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Other LAN Technologies

Other LAN Technologies. LAN Standards. 802 Working Groups 802.3 Ethernet LANs 802.5 Token-Ring Networks 802.11 Radio LANs 802.12 100VG-AnyLAN. 802.5 Token-Ring Network Standard. Championed by IBM Official IEEE and OSI standard, but most vendors follow IBM extensions to the standard

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Other LAN Technologies

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  1. Other LAN Technologies

  2. LAN Standards • 802 Working Groups • 802.3 Ethernet LANs • 802.5 Token-Ring Networks • 802.11 Radio LANs • 802.12 100VG-AnyLAN

  3. 802.5 Token-Ring Network Standard • Championed by IBM • Official IEEE and OSI standard, but most vendors follow IBM extensions to the standard • More reliable than 802.3 Ethernet LANs • More complex and therefore more expensive • Lower market share than Ethernet LANs • Mostly in firms with large IBM mainframe networks • Tightly integrated into SNA • Read a tutorial in token-ring networks

  4. Ring Topology in Token-Ring Networks Station C Station B Station B only receives frames from Station A and only transmits frames to Station C Frame Ring Ring Frame Station A Station D Station E

  5. Problem with Rings • If the ring breaks, LAN stops • Signals must go all the way around the ring, back to the sender • This becomes impossible

  6. Use a Double Ring • One is unused in normal operation • If there is a break, the ring is wrapped • Still a ring Normal Wrapped

  7. UTP and STP Wiring Plastic Cover (Non-Shielding) Twisted Pair Unshielded Twisted Pair (UTP) Twisted Pair Outer Shield Around Bundle Twisted Pair Shielded Twisted Pair (STP) Twisted Pair Shielding Around Pair

  8. STP vs. UTP • STP • Little interference • Thick: difficult to install • Expensive • UTP • Thin: easy to install • Inexpensive • Interference is rarely a practical problem • Does the job at a reasonable price, so dominates

  9. Access Units in a Ring STP link between Access Units Access Unit Access Unit Access Unit Access Unit STP link from Station to Access Unit UTP Link from Station to Access Unit Stations Station

  10. Within the Access Unit • The ring is retained • Powered-up NICs added automatically • Powered-off NICs bypassed automatically Bypassed Node Ring NIC NIC NIC Missing NIC

  11. Token Passing in 802.5 Token-Ring Networks Station B may only transmit when it receives a special frame called a token. Station B Token

  12. Ethernet (802.3) vs Token-Ring (802.5) • Physical Layer • Ethernet primarily uses UTP wiring • Token-Ring Networks primarily use shielded twisted pair (STP) wiring • Topology (Layout) of the Wiring • Ethernet always uses bus (broadcast) topology • Token-Ring always uses a ring topology (connectivity) • Access Control • (Control of When Stations May Transmit) • Ethernet always uses CSMA/CD • Token-Ring always uses token passing

  13. Ethernet (802.3) vs Token-Ring (802.5) • Speed • Ethernet primarily 10 Mbps (moving to 100 Mbps and gigabit speeds) • Token-Ring Networks usually at 16 Mbps • TRNs can get closer to full capacity because token passing is more efficient than CSMA/CD at high traffic loads • Priority levels for real-time traffic (video teleconferencing, etc.) • Cost • TRN is more complex, so NICs cost much more • TRN has low market share; low vendor competition adds to high NIC costs • Most firms do not find the benefits of TRNs to outweigh the costs

  14. Shared Media LANs • Ethernet (802.3) and Token-Ring Networks (802.5) are Shared Media LANs • Only one station may transmit at any moment. • Every station hears every transmission • Stations must wait their turn to transmit

  15. Congestion and Latency in Shared Media LANs Station B is Transmitting But Must Stop Soon Station A Must Wait to Transmit Station C Must Wait to Transmit Shared Media LAN Transmission

  16. Congestion and Latency • As the number of stations on a shared media LAN increases... • Traffic increases, so • Stations must wait longer to transmit • Latency (delay) increases • This is called congestion • At 200-300 stations, a 10 Mbps (4-16 Mbps) shared media LAN becomes saturated

  17. 100 Mbps LANs • Reducing Congestion • One way to decrease congestion is to increase LAN speed from 10 Mbps to 100 Mbps or higher • Each transmission will be briefer, because it can be transmitted faster • Therefore more stations can share the LAN before saturation occurs • Only postpones the problem

  18. FDDI Network FDDI Ring

  19. FDDI • FDDI • Fiber distributed data interface • Token-ring technology (but incompatible with 802.5) • 100 Mbps • Mature (1987) • 200 km maximum diameter: popular for connecting LANs to local internets, not to connect desktops. • Priority levels for real-time traffic (voice, video) • Expensive NICs and other equipment • Read a tutorial in FDDI

  20. 100Base-TX • Many install 100Base-TX instead of 10Base-T Today • Requires 100 Mbps hubs instead of 10 Mbps • Requires 100 Mbps NICs instead of 10 Mbps • Some hubs can also serve 10Base-T NICs, so not all stations have to be upgraded at once • Uses Category 5 wiring, making upgrading easy

  21. Upgrading from 10Base-T to 100Base-T • Need New Hub • All 100Base-TX is expensive • Often many 10Base-T hubs for client PCs • A few 100Base-TX hubs for servers • Need New NICs • Only in stations with 100Base-T NICs • Retain Old Wiring • If Cat 5 • Avoids a major expense

  22. Ethernet 100Base-TX Network 100Base-TX Hub 100Base-TX Hub ~50 maximum 100 m Segment Maximum 100 m Segment Maximum - 5 UTP wiring - NICs are replaced Station A Station B Station C

  23. Ethernet 100Base-TX Network • The most popular 100Base-X standard, runs over existing 5 UTP wire of 10Base-T • Only two segments, length ~200m • Can mix 10 Base-T and 100Base-T stations/NICs with hubs that take both types • Use the same 802.3 MAC standard of 10 Base-T • Market has chosen Ethernet 100Base-TX for desktop connection over FDDI • Read classic tutorial on Fast Ethernet

  24. 1000Base-X (Gigabit Ethernet) • 1000 Mbps • Usually used to link 100Base-X hubs 1000Base-X Hub 100Base-T Hubs

  25. 1000Base-X • Family of Standards (802.3z) • 1000Base-LX • Long-wave (lower frequency) laser • 550 meters on multimode optical fiber • 3 km on single mode fiber • 1000Base-SX • Short-wave ( higher frequency) laser • 300 meters on 62.5 micron multimode fiber

  26. Full Duplex Ethernet • CSMA/CD is half duplex • Only one station may transmit at a time • Others must wait • Because transmission system is shared • If station or hub connects directly to a hub, • The access line is not shared • Some 100Base-X and 1000Base-X hubs and NICs support full duplex operation • Disable CSMA/CD • 802.3x standard

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