lecture 1 (Telephony systems and links)_588234c88978e448e7e07efe77774230 Copy.pdf
- 1. Lecturer Dr. Sherif Ismail Elsanadily Lecture 1 Telephony systems and links ECO 353 Communication Networks Weekly: 2 lectures + 2 tutorials
- 2. Syllabus * Introduction to telecommunication networks * Network topology * Switching: telegraph, telephone, telex, data, signaling, ISDN, broadband private switching * Management network multiplexing: analog digital wavelength division * Data transmission interface equipment: modems digital data interface equipment * Codecs: audio, video * Copper lines: open wire, twisted pair cable * Optical fiber technology: types of optical fibers, cables, wavelength division, multiplexing in optical networks, applications, radio relay technology systems * Mobile radio: service mode technology * Satellites: services, technology * DSL
- 3. * This subject aims at introducing to the students the knowledge about the telecommunication industry, theoretical basis about performance and operation (multiplexing, switching, routing, and signaling) in telecom networks. * To familiarize the student with the Public Switched Telephone Network (PSTN), and understand how the physical telephone network is organized, the characteristics of basic telephone service, how calls are established end-to-end. * To familiarize the student with the design, analysis operation and management of modern data communications networks. * To provide the student with a working knowledge of the types of communications network management systems * To become familiar with various types of networks (LAN, MAN, WAN and Wireless networks) and their protocols * To become familiar with satellites, orbits, links and satellite access. * To give the student a broad treatment of the diverse subsystems that make up a complete satellite communication system. text books * Andy Valdar, "Understanding Telecommunications Networks", 1st edition, IET Telecommunications Series 52, 2006 . * Tarmo Anttalainen, "Introduction To Telecommunications Network Engineering", 2nd ed., Artech House (2003). Handouts * Lectures slides * Problem sheets and solutions Course Objectives
- 6. telephone network (PSTN) There are also practical limitations on the lengths of telephone lines which constrain the size of the catchment area of lines dependent on one exchange.
- 7. History of Network Structure Traffic routing hierarchy: For guaranteeing full connectivity between exchanges and reducing the number of employed links, it is needed to classify them and make the appropriate arrangements.
- 8. How does a network set up a call connection? Local exchange Trunk exchange Trunk exchange Local exchange user user long distance
- 9. Waveforms and their spectrum in comm. networks
- 10. Interconnection of different telephone service providers mobile telephone network Networks linked appropriately to provide various types of call connections between subscribers across the world. Differences in mobile telephone network (from PSTN): * two-way radio link to connect mobile handset to its exchange (need identifying the calling handset + keep track) * a set of cells forming an area (1–10 km radius) - centrally located radio transceiver in a base station (BS). * A two-way radio link available to all handsets in the cell area * BSC (BS controller)serves several cells with their connected BSs (via fixed links carried over either p-p microwave or optical fiber) * 2-radio ch-s allocated on demand by BSC to a handset * During the call, if the handset travels towards the boundary of its cell, the varying signal is detected by BSC performing a ‘handover’ between the two cells * Mobile switching center (MSC), similar to a large local PSTN performs switching of calls between all handsets operating in its area or to other MSCs
- 11. Cable TV Network Cable Networks often deployed in only certain areas (which delivers mainly TV broadcast) * these networks sometimes provide telephone service * 2 separate feeds: a coaxial cable terminating on a set-top box (STB) linked to TV and copper wires provides telephone service * At the street cabinet, TV distribution and the telephone lines multiplexed onto optical fibre cable. * The telephone portion of the Cable TV network is similar to the standard PSTN Interconnection of different telephone service providers
- 12. Mobile to mobile via the PSTN Interconnection of different telephone service providers The first case: a call between a terminal registered with a service provider using mobile network A and a terminal belonging to mobile network B. The second case ‘roaming process’: a call between 2 terminals belonging to mobile network A, but the second terminal moved temporarily onto (visiting) mobile network B. ExampLe in figure: a call made to terminal a1 (roaming) from another terminal, a2 On receiving a call request from A, MSC on Network B allocates temporary PSTN number and informs the originating MSC on A with this number. Then originating MSC routes the call via its gateway to PSTN, using the allocated PSTN number as destination address and MSC of B can then associate the call with the required BS currently serving terminal a1. Calls between mobile networks in the same country often delivered over direct links between MSCs (but more economical to route calls to other mobile operators and wide range of fixed PSTNs). Each mobile network has at least one MSC acting as gateway to the PSTN.
- 13. The Internet: Internet Access Interconnection of different telephone service providers Each of the component networks in the Internet constellation owned and operated by ISPs. Users and providers of information access to ISP for Internet service: ** Users access over links provided by one of a range of networks (PSTN, ISDN, mobile, leased line, ADSL/broadband and Cable TV) ** ISP networks comprise a number of IP switching units (routers) located at various points and linked by TX circuits leased from PSTN (leased lines) or private circuits. Smaller (less widespread) ISP networks connect to larger ISP swith international coverage ‘backbone ISPs’.
- 14. The Internet Access: Dial-up via the PSTN and ISDN Interconnection of different telephone service providers * Internet access through a telephone call (using PSTN). 1) telephony call to ISP; 2) data transfer session between computer and Internet via the ISP. * A modem in computer acts as a telephone (equivalent of (‘off-hook’), detecting dial tone, and sending out dialled digit tones). Modem enables data to be passed over standard telephone line. * ISP connected to PSTN over standard local line or by ISDN local line (in either case standard telephone numbers are allocated) * Interchanging of data: ISP verify user identification and establish a data session to Internet (IP used between PC and the ISP’s IP router during the session). When session is over, Modem signals causing the exchange to clear the call Note: Internet Access via ISDN, same as PSTN, except interface between PC & ISDN line is digital rather than analogue (higher speeds up to 64 kbit/s or even 128 k bit/s are possible). Integrated Services Digital Network, ISDN, (first defined in 1988) is a standard for simultaneous digital transmission of voice, video, data, and other services over the traditional PSTN.
- 15. The Internet Access: Over ADSL Interconnection of different telephone service providers * Using ADSL enables high-speed data service, carried over telephone line copper pair * Telephone line & PC separately connected to splitter within the ADSL termination equipment. * At the exchange: they similarly separate telephone call & data signal (call over copper pair to local exchange switch and data stream connected to DSLAM (digital subscriber line access multiplexor) which combines data from many lines onto high speed link to data network --> carrying data, interleaving with other sources, to various ISPs.
- 16. The Internet Access: Over a cable modem or Leased line access Interconnection of different telephone service providers * Cable TV networks can provide a high speed data link to ISP over a spare TV channel. Cable modem converts PC O/P into compatible signal with the TV distribution system. * Both carried as a composite TV signal over coaxial cable from street cabinet. Street cabinet performs a similar aggregating function as DSLAM. Cable TV operator routes the aggregated traffic over data network. Leased line access: Leased lines, providing high capacity dedicated Internet access to office blocks and industrial sites (Concept of leased lines explained later)
- 17. Specialist Networks associated with a PSTN Needing to provide range of services beyond the standard PSTN calls. (extra services: 1) grouped available to all customers; 2)aimed at business customers). Operator-services network *containing specialist telephone exchanges but supporting suite of operator consoles with more control of calls than provided to normal subscribers; providing call assistance, access to emergency services, directory enquiry, and blind and disabled special assistance services. *Calls to this network either routed directly from originating exchange or from parent trunk exchange Intelligent network *comprises several centers around the country containing control systems and data-bases that provide advanced switched services based on the translation of the number dialed by subscriber to another number (e.g. the recipient rather than the caller pays)as is the case of ‘0800’ services. The translations might be fixed or varying, for example, according to the time of day, day of the week, caller location,..etc. *Calls routed to IN center when PSTN exchange detects that dialed number requires translation. Business-services network *range of services designed for businesses provide direct desk-to-desk dialing using private numbering schemes (between offices and factory sites). using separate dedicated special exchanges for these services with most calls within the businesses and only few calls to or from a trunk exchange in PSTN. *Access to these services use direct dialing in – DDI, with special telephone instruments. Subscriber lines over local PSTN copper pairs, specially optical fiber cables, or microwave radio links.
- 18. Specialist Networks associated with a PSTN Private-circuit services network *Provides point-to-point un-switched links, known as ‘private circuits’ or ‘leased lines’, for business organization offices, factories or warehouses. Although it is non-switched, it may use automatic digital cross- connection units (DXC), a form of switching equipment for private circuits (electronic jumpering). DXCs Connections once set up are held for duration of the circuit lease, typically several years. Such circuits used for linking telephones (voice) or data terminals and computers (data). *Two examples are given in the figure (a) manual jumpering at local exchange (Longer circuits obtained by jumpering transmission links in concatenation) (b) automatic cross-connection units with control and monitoring from central network management center. Data services networks *Providing services using packet switching technique, rather than circuit switching technique (used for telephone calls). In addition, businesses now use data networks within their buildings, such as LANs. *The most common of these data services are: - SMDS (switched multi-megabit data service) - Frame Relay - ATM ('asynchronous transfer mode' not the bank machine) - IP - MPLS (multi-protocol label switching). note: Data services and networks are discussed in other courses (computer networks)
- 19. * Private Branch Exchange (PBX) is small version of PSTN providing call connections between a business telephones ‘extensions’ and links into PSTN. * private numbering scheme required to enable internal dialing and Incoming calls from PSTN answered by a operator manually (Alternatively, calls from PSTN directly switched by PBX to the required extension, known as DDI, automatically). if a company extends over two or more sites, PBXs on each site linked by private circuits ‘private network’. * A virtual private network (VPN) is an alternative for private circuits between each PBX. VPN exchange switches calls between connected PBXs. However, VPN provided over public exchanges where each VPN exchange switches private network calls of several private corporate networks (each separately using its own numbering scheme.) * Each corporate network exploits a private set of links between their PBXs, even though provided connectivity over public exchanges Centrex: *Centrex is a central exchange, providing functions similar to PBX, but its equipments located at PSTN company. its drawback is the customer will be at the mercy of local exchange *The centrex exchange serves many centrex customers, each with their own private extension numbering scheme. PBX and CENTREX
- 20. An IP PBX is a PBX system with IP connectivity connecting extensions to PSTN (for a business firms) with capabilities of additional audio, video, or instant messaging communication utilizing the TCP/IP protocol. IP PBX