1. 1 NAT & RTP Proxy Date: 2009/7/2 Speaker: Ni-Ya Li Advisor: Quincy Wu

2. 2 Outline  NAT – Network Address Translator  RTP Proxy  Reference

3. NAT  What is NAT? Network Address Translator, maps a private IP address to a public one  Why use NAT? Public IP addresses are almost exhausted  Four types Full cone Restricted cone Restricted port cone Symmetric 3

4. NAT – Schematic 4 Client NAT Server Mapping Table Public NIC Private NIC

5. 5

6. Demo - Illustration 6

7. NAT – Simple architecture 7 Client AT Server Mapping Table 192.168.0.191 : 1668  10.10.59.11 : 60255 NAT Public NIC Private NIC

8. Four type NAT  Full cone  Restricted cone  Restricted port cone  Symmetric 8

9. Full cone NAT 9 Client IP: 192.168.0.1 Port: 21 NAT Port: 12345 Mapping Table Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 IP: 123.123.123.123 192.168.0.1:21 12345

10. Restricted cone NAT 10 Client IP: 192.168.0.1 Port: 21 NAT Port: 12345 Mapping Table Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 IP: 123.123.123.123 192.168.0.1:21 12345 (for A) Client IP: 192.168.0.1 Port: 21 NAT IP: 123.123.123.123 Port: 12345 Mapping Table 192.168.0.1:21 12345 (for A) Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 192.168.0.1:21 12345 (for B)

11. Restricted port cone NAT 11 Client IP: 192.168.0.1 Port: 21 NAT IP: 123.123.123.123 Port: 12345 Mapping Table 192.168.0.1:21 12345 (for A : 20202) 192.168.0.1:21 12345 (for A : 30303) Computer A IP: 222.111.99.1 Port: 20202 Port: 30303

12. Symmetric NAT 12 Client IP: 192.168.0.1 Port: 21 NAT IP: 123.123.123.123 Port: 12345 Mapping Table 192.168.0.1:21 12345 (for A : 20202) 192.168.0.1:21 45678 (for B : 10101) Computer A IP: 222.111.99.1 Port: 20202 Computer B IP: 222.111.88.2 Port: 10101 IP: 123.123.123.123 Port: 45678

13. NAT–drawback & solution  The drawback of using NAT? Unfriendliness for end-to-end applications, such as transmission of RTP streams.  How to overcome the disadvantage? RTP Proxy

14. 14 RTP Proxy  RTP The real-time transport protocol to carry data that has real-time properties.  RTP Proxy A software proxy for RTP streams, works with SIP server  Why use RTP Proxy? Originally created for handling NAT scenarios

15. RTP Proxy – Simple architecture 15 UA1 NAT UA2 RTP ProxySIP Proxy

16. 16 RTP Proxy - Operation  When SIP server receives INVITE request INVITE request, extracts call-id Session of call-id exist? Yes, returns UDP port number No, Creates a new session, return UDP port number Rewrite media ip:port

17. 17 RTP Proxy - Operation  When SIP server receives SIP response from UA2 with SDP Session of call-id exist? extracts call-id No, return error code Yes, return UDP port number Rewrite media ip:port

18. 18 RTP Proxy - Operation  After session is created, RTP proxy listens on the port for filling in the ip:port structure of two side parties. RTP streams 10.10.59.62 : 32768 10.10.21.17 : 7080

19. 19 Reference  RTP Proxy http://www.voip-info.org/wiki/view/RTPProxy  NAT http://www.wisegeek.com/what-is-nat.htm  STUN http://ms11.voip.edu.tw/~webmaster/meeting/961/ppt/Wen ping/20071122_wenping_STUN_v1.ppt