Telephone (kỹ THUẬT TRUYỀN số LIỆU SLIDE)

Using Telephone and Cable Networks for Data Transmissions Outline  Telephone lines  Dial-up modems  Digital Subscriber Line (DSL)  Cable TV networks Telephone Lines  Traditional telephone lines can carry frequencies between 300 and 3300 Hz  Giving them a bandwidth of 3000 Hz  All this range is used for transmitting voice  A great deal of interference and distortion can be accepted without loss of intelligibility Telephone Line Bandwidth Dial-Up Modems Modem stands for modulator/demodulator V.32 and V.32bis 56K Modems Digital Subscriber Line (DSL)  Provides higher-speed access to the Internet  Supports high-speed digital communication over the existing local loops  The existing local loops can handle bandwidths up to 1.1 MHz ADSL  ADSL – Asymmetric Digital Subscriber Line  Downstream bit rate > upstream bit rate  Designed for residential users  Unsuitable for businesses  ADSL operates on existing local loops  Local loops can handle up to 1.1 MHz of bandwidth  The distance limit is ~18,000 feet  The system uses a data rate based on the condition of the local loop line Bandwidth Division in ADSL 10 Bandwidth Division kHz Allocation and modulation of each channel are determined adaptively 12 Bandwidth Division  Voice – Channel  Idle – Channels 1-5  Upstream – Channels 6-30  24 data channels, control channel  1.44 Mbps (max) upstream bit rate  Actual bit rate: 64 Kbps to Mbps  Downstream – Channels 31-255  224 data channels, control channel  13.4 Mbps (max) downstream bit rate  Actual bit rate: 500 Kbps to Mbps 13 ADSL Customer Residence 14 DSL Access Multiplexer  Or DSLAM 15 Other DSL Technologies  HDSL – High-bit-rate DSL  VDSL – Very-high-bit-rate DSL  SDSL – Symmetric DSL Source: AWARE ADSL2 and ADSL2+ The new ADSL standard  ADSL2  ADSL2+  See also  http://en.wikipedia.org/wiki/Digital_subscriber_line 16 OFDM  Orthogonal Frequency-Division Multiplexing  Widely used in wideband digital communications  Digital TV  ADSL  Powerline communications  Wireless networks: Wi-Fi, WiMAX  4G mobile communications 17 OFDM Concept  Sub-carriers are orthogonal to each other  No cross-talk; guard bands not necessary Source: http://connectedplanetonline.com 18 Orthogonality in OFDM 20 ms Modulated @500 Hz t Modulated @550 Hz t Modulated @600 Hz t 200 300 400 500 600 700 Frequency (Hz) 19 800 OFDM Implementation Transmitter Receiver Source: Wikipedia 20 Cable TV Networks  Started as a video service provider, then moved to the business of Internet access Communication is simplex 21 Hybrid Fiber-Coaxial Network  Or HFC  Bidirectional communication is achieved 22 Data Transfer over CATV  Standard: DOCSIS (Data Over Cable Service Interface Specification)  Division of coaxial cable band by Cable TV  Theoretical downstream data rate is 30 Mbps  Theoretical upstream data rate is 12 Mbps 23 Cable Modem 24 Cable Modem Transmission System  Or CMTS 25 Fiber To The X  Optical broadband network architectures Fiber-to-thenode Fiber-to-thecurb Fiber-to-thebuilding Fiber-to-theSource: Wikipedia home 26 ...Outline  Telephone lines  Dial-up modems  Digital Subscriber Line (DSL)  Cable TV networks Telephone Lines  Traditional telephone lines can carry frequencies... voice  A great deal of interference and distortion can be accepted without loss of intelligibility Telephone Line Bandwidth Dial-Up Modems Modem stands for modulator/demodulator V.32 and V.32bis