[rtcweb] Minimal SDP negotiation mechanism

[Harald Alvestrand <[e-mail]>]

I am looking at the WEBRTC API spec, which specifies a rudimentary 
negotiation framework: SDP objects prefixed by the string "SDP".

It seems clear to me that this needs at least information about whether 
something is an offer or an answer, and some way to complete the 
transaction when an offer is sent and something prevents it from completing.
Until we know we need more, what about the following, to be specified in 
the WEBRTC API?

SDP objects are sent through the API, prefixed with either of

SDP OFFER
SDP ANSWER

Alternatively, one can pass

SDP ERROR

to reply to an SDP OFFER when something goes wrong.

If one gets an OFFER and sends out an ANSWER, state changes.
If OFFER gets an ANSWER back, state changes.
In all other cases, state is as before.

We need to handle glare - when one sends an OFFER and gets back an 
OFFER, reply with SDP ERROR, enter a "glare" state, wait a bit, and send 
out an offer again.

Do we really have to have anything else?