intelligent network The Intelligent Network (IN) is the standard network architecture specified in the ITU-T Q.1200 series recommendations. It is intended for fixed as well as mobile telecom networks. It allows operators to differentiate themselves by providing ...

s (IN) and cellular networks, service layer is a conceptual layer within a network service provider architecture. It aims at providing

middleware Middleware is a type of computer software program that provides services to software applications beyond those available from the operating system. It can be described as "software glue". Middleware makes it easier for software developers to imple ...

that serves third-party

value-added service A value-added service (VAS) is a popular telecommunications industry{{cite web, url=https://www.prweb.com/releases/global_mobile_value_added_services_vas_market_worldwide_industry_share_investment_trends_growth_size_strategy_and_forecast_research_ ...

s and applications at a higher

application layer An application layer is an abstraction layer that specifies the shared communication protocols and interface methods used by hosts in a communications network. An ''application layer'' abstraction is specified in both the Internet Protocol Su ...

. The service layer provides ''capability servers'' owned by a telecommunication network service provider, accessed through open and secure

Application Programming Interface An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...

s (APIs) by application layer servers owned by third-party content providers. 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 In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end c ...

(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 network The Intelligent Network (IN) is the standard network architecture specified in the ITU-T Q.1200 series recommendations. It is intended for fixed as well as mobile telecom networks. It allows operators to differentiate themselves by providing ...

s (IN), WAP, 3G and

IP Multimedia Subsystem The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is a standardised architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched-sty ...

(IMS). It is defined in the

3GPP The 3rd Generation Partnership Project (3GPP) is an umbrella term for a number of standards organizations which develop protocols for mobile telecommunications. Its best known work is the development and maintenance of: * GSM and related 2G and ...

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 In software engineering, service-oriented architecture (SOA) is an architectural style that focuses on discrete services instead of a monolithic design. SOA is a good choice for system integration. By consequence, it is also applied in the field ...

, the concept of service layer has a different meaning.

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). The ISC interface uses the SIP signalling protocol.

Elements of the IMS service layer

The network elements contained within 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 A camel (from and () from Ancient Semitic: ''gāmāl'') is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. Camels have long been domesticated and, as livestock, they provid ...

Service layer in SOA

service-oriented architecture In software engineering, service-oriented architecture (SOA) is an architectural style that focuses on discrete services instead of a monolithic design. SOA is a good choice for system integration. By consequence, it is also applied in the field ...

(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.Service-oriented Architecture Compass: Business Value, Planning, and Enterprise Roadmap. Author: Norbert Bieberstein, Sanjay Bose, Marc Fiammante, Keith Jones, Rawn Shah. Edition: illustrated. Published by: FT Press, 2005.
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

{{Reflist Application layer protocols Service-oriented (business computing) Middleware