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Sdp:session description Protocol. Painting Description Protocol

The SDP descriptions mainly include: Session name, session purpose, session validity time, the media that constitutes the session, and the information that accepts the media (address, port, format), and so on.

1. Overview
SDP is also a product of the Mmusic workgroup, and is used much in mbone content. The purpose is to pass the media stream information in the media session, allowing the recipient of the session description to participate in the session. The SDP basically works on the Internet. He defines the uniform format of the session painting description, but does not define the allocation of multicast addresses and the transmission of SDP messages, nor does it support the negotiation of media encoding schemes, which are completed by the lower-level transport protocol. Typical session transfer protocols include: SAP (announcement Protocol Session Announcement protocol), Sip,rtsp,http, and using MIME e-mail. (Note: Only one session description can be included for SAP, and the SDP for other session-to-protocol can contain multiple painting descriptions)

The SDP includes some of the following:
1) name and purpose of the session
2) Session Survival time
3) The media information contained in the session, including:
Media type (video, audio, etc)
Transport protocol (RTP/UDP/IP, h.320, etc)
Media Format (h.261 video, MPEG video, etc)
multicast or remote (unicast) addresses and ports
4) information required for receiving media (addresses, ports, formats and so on)
5) The bandwidth information used
6) Trusted Engagement information (contact information)
7) etc...

2. Agreement:
Session description//format and examples
v= (protocol version)//v=0
O= (Owner/creator and session identifier).
o=< username >< session id>< version >< network type >< address type >< address >
O=sname 1234567890 0987654321 I IP4 126.15.64.3
S= (Session name)//conversation name
I=* (Session information)//conversation information
u=* (URI of description)//u=http://www.zte.com.cn/staff/sdp.ps
e=* (email address)//[email protected](General text such as: Mr. Wang)
or E=MR. wang<[email protected]>
p=* (phone number)//p=+86-0755-26773000-7110 (Wang) or p=+1 617 253 6011
c=* (Connection information-the row is not required if it is already included in all media)
c=< Network type >< address information >< Connection address >
Multipoint meetings include TTL
Connection address: <base multicast address>/<ttl>/<number of addresses>
C=in IP4 224.2.13.23/127
C=in IP4 224.2.1.1/127/3
b=* (bandwidth information)//b=< revision (CT Conference total
IAS application-specific Max) >:< bandwidth value (KB/S) >
b=ct:120

One or more time descriptions (see below)
z=* (time zone Adjustments)//TimeZone adjustment
k=* (encryption Key)//k=< method >:< key > or k=< method >
a=* (zero or more session attribute lines)//a=< properties > or a=< properties >:< values >

Zero or more media descriptions (see below)
The lines are strictly in order, where:
Time Description:
T= (time the session is active)//< start >< end time, unit seconds, decimal NTP
t=2873397468 2873404969
r=* (zero or more repeat times)//< repeat time >< activity duration to start time reference offset list > unit seconds
r=604800 3666 90000 or written r=7d 1h 0 25h

Media Description:
m= (media name and transport address)
m=< Media >< ports >< Routing >< format list >
M=audio 49170 RTP/AVP 0 3
Protocol is RTP, section is AVP
Reference Rtp-parameters.txt
i=* (media title)//Press Address
c=* (connection information– is optional if already included in the session-level description)
b=* (bandwidth information)//Same as C
k=* (encryption key)//session level for recognition value, same as C
a=* (zero or more media attribute lines)
Two forms: (also with C) (see below)
A=<attribute> such as:
A=recvonly
A=<attribute>:<value>
Note: V,o,s,t,m is required, other items are optional.
If the SDP parser does not recognize a class type (type), the entire description is lost;
If a property value of "a=" is not understood, it is lost
The entire protocol is case-sensitive
Spaces are not allowed on both sides of "="
Session-level descriptions are the default values for media-level descriptions
All formats are <type>=<value>
An example SDP description is:

V=0
O=mhandley 2890844526 2890842807 in IP4 126.16.64.4
S=SDP Seminar
I=a Seminar on the session Description protocol
U=http://www.cs.ucl.ac.uk/staff/m.handley/sdp.03.ps
[email protected](Mark Handley)
C=in IP4 224.2.17.12/127
t=2873397496 2873404696
A=recvonly
M=audio 49170 RTP/AVP 0
M=video 51372 RTP/AVP 31
M=application 32416 UDP WB
A=orient:portrait

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