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Signalling Systems. System which allows various network components to exchange information In particular, it supports call / connection control network management. Signalling Environments. Subscriber Signalling Applied on Access Links Tends to be only Call Control Relatively Simple

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signalling systems
Signalling Systems
  • System which allows various network components to exchange information
    • In particular, it supports
      • call / connection control
      • network management
signalling environments
Signalling Environments
  • Subscriber Signalling
    • Applied on Access Links
    • Tends to be only Call Control
    • Relatively Simple
    • e.g. DSS1 in ISDN
  • Network Signalling
    • In the network
    • Call Control and Network Control
    • Complex
    • e.g Signalling System 7 (SS7)
signalling
Signalling
  • Types of signalling
    • in-band signalling
      • signalling messages carried in same channel as user information
      • e.g.
        • TCP/IP
        • analogue access links in telephone networks
    • out-band signalling
      • Separate signalling channel for signalling messages
      • e.g.
        • ISDN access links (Frame Relay)
        • SS7
signalling4
Signalling
  • Within out-band signalling another distinction can be made
    • Channel Associated Signalling (CAS)
      • Direct relationship between the signalling channel and information channel
    • Common channel signalling (CCS)
      • Signalling channel is shared on a demand basis
signalling5
Signalling
  • Modern signalling systems use out-band CCS
    • More secure (main reason why out-band signalling developed)
    • Signalling can be carried out at the same time as user information is exchanged
    • More efficient use of resources - allocated on a demand basis
    • Separate signalling network means less processing on messages - no need to separate signalling from user information
    • Signalling protocol can evolve independently, without effecting user application communication stack, can also be more complex.
    • At call set-up, signalling messages can be transmitted in parallel with the establishment of information channel (Not possible with CAS)
      • set-up times tend to be shorter
signalling6
Signalling
  • Signalling network is a separate network
    • Two modes of operation are possible with CCS
      • Associated mode
        • Same topology as information network
        • Signalling switches located with information switches
      • Non Associated mode
        • Combined signalling / information switches
        • Also, separate signalling switches called Signalling Transfer Points (STPs)
        • Result is a separate signalling network topology, with links and interfaces into underlying information network
signalling7
Signalling
  • Two signalling standards which operate
    • Subscriber signalling
      • e.g. Digital subscriber system 1
    • Network signalling
      • Signalling System 7 (SS7)
signalling9
Signalling
  • SS7
    • Concerned with connection set-up and network management
    • Defined in Q700 series
    • Network components are
      • Signalling Points
        • Process signalling messages
      • Signalling Transfer Points
        • SPs with switching facilities
      • Signalling links
signalling10
Signalling
  • SS7 Protocol architecture
    • Message Transfer Part
      • 3 layers, which provide a reliable, but connectionless service
      • similar in functionality to IP
      • i.e. provides carrier for higher layers
    • Signalling Data Link
      • typical physical layer functionality
    • Signalling Link Layer
      • provides typical layer 2 functionality, i.e. error free link
    • Signalling Network Layer
      • Signalling Message Functions
        • Switching of signalling messages across the network
      • Signalling Network Management Functions
        • traffic, link and route management functions
signalling11
Signalling
  • Signalling Connection Control Part (SCCP)
    • Equivalent to upper layer 3
      • (so concerned with routing)
      • Augments the basic service provided by MTP
      • A range of services
        • 2 connectionless services
        • 2 connection-oriented services
signalling12
Signalling
  • User Parts
    • Equivalent to layer 4
    • These typically relate to the control of specific types of calls
      • e.g. ISDN User Part
      • Used to set-up ISDN calls
signalling13
Signalling
  • Transaction Capabilities Part (TCAP)
      • Used to
        • execute remote processes
        • provide means for transfer of data between nodes
      • Used extensively in Intelligent Networks (INs)
      • Essentially application layers
signalling14
Signalling
  • Consider how SS7 supports setting up a call
  • Consider how SS7 supports the 0800 service