Telecommunications systems (Part 1) School of Business Eastern Illinois University © Abdou Illia, Spring 2007 (Week 12, Tuesday 3/27/2007)

2 Learning Objectives n Describe and compare types of connection to subnets and networks offered by telephone companies

3 Types of connection n Dial-up: standard telephone line n 56K Leased line n T-Carrier (T-1, T3) n Integrated Services Digital Network (ISDN) n Digital Subscriber Line (DSL) (Frame Relay) (Asynchronous Transfer Mode - ATM)

4 Dial up: standard telephone line n Many home computer users use standard telephone lines and conventional modems to connect to networks. n A dial-up connection is not always active n Speed limited by: – Bandwidth of standard telephone line (3.1 KHz) Shannon Equation: Maximum speed = Bandwidth * Log 2 (1 + Signal Power/Noise) ~ 35 kbps

5 Modems Standards NameReceiving speedSending speed V.9256 kbps48 kbps V.9056 kbps33.6 kbps V kbps Modem standards V.32 bis14.4 kbps

6 Dial up connection with modem at both ends PSTN (Digital) Client A Server A Telephone 33.6 kbps Modem Digital Signal Modulated Signal Modem Need Modem at Each End * PSTN: Public Switched Telephone Network

7 Standard telephone line w/ Digital Access Line PSTN (Digital) Client B Server B Telephone Digital Access Line 56 kbps Modem For 56 kbps Download Speed Server Must Have a Digital Connection, Not a Modem

8 Standard telephone line Although only 35 kbps can be sent through a typical 3.1 Khz telephone bandwidth, telephone system is digital internally with 56 kbps channels for individual telephone calls

9 Standard telephone line n ADC limits transmission speed n ADC needed because internal telephone system is digital

10 Standard telephone line n Internet Service Provider (ISP) is not going through ADC n So, ISP can make full use of telephone system’s 56 kbps

11 Standard telephone line n When 56 kbps signal reaches the last telephone switch: – DAC translates the digital signal into an analog signal – DAC sends the analog signal to your telephone (therefore to modem) * DAC do not impose 3.1 kHz limitations. So modem can receive at 56 kbps

12 Standard telephone line (w. modem) Typical max speed 33.6 Upstream 56 kbps Downstream Characteristics Data or Voice Both Cost per month ~$12.00 Mode of connection Dial-up

13 56K Leased line PSTN (Digital) 56K leased Line For 56 kbps Upload/Download Speed Always on LAN A LAN B 56K leased Line n Most businesses need permanent high-speed connection: – to the Internet – to other businesses – to remote databases n A 56K Leased line is a an option Q: what type of conversion device will be needed at the LANs ends?

14 56K Leased line n 56K leased lines: – Are dedicated lines leased from telephone companies – Connect the Client to another party (Office, ISP, supplier, etc) – Are always active (No need for Dial) – Transfer data at 56,000 bps n Cost depends on distance: – ~$100/mo for local connection (non long-distance) – ~$500/mo plus 1.00/mile for long-distance connection n For more about 56 Leased lines, see: – –

15 Summary Questions 1. When a standard telephone line is used to connect to a network: (a) What device limits the speed? (b) Where is this device located? (a) The analog-to-digital converter (ADC). (b) It is located at the telephone company’s switch at the end of your local loop access line. 2. (a) In using a V.90 modem for dial-up connection to the Internet, what is needed at the ISP end? (b) What does the telephone company need? (a) A digital access line to the telephone carrier (and some internal equipment). Note: The ISP does not have a V.90 modem. If it did, it could only transmit at 33.6 kbps. (b) The telephone company does not have to do anything differently. Note: the telephone company does not have to install ADCs. These are already there. You use ADCs and DACs every time you make a voice telephone call.

16 Summary Questions 3. (a) How are 56K Leased lines and standard telephone lines different in terms of their operation? (b) How are they different in terms of speed and cost? (a) With standard telephone lines you need to dial a telephone number to connect. The connection is not permanent (active only during a call). With 56K Leased line, there is no need to dial a telephone number, and the connection is always active. (b) 56K Leased lines are faster and more expensive.

17 Elements of the Public Switched Telephone Network (PSTN) 1. Customer Premises Equipment

18 Elements of the Public Switched Telephone Network (PSTN), Continued 2. Access Line (Local Loop) 2. Access Line (Local Loop) The Access System consists of the access line to the customer (called the local loop) and termination equipment at the end office (nearest telephone office switch)

19 Elements of the Public Switched Telephone Network (PSTN), Continued 3. Transport Core 3. Trunk Line 3. Switch The Transport Core is a subnet. It includes Telephone switches and Trunk lines that interconnect the teelphone switches.