################################################ Interactive Connectivity Establishment ################################################ .. include:: ../links.ref .. include:: ../tags.ref .. include:: ../abbrs.ref ============ ========================================= **Abstract** Interactive Connectivity Establishment **Authors** Walter Fan **Status** WIP as draft **Updated** |date| ============ ========================================= .. contents:: :local: Ovewview ================ `RFC8445`_ Interactive Connectivity Establishment (ICE) 交互式连接建立是一个网络地址转换 NAT 穿透的协议 ICE and related specs ---------------------------- * RFC 5245 - ICE * RFC 5768 – ICE–SIP * RFC 6336 – ICE–IANA Registry * RFC 6544 – ICE–TCP * RFC 5928 - TURN Resolution Mechanism NAT ====================== NAT 是指路由器把本地私有子网IP地址转换称公网 IP 地址的过程。 ICE/STUN/TURN 主要是解决如何在各自内网中的客户端之间如何连接 根据最少限制性到最多限制性来排序可以分为： * Full cone（全锥型） * Address-restricted cone （地址限制型锥形） * Port-restricted cone（端口限制型锥型） * Symmetric（对称型） ICE procedure ========================= 1. Candidate gathering * STUN * TURN 2. Prioritisation 3. Exchange 4. Connectivity checks 5. Coordination 6. Communication ICE candidae ========================= ICE candiate type * host: Host Candidate A candidate obtained by binding to a specific port from an IP address on the host. This includes IP addresses on physical interfaces and logical ones, such as ones obtained through VPNs. * srflx: Server-Reflexive Candidate A candidate whose IP address and port are a binding allocated by a NAT for an ICE agent after it sends a packet through the NAT to a server, such as a STUN server. * prflx: Peer-Reflexive Candidate A candidate whose IP address and port are a binding allocated by a NAT for an ICE agent after it sends a packet through the NAT to its peer. * relay: Relayed Candidate A candidate obtained from a relay server, such as a TURN server. TCP Candidates with Interactive Connectivity Establishment (ICE) =========================================================================== ICE defines a mechanism for NAT traversal for multimedia communication protocols based on the offer/answer model of session negotiation. The ICE Candidate can also be TCP-based , refer to RFC6544 and RFC4571 .. code-block:: +----------+ | | | App | +----------+----------+ +----------+----------+ | | | | | | | STUN | (D)TLS | | STUN | App | +----------+----------+ +----------+----------+ | | | | | RFC 4571 | | RFC 4571 | +---------------------+ +---------------------+ | | | | | TCP | | TCP | +---------------------+ +---------------------+ | | | | | IP | | IP | +---------------------+ +---------------------+ Figure 1: ICE TCP Stack with and without (D)TLS Framing RTP and RTCP Packets over TCP ============================================================ 参见 RFC4571 * The Framing Method .. code-block:: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 --------------------------------------------------------------- | LENGTH | RTP or RTCP packet ... | --------------------------------------------------------------- Figure 1: The bit field definition of the framing method The session descriptions in Figures 3 and 4 define a TCP RTP/AVP session. .. code-block:: v=0 o=first 2520644554 2838152170 IN IP4 first.example.net s=Example t=0 0 c=IN IP4 192.0.2.105 m=audio 9 TCP/RTP/AVP 11 a=setup:active a=connection:new Figure 3: TCP session description for the first participant .. code-block:: v=0 o=second 2520644554 2838152170 IN IP4 second.example.net s=Example t=0 0 c=IN IP4 192.0.2.94 m=audio 16112 TCP/RTP/AVP 10 11 a=setup:passive a=connection:new Figure 4: TCP session description for the second participant Reference ================ * `RFC8445`_: Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal * _RFC8445: https://datatracker.ietf.org/doc/html/rfc8445