networking notes

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5. Introduction to Networking
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What is a Network?

• A network consists of 2 or more computers
  connected together, and they can communicate and
  share resources (e.g. information)

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Why Networking?

• Sharing information i.e. data communication

• Do you prefer these?

• Or this?

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• Sharing hardware or software

• E.g. print document

• Centralize administration and support

• E.g. Internet-based, so everyone can access the
  same administrative or support application from
  their PCs

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How many kinds of Networks?

• Depending on ones perspective, we can classify
  networks in different ways

• Based on transmission media Wired (UTP, coaxial
  cables, fiber-optic cables) and Wireless
• Based on network size LAN and WAN (and MAN)
• Based on management method Peer-to-peer and
  Client/Server
• Based on topology (connectivity) Bus, Star, Ring
  

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Transmission Media

• Two main categories
• Guided ? wires, cables
• Unguided ? wireless transmission, e.g. radio,
  microwave, infrared, sound, sonar
• We will concentrate on guided media here
• Twisted-Pair cables
• Unshielded Twisted-Pair (UTP) cables
• Shielded Twisted-Pair (STP) cables
• Coaxial cables
• Fiber-optic cables

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Twisted-Pair Cables

• If the pair of wires are not twisted,
  electromagnetic noises from, e.g., motors, will
  affect the closer wire more than the further one,
  thereby causing errors

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Copper - Twisted Pair

• Dialup over telephone line.
• DSL (Digital Subscriber Line)
• High-speed (256 Kbps 55 Mbps), Full-duplex.
• Asymmetric Digital Subscriber Line (ADSL) and
  High-bit-rate Digital Subscriber Line (HDSL)
• CAT5
• Ethernet cable standard defined by the Electronic
  Industries Association and Telecommunications
  Industry Association (EIA/TIA).
• Speeds up to 100 Mbps.
• Connector
• RJ-45 - Standard connectors used for unshielded
  twisted-pair cable.

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• Unshielded Twisted-Pair (UTP)
• Typically wrapped inside a plastic cover (for
  mechanical protection)
• A sample UTP cable with 5 unshielded twisted
  pairs of wires

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• Shielded Twisted-Pair (STP)
• STP cables are similar to UTP cables, except
  there is a metal foil or braided-metal-mesh cover
  that encases each pair of insulated wires

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• Categories of UTP Cables
• EIA classifies UTP cables according to the
  quality
• Category 1 ? the lowest quality, only good for
  voice, mainly found in very old buildings, not
  recommended now
• Category 2 ? good for voice and low data rates
  (up to 4Mbps for low-speed token ring networks)
• Category 3 ? at least 3 twists per foot, for up
  to 10 Mbps (common in phone networks in
  residential buildings)
• Category 4 ? up to 16 Mbps (mainly for token
  rings)
• Category 5 (or 5e) ? up to 100 Mbps (common for
  networks targeted for high-speed data
  communications)
• Category 6 ? more twists than Cat 5, up to 1 Gbps

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Common Network Media

• Electrical (copper)
• Coaxial Cable
• Single copper conductor in the center surrounded
  by a plastic layer for insulation and a braided
  metal outer shield.
• Twisted pair
• Four pairs of wires twisted to certain
  specifications.
• Available in shielded and unshielded versions.
• Fiber-optic - A cable, consisting of a center
  glass core surrounded by layers of plastic, that
  transmits data using light rather than
  electricity.
• Atmosphere/Wireless Uses Electromagnetic waves.
  whose frequency range is above that of
  microwaves, but below that of the visible
  spectrum.
• Choose Media based on
• Wiring configurations
• Distance and location limitations
• Speed
• Reliability
• Security
• Budget

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• Coaxial Cables
• In general, coaxial cables, or coax, carry
  signals of higher freq (100KHz500MHz) than UTP
  cables
• Outer metallic wrapping serves both as a shield
  against noise and as the second conductor that
  completes the circuit

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• Infrared light is transmitted through fiber and
  confined due to total internal reflection.
• Fibers can be made out of either plastic or
  glass.
• Used for high speed backbones and pipes over long
  distances.
• Comparatively expensive.

Optical Fiber
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• Fiber-Optic Cables
• Light travels at 3?108 ms-1 in free space and is
  the fastest possible speed in the Universe
• Light slows down in denser media, e.g. glass
• Refraction occurs at interface, with light
  bending away from the normal when it enters a
  less dense medium
• Beyond the critical angle ? total internal
  reflection

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• An optical fiber consists of a core (denser
  material) and a cladding (less dense material)
• Simplest one is a multimode step-index optical
  fiber
• Multimode multiple paths, whereas step-index
  refractive index follows a step-function profile
  (i.e. an abrupt change of refractive index
  between the core and the cladding)
• Light bounces back and forth along the core
• Common light sources LEDs and lasers

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• Advantages and Disadvantages
• Noise resistance ? external light is blocked by
  outer jacket
• Less signal attenuation ? a signal can run for
  miles without regeneration (currently, the lowest
  measured loss is about 4 or 0.16dB per km)
• Higher bandwidth ? currently, limits on data
  rates come from the signal generation/reception
  technology, not the fiber itself
• Cost ? Optical fibers are expensive
• Installation/maintenance ? any crack in the core
  will degrade the signal, and all connections must
  be perfectly aligned

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• 10BaseT
• Ethernet specification for unshielded twisted
  pair cable (category 3, 4, or 5), transmits
  signals at 10 Mbps (megabits per second) with a
  distance limit of 100 meters per segment.
• 10BaseF
• Ethernet specification for fiber optic cable,
  transmits signals at 10 Mbps (megabits per
  second) with a distance limit of 2000 meters per
  segment.
• 100BaseT
• Ethernet specification for unshielded twisted
  pair cabling that is used to transmit data at 100
  Mbps (megabits per second) with a distance limit
  of 100 meters per segment.
• 1000BaseTX
• Ethernet specification for unshielded twisted
  pair cabling that is used to transmit data at 1
  Gbps (gigabits per second) with a distance
  limitation of 220 meters per segment.

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LAN and WAN

• Local Area Network (LAN)
• Small network, short distance
• A room, a floor, a building
• Limited by no. of computers and distance covered
• Usually one kind of technology throughout the LAN
• Serve a department within an organization
• Examples
• Network inside the Student Computer Room
• Network inside CF502
• Network inside your home

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LANs

• Definition LAN
• "local area network"
• Is a group of computers and associated devices
  that share a common communications line or
  wireless link and typically share the resources
  of a single processor or server within a small
  geographic area (for example, within an office
  building).
• Usually, the server has applications and data
  storage that are shared in common by multiple
  computer users.
• A local area network may serve as few as two or
  three users (for example, in a home network) or
  many as thousands of users.

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LANs

• Definition Wireless LAN
• A local area network that transmits over the air
  typically in an unlicensed frequency such as the
  2.4GHz band.
• A wireless LAN does not require lining up devices
  for line of sight transmission.
• Wireless access points (base stations) are
  connected to an Ethernet hub or server and
  transmit a radio frequency over an area of
  several hundred to a thousand feet which can
  penetrate walls and other non-metal barriers.
• Roaming users can be handed off from one access
  point to another like a cellular phone system.
• Laptops use wireless network cards that plug into
  an existing PCMCIA slot or that are self
  contained on PC cards, while stand-alone desktops
  and servers use plug-in cards (ISA, PCI, etc.).

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LANs

• Characteristics LAN
• Topology
• The geometric arrangement of devices on the
  network or the shape of a local-area network
  (LAN) or other communications system.
• Protocols
• The rules and encoding specifications for sending
  data. The protocol defines the format and meaning
  of the data that is exchanged. The protocols also
  determine whether the network uses a peer-to-peer
  or client/server architecture.
• Media
• Devices can be connected by twisted-pair wire,
  coaxial cables, or fiber optic cables. Some
  networks do without connecting media altogether,
  communicating instead via radio waves.

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• Wide Area Network (WAN)
• A network that uses long-range telecommunication
  links to connect 2 or more LANs/computers housed
  in different places far apart.
• Towns, states, countries
• Examples
• Network of our Campus
• Internet

Your home
USA
WAN
Student Computer Centre
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• Example WAN technologies
• ISDN Integrated Service Digital Network
• Basic rate 192 Kbps Primary rate 1.544Mbps
• T-Carriers ? basically digital phone lines
• T1 1.544Mbps T3 28?T1
• Frame relay
• Each link offers 1.544Mbps or even higher
• ATM Asynchronous Transfer Mode
• Support B-ISDN 155Mbps or 622Mbps or higher
• SONET Synchronous Optical Network
• Basic rate OC1 51.84Mbps
• Support OC12 and up to OC192 (9953.28Mbps) or
  even higher in the future

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• Example of WAN Broadband Cable Network

• Cable TV services have been extensively developed
  in most modern cities
• Cable TV companies try to make use of their
  coaxial cable installed (that are supposed to
  carry TV signals) to deliver broadband data
  services
• Many cable network wiring has been replaced with
  hybrid fiber-coax (HFC) ? i.e. use of fiber-optic
  cable to connect to the subscribers buildings,
  and then the original coaxial cable to connect to
  each household

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The connection is shared by a number of
subscribers, hence may raise performance and
security problems
PC
TV
Fiber-optic cable
Cable Drop
Cable company
Coaxial Cable
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• Cable is an asymmetrical technology
• Downstream max 36 Mbps
• Upstream max 10 Mbps
• May be reduced to 3 10 Mbps downstream and 2
  Mbps upstream, depending on no. of subscribers
• Need a special cable modem

Ethernet link to PC
Teryon Cable Modem
Coaxial link from cable TV socket
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Wireless Media

• Wireless LAN or WLAN
• Wireless local area network that uses radio
  waves as its carrier
• Wi-Fi ("Wireless Fidelity)
• A set of standards for WLANs based on IEEE 802.11
  
• Wi-Max
• Emerging technology that can cover ranges up to
  10 miles or more
• Satellite/Microwave
• High speed media used for longer distances and
  remote locations

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Sample LAN ImplementationHome Configuration
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Sample LAN ImplementationBusiness Configuration
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Sample LAN ImplementationBusiness Configuration
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Topology ? 3 basic types

• How so many computers are connected together?
• Bus Topology Ring Topology
• Star Topology

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LANs

• Topology types
• bus topology All devices are connected to a
  central cable, called the bus or backbone. Bus
  networks are relatively inexpensive and easy to
  install for small networks. Ethernet systems use
  a bus topology.
• star topology All devices are connected to a
  central hub. Star networks are relatively easy to
  install and manage, but bottlenecks can occur
  because all data must pass through the hub. This
  is not much of a problem anymore with the
  widespread deployment of switches.
• ring topology All devices are connected to one
  another in the shape of a closed loop, so that
  each device is connected directly to two other
  devices, one on either side of it. Ring
  topologies are relatively expensive and difficult
  to install, but they offer high bandwidth and can
  span large distances.

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• Bus Topology
• Simple and low-cost
• A single cable called a trunk (backbone, segment)
• Only one computer can send messages at a time
• Passive topology - computer only listen for, not
  regenerate data

• Star Topology
• Each computer has a cable connected to a single
  point
• More cabling, hence higher cost
• All signals transmission through the hub if
  down, entire network down
• Depending on the intelligence of hub, two or more
  computers may send message at the same time

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How to construct a network with Bus / Star
Topology?
Bus Topology
Coaxial cable
Star Topology
BNC T-Connector
Network Card
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• Ring Topology
• Every computer serves as
• a repeater to boost signals
• Typical way to send data
• Token passing
• only the computer who
• gets the token can send
• data
• Disadvantages
• Difficult to add computers
• More expensive
• If one computer fails, whole network fails

T
T
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Peer-to-Peer Networks

• Peer-to-peer network is also called workgroup
• No hierarchy among computers ? all are equal
• No administrator responsible for the network

Peer-to-peer
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• Advantages of peer-to-peer networks
• Low cost
• Simple to configure
• User has full accessibility of the computer

• Disadvantages of peer-to-peer networks
• May have duplication in resources
• Difficult to uphold security policy
• Difficult to handle uneven loading

• Where peer-to-peer network is appropriate
• 10 or less users
• No specialized services required
• Security is not an issue
• Only limited growth in the foreseeable future

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Clients and Servers

• Network Clients (Workstation)
• Computers that request network resources or
  services
• Network Servers
• Computers that manage and provide network
  resources and services to clients
• Usually have more processing power, memory and
  hard disk space than clients
• Run Network Operating System that can manage not
  only data, but also users, groups, security, and
  applications on the network
• Servers often have a more stringent requirement
  on its performance and reliability

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• Advantages of client/server networks
• Facilitate resource sharing centrally
  administrate and control
• Facilitate system backup and improve fault
  tolerance
• Enhance security only administrator can have
  access to Server
• Support more users difficult to achieve with
  peer-to-peer networks

• Disadvantages of client/server networks
• High cost for Servers
• Need expert to configure the network
• Introduce a single point of failure to the system

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Network Hardware

• Hub
• An unintelligent network device that sends one
  signal to all of the stations connected to it.
• All computers/devices are competing for attention
  because it takes the data that comes into a port
  and sends it out all the other ports in the hub.
• Traditionally, hubs are used for star topology
  networks, but they are often used with other
  configurations to make it easy to add and remove
  computers without bringing down the network.
• Resides on Layer 1 of the OSI model

OSI Model Layers
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
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• Switch
• Split large networks into small segments,
  decreasing the number of users sharing the same
  network resources and bandwidth.
• Understands when two devices want to talk to each
  other, and gives them a switched connection
• Helps prevent data collisions and reduces network
  congestion, increasing network performance.
• Most home users get very little, if any,
  advantage from switches, even when sharing a
  broadband connection.
• Resides on Layer 2 of the OSI model.

OSI Model Layers
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
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Network Hardware

• Bridge
• Connects two LANs and forwards or filters data
  packets between them.
• Creates an extended network in which any two
  workstations on the linked LANs can share data.
• Transparent to protocols and to higher level
  devices like routers.
• Forward data depending on the Hardware (MAC)
  address, not the Network address (IP).
• Resides on Layer 2 of the OSI model.

OSI Model Layers
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
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Network Hardware

• Repeater
• Used to boost the signal between two cable
  segments or wireless access points.
• Can not connect different network architecture.
• Does not simply amplify the signal, it
  regenerates the packets and retimes them.
• Resides on Layer 1 of the OSI model.

OSI Model Layers
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
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Network Hardware

• Router
• A device that connects any number of LANs.
• Uses standardized protocols to move packets
  efficiently to their destination.
• More sophisticated than bridges, connecting
  networks of different types (for example, star
  and token ring)
• Forwards data depending on the Network address
  (IP), not the Hardware (MAC) address.
• Routers are the only one of these four devices
  that will allow you to share a single IP address
  among multiple network clients.
• Resides on Layer 3 of the OSI model.

OSI Model Layers
7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
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Network Hardware

• Additional Network Hardware Devices
• Network Interface Cards (NICs)
• Puts the data into packets and transmits packet
  onto the network.
• May be wired or wireless.
• Gateway
• Connects networks with different protocols like
  TCP/IP network and IPX/SPX networks.
• Routers and Gateways often refer to the same
  device.
• Proxy server
• Isolates internal network computers from the
  internet.
• The user first access the proxy server and the
  proxy server accesses the internet and retrieves
  the requested web page or document. The user then
  gets a copy of that page from the proxy server.

Source http//www.camas.wednet.edu/chs/tech/compu
ter_tech/info/routers_hubs_bridges.htm