A mobile telephony application server (mobile TAS), sometimes known as an MMTel-AS, is a component used in the core network of a mobile network operator to provide telephony applications and additional multimedia functions to mobile devices.
A mobile TAS is typically deployed in mobile networks using 4G/LTE and IP Multimedia Subsystem (IMS) architectures, alongside components providing such as the Call Session Control Function (CSCF) and Home Subscriber Server (HSS).
A mobile TAS can serve multiple functions, including:
- Functioning as a multimedia telephony application server (MMTel-AS), providing call control for voice and video, including support for GSMA standards IR.92 and IR.94 for VoLTE, and IR.51 for VoWiFi
- Emulating GSM supplementary services, such as call forwarding and conferencing, and maintaining feature parity between TDM and IP network infrastructures
- Interworking between circuit switched and packet switched networks
- Delivery of additional services and applications, such as anonymous call rejection and explicit call transfer
- Providing a framework for the creation of new services and applications, sometimes with an open development environment encouraging third-party development.
A mobile TAS that supports both TDM and IP network infrastructures can be an essential element in IP network transformation.
Some mobile TASs are purpose-built hardware appliances while some are virtualized network functions (VNFs) capable of running on general-purpose hardware or in a cloud environment as part of an NFV deployment.