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Subject Name: Digital Switching Systems Subject Code:10EC82 Prepared By: Aparna.P, Farha Kowser Department: Electronics and Communication Date:3-3-2015. UNIT 1 The development of Telecommunication. Introduction Network Structures Network services Terminology, Regulation, Standards
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Subject Name: Digital Switching SystemsSubject Code:10EC82Prepared By: Aparna.P, Farha KowserDepartment: Electronics and CommunicationDate:3-3-2015
Introduction • Network Structures • Network services • Terminology, Regulation, Standards • Four -wire circuits • Digital Transmission • PDH, SDH
Introduction • Telecommunication networks carry information signals among entities, which are geographically far apart. • The future challenges are enormous as we anticipate rapid growth items of new services and number of users. • Telecommunication has evaluated and growth at an explosive rate in recent years and will undoubtedly continue to do so.
Network Topologies • Bus, ring, star, and other types of network topology In computer networking. • Topology refers to the layout of connected devices. • This article introduces the standard topologies of networking. • Topology in Network Design Think of a topology as a network's virtual shape or structure. • This shape does not necessarily correspond to the • Actual physical layout of the devices on the network.
Bus Topology : Bus networks (not to be confused with the system bus of a computer) • Use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector.
Ring Topology In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise” or "counterclockwise").
Star Topology • Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. • Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Mesh Topology • Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination.
Telecommunication Network • A telecommunications network consists of • Transmission systems • Switching systems • Stations
Transmission Systems • Transmission (abbreviation: Tx): • is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. • Transmission System: • is a system that transmits a signal from one place to another. The signal can be an electrical, optical or radio signal. • carries messages from an originating station to one or more distant stations. • is engineered and installed in sufficient quantity to provide a quality of service compatible with the cost and expected benefits.
Transmission Systems • The source may be a simple telephone microphone, keyboard • The destination may be a simple telephone speaker, monitor • It can be a single electrical medium, or a cascade of electrical media
Switching systems • Switching systems are an assembly of switching and control devices provided so that any station in a communications system may be connected as desired with any other station. • To enable the transmission facilities to be shared, stations are connected to and reached through switching system nodes that are part of most telecommunications networks. • Switching Systems act under built-in control to direct messages toward their ultimate destination or address.
High Availability Network Design Simplified Using Virtual Switching System
Network Structures User1 User 4 User 2 User 3 Ring Network N=1 Bus Network N=1 Mesh Network N=1/2n(n-1) Tree Network Star Network N=n
Exchange Area with a single exchange Area with several exchanges Solution can be provided by connecting a line from each user’s station to the central switching center/telephone exchange a telephone exchange or telephone switch is a system of electronic components that connects telephone calls
Telecommunication networks hierarchy L L L L L T L L L Junction circuits L Junction Network Multi exchange area. L= Local Exchange T=Tandem Exchange L L • A National Public Switched Telecommunication Network (PSTN) consists of: • Local network • connects customers’ station to their local exchanges. • These are also called subscribers’ distribution networks, customer access networks or the customer loop. • Junction networks • interconnects a group of local exchanges serving as area and a tandem or trunk exchange. • The trunk network or toll network • which provides long-distance circuits between local areas throughout the country.
National Telecommunication Network Satellite Links and Submarine Cables nodes International Gateway Exchange (Centre de Transit3) International Network National Tandem Exchanges (tertiary trunk switching centres) PBX Trunk Network Regional Tandem Exchanges (Secondary trunk switching centres) Core Network Junction Network Local Tandem Exchanges (Primary trunk switching centres) Local Exchanges Local Network Customer Lines
Elements of a Telecommunication Network • Transmission System • Switching System • Signaling system • Responsible for interchange of information • Which are made up by interconnecting • Customer nodes • Switching nodes • Transmission nodes • Service nodes
Network Services • Customers of a PTO may require different services which appear to require different networks. Examples include: • Public Switched Telephone Network (PSTN) • The Public Switched Telegraph Network (Telex) • Private Networks for voice and data • Radio networks providing mobile communication • Public data networks (PDN) • Special Service Networks
Visual PDN Telex PC PSTN Transmission Bearer Network Loop • Customers are connected to transmission bearer network at their local exchange via the local access network or local loop. • The services provided over the telecommunication network can thus be divided into two categories: • Teleservices • Provision of the service depends on particular terminal apparatus ( e.g. telephone or tele-printer). • Bearer Services • Present the customer with transmission capacity that can be used for any desired function (e.g. private circuits)
Four Wire Circuits • The amplifiers are used to compensate for the attenuation of a transmission path. These amplifiers are unidirectional so it is necessary to provide two channels for the go and return path. This can be achieved by using four-wire circuit. • At each end the four-wire circuit must be connected to a two wire line leading to a telephone. • It consists of four wire/ two wire circuit to avoid singing.
Frequency division multiplexing (FDM) • In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication channel is divided into a series of non-overlapping frequency sub-bands, each of which is used to carry a separate signal. • The example of frequency-division multiplexing is radio and television broadcasting in which multiple radio signals at different frequencies pass through the air at the same time. Another example is cable television, in which many television channels are carried simultaneously on a single cable. FDM is also used by telephone systems to transmit multiple telephone calls through high capacity trunk lines.
Time division multiplexing (TDM) • Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. This form of signal multiplexing was developed in telecommunications for telegraphy systems. Later applied to telephony systems. • Time-division multiplexing is used first for digital signals later it is applied to analog signals. • In TDM the time domain is divided into several time slots of fixed length, one for each sub-channel. sub-channel 1 is transmitted during time slot 1, sub-channel 2 during time slot 2 and etc..
Plesiochronous Digital Hierarchy(PDH) • The plesiochronous digital hierarchy (PDH) is a technology used in telecommunication to transport large quantities of data over digital transport equipment such as fiber optic and microwave radio systems. • PDH networks run in a state where different parts of the network are nearly, but not quite perfectly, synchronized.
Synchronous Digital Hierarchy (SDH) • Synchronous Digital Hierarchy (SDH) is a standardized protocol that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light emitting diodes(LEDs). In USA this is called Synchronous optical network(SONET).
