TAILIEUCHUNG - Signaling System No.7 Protocol Architecture And Sevices part 3

Channel Associated Signaling The key feature that distinguishes Channel Associated Signaling (CAS) from CCS is the deterministic relationship between the call-control signals and the bearers (voice circuits) | Channel Associated Signaling The key feature that distinguishes Channel Associated Signaling CAS from CCS is the deterministic relationship between the call-control signals and the bearers voice circuits they control in CAS systems. In other words a dedicated fixed signaling capacity is set aside for each and every trunk in a fixed pre-determined way. Channel Associated Signaling CAS is often still used for international signaling national systems in richer nations almost exclusively use Common Channel Signaling CCS . CCS is replacing CAS on international interfaces. CAS can be implemented using the following related systems Bell Systems MF R2 R1 and C5. Single-frequency SF in-band and out-of-band signaling Robbed bit signaling The following sections discuss these methods in context with the type of signal either address or supervisory. Address Signals Multifrequency systems such as the Bell System MF R2 R1 and C5 are all types of address signals used by CAS. Multifrequency The CAS system can be used on either analog Frequency Division Multiplexed FDM or digital Time Division Multiplexed TDM trunks. MF is used to signal the address digits between the switches. Multifrequency MF signaling can still be found in traces within the United States and it is still often found on international interfaces. On international interfaces outside of North America MF is still used via the CCITT System 5 C5 implementation. C5 is quite similar to Bell MF and was developed jointly by Bell Laboratories and the British Post Office 102 . R2 is the MF system that was deployed outside North America and is still used in less developed nations. R2 was developed by CEPT which later became ETSI see Chapter 2 and was previously known as Multifrequency Compelled MFC signaling. The CCITT later defined an international version see Chapter 2 for additional information regarding the international version 102 . MF simultaneously sends two frequencies from a choice of six to convey an address signal.

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