mmusic Y. Gao Internet-Draft LB. Wang Intended status: Standards Track ZTE Expires: August 9, 2009 February 5, 2009 Classification of SDP draft-gaoyang-mmusic-classification-of-sdp-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may not be modified, and derivative works of it may not be created, and it may not be published except as an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 9, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Gao & Wang Expires August 9, 2009 [Page 1] Internet-Draft Classification of SDP February 2009 Abstract Generally, next SDP is alternative descriptions for the previous one of the same session. But there is other type of SDP which describe part of the session, not all aspects of the session. It must be combined with the previous one(or ones) to show the effects. There has been such usage of SDPs in RFC3108. But there is no such guidance for that extension and usage. This text is aimed for that. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Classification of SDP . . . . . . . . . . . . . . . . . . . . . 4 2.1. Integrative SDP . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Non-Integrative SDP . . . . . . . . . . . . . . . . . . . . 4 2.2.1. Partitive SDP . . . . . . . . . . . . . . . . . . . . . 4 2.2.2. Incremental SDP . . . . . . . . . . . . . . . . . . . . 4 3. Normative references . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Gao & Wang Expires August 9, 2009 [Page 2] Internet-Draft Classification of SDP February 2009 1. Introduction There has been SDPs usage that make one SDP just part description of the session. So we should have a detailed classification of SDP, and the classification will be guidance for complex extension and usage in the future. Gao & Wang Expires August 9, 2009 [Page 3] Internet-Draft Classification of SDP February 2009 2. Classification of SDP 2.1. Integrative SDP The SDP describes all aspects of the session.So we can say the new SDP is alternative description of the old one for same session. 2.2. Non-Integrative SDP The SDP describe part of the session, not all aspects of the session. It must be combined with the previous one(or ones) to show the effects, as the formula: "current session state" = "previous session state" + "modification session description" Considering the distinction of different usages, it can be further divided into two categories. Both of the usage categories obey the formula mentioned above. 2.2.1. Partitive SDP The SDP describe part of the session, and the description of this part is self-governed. One nice example is the usage in RFC3108: these different SDP describe different layers of the same connection, and SDP descriptors for different layers to remain simple and clean. The self-government is just confined in semantics of description. Relationship between the parts is not confined. For example, one part of modification takes the modification of another part as precondition. Then the modification will have predefined sequence. And it forms the Incremental SDPs in viewpoint of session level. 2.2.2. Incremental SDP The SDP describe part of the session, and the description of this part must be combined with the previous one(or ones) to show the meaning and effect. SDP has any or more than one characteristic of the three ones below can be treated as incremental SDP. 2.2.2.1. attributes value means unchangge for absence For some type of medias, it must pre-set a lot of attributes, but there attributes do not change in high frequency. So, this kind of attributes might be practical. Gao & Wang Expires August 9, 2009 [Page 4] Internet-Draft Classification of SDP February 2009 2.2.2.2. attributes using incremental value For some type of medias, some of its attributes needed to be adjusted frequently. And the value of the attributes is incremental. One example of such usage is virtual reality and multi-projector 3D displays. the location and angle of there projectors are usually controlled by stepper motor(stepping motor). The control signal of the stepper motor is a discrete and incremental value, which will only be meaningful in the basis of the original value. We may draw an analogy between it and whiteboard application: Whiteboard application has the attribute "a=orient:orientation" which has clearly predefined permitted values. But in virtual reality application, we should adjust the cameras and projectors according the movement of the viewer(user). Further, location and angle of there projectors might has some king of relationship for achieving seamless imagery. So,the predefined permitted values is not enough for virtual reality application. And the attributes with incremental value will be effective. 2.2.2.3. Partitive SDPs have predefined sequence If There is some relationship in the SDPs, such as one part of modification takes the modification of another part as precondition, the modification will have predefined sequence, and forms a big nested transaction. And the sub-modification in the whole nested transaction must be issued one by one. And in the whole, it forms a kind of incremental SDP. Gao & Wang Expires August 9, 2009 [Page 5] Internet-Draft Classification of SDP February 2009 3. Normative references [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC3308] Calhoun, P., Luo, W., McPherson, D., and K. Peirce, "Layer Two Tunneling Protocol (L2TP) Differentiated Services Extension", RFC 3308, November 2002. [RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, October 2002. Gao & Wang Expires August 9, 2009 [Page 6] Internet-Draft Classification of SDP February 2009 Authors' Addresses Gao yang ZTE CHINA Email: gao.yang2@zte.com.cn Wang Libo ZTE CHINA Email: wang.libo@zte.com.cn Gao & Wang Expires August 9, 2009 [Page 7]