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NAT & RTP ProxyDate: 2009/7/2

Speaker: Ni-Ya Li

Advisor: Quincy Wu

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Outline NAT – Network Address Translator RTP Proxy Reference

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

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NAT – Schematic

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Client NAT Server

Mapping TableP

ub

lic NIC

Private N

IC

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Demo - Illustration

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NAT – Simple architecture

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Client AT Server

Mapping Table

192.168.0.191 : 1668 10.10.59.11 : 60255

NAT

Pu

blic N

IC

Private N

IC

Four type NAT Full cone Restricted cone Restricted port cone Symmetric

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Full cone NAT

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ClientIP: 192.168.0.1

Port: 21

NAT

Port: 12345

Mapping Table

Computer AIP: 222.111.99.1

Port: 20202

Computer BIP: 222.111.88.2

Port: 10101

IP: 123.123.123.123

192.168.0.1:21 <-> 12345

Restricted cone NAT

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ClientIP: 192.168.0.1

Port: 21

NAT

Port: 12345

Mapping Table

Computer AIP: 222.111.99.1

Port: 20202

Computer BIP: 222.111.88.2

Port: 10101

IP: 123.123.123.123

192.168.0.1:21 <-> 12345 (for A)

ClientIP: 192.168.0.1

Port: 21

NAT

IP: 123.123.123.123Port: 12345

Mapping Table192.168.0.1:21 <-> 12345 (for A)

Computer AIP: 222.111.99.1

Port: 20202

Computer BIP: 222.111.88.2

Port: 10101

192.168.0.1:21 <-> 12345 (for B)

Restricted port cone NAT

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ClientIP: 192.168.0.1

Port: 21

NATIP: 123.123.123.123Port: 12345

Mapping Table192.168.0.1:21 <-> 12345 (for A : 20202)192.168.0.1:21 <-> 12345 (for A : 30303)

Computer AIP: 222.111.99.1

Port: 20202Port: 30303

Symmetric NAT

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ClientIP: 192.168.0.1

Port: 21NAT

IP: 123.123.123.123Port: 12345

Mapping Table192.168.0.1:21 <-> 12345 (for A : 20202)192.168.0.1:21 <-> 45678 (for B : 10101)

Computer AIP: 222.111.99.1

Port: 20202

Computer BIP: 222.111.88.2

Port: 10101IP: 123.123.123.123Port: 45678

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

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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

RTP Proxy – Simple architecture

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UA1NAT

UA2

RTP ProxySIP Proxy

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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

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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

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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

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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/Wenping/20071122_wenping_STUN_v1.ppt