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Infokommunikációs rendszerek9. előadás
ADSL
Takács György
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2004
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maximális letöltési sebesség (kbit/s)
maximális feltöltési sebesség (kbit/s)
Havidíj hűségnyilatkozattal (Ft)
ADSL Optimum 512 96 4900
ADSL Prémium 1024 128 7900
ADSL Maximum
2048 192 9900
2006. november
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maximális letöltési sebesség (kbit/s)
maximális feltöltési sebesség (kbit/s)
Havidíj hűségnyilatkozattal (Ft)
DSL CLASSICHappy
2 Mbit/sec 192 kbit/sec
3 990 Ft
DSL CLASSIC MEDIUM
8 Mbit/sec 480 kbit/sec
6 890 Ft
DSL CLASSIC EXTRA
25 Mbit/sec
4 Mbit/sec 9 890 Ft
2008. november
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2012. November
maximális (garantált)
letöltési sebesség (Mbit/s)
Maximális (garantált)
feltöltési sebesség (Mbit/s)
Havidíj 2 év hűségnyilatkozattal (Ft)
NetMániaS 10 (1) 0,5 (0,2) 3990
NetMániaM 20 (10) 1 (0,5) 4690
NetMániaL 30 (20) 1 (1) 5490
2014. November
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What is ADSL?
• Asymmetric Digital Subscriber line,• A modem technology,• Convert existing twisted-pair telephone lines into
access paths for multimedia and high speed data communication,
• Can transmit to 6-25Mbps downstream (VDSL 15-60 Mbps) ,
• Can transmit up to 0,8-4 Mbps upstream,• Transform the existing PSTN network to a
powerful system capable of bringing multimedia, full motion video to the subscriber’s home.
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ADSL system components
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ADSL components at the subscriber
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ADSL components at SOHO
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ADSL components at Central Office
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DSL access and IP/content provider network
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What is the future of the ADSL?
• Will play a crucial role over the next ten years for telephone companies and other service providers
• New broadband cabling will take decades to reach all prospective subscribers.
• EU regulation document on local loop unbundling because no competitive technology!
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What can we learn from ADSL story?
• No ultimate technology!!• Frequency division multiplexing, time division
multiplexing, modulation, error control, flow control, scrambling, signal processing, adaptation, STM-ATM, trellis coding, in-service performance monitoring and surveillance, initialization, handshaking, channel analysis, are mixed in ADSL
• More room for further development….
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key requirements (1)
• Test loops – makeup and topology (to ensure adequate penetration).
• Cross talk or steady state noise margin (to allow for interactions from other DSL in a multi-pair cable).
• Data rates (both line and payload). • Impulsive or transient noise margin (to allow for noise
spikes e.g. ringing). • Transmitter power spectral density limits (to ensure
spectral compatibility and minimise unwanted RF emissions).
• Return loss (to ensure good line matching and signal power transfer).
• Line interface balance (to prevent EMC problems).
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key requirements (2)
• Framing and data scrambling (to prevent cyclo-stationary effects e.g. line spectra).
• Latency (to minimise delay e.g. for voice traffic). • Jitter and wander (to minimise data loss). • Start up protocols (handshaking). • Warm/cold start limits (time taken to synchronise and
achieve reliable bit transport – to minimise circuit unavailability).
• Line coding (to achieve efficiency in terms of bits/s/Hz) • Duplexing (e.g. time, frequency, echo cancellation).
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key requirements (3)
• Forward error correction (to self-correct physical layer transmission errors and not burden higher layer protocols with data re-transmission.)
• Embedded operations and maintenance (for the transfer of service related information e.g. QoS).
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ADSL bitrate as a function of line length
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Discrete MultiTone
• Copper lines have a frequency spectrum of 1.1Mhz which can be used to data communication under two main limitations:
1.The lower 4Khz are being used by the POTS. 2.The amplification isn't the same in all frequencies.
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The technology being used is DMT which divides the frequency range to 256 sub-frequencies from 64Khz to 1.1Mhz Each sub-ferqency is an independent channel and has it own stream of signals . The ADSL protocol defines a basic stream of data which is known to both endpoints in advanced and enables them to find the specific SNR for each sub-frequency , and uses this information to split the data over the sub-frequencies
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dividing the spectrum to 256 subfrequencies
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adaptive SNR discovery
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Code & Error Correction One of the most important technology breakthrough that helped the ADSL is the coding . Using a method called consellation encoding and based on Reed Solomon coding decoding the information on the line can be damaged and yet the decoder rebuild the information in a very high reliability.To improve the performance of ADSL system some companies use 16 state 4 dimensional trellis code on top of the consellation encoding. Another useful method to increase the ADSL systems reliability is Forward Error Correction (FEC).
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Framing & Scrambling As most of the Computer communication networks the ADSL uses a specific framing method . The main frame is called Superframe and it is composed of 68 ADSL data frames , the ATU-C sends a superframe every 17 msec . Each data frame gets his information from two data buffers (interleaved buffer and fast buffer)which are scrambled at a specific sequence , this scrambling method makes the error correction and coding more efficient.
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ADSL 2/2+ bitrate as a function of line length
MAGYAR TELEKOM FELAJÁNLOTT DLSAM HELYSZÍNEK AZ ITK KÖZELÉBEN
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