Other LAN Technologies Chapter 5 Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4 th edition

Other LAN Technologies

Chapter 5

Copyright 2003 Prentice-HallPanko’s Business Data Networks and Telecommunications, 4th edition

2

Other LAN Technologies

Large Ethernet networks

Wireless LANs

ATM LANS and QoS

Legacy LANs Token-Ring Networks

10 Mbps Ethernet co-axial cable LANs

3

Figure 5.1: Multi-Switch Ethernet LAN

Switch 2

Switch 1 Switch 3

Port 5 on Switch 1to Port 3 on Switch 2


C3-2D-55-3B-A9-4FSwitch 2, Port 5

A1-44-D5-1F-AA-4CSwitch 1, Port 2

E5-BB-47-21-D3-56Switch 3, Port 6

D4-55-C4-B6-9FSwitch 3, Port 2

B2-CD-13-5B-E4-65Switch 1, Port 7

4

Switching Table Switch 1Port Station

2 A1-44-D5-1F-AA-4C7 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F5 D4-47-55-C4-B6-9F5 E5-BB-47-21-D3-56


Switch 2

Switch 1



B2-CD-13-5B-E4-65Switch 1, Port 7


5


Switch 2

Switch 1 Switch 3



C3-2D-55-3B-A9-4FSwitch 2, Port 5


3 A1-44-D5-1F-AA-4C3 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F7 D4-47-55-C4-B6-9F7 E5-BB-47-21-D3-56 E5-BB-47-21-D3-56

Switch 3, Port 6

6


Switch 2

Switch 3



D4-55-C4-B6-9FSwitch 3, Port 2


4 A1-44-D5-1F-AA-4C4 B2-CD-13-5B-E4-654 C3-2D-55-3B-A9-4F2 D4-47-55-C4-B6-9F6 E5-BB-47-21-D3-56


7

Figure 5.2: Hierarchical Ethernet LAN

Ethernet Switch F

Server YServer X

Client PC1

Only OnePossible Path

BetweenAny TwoStations

PC Client 2

EthernetSwitch E

EthernetSwitch D

EthernetSwitch B

EthernetSwitch A

EthernetSwitch C

8

Figure 5.3: Single Point of Failure in a Switch Hierarchy

No CommunicationNo Communication

Switch 1

Switch 2

Switch 3

Switch Fails

A1-44-D5-1F-AA-4C

B2-CD-13-5B-E4-65

C3-2D-55-3B-A9-4F

D4-47-55-C4-B6-9F

E5-BB-47-21-D3-56

9

Figure C.10: 802.1D Spanning Tree Protocol

Switch 1

Switch 2

Switch 3

A1-44-D5-1F-AA-4C

B2-CD-13-5B-E4-65

C3-2D-55-3B-A9-4F

D4-47-55-C4-B6-9F

E5-BB-47-21-D3-56

Activated

Activated

Deactivated

Normal OperationLoop, but Spanning Tree ProtocolDeactivates One Link

Module C

10

Figure C.10: 802.1D Spanning Tree Protocol

Switch 1

Switch 2

Switch 3

A1-44-D5-1F-AA-4C

B2-CD-13-5B-E4-65

C3-2D-55-3B-A9-4F

D4-47-55-C4-B6-9F

E5-BB-47-21-D3-56

Deactivated Deactivated

Activated

Switch 2 FailsModule C

11

Figure 5.2: Hierarchical Ethernet LAN

Core

WorkgroupEthernet Switch F

Server YServer XClient PC1

PC Client 2

WorkgroupEthernetSwitch E

WorkgroupEthernetSwitch D

Core EthernetSwitch B

CoreEthernetSwitch A

Core EthernetSwitch C

12

Figure C.8: Switching Matrix with Queue

Switch Matrix

Input Queue

IncomingSignal

OutgoingSignal

Port1

Port2

Port3

Port4

Port5

Port6

Port7

Port8

Module C

13

Figure 5.4: Workgroup Switches versus Core Switches

Ports = 4

Speed = 1 Gbps

Maximum input = 4 Gbps

Nonblocking switch matrix capacity = 4 Gbps

1 Gbps

1 Gbps

1 Gbps1 Gbps

Switching Matrix4Gbps

Nonblocking

14

Figure 5.4: Workgroup Switches versus Core Switches

Connects

Typical PortSpeeds

Switching Matrix

Workgroup Switches

Client or Server to theEthernet Network via An access line

10/100 Mbps

Lower Percentage ofNonblocking CapacityBut not less than 25%

Core Switches

Ethernet Switchesto One Another viaA trunk line

100 Mbps, Gigabit Ethernet,10 Gbps Ethernet

80% or More ofNonblocking Capacity

15

Client A

Client B

Client C

Server D Server E

ServerBroadcast

Figure 5.5: Virtual LAN with Ethernet Switches

Server Broadcasting without VLANS

Frame is BroadcastGoes to all stationsCreates congestion

16

Figure 5.5: Virtual LAN with Ethernet Switches

Server Multicasting with VLANS

Client Aon VLAN1

Client Bon VLAN2

Client Con VLAN1

Server Don VLAN2

Server Eon VLAN1

ServerBroadcast

VLANs are collections of servers and their clients

Multicasting (some), not Broadcasting (all)

17

Figure 5.6: Tagged Ethernet Frame

Source Address (6 Octets)

Length (2 Octets)Length of Data Field in

Octets1,500 (Decimal) Maximum

Tag Protocol ID (2 Octets)1000000100000000

81-00 hex; 33,024 decimalLarger than 1,500, So not

A Length

By lookingat the value

in the 2octets after

theaddresses,the switchcan tell ifthis frameis basic(value < 1,500)

or tagged(value = 33,024)

Basic 802.3 MAC Frame Tagged 802.3 MAC Frame

Source Address (6 Octets)

Tag Control Information(2 Octets) Priority Level (0-7)

(3 bits); VLAN ID (12 bits)(1 other bit)

Length (2 Octets)

Data Field (variable)

18

Figure 5.7: Ethernet Physical Layer Standards

Physical LayerStandard

SpeedMaximum

Run Length

UTP

10Base-T

100Base-TX

10 Mbps

100 Mbps

100 meters

100 meters

Medium

4-pair Category 3, 4, or 5

4-pair Category 5

1000Base-T 1,000 Mbps 100 meters4-pair Category 5, 4-pairEnhanced Category 5 is

preferred

19

Figure 5.7: Ethernet Physical Layer Standards

Physical LayerStandard

SpeedMaximum

Run Length

Optical Fiber

Medium

10Base-F* 10 Mbps UP to 2 km*62.5/125 micron

multimode, 850 nm.

100Base-FX 100 Mbps 412 m62.5/125 multimode,

1,300 nm, hub

100 Base-FX 100 Mbps 2 km62.5/125 multimode,

1,300 nm, switch

* Several 10 Mbps fiber standards were defined in 10Base-F.

Wireless LANs

21

Figure 5.8: Typical 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

22


WirelessNotebook

NIC

Access Point

IndustryStandard

CoffeeCup

To EthernetSwitch

Antenna(Fan) PC Card

Connector

23


D-LinkWirelessAccessPoint

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

24

LinksysSwitchWith

Built-InWirelessAccess Point

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


25


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

26


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

27

802.11 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

28

802.11 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

29

Figure 5.9: CSMA/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

Correction

30


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

Correction

31


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

32

Who Implements CSMA/CA+ACK?

Stations (when they send)

Access Points (when they send)

MobileStation

AccessPoint

802.11Frame

CSMA/CA+ACK

33

Request 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

New

34

Ad 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

Module C

35

Wired Core / Wireless to the Desktop

Normal Networks: Core & Workgroup Switches

Core

WorkgroupEthernet Switch FWorkgroup

EthernetSwitch D



Core EthernetSwitch CWorkgroup

SwitchesAttach toStationsBy UTP

Module C

36

Wired Core / Wireless to the Desktop

With High-Speed Wireless LANs, Replace Workgroup Switches with Access Points

Core

AccessPoint 2

AccessPoint 1



Core EthernetSwitch CAccess

PointsServe

Stations

Module C

37

802.11 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

New

38

802.11 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.

New

39

Personal Area Networks (PANs)

Connect Devices On or Near a Single User’s Desk PC, Printer, PDA, Notebook Computer,

Cellphone

Connect Devices On or Near a Single User’s Body Notebook Computer, Printer, PDA,

Cellphone

The Goal is Cable Elimination

40

Personal Area Networks (PANs)

There May be Multiple PANs in an Area May overlap

Also called piconets

41

Figure 5.10: 802.11 versus Bluetooth LANs

Focus

Speed

802.11 Bluetooth

Large WLANs Personal Area Network

11 Mbps to 54 MbpsIn both directions

722 kbps with backchannel of 56 kbps.

May increase.

Distance100 meters for 802.11b(but shorter in reality)

Shorter of 802.11a

Numberof Devices

Limited in practice onlyby bandwidth and traffic

Only 10 piconets,each with

8 devices maximum

10 meters(may increase)

42

Figure 5.10: 802.11 versus Bluetooth LANs

Scalability

Cost

Battery Drain

802.11 Bluetooth

Good through havingmultiple access points

Poor(but may get

access points)

Probably higher Probably Lower

Higher Lower

Discovery No Yes

Discovery allows devices to figure out how to work together automatically

43

Figure 5.11: Bluetooth Operation

File Synchronization

Client PCSlave

NotebookMaster

Printer SlavePrinting

Cellphone

Telephone

Piconet 1

44


Client PC

Notebook


Call Through CompanyPhone System

CellphoneMaster

Telephone Slave

Piconet 2

45


File Synchronization

Client PCSlave

NotebookMaster


Call Through CompanyPhone System

CellphoneMaster

Telephone Slave

Piconet 1

Piconet 2

46

Figure 5.12: Normal Radio Transmission and Spread Spectrum Transmission

Channel BandwidthRequired for a specificSignal speed

Normal Radio:Use only the requiredBandwidth to conserveThe frequency spectrum

Note: Height of Box Indicates Bandwidth of Channel

Shannon’s Law: W = B log2 (1/S/N)

Defines minimum bandwidth needed for a signal of a specific speed.

47

Figure 5.12: Normal Radio Transmission and Spread Spectrum Transmission

Channel BandwidthRequired for Signal

Frequency HoppingSpread Spectrum (FHSS)

802.11

Direct SequenceSpread Spectrum (DSSS)

802.11b

Note: Height of Box Indicates Bandwidth of Channel

Wideband but Low-Intensity Signal

48

Figure 5.13: Code Division Multiple Access (CDMA) Spread Spectrum Transmission

Client PC 1

Client PC 2

Low-Density Orthogonal Signal 1

Low-Density Orthogonal Signal 2

Server A

Server B

Radio Spectrum

Used in Some Cellular Telephone Systems

49

OFDM

Orthogonal Frequency Division Multiplexing (OFDM) Divide a large channel into many subchannels Send part of the signal in each channel Stops using channels with impairment Used in 802.11a, 802.11g at 54 Mbps

Module B

Channel

Subchannel

ImpairedSubchannel(Not Used)

50

Spread Spectrum Methods

Spread Spectrum Techniques

DSSS FHSS(Original802.11)

802.11bDSSS

CDMA(Cellular

Telephony)

OFDM(802.11a,802.11g)

51

Ultrawideband (UWB)

EWB Uses Extremely Wide Channels

EWB channels are enormously wide—often cutting across several entire service bands

Extremely high speeds are possible

Can travel through thick walls

Because of concerns that EWB may it interfere with services in the service bands spanned, regulators require power to be kept extremely low

NewNot in Book

52

ATM (Asynchronous Transfer Mode)

Ethernet competitor for switched LANs

Quality of Service (QoS) for telephony and multimedia transmissions

As scalable in speed as Ethernet

Highly complex and expensive to buy and manage

Not selling well for LANs

Increasingly popular for WANs

53

Figure 5.15: Handling Brief Traffic Peaks

Traffic

Network Capacity

Momentary Traffic Peak:Congestion and Latency

Time

Congestion and Latency

54


Traffic

Network Capacity

Traffic Peak

Time

Quality of Service (QoS) Guarantees in ATM

Traffic with ReservedCapacity Always Goes(Voice)

Other Traffic Must Wait(Data)

55


Traffic

Overprovisioned Network CapacityTraffic Peak:No Congestion or Latency

Time

Overprovisioned Traffic Capacity in Ethernet

56


Traffic

Network Capacity

Peak Load

Time

Priority in Ethernet

High-Priority Traffic FirstLow-Priority Waits

57

Figure 5.16: ATM Network with Virtual Circuits

Server

Client PC

ATM Switch 1 ATM Switch 2

ATMSwitch 3

ATM Switch 4

ATM Switch 5ATM switches can be arranged in amesh, so there are alternative paths. This makes switching slow and expensive.

58


Server

Client PC


ATMSwitch 3

ATM Switch 4

ATM Switch 5

VirtualCircuit

VirtualCircuit

ATM selects a single path, called aVirtual circuit, before two stationsBegin transmitting. This simplifiesSwitching and so lowers switching cost

59


Server

Client PC


ATMSwitch 3

ATM Switch 4

ATM Switch 5

VirtualCircuit

VirtualCircuit

Virtual CircuitA . . .B . . .C . . .D . . .

Port1234

Switch 4 Switching Table

ATM switching tables are as simple asEthernet switching tables

60

ATM Reduces Switching Costs

Virtual circuits simplify switching, reducing switching costs

ATM (like Ethernet) is unreliable, also reducing switching costs by avoiding the expense of step-by-step error correction

Switches are the most expensive element in most networks, so minimizing switching cost usually is a major goal in network standards

61

Figure 5.17: Virtual Circuit with VPI and VCI

Virtual Path is a Path to a SiteVirtual Channel is a Connection to a Particular Computer at the Site

Switches in Backbone Only Have to Look at the Virtual Path Indicator (VPI)

VirtualChannels Virtual Path

Site 1 Site 2

ATM Backbone

62

Figure 5.17: ATM Cell

Bit 1 Bit 4Bit 3Bit 2 Bit 8Bit 7Bit 6Bit 5

Virtual Channel Identifier

Virtual Path Identifier Virtual Channel Identifier

Virtual Channel Identifier ReservedCall LossPriority

Payload Type

Header Error Check

Payload(48 Octets)

Virtual Path Identifier

VPI: Specifies a VC to siteVCI: Specifies a station at siteSwitches between sites only look at VPI

5 octets of header48 octets of payload53 octets total

63

ATM Cells

ATM frames are short and fixed in length; called cells Only 53 octets long 5 octets of header 48 octets of data

Short length reduces latency at switches Switch may have to wait until entire frame arrives

before sending it back out—faster with short cells

Fixed length gives predictability for faster processing

Token-Ring Networks

Legacy LAN Technologies

65

Token-Ring Networks

Ring Topology

Inner Ring Outer Ring

Frame

NormalOperation

Dual Ring; normally only one is used

66

Token-Ring Networks

Ring is wrapped if there is a break The wrapped ring is still a full ring

BreakWrapped Ring

67

Token-Ring Networks

Special Frame Called Token Circulates when no station is transmitting For access control, station must have token to send

Inner Ring Outer Ring

Token

68

Ring Network Technologies

802.5 Token-Ring Network

FDDI (Fiber Distributed Data Interchange)

SONET/SDH

16 Mbps 100 Mbps: 200 km circumference

54 Mbps to several Gbps

Small to Mid-size LANs

LAN Backbones Telephony

Lost out to cheaper and eventually faster Ethernet

Lost out to faster gigabit Ethernet

Growing rapidly in the telephone network core

69

Figure 5.19: 802.5 Token-Ring Network

STP or UTP

STPOr Fiber

Wiring hubs are called multistation access units (MAUs).

Prefers to use shielded twisted pair (STP) wire for runs to stations and to link MAUs but will use UTP for stations and fiber for trunks.

STP has two twisted pairs. There is a metal mesh around each pair and around both pairs to reduce interference. STP is bulky and expensive.

MultistationAccess Unit

(MAU)

70

Figure 5.18: Major Legacy Networks

Early Ethernet Standards General

Only 10 Mbps—shared by all stations

Before switches and hubs

Used coaxial cable (central wire surrounded by a conducting cylinder) You use this to connect your TV to your VCR

InnerWire

Outer Conductor Wrapped in Jacket

71


Early Ethernet Standards 10Base5

Multidrop topologyThick trunk cable uses coaxial cable

technology; 500-meter limitDrop cable has 15 wiresNIC has 15-hole Attachment Unit Interface

(AUI) port

Trunk CableDrop Cable

15-HoleAUI Port

72


Early Ethernet Standards 10Base2

Daisy chain topologyThin coaxial cable between stationsCircular BNC connector

BNCConnector

73


Ethernet 10Base2

To NextStation

T-Connector to Link NIC to next segments

NIC

74


RJ-45UTP

Connectors

BNC Connector10Base2T-Connector

UTP

ThinCoax

Ethernet 10Base2: UTP versus BNC Connectors

75


Ethernet 10Base2

BNC Connector

T-ConnectorTo NextStation

Documents

Other LAN Technologies Chapter 5 Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4 th edition