15. A method according to claim 14 wherein generating the input file comprises modifying an existing input file.
14. A method for operating a signalling gateway, the method comprising: generating an input file comprising a plurality of input expressions and a plurality of routing keys corresponding to the input expression, wherein the input expressions comprise parameters of signalling messages in accordance with a first signalling protocol and the routing keys correspond to destination addresses in accordance with a second protocol; supplying the input file to a lexical analyser generator to generate a lexical analyser by generating an output comprising a source code file and the method comprises compiling the source code file to provide the lexical analyser, the generated lexical analyzer for use in analysing messages for routing keys, said routing keys useable to forward messages by the signaling gateway from one network to another network; passing the lexical analyser to the signalling gateway; and providing a routing key interpreter using the lexical analyser; wherein the lexical analyser comprises executable codes.