7-1

Establishing Communication Channels: Completing the

Physical Layer

Chapter 4

Knowledge Checkpoints

Be able to identify major hardware components of a network Hub Server Nodes

Remote access Connection vs connectionless

Important Goals for Networks

Faster More efficient More reliable More secure

What Does a LAN Do?

Information sharing Allows sharing of same data filesExchange of information via e-mailPass-thru to the Internet for information

Resource sharing Enables sharing a hardware device (e.g., printer) Software packages used by many users on the network Improves storage spaceProvides daily back-up

Why Use a LAN?

Saves Money!Sharing hardware is cheaperNetwork versions of applications are cheaperProductivity improves with common accessIncreased security

LANs often Link to Legacy Systems

What is Telnet?

Terminal emulation program (client-server) Interactive session with a server Port 23/24 Try open cyberspace.org At login type newuser

Using Telnet

Sharing Software on a LAN

LAN metering software prohibits using more copies of a package than there are installed licenses

The Software Publishers Association (SPA) estimates that about 40% of all the software in the world is used illegallyUtah has the largest amount of unlicensed software in use –

next to P.R. China!SPA has undertaken an aggressive software audit program to

check the number of illegal software copies on LANs.

LANs Carry Identifiable Traffic

Dedicated Server LANs

A dedicated server LAN has one or more computers that are permanently assigned to being the network server(s) for one (or more) activities

In a dedicated server LAN, the server’s usual operating system is replaced by a network operating system

Dedicated Server LANs

File servers - allow many users to share the same set of files on common, shared disk drive(s)

Database servers - not only provides shared access to the database on the server, but also can perform database processing on those files associated with client-server computing

Dedicated Server LANs

Print servers -handle print requests on the LAN from multiple users on the network

Communications servers - are dedicated to performing communications processing Examples are :Fax servers - manage fax boardsModem servers - for dialing out of the networkRemote access servers - for dialing into the networkMiddleware servers –for managing communications and

transaction load

LAN Components

There are 5 basic components to a LAN Client (node) Server Network Interface Cards (NICs) Network Cables and Hubs Network Operating Systems (NOS)

Where Do you Start?

Components of a 10BaseT Network

Network Interface Cards

The Network Interface Card (or NIC) allows the computer to be physically connected to the network cable, which provides the physical layer connection among computers in the network

NICs

NICs Match the Network

Putting it Together

Network Cables and Hubs

Each computer must be physically connected by network cable to the other computers in the network

The selection of a LAN can be influenced greatly by the type of cable that already exists where the LAN is to be installed

Network Cable

Most LANs are formed with a blend of unshielded twisted pair (UTP) wire, shielded twisted pair (STP), coaxial cable, and fiber optic cable.

Cable Limits the Distance of a LAN

Types of Fiber Optic Connectors

•SC Stick & Click

•ST Stick & Turn

Network Configuration

There are two fundamental network configurations:

Point-to-point configuration (2-point) - sometimes called dedicated circuits

Multipoint configuration (or multidrop)

Connectivity

Media Selection Criteria

• Cost• Speed• Distance and expandability• Environment• Security

Network Hubs

Network hubs go by many names depending on the type of network and the specific vendorConcentratorMultistation access unit (MAU)TransceiverRepeater

Network Hubs

Network hubs serve two purposes:They provide an easy way to connect network cablesHubs act as repeaters or amplifiers to prevent

attenuation

Some hubs are “smart”, because they can detect and respond to network problems, as well as have managed ports

Connecting to a NIC

Hubs

Come in common speeds to match NICs10, 100, 10/100, 1000

Variable number of connection ports 8, 16, 24

Hubs

Single-hub (repeater) or single-switch LAN

Share speed of network200 meter maximum distance span

between farthest two stations with UTP

What is a USB hub?

100 m

100 m

X

Y

200 m

How Hubs Work

Ethernet 802.3 Physical Layer

• Topology: Order in which stations receive bits• Ethernet hubs use a bus topology

Signal is broadcastAll stations receive almost simultaneously

Hubs

Multiple-hub LANsIncrease maximum distance span

100 m

100 m

100 m

Multiple Hubs in 10Base-T

Farthest stations in 10Base-T can be five segments 500 meters apart

100 meters per segment

Separated by four hubs

100m

100m

100m

100m

100m

500m, 4 hubs

10Base-T hubs

Multiple Hubs in 10Base-T

Practical Limit in 10Base-T is Number of StationsDegradation of service beyond 100 stations

Unacceptable service beyond 200 stations

Maximum possible span normally includes no more than 200 stations

In 10Base-T, the number of stations is the real limit to distance spansIt is possible to have a LAN with more than a 200 meter maximum

span

Physical Layer: 802.3 UTP Standards

• Wiring

100 meters maximum UTP distance hub-to-station or hub-switch

200 meters maximum distance between stations

100 m 100 m

200 m

Mixing Circuit Media

Hooking up a Network

Connections Through a Hub

Multiple Hubs in 100Base-TX

Limit of Two Hubs in 100Base-TXMust be within a few meters of each otherMaximum span is 200 metersShorter maximum span than 10Base-T

100m

100m2 Collocated

Hubs

100Base-TXHubs

~200 m

4-wire phone station wire

Flat gray modular

Unshielded twisted pair

Shielded twisted pair

Coax- thick

Coax-thin

Coax-thin

Fiber-optic cable

Fiber Glass

RG-62

RG-58, thinnet,

cheapernet

Frozen yellow

garden hose

STP

UTP

Flat satin, telephone

cable, silver satin

Quad RYGB 3 Kbps

14.4 Kbps

100 Mbps

16 Mbps

10 Mbps

10 Mbps

2.5 Mbps

several Gbps

several kilometers

200 feet

200 feet

500 feet

100 feet

100 feet

10-20 feet

200 feet RJ-11 jacks

RJ-11 or RJ-45 plugs

RJ-45

RJ-45 or IBM data

connectors

AUI (attachment

unit interface)

BNC connector

BNC or IBM data connector

SI or SMA 905 or SMA 906

1.00/foot

0.32/foot

1.10 foot

0.42/foot

0.10/foot

0.09-0.18/foot

0.09/foot

0.32/foot

4 insulated wired-red,green, yellow, black. Home phone wiring. Voice Applications

Comes with 4,6,8 conductors. Used for short data cables using modular (mod-tap) adapters

5 Designated categories. Twists prevent interference, increase bandwidth. Voice grade usually not suitable for data

Shielding reduces interference but complicates installation

Original Ethernet cabling

Looks like cable TV cable. Easier to work with than thick coax.

Similar to RG-58 (thinnet) but different electrical characteristics make these cables NOT interchangeable

Difficult to install but technology is improving. High bandwidth, long distance, virtually error free, high security

Media Type Also Called BandwidthDistance

Limits Connectors Comments/Applications Price ($)Toke

n R

ing

Eth

erne

tF

DD

IC

DD

IF

ast

Eth

erne

t

AT

M

Architectures

Gig

abit

Eth

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t

GOLDMAN & RAWLES: ADC3e FIG. 05-07

How Would You Wire This?

Business Issues & Remote Access

Cost of offices vs cost of remote set-up Employee access to network services Customer access/service

Categories of Remote Access

TelecommutingCosts – connect charges, equipment, wiring

Mobile computingAnywhere communication

Technical SupportCosts of on-site service

Design Steps for Dial-up

Needs analysis (who do you talk to?) Logical topology Physical topology Current technology review

Needs Analysis

What applications should be accessed by dial up?

Who will dial up? Is there a business benefit? How many will use the dial up? Special access required?

Logical Topology

Remote nodeOperate as locally connectedApplications run on remote PCMinimize downloads

Remote controlSimulates a PC attached to the networkDrives are mapped to network

Remote Node vs. Remote Control InstallationsRemote Node vs. Remote Control Installations

Applications execute here or are distributed

across client and server.

NOS-compliant client protocol stack including communications

software is installed here.NOS-compliant remote access

services software is installed here.

LAN-Attached Server (local server)

Remote PC (remote client)

Full Client/Server application traffic

WAN link

Modem Modem

To local area network-attached

resources

Remote Access

Remote control software is installed. Resultant images

and text displayed with keystrokes echoed.

Remote control software is installed. Applications execute

here and return results to "guest."

LAN-Attached Server (host)

Remote PC (guest)

Keystrokes and screen images ONLY

WAN link

Modem Modem

To local area network-attached

resources

Remote Control

GOLDMAN & RAWLES: ADC3e FIG. 10-02

Security Issues & Remote Access

Password managementVerifying employee access

Locking accounts Multiple tries may be a hacker

Separation of data Original data should be stored behind a firewall

EncryptionPreventing “sniffing”

Dial-back Insure correct user

Authentication Device or software?

Physical Design Options

Dedicated PC Communications server LAN modem

Physical Topology: Alternative Access Points

File server

network hub

Local PC (office)

Modem LAN modem

Remote PC (home)

LAN

Access Point 3: LAN Modems

Access Point 2: Communications Server

Communications server

Local PC (office)

Access Point 1: Serial Port of LAN-Attached PC

File server

network hub

Local PC (office)

ModemRemote PC (home)

LAN

File server

network hub

Local PC (office)

ModemRemote PC (home)

LAN

Modem

Modem

GOLDMAN & RAWLES: ADC3e FIG. 10-04

Network Access Methods

PSTNModem @ 56KbpsAnalog

ISDN ISDN modemDigital

XDSLDSL modemDigital service on top of PSTN

VPNSecure communication channelVPN software, ISP

Alternative Network Access Services

GOLDMAN & RAWLES: ADC3e FIG. 10-05

VPN

Remote User

Regional Office -or- Corporate Headquarters

ISP

Ethernet SwitchPSTN

ISDN

PSTN

Modem

ISDN Modem

DSL Modem

Modem

Modem

ISDN Modem

DSL Modem

Modem

RAS Server

secure tunnel

Remote Access Hardware

Communication servers Simultaneous loginsMonitor with phone linesRequires multiple NICs to network resourcesModems connect to serial portsCan be used for remote control applications in

lieu of PCsActs as a gateway

Remote Node Server Solutions

Software-only Turnkey hardware (integrated modems) LAN modems (dial-up servers) Monster RAS

Remote Node Software

Common software include Windows NT RAS and Netware Connect

Client OS compatibility

Communications Server Components

Modems

Communications Server

To local area network-attached

resources

Serial port connections

Network interface

cards (NIC)

ProcessingInput Output

Serial data are transmitted over dial-up phone lines via modems and into serial ports on communications server.

Process input from remote PC, making requests of network

resources as required. Redirector or equipment

directs requests to proper local or

networked resources.

Network resources are accessed through a

network adapter card attached to the communications

server. Data format is compatible with

network architecture.

or other WAN access device dependent on WAN service

WAN SERVICESDial-Up ISDN Frame Relay

GOLDMAN & RAWLES: ADC3e FIG. 10-06

Remote Control Software

Taking over a remote PC Software on guest and host systems Lock-ups of host PCs Disable monitor and keyboard Virus detection Popular packages include, PCAnywhere and

LapLink

Remote Node Server Software Characteristics

NOS protocols supported Support for modem pools & dial out Management of time limits Security with forced password & token

authentication Client platforms

Circuit & Packet Switching

Differences center on voice and data transmission Circuit switching

Continuous, exclusive, temporaryLow latency and few delays

Packet switchingData transmitted in a container (packet)Routed base on header informationRouters distribute data to appropriate destination

Issues to Consider

Designing a network is a multi-step process The use of the network is important How users access the network is important The type of data will determine the speed