SDP (Session Description Protocol)

SDP
(Session Description
Protocol)

SDP is purely a format for session
description. It does not incorporate a
transport protocol and it is intended to use
different transport protocols as SIP, SAP,
RTSP, HTTP.
SDP

● Session Initiation
● Streaming Media
● Email and the WWW
● Multicast Session Announcement
Example of SDP Usage

In general, SDP must convey sufficient
information to enable applications to join a
session and to announce the resources to
be used to any non-participants that may
need to know.
SDP

● Session name and purpose
● Times the session is active
● The media comprising the session
● Information needed to receive those
media(addresses, ports,formats , etc.)
SDP

● "application/sdp"
● ISO 10646 character set in UTF-8
encoding.
● <type>=<value>
SDP Specification

● Session Description
● Time Description
● Media description
SDP description order

v= (protocol version)
o= (originator and session identifier)
s= (session name)
i=* (session information)
u=* (URI of description)
e=* (email address)
p=* (phone number)
c=* (connection information -- not required if included in
all media)
b=* (zero or more bandwidth information lines)
z=* (time zone adjustments)
k=* (encryption key)
a=* (zero or more session attribute lines)
Session Description

t= (time the session is active)
r=* (zero or more repeat times)
Time Description

m= (media name and transport address)
i=* (media title)
c=* (connection information -- optional if included at
session level)
b=* (zero or more bandwidth information lines)
k=* (encryption key)
a=* (zero or more media attribute lines)
Media Description

● Protocol version (“v=”)
v=0
● Origin (“o=”)
o=<username> <sess-id> <sess-version> <nettype>
<addrtype> <unicast-address>
● Session name (“s”)
s=<session name>
● Session information (“i=”)
i=<session description>

● URI (“u=”)
u=<uri>
● Email and Phone (“e=” and “p=”)
e=<email-address> (e=j.doe@example.com (Jane Doe))
p=<phone-number> (p=+1 617 555-6011)
● Connection Data (“c=”)
c=<nettype> <addrtype> <connection-address>
(c=IN IP4 224.2.36.42/127)
● Bandwidth (“b=”)
b=<bwtype>:<bandwidth>

● Timing (“t=”)
t=<start-time> <stop-time>
● Repeat time (“r=”)
r=<repeat interval> <active duration> <offsets from
start-time>
t=3034423619 3042462419
r=604800 3600 0 90000
● Encription Keys (“k=”)
k=<method>
k=<method>:<encryption key>
k=base64:<encoded encryption key>

● Attributes (“a=”)
a=<attribute>:<value>
● Media Description
m=<media> <port> <proto> <fmt>
m=video 49170/2 RTP/AVP 31

a=cat:<category>
a=keywds:<keywords>
a=tool:<name and version of tool>
a=ptime:<packet time>
a=maxptime:<maximum packet time>
a=rtpmap:<payload type> <encoding
name>/<clock rate> [/<encoding
parameters>]
SDP Attributes

a=recvonly
a=sendrecv
a=sendonly
a=inactive
a=orient:<orientation>
a=type:<conference type>
a=charset:<character set>
SDP Attributes

a=sdplang:<language tag>
a=framerate:<frame rate>
a=quality:<quality>
SDP Attributes

[Offer]
v=0
o=alice 2890844526 2890844526 IN IP4 host.atlanta.
example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=audio 49170 RTP/AVP 0 8 97
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 51372 RTP/AVP 31 32
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
Audio and Video
[Answer]
v=0
o=bob 2808844564 2808844564 IN IP4
host.biloxi.example.com
s=
c=IN IP4 host.biloxi.example.com
t=0 0
m=audio 49172 RTP/AVP 0 8
a=rtpmap:8 PCMA/8000
m=video 0 RTP/AVP 31
a=rtpmap:31 H261/90000

[Second-Offer]
v=0
o=alice 2890844526 2890844527 IN IP4
host.atlanta.example.com
s=
t=0 0
m=audio 51372 RTP/AVP 0
a=rtpmap:31 H261/90000
Audio and Video
[Second-Answer]
v=0
o=bob 2808844564 2808844565 IN IP4
s=
t=0 0
a=rtpmap:31 H261/90000

[Offer]
v=0
o=alice 2890844526 2890844526 IN IP4
s=
t=0 0
a=rtpmap:98 telephone-event/8000
a=sendonly
Two Audio Streams
[Answer]
v=0
o=bob 2808844564 2808844564 IN IP4
s=
t=0 0

[Offer]
v=0
o=alice 2890844526 2890844526 IN IP4
s=
t=0 0
Hold and Unhold
[Answer]
v=0
o=bob 2808844564 2808844564 IN IP4
s=
c=IN IP4 placeholder.biloxi.example.
com
t=0 0
a=sendonly

[Second-Offer]
v=0
o=bob 2808844564 2808844565 IN IP4 host.
biloxi.example.com
s=
t=0 0
Hold and Unhold
[Second-Answer]
v=0
o=alice 2890844526 2890844527 IN IP4
s=
t=0 0

[Offer]
v=0
o=alice 2890844526 2890844526 IN IP4
s=
t=0 0
a=sendonly
Hold with two streams
[Answer]
v=0
o=bob 2808844564 2808844564 IN IP4
s=
t=0 0
a=recvonly

[Second-Offer]
v=0
o=bob 2808844564 2808844565 IN IP4
s=
t=0 0
a=sendonly
a=recvonly
Hold with two streams
[Second-Answer]
v=0
o=alice 2890844526 2890844527 IN IP4
s=
t=0 0
a=sendonly

[Offer]
v=0
o=alice 2890844526 2890844526 IN IP4
s=
t=0 0
Audio, then Video Added
[Answer]
v=0
o=bob 2808844564 2808844564 IN IP4
s=
t=0 0

[Second-Offer]
v=0
o=alice 2890844526 2890844527 IN IP4 host.
atlanta.example.com
s=
t=0 0
a=rtpmap:31 H261/90000
Audio, then Video Added
[Second-Answer]
v=0
o=bob 2808844564 2808844565 IN IP4
s=
t=0 0
a=rtpmap:31 H261/90000

SDP (Session Description Protocol)

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