78. A method as claimed in claim 77 , wherein the extracting step determines from the device type identifiers table, for the identification information obtained from the header, a corresponding device type identifier is available and, if not, generates an indication that the user device is unrecognised.
77. A method as claimed in claim 45 , wherein the extracting step extracts identification information from a header of the request message and determines the device type identifier by referring to a table of device type identifiers for which device dependent information is stored in the second memory means.