University:
Massachusetts Institute of Technology
Course:
15.501/516 | Accounting
Academic year:

2023
Views:

153

Pages:

7
Author:

Farovkamip9z

THE DIGITAL “LAST MILE” INTERNET • CHALLENGES – EXPENSIVE – DISRUPTIVE • APPROACHES – “JUST DO IT” (FIBER TO THE HOME) – “USE EXISTING” (TELEPHONE, CABLE) – “BYPASS” (RADIO, SATELLITE) 56K MODEMS EMERGING REMOTE ACCESS TECHNOLOGIES Voice/ Media Data Speed Data Copper pair Cable Data modem Coaxial cable HDSL Data Copper pair ISDN Both Copper pair ADSL Traffic Flow Availability Distance limitation 1 Equipment T1 to 9 Mbit/s Asymmetric Point-to-point downstream, 16- to 640 Kbit/s upstream 500 Kbit/s to 30 Both Point-to-point Mbits downstream, 640 Kbit/s to 15 Mbit/s upstream 384 Kbit/s to T1 Symmetric Point-to-point Limited 18,000 feet DSL modem Limited None2 Cable, modem, Ethernet card Limited 12,000 feet DSL modem 128 kbit/s Nationwide 18,000 feet (though not everywhere) Symmetric Connection Switched Terminal adapter 2 Customer must have cable service From central office or head-end ADSL = Asymmetric digital subscriber line, HDSL = High-speed digital subscriber line, T1 = 1.544 M 1 CABLE MODEMS COAX FIBER NETWORK A B C CABLE HEAD SUBSCRIBERS • HOW SIMILAR TO AND DIFFER FROM ETHERNET – IMPACT ON PERFORMANCE / PRIVACY • WHY ASYMMETRIC (NORMALLY) • DIRECTION OPTIONS: – NO UPSTREAM (UNI-DIRECTION) – LIMITED UPSTREAM (ASYMMETRIC) – SYMMETRIC • ROLE OF SATELLITE TV AND TELCO’s SOURCE xDSL MODEMS • DSL = DIGITAL SUBSCRIBER LINE SUBSCRIBERS LOCAL OFFICE A DATA NETWORK DATA SOURCE B VOICE NETWORK C PHONE • • • • xDSL MODEM POTS SPLITTER POTS MERGER PHONE VOICE SOURCE USES UNUSED PHONE LINE CAPACITY -- VARIOUS ENCODING TECHNIQUES DISTANCE KEPT SHORT -- TRADE-OFF: DISTANCE VS. SPEED CAN BE SYMMETRIC OR ASYMMETRIC (e.g.., ADSL) WHAT ARE REASONS FOR DELAY IN DEPLOYMENT? TYPES OF DSL TECHNOLOGIES • ADSL: ASYMMETRIC DSL • R-ADSL: RATE ADAPTIVE DSL – ADJUSTS DYNAMICALLY TO LINE LENGTH AND QUALITY • ADSL LITE (Bell Atlantic, Microsoft) – SLOWER SPEED AND WITHOUT POTS SPLITTER – LARGER DISTANCES AND SIMPLIFY INSTALLATION HIGH BIT RATE DSL • HDSL: – SYMMETRIC AND HIGH SPEED (T1) – SHORTER DISTANCES AND MULTIPLE WIRE PAIRS • SDSL: SINGLE LINE DSL – USES SINGLE WIRE PAIR AND SHORTER DISTANCES • VDSL : VERY HIGH BIT-RATE DSL – ASYMMETRIC AND FASTEST (13-52M DOWN, 1.5-2.3M UP) – SHORTEST DISTANCE (1000-4500 FEET) • • • • • • • • • • • • APPLICATIONS (with differing needs) Internet / Intranet Access Web browsing vs hosting E-mail Remote LAN Video conferencing Transaction processing IP telephony Call center services Video telephony (video conference) High-definition TV Video-on-demand Leased line backup