1. CSCI 465 D ata Communications and Networks Lecture 12 Martin van Bommel CSCI 465 Data Communications & Networks 1

2. Multiplexing It was impossible to get a conversation going, everybody was talking too much. - Yogi Berra

3. Multiplexing Several data sources share a common medium, with each source having its own channel Line sharing saves transmission costs More cost-effective transmissions Common on long-haul, high capacity links

4. Frequency Division Multiplexing Requires analog signaling & transmission Bandwidth = sum of inputs + guardbands Modulates signals so that each occupies a different frequency band Standard for radio broadcasting, analog telephone network, and television (broadcast, cable, & satellite)

5. FDM System Overview

6. ADSL Asymmetric Digital Subscriber Line Uses FDM to exploit 1-MHz capacity of TP – Reserves lowest 25 kHz for voice (POTS) – Use either echo cancellation or FDM to allocate two bands, a smaller upstream and larger down – Use FDM within bands to split bit stream into multiple parallel bit streams - discrete multitone Range up to 5.5 km

7. Discrete Multitone in ADSL Uses multiple carrier signals at different frequencies, sending some bits on each Available band divided into 4-kHz channels, each capable of carrying 60 kbps Test signals determine noise at each channel Sends less bits over noisy channels 256 downstream channels = 15.26 Mbps capacity, but only between 1.5 to 9 actual

8. Synchronous TDM Synchronous Time Division Multiplexing Used in digital transmission Requires data rate of the medium to exceed data rate of signals to be transmitted Signals “take turns” over medium Slices of data are organized into frames

9. Synch. TDM System Overview

10. Synchronous TDM and PSTN Used in modern digital telephone system – US, Canada, Japan: DS-1(T-1), DS-3(T-3),... – Europe, elsewhere: E1, E3,... DS-1: Data rate of 1.544 Mbps Uses PCM to digitize voice transmission at 8000 times/sec with 8 bits/sample = 64kbps 24 channels x 8 bits/channel + 1 frame bit = 193 bits/frame with 8000 frames/sec

11. Statistical TDM requires digital signaling & transmission data rate capacity required is well below the sum of connected capacity uses memory buffers to avoid loss of data frame slots only to devices with full buffers widely used for remote communications with multiple terminals similar to medium-sharing done by LANs

12. SONET Synchronous Optical Network Specification for high-speed digital transfer via optical fiber Rates from 51.84Mbps to 13.2Gbps Uses Synchronous TDM

13. WDM Wavelength Division Multiplexing used in optical fiber links Multiple beams of light at differing freq. over a single fibre Commercial systems – 160 channels of 10 Gbps Lab testing systems – 256 channels of 39.8 Gbps

14. Cable Modem Two channels dedicated on cable, one for transmission in each direction Each channel shared by number of subscribers using statistical TDM If more than one subscriber active, get fraction of downstream capacity Request future time slots via TDM upstream channel

15. Cable Spectrum Division to support both cable television programming and data channels, the cable spectrum is divided in to three ranges: to support both cable television programming and data channels, the cable spectrum is divided in to three ranges: – user-to-network data (upstream): 5 - 40 MHz – television delivery (downstream): 50 - 550 MHz – network to user data (downstream): 550 - 750 MHz