3.1.5.3 Checking the Attributes of the Request

Schema validation MUST be done as specified in section 3.1.5.1.1, which checks if all the attributes of the request conform to the schema rules. If schema validation succeeds, some more checks MUST be done as follows.

The version validation is done as specified in section 3.1.5.2.1. The server can include an optional serverVersion attribute in the response which, if present, SHOULD<6> be the same as the server version. If the client’s request is valid and the version is "1.0" in the protocol client’s request, the server MUST NOT include the serverVersion attribute.

The from and to attributes MUST be SIP URIs. If the server is not able to parse the URI, the server MUST send an error message with reasonPhrase with the value "Request Malformed". If these attributes are valid, the values of these attributes along with requestID are copied to the response. The client SHOULD use the requestID to correlate the server response with its request in case multiple requests are pending at the same time to the server.