Other LAN Technologies LAN Standards u 802 Working

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Other LAN Technologies

Other LAN Technologies

LAN Standards u 802 Working Groups – 802. 3 Ethernet LANs – 802. 5

LAN Standards u 802 Working Groups – 802. 3 Ethernet LANs – 802. 5 Token-Ring Networks – 802. 11 Radio LANs – 802. 12 100 VG-Any. LAN 2

802. 5 Token-Ring Network Standard u Championed by IBM – Official IEEE and OSI

802. 5 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 802. 3 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 networks 3

Ring Topology in Token-Ring Networks Station B only receives frames from Station A and

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

Problem with Rings u If the ring breaks, LAN stops – Signals must go

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 5

Use a Double Ring u One is unused in normal operation u If there

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

UTP and STP Wiring Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP) Twisted Pair

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

STP vs. UTP u STP – Little interference – Thick: difficult to install –

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 8

Access Units in a Ring Access Unit STP link between Access Units Access Unit

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

Within the Access Unit u The ring is retained u Powered-up NICs added automatically

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

Token Passing in 802. 5 Token-Ring Networks Station B may only transmit when it

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 11

Ethernet (802. 3) vs Token-Ring (802. 5) u Physical Layer – Ethernet primarily uses

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 12

Ethernet (802. 3) vs Token-Ring (802. 5) 13 u Speed – Ethernet primarily 10

Ethernet (802. 3) vs Token-Ring (802. 5) 13 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

Shared Media LANs u Ethernet (802. 3) and Token-Ring Networks (802. 5) are Shared

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 14

Congestion and Latency in Shared Media LANs Station A Must Wait to Transmit Station

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

Congestion and Latency u As the number of stations on a shared media LAN

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 200 -300 stations, a 10 Mbps (4 -16 Mbps) shared media LAN becomes saturated 16

100 Mbps LANs u Reducing Congestion – One way to decrease congestion is to

100 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 17

FDDI Network FDDI Ring 18

FDDI Network FDDI Ring 18

FDDI u FDDI – Fiber distributed data interface – Token-ring technology (but incompatible with

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 FDDI 19

802. 12 100 VG-Any. LAN u 100 Mbps u Demand Priority Access Method –

802. 12 100 VG-Any. LAN u 100 Mbps u Demand Priority Access Method – Station sends high- or low-priority requests – All high-priority requests on all repeaters served first – Good for real-time applications u Hubs (repeaters) organized as a Tree – One is the master repeater u Not achieving market acceptance 20

802. 12 100 VG-Any. LAN Hub Hierarchy Repeater A First Level Repeater Second Level

802. 12 100 VG-Any. LAN Hub Hierarchy Repeater A First Level Repeater Second Level Repeaters Third Level Repeaters Master Repeater B Repeater D High-Priority Request Station 1 Repeater C Repeater E Low-Priority Request Station 2 21

100 Base-X u 100 Mbps u Uses Normal 802. 3 MAC Layer Frame u

100 Base-X u 100 Mbps u Uses Normal 802. 3 MAC Layer Frame u Family of Standards – 100 Base-TX uses Cat 5 wiring (most popular to desk) – 100 Base-T 4 uses Cat 3 and Cat 4 wiring – 100 Base-FX uses optical fiber 22

100 Base-TX u Many install 100 Base-TX instead of 10 Base-T Today u Requires

100 Base-TX u Many install 100 Base-TX instead of 10 Base-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 10 Base-T NICs, so not all stations have to be upgraded at once u Uses easy Category 5 wiring, making upgrading 23

Upgrading from 10 Base-T to 100 Base-T u Need New Hub – All 100

Upgrading from 10 Base-T to 100 Base-T u Need New Hub – All 100 Base-TX is expensive – Often many 10 Base-T hubs for client PCs – A few 100 Base-TX hubs for servers u Need New NICs – Only in stations with 100 Base-T NICs u Retain Old Wiring – If Cat 5 – Avoids a major expense 24

25 Ethernet 100 Base-TX Network 100 Base-TX Hub ~50 maximum 100 m Segment Maximum

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

Ethernet 100 Base-TX Network 26 u The most popular 100 Base-X standard, runs over

Ethernet 100 Base-TX Network 26 u The most popular 100 Base-X standard, runs over existing 5 UTP wire of 10 Base-T u Only two segments, length ~200 m u Can mix 10 Base-T and 100 Base-T stations/NICs with hubs that take both types u Use the same 802. 3 MAC standard of 10 Base-T u Market has chosen Ethernet 100 Base-TX for desktop connection over FDDI and 100 VGAny. LAN u Read classic tutorial on Fast Ethernet

1000 Base-X (Gigabit Ethernet) u 1000 Mbps u Usually used to link 100 Base-X

1000 Base-X (Gigabit Ethernet) u 1000 Mbps u Usually used to link 100 Base-X hubs 1000 Base-X Hub 100 Base-T Hubs 27

1000 Base-X u Family of Standards (802. 3 z) u 1000 Base-LX – Long-wave

1000 Base-X u Family of Standards (802. 3 z) u 1000 Base-LX – Long-wave (lower frequency) laser – 550 meters on multimode optical fiber – 3 km on single mode fiber u 1000 Base-SX – Short-wave ( higher frequency) laser – 300 meters on 62. 5 micron multimode fiber 28

29 Full Duplex Ethernet u CSMA/CD is half duplex – Only one station may

29 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 100 Base-X and 1000 Base-X hubs and NICs support full duplex operation – Disable CSMA/CD – 802. 3 x standard

Shared media LANs u Limits to Shared Media LANs – FDDI, 100 Base-X, 100

Shared media LANs u Limits to Shared Media LANs – FDDI, 100 Base-X, 100 VG-Any. LAN all shared media LANs v Only one station can transmit at a time, causing latency v Every station hears every message, so as the number of stations grow, the LAN saturates – 100 Mbps speed only delays saturation 30

Shared media LANs u Shared Media Networks with Hubs (such as 10 Base-T) –

Shared media LANs u Shared Media Networks with Hubs (such as 10 Base-T) – Incoming frame arrives through a single port – Hub broadcasts frames out all ports – Congestion on output ports Hub 31

Switched LANs u In a switched network – Incoming frame arrives on a single

Switched LANs u In a switched network – Incoming frame arrives on a single port – Frame sent out again only on a single port--the one leading to the receiver – No congestion on other ports Switch 32

Switch With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows.

Switch With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows. Station A Station B 33 Switch Station C Connection 1 A-C Connection 2 B-D Station D

Switching in Perspective u Switching is the wave of the future for LANs –

Switching in Perspective u Switching is the wave of the future for LANs – Congestion does not increase as the number of stations grows u However, – Today, however, switches are still more expensive than 10 Base-T or 100 Base-X hubs u Read CISCO white paper – discount the sales talk – see 3 COM images of switches. 34

Switch connections u paths called connections must be pre-defined between stations ua fixed logical

Switch connections u paths called connections must be pre-defined between stations ua fixed logical data link (logical connection) is established between stations before transmission even begins u during the transmission, all traffic between the stations must pass over that data link u unless a data link has been pre-established, two stations may not communicate at all u only OSI Layer 2 (Data Link Layer) protocols are needed 35

Ethernet Switches u Ethernet u Most Hubs are Half Duplex Ethernet Switches are Full

Ethernet Switches u Ethernet u Most Hubs are Half Duplex Ethernet Switches are Full Duplex – No collisions are possible – So two stations can both transmit to each other at the same time (full duplex operation) – Requires full duplex switches – Requires full duplex NICs u Lowest-cost u Not LAN switches standardized, so buyers tend to get locked into a single vendor 36

ATM Switches u Asynchronous u Will Transfer Mode allow much higher speeds – 155

ATM Switches u Asynchronous u Will Transfer Mode allow much higher speeds – 155 Mbps to a few Gbps u Can also be used for long-distance networking – A single solution for both needs u Quality u Far of service guaranteed more expensive than Ethernet LAN switches 37

ATM Switches u standardized u scalable: (others not yet) as low as 1 Mbps

ATM Switches u standardized u scalable: (others not yet) as low as 1 Mbps to 2. 4 Gbps – can start with relative slow speeds (cheaper) – increase the speed as needs arise – without changing protocol 38

ATM and Ethernet u 100 Mbps and Gigabit Ethernet are outselling ATM for LAN

ATM and Ethernet u 100 Mbps and Gigabit Ethernet are outselling ATM for LAN usage u High-speed u Staff Ethernet is less expensive does not have to learn ATM technology u Sales ATM. of NICs - Ethernet, Token Ring and 39

Wireless LAN Broadcast Signal Transceiver Transmitting Wireless LAN Transceiver Receiving Antenna Cluster Transceiver Receiving

Wireless LAN Broadcast Signal Transceiver Transmitting Wireless LAN Transceiver Receiving Antenna Cluster Transceiver Receiving Hub Controller 40

Typical 802. 11 Wireless LAN Operation with Access Points 41 CSMA/CA+ACK Switch UTP Radio

Typical 802. 11 Wireless LAN Operation with Access Points 41 CSMA/CA+ACK Switch UTP Radio Link Access Point A UTP Access Point B Client PC Server Large Wired LAN Notebook Handoff If mobile computer moves to another access point, it switches service to that access point

Typical 802. 11 Wireless LAN Operation with Access Points Access Point Industry Standard Coffee

Typical 802. 11 Wireless LAN Operation with Access Points Access Point Industry Standard Coffee Cup Antenna (Fan) Wireless Notebook NIC PC Card Connector To Ethernet Switch 42

Typical 802. 11 Wireless LAN Operation with Access Points D-Link Wireless Access Point Using

Typical 802. 11 Wireless LAN Operation with Access Points D-Link Wireless Access Point Using Two Antennas Reduces Multipath Interference (See Ch. 3) 43

Typical 802. 11 Wireless LAN Operation with Access Points Linksys Switch With Built-In Wireless

Typical 802. 11 Wireless LAN Operation with Access Points Linksys Switch With Built-In Wireless Access Point Using Two Antennas Reduces Multipath Interference (See Ch. 3) 44

Typical 802. 11 Wireless LAN Operation with Access Points u The Wireless Station sends

Typical 802. 11 Wireless LAN Operation with Access Points u The Wireless Station sends an 802. 11 frame to a server via the access point u The access point is a bridge that converts the 802. 11 frame into an 802. 3 Ethernet frame and sends the frame to the server 802. 11 Frame Mobile Station 802. 3 Frame Access Point Ethernet Switch Server 45

Typical 802. 11 Wireless LAN Operation with Access Points u The server responds, sending

Typical 802. 11 Wireless LAN Operation with Access Points u The server responds, sending an 802. 3 frame to the access point u The access point converts the 802. 3 frame into an 802. 11 frame and sends the frame to the mobile station. 802. 11 Frame Mobile Station 802. 3 Frame Access Point Ethernet Switch Server 46

802. 11 Wireless LAN Speeds u 802. 11 2 Mbps (rare) 2. 4 GHz

802. 11 Wireless LAN Speeds u 802. 11 2 Mbps (rare) 2. 4 GHz band (limited in bandwidth) u 802. 11 b 11 Mbps, 2. 4 GHz 3 channels/access point u 802. 11 a 54 Mbps, 5 GHz (> bandwidth than 2. 4 GHz) 11 channels/access point u 802. 11 g 54 Mbps, 2. 4 GHz limited bandwidth 47

802. 11 Broadcast Operation u The Wireless Stations and Access Points Broadcast their Signals.

802. 11 Broadcast Operation u The Wireless Stations and Access Points Broadcast their Signals. – Only one access point or wireless station may transmit at any moment or signals will become scrambled. Access Point Wireless Station Collision About to Occur Wireless Station 48

CSMA/CA + ACK in 802. 11 Wireless LANs u CSMA/CA (Carrier Sense Multiple Access

CSMA/CA + ACK in 802. 11 Wireless LANs u CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) – Station or access point sender listens for traffic v If there is no traffic, can send if there has been no traffic for a specified amount of time v If the specified amount of time has not been met, must wait for the specified amount of time. Can then send if the line is still clear 49

CSMA/CA + ACK in 802. 11 Wireless LANs u CSMA/CA (Carrier Sense Multiple Access

CSMA/CA + ACK in 802. 11 Wireless LANs u CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) – Station or access point sender listens for traffic v If there is traffic, the sender must wait until traffic stops v The sender must then set a random timer and must wait while the timer is running v If there is no traffic when the station or access point finishes the wait, it may send 50

CSMA/CA + ACK in 802. 11 Wireless LANs u ACK (Acknowledgement) – Receiver immediately

CSMA/CA + ACK in 802. 11 Wireless LANs u ACK (Acknowledgement) – Receiver immediately sends back an acknowledgement; no waiting because ACKs have highest priority – If sender does not receive the acknowledgement, retransmits using CSMA/CA 51

Who Implements CSMA/CA+ACK? u Stations u Access (when they send) Points (when they send)

Who Implements CSMA/CA+ACK? u Stations u Access (when they send) Points (when they send) Mobile Station 802. 11 Frame CSMA/CA+ACK Access Point 52

Request to Send (RTS) / Clear to Send (CTS) u There is a widely

Request to Send (RTS) / Clear to Send (CTS) u There is a widely used option we should cover. – After a station may send, its first message may be a Request-to-Send (RTS) message instead of a data message – Only if the other party sends a Clear-to-Send (CTS) message does the sender begin sending data Mobile Station RTS CTS Access Point 53

Ad Hoc 802. 11 Networks u Ad – – Hoc Mode There is no

Ad Hoc 802. 11 Networks u Ad – – Hoc Mode There is no access point. Stations broadcast to one another directly Not scalable but can be useful for SOHO use NICs automatically come up in ad hoc mode 54

55 802. 11 Security u Attackers can lurk outside your premises – In “war

55 802. 11 Security u Attackers can lurk outside your premises – In “war driving, ” drive around sniffing out unprotected wireless LANs – In “drive by hacking, ” eavesdrop on conversations or mount active attacks. Outside Attacker Site with 802. 11 WLAN

802. 11 Security u By default, security on 802. 11 WLAN NICs and access

802. 11 Security u By default, security on 802. 11 WLAN NICs and access points is turned off, making external attacks trivial u WLAN vendors offer Wired Equivalent Privacy (WEP), but this is weak and easily broken. u The 802. 11 Working Group is working on a temporary replacement (TKIP) and longer-term security replacement, 802. 11 i u Even if corporate access points can be secured, many departments create unauthorized rogue access points that are seldom secured. 56