Chapter 9 HighSpeed Digital Access DSL Cable Modems

Chapter 9. High-Speed Digital Access: DSL, Cable Modems Kyung Hee University 1

9. 1 Digital Subscriber Line (DSL) q uses a newer technology that used the existing telecommunications networks such as the local loop telephone line. q is an asymmetric communication technology designed for residential users; it is not suitable for business. q x. DSL: where x can be replaced by A, V, H, or S q The existing local loops can handle bandwidths up to 1. 1 MHz v by removing the filter at the end of line of telephone company v but, limitation because of distance between the residence and the switching office, size of cable q ADSL is an adaptive technology. The system uses a date rate based on the condition of the local loop line Kyung Hee University 2

DSL q. DMT v Modulation technique that has become standard for ADSL is called the discrete multitone technique (DMT) which combines QAM and FDM. v Kyung Hee University 3

DSL qvoice : channel 0 is reserved for voice q. Idle : channel 1 to 5 are not used; gap between voice and data communication q. Upstream data and control : channels 6 to 30 (25 channels); one channel for control q. Downstream data and control : channels 31 to 255(225 channels); 13. 4 Mbps; one channel for control Kyung Hee University 4

DSL q q. Actual Bit Rate v Upstream : 64 Kbps to 1 Mbps v Downstream : 500 Kbps to 8 Mbps * Because of the high signal/noise ratio Kyung Hee University 5

ADSL Frequency Spectrum Kyung Hee University 6

ADSL Kyung Hee University 7

DSL q Customer site : ADSL modem v Kyung Hee University 8

DSL q Telephone Company Site : DSLAM Kyung Hee University 9

DSL q Other DSL Technologies v SDSL: Symmetric Digital Subscriber Line v HDSL: High-bit-rate digital subscriber line l an alternative to the T-line (1. 544 Mbps) l using 2 B 1 Q encoding l up to 3. 6 Km l using 2 twisted-pair wires for full-duplex transmission v VDSL : Very-high-rate digital subscriber l l using coaxial cable, fiber-optic, or twisted pair cable for short distances (300 to 1800 m) using DMT with a bit rate of 50 to 55 Mbps downstream and 1. 5 to 2. 5 Mbps upstream Kyung Hee University 10

9. 2 Cable Modem q Traditional cable Networks v community antenna TV (CATV) q Communication in the traditional cable TV network is unidirectional. Kyung Hee University 11

Cable Modem q HFC Network v. RCH : Regional cable head; serving 400, 000 subscribers; v. Distribution hub: serving 40, 000 subscribers v. Coaxial cable : serving 1, 000 subscribers v. Communication in HFC cable TV network can be bidirectional. Kyung Hee University 12

Cable Modem q Bandwidth v video band l l 54 to 550 MHz TV channels : 6 Mhz x 80 channels v Data downstream band : dividing into 6 Mhz channels Kyung Hee University 13

Cable Modem v Modulation l Downstream data are modulated using 64 -QAM v Data rate l 6 bits for each baud in 64 -QAM (1 bit : control bit) l Theoretically, 5 bits/Hz x 6 Mhz = 30 Mbps q Upstream data band v Modulation l l upstream data band uses lower frequencies that are more susceptible to noise and interference for this reason, using QPSK instead of QAM v Data rate : 2 bits/hz x 6 Mhz = 12 Mbps Kyung Hee University 14

Cable Modem q CM is installed inside the distribution hub by the cable company. Kyung Hee University 15

Cable Mode q Cable modem transmission system (CMTS) Kyung Hee University 16