ICE solution on RFC 6314

Question

in RFC6314, section 5.2.1.2, it mentions that after Client_L collected its candidate list, it sends INVITE to Client_R with the list, and then both ends can start connectivity check.

I have a question is that why Client_L can send INVITE to Client_R? or why Client_R can receive those data (candidate list)? I think in this time Client_L should have no address info of Client_R. Thanks your answer in advanced.

https://www.rfc-editor.org/rfc/rfc6314#section-5.2.1

Answer 1

In order for clients to establish a P2P ICE session, they have to rendezvous through a reliable signaling server. The signaling server exists for clients to exchange address candidates in order for ICE negotiation to actually begin. This is typically a SIP server. Although ICE allows for almost anything to be used for exchanging addresses.

When the INVITE is sent out, it gets sent to a server that knows how to forward that message to the other client. When the remote client gets the INVITE, it responds back with a series of SIP messages - one of which is the "180 RINGING" or "200 OK" message that contains the address candidates from the client that received the INVITE.