20081218 linear rtpproxy v3

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RTP ProxyDate: 2008/12/18

Speaker: Ni-Ya Li

Advisor: Quincy Wu



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Outline Introduction

NAT STUN

Operation of RTP Proxy

Future work

Reference



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Introduction 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



Introduction (cont.) What is the 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

Symmetric4



Full cone NAT

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Picture from: http://ms11.voip.edu.tw/~webmaster/meeting/961/ppt/Wenping/20071122_wenping_STUN_v1.ppt



R estricted cone NAT

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R estricted port cone NAT

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Symmetric NAT

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Simple Traversal of UDP Through

Network Address Translators (STUN)

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10.10.21.17 : 5060

1. Client(10.10.21.17:5060) sends a request to STUN server with pubic IP

address (163.22.23.24)

2. STUN server gives a response with client¶s public IP address and port number

(163.22.5.59 : 56789)

3. Client use the public IP address and port (163.22.5.59 : 56789) to register to

SIP server

163.22.23.24

10.10.21.17 : 5060

163.22.5.59 : 56789




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STUN (cont.) STUN can deal with the three type of cone NAT

Allocate a new media port, and every external host can

connect to internal client.

If client locates behind a symmetric NAT?

The previous allocated media port can not be used by the

other hosts.

Nothing heard !!We need a new tool to relay RTP pack ets

behind a symmetric NAT

RTP Proxy!!



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Operation of RTP Proxy 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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Operation of RTP Proxy 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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Operation of RTP Proxy 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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Future work s Loading balance

Distributed RTP proxies

A central control SIP server, decides which RTP proxy will be responsible for this conversation.

SIP server gives a call to one of these RTP proxies

randomly, and the decision of doing a load balance is

made by proxies.



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R ef erence RTP Proxy

http://www.voip-info.org/wiki/view/RTPProxy

NAT, STUNhttp://ms11.voip.edu.tw/~webmaster/meeting/961/ppt/Wenping/20071122_wenping_STUN_v1.ppt

Nathelper module

http://www.kamailio.org/docs/modules/1.2.x/nathelper.html

SER Getting Started

http://siprouter.teigre.com/doc/gettingstarted/ch04s05.html

20081218 linear rtpproxy v3

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