B roadband local access technology (B.A.Forouzan, Business Data Communications

1. Broadband local access technology (B.A.Forouzan, Business Data Communications A.S.Tanenbaum, Computer Networks 4/e)

2. Figure 8-1 A telephone system

3. Local loops Analog twisted pairs going to houses and businesses Trunks Digital fiber optics connecting the switching offices Switching offices Where calls are moved from one trunk to another Major Components of the Telephone System

4. Figure 8-5 Internet access via the local loop Modems are used to transmit digital signal via analog local loop.

5. Figure 8-6 Modem concept

6. Figure 8-7 56K modem

7. Bandwidth versus distanced over category 3 UTP for DSL. Digital Subscriber Lines How does the xDSL concept extend the date rate to the Mbps?

8. DSL Type Description Data RateDownstream;Upstream Distance Limit Application DSL Lite (same as G.Lite) "Splitterless" DSL without the "truck roll" From 1.544 Mbps to 6 Mbps downstream, depending on the subscribed service 18,000 feet on 24 gauge wire The standard ADSL; sacrifices speed for not having to install a splitter at the user's home or business HDSL High bit-rate Digital Subscriber Line 1.544 Mbps duplex on two twisted-pair lines;2.048 Mbps duplex on three twisted-pair lines 12,000 feet on 24 gauge wire T1/E1 service between server and phone company or within a company;WAN, LAN, server access SDSL Symmetric DSL 1.544 Mbps duplex (U.S. and Canada); 2.048 Mbps (Europe) on a single duplex line downstream and upstream 12,000 feet on 24 gauge wire Same as for HDSL but requiring only one line of twisted-pair ADSL Asymmetric Digital Subscriber Line 1.544 to 6.1 Mbps downstream;16 to 640 Kbps upstream 1.544 Mbps at 18,000 feet;2.048 Mbps at 16,000 feet;6.312 Mpbs at 12,000 feet;8.448 Mbps at 9,000 feet Used for Internet and Web access, motion video, video on demand, remote LAN access RADSL Rate-Adaptive DSL from Westell Adapted to the line, 640 Kbps to 2.2 Mbps downstream; 272 Kbps to 1.088 Mbps upstream Not provided Similar to ADSL VDSL Very high Digital Subscriber Line 12.9 to 52.8 Mbps downstream;1.5 to 2.3 Mbps upstream;1.6 Mbps to 2.3 Mbps downstream 4,500 feet at 12.96 Mbps;3,000 feet at 25.82 Mbps; 1,000 feet at 51.84 Mbps ATM networks;Fiber to the Neighborhood xDSL Summary Table

9. Asymmetric Greater capacity downstream than upstream Frequency division multiplexing Lowest 25kHz for voice Plain old telephone service (POTS) Use echo cancellation or FDM to give two bands Use FDM within bands Range 5.5km ADSL Design

10. Figure 8-8 Bands for ADSL

11. Digital Subscriber Lines (2)

12. DMT: Discrete Multitone Multiple carrier signals at different frequencies Some bits on each channel 4kHz subchannels Send test signal and use subchannels with better signal to noise ratio Discrete Multitone

13. DMT Transmitter

14. Typical ADSL configuration

15. Community Antenna Television

16. Internet over Cable (2)

17. Spectrum Allocation

18. Modulation and data rate

19. Cable Modems Cable modems are devices that allow high-speed access to the Internet via a cabletelevision network.

20. effective capacity unpredictable Seriously affect If you have a cable Encryption Cable vs. ADSL • Specific bandwidth for every one user • Increase numbers of user has little affect • Max coverage 5.5km • More secure, more reliable

21. DSL vs. T1 DSL vs. ISDN DSL vs. 56K Modem Comparison With Other Broadband Technologies

22. An ADSL system using DMT allocates 3/4 of the available data channels to the downstream link. It uses QAM-64 modulation on each channel. What is the capacity of the downstream link? (Assuming ADSL modulate at 4000 baud). • There are 256 channels in all, minus 6 for POTS and 2 for control, leaving 248 for data. • If 3/4 of these are for downstream, that gives 186 channels for downstream. • ADSL modulation is at 4000 baud, so with QAM-64 (6 bits/baud) we have 24,000 bps in each of the 186 channels. • The total bandwidth is then 186*24kbps=4.464 Mbps downstream.