Definition of CS domain

In the R99 specification CN, there are actually only two transmission forms: circuit switching and packet switching. Circuit switched domain (CS domain) and packet switched domain (PS domain). CS (Circuit Switched Domain) refers to all network element entities that provide circuit-switched connections for user services in the core network and all network element entities that support related signaling. Circuit-switched connections allocate private network resources when the connection is established and release the private resources when the connection is released.

CS domain is the circuit bearer domain, which takes voice, PS domain is the data domain, and IP domain is used for mobile phone surfing.

Under 3G, the access network connects CS and PS at the same time, that is, the core network is divided into CS and PS, and the call signal takes CS and the data service signal takes PS.

Under LTE, CS domain is cancelled, and CS domain services are implemented in PS domain, such as VOIP.