1 Introduction to Communications and Networks ECI Dr. Vincent Siyau

2 Communication System Model

3 A Simple Telephone Off hook now !!

4 A More Realistic Telephone On hook now !!

5 Signalling in Telephone Network LE: Local Exchange (i.e., Central Office)

6 Dialling in Telephone Network Rotary dialling (Pulse dialling) Dual-tone Multi-frequency (DTMF) (Touch-tone dialing ) Dual tones for each key

7 Why DTMF ? allows dialling numbers via microphone allows in-band signalling allows end-to-end signalling between two telephones

8 Telephone Network Point-to-point telephone connection Mesh network Resource utilisation ? Scalability ? connection

9 Telephone Network Star network More efficient resource utilisation Scalable Allows hierarchical routing

10 Telephone Network Routing – Circuit Switching

11 Routing in Telephone Network Hierarchical routing paradigm Intra-LATA services are offered by common carriers (Telephone Companies) within a LATA. Handled by local exchange carrier (LEC). Inter-LATA services between LATAs are handled by interexchange carriers (IXCs) or (long distance companies). : LATA – Local access transport areas:

12 National/International Routing POP – Points of Presence: A switching office that handles carriers exchange LEC & IXC

13 Voice Communication Service Offerings Wide Area Telecommunication Services (WATS)  non-standard billing for businesses with high call volume Inward WATS  business agrees to pay for all INCOMING long-distance calls from certain areas (e.g., 0800, 0870) Foreign exchange  phone numbers in distant cities where your customers can call your company at local charges Leased lines  permanent point-to-point connection  annual rent

14 Customer Premises Equipment Centrex –Central Office is acting as the customer’s exchange or switch Private Branch Exchange (PBX) –Acts as a mini-central office for a company, dedicated to customer who owns it (not owned by Central-Office).

15 Customer Premises Equipment Centrex service: Very Dependable & Reliable - because services are maintained by Central-office (full-time maintenance & troubleshooting staff). Inflexible – additional lines can only be fitted by central-office. Inefficient – Calls within company are routed all the way through Central Office and back. Hence expensive – regular fees for each month

16 Customer Premises Equipment Private Branch Exchange (PBX): Suitable for large business – provide thousands of lines. VERY flexible – can add/remove a line anytime Efficient – internal calls are routed within PBX without going through Central-office, hence provide quick access. Maintenance is CRUCIAL – need a team to always maintain it. Does not need local loop for each employee. Only a few local loops are needed for external call. Internal calls are free using ext. assigned to each one.

17 Regulatory Bodies OFCOM (Office of Communications) ITC (Independent Television Commission) Radio Authority Radio Communications Agency OFTEL (Office of Telecommunications)

18 OFTEL's functions Promoting the interests of consumers. Maintaining and promoting effective competition. Making sure that telecommunications services are provided in the UK to meet all reasonable demands, including: Regulatory Bodies  emergency services;  public call boxes;  directory information; and  services in rural areas

19 Beyda, W.J. ”Basic Data Communications” Chapter-2, Prentice-Hall, Forouzan, B. ”Data Communications and Networking” 3 rd Ed., Chp:8. Recommended reading

20 Tutorial 1 Describe the signaling procedure for making a call through telephone network. List three signals that your phone sends to local exchange List three signals that local exchange sends to your phone Describe how rotary dialing and touch-tone dialing is made. What is a mesh network? What is a star network? What is local loop and Central Office?

21 Why Telephone network uses star network? Describe how your local call is routed. Describe how your international call is routed. Briefly describe two types of Customer Premises Equipment Describe the advantages and disadvantages of using a Centrex Service? Describe the advantages and disadvantages of using a private branch exchange (PBX)?