1. NAT/Firewall穿越技术

2. 常见的NAT种类
Full Cone
Restricted Cone
Port Restricted Cone
Symmetric NAT

3. Full Cone

4. Restricted Cone(1/2)

5. Restricted Cone(2/2)

6. Port Restricted Cone

7. Symmetric NAT

8. NAT Detection Flow

9. 防火牆造成的問題

10. NAT 造出的问题

11. NAT/Firewall穿越技术 IPV6(Internet Protocol Version 6)
UPnP(Universal Plug and Play)
TRUN(Traversal Using Relay NAT)
ALG(Application Layer Gatewqy)
ICE(Interactive Connectivity Establish)
STUN(Simple Traversal of UDP Through Netwoek Address Translators)

12. UPnP Universal Plug and Play It's being pushed by Microsoft
A UPnP-aware client can ask the UPnP-enabled NAT how it would map a particular IP:port through UPnP

13. UPnP Operation

14. STUN(1/2) Simple Traversal of UDP Through Network Address Translators
需要在NAT外部架设 STUN Server
Client 端需有特殊的 STUN Client 功能
无法穿透 symmetric NAT
未来将被ICE整合

15. STUN(2/2)

16. TURN(1/2) Traversal Using Relay NAT 主要是为了解決 symmetric NATs
必须要架設 TURN Server
未来也将被包含进 ICE

17. TURN(2/2)

18. SIP using STUN User Agent 1 STUN Server Registrar/Proxy User Agent 2
1 STUN SharedSecretRequest/TLS
9 100 Trying
User Agent 1
STUN Server
Registrar/Proxy
User Agent 2
7 INVITE OK
NAT
2 STUN SharedSecretResponse/TLS
3 STUN BindingtRequest/UDP
4 STUN BindingResponse/UDP
6 200 OK
5 REGISTER
8 INVITE OK
12 ACK
13 ACK
RTP Media Session

19. SIP using TURN User Agent 1 STUN/TURN Svr 1 STUN/TURN Svr 2
STUN/TURN Svr 1
STUN/TURN Svr 2
User Agent 2
NAT 1
NAT 2
1 STUN Requests
2 STUN Responses
3 STUN Requests
4 STUN Responses
7 180 Ringing
8 200 OK
9 ACK
12 Peer-to-Peer STUN Responses
11 Peer-to-Peer STUN Requests
14 Peer-to-Peer STUN Responses
13 Peer-to-Peer STUN Requests
RTP Media Session
Established using Derived Transport Addresses
Proxy
5 INVITE
6 INVITE
10 ACK

20. ALG(1/2) Application Layer gateway
It Understands the signalling messages and their relationship with the resulting media flows.
It can modify the signalling to reflect the public IP address and ports being used by singalling and media traffic.

21. ALG(2/2)

22. ICE Interactive Connectivity Establishment 非 protocol 而是 framework
主要技术包括：STUN, TRUN, SIP
目前仍在RFC草案讨论阶段