Infokom nov Infokommunikációs rendszerek 9. előadás ADSL Takács György 2011.

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Infokom nov maximális letöltési sebesség (kbit/s) maximális feltöltési sebesség (kbit/s) Havidíj hűségnyilatkozattal (Ft) ADSL Optimum ADSL Prémium ADSL Maximum november

Infokom nov maximális letöltési sebesség (kbit/s) maximális feltöltési sebesség (kbit/s) Havidíj hűségnyilatkoz attal (Ft) DSL CLASSIC Happy 2 Mbit/sec192 kbit/sec Ft DSL CLASSIC MEDIUM 8 Mbit/sec480 kbit/sec Ft DSL CLASSIC EXTRA 25 Mbit/sec 4 Mbit/sec9 890 Ft november

Infokom nov November maximális (garantált) letöltési sebesség (Mbit/s) Maximális (garantált) feltöltési sebesség (Mbit/s) Havidíj 2 év hűségnyilatko zattal (Ft) NetMániaS10 (1) 0,5 (0,2) 3990 NetMániaM20 (10) 1 (0,5) 4690 NetMániaL30 (20) 1 (1) 5490

Infokom nov 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.

Infokom nov ADSL system components

Infokom nov ADSL components at the subscriber

Infokom nov ADSL components at SOHO

Infokom nov ADSL components at Central Office

Infokom nov DSL access and IP/content provider network

Infokom nov 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!

Infokom nov 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….

Infokom nov 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).

Infokom nov 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).

Infokom nov 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).

Infokom nov ADSL bitrate as a function of line length

Infokom nov 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. POTS

Infokom nov 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-frequenciesSNR

Infokom nov dividing the spectrum to 256 subfrequencies

Infokom nov adaptive SNR discovery

Infokom nov 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).Reed SolomonForward Error Correction

Infokom nov 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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Infokom nov ADSL 2/2+ bitrate as a function of line length

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