View page as slide show

Communications software, protocols and architecture

Communication in layered architecture

  • Horizontal communication (protocol)
    • Communication of peer entities. Peer entities form virtual channel between each other
    • Communication between peer entities are conducted with Protocol Data Units (PDU's)
  • Vertical communication
    • Messages are called primitives
    • Layer N produces service to layer n+1 and uses the service of layer n-1
    • Service is accessed via service access point (SAP)
    • PDU is enveloped and given to lower layer



  • Layer N entity passes IDU to layer N-1 via N-1 SAP
    • SDU : Service data unit (protocol data)
    • PCI : Protocol control information (protocol header)
    • PDU : protocol data unit (N PDU is usually N-1 SDU)
    • ICI : Interface control information
    • IDU : Interface data unit

Protocol system structure


Service types of protocol entity


  • Confirmed service
    • primitives: request → indication → response→confirmation
  • Unconfirmed service
    • no handshake
    • request → indication
  • Provider initiated
    • indication to both sides from lower layer
    • e.g. lost connection

Protocol Entity in layered architecture


Data flow in protocol system


Physical layer

Network layer

Transport layer

Session layer

Presentation layer

Application layer

Last modified: 2013/07/01 14:42