Figure 100 sip call through proxy servers, Table 59 sip call progression – ZyXEL Communications P-2602HWLNI User Manual

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Chapter 11 Voice

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The following figure shows the SIP and session traffic flow between the user agents (UA 1
and UA 2) and the proxy servers (this example shows two proxy servers, PROXY 1 and
PROXY 2).

Figure 100 SIP Call Through Proxy Servers

The following table shows the SIP call progression.

1 User Agent 1 sends a SIP INVITE request to Proxy 1. This message is an invitation to

User Agent 2 to participate in a SIP telephone call. Proxy 1 sends a response indicating
that it is trying to complete the request.

2 Proxy 1 sends a SIP INVITE request to Proxy 2. Proxy 2 sends a response indicating

that it is trying to complete the request.

3 Proxy 2 sends a SIP INVITE request to User Agent 2.
4 User Agent 2 sends a response back to Proxy 2 indicating that the phone is ringing. The

response is relayed back to User Agent 1 via Proxy 1.

Table 59 SIP Call Progression

UA 1

PROXY 1

PROXY 2

UA 2

Invite

100 Trying

Invite

100 Trying

180 Ringing

200 OK

ACK

RTP

BYE

200 OK

UA 1

UA 2

PROXY 1

PROXY 2

SIP

RTP