Telecommunication signal processing method e.g. for teletext system

摘要

The method involves comparing at least one data field in a "demand to establish communication" signal with the predetermined, memorised data field in a terminal on reception of the signalling message. The "demand to establish communication" signal is transmitted and input to an application device when the comparison is positive. A "refuse to establish communication" message is transmitted to a forwarding device when the comparison is negative. During the phase of establishing communication, "call in progress" and "alarm" messages are safeguarded (341S) in an intermediate layer (34a). Certain fields of data in these messages are restored (342S) in a higher level message which is re-transmitted to higher levels (4a-7a).