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SIP: Why does proxy server respond with 100 trying message ? What if it does not do this ?

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SIP: Why does proxy server respond with 100 trying message ? What if it does not do this ?
posted Aug 14, 2016 by Vikram Singh

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2 Answers

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When a user agent client sends INVITE request to another user agent, it will go through proxy server. Just to avoid re-transmission of INVITE message, Proxy sever responds back to User agent client with 100 trying.

answer Aug 15, 2016 by Harshita
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It is kind of Provisional acknowledgment from proxy to user agent that it has received the INVITE.
The 100 Trying provides you the feedback that your request is being processed by a SIP proxy.
If 100 trying is not sent and if T1 timer gets expired, UAC will send one more invite in order to avoid that 100 trying is being sent back.

answer Dec 2, 2016 by Bhushan Patil
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