Lecture Outline

1
Lecture Outline

• Data Requirements
• Digital vs. Analog
• Bandwidth
• Network Models
• Transmission Media
• LANs Internetworking

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Multimedia

• Data
• Voice
• Image
• Video

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Digitising Voice

• Analog voice data can be sent over digital
  networks using a pair of special devices called
  CODECs (Coder/Decoder).
• These devices perform PCM pulse code
  modulation.

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Compression

• Compression is used to reduce the amount of
  storage required and the amount of bandwidth
  required in transport by encoding series of
  occurrences of such things such as blank spaces
  in a document. This encoding reduces the
  redundancies transmitted.
• Lossy vs. lossless compression

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Effective bandwidth

• Effective bandwidth is equal to the channels
  native bandwidth, minus the effects of noise and
  overhead plus that gained due to compression.

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Bandwidth Examples

• Modem 28,800 bit/s
• ISDN 64 Kbit/s
• Ethernet 10 Mbit/s
• Token Ring 4/16 Mbit/s
• Fast-Ethernet 100 Mbit/s
• FDDI 100 Mbit/s
• ATM gt 155 Mbit/s

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Transfer rates for 10 MB file
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Benefits of digital transmission

• Digital transmission offers four key benefits
  over analog transmission.
• Fewer errors than analog transmission.
• Permits higher maximum transmission rates.
• More secure.
• Integrating voice, video and data on the same
  circuit is far simpler with digital transmission.

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Digital vs. Analog

• Data
• Data Representation
• Signal
• Encoding of information onto signal
• Transmission

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Data Signals
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Modulation

• Modulation is the technique of modifying a
  carrier signal to represent data.
• There are three fundamental modulation methods
• Amplitude Modulation (AM)
• Frequency Modulation (FM)
• Phase Modulation(PM)

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Amplitude Modulation and ASK
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Frequency Modulation and FSK
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Phase Modulation and PSK
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Sending Multiple Bits Simultaneously
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Network Model

• A method of describing and analyzing data
  communication networks, by breaking the entire
  set of communication functions into a series of
  layers, each of which can be defined separately.
• This allows vendors to develop software and
  hardware to provide the functions separately.

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4-layer model

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Networking Model
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Guided Media

• Twisted Pair Wire - insulated pairs of wire,
  twisted to minimize electromagnetic interference
  between wires.
• Coaxial Cable - wire with a copper core and an
  outer cylindrical shell for insulation.
• Fiber Optic Cable - high speed streams of light
  pulses from lasers or LEDs carry information
  inside hair-thin strands of glass or plastic
  called optic fibers.

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Twisted Pair

• (a) Category 3 UTP.
• (b) Category 5 UTP.

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Radiated Media

• Radio (wireless) data transmission uses the same
  basic principles as standard radio transmission.
• Infrared Transmission uses low frequency light
  waves to carry data through the air on a direct
  line-of-sight path between two points.

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Radiated Media

• A microwave is an extremely high frequency radio
  communication beam that is transmitted over a
  direct line-of-sight path between two points.
• Transmission via satellite is similar to
  transmission via microwave except, instead of
  transmitting to another nearby microwave dish
  antenna, it transmits to a satellite 22,300 miles
  in space.

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The Electromagnetic Spectrum
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Communication Satellites
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Media Selection
Guided Media Radiated Media
Network Transmission Error Media Type Cost Di
stance Security Rates Speed Twisted
Pair LAN Low Short Good Low Low-high Coaxial
Cable LAN Mod. Short Good Low Low-high Fiber
Optics any High Mod.-long V. Good V.Low High-V.Hig
h
Network Transmission Error Media Type Cost Di
stance Security Rates
Speed Radio LAN Low Short Poor Mod
Low Infrared LAN, BN Low Short Poor Mod
Low Microwave WAN Mod Long
Poor Low-Mod Mod Satellite WAN Mod Long
Poor Low-Mod Mod
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• LANs VLANs

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Media Access Control

• Ethernet uses a contention-based technique called
  Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD)
• Like all contention-based techniques, CSMA/CD is
  very simple wait until the bus is free and then
  transmit.
• If two computers attempt to transmit at the same
  time, they detect the collision, send a jamming
  signal, wait a random amount of time, then
  re-broadcast.

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Switched Ethernet

• The concept behind switched ethernet - and all
  switched media technologies - is simple replace
  the LAN hub with a switch. Each computer now has
  its own dedicated point-to-point circuit.
• Switched ethernet dramatically improves LAN
  performance. However, since much of the network
  traffic is to and from the server, the circuit to
  the server is often the network bottleneck.

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1.       
Types of Ethernet
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Virtual LAN Design

• Switches also have enabled the creation of
  Virtual LANs (VLANs). VLANs are usually faster
  and provide greater opportunities to manage the
  flow of traffic on the LAN.
• VLANs are groups of computers in an intelligent
  switched network.

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Port-Based VLANs
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MAC-Based VLANsLayer-2 VLANs

• MAC-based VLANs use the data link layer addresses
  to form the VLAN groups.
• The advantage is that they are simpler to manage
  when computers are moved.

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IP-Based VLANsLayer-3 VLANs

• IP-based VLANs use the network layer address
  (i.e. TCP/IP address) to form the VLAN groups.
  Layer-3 VLANs reduce the time spent reconfiguring
  the network when a computer is moved as well.
• Some layer-3 VLANs can also use the network layer
  protocol to create VLAN groups. This flexibility
  enables even greater precision in the allocation
  of network capacity.

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Application-Based VLANsLayer-4 VLANs

• Application-based VLANs use the application layer
  protocol in combination with the data link layer
  and network layer addresses to form the VLAN
  groups.
• The advantage is a very precise allocation of
  network capacity.

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• Internetworking Devices

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Repeaters

• A repeater is the simplest type of hardware that
  can be used to connect network segments.
• Receives a signal and regenerates it.
• Operates at the physical layer of OSI model.
• Transparent to data flow.
• Repeaters are used mainly to extend coverage of a
  network by extending the length of any segment.

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Bridges
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Routers
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Gateways
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Comparison of Linkage Alternatives
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Comparison of Linkage Alternatives
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Comparison of Linkage Alternatives