Component ID in Ice Candidate

Question

Typical SDP Message

v=0 o=- 3376022867449415700 2 IN IP4 127.0.0.1 s=Doubango Telecom - chrome t=0 0 a=group:BUNDLE audio video a=msid-semantic: WMS Jyup2XWPA5tOgvau9NIBMjlZFQzSEl6g3P0b m=audio 57008 UDP/TLS/RTP/SAVPF 111 103 104 9 0 8 106 105 13 126 c=IN IP4 202.53.167.164 a=rtcp:57008 IN IP4 202.53.167.164 a=candidate:2068563606 1 udp 2122194687 192.168.10.148 57008 typ host generation 0 a=candidate:2068563606 2 udp 2122194687 192.168.10.148 57008 typ host generation 0 a=candidate:902314598 1 tcp 1518214911 192.168.10.148 0 typ host tcptype active generation 0 a=candidate:902314598 2 tcp 1518214911 192.168.10.148 0 typ host tcptype active generation 0 a=candidate:3083270405 1 udp 1685987071 202.53.167.164 57008 typ srflx raddr 192.168.10.148 rport 57008 generation 0 a=candidate:3083270405 2 udp 1685987071 202.53.167.164 57008 typ srflx raddr 192.168.10.148 rport 57008 generation 0 a=ice-ufrag:cinBWZB6tiSnOnf1 a=ice-pwd:50yVBGm5WuKlbZeyRrmjOvMn a=ice-options:google-ice a=fingerprint:sha-256 7C:69:84:B5:D5:C1:86:D0:56:8F:22:BA:5F:61:AD:1E:55:21:5A:6A:50:35:0C:49:E2:43:E9:C0:03:CC:B5:31 

Any candidate priority depends on the typical preference, local preference and component identifier with reference to RFC 5245

For the identifier of the component RTP 1, for the component of the component RTCP 2

therefore, based on the identifier of the component, the priority of the candidate changes.

But in the above code example, why the priority is the same for different component identifiers of the same candidate type.

Answer 1

Quote from RFC5245

Agent MUST calculate this priority using the formula in Section 4.1.2.1

Pay attention to the word SHOULD. Let's see what this means from RFC2119

SHOULD This word or the adjective “RECOMMENDED” means that there may be reasonable reasons in certain circumstances to ignore a specific point, but all the consequences should be understood and carefully weighed before choosing another course.

This means that it is not necessary to follow the algorithm exactly to calculate the priority of the candidate. The algorithm can be changed if necessary. I think the SDP you provided is such a thing. When calculating the priority, they ignored the identifier of the candidate component.