Message modification apparatus for use in a telecommunication signalling network

摘要

A programmable message substitution unit PMSU (60) is provided for modifying signalling messages passing across a link (61) of a telecommunications signalling network without disrupting the link-level procedures operating over the link. In the event of a power failure or upon the detection of an operational anomaly, a bypass relay arrangement (65) is used to bypass the PMSU (60). The PMSU (60) comprises a substitution block for modifying selected messages, a database block for doing database lookups to ascertain new message parameter values to be substituted for existing ones, and a supervision block for checking the operation of the substitution block. The PMSU may be used to implement local number portability or other services.