Re: Issue 48: Undefined RTCRtpListener behavior

Here is draft text to resolve Issue 48, based on my understanding of your suggestion (see https://github.com/openpeer/ortc/issues/48).
8.3 Matching rules

When the RTCRtpListener object receives an RTP packet over an RTCDtlsTransport, the RTCRtpListener attempts to determine which RTCRtpReceiver object to deliver the packet to, based on the values of the SSRC and payload type fields in the RTP header, as well as the value of the MID RTP header extension, if present.

The RTCRtpListener maintains four tables in order to facilitate matching: the ssrc_table which maps SSRC values to RTCRtpReceiver objects; the muxId_table which maps values of the MID header extension to RTCRtpReceiver objects, the pt_table which maps payload type values to RTCRtpReceiver objects, and the receiver_table which keeps track of payload types supported by each receiver.

For an RTCRtpReceiver object receiver, table entries are added when receiver.receive(parameters) is called, and are removed when receiver.stop() is called. If receiver.receive(parameters) is called again, all entries referencing receiver are removed prior to adding new entries.

SSRC table: ssrc_table[parameters.encodings[i].ssrc] is set to receiver for each entry where parameters.encodings[i].ssrc is set, for values of i from 0 to the number of encodings. If ssrc_table[ssrc] is already set to a value other than receiver, then receiver.receive(parameters) will throw an InvalidParameters exception.

muxId table: If parameters.muxId is set, muxId_table[parameters.muxId] is set to receiver. If muxId_table[muxId] is already set to a value other than receiver, then receiver.receive(parameters) will throw an InvalidParameters exception.

payload type table: If parameters.muxId is unset and parameters.encodings[i].ssrc is unset for all values of i from 0 to the number of encodings, then add entries to pt_table by setting pt_table[parameters.codecs[j].payloadType] to receiver, for values of j from 0 to the number of codecs. If pt_table[pt] is already set to a value other than receiver, or parameters.codecs[j].payloadType is unset for any value of j from 0 to the number of codecs, then receiver.receive(parameters) will throw an InvalidParameters exception.

Receiver table: receiver_table[receiver] is set to an array of payload types, parameters.codecs[j].payloadtype, where j varies from 0 to the number of codecs.

When an RTP packet arrives, if ssrc_table[packet.ssrc] is set: set packet_receiver to ssrc_table[packet.ssrc] and check whether the value of packet.pt is included in any of the entries in receiver_table[packet_receiver]. If so, route the packet to packet_receiver. If packet.pt does not match, unhandledrtp event.

Else if packet.muxId is set: If muxId_table[packet.muxId] is unset, fire the unhandledrtp event, else set packet_receiver to muxId_table[packet.muxId] and check whether the value of packet.pt is included in any of the entries in receiver_table[packet_receiver]. If so, set ssrc_table[packet.ssrc] to packet_receiver and route the packet to packet_receiver. If packet.pt does not match, fire the unhandledrtp event.

Else if pt_table[packet.pt] is set: set packet_receiver to pt_table[packet.pt], set ssrc_table[packet.ssrc] to packet_receiver and route the packet to packet_receiver.

Question: Do we also remove the pt_table[packet.pt] entry?

Else, fire the unhandledrtp event.

TODO: Revise this paragraph based on the outcome of the discussion on FEC/RTX/RED.