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

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Presentation on theme: "1. Broadband local access technology (B.A.Forouzan, Business Data Communications A.S.Tanenbaum, Computer Networks 4/e)"— Presentation transcript:

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

2 2. Figure 8-1 A telephone system

3 3. Major Components of the Telephone System 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

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

5 5. Figure 8-6 Modem concept

6 6. Figure K modem

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

8 8. xDSL Summary Table DSL TypeDescription Data Rate Downstream; Upstream Distance LimitApplication DSL Lite (same as G.Lite) "Splitterless" DSL without the "truck roll" From 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 Mbps duplex on two twisted-pair lines; 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 SDSLSymmetric DSL Mbps duplex (U.S. and Canada); 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 to 6.1 Mbps downstream; 16 to 640 Kbps upstream Mbps at 18,000 feet; Mbps at 16,000 feet; Mpbs at 12,000 feet; 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 Mbps upstream Not providedSimilar 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 Mbps; 3,000 feet at Mbps; 1,000 feet at Mbps ATM ATM networks; Fiber to the Neighborhood

9 9. ADSL Design 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

10 10. Figure 8-8 Bands for ADSL

11 11. Digital Subscriber Lines (2)

12 12. Discrete Multitone 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

13 13. DMT Transmitter

14 14. Typical ADSL configuration

15 15. Community Antenna Television

16 16. Internet over Cable (2)

17 17. Spectrum Allocation

18 18. Modulation and data rate DownstreamUpstream Bandwidth =200MHz42-5=37M channels200/6=3337/6=6 Modulation64-QAM or 256-QAM QPSK Theoretical Data rate 5  6M = 30 Mbps (1bit for error con) 2  6M = 12 Mbps Limited data rate 10 Mbps as 10base- T interface to PC Less than 12 Mbps Sharingbroadcasttimesharing

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

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

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

22 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.

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