| Element | Case Sensitive? |
|---|---|
| Via branch | insensitive (token) |
| Call-ID | sensitive - Byte for byte compare |
| SIP-Version | insensitive - must send uppercase though |
| Header field names | insensitive |
From RFC 3261, sect 7.3.1:
When comparing header fields, field names are always case-insensitive. Unless otherwise stated in the definition of a particular header field, field values, parameter names, and parameter values are case-insensitive. Tokens are always case-insensitive. Unless specified otherwise, values expressed as quoted strings are case-sensitive.