SIP 100 Trying vs 483 Too Many Hops
SIP 100 (Trying) is a 1xx Provisional response, while 483 (Too Many Hops) 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, 483 means that the Max-Forwards header has reached zero, indicating the request has passed through too many proxies.
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 Max-Forwards header has reached zero, indicating the request has passed through too many proxies.
When You See It
When a request traverses more proxies than the Max-Forwards counter allows (default 70). Often indicates a routing loop.
How to Fix
Check for routing loops. If the path is legitimately long, increase Max-Forwards. Usually indicates misconfigured routing.
Key Differences
100 is a 1xx Provisional response, while 483 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 483: The Max-Forwards header has reached zero, indicating the request has passed through too many proxies.
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 483 when when a request traverses more proxies than the Max-Forwards counter allows (default 70). Often indicates a routing loop.
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 483 (Too Many Hops): Check for routing loops. If the path is legitimately long, increase Max-Forwards. Usually indicates misconfigured routing.