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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[1]. 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.

Contents

Service layer in IMS

The service layer of an IMS architecture provides multimedia services to the overall IMS network. This layer contains network elements which connect to the Serving-CSCF (Call Session Control Function) using the IP multimedia Subsystem Service Control Interface (ISC)[2]. The ISC interface uses the SIP signalling protocol.

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Elements of the IMS service layer

The network elements contained with in the service layer are generically referred to as 'service platforms' however the 3GPP specification (3GPP TS 23.228 V8.7.0) defines several types of service platforms:

  • SIP Application Server
  • OSA Service Capability Server
  • IM-SSF

SIP Application Server

The SIP Application Server (AS) performs the same function as a Telephony Application Server in a pre-IMS network, however it is specifically tailored to support the SIP signalling protocol for use in an IMS network.

OSA Service Capability Server

An OSA Service Capability Server acts as a secure gateway between the IMS network and an application which runs upon the Open Services Architecture (this is typically a SIP to Parlay gateway)

IM-SSF

The IM-SSF (IP Multimedia Service Switching Function) acts as a gateway between the IMS network and application servers using other telecommunication signalling standards such as INAP and CAMEL.

Service layer in SOA

In Service oriented architecture (SOA), the service layer is the third layer in a five abstraction layer model. The model consists of Object layer, Component layer, Service layer, process layer and Enterprise layer.[3]. The service layer can be considered as a bridge between the higher and lower layers, and is characterized by a number of services that are carrying out individual business functions.

References

See also


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