HK1099146B - System, apparatus, and method for establishing circuit-switched communications via packet switched network signaling - Google Patents

Description

System, apparatus and method for establishing circuit switched communications via packet switched network signaling

Technical Field

The present invention relates generally to network communications, and more particularly to systems, devices and methods for establishing circuit-switched communications using signaling in a packet-switched network. In this way, services provided via the packet switched network may be provided to circuit switched communication subscribers.

Background

The development of communication infrastructures and protocols has allowed standard computing devices to become valuable communication tools. Computers communicate with each other and other electronic devices over networks ranging from Local Area Networks (LANs) to wide Global Area Networks (GANs), such as the internet. Other electronic devices have undergone similar changes, such as mobile phones, Personal Digital Assistants (PDAs), and the like. Currently, these wireless devices are used for a variety of different types of communications. For example, while analog mobile phones have traditionally been used for analog voice communications, today's mobile phones are powerful communication tools capable of delivering voice, data, images, video, and other multimedia content. PDAs that once were portable calendars and organizational tools now tend to include network communication capabilities such as email, internet access, etc. With the integration of wireless and landline network infrastructures, all types of information can be conveniently communicated between wireless and landline terminals.

There are network architectures that facilitate real-time services in the operator networks of such terminals. For example, the third generation partnership project (3GPP) IP multimedia core network subsystem (IMS) is an architecture for supporting multimedia services via a Session Initiation Protocol (SIP) infrastructure. The 3GPP has standardized the Universal Mobile Telecommunications System (UMTS) in various stages, where release 5 includes systems where the packet switched core network (PS-CN) dominates circuit switching and is also responsible for telephony services. Release 5 introduces a new core network into the UMTS architecture, the IMS core supporting telephony as well as multimedia services. IMS interacts with the Public Switched Telephone Network (PSTN) as well as the internet (or other such large-scale networks) to provide various multimedia services to users. In an IMS environment, proxies are identified as Call State Control Functions (CSCFs), and there are various types of them, including proxy CSCFs (P-CSCFs), serving CSCFs (S-CSCFs), and interrogating CSCFs (I-CSCFs). Generally, the S-CSCF performs and/or facilitates the performance of a number of functions including controlling session management functions of the IMS, providing access to home network servers, such as location services, authentication, etc. The P-CSCF generally serves as a contact point for applications, such as mobile terminal client applications, and performs and/or facilitates functions such as translation, security, authorization, and the like. The I-CSCF generally serves as the contact point in the home network for connections to subscribers of that home network or roaming subscribers currently located within the service area of that network. It may perform a number of functions such as allocating an S-CSCF to a user performing a registration, contacting a Home Subscriber Server (HSS) to obtain an S-CSCF address, forwarding SIP requests/responses to the S-CSCF, etc.

The 3GPP IMS makes use of SIP in order to exploit the network to achieve a large amount of functionality. SIP, as defined by the Internet Engineering Task Force (IETF), is an end-to-end signaling protocol that, among other things, facilitates the establishment, handling and release of end-to-end multimedia sessions. It may be used for applications such as internet conferencing, telephony, presence, event notification, instant messaging, etc. SIP enables network endpoints, or "user agents" (UAs), to discover each other and negotiate session characterizations. A User Agent (UA) represents a network endpoint that initiates SIP requests to establish media sessions and send/receive information. To locate other users, SIP makes use of the infrastructure of a network proxy server, such as the CSCF described above, to which users can send registrations, session invitations and other requests via their terminals. SIP supports various aspects of establishing and terminating sessions, such as user availability, session establishment such as ringing, session management and some limited terminal capabilities.

For IMS communications, information transfer is based on the Internet Protocol (IP). IP is designed for use in interconnected systems of packet-switched communication networks, such as the internet. This network layer protocol separates messages into datagrams that are transmitted over the network to the receiving device via various network media and reassembled at the receiving device. IP is a "connectionless" protocol, meaning that there is no continuous connection between the endpoints of the communication. Instead, packets are sent from the sender, where the packets may take different paths, and network congestion may occur along any of the paths. Thus, the order in which packets are received may be different from the order in which they are sent, and transmission latency may adversely affect real-time or streaming communications.

For this reason, such real-time/streaming communication is often performed in the Circuit Switched (CS) domain, as is conventionally done. CS networks are those in which a physical path is obtained for a single connection between endpoints, where this physical path is dedicated to the connection for its duration. Real-time and other streaming services (e.g., audio, video) are traditionally provided via CS networks in order to preserve the temporal relationship between the endpoints of the communication. As mentioned above, such services may now be provided via the Packet Switched (PS) domain. For example, "voice over IP" (VoIP) generally denotes a service for managing the transfer of voice information employing IP such that voice data is transmitted via packets in a PS domain instead of a conventional CS domain. To address possible network latency issues, VoIP employs real-time protocol (RTP) to help achieve the goal of delivering packets in a timely manner.

However, many Mobile Stations (MSs) and other terminals do not support RTP-based VoIP or other real-time and/or IP-based streaming services. The complexity of providing real-time IP services in mobile networks is mainly due to the demands placed on the networks, where IP networks are typically based on a best effort model. The requirement of high data transmission rates and proper quality of service support to ensure adequate bit rates and other such requirements are current obstacles to ubiquitous real-time IP services. Furthermore, the MS may not currently or in the future support real-time and/or streaming services over PS networks employing protocols other than IP. For example, future PS networks may employ network protocols other than IP, where some legacy devices do not support packet-based communications employing such network protocols.

However, there may be services associated with such IP or other PS networks that may be desired by users of such devices but not available to such users. For example, IMS provides a wide variety of different services to users. MSs that do not support VoIP or other similar services need to engage in such communications in other ways, such as through circuit switched telephone service. In such cases, if the MS communicates via VoIP or other services through IMS, the user cannot utilize the various IMS services that would otherwise be available. Further, third generation (3G) networks of operators (or beyond) may provide VoIP and similar services, but may not provide all services available via IMS networks. In these situations, it is often desirable to provide IMS services to the user while allowing other communications over CS networks, VoIP enabled 3G networks, and the like.

There is therefore a need in the communications industry for ways to establish circuit switched communications using signaling in packet switched networks. There is also a need for ways to allow users to communicate via a circuit switched network to benefit from services provided in non-circuit switched networks. The present invention fulfills these and other needs, and provides other advantages over the prior art.

Disclosure of Invention

To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses systems, devices and methods for establishing circuit switched communications using signaling in a packet switched network.

According to one embodiment of the method of the present invention, a user communicating in the Circuit Switched (CS) domain is provided with a service via a Packet Switched (PS) multimedia network. A session is established between the terminals over the PS multimedia network. At least one of the terminals is provided with a service through a session. CS bearer information containing an indication to request a communication flow via the CS network is also communicated between the terminals over the dialog. The communication flow over the CS network is implemented between the terminals as directed by the CS bearer information.

According to a more specific embodiment of such a method, establishing a dialog between terminals over the PS multimedia network involves establishing a dialog between terminals using Session Initiation Protocol (SIP) via the PS multimedia network. In another particular embodiment, the PS multimedia network comprises an internet protocol multimedia subsystem (IMS), and establishing the dialog between the plurality of terminals involves establishing the dialog using Session Initiation Protocol (SIP) over the IMS. In one embodiment, a SIP INVITE request from one of the terminals to another or more is employed to establish a dialog in which the transfer of CS bearer information may be accomplished through a session description provided via SIP INVITE message body. In another embodiment, the session description is provided using the Session Description Protocol (SDP), in which CS bearer information is provided via the SDP. Some or all of the CS information may be carried by the SDP by, for example, a media type specific to communication flow via the CS network, an SDP connection data field identifying the CS network, a sub-field of a media type specific to communication flow via the CS network, an SDP attribute indicating the type of communication flow to be performed via the CS network, a sub-field of an application media type specific to communication flow via the CS network, and/or a session-level attribute indicating that communication flow is to be effectuated via the CS network. In other embodiments, the CS bearer information is conveyed by a CS-specific content type value associated with a SIP content-type header or by a CS-specific value associated with a CS-specific SIP header.

The services provided may be any services available via the IMS or other PS multimedia network. Such services may include, for example, multimedia forms of calling line identification services (referred to herein as multimedia CLI or MCLI), video services, audio services, video telephony, and other streaming video services, multimedia conferencing services, voice mail, call forwarding, or application sharing services. CS-based communication may also take various forms, such as real-time media transmission, conversational quality of service class streaming, streaming quality of service class streaming, voice calls, video and/or audio transmission, facsimile transmission, and so forth.

According to another embodiment of the present invention, a method of establishing a circuit-switched (CS) connection between at least two terminals is provided. A session is established between terminals over a Packet Switched (PS) multimedia network. CS bearer information is communicated between terminals via a dialog in which the CS bearer information contains some indication that a communication flow is requested via the CS network. The connection is established via the CS network based at least in part on CS bearer information provided through the dialog. The communication flow is implemented between the terminals using a connection established over the CS network.

According to another embodiment of the present invention, a terminal for receiving a service via a Packet Switched (PS) multimedia network and for communicating via a Circuit Switched (CS) network is provided. The terminal includes a processing system. The first user agent is operable with the processing system and is configured to establish a dialog with at least one other intended recipient terminal over the PS multimedia network and to communicate CS bearer information to the intended recipient terminal via the dialog, wherein the CS bearer information contains at least an indication of a request for communication flow via the CS network. A second user agent, operable via the processing system, is configured to conduct a communication flow between the terminal and the intended recipient terminal over the CS network as directed by the CS bearer information.

In a more specific embodiment of such a terminal, the first user agent is configured to utilize at least one service provided via a PS multimedia network, which may be, for example, an IP Multimedia Subsystem (IMS). In other particular embodiments, the first user agent comprises a Session Initiation Protocol (SIP) user agent, wherein the dialog is implemented using SIP. In other particular embodiments, the session description user agent is operatively coupled to the SIP user agent and is configured to provide CS bearer information to be communicated by the SIP user agent. Such a session description user agent may be provided, for example, by a Session Description Protocol (SDP) user agent. Such SDP user agents may be configured to provide CS bearer information by, for example, a communication flow specific media type via the CS network, a sub-field of an application media type specific to communication flow via the CS network, and/or a session-level attribute indicating that the communication flow is to be effectuated via the CS network. In still other embodiments, the SIP user agent is configured to provide the CS bearer information, for example, by a CS-specific content type value associated with a SIP content-type header and/or a CS-specific value associated with a CS-specific SIP header. The terminal may be a landline terminal such as a desktop computer, workstation, or the like, or may be a wireless device such as a mobile telephone, PDA, or other wireless device that may be coupled to the IMS system via some Radio Access Network (RAN).

In accordance with another embodiment of the present invention, a system for providing IMS-based services to a user communicating delay-sensitive information over a circuit-switched (CS) network is provided. Such delay sensitive information may include, for example, voice calls, video calls, facsimile transmissions, or other conversational and/or streaming QoS-like streams. The system at least comprises a sender terminal and a receiver terminal. The sender terminal comprises a processing system and a SIP user agent configured to initiate a dialog with the receiver terminal over IMS and to deliver CS bearer information to the receiver terminal via the dialog. The sender terminal also includes a CS communication user agent configured to effectuate communication flow with the receiver terminal via the CS network as directed by the CS bearer information. The recipient terminal includes a processing system and a SIP user agent configured to identify the CS bearer information and to acknowledge receipt of the CS bearer information in response to the sender terminal. The receiving terminal also includes a CS communication user agent configured to effectuate communication flow with the sending terminal via the CS network as directed by the CS bearer information.

According to another embodiment of the present invention, a computer-readable medium has stored therein instructions executable by a computer system for establishing a circuit-switched (CS) connection between at least two terminals. The instructions perform steps comprising establishing a dialog between at least two terminals over a packet-switched (PS) multimedia network, communicating CS bearer information comprising at least an indication to request a communication flow via the CS network between the at least two terminals via the dialog, establishing a connection via the CS network based at least in part on the CS bearer information provided via the dialog, and effectuating the communication flow between the at least two terminals with the connection established via the CS network.

These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of a system, apparatus, and method in accordance with the invention.

Brief description of the drawings

The invention will be described in connection with the embodiments shown in the drawings.

Fig. 1 is a block diagram generally illustrating the ability of a user without VoIP or other IP-based real-time/streaming communication capabilities to utilize IMS services, according to one embodiment of the invention;

fig. 2 is a block diagram illustrating one embodiment of establishing a CS session via IMS in accordance with the present invention;

fig. 3 is a diagram illustrating an exemplary manner of performing service control by IMS using SIP in accordance with one embodiment of the present invention;

fig. 4 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which new sub-fields are provided to media types;

fig. 5 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which application media types are implemented;

fig. 6 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which session-level attributes are used to identify CS-specific information;

fig. 7 is a diagram illustrating an embodiment of the present invention in which CS-specific information is provided as part of SIP information;

fig. 8 is a block diagram illustrating an exemplary manner of providing IMS services to a user while communicating via a CS domain in accordance with the present invention;

FIG. 9 is a flow diagram illustrating various embodiments of a method of providing services to users communicating in the CS domain via a PS multimedia network; and

fig. 10 illustrates a typical example of a mobile device that may be used as a UE in accordance with the present invention.

Detailed description of the invention

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the patent and trademark office patent file or records, but otherwise reserves all copyright rights whatsoever.

In the following description of various exemplary embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, as structural and operational changes may be made without departing from the scope of the present invention.

Generally, the present invention provides a way to establish Circuit Switched (CS) communications using signaling in a Packet Switched (PS) network. A user may establish a dialog with another user over a PS multimedia network, such as IMS, via a signaling protocol. By communicating via a PS multimedia network, the services provided by that PS multimedia network are available to one or both users. However, other communications may occur between users through one or more CS networks, in which a session established via a PS multimedia network includes information related to CS network communications. For example, a user without VoIP capability may establish a conversation via a PS multimedia network, utilize services provided by that PS multimedia network, and conduct telephone or other communications that require real-time conversation interaction via a CS network.

For internet protocol multimedia subsystem (IMS) communication, the information transfer is based on the Internet Protocol (IP) designed for interconnected systems of packet-switched communication networks, such as the internet. Such network layer protocols break messages into packets or "datagrams" (used interchangeably herein) that include unique network addresses for both the sender and the recipient. The packets are transmitted over a network, via various network media, to a receiving device, and reassembled at the receiving device (e.g., using transmission control protocol, user datagram protocol, etc.). IP is a "connectionless" protocol, meaning that there is no continuous connection between the endpoints of the communication. Instead, packets are sent from the sender, where the packets may take different paths, and network congestion may occur along any of the paths. Thus, the order in which packets are received may be different from the order in which they are sent, and transmission latency may adversely affect real-time or streaming communications.

Due to these latency possibilities, real-time/streaming communication is typically performed in the CS domain. Real-time services, such as telephony and streaming services, are traditionally provided via CS networks in order to preserve the temporal relationship between the endpoints of the communication. As previously mentioned, such services as VoIP have recently entered the Packet Switched (PS) domain. To address possible network latency issues, VoIP employs real-time protocol (RTP) to help achieve the goal of delivering packets in a timely manner. However, many Mobile Stations (MSs) and other terminals do not support RTP-based VoIP or other real-time and/or IP-based streaming services. Furthermore, the MS may not currently or in the future support real-time and/or streaming services over PS networks (e.g., IMS) that employ protocols other than IP. However, services made available via such networks as IMS may be desirable for such users who cannot utilize such services without the benefit of the present invention. MSs that do not support VoIP or other similar services need to engage in such communications in other ways, such as through circuit switched telephone service. In such cases, if the MS communicates via VoIP or other services through IMS, the user cannot utilize the various IMS services that would otherwise be available. Further, third generation (3G) networks of operators (or beyond) may provide VoIP and similar services, but may not provide all services available via IMS networks. In these situations, it is often desirable to provide IMS services to the user while allowing other communications over CS networks, VoIP enabled 3G networks, and the like.

The present invention allows IMS services to be provided to users in the CS domain or other network domains that otherwise would not use IMS. Thus, IMS services can be provided to users even if the operator's 3G network already has VoIP (or similar) functionality, or even if the MS does not support such VoIP or similar services or other situations in which IMS is not otherwise involved. It should be noted that while the various embodiments of the present invention set forth herein are described in terms of IMS, it will be apparent to those skilled in the art from the description provided herein that the present invention is applicable to other similar situations in which a network subsystem facilitates communication via certain protocols that are not supported by an MS, or in which an MS may only benefit from employing services from such a network subsystem. Thus, the invention is equally applicable to network subsystems other than IMS (e.g. PS multimedia networks). For example, the invention is applicable to other infrastructures supporting the signaling protocol for establishing PS sessions. In a more specific example, where SIP is used as the signaling protocol for establishing PS sessions, the present invention is applicable to SIP infrastructure operated by any operator/service provider. IMS operates such a SIP infrastructure.

Fig. 1 is a block diagram generally illustrating the ability of a user without VoIP or other IP-based real-time/streaming communication capabilities to utilize IMS services, according to one embodiment of the invention. The illustrated embodiment of fig. 1 relates to communication between two mobile devices 100, 102, however, the present invention is equally applicable to landline terminals such as desktop computers, workstations, and the like. The invention is equally applicable to communications involving an application server or other network entity (e.g. a conference server, etc.) providing a particular service to a user. Thus, while the various embodiments described herein are described in connection with communication between mobile devices, it should be appreciated that the present invention is applicable to communication involving other mobile or landline terminals. In the illustrated embodiment of FIG. 1, the mobile devices 100, 102 may include devices such as a mobile telephone 104, a Personal Digital Assistant (PDA)106, a portable computer 108, or other device capable of accessing a network via wireless communication.

According to the present invention, IMS services requiring substantial preservation of the time relationship between the communication endpoints 100, 102 employ CS domain bearers to carry real-time/streaming media, such as voice calls, to be provided to users. For example, conversational QoS class flows 112, such as voice calls, are carried in the CS domain, as shown by CS network 114. Other classes of flows that are sensitive to the temporal relationship between the communication endpoints may also be carried over the CS network 114, such as streaming QoS classes that include applications such as streaming video, audio, and so forth. While such communication is conducted over the CS domain, the present invention allows IMS services to be provided to the user of the device 100, 102 by performing service control 116 via the IMS or other similar multimedia IP network 118 associated with the PS network 120. For example, in one embodiment of the invention, the Session Initiation Protocol (SIP) is used to establish, modify, and terminate sessions over the IMS 118, and service control is performed by the IMS 118 using SIP. IMS services available to the user may include, for example, Multimedia Calling Line Identification (MCLI), streaming video and audio services, multimedia conferencing, application sharing, voicemail, call forwarding, and the like. In accordance with the present invention, users 100, 102 who otherwise would not want or have no ability to communicate conversational, streaming, or other time-sensitive class flows via the PS network 120 and the multimedia IP network 118 may communicate these class flows via the CS network 114 while still receiving one or more services via the multimedia IP network (e.g., IMS) 118.

According to one embodiment, the CS session 112 over the CS network 114 and the dialog 116 over the multimedia IP network 118 are bundled together on the terminal. For example, in the IMS context, the CS session 112 and the SIP dialog 116 are bundled together using a specific session description definition on the terminal 100, 102. No changes or additions to the network are required as the operator can configure the IMS elements to support this functionality. However, SIP messages carrying CS-specific session descriptions should not be blocked by the Call Session Control Function (CSCF) in the IMS domain, which is an operator policy decision.

In one embodiment of the invention, the session description is extended or modified to carry CS-specific information between the endpoints 100, 102 in connection with the session establishment. For example, in SIP session establishment, CS specific information may be carried using Session Description Protocol (SDP). The session description includes an indication from the terminal (e.g., MS 100) that the CS domain is to be used for conversational, streaming, or other delay-sensitive type flows. The routing number may be carried in a response to the request (e.g., a SIP response). Such a routing number may be used, for example, in conferencing or multiparty peer-to-peer communications to derive a dynamic conference number from the server to the originating terminal.

When the SIP dialog establishment is complete or in an appropriate session progress state, the originator, such as MS-a 100, initiates the CS call using the MS-B number. Thus, the MS is configured as a SIP dialog and corresponding CS bearer in which the MS is configured to work with technologies that transport multiple services simultaneously. For example, dynamic synchronous transfer mode (DTM), which is a synchronous transfer network technology capable of simultaneously transferring multiple services at different data rates, may be employed. DTM is a form of circuit switching for networks that employ Time Division Multiplexing (TDM) in a manner that dynamically allocates available bandwidth to users who need it. As another example, multiple Radio Access Bearers (RABs), called multi-RABs, of Wideband Code Division Multiple Access (WCDMA) provide the ability to allow the MS to use two RABs simultaneously. These or other similar current or future technologies may be used to support concurrent service control 116 and conversational/streaming flows 112 in accordance with the present invention.

As mentioned above, MS-a 100 may initiate a CS call upon completion of the SIP dialog setup or prior to completion of the SIP dialog setup. For example, one embodiment involves initiating a CS call by MS-A100 upon receiving an acknowledgement (e.g., a 200/OK response) from MS-B102 indicating a successful session establishment completion. In other embodiments, the CS call may be initiated prior to the full negotiation session. This may allow for a reduction in total setup time, and in some cases may allow for different user experiences in some applications. For example, MS-a 100 may initiate a CS call (e.g., send SETUP) upon receiving a provisional response, such as a session progress message (e.g., SIP 183 response).

In addition, the MSs 100, 102 register with the multimedia IP network 118 to facilitate service control 116. For example, the MS 100, 102 may register with the IMS using the SIP REGISTER message. In a more specific example, the SIP REGISTER message may be sent to the nearest proxy call session control function (P-CSCF) for that user, where the nearest P-CSCF may be located using Domain Name Service (DNS) SRV, Dynamic Host Configuration Protocol (DHCP), or the like. If the P-CSCF is in a visited network, the P-CSCF locates an interrogating CSCF (I-CSCF) of the user' S home network and sends a REGISTER message to the serving (S-CSCF). Once registered, the MS may be located for the communication. It should be noted that IMS roaming is supported between the visited and home networks, where the P-CSCF is located in the visited network. However, this is not a requirement, as other roaming support, such as GPRS roaming support, is sufficient and the P-CSCF may be located in the home network.

Referring now to fig. 2, a block diagram illustrates one embodiment of establishing a CS session via IMS, in accordance with the present invention. This embodiment again employs communication between two wireless devices, labeled MS-a200 and MS-B202. MS-a200 initiates SIP dialog 204 through GPRS/IMS network 206A over Visited Public Land Mobile Network (VPLMN) 208. SIP dialog 204 is established for MS-B202 through IMS domain 210 via GPRS/IMS 206B associated with VPLMN-B212 associated with MS-B202. More specifically, the MS-a200 sends a SIP request, such as the SIP INVITE request, to the P-CSCF-a 214 associated with the VPLMN-a 208. The INVITE is routed through S-CSCF-a 216, which in turn routes the request through S-CSCF-B218 and P-CSCF-B220 associated with VPLMN-B212. According to the invention, the sip invite request has a message body containing a session description carrying CS specific information, including a CS bearer media description. This session description is described in more detail below. Thus, SIP dialog 222 is established between MS-A200 and MS-B202 via IMS.

MS-B202 will parse the CS-specific information from the INVITE request and MS-B202 will thus become aware that MS-a200 is to engage in CS-based communications. Other IMS services may be used, such as Multimedia Calling Line Identification (MCLI), where a photograph or other image of the caller, a company logo, vCard, other graphics, audio clips, etc. may be provided to MS-B202. When MS-B202 responds to the INVITE, the session description for MS-B202 is provided to MS-a200, where the session description also provides the CS bearer media description.

When SIP dialog 222 has been established and session descriptions have been exchanged, MS-a200 initiates a call setup procedure over CS domain 224 using MS-B's 202 number, as shown by CS call control 226. For example, in a global system for mobile communications (GSM) network, call setup determines the locally responsible switch, which in the depicted embodiment is the Visited Mobile Switching Center (VMSC) 228. The VMSC 228 signals a visitor location register (VLR; not shown) to inform that the MS-a200 identified by the temporary TMSI in the location area LAI has requested service access. After authentication and other procedures, the remote VMSC 230 is notified of the connection request, and CS call control 232 occurs for MS-B202. MS-B202 will expect a CS call due to the SIP dialog 222 previously established indicating this. In this manner, the CS call 234 is established.

As previously described, a session over IMS may be established using SIP. Fig. 3 is a diagram illustrating an exemplary manner of performing service control by IMS using SIP in accordance with one embodiment of the present invention. The syntax of SIP message 300 generally includes at least a message header 301 and a message body 302. The message header 301 includes: a field, such as a "via" field, that identifies the address of the expected response; "to" and "from" fields, identifying the intended recipient and sender, respectively; a "call-ID" representing a unique identifier of a call; content length and type, etc.

Details of the session, media type, codec, sampling rate, and/or other details are not described using SIP. The message body 302 of the SIP message contains instead a description of the session encoded in some other protocol format, such as the Session Description Protocol (SDP). SDP can be used to describe multimedia sessions for the purposes of session announcements, session invitations, and other forms of multimedia session initiation. Other protocol formats may also be used to provide such a session description via the body of a SIP message, and any well-defined format for conveying sufficient information to participate in a multimedia session may be used in accordance with the present invention. SDP is taken in the embodiments of fig. 3-6 and represents only one way in which such session description details may be provided in accordance with the present invention. Thus, in the illustrated embodiment of fig. 3, the message body 302 includes an SDP message 304 as at least a portion of the SIP message body 302. The SDP message 304 is carried by a SIP message in a manner similar to the way a web page is carried via an HTTP message.

In the example of fig. 3, the SDP message 304 comprises a representative instance of the common portion 306 of the SDP message. The message line of this portion 306 illustrates exemplary description information that may be associated with an exemplary SDP message. The session description includes session level descriptions so that the description is applicable to the entire session as well as all media streams. The SDP structure generally involves a session-level portion followed by zero or more media-level portions. The session-level section begins with the "v" line 310 associated with the protocol version and continues to the first media-level section beginning with the "m" line associated with the media name. The media level part continues to the end of the session description or to the next media description. For example, in the illustrated embodiment, one media level portion begins at row 320 and another begins at row 322. In general, session level values are default for all media unless overridden by equivalent media level values.

Other session description entries are included in the SDP message portion 306, as is known in the art. For example, the "o" field 312 may represent the originator of the session (IN the illustrated example, "-" indicates that the originating device does not support or include a username) plus a session ID, a session version number (e.g., IN IP6), and so on. The "s" field 314 indicates the session name. The "c" field 316 represents connection data, which in the illustrated embodiment represents session-level connection data. It includes a network type (IN) and an address type (IP6) and a connection address (e.g., 5555:: aaa: bbb: ccc: ddd:). The "t" field 318 indicates the time the session is active for the conference (start/stop time "00" in the illustrated embodiment). The "m" field 320 represents a media description that includes several sub-fields including the media type (e.g., audio), the transport port to which the media stream is to be sent (e.g., 49170), the transport protocol (e.g., RTP/AVP as a real-time transport protocol employing an audio/video profile), and the media format (e.g., 0).

According to one embodiment of the invention, an SDP extension 308 is provided which represents an additional SDP message line that may be included to convey CS specific information for indicating that a CS connection is to be used. In this example, the SDP extension provides a new media type. More specifically, the SDP extension 308 includes a media description 322 containing a new media type "pstn _ audio". In accordance with the present invention, various new media types are provided to identify the CS bearer and associated media types. For example, the new media type "pstn _ audio" represents the audio media type carried by the CS. Similarly, new media types, such as "pstn _ video", "pstn _ fax", etc., may be provided for video, fax, and other media types carried by the CS. Such new media types may be registered, for example, by registering with the Internet Assigned Numbers Authority (IANA). In some embodiments, the media description 322 may also carry additional information related to the media, such as audio/video codecs, and the like.

The exemplary SDP extension 308 of fig. 3 also includes a connection data field 324. The network type "PSTN" describes the connection parameters of a PSTN call, including the telephone number of the SDP sender (e.g., + 358501234567). Or other network types of CS networks may be provided as well. A telephone number format (e.g., E164) may also be provided.

Attributes may be provided as shown on SDP extension lines 326, 328. The attribute field may have different forms. The property attribute has the form "a ═ flag >. They are binary attributes and the presence of such attributes indicates that the attributes are properties of the session. The value attribute has the form "a ═ attribute >: < value > ", where < value > defines the property of < attribute >. In the illustrated embodiment, a property attribute, as shown in expanded line 326, may optionally be provided to add more information about the media, where an "attribute" is any desired registered attribute. Similarly, x extension line 328 may optionally be used to identify unregistered properties.

Note that the same SDP 304 may include definitions of CS (e.g., PSTN) as well as IP sessions. For example, the media description shown in line 320 may be used for an IP session and the media description shown in line 322 of the SDP extension 308 may be used for PSTN communications.

Fig. 4 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which new sub-fields are provided to media types. According to an alternative embodiment of the invention, the SDP message 400 comprises a first SDP message portion 402 and SDP extensions 404A, 404B. SDP extensions 404A and 404B illustrate alternative exemplary SDP extensions in which new sub-fields of media types are provided in accordance with the present invention.

The first SDP message portion 402 is similar to the SDP message portion 306 described in connection with fig. 3 and will not be described further herein. The first exemplary SDP extension 404A includes a media description 406 that contains existing media types, such as audio, video, etc. In the depicted embodiment, media description 406 contains the known media type "audio". According to the described embodiment of the invention, the media description 406 of the SDP description 400 comprises a new sub-field type of media type. One such new subfield type in the media description 406 is a "PSTN" subfield type, representing the Public Switched Telephone Network (PSTN). This subfield type indicates that the media type, i.e. audio, is to be delivered via a CS bearer, which in the example is the PSTN. A new subfield type "PSTN" may be introduced to add PSTN call information. Other subfield types of different CS bearers may be designated as media subfield types according to the embodiment described in connection with fig. 4.

The connection data field 408 also includes a new subfield type, which is "PSTN" in the SDP extension 404A. This new subfield type describes the connection parameters of the PSTN call, including, for example, the phone number of the sender of the SDP message 400 (e.g., +358501234567) and, if necessary, the phone number format (e.g., E164). The type of service may be identified, such as audio, video, fax, etc. The attribute field 410 may be used to identify a new attribute to indicate a connection type. The new attribute type is denoted "cType" in the SDP extension 404A, which corresponds to the new connection attribute, and the attribute value is "Phone". The new attribute type may be used to identify any expected connection attribute of the CS bearer, such as "a ═ cType: telephony", "a ═ cType: video _ telephony", "a ═ cType: fax", and so on. In addition, other attributes may be provided, whether registered or not. For example, the exemplary SDP extension 404A includes an X extension line 412 to optionally identify an unregistered attribute, denoted as "X-other-attribute".

It is noted that the connection data field 408 may be omitted if all necessary parameters are added on the media description line. Such an embodiment is illustrated by the SDP extension 404B, in which the media description 414 includes the audio type and the new subfield type PSTN, as well as the telephone number of the sender of the SDP message 400 (e.g., +358501234567) and, if necessary, the telephone number format (e.g., E164). The new connection type "cType" may likewise be identified, as shown on attribute field 416, and other attributes as shown on x extension row 418 may optionally be used to identify unregistered attributes.

Fig. 5 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which application media types are implemented. In accordance with an alternative embodiment of the present invention, the SDP message 500 includes a first SDP message portion 502 and SDP extensions 504A, 504B. SDP extensions 504A and 504B illustrate alternative exemplary SDP extensions in which new application media types are provided in accordance with the present invention.

The first SDP message portion 502 is similar to the SDP message portion 306 described in connection with fig. 3 and will not be described further herein. The first exemplary SDP extension 504A includes a media description 506 in the standard "application" media type, with a new sub-type "PSTN" inserted to define a PSTN call. Other similar subtypes of CS bearers are identified or may be used in such embodiments. The media description 506 may also carry additional information about the media, such as audio/video codecs, etc., if desired or necessary.

In the depicted embodiment, the connection data field 508 describes connection parameters for a PSTN call. The connection parameters may include, for example, the phone number of the sender of the SDP (e.g., +358501234567) and, if necessary, the phone number format (e.g., E164). The type of service may be identified, such as audio, video, fax, etc. The attribute field 510 may be used to identify a new attribute to indicate the connection type. The new attribute type is denoted "cType" in the SDP extension 504A, which corresponds to the new connection attribute, and the attribute value is "Phone". The new attribute type may be used to identify any expected connection attribute of the CS bearer, such as "a ═ cType: telephony", "a ═ cType: video _ telephony", "a ═ cType: fax", and so on. Other attributes may also be provided by using the appropriate attribute or x-attribute, regardless of whether such attributes are registered.

It is noted that the connection data field 508 may be omitted if all necessary parameters are added on the media description line. Such an embodiment is illustrated by SDP extension 504B, in which media description 512 includes an "application" type and a new sub-type "PSTN" as previously described, and also includes connection parameters. The connection parameters may include, for example, the phone number of the sender of the SDP (e.g., +358501234567) and, if necessary, the phone number format (e.g., E164). Attributes may also be provided via the new connection type "cType", as shown on attribute field 514, and other attributes as shown on x extension row 516 may optionally be used to identify unregistered attributes.

Fig. 6 is a diagram illustrating another embodiment of an SDP extension in accordance with the present invention, in which session-level attributes are used to identify CS-specific information. In this embodiment, the CS bearer is not defined as a new media type, but a new session level attribute is added to inform that this session is related to CS communication. If the recipient does not understand the attribute, it simply ignores the attribute. The attribute parameters may include, for example, "x-pstn _ audio," "x-pstn _ video," "x-pstn _ fax," and so forth. If it is associated with a distinguished telephone number format, other attribute names may be used, such as "x-e 164_ audio", "x-e 164_ video", "x-e 164_ fax", and so forth.

Fig. 6 illustrates an example of session-level attributes used to identify CS-specific information, according to an embodiment of the present invention. The SDP description 600 is similar to the SDP message portion 306 described in connection with fig. 3, except that a session-level attribute 602 is newly added. In this example, the attribute parameters include an "x-PSTN _ audio" parameter indicating an unregistered attribute that the CS bearer (PSTN) carries audio communications. An associated attribute value, such as the phone number of the sender of the SDP, is provided (e.g., + 358501234567).

The various SDP extension embodiments described in connection with fig. 3-6 are representative of the types of SDP extensions that may be used in accordance with the principles of the present invention. It should be appreciated that other ways of communicating CS-specific information using SIP over IMS may be utilized. Thus, SDP or other session description is not the only mechanism for carrying such data. For example, a completely new data format may be defined, which contains CS specific information. For example, data may be added to the INVITE message as a new content type (i.e., a new MIME type). Alternatively, the CS specific information may be added as a new header in the SIP request. An example of such an embodiment is illustrated in fig. 7 below.

Fig. 7 is a diagram illustrating various embodiments of the invention in which CS-specific information is provided as part of SIP information. Fig. 7 illustrates a typical example of a SIP message header 700. According to one embodiment of the invention, the CS-specific information according to the invention may be added to the SIP message, as requested by SIP INVITE, as a new content type. For example, SIP header field 702 indicates "content-type". As known to those skilled in the art, a "content-type" is a Multipurpose Internet Mail Extension (MIME) header field used in a SIP header. The purpose of the MIME content-type field is to describe the data contained in the body so that the receiving user agent can identify the appropriate agent or other mechanism for providing the data or processing the data in an appropriate manner.

The value associated with the content-type field is referred to as the media type. According to one embodiment of the invention, a new CS media type 704 of content-type value is provided that identifies the media type as a CS bearer for communicating information via the corresponding CS domain. For example, the currently existing media types include "text", "image", "audio", "video", "application", and the like. In one embodiment of the invention, one or more new media types 704 of the content-type header field 702 are provided to identify CS specific information. According to the present invention, a media type may be defined as "cs _ bearer", "pstn _ audio", "pstn _ video", "pstn _ fax", etc. Alternatively, a new generic media type, such as "cs _ bearer," may be provided with the capability of being associated with one or more sub-types. For example, the current MIME text media type can be designated as a "text" media type, with a "plain" subtype identifying text as plain text. Similarly, "cs _ bearer" (or other selected media type name) may be associated with sub-types such as "pstn _ audio," "pstn _ video," "pstn _ fax," and so forth.

In another embodiment, the CS-specific information may be identified by a new header in the request. For example, a new header field 706, such as a "CS bearer" header field, may be provided. The media type 708 may be associated with such new header fields as "pstn _ audio", "pstn _ video", "pstn _ fax", etc. It should be appreciated that the header fields 702, 706 represent alternative embodiments, and that one or the other may be used in the SIP header field. For illustrative purposes only, header fields 702 and 706 are described in SIP message header 700.

As can be seen from the examples of fig. 3-7, CS specific information may be provided in any way according to the present invention. The present invention therefore contemplates providing such CS-specific information in any convenient manner.

Fig. 8 is a block diagram illustrating an exemplary manner of providing IMS services to a user while communicating via a CS domain in accordance with the present invention. The example of fig. 8 is directed to the use of IMS Multimedia Calling Line Identification (MCLI) services in conjunction with CS domain telephony communication. Generally, CLI is a service provided by many telephone providers in which a telephone number is transmitted when a telephone call is made. With a CLI-equipped receiving terminal, the user can see the telephone number of the caller before answering the call. MCLI denotes CLI where multimedia content is accompanied by or provided in place of a phone number. For example, a digital picture of the caller may be sent, and/or an audio clip, a graphic, a company logo, and/or the like. Although MCLI stands for IMS service in the illustrated example of fig. 8, other IMS services may be provided in a similar manner.

A first user associated with user equipment a (UE-a)800 sends SIP INVITE a request 802A to a target call recipient UE-B804. In the described embodiment, the INVITE request includes an SDP message (SDP- ｃA) associated with UE- ｃA 800. SDP- ｃA includes offered mediｃA including MCLI datｃA such as text, images, business cards, logos, audio clips, and/or other content. In one embodiment, SDP- ｃA also includes ｃA special "CS bearer" mediｃA description line indicating that ｃA bearer for audio is to be allocated from the CS domain. As mentioned before, the CS-specific information may also be provided in other ways than in the media description lines.

The Uniform Resource Identifier (URI) of UE-B804 is used to route the INVITE in the IMS. More specifically, the INVITE 802A is received at A P-CSCF 806 in A home public land mobile network (HPLMN-A)808 of the UE-A. The INVITE 802B is forwarded to S-CSCF 810 in the IMS and to P-CSCF 812 in UE-B' S804 HPLMN-B814, as shown by INVITE 802C. The INVITE 802D is provided from its P-CSCF 812 to UE-B804.

UE-B804 parses the "CS bearer" mediｃA description line (or other header, attributes, etc. carrying CS bearer information) from SDP- ｃA. SDP- ｃA carries the 800 telephone number of UE- ｃA, at which time UE-B804 expects ｃA telephone call from that number based on the CS bearer information. The UE-B804 also displays or otherwise provides MCLI via the UE-B804.

The UE-B804 responds with an appropriate SIP response message 816A-816D, which in the example is a SIP "183" response. As is known in the art, the SIP "183" response represents "session progress" which is used to convey information about the progress of the call without classification. Alternatively, UE-B804 may respond with SIP "200" (OK) messages 818A-818D. In either case, the response carries the SDP description for UE-B (i.e., SDP-B), which carries the "CS bearer" media description. Other SIP messages and responses that may occur are not shown.

UE-a 800 may initiate call setup 820 upon receiving a200 (OK) response 818D, or may initiate call setup 820 in response to receiving an intermediate SIP response, such as 183 (session progress) response 816D. UE-a 800 initiates a call setup 820 with UE-B's 804 number (ms _ B _ nbr), which is continued between VMSCs 822, 824 HPLMN-a 808 and HPLMN-B814 via Initial Address Message (IAM) 826. As is known in the art, an IAM is a message in the signaling system seven (SS7) or similar circuit switched signaling network for CS call setup. Call setup continues to UE-B804 where UE-B804 expects a CS call from UE-a 800 at this time due to the SIP signaling that occurred previously. Assuming that the user of UE-B804 decides to answer the call, the CS call is established via CS call connection paths 828A, 828B, 828C as shown.

Fig. 9 is a flow diagram illustrating various embodiments of a method of providing services to users communicating in the CS domain via a PS multimedia network. The PS multimedia network may be an IMS or other PS-based network for facilitating communication via internet protocols or other protocols that are not used for communicating information in the CS domain. A conversation is established 900 between two or more terminals over a PS multimedia network. At any point in the dialog, e.g., in connection with an initial request, response, or other signaling phase of the dialog, one or more services are provided 902 to at least one of the terminals, and CS bearer information is communicated 904 via the dialog. The terminals may communicate 906 with each other via the CS domain in a manner set forth by the CS bearer information provided via the dialog over the PS multimedia network. In this way, the terminal may communicate via the CS domain while receiving services via the IMS or other PS multimedia network.

According to one embodiment of the invention, establishing a dialog between terminals over an IMS or other PS multimedia network includes initiating the dialog using SIP INVITE request 908 or other signaling protocol message 910. In other embodiments, providing services to one or more terminals includes providing services such as MCLI 912, application sharing 914, multimedia conferencing 916, video 918, audio 920, other streaming/real-time services 922, and the like. In still other embodiments, communicating CS bearer information via a dialog may be performed in various ways, such as through the use of SDP extensions. Such SDP extensions include, for example, SDP media type extension 924, SDP media type subfield extension 926, SDP application media type extension 928, SDP session level attribute extension 930, and the like. The CS bearer information may be conveyed in other ways, such as via a new SIP content type 932, a new SIP header 934, or other signaling protocol content type or header 936. In still other embodiments, the CS communication between the terminals may involve real-time/streaming communication, such as telephone 938, videophone 940, facsimile transmission 942, and so on.

According to the present invention, hardware, firmware, software, or a combination thereof may be used to perform User Equipment (UE) functions and operations. The UE device according to the invention comprises communication means, such as SIP enabled devices, complying with the signalling protocol used. These devices include, for example, mobile phones, PDAs, and other wireless communicators, as well as landline computing systems and communicators. A typical example of a mobile device that may be used as a UE in accordance with the present invention is illustrated in fig. 10. The mobile device 1000 utilizes a computing system to control and manage the legacy device activities as well as the functionality provided by the present invention. The exemplary mobile device 1000 includes a computing system capable of performing operations in accordance with the present invention. For example, the exemplary mobile device 1000 includes a processing/control unit 1002, such as a microprocessor, Reduced Instruction Set Computer (RISC), or other central processing module. The processing unit 1002 need not be a single device and may include one or more processors. For example, a processing unit may include a master processor and associated slave processors coupled to communicate with the master processor.

The processing unit 1002 controls the basic functions of the mobile device 1000 as dictated by programs available in the program storage/memory 1004. Storage/memory 1004 may include an operating system as well as various program and data modules associated with the present invention. In one embodiment of the invention, the program is stored in a non-volatile Electrically Erasable Programmable Read Only Memory (EEPROM), flash ROM, or the like, so that the program is not lost when the mobile device is powered down. The storage 1004 may also include one or more of other types of read-only memory (ROM) and programmable and/or erasable ROM, Random Access Memory (RAM), a Subscriber Interface Module (SIM), a Wireless Interface Module (WIM), a smart card, or other fixed or removable storage. Coherent software for performing mobile device operations in accordance with the present invention may also be transmitted to the mobile device 1000 via data signals, such as being downloaded electronically via one or more networks, e.g., the internet and intermediate wireless networks.

To perform other standard mobile device functions, the processor 1002 is also coupled to a user interface 1006 associated with the mobile device 1000. The User Interface (UI)1006 may include, for example, a display 1008 such as a liquid crystal display, a keypad 1010, a speaker 1012, and a microphone 1014. These and other UI components are coupled to the processor 1002 as is known in the art. Keypad 1010 may include alphanumeric keys for performing various functions including dialing of conventional cellular/CS communications and/or for enabling SIP-based communications. Other UI mechanisms may be employed such as voice commands, switches, touch pad/screen, graphical user interface employing a pointing device, trackball, joystick, or any other user interface mechanism.

The wireless device 1000 may also include conventional circuitry for performing wireless transmissions over a mobile network. The DSP 1016 may be used to perform various functions including analog-to-digital (a/D) conversion, digital-to-analog (D/a) conversion, speech encoding/decoding, encryption/decryption, error detection and correction, bit stream conversion, filtering, and so forth. A transceiver 1018, generally coupled to an antenna 1020, transmits outgoing radio signals 1022 and receives incoming radio signals 1024 associated with the mobile device 1000. For example, the signals 1022, 1024 may be transmitted to the CS network or the PS network via a Radio Access Network (RAN), such as provided by GSM.

In the depicted embodiment, storage/memory 1004 stores various client programs, such as User Agents (UAs) involved in a conversation with another UE. For example, storage 1004 includes SIP UA 1026 or other similar UA associated with the signaling protocol used. In case a new SIP content-type or SIP header is used for sending CS-specific information according to the present invention, the calling SIP UA 1026 includes such information in the sent SIP message. The SIP UA 1026 on the "called" terminal receives the SIP request, parses the message, and identifies the CS-specific information. SIP UA 1026 also parses and processes other SIP message information.

As previously mentioned, other embodiments of the invention relate to sending CS-specific information via a session description, such as SDP. In one embodiment of the present invention, SDP (or similar) UA1028A is used on the calling UE to include such information in the SDP definition. On the receiving UE, SDP UA1028A is used to parse the incoming SDP, identify CS-specific information (and other session description information), and basically bundle the CS session and IMS/SIP dialog together in the terminal. Such an SDP UA may also be provided as part of SIP UA 1026, as shown in SDP UA 1028B.

The terminal also includes one or more CS communication agents 1030. For example, the CS-based telephony agent operates in conjunction with the processor 1002 to perform voice call setup and facilitate communication between the terminal and another terminal(s). The CS communication agent 1030 may also represent other and/or additional CS-based user agents such as a streaming video user agent, a streaming audio user agent, a videotelephony user agent, and so forth.

A similar computing architecture is provided for landline communicators. For example, a SIP (or other) UA and an SDP UA may be provided for execution by a processing system to perform functions in accordance with the present invention. Such landline communicators may include transceivers and/or other network interfaces to communicate information with the network.

The foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims (33)

1. A method for providing services to a user communicating in a circuit switched, CS, domain via a packet switched, PS, multimedia network, comprising:

receiving a session initiation protocol SIP INVITE message via an internet protocol multimedia subsystem, IMS, network to provide IMS-specific services between a plurality of terminals connected to the IMS network;

establishing a SIP dialog between a plurality of terminals through the PS multimedia network based on the INVITE message;

communicating CS bearer information between the plurality of terminals via the SIP dialog and by means of a session description protocol, SDP, message having an SDP extension indicating CS bearer information, wherein the CS bearer information contains at least an indication that a CS communication flow is requested via a CS network, and wherein the CS communication flow is bundled with an IMS-specific service in the plurality of terminals;

parsing the SDP message to determine the CS bearer information; and

the CS communication flow is effected between the plurality of terminals via the CS network as directed by the CS bearer information and in conjunction with provision of the IMS-specific service.

2. The method of claim 1, wherein communicating CS bearer information comprises communicating the CS bearer information by way of a session description provided via a message body of the SIP INVITE message.

3. The method of claim 1, wherein communicating the CS bearer information by way of SDP messages comprises communicating at least a portion of the CS bearer information via a media type specific to a flow of communication via the CS network.

4. The method of claim 3, wherein communicating the CS bearer information by way of an SDP message further comprises communicating at least a portion of the CS bearer information via an SDP connection data field identifying the CS network.

5. The method of claim 1, wherein communicating the CS bearer information by way of an SDP message comprises communicating at least a portion of the CS bearer information via a sub-field of a media type, wherein the sub-field is specific to a flow of communication via the CS network.

6. The method of claim 5, wherein communicating the CS bearer information by way of an SDP message further comprises communicating at least a portion of the CS bearer information via an SDP connection data field identifying the CS network.

7. The method of claim 5, wherein communicating the CS bearer information by way of an SDP message further comprises communicating at least a portion of the CS bearer information via an SDP attribute indicating a type of the communication flow to be effectuated via the CS network.

8. The method of claim 1, wherein communicating the CS bearer information by way of an SDP message comprises communicating at least a portion of the CS bearer information via a sub-field of an application media type, wherein the sub-field is specific to the communication flow via the CS network.

9. The method of claim 8, wherein communicating the CS bearer information by way of an SDP message further comprises communicating at least a portion of the CS bearer information via an SDP connection data field identifying the CS network.

10. The method of claim 8, wherein communicating the CS bearer information by way of an SDP message further comprises communicating at least a portion of the CS bearer information via an SDP attribute indicating a type of the communication flow to be effectuated via the CS network.

11. The method of claim 1, wherein communicating the CS bearer information by way of an SDP message comprises communicating at least a portion of the CS bearer information via a session-level attribute indicating that the communication flow is to be effectuated via the CS network.

12. The method of claim 1, wherein communicating CS bearer information comprises communicating the CS bearer information via a CS-specific content type value associated with a SIP content-type header.

13. The method of claim 1, wherein communicating CS bearer information comprises communicating the CS bearer information through a CS-specific value associated with a CS-specific SIP header.

14. The method of claim 1, wherein communicating CS bearer information comprises communicating the CS bearer information via a CS-specific content type value associated with a header of a signaling protocol operating in the PS multimedia network.

15. The method according to claim 1, wherein communicating CS bearer information comprises communicating the CS bearer information through a CS-specific value associated with a CS-specific header of a signaling protocol operating in the PS multimedia network.

16. The method of claim 1, wherein providing the IMS-specific service comprises providing at least one of a multimedia calling line identification service, a video service, an audio service, a videophone service, a multimedia conferencing service, voicemail, call forwarding, and application sharing service.

17. The method of claim 1 wherein effecting the CS communication flow between the plurality of terminals via the CS network comprises communicating real-time media over the CS network.

18. The method of claim 1 wherein effecting the CS communication flow between the plurality of terminals via the CS network comprises communicating a conversational quality of service class flow over the CS network.

19. The method of claim 1 wherein effecting the CS communication flow between the plurality of terminals via the CS network comprises communicating a streaming quality of service class flow over the CS network.

20. The method of claim 1 wherein effecting the CS communication stream between the plurality of terminals via the CS network comprises communicating at least one of a voice call, a video transmission, an audio transmission, and a facsimile transmission over the CS network.

21. A method for establishing a circuit switched, CS, connection between at least two terminals, comprising:

sending SIP INVITE a message via the internet protocol multimedia subsystem, IMS, network to provide IMS specific services between the at least two terminals connected to the IMS network;

establishing a SIP dialog between the at least two terminals through a PS multimedia network based on the INVITE message;

communicating CS bearer information between the at least two terminals via the SIP dialog and by means of an SDP message having an SDP extension indicating CS bearer information, wherein the CS bearer information contains at least an indication that a CS communication flow is requested via a CS network, and wherein the CS communication flow is bundled with IMS specific services in the at least two terminals;

establishing a connection via the CS network based at least in part on the CS bearer information provided via the SIP dialog; and

implementing the CS communication flow between the at least two terminals with the connection established via the CS network and in connection with the provision of the IMS-specific service.

22. The method of claim 21, wherein establishing the SIP dialog with the terminal over the PS multimedia network comprises establishing the dialog via a SIP infrastructure.

23. A terminal for receiving services via an internet protocol multimedia subsystem, IMS, network and communicating via a circuit switched, CS, network, comprising:

a processing system;

a SIP user agent operating via the processing system and configured to establish a SIP dialog with at least one target recipient terminal over the IMS network via transmission of an SIP INVITE message, wherein the SIP dialog is to provide IMS-specific services between the terminal and at least one target terminal of the IMS network, wherein the SIP dialog is established by passing an SDP message to the at least one target recipient terminal, the SDP message having an SDP extension with CS bearer information, the CS bearer information containing at least an indication that a CS communication flow is requested via a CS network, wherein the SIP user agent causes the processing system to identify the CS bearer information in an SDP message;

a CS communication user agent, operating via the processing system, and configured to effectuate the CS communication flow between the terminal and the at least one target recipient terminal via the CS network as directed by the CS bearer information;

wherein the CS communication flow is bundled with IMS specific services in the terminal.

24. A terminal as in claim 23, where said SIP user agent is further configured to utilize at least one service provided via said IMS network.

25. The terminal of claim 23, further comprising a session description user agent operatively coupled to the SIP user agent, wherein the session description user agent is configured to provide the CS bearer information to be communicated by the SIP user agent.

26. The terminal of claim 25 wherein the session description user agent comprises an SDP user agent configured to provide the CS bearer information via a media type specific to a flow of communication through the CS network.

27. The terminal of claim 25 wherein the session description user agent comprises an SDP user agent configured to provide the CS bearer information via a subfield of a media type, wherein the subfield is specific to communication flows via the CS network.

28. The terminal of claim 25 wherein the session description user agent comprises an SDP user agent configured to provide the CS bearer information via a subfield of an application media type, wherein the subfield is specific to the communication flow via the CS network.

29. The terminal of claim 25 wherein the session description user agent comprises an SDP user agent configured to provide the CS bearer information via a session-level attribute indicating that the communication flow is to be effectuated via the CS network.

30. The terminal of claim 23, wherein the SIP user agent is configured to provide the CS bearer information via a CS-specific content type value associated with a SIP content-type header.

31. The terminal of claim 23, wherein the SIP user agent is configured to provide the CS bearer information via a CS-specific value associated with a CS-specific SIP header.

32. A terminal as in claim 23, where said terminal comprises a mobile station that is wirelessly coupled to the IMS network and a CS network via a radio access network, RAN.

33. A system for providing internet protocol multimedia subsystem, IMS, based services to a user communicating delay sensitive information over a circuit switched, CS, network, comprising:

a receiver terminal;

a sender terminal, comprising:

a sender terminal processing system;

a sender terminal SIP user agent operating via the sender terminal processing system and configured to initiate a SIP dialog with the receiver terminal by transmission of the IMS via SIP INVITE message to provide an IMS-specific service to the receiver terminal and to communicate CS bearer information to the receiver terminal via an SDP message with an SDP extension with CS bearer information containing at least an indication that a communication flow is requested via a CS network with the receiver terminal; and

a sender terminal CS communication user agent operating via said sender terminal processing system and configured to effect said communication flow with said receiver terminal via said CS network as directed by said CS bearer information and to bundle said CS communication flow with said IMS-specific service in said sender terminal;

wherein the receiver terminal includes:

a receiver terminal processing system;

a receiver terminal SIP user agent operative via the receiver terminal processing system to receive the IMS-specific service from a sender terminal and configured to identify the CS bearer information and to acknowledge receipt of the CS bearer information in response to the sender terminal; and

a receiver terminal CS communication user agent, operating via the receiver terminal processing system and configured to effect the communication flow with the sender terminal via the CS network as directed by the CS bearer information, and to bundle the CS communication flow with the IMS-specific service in the receiver terminal.