SIP 100 Trying vs 438 Invalid Identity Header
SIP 100 (Trying) is a 1xx Provisional response, while 438 (Invalid Identity Header) 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, 438 means that the server obtained the certificate from the Identity-Info header but the signature in the Identity header is invalid.
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
The server obtained the certificate from the Identity-Info header but the signature in the Identity header is invalid.
When You See It
When the cryptographic signature in the Identity header does not match the message content, indicating possible tampering.
How to Fix
Regenerate the Identity header with a correct signature. Ensure no intermediary is modifying signed headers after signing.
Key Differences
100 is a 1xx Provisional response, while 438 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 438: The server obtained the certificate from the Identity-Info header but the signature in the Identity header is invalid.
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 438 when when the cryptographic signature in the Identity header does not match the message content, indicating possible tampering.
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 438 (Invalid Identity Header): Regenerate the Identity header with a correct signature. Ensure no intermediary is modifying signed headers after signing.