Other LAN Technologies

2LAN Standards

802 Working Groups

– 802.3 Ethernet LANs

– 802.5 Token-Ring Networks

– 802.11 Radio LANs

– 802.12 100VG-AnyLAN

3802.5 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

4Ring Topology in Token-Ring Networks

StationB

StationA

StationE

StationD

StationCFrame

Frame

Ring

Station B only receives frames from Station A and only transmits frames to Station C

Ring

5Problem with Rings

If the ring breaks, LAN stops– Signals must go all the way around the ring, back

to the sender

– This becomes impossible

6Use a Double Ring

One is unused in normal operation If there is a break, the ring is wrapped

– Still a ring

Normal Wrapped

7UTP and STP Wiring

UnshieldedTwisted Pair

(UTP)

ShieldedTwisted Pair

(STP)

TwistedPair

TwistedPair

Shielding Around Pair

Outer ShieldAround Bundle

Plastic Cover (Non-Shielding)TwistedPair

TwistedPair

8STP 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

9Access Units in a Ring

Access Unit Access Unit

Access Unit Access Unit

STP link betweenAccess Units

STP linkfrom Stationto Access

UnitStations

Station

UTP Linkfrom Stationto Access

Unit

10

NIC NICNIC

Within the Access Unit

The ring is retained Powered-up NICs added automatically Powered-off NICs bypassed automatically

Ring

MissingNIC

Bypassed Node

11Token Passing in 802.5 Token-Ring Networks

Token

StationB

Station B may only transmit when it receives a special frame called a token.

12Ethernet (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

13Ethernet (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

14Shared 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

15Congestion and Latency in Shared Media LANs

Transmission

Shared Media LAN

Station Bis Transmitting

But MustStop Soon

Station AMust Wait

to Transmit

Station CMust Wait

to Transmit

16Congestion 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

17100 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

18FDDI Network

FDDI Ring

19FDDI 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

20802.12 100VG-AnyLAN

100 Mbps

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

Hubs (repeaters) organized as a Tree– One is the master repeater

Not achieving market acceptance

21802.12 100VG-AnyLAN Hub Hierarchy

Repeater A

Repeater B Repeater C

Repeater D Repeater E

MasterRepeater

Station 1Station 1 Station 2Station 2

High-Priority Request Low-Priority Request

FirstLevelRepeater

SecondLevelRepeaters

ThirdLevelRepeaters

22100Base-X

100 Mbps

Uses Normal 802.3 MAC Layer Frame

Family of Standards– 100Base-TX uses Cat 5 wiring (most popular to

desk)

– 100Base-T4 uses Cat 3 and Cat 4 wiring

– 100Base-FX uses optical fiber

23100Base-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

24Upgrading 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

25Ethernet 100Base-TX Network

100Base-TX Hub

Station A Station B Station C

100 mSegmentMaximum

100 mSegmentMaximum

~50 maximum

- 5 UTP wiring- NICs are replaced

100Base-TX Hub

26Ethernet 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 and 100VG-AnyLAN

Read classic tutorial on Fast Ethernet

271000Base-X (Gigabit Ethernet)

1000 Mbps

Usually used to link 100Base-X hubs

1000Base-X Hub

100Base-T Hubs

281000Base-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

29

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

30Shared media LANs

Limits to Shared Media LANs

– FDDI, 100Base-X, 100VG-AnyLAN all shared media LANs

Only one station can transmit at a time, causing latency

Every station hears every message, so as the number of stations grow, the LAN saturates

– 100 Mbps speed only delays saturation

31Shared media LANs

Shared Media Networks with Hubs (such as 10Base-T)– Incoming frame arrives through a single port

– Hub broadcasts frames out all ports

– Congestion on output ports

Hub

32Switched LANs

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

33Switch

Switch

StationA

StationB

StationC

StationD

Connection 1A-C

Connection 1A-C

Connection 2B-D

Connection 2B-D

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

34Switching in Perspective

Switching is the wave of the future for LANs

– Congestion does not increase as the number of stations grows

However,

– Today, however, switches are still more expensive than 10Base-T or 100Base-X hubs

Read CISCO white paper

– discount the sales talk

– see 3COM images of switches.

35Switch connections paths called connections must be pre-defined

between stations

a fixed logical data link (logical connection) is established between stations before transmission even begins

during the transmission, all traffic between the stations must pass over that data link

unless a data link has been pre-established, two stations may not communicate at all

only OSI Layer 2 (Data Link Layer) protocols are needed

36Ethernet Switches Ethernet Hubs are Half Duplex

Most 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

Lowest-cost LAN switches

Not standardized, so buyers tend to get locked into a single vendor

37ATM Switches

Asynchronous Transfer Mode

Will allow much higher speeds– 155 Mbps to a few Gbps

Can also be used for long-distance networking– A single solution for both needs

Quality of service guaranteed

Far more expensive than Ethernet LAN switches

38ATM Switches

standardized (others not yet)

scalable: 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

39ATM and Ethernet

100Mbps and Gigabit Ethernet are outselling ATM for LAN usage

High-speed Ethernet is less expensive

Staff does not have to learn ATM technology

Sales of NICs - Ethernet, Token Ring and ATM.

40Wireless LAN

BroadcastSignal

TransceiverTransmitting

TransceiverReceiving

ClusterTransceiver

Receiving

Antenna

Hub Controller

Wireless LAN

41Typical 802.11 Wireless LAN Operation with Access Points

Switch

Client PCServer

Large Wired LAN

AccessPoint A

AccessPoint B

UTP Radio Link

HandoffIf mobile computermoves to another

access point,it switches serviceto that access point

Notebook

CSMA/CA+ACK

UTP

42 Typical 802.11 Wireless LAN Operation with Access Points

WirelessNotebook

NIC

Access Point

IndustryStandard

CoffeeCup

To EthernetSwitch

Antenna(Fan) PC Card

Connector

43Typical 802.11 Wireless LAN Operation with Access Points

D-LinkWirelessAccessPoint

Using Two Antennas Reduces Multipath Interference (See Ch. 3)

44

LinksysSwitchWith

Built-InWirelessAccess Point

Using Two Antennas Reduces Multipath Interference (See Ch. 3)

Typical 802.11 Wireless LAN Operation with Access Points

45Typical 802.11 Wireless LAN Operation with Access Points

The Wireless Station sends an 802.11 frame to a server via the access point

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

MobileStation

AccessPoint

EthernetSwitch

Server

802.11Frame

802.3Frame

46Typical 802.11 Wireless LAN Operation with Access Points

The server responds, sending an 802.3 frame to the access point

The access point converts the 802.3 frame into an 802.11 frame and sends the frame to the mobile station.

MobileStation

AccessPoint

EthernetSwitch

Server

802.11Frame

802.3Frame

47802.11 Wireless LAN Speeds

802.11 2 Mbps (rare)2.4 GHz band (limited in

bandwidth)

802.11b 11 Mbps, 2.4 GHz3 channels/access point

802.11a 54 Mbps, 5 GHz (> bandwidth than 2.4 GHz)11 channels/access point

802.11g 54 Mbps, 2.4 GHzlimited bandwidth

48802.11 Broadcast Operation

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.

CollisionAbout toOccurAccess

Point

WirelessStation

WirelessStation

49CSMA/CA + ACK in 802.11 Wireless LANs

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)– Station or access point sender listens for traffic

If there is no traffic, can send if there has been no traffic for a specified amount of time

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

50CSMA/CA + ACK in 802.11 Wireless LANs

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)– Station or access point sender listens for traffic

If there is traffic, the sender must wait until traffic stops

The sender must then set a random timer and must wait while the timer is running

If there is no traffic when the station or access point finishes the wait, it may send

51CSMA/CA + ACK in 802.11 Wireless LANs

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

52Who Implements CSMA/CA+ACK?

Stations (when they send)

Access Points (when they send)

MobileStation

AccessPoint

802.11Frame

CSMA/CA+ACK

53Request to Send (RTS) / Clear to Send (CTS)

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

MobileStation

AccessPoint

RTS

CTS

54Ad Hoc 802.11 Networks

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

55802.11 Security

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.

Site with 802.11 WLAN

OutsideAttacker

56802.11 Security

By default, security on 802.11 WLAN NICs and access points is turned off, making external attacks trivial

WLAN vendors offer Wired Equivalent Privacy (WEP), but this is weak and easily broken.

The 802.11 Working Group is working on a temporary replacement (TKIP) and longer-term security replacement, 802.11i

Even if corporate access points can be secured, many departments create unauthorized rogue access points that are seldom secured.