1. Types of Communication Links Modem dial-up Leased Line ISDN Broadband –ADSL –cable broadband –Ethernet broadband

2. Modem Dial up –run-on telephone system –no connection until dial-up OK –a circuit-switched facility not packet-switched technology = connection between 2 end-points in the network is occupied once it is connected when the connection is over, the line is freed up for the other call

3. Modem Dial-up (Cont’d) –a normal computer cannot perform connection to and signal transmission through telephone system Computer uses digital signal –with only 0 / 1 …….. Either OFF or ON –no in-between states Telephone line can transmit only analogue pulses –signal constantly varies in amplitude and frequency

4. Digital Signal

5. Analogue Signal

6. Modem dial-up (cont’d) –In order for the successful transmission of signal MODEM is required MODEM = modulator demodulator Convert Digital Signal to analogue signal and vice versa ? ?

8. Modem dial-up (cont’d) –dial up connection –dedicated to the duration of the communication session –no other dial up connection is allowed until that dial up connection is finished –Circuit-switched facility / Circuit- switching connection between two end points is occupied once connected

9. Leased Lines –a telephone line that has been leased for private use –also circuit-switched facility –adv : has guaranteed bandwidth simplify planning –Disadv : billing is fixed regardless how much bandwidth is used no capacity to growth

10. ISDN (Integrated Services Digital Network) –integrate both analogue data and digital data over the same network (upgrade switches of ISP) –can use the telephone system during data transmission –Two types of services (by ISP) BRI (Basic Rate Interface) –for home use and small enterprise PRI (Primary Rate Interface) –for large corporation

11. ISDN (Cont’d) –BRI consists of 2 x 64 Kbps B-channels –1 channel for 1 job 1 x 16 Kbps D-channel –carrying control and signalling information Total bandwidth (2B + D) = –2 x 64 + 1 x 16 = 144 Kbps

12. ISDN (Cont’d) –PRI (in USA) consists of 23 x 64 Kbps B-channels –1 channel for 1 job 1 x 64 Kbps D-channel –carrying control and signalling information Total bandwidth (23B + D) = –23 x 64 + 1 x 64 + ??? = 1.544 Mbps

13. ISDN (Cont’d) –PRI (in Europe) consists of 30 x 64 Kbps B-channels –1 channel for 1 job 1 x 64 Kbps D-channel –carrying control and signalling information Total bandwidth (30B + D) = –30 x 64 + 1 x 64 + ??? = 2.048 Mbps