Telecommunications systems (Part 1)

Transcription

1 School of Business Eastern Illinois University Telecommunications systems (Part 1) (Week 11, Thursday 11/02/2006) Abdou Illia, Fall 2006 Learning Objectives 2 Describe and compare types of connection to subnets and networks offered by telephone companies Types of connection 3 Standard telephone line 56K Leased line T-Carrier (T-1, T3) Integrated Services Digital Network (ISDN) Digital Subscriber Line (DSL) (Frame Relay) (Asynchronous Transfer Mode - ATM) 1

2 Standard telephone line Many home computer users use standard telephone lines and conventional modems to connect to networks. Dial-up connection (not always active) Speed limited by: Bandwidth of standard telephone system (3.1 KHz) 4 ~ 35 kbps Shannon Equation: Maximum speed = Bandwidth * Log 2 (1 + Signal Power/Noise) Modems Standards 5 Modem standards Name Receiving speed Sending speed V kbps 48 kbps V kbps 33.6 kbps V kbps 33.6 kbps V.32 bis 14.4 kbps 14.4 kbps 6 Standard telephone line w/ Modem at each end Need Modem at Each End Digital Signal Modulated Signal Client A 33.6 Telephone kbps Modem Modem Telephone Server A PSTN (Digital) * PSTN: Public Switched Telephone Network 2

3 Standard telephone line w/ Digital Access Line 7 PSTN (Digital) Digital Access Line Client B 56 kbps Modem Telephone Server B For 56 kbps Download Speed Server Must Have a Digital Connection, Not a Modem 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 8 Standard telephone line 9 ADC limits transmission speed ADC needed because internal telephone system is digital 3

4 Standard telephone line 10 Internet Service Provider (ISP) is not going through ADC So, ISP can make full use of telephone system s 56 kbps Standard telephone line 11 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 Standard telephone line (w. modem) 12 Characteristics Typical max speed Data or Voice Mode of connection Cost per month 33.6 Upstream 56 kbps Downstream Both Dial-up ~$

5 56K Leased line Most businesses need permanent high-speed connection: to the Internet to other businesses to remote databases A 56K Leased line is a possible solution 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 Cost depends on distance: ~$100/mo for local connection (non long-distance) ~$500/mo plus 1.00/mile for long-distance connection 13 Summary Questions 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. 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. 15 5

6 Elements of the Public Switched Telephone 16 Network (PSTN) 1. Customer Premises Equipment 1. Customer Premises Equipment Elements of the Public Switched Telephone Network (PSTN), Continued 17 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) 2. Access Line (Local Loop) 2. Access Line (Local Loop) Elements of the Public Switched Telephone Network (PSTN), Continued Transport Core 3. Switch 3. Trunk Line The Transport Core is a subnet. It includes Switches and Trunk lines that interconnect the switches. 6