Youth Carnival
VoLTE provides all the necessary mechanisms for conversational voice service over packet data network, including; QoS, authentication, bearer management, policy control, supplementary services, regulatory services
CS coexistence
There are number of reasons why CS coexistence may be needed for an operator including for example:
- Reuse of existing CS roaming agreements
- CS Emergency call handling already in place
- Lack of LTE radio coverage in some areas
Circuit Switch Fall Back (CSFB)
For early deployments of LTE with handheld devices, operators may consider complementing LTE data services with CS voice, using Circuit Switch Fallback (CSFB). CSFB is a standardized solution utilizing existing MSC-network to provide services to LTE-capable devices before homogenous LTE- coverage is built.
IMS Centralized Services (ICS)
ICS handles the situation where a VoLTE user makes or receives a call when outside LTE coverage. In a single service engine scenario, the user is still being served by IMS but cannot make use of LTE/EPC, but rather need to rely on legacy 2G/3G access and transport.
Single Radio Voice call continuity (SR-VCC)
For the situation where a VoLTE user leaves LTE coverage during an established session, mechanisms for voice call continuity will be needed to avoid dropped calls. According to 3GPP release 10, SR-VCC means that UE is connected to either CS or LTE at one point in time. Terminal then needs to flag to network when running into poor LTE coverage and tune over to CS while network reestablish connection to the CS side of UE. SR-VCC is promoted for 3GPP markets.
SMS over LTE
There are two options to deliver SMS service over LTE by existing SMS-C.
- SMS over SGs
UE can send and retrieve SMS using NAS signalling over LTE. It requires SGs interface between CS Core and EPC to transport SMS to/from UE.
- SMS over IP
The solution is to transport SMS over any PS access using IMS and mandated to be supported by VoLTE terminals.