Infokom. 9. 2012. nov. 12. 1

Infokommunikációs rendszerek9. előadás

ADSL

Takács György

2011.

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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

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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 up to 6-25Mbps downstream,• 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

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