NAT RTP Proxy Date 200972 Speaker NiYa Li

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

Outline NAT – Network Address Translator o RTP Proxy o Reference o 2

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

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

5

Demo - Illustration 6

NAT – Simple architecture NAT AT Public NIC Private NIC Client Server Mapping Table 192. 168. 0. 191 : 1668 10. 59. 11 : 60255 7

Four type NAT o o Full cone Restricted port cone Symmetric 8

Full cone NAT IP: 123 Port: 12345 Client IP: 192. 168. 0. 1 Port: 21 NAT Computer A IP: 222. 111. 99. 1 Port: 20202 Computer B IP: 222. 111. 88. 2 Port: 10101 Mapping Table 192. 168. 0. 1: 21 <-> 12345 9

Restricted cone NAT IP: 123 Port: 12345 Client IP: 192. 168. 0. 1 Port: 21 NAT Computer A IP: 222. 111. 99. 1 Port: 20202 Computer B IP: 222. 111. 88. 2 Port: 10101 Mapping Table 192. 168. 0. 1: 21 <-> 12345 (for A) Client IP: 192. 168. 0. 1 Port: 21 NAT IP: 123 Port: 12345 Mapping Table 192. 168. 0. 1: 21 <-> 12345 (for A) 192. 168. 0. 1: 21 <-> 12345 (for B) Computer A IP: 222. 111. 99. 1 Port: 20202 Computer B IP: 222. 111. 88. 2 Port: 10101 10

Restricted port cone NAT Client IP: 192. 168. 0. 1 Port: 21 NAT IP: 123 Port: 12345 Computer A IP: 222. 111. 99. 1 Port: 20202 Port: 30303 Mapping Table 192. 168. 0. 1: 21 <-> 12345 (for A : 20202) 192. 168. 0. 1: 21 <-> 12345 (for A : 30303) 11

Symmetric NAT IP: 123 Port: 12345 Client IP: 192. 168. 0. 1 Port: 21 Computer A IP: 222. 111. 99. 1 Port: 20202 NAT IP: 123 Port: 45678 Computer B IP: 222. 111. 88. 2 Port: 10101 Mapping Table 192. 168. 0. 1: 21 <-> 12345 (for A : 20202) 192. 168. 0. 1: 21 <-> 45678 (for B : 10101) 12

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

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

RTP Proxy – Simple architecture SIP Proxy UA 1 NAT RTP Proxy UA 2 15

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

RTP Proxy - Operation o When SIP server receives SIP response from UA 2 with SDP Yes, return UDP port number extracts call-id Rewrite media ip: port No, return error code Session of call-id exist? 17

RTP Proxy - Operation o After session is created, RTP proxy listens on the port for filling in the ip: port structure of two side parties. RTP streams 10. 59. 62 : 32768 10. 21. 17 : 7080 18

Reference RTP Proxy http: //www. voip-info. org/wiki/view/RTPProxy o NAT http: //www. wisegeek. com/what-is-nat. htm o STUN http: //ms 11. voip. edu. tw/~webmaster/meeting/961/ppt/Wen ping/20071122_wenping_STUN_v 1. ppt o 19