Snom 4S Manuale Utente

16 • Architecture

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S N O M

4 S N A T F

I L T E R

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0637ced821ef40a3;ua=c9b140ab598290e5bb491e9c3aaca440

Via: SIP/2.0/UDP 203.145.183.113:12975;branch=z9hG4bK-

abx3au3mxb01;rport=17401

From: <sip:denny@snomag.de>;tag=k9p6fmeg7h

To: <sip:denny@snomag.de>;tag=epuy85kzm5

Call-ID: 3c26701d7cb9-pady07b5783t@203-145-183-113

CSeq: 14 REGISTER

Contact: <sip:217.115.141.99:5082;ua=c9b140ab598290e5bb491e9c3aaca44

0>;expires=3600;gruu=”sip:denny@snomag.de;gruu=hobiv52b”

Date: Wed, 26 May 2004 16:03:33 GMT

Content-Length: 0
SIP/2.0 200 Ok

Via: SIP/2.0/UDP 203.145.183.113:12975;branch=z9hG4bK-

abx3au3mxb01;rport=17401

From: “denny” <sip:denny@snomag.de>;tag=k9p6fmeg7h

To: “denny” <sip:denny@snomag.de>;tag=epuy85kzm5

Call-ID: 3c26701d7cb9-pady07b5783t@203-145-183-113

CSeq: 14 REGISTER

Contact: <sip:denny@203.145.183.113:12975;line=lhynyb3y>;expires=360

0;gruu=”sip:denny@snomag.de;gruu=hobiv52b”

Date: Wed, 26 May 2004 16:03:33 GMT

Content-Length: 0

The SBC will make the registration short enough to keep the con-

nection alive. The UA will reregister shortly after. However, because the

registration binding time in the registrar is longer, the SBC will not forward

the request to the registrar and answer it locally.

2.3.3 RTP Relay

When initiating a call, user agents usually include a Session De-

scription Protocol (SDP) attachment that describes where they expect

media. If the user agent operates on a public Internet address, there is

no need to interfere in this process. In this case the SBC will just forward

the request.

Operators should encourage customers to use equipment that

operates on a public Internet address or properly allocates a globally

routable Internet address. Because media relay is an expensive opera-

tion, it reduces the overall load on the network and at the same time in-

creases the quality of the service.

However, when a user agent is behind NAT, it might not be able

to receive media directly. In some cases this is because the user agent is