Other LAN Technologies

2 LAN Standards u 802 Working Groups –802.3Ethernet LANs –802.5Token-Ring Networks –802.11Radio LANs – VG-AnyLAN

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

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

5 Problem with Rings u 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 u One is unused in normal operation u If there is a break, the ring is wrapped –Still a ring NormalWrapped

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

8 STP vs. UTP u STP –Little interference –Thick: difficult to install –Expensive u 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 Access Unit STP link between Access Units STP link from Station to Access Unit Stations Station UTP Link from Station to Access Unit

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

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

12 Ethernet (802.3) vs Token-Ring (802.5) u Physical Layer –Ethernet primarily uses UTP wiring –Token-Ring Networks primarily use shielded twisted pair (STP) wiring u Topology (Layout) of the Wiring –Ethernet always uses bus (broadcast) topology –Token-Ring always uses a ring topology (connectivity) u 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) u 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.) u 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 u 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 Transmission Shared Media LAN Station B is Transmitting But Must Stop Soon Station A Must Wait to Transmit Station C Must Wait to Transmit

16 Congestion and Latency u 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 u At stations, a 10 Mbps (4-16 Mbps) shared media LAN becomes saturated

Mbps LANs u 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 u 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 FDDItutorial

20 100Base-TX u Many install 100Base-TX instead of 10Base-T Today u Requires 100 Mbps hubs instead of 10 Mbps u 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 u Uses Category 5 wiring, making upgrading easy

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

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

23 Ethernet 100Base-TX Network u The most popular 100Base-X standard, runs over existing 5 UTP wire of 10Base-T u Only two segments, length ~200m u Can mix 10 Base-T and 100Base-T stations/NICs with hubs that take both types u Use the same MAC standard of 10 Base-T u Market has chosen Ethernet 100Base-TX for desktop connection over FDDI100Base-TX u Read classic tutorial on Fast EthernetFast Ethernet

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

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

26 Full Duplex Ethernet u CSMA/CD is half duplex –Only one station may transmit at a time –Others must wait –Because transmission system is shared u 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