SIP 100 Trying vs 608 Rejected
SIP 100 (Trying) is a 1xx Provisional response, while 608 (Rejected) is a 6xx Global 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, 608 means that an intermediary machine or process rejected the call attempt. Similar to 607 but the rejection comes from the network rather than the end user.
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.
When You See It
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.
How to Fix
No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.
Description
An intermediary machine or process rejected the call attempt. Similar to 607 but the rejection comes from the network rather than the end user.
When You See It
When a network element (not the callee) blocks the call. Used by analytics engines and call-blocking services in the network path.
How to Fix
This is a network-level block. Contact the network administrator or carrier to understand why the call was blocked.
Key Differences
100 is a 1xx Provisional response, while 608 is a 6xx Global 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 608: An intermediary machine or process rejected the call attempt. Similar to 607 but the rejection comes from the network rather than the end user.
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 608 when when a network element (not the callee) blocks the call. Used by analytics engines and call-blocking services in the network path.
When to Use Which
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 608 (Rejected): This is a network-level block. Contact the network administrator or carrier to understand why the call was blocked.