6_adsl.ppt.pptVIP

Asymmetrical Digital Subscriber Line (ADSL) Asymmetrical Digital Subscriber Line Background motivation for developing ADSL historical development DSL end-to-end environment and reference model Line environment - characteristics of local loop (LL) Why conventional modems don’t work so well in LL? Modem technology in ADSL DSL flavors: ISDN (!), HDSL, ADSL, VDSL ... Standards Motivation for developing ADSL Need for high-speed Internet access - also telephone modem speeds have peaked and cable modems have turned out DSL means methods to transmit high speed data to local loop by using unshielded 2-wire twisted pairs DSL allows rates varying from 160 kb/s up 50 Mb/s on down link (DL) depending on technology used! In the most popular commercial ADSL 512 kbit/s upstream and 2048 kb/s downstream Different operation modes developed to serve symmetric and asymmetric traffic requirements and different rates (STM and ATM supported by ADSL) History of digital access in PSTN Digital access in PSTN (cont.) POTS FDM splitters separate voice and DSL channels Comparing modem technologies Short history of ADSL Generic DSL reference model CO: Central office CP: Customers premises - local loop connects to switch (CO) TE: Terminal equipment - PC or telephone NT: Network terminal - DSL modem at CP NID: Network interface device - all customer’s installation reside right from this point and telephone companys to the left in the diagram MDF: Main distribution frame - wire cross-connection field connects all loops to CO LT: Line termination eg DSL modem repeater: signal regeneration for transmission introduced impairments local loop: in ADSL 2-wire connection between CO and CP ADSL and ADSL-litereference model DSL access multiplexer (DSLAM) DSLAM provides access to LANs, WANs and other services DSLAM consists of subscriber links (ATU-R to ATU-C) connections to other DSL/broadband-circuits interfaces to ISDN exchange Using DSLAM What is specified in ADSL standard?ANSI T1.413 ADSL re