Compact Headers
SIP provides a mechanism to represent common header field names in an abbreviated form. This may be useful when messages would otherwise become too large to be carried on the transport available to it (exceeding the maximum transmission unit (MTU) when using UDP, for example).
| Compact Value | Header |
|---|---|
| a | Accept-Contact |
| b | Referred-By |
| c | Content-Type |
| e | Content-Encoding |
| f | From |
| i | Call-ID |
| k | Supported |
| l | Content-Length |
| m | Contact |
| o | Event |
| r | Refer-To |
| s | Subject |
| t | To |
| u | Allow-Events |
| v | Via |