SIP 100 Trying vs 439 First Hop Lacks Outbound Support
SIP 100 (Trying) is a 1xx Provisional response, while 439 (First Hop Lacks Outbound Support) is a 4xx Client Failure response. 100 indicates that the request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses. In contrast, 439 means that the first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
Description
The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.
Quand vous le voyez
Immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.
Comment résoudre
No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.
Description
The first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
Quand vous le voyez
When a UA configured for SIP outbound connects to a proxy that doesn't support the outbound option-tag.
Comment résoudre
Upgrade the outbound proxy to support RFC 5626, or configure the UA to not require outbound support.
Différences clés
100 is a 1xx Provisional response, while 439 is a 4xx Client Failure response.
SIP 100: The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.
SIP 439: The first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
You encounter 100 when immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.
You encounter 439 when when a UA configured for SIP outbound connects to a proxy that doesn't support the outbound option-tag.
Quand utiliser lequel
For 100 (Trying): No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration. For 439 (First Hop Lacks Outbound Support): Upgrade the outbound proxy to support RFC 5626, or configure the UA to not require outbound support.