13. A communications node comprising: a first dictionary containing string expressions for use in message compression and decompression; a dynamic dictionary that stores expressions for use in the message compression and decompression for exclusive use in the communications node; and a compression/decompression module that receives a message containing individual expressions, the compression/decompression module further determining all matches between the individual expressions of the message and corresponding expressions in the first dictionary, and yet further, among the determined matches of individual expressions, determining different sequences of matches of individual expressions which are contiguous to each other in the message, each of the different matching sequences including one or more contiguous individual expressions and the different sequences which are determined to be contiguous to each other forming at least one new combined expression, and that creates in the dynamic dictionary the at least one new combined expression.
13. A communications node comprising: a first dictionary containing string expressions for use in message compression and decompression; a dynamic dictionary that stores expressions for use in the message compression and decompression for exclusive use in the communications node; and a compression/decompression module that receives a message containing individual expressions, the compression/decompression module further determining all matches between the individual expressions of the message and corresponding expressions in the first dictionary, and yet further, among the determined matches of individual expressions, determining different sequences of matches of individual expressions which are contiguous to each other in the message, each of the different matching sequences including one or more contiguous individual expressions and the different sequences which are determined to be contiguous to each other forming at least one new combined expression, and that creates in the dynamic dictionary the at least one new combined expression. 20. The communications node claimed in claim 13 , wherein the first dictionary comprises a static dictionary and the dynamic dictionary.