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The Current Situation• 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”
3
Well, that’s kind of lame• What if we want to add something else?
• For instance, a message ID
• Maybe some structure would be nice….
4
A JSON version• {
“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
• }
5
How do we tell offers from answers?• 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?
6
Message types• {
“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”
}
• }
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How do we identify sessions?• We might have multiple sessions going on
• Either simultaneously or in sequence
• Message delays can make these look like each other
8
Session ID• {
“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
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How session IDs get established• {
“messageType”: “OFFER”,
"callerSessionId":"13456789ABCDEF",
…
}
• {“messageType”: “ANSWER”,
"callerSessionId":"13456789ABCDEF",
"calleeSessionId":"abc1234356",
…
}
• Each side contributes a session ID
• Session defined by combination of each side
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Multiple offer/answer pairs• A session has a sequence of offer/answer pairs
• Example: upgrade to videoWe have an audio call
You decide to add video
• This requires multiple offer/answer pairs
• How do we distinguish them?
11
Sequence field• {
“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
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ANSWER confirmation• 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
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OK message• {
“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
14
ICE Pipelining• 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 callFor instance, he might accept audio but not video
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moreComing flag• {
“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
16
Configuration • 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”], …
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Syntax for Offer / Answer Messages• JS Objects
• JSON strings
• Other
• Use ROAP?
• Move def of application/html-peer-connection-deta to ROAP?
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Label• Help !
• Draft hasAll 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?
19
Stats
• 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
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Hints• 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
• ProposalIANA registry of well known hints
Have some sort of setHints method on a media streams
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Glare• It happens (lets add video … )
• Deal with this in IETF
• ROAP takes care of it
22
Data Channel• Proposal – Focus on the API
• Send and receive a string/blobUnreliable delivery ?
Reliable delivery ?
Out of order delivery?
Stream of data ?
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DTMF on Audio Stream• 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
24
Track Order• 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
