Halloween, 2011
Cullen Jennings
fluffy@cisco.com
1
• PeerConnection emits messages like this:
“SDP\n
v=0\n
o=- 2890844526 2890842807 IN IP4 192.0.2.1\n
s= \n
c=IN IP4 192.0.2.1\n
t=2873397496 2873404696\n
m=audio 49170 RTP/AVP 0”
2
• What if we want to add something else?
• For instance, a message ID
• Maybe some structure would be nice….
3
• {
“sdp”:”v=0\n
o=- 2890844526 2890842807 IN IP4 192.0.2.1\n
s= \n
c=IN IP4 192.0.2.1\n
t=2873397496 2873404696\n
m=audio 49170 RTP/AVP 0”
}
• Now at least we can extend things
4
• Easy to get confused if we have glare
• We both send SDP at the same time
• Is the SDP I just got a new call or an answer to my offer?
5
• {
“messageType”: “OFFER”,
“sdp”:”v=0\n
o=- 2890844526 2890842807 IN IP4 192.0.2.1\n
s= \n
c=IN IP4 192.0.2.1\n
t=2873397496 2873404696\n
m=audio 49170 RTP/AVP 0”
}
6
• We might have multiple sessions going on
• Either simultaneously or in sequence
• Message delays can make these look like each other
7
• {
“messageType”: “ANSWER”,
"callerSessionId":"13456789ABCDEF",
"calleeSessionId":"abc1234356",
“sdp”:”v=0\n
o=- 2890844526 2890842807 IN IP4 192.0.2.1\n
s= \n
c=IN IP4 192.0.2.1\n
t=2873397496 2873404696\n
m=audio 49170 RTP/AVP 0”
}
• Session ID must be globally unique
8
• {
“messageType”: “OFFER”,
"callerSessionId":"13456789ABCDEF",
…
}
• {
“messageType”: “ANSWER”,
"callerSessionId":"13456789ABCDEF",
"calleeSessionId":"abc1234356",
…
}
• Each side contributes a session ID
• Session defined by combination of each side
9
• A session has a sequence of offer/answer pairs
• Example: upgrade to video
We have an audio call
You decide to add video
• This requires multiple offer/answer pairs
• How do we distinguish them?
10
• {
“messageType”: “OFFER”,
"callerSessionId":"13456789ABCDEF",
“seq”:1,
“sdp”:”v=0\n
o=- 2890844526 2890842807 IN IP4 192.0.2.1\n
s= \n
c=IN IP4 192.0.2.1\n
t=2873397496 2873404696\n
m=audio 49170 RTP/AVP 0”
}
• Sequence indicates the current offer/answer exchange
• OFFER and ANSWER have same sequence number
11
• It’s not safe to have multiple OFFERs outstanding
• What happens if I do two changes in succession?
• Example:
Other side adds video
I accept but then user changes camera to one with different capabilities
I need to re-OFFER but when?
After he’s gotten my ANSWER
12
• {
“messageType”: “OK”,
“seq”:”2”,
"callerSessionId":"13456789ABCDEF",
"calleeSessionId":"abc1234356”,
}
• OK message indicates ANSWER received and accepted
• New session parameters are active
• Safe to do a new OFFER/ANSWER pair
13
• ICE is slow (can take 3-5 seconds to converge)
• We want to start ICE as soon as possible
• Best experience is to start ICE when Bob receives the OFFER
even before he accepts the call
• But we don’t know the media parameters till he answers the call
For instance, he might accept audio but not video
14
• {
“messageType”: “ANSWER”,
"callerSessionId":"13456789ABCDEF",
"calleeSessionId":"abc1234356",
“moreComing”:true,
“sdp”:…
// ICE candidates but recvonly media
}
• moreComing flag means that another ANSWER will follow to this
OFFER
• OFFER/ANSWER transaction isn’t complete till
moreComing=false
• No OK for moreComing=true
15
• Need to pass in TURN and STUN servers and credentials
• Often optimal to use more than one
• Proposal, array of URL
• Note Current text broken for IPv6 IP addresses
• Draft has:
new PeerConnection( “TURNS 203.0.113.2:3478”, …
• Proposal:
New PeerConnection( [“turns://203.0.112.2:3478”,”stun://example.com”], …
16
• JS Objects
• JSON strings
• Other
• Use ROAP?
• Move def of application/html-peer-connection-deta to ROAP?
17
• Help !
• Draft has
All SDP media descriptions for streams represented by MediaStream objects
must include a label attribute ("a=label:") whose value is the value of the
MediaStream object's label attribute. [SDP] [SDPLABEL]
• Is this label really the same as the SDP “a=label” ?
• Can’t require that we have this with legacy things?
• Why do we have this?
18
• Proposal
• Have a stats method on PeerConnection
• Have it return a dictionary of stats
• Define an IANA registry of well known stat names
• The dictionary value for a stat can be primitive type or an array or
object
19
• Tell CODECs something about the application that they may need
to understand to make good encoding choices
• Audio: is music or is spoken voice
• Video: prefer spatial or temporal fidelity
• Proposal
IANA registry of well known hints
Have some sort of setHints method on a media streams
20
• It happens (lets add video … )
• Deal with this in IETF
• ROAP takes care of it
21
• Proposal – Focus on the API
• Send and receive a string/blob
Unreliable delivery ?
Reliable delivery ?
Out of order delivery?
Stream of data ?
22
• Need to callback when received DTMF and way to tell audio
stream to send DTMF
• Proposal:
Add callback and method to send to audio streams
Add a way to disable it when creating stream
23
• Draft has
The relative order of all tracks in a user agent must be stable. All audio tracks
must precede all video tracks.
• Why do we need audio before video?
• Complicates mapping to SDP which is not this way
24