In intelligent networks (IN), and in cellular communication systems such as GPRS and UMTS, service layer is a conceptual layer within a network service provider architecture. It aims at providing middleware that serves third-party applications at a higher application layer. The service layer provides capability servers owned by a telecommunication network service provider, accessed through open and secure Application Programming Interfaces (APIs) by third-party application layer servers. The service layer also provides an interface to core networks at a lower resource layer. The lower layers may also be named control layer and transport layer (the transport layer is also referred to as the access layer in some architectures).
The concept of service layer is used in contexts such as Intelligent networks (IN), WAP, 3G and IP Multimedia Subsystem (IMS). It is defined in the 3GPP Open Services Architecture (OSA) model, which reused the idea of the Parlay API for third-party servers.
In software design, for example Service-oriented architecture, the concept of service layer has a different meaning.