100 1xx Provisional RFC 3261
SIP 100 Trying
The next hop received the request and is working on it. 100 Trying only travels one hop and stops the caller from retransmitting the INVITE.
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Common causes
- Normal behaviour at the start of every INVITE transaction.
How to fix it
- No action needed. If a call stays on 100 Trying for many seconds, the next hop is slow to route or the far end is unreachable. Check the logs of the proxy that sent it.
Seeing 100 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 1xx responses
The request was received and is being processed. The call is not finished yet.