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 e.g. DSS1 in ISDN –Network Signalling In the network Call Control and Network Control Complex e.g Signalling System 7 (SS7)

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

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

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

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

Signalling Two signalling standards which operate –Subscriber signalling e.g. Digital subscriber system 1 –Network signalling Signalling System 7 (SS7)

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

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

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

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

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

Signalling Consider how SS7 supports setting up a call Consider how SS7 supports the 0800 service