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Interfaces and Services

  • Last Updated : 28 Jul, 2020

Interfaces and Services is a process that generally provides and gives a common technique for each layer to communicate with each other. Standard terminology basically required for layered networks to request and aim for the services are provided.

Service is defined as a set of primitive operations. Services are provided by layer to each of layers above it.

Below is diagram showing relation between layers at an interface. In diagram, layers N+1, N, and N-1 are involved and engaged in process of communication among each other.

Components Involved and their Functions :



  • Service Data Unit (SDU) –
    SDU is a piece of information or data that is generally passed by layer just above current layer for transmission. Unit of data or information is passed down to a lower layer from an OSI (Open System Interconnection) layer or sublayer. Data is passed with request to transmit data. SDU basically identifies or determines information that is been transferred among entities of peer layers that are not interpreted by supporting entities of lower-layer.

  • Protocol Data Unit (PDU) –
    PDU is a single unit of information or data that is transmitted or transferred among entities of peer layers of a computer network. When application data is passed down to protocol stack on its way to being transmitted all over network media, some of protocols add information an data to it at each and every level. PDU is used to represent and describe data is it gets transferred from one layer of OSI model to another layer.

  • Interface Data Unit (IDU) –
    IDU is used to have an agreed way of communication among two layers in a network layered architecture. It is passed from (N+1 to N).
  • Service Access Point (SAP) –
    SAP is generally used as an identifier label for endpoints of network in OSI networking or model. It is a data structure and identifier also for a buffer area in memory of system. It is a point in a layer of a layered architecture where a network is usually provided and where layer just above layer that provides service can probably have access to it.
  • Interface Control Information (ICI) –
    ICI is a temporary parameter that is passed between N and N-1 layers to include service functions among two layers.

Benefits :

  • Increase in Compatibility –
    Layered approach to networking and communication protocols generally provides and shows greater compatibility among all devices, systems, and networks that they deliver.
  • Less expensive –
    Easy way of development and implementation converts to increase in an efficiency and even effectiveness that in turn converts into larger economic rationalization and very cheaper products while not compromising with quality.
  • Increase in Mobility –
    Whenever we use layered and segmented strategies into architecture design, there will always be an increase in mobility.
  • Better Scalability –
    Whenever we use a layered or hierarchical approach to networking protocol, design, and implementation scale much better than horizontal approach.

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