Common Channel Signaling (CCS)
Common channel signaling (CCS) is a digital communications technique that provides simultaneous transmission of user data, signaling data, and other related traffic throughout a network. For second generation wireless communications systems, CCS is used to pass user data and control/supervisory signals between the subscriber and the base station, between the base station and the MSC, and between MSCs.The concept of CCS implies dedicated, parallel channels; it is implemented in a TDM format for serial data transmissions
Features of CCS:
- CCS is an out-of-band signaling technique which allows much faster communications between two nodes within the PSTN
- CCS supports signaling data rates from 56 kbps to many megabits per second.CCS provides a substantial increase in the number of users which are served by trunked PSTN lines.
- But CCS requires that a dedicated portion of the trunk time be used to provide a signaling channel used for network traffic.
- CCS generally uses variable length packet sizes and a layered protocol structure.
CCS network architecture(Fig 8.3):
- Switching end points (SEPs), signaling transfer points (STPs), a service management system(SMS), and a base service management system (DBAS)
- The MSC provides subscriber access to the PSTN via the SEP. The SEP implements a stored-program-control switching system known as the service control point (SCP) that uses CCS to set up calls and to access a network database.The SCP instructs the SEP to create billing records based on the call informationrecorded by the SCPThe STP controls the switching of messages between nodes in the CCS network.
- For higher reliability of transmission (redundancy)
- This combination of two STPs in parallel is known as a mated pair, and provides connectivity to the network in the event one STP.
- The SMS contains all subscriber records, and also houses toll-free databases which may be accessed by the subscribers fails.
- The DBAS is the administrative database that maintains service records and investigates fraud throughout thenetwork