to the H.323 protocol as shown by step  13   a.  SIP protocol is converted to H.323 messages (which are Q.931 type of call control messages and H.245 control messages sent inside the H323 domain). In the described embodiment of this invention, when this conversion is effected the prefix is removed and the existing E.164 address is read so that the call is routed to the H. 324 M gateway  20  and from there to the called party  8 . This is shown in  FIG. 2  by the setup requests labelled  14 ,  15  and  16 . A response is sent from the called party  8  to the MSS  10  (step  17 ) which similarly returns a response to the H.324M gateway  20  (step  18 ). This allows the H.324M gateway  20  to connect to the SIP gateway  18  to continue the SIP session which was initiated when the Invite was received from CPS to SIP gateway. The SIP gateway  18  accordingly dispatches an SIP  200  okay message indicating that the request has been successfully processed.  
         [0029]      FIG. 5  is a schematic diagram illustrating in more detail the architecture of a mobile communications network supporting IMS and circuit switched calls.  FIG. 5  shows the radio network  2  divided into a call network CN and a radio access network RAN. The call network entities typically include various control entities and gateways for enabling the communication via a number of radio access networks and also for interfacing a single communications system with one or more communications system such as with other cellular systems and/or fixed line communications systems. In this case the call network CN includes the MSC server system  10  and the H.324M gateway  20 . The MSS is connected to the RAN over the Iu-CS interface. The radio access network for the IMS side includes a GPRS backbone which includes a number of service nodes which are referred to herein as serving GPRS support nodes (SGSN). One of these  32  is shown connected to the call network CN via a general GPRS support node (GGSN)  34 .  
         [0030]     It will readily be appreciated that while  FIG. 5  shows a wireless SIP user equipment, and the existing IMS network supports such equipment, a SIP terminal may also be non-wireless as denoted by reference numeral  60  in which case it communications with the CPS  14  via a suitable server or other network arrangement  62 .  
         [0031]     It will be appreciated that the difference which is implied herein between the 3G-UE and the SIP-UE is that the former supports circuit switched video and the second supports packet switched video. The mechanism by which the packet switched data is transferred (i.e. wireless as opposed to non-wireless) is not important.