Internet DRAFT - draft-gaoyang-mmusic-classification-of-sdp
draft-gaoyang-mmusic-classification-of-sdp
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
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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
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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.
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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.
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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.
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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.
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Authors' Addresses
Gao yang
ZTE
CHINA
Email: gao.yang2@zte.com.cn
Wang Libo
ZTE
CHINA
Email: wang.libo@zte.com.cn
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