MASSACHUSETTS INSTITUTE OF TECHNOLOGY SLOAN SCHOOL OF MANAGEMENT 15.565 Integrating Information Systems: Technology, Strategy, and Organizational Factors 15.578 Global Information Systems: Communications & Connectivity Among Information Systems Spring 2002 Lecture 7 LOCAL AREA NETWORKS (LAN)2LOCAL AREA NETWORKS (LAN)• CONNECTING BETWEEN INFORMATION ENTITIES IN CLOSE PROXIMITY- USUALLY ON COMPANY PREMISES- LOCAL AREA NETWORK (LAN)• CONNECTING BETWEEN INFORMATION ENTITIES IN DISTANT LOCATIONS- INTER-PREMISES NETWORK (IPN) / WIDE AREA NETWORK (WAN)• LAN ENVIRONMENTS- GREAT DIVERSITYLANLOCAL-AREANETWORK(LAN)LANINTER-PREMISESNETWORK(IPN)MODERN “PEER-TO-PEER” LOCAL NETWORKS TRADITIONAL “MASTER-SLAVE” LOCAL NETWORK MAINFRAME / PBX 3 MAINFRAME SERVER SERVER (PRINT/FILE/ COMMUNICATIONS) PC / WORKSTATIONSLOCAL AREA NETWORK CHARACTERISTICS 1. COMMUNICATE AMONG “INTELLIGENT DATA DEVICES” 2. SMALL AREA (USUALLY SINGLE BUILDING, UP TO 50 KM) 3. USUALLY PRIVATELY OWNED 4. HIGH DATA RATES (1--100M BPS) NOVEL APPLICATIONS EMERGING Topography of vehicle multi-plex system with central control, modules for the instrument readings, lights, doors, seats, centre console and central rear light unit. 4NETWORK TOPOLOGIES (LOGICAL VS PHYSICAL) STAR BUS RING 5----MEDIA ACCESS CONTROL--BUS BUS • CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION (CSMA/CD) • ETHERNET (1972) AND IEEE 802.3 COLLISION HANDLING - IF COLLISION DETECTED, IMMEDIATELY STOP TRANSMISSION - WAIT RANDOM AMOUNT OF TIME, THEN RETRANSMIT (AMOUNT GROWS WITH EACH COLLISION) COLLISION DETECTION - SIGNAL EXCEEDS VOLTAGE LIMIT (2 OR MORE TRANSMISSIONS) - LIMITATION ON MIN PACKET SIZE AND CABLE LENGTH TO GUARANTEE COLLISION DETECTION VOLTAGE (e.g., 500 METERS) - COLLISION MUST BE PROPAGATED ACROSS REPEATERS 6------MEDIA ACCESS CONTROL--RING RING • TOKEN RING -- IEEE 802.5 STATIONS FORM LOGICAL ORDERED RING CONTROL PACKET (TOKEN) REGULATES ACCESS TOKEN PASSED IN STATION ORDER (LOGICAL) • CSMA/CD VERSUS TOKEN RING CSMA/CD TOKEN •SIMPLER • REGULATE TRAFFIC (HOLD PERIOD) • NO TOKEN PASSING DELAY • “DETERMINISTIC” (?) 7MEDIA ACCESS CONTROL--RING • TOKEN RING--IBM AND IEEE 802.5 • EXAMPLE: “A” WANTS TO SEND DATA TO “C” FREE TOKEN B A C D SENDER LOOKS FOR FREE TOKEN CHANGES FREE TOKEN TO BUSY TOKEN AND APPENDS DATA C SENDER GENERATES FREE TOKEN UPON PHYSICAL TRANSMISSION HEADER (FROM ADDRESSEE) A D B DATA RECEIVER COPIES DATA ADDRESSED TO IT. FREE TOKENA C D B DATA 8----------------• BUSY TOKEN DESTINATION STATION ADDS STATUS INFO TO TOKEN SOURCE STATION REMOVES BUSY TOKEN (CHECK STATUS) • “ACTIVE MONITOR” STATION DETECTS LOST TOKEN USING TIME-OUT DETECTS CIRCULATING BUSY TOKEN (VIA “MONITOR BIT”) • OTHERS STATIONS CHECK STATUS OF “ACTIVE MONITOR” TAKE ON ROLE IF NECESSARY • ADVANTAGES TRAFFIC REGULATION DETERMINISTIC, ALSO ALLOWS PRIORITIES • DISADVANTAGES TOKEN MAINTENANCE 9------------BUS VERSUS RING TOPOLOGY • BUS FAIRLY STRAIGHTFORWARD • RING PROBLEMS (INITIALLY) CABLE VULNERABILITY: SINGLE BREAK FATAL REPEATER FAILURE: EACH REPEATER CRITICAL FAILURE LOCATION DETERMINATION: EACH REPEATER MUST BE EXAMINED INSTALLATION DISRUPTION: INSERTION OF NEW REPEATER NECESSARY RECOVERY CONTROL: HOW ARE PROBLEMS HANDLED (E.G., FAULTY ADDRESS) SIZE LIMITATION: EACH REPEATER ADDS TO DELAY AROUND RING 10ENHANCED RING ARCHITECTURE • CONCENTRATOR BOX -- CENTRALIZES REPEATERS Multi-Station Access Unit (MAU) 11RING BRIDGES -- SPLITS LARGE RING INTO SMALLER RINGS 12 LOBE BY-PASSED BRIDGE GATEWAY NODE NODE NODE NODE NODE TP LINKS LOBE ACTIVE RING WIRING CONCENTRATIONS E51 E52--------BUS VERSUS RING TOPOLOGY (REVISITED) ADVANTAGES • BUS - PASSIVE TAP - MEDIA FAILURE UNLIKELY • RING REGENERATED BIT MINIMIZES ERROR PROPAGATION GREATER DISTANCES POSSIBLE (VIA BRIDGES) FAULT LOCATION CENTRALIZED SUITABLE FOR FIBER OPTICS [ e.g., FIBER DISTRIBUTED DATA INTERFACE ( FDDI ) ] 13--CSMA/CD BUS VS. TOKEN RING PERFORMANCE • PERFORMANCE STUDY -- LIGHT LOAD: 1 OUT OF 100 STATIONS BUSY HEAVY LOAD: ALL 100 STATIONS BUSY • RESULTS -- SHORTER PACKETS FAVOR TOKEN RING -- TOKEN RING LEAST EFFECTED BY LOAD -- CSMA/CD DETERIORATES UNDER HEAVY LOAD -- TOKEN RING HAS MORE DELAY UNDER LIGHT LOAD 14CSMA/CD BUS VS. TOKEN RING PERFORMANCE LIGHT LOAD: 1 station active out of 100 stations. 25 20 15 10 TOKEN-RING CSMA/CD 5 Comments: 0 Token-ring CSMA/CD • 2000 bits per packet0 4 8 12 16 20 24 • Axis: Data rates (M bps) HEAVY LOAD: 100 stations active out of 100 stations. 25 20 15 10 5 TOKEN-RING CSMA/CD 0 Token-ring CSMA/CD 15 0 4 8 12 16 20 24SUMMARY POINTS IMPORTANT FACTORS • WORKSTATIONS MORE POWERFUL & LANS PROLIFERATING • FIBER COST DROPPING LANS INCREASINGLY INTERCONNECTED (LOCAL & WIDE AREA) • HUB - CONNECTS PARTS OF NETWORK, TYPICALLY DIFFERENT PARTS OF SAME LAN • BRIDGE - CONNECTS TWO LANS, TYPICALLY USING SOFTWARE • SWITCH - CONNECTS DIFFERENT LANS, TYPICALLY USING HARDWARE ONLY • ROUTER - CONNECTS TWO NETWORKS THAT MAY OR MAY NOT BE SIMILAR AND ROUTES PACKETS APPROPRIATELY • GATEWAY - CONNECTS NETWORKS THAT USE DIFFERENT PROTOCOLS 16APPENDIX: INTERCONNECTING LANs – SOME TECHNIQUES 17 •Protocol converter •Operates at Network layer of OSI model •Connection between LAN and WAN w/ different protocols GATEWAY •Sophisticated bridge •Chooses the best path for data transmission to avoid digital jams •Operates at Network layer of OSI model •Network routing of packets •Routing between networks w/ different protocols •Isolates a part of a LAN (no access) •Can work as a level of security ROUTER •Interpret data link portion Determines to send to connected LAN •Operates at Data link layer of OSI model • Connects two LANs using same protocols - but different medium -(e.g. twisted pair cable + coaxial cable) BRIDGE •Accepts signal and Amplifies it •Extend cable 2,500 meters (4 segments) • Extends cable longer than 500 meters (IEEE 802.3) REPEATER What does it do?Why use