WO2012025802A2

WO2012025802A2 - Method for session modifying in the session description protocol

Info

Publication number: WO2012025802A2
Application number: PCT/IB2011/001669
Authority: WO
Inventors: Wally Zhao
Original assignee: Alcatel Lucent
Priority date: 2010-08-26
Filing date: 2011-06-20
Publication date: 2012-03-01
Also published as: WO2012025802A3; CN102387119B; CN102387119A

Abstract

Embodiments of the present invention disclose a technical solution for session modifying via SDP session description in communication network system. One network equipment determines a target attribute to be modified in the session; generating an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute. Network equipment receiving the SDP offer message can do selective modification based on the SDP description information, omitting the modification to irrelevant attributes. The SDP description information can be defined as a SDP extension attribute, which is set in the media stream in the session as a media-level attribute. The technical solution can achieve selective modification to the target attributes in the SDP session, and avoid changing other attributes than the target attribute in the session by mistake and therefore impacting on normal media stream communication.

Description

METHOD FOR SESSION MODIFYING IN THE SESSION DESCRIPTION

PROTOCOL

TECHNICAL FIELD

The present invention relates to the field of communication technology, and more specifically, to a method and apparatus for modifying a session in a multimedia communication system.

DESCRIPTION OF THE RELATED ART

The Session Description Protocol (SDP) is a format for describing media stream parameters. Published by the Internet Engineering Task Force (IETF) as RFC 4566, SDP provides multimedia sessions description for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. SDP can apply to various transport protocols and messaging between them so as to implement session announcement, session invitation, and session initiation. Typical transport protocols comprise, for example, Session Announcement Protocol (SAP), Session Initiation Protocol (SIP), Real-Time Steaming Protocol (RTSP), Multipurpose Internet Email Extension (MIME), Hypertext Transfer Protocol (HTTP), etc.

IETF RFC 3264 proposes a session negotiation mechanism/model by which network equipment A and network equipment B may use the Session Description Protocol (SDP) to negotiate a multimedia session procedure between them. Based on this model, Party A sends to Party B an offer containing a description of the desired session for Party A, for example, information on one or more media streams which Party A wants to initiate. Upon receipt of the offer, Party B will return to Party A an answer containing corresponding replies to each of the media streams information in the Offer. Each media stream can be enabled or disabled. So far, Party A and Party B come to an agreement of a multimedia session between them, and subsequent sessions between them will proceed based on this agreement until modified by a session update mechanism. IETF RFC 3264 also defines that a session modification mechanism is implemented after the establishment of session initiation.

In a session with multiple media streams, modifying one or more of the media streams or other session target attributes may change other irrelevant media stream in this session.

As stated in IETF RFC 3264, at any point during the session, either participant

MAY issue a new offer to modify attributes of the session. Here, a gateway may issue a new offer message in the following ways:

In the first way, the new offer is identical to the previous offer sent from the offerer side. That is, the origin field of this new offer may have the completely same session ID and version number as that of the previous SDR In this case, the answerer MUST generate a valid Answer which MAY be the same as the previous SDP Answer from the answerer, or MAY be different.

In the second way, the new offer is different from the previous offer sent from the offerer side. If an SDP offer different from the previous SDP is to be generated, the new offer MUST have respective media streams corresponding to each media stream in the previous SDP. In other words, if the previous SDP had N media streams, the new SDP MUST have at least N media streams. The i-th media stream in the previous SDP, counting from the top, matches the i-th media stream in the new SDP, counting from the top.

In reality, however, when issuing the new offer to modify a session of a certain media stream, the offerer side does not want to have any impact on the other streams. But according to the offer/answer model provided by IETF RFC 3264, the offer sent by the gateway has to include at least all the media streams no matter for the first way or the second way. Upon receipt of the new offer carrying all the media streams, Party B might generate an answer that is different from the previous SDP answer. Now a problem comes. That is, in this different answer, not only the media stream to be modified by Party A could be modified by Party B, the answerer, but also the irrelevant streams could get modified by Party B, which is however not desired by Party A.

SUMMARY OF THE INVENTION The present invention is intended to provide a technical solution for session modifying in the Session Description Protocol, which can achieve selective modification of target attributes in the session.

According to an aspect of the present invention, there is provided a method for SDP session modifying in network equipment. The network equipment determines a target attribute to be modified in the session, generates an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute, and sends the SDP offer message.

Preferably, the target attribute may be a media stream in the SDP session; the SDP description information may also be defined as an SDP extension attribute; the network equipment may set the SDP extension attribute as a media-level attribute in a media stream description in the session.

According to another aspect of the present invention, there is provided network equipment for SDP session modifying. The network equipment comprises: determining means for determining a target attribute to be modified in the session; processing means for generating an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute; and sending means for sending the SDP offer message.

According to another aspect of the present invention, there is provided a method for session modifying in network equipment. The network equipment receives an SDP offer message, identifies whether the SDP offer message contains SDP description information for identifying modification to a target attribute in the session, thereby generates a corresponding SDP answer message and sends the SDP answer message.

Preferably, the network equipment may selectively modify media streams in the session according to the SDP description information; the network equipment may select an answer to a media stream in the session from corresponding media stream descriptions that are provided in the previous SDP. According to another aspect of the present invention, there is provided network equipment for SDP session modifying. The network equipment comprises: receiving means for receiving an SDP offer message; processing means for identifying whether the SDP offer message contains SDP description information for identifying modification to a target attribute in the session, and thereby generating a corresponding SDP answer message; and answering means for sending the SDP answer message.

Preferably, the processing means may selectively modify media streams in the session according to the SDP description information; the processing means may select an answer to a media stream in the session from corresponding media stream description answers that are provided in the previous SDP at this side.

According to another aspect of the present invention, there is provided a communication network system, wherein two network equipments negotiate a multimedia session via an SDP session with each other. One of the network equipment determines a target attribute to be modified in the session and generates an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute; the other of the network equipment receives the SDP offer message and selectively modifies media streams in the session according to the SDP description information.

Technical advantages of the present invention:

According to the technical solutions provided by the present invention, after a session is established between two network equipment that use the SDP protocol to negotiating a multimedia session with each other, one or more media streams or other session target attributes in the session can be modified by using the technical solutions provided by the present invention, without changing other attributes than the target attribute(s) in the session and further without having impact on normal media stream communication.

BRIEF DESCRIPTION OF THE DRAWINGS Other features, properties, and advantages of the present invention will become more apparent from the detailed description, when taken in conjunction with the figures wherein,

Fig. 1 illustrates a multimedia communication system provided by an embodiment of the present invention;

Fig. 2 illustrates a media stream modifying flow based on the SDP protocol in the multimedia communication system provided by the embodiment of the present invention;

Fig. 3 illustrates a structural layout of a gateway provided by an embodiment of the present invention; and

Fig. 4 illustrates a structural layout of a terminal provided by an embodiment of the present invention.

Like elements have the same signs throughout the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Detailed description is presented below to preferred embodiments of the present invention with reference to the figures.

Fig. 1 is a multimedia communication system provided by an embodiment of the present invention. The multimedia communication system is a typical multimedia system performing interactions of audio and video by SIP. In the system, terminals 11 and 12 are connected via a gateway, and connections for audio and video media streams are established via the gateway. During the establishment of an audio session between the terminals 11 and 12, it is found, while negotiating media, that audio capabilities of the two parties are not compatible with each other. In this case, the gateway 10 will provide codec transcoding for the audio media stream between the terminals 11 and 12. For the video media stream, the gateway 10 is just responsible for forwarding the media stream, without involving codec transcoding.

According to an embodiment provided by the present invention, after the gateway 10 establishes with the terminal 11 a multimedia session including the audio and video media streams, for some reasons such as codec utilization efficiency, bandwidth and so on, the gateway 10 has to change the codec transcoding for the audio media stream used between the terminal 11 and itself and maintain original attributes for the video media stream. Attributes of the audio and video media streams between the gateway and the terminal 12 keep unchanged. And the gateway may perform a session negotiate with the terminal 11 by using the SDP offer/answer model, so as to complete modifying of the coding scheme in the audio media stream. In addition to setting the modified coding scheme in the audio streaming media information description using a new SDP offer message, the gateway 10 further sets SDP description information that is capable of identifying the session's target attribute, audio media steam modifying. For example, the SDP description information may be defined as a media-level SDP extension attribute that is added to an audio or/and video media stream description in the session. The terminal 11 may selectively modify media streams in the session according to the SDP extension attribute setting, for example, only modifying the coding scheme of the audio media stream while keeping attributes of the video media stream unchanged.

Hereinafter, detailed description is presented to the embodiment for a media stream modifying flow based on the SDP protocol in the multimedia communication system as provided in conjunction with Fig. 2.

First of all, a brief introduction is given to the SDP protocol involved in the present invention. One SDP message contains two layers, namely a session layer and a media layer. One session description might contain information on one or more media layers, whose basic content comprises: 1) a session information description, i.e., session name and purpose, session time, bandwidth used in a session, and user information of a session; 2) a media information description, i.e., media type such as video or audio, transport protocol such as RTP/UDP/IP, media format such as H.263 video or MPEG video, multicast address and media transport port (IP multicast session), etc. Usually the session description consists of many text lines each of which is in the format of type = value, wherein "type" is a letter and "value" is a structured text string.

Referring to steps S201, S202, and S203, brief description is presented below to the procedure of using the offer/answer model to negotiate establishment of an SDP session.

In step S200, the terminal 11 provides an SDP offer message to the gateway 10 before establishing a session with the terminal 12, the message containing a session description desired by the terminal 11. The media stream description portion is as below:

m=audio 49170 RTP/AVP 0 97

a=rtpmap:0 PCMU/8000

a=rtpmap:97 iLBC/8000

m=video 51372 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

Here, the m lines represent media stream information, i.e., audio represents audio, video represents a video stream. 49170 and 51372 represent UDP port numbers corresponding to the audio media stream and the video media stream, respectively. RTP/AVP indicates that the media transport protocol uses RTP/AVP. 0 and 97 in the audio media stream information description line indicate the respective two audio media stream coding schemes supported by the terminal 11, whose coding attributes are defined thereafter. 31 and 32 in the video media stream information description line indicate the respective two video media stream coding schemes supported by the terminal 11, whose coding attributes are defined thereafter.

In step 201, the gateway 10 further issues an SDP offer towards the terminal 12 according to its own media stream processing capability. The media stream description portion is as follows.

m=audio 49176 RTP/AVP 0 8 97

a=rtpmap:0 PCMU/8000

a=rtpmap:8 PCMA/8000

a=rtpmap:97 iLBC/8000

m=video 51378 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

Here, 0, 8, and 97 in the audio media stream information description line indicate the respective audio media stream coding schemes supported by the gateway 10, whose coding attributes are defined thereafter.

In step S202, the terminal 12 responds to the gateway via an SDP answer message. The media stream description portion is as follows:

m=audio 49174 RTP/AVP 8

a=rtpmap:8 PCMA/8000

m=video 51376 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

Here, 8 in the audio media stream information description line indicates that the terminal 12 selects a supported audio media stream coding scheme from the provided offer, whose coding attribute is defined thereafter. 31 and 32 in the video media stream information description line indicate that the terminal 12 selects a supported video media stream coding scheme from the offer provided by the gateway.

In step S203, the gateway 10 responds to the terminal 11 via an SDP answer message. The media stream description portion is as follows:

m=audio 49172 RTP/AVP 0

a=rtpmap:0 PCMU/8000

m=video 51374 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

Here, 0 in the audio media stream information description line indicates that the gateway selects a supported audio media stream coding scheme from the offer provided by the terminal 11, whose coding attribute is defined thereafter. 31 and 32 in the video media stream information description line indicates that the gateway selects a supported video media stream coding scheme from the offer provided by the terminal 11. In this embodiment, the gateway is not capable of codec transcoding for video. Hence, 31 and 32 indicates that the gateway transparently forwards to the terminal 11 the video coding scheme that is returned by the terminal 12.

In step S204, the terminals 11 and 12 perform audio and video media stream communication between them according to the negotiated media stream information and parameters in steps S201 to S203. For the audio media stream, terminals 11 and 12 use different coding schemes, and the gateway 10 bridges the audio media stream between them. For the video media stream, the same coding scheme is used for the terminals 11 and 12, and the gateway is only responsible for forwarding the media stream.

Hereinafter, description is presented to an audio media stream modifying flow between the gateway 10 and the terminal 11.

In step S205, the gateway 10 determines a target attribute to be modified in the session, namely an audio media stream description. For some reasons such as codec utilization efficiency, bandwidth and so on, the gateway 10 has to modify the audio media stream code transcoding scheme between the terminal 11 and itself but desires to maintain original attributes of the video media stream. Those skilled in the art would appreciate that the present invention is also suitable to modify one or more media streams and other target attributes in the session, for example, modifying an address, port or transmission, modifying a media stream format, modifying a media type, modifying media stream attributes, etc.

In view of RFC 3264, at any point during the session, the gateway 10 may issue a new offer to modify attributes of the session; whether the new offer is identical to or different from the previous SDP sent from the offerer side, the new SDP will contain at least all the media streams. Here, in addition to setting the new coding scheme in the audio media stream, the new offer message further contains SDP description information for identifying audio media steam modifying. The SDP description information may be defined as a media-level SDP extension attribute that is added to an audio media stream description in the session.

In an embodiment, the SDP extension attribute may be added to the video media stream (i.e., an irrelevant media stream) description in the session as a media-level attribute. The video media stream information in the offer message is identical to that of the previous SDP. An example of syntax for the SDP extension attribute is presented, which syntax is defined as follows:

Selective_Session_Modifying_Indicator= "a=StreamOmitted"

As such, the media stream description in the SDP offer message generated by the gateway 10 is as follows: m=audio 49172 RTP/AVP 97

a=rtpmap:97 iLBC/8000

m=video 51374 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

a=StreamOmitted

Those skilled in the art would appreciate that no value is defined for the SDP extension attribute in the foregoing recommended embodiment. However, the attribute may be further defined such that specific modifications are indicated by different values. For example, a=StreamsOmitted:0 indicates that modification is required, and a=StreamsOmitted: 1 indicates that modification is ignored. For the SDP extension attribute setting, it may be added to other irrelevant media stream description in the session as a media-level attribute or added to a target media stream description in the session as a media- level attribute, so long as which can provid indication of modification to the target media stream identifiable by a recipient.

In step S206, the terminal 11 receives the SDP offer message, identifies whether the SDP offer message contains SDP description information identifying audio media stream modifying, processes, according to the SDP description information, the media stream description provided by the offer, selectively modifies media streams in the session, and generates a corresponding SDP answer message whereby the terminal 11 responds to the gateway 10.

In the embodiment as provided by step S205, if the terminal 11 identifies that the video media stream description of the SDP offer message has an SDP extension attribute, namely "a=StreamOmitted," the terminal 11 will then omit modification to the video media stream based thereon, i.e., keeping the video media stream unchanged in the session modifying, and the terminal 11 will respond according to the media description of the previous SDP negotiation; for the audio media stream, the answer message will carry the modified audio media stream information. The answer message generated by the terminal 11 is as follows:

m=audio 49170 RTP/AVP 97

a=rtpmap:97 iLBC/8000 m=video 51372 RTP/AVP 31 32

a=rtpmap:31 H261/90000

a=rtpmap:32 MPV/90000

a=StreamOmitted

On the contrary, if the terminal 11 does not support the SDP extension attribute, according to RFC 4566, it will omit this extension attribute, and session modifying will proceed in a way as stipulated in RFC 3264. The answer message generated by the terminal 11 is perhaps as follows:

m=audio 49170 RTP/AVP 97

a=rtpmap:97 iLBC/8000

m=video 51372 RTP/AVP 31

a=rtpmap:31 H261/90000

It is worth noting that compared with the previous SDP parameters, the parameters of the video media stream become a subset of old parameters, i.e., a=rtpmap:31 H261/90000, which is allowed by RFC 3264. However, since the video media stream between the gateway 10 and the terminal 12 is still based on the old coding scheme, i.e., a=rtpmap:31 H261/90000; a=rtpmap:32 MPV/90000, the gateway 10 must bridge the two video media streams between the gateway 10 and the terminal 11 and between the gateway 10 and the terminal 12, which are based on different coding schemes. As described above, since the gateway 10 is merely capable of forwarding the video media stream instead of bridging the video media stream, the video stream between the terminal 11 and the terminal 12 will possibly be interrupted.

Those skilled in the art would appreciate that in the offer message received in the above recommended embodiment, no value is defined for the SDP extension attribute a=StreamOmitted. If the extension carrying a value is received, the value should be ignored. Further, if the two sides of SDP offer/answer have agreed on the SDP extension attribute and its value definition, the terminal 11 will process and modify the media stream description according to the agreed value definition.

Fig. 3 is a structural layout of the gateway 10 provided by an embodiment of the present invention, the gateway comprising determining means 311, generating means 312, and first sending means 313.

The determining means 311 determines a target attribute to be modified in an established SDP session. For some reasons such as utilization efficiency of codec resources, bandwidth and so on, the gateway 10 has to modify the codec transcoding scheme for an audio media stream between a client, namely the terminal 11, and itself while maintaining original attributes of other irrelevant media streams in the session. Those skilled in the art would appreciate that the present invention is also suitable to modify one or more media streams and other target attributes in the session, for example, modifying an address, port or transmission, modifying a media stream format, modifying a media type and media stream attributes, etc.

The generating means 312 issues a new offer to modify attributes of the session, as stated in RFC 3264. Whether the new offer is identical to or different from the previous SDP sent from the generating means 312, the SDP offer contains at least all media streams in the session. Here, in addition to setting a new coding scheme in a target audio media stream of the new offer message, the new offer message further contains SDP description information for identifying audio media steam modifying. The SDP description information may be defined as a media-level SDP extension attribute that is added to the target audio media stream and/or other irrelevant media stream description in the session.

The first sending means 313 sends the SDP offer message that is generated by the generating means 312 to the terminal via a specific transport protocol, such as SIP (Session Initiation Protocol), RTSP (Real-Time Streaming Protocol), etc.

Fig. 4 is a block diagram of the terminal 11 provided by an embodiment of the present invention, the terminal comprising receiving means 411, processing means 412, and second sending means 413.

The receiving means 412 receives an SDP offer message via a specific transport protocol, such as SIP (Session Initiation Protocol), RTSP (Real-Time Streaming Protocol), etc.

The processing means 412 identifies whether the SDP offer message contains SDP description information identifying modification to a target attribute. As agreed, the SDP description information may be defined as a media-level SDP extension attribute that is added to a target or/and non-target media stream description in the session. According to the SDP extension attribute, the processing means 412 may selectively modify media stream attributes in the SDP offer, for example, modifying the target audio media stream according to an attribute description provided in the offer, keeping other irrelevant media stream attributes unchanged and responding according to a media description provided in the previous SDP answer. Finally, the processing means constructs an SDP answer message according to the result of the processing.

The second sending means 413 sends the SDP answer message that is generated by the processing means 412 to the gateway 10 via a specific transport protocol.

Although some embodiments have been provided for the present invention the foregoing description, they are not used to limit the protection scope of the present invention. Those skilled in the art would further appreciate that various illustrative logic modules and steps described in conjunction with the embodiments disclosed here may be implemented as electronic hardware, computer software or a combination thereof. In order to clearly explain the interchangeability between hardware and software, the various illustrative logic modules and steps are generally illustrated in terms of functionality. Whether the functionality is implemented as hardware or software, this depends on specific applications and designs which are used by the entire system. Those skilled in the art would appreciate the interchangeability between hardware and software in these cases and how to best fulfill the function of each specific application. Those skilled in the art may possibly implement the function in a different way for each specific application, it is determined that such implementation should not be construed as departing from the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A method for SDP session modifying in network equipment, characterized by comprising the steps of:

A) determining a target attribute to be modified in the session;

B) generating an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute; and

C) sending the SDP offer message.

2. The method according to Claim 1, characterized in that the target attribute in step B) is a media stream in the session.

3. The method according to Claim 1 or 2, characterized in that the network equipment defines the SDP description information as an SDP extension attribute in step B).

4. The method according to Claim 3, characterized in that in step B), the network equipment sets the SDP extension attribute as a media-level attribute in a media stream description in the session.

5. Network equipment for SDP session modifying, characterized by comprising:

determining means for determining a target attribute to be modified in the session;

generating means for generating an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute; and first sending means for sending the SDP offer message.

6. The network equipment according to Claim 5, characterized in that the target attribute is a media stream in the session.

7. The network equipment according to Claim 5 or 6, characterized in that the generating means defines the SDP description information as an SDP extension attribute, which is set in a media stream description in the session as an media-level attribute.

8. A method for session modifying in network equipment, characterized by comprising the steps of:

A) receiving an SDP offer message;

B) identifying whether the SDP offer message contains SDP description information for identifying modification to a target attribute in the session, thereby generating a corresponding SDP answer message; and

C) sending the SDP answer message.

9. The method according to Claim 8, characterized in that in step B), the network equipment may selectively modify media streams in the session according to the SDP description information.

10. The method according to Claim 9, characterized in that in step B), the network equipment may select corresponding media stream descriptions that are provided in the previous SDP, for media streams in the session according to the SDP description information.

11. Network equipment for SDP session modifying, characterized by comprising:

receiving means for receiving an SDP offer message;

processing means for identifying whether the SDP offer message contains SDP description information for identifying modification to a target attribute in the session, and thereby generating a corresponding SDP answer message; and second sending means for sending the SDP answer message.

12. The network equipment according to Claim 11, characterized in that the processing means may selectively modify media streams in the session according to the SDP description information.

13. The network equipment according to Claim 12, characterized in that the processing means may select a corresponding media stream description answer that is provided in the previous SDP answer at own side, for a media stream in the session according to the SDP description information.

14. A communication network system, within which two network equipment negotiate a multimedia session via a Session Description Protocol (SDP) session with each other, characterized in that

one of the network equipment determines a target attribute to be modified in the session and generates an SDP offer message with SDP description information that is adapted for identifying modification to the target attribute;

the other of the network equipment receives the SDP offer message and selectively modifies media streams in the session according to the SDP description information.