Establishing Communication Channels: Completing the Physical Layer

1
Establishing Communication Channels Completing
the Physical Layer

• Chapter 4

2
Knowledge Checkpoints

• Be able to identify major hardware components of
  a network
• Hub
• Server
• Nodes
• Remote access
• Connection vs connectionless

3
Important Goals for Networks

• Faster
• More efficient
• More reliable
• More secure

4
What Does a LAN Do?

• Information sharing
• Allows sharing of same data files
• Exchange of information via e-mail
• Pass-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 space
• Provides daily back-up

5
Why Use a LAN?

• Saves Money!
• Sharing hardware is cheaper
• Network versions of applications are cheaper
• Productivity improves with common access
• Increased security

6
LANs often Link to Legacy Systems
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What is Telnet?

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

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Using Telnet
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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 illegally
• Utah 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.

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LANs Carry Identifiable Traffic
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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 servers usual
  operating system is replaced by a network
  operating system

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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

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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 boards
• Modem servers - for dialing out of the network
• Remote access servers - for dialing into the
  network
• Middleware servers for managing communications
  and transaction load

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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?
15
Components of a 10BaseT Network
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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

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NICs
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NICs Match the Network
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Putting it Together
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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

21
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.

22
Cable Limits the Distance of a LAN
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Types of Fiber Optic Connectors

• SC Stick Click
• ST Stick Turn

24
Network Configuration

• There are two fundamental network configurations
• Point-to-point configuration (2-point) -
  sometimes called dedicated circuits
• Multipoint configuration (or multidrop)

25
Connectivity
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Media Selection Criteria

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

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Network Hubs

• Network hubs go by many names depending on the
  type of network and the specific vendor
• Concentrator
• Multistation access unit (MAU)
• Transceiver
• Repeater

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Network Hubs

• Network hubs serve two purposes
• They provide an easy way to connect network
  cables
• Hubs 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

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Connecting to a NIC
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Hubs

• Come in common speeds to match NICs
• 10, 100, 10/100, 1000
• Variable number of connection ports
• 8, 16, 24

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Hubs

• Single-hub (repeater) or single-switch LAN
• Share speed of network
• 200 meter maximum distance span between farthest
  two stations with UTP
• What is a USB hub?

Y
100 m
100 m
X
200 m
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How Hubs Work
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Ethernet 802.3 Physical Layer

• Topology Order in which stations receive bits
• Ethernet hubs use a bus topology
• Signal is broadcast
• All stations receive almost simultaneously

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Hubs

• Multiple-hub LANs
• Increase maximum distance span

100 m
100 m
100 m
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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
10Base-T hubs
500m, 4 hubs
100m
100m
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Multiple Hubs in 10Base-T

• Practical Limit in 10Base-T is Number of Stations
• Degradation 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 spans
• It is possible to have a LAN with more than a 200
  meter maximum span

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Physical Layer 802.3 UTP Standards

• Wiring
• 100 meters maximum UTP distance hub-to-station or
  hub-switch
• 200 meters maximum distance between stations

200 m
100 m
100 m
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Mixing Circuit Media
39
Hooking up a Network
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Connections Through a Hub
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Multiple Hubs in 100Base-TX

• Limit of Two Hubs in 100Base-TX
• Must be within a few meters of each other
• Maximum span is 200 meters
• Shorter maximum span than 10Base-T

2 Collocated Hubs
100m
100Base-TX Hubs
100m
200 m
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How Would You Wire This?
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Business Issues Remote Access

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

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Categories of Remote Access

• Telecommuting
• Costs connect charges, equipment, wiring
• Mobile computing
• Anywhere communication
• Technical Support
• Costs of on-site service

46
Design Steps for Dial-up

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

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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?

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Logical Topology

• Remote node
• Operate as locally connected
• Applications run on remote PC
• Minimize downloads
• Remote control
• Simulates a PC attached to the network
• Drives are mapped to network

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Remote Node vs. Remote Control Installations
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Security Issues Remote Access

• Password management
• Verifying employee access
• Locking accounts
• Multiple tries may be a hacker
• Separation of data
• Original data should be stored behind a firewall
• Encryption
• Preventing sniffing
• Dial-back
• Insure correct user
• Authentication
• Device or software?

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Physical Design Options

• Dedicated PC
• Communications server
• LAN modem

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Physical Topology Alternative Access Points
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Network Access Methods

• PSTN
• Modem _at_ 56Kbps
• Analog
• ISDN
• ISDN modem
• Digital
• XDSL
• DSL modem
• Digital service on top of PSTN
• VPN
• Secure communication channel
• VPN software, ISP

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Alternative Network Access Services
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Remote Access Hardware

• Communication servers
• Simultaneous logins
• Monitor with phone lines
• Requires multiple NICs to network resources
• Modems connect to serial ports
• Can be used for remote control applications in
  lieu of PCs
• Acts as a gateway

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Remote Node Server Solutions

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

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Remote Node Software

• Common software include Windows NT RAS and
  Netware Connect
• Client OS compatibility

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Communications Server Components
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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

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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

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Circuit Packet Switching

• Differences center on voice and data transmission
• Circuit switching
• Continuous, exclusive, temporary
• Low latency and few delays
• Packet switching
• Data transmitted in a container (packet)
• Routed base on header information
• Routers distribute data to appropriate destination

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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