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B roadband local access technology (B.A.Forouzan, Business Data Communications A.S.Tanenbaum, Computer Networks 4/e). Figure 8-1. A telephone system. Local loops Analog twisted pairs going to houses and businesses Trunks Digital fiber optics connecting the switching offices - PowerPoint PPT Presentation
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1.
Broadband local access technology
(B.A.Forouzan, Business Data CommunicationsA.S.Tanenbaum, Computer Networks 4/e)
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.
Figure 8-5 Internet access via the local loop
Modems are used to transmit digital signal via analog local loop.
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.
xDSL Summary TableDSL 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
HDSLHigh 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 DSL1.544 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
ADSLAsymmetric 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
RADSLRate-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
VDSLVery 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
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
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
18.
Modulation and data rate Downstream Upstream
Bandwidth 750-550=200MHz 42-5=37M
channels 200/6=33 37/6=6
Modulation 64-QAM
or 256-QAM
QPSK
Theoretical Data rate
56M = 30 Mbps
(1bit for error con)
26M = 12 Mbps
Limited data rate
10 Mbps as 10base-T interface to PC
Less than 12 Mbps
Sharing broadcast timesharing
19.
Cable ModemsCable modems are devices that allow high-speed access to the Internet via a cable television network.
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
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.