Associated vs Common channel signalling: The out band signalling suffers from the very limited bandwidth. Both are capable of having only a small signal repertoire. The trend in modern networking is to provide enhanced signalling facilities for the subscriber, the switching system and the telephone administration. Such a need is met by common channel signalling which may be common channel signalling which may be implemented in two ways: channel associated mode4 and channel non associated mode. In the former, the common signalling channel closely tracks the trunk groups along the entire length of a connection. In the letter, there is no close or simple assignment of control channels to trunk groups. These modes are illustrated in Fig. In the associated mode of operation shown in Fig. The signalling paths for the speech paths A-B, A-C-B and B-D are A-B, A-C-B and B-D respectively. The term ‘associated signalling’ in the CCS should not be confused with in channel signalling. The signalling in CCS associated mode is still done on a separate signalling channel; only that the signalling path passes through the same set of switches as does the speech path. Network topologies of the signalling network and the speech network are the same. The advantages of the scheme are the economic implementation and simple assignment of trunk groups to signalling channels.