### Description
I use TCP transport to relay SIP messages. When Kamailio cannot connect to another server then Kamailio generates response `408 Request Timeout`. inside `event_route[dialog:failed]` route block I check error code `$rs` but this value is `null`. This happens because Kamailio does not able to relay SIP messages and is not able to receive responses. But `tm` module generates a response `408 Request Timeout` and will be fine to init `$rs` pseudo-variable using tm module response.
### Expected behavior `$rs` pseudo-variable contains `tm` module response when kamailio does not receive a response from another server.
#### Actual observed behavior `$rs` pseudo-variable contains `null` value when kamailio does not receive a response from another server.
To check you can use ``` event_route[dialog:failed] { $var(code_xxx) = $(rs{re.subst,/([0-9])[0-9]{2}/\1xx/}); xlog("L_INFO", "websocket|log|dialog failed $rs; $var(code_xxx)\n"); } ``` And relay SIP message to host that reachable.