Ch'2 Basic Concepts

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Ch.2 Basic Concepts

• Lecturer Tae-Hyong Kim (B201-4)
• thkim_at_cespc1.kumoh.ac.kr

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Contents

• Fives general concepts provide the basis for the
  relationship between the communicating devices.
• Line configuration
• Topology
• Transmission mode
• Categories of Networks
• Internetworks

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2.1 Line Configuration

• Refer to the way two or more communication
  devices attach to a link.
• Defines the attachment of communication devices
  to a link

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2.1 Line Configuration

• Point-to-point

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2.1 Line Configuration

• Multipoint

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2.2 Topology

• Refer to the way a network is laid out, either
  physically or logically
• Defines the physical or logical arrangement of
  link in a network
• A consideration when choosing a topology is the
  relative status of the devices to be linked.
• peer-to-peer
• the devices share the link equally(ring, mesh)
• primary-secondary
• one device controls traffic
• the others must transmit through it

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Categories of topology

• Interconnection topology
• Satellite, ground radio system
• broadcast

• Topologies for a point-to_point subnet

• Star
• Ring
• Tree
• Complete (mesh)
• Intersecting ring
• Irregular

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Star

• Each device has a dedicated point-to-point link
  only to a central controller, usually called a
  hub
• Advantage
• Each device needs only one link and one I/O port
  to connect it to any number of others (easy to
  install and reconfigure)
• Robustness
• if one link fails, only that link is affected

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Ring

• Each device has a dedicated point-to-point line
  configuration only with the two devices on either
  side of it
• Advantage
• relatively easy to install and reconfigure
• Disadvantage
• unidirectional traffic
• break in the ring can disable the entire network
• needs dual ring

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Tree

• a variation of a star
• active hub(central hub)
• contains a repeater, which is a hardware device
  that generates the received bit patterns before
  sending them out
• passive hub
• provides a simple physical connection between the
  attached devices
• Advantage Disadvantage
• are generally the same as those of a star

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Mesh(Complete)

• dedicated point-to-point link to every other
  device.
• n(n-1)/2 physical channels to link n devices.
• Advantages
• Traffic guarantees due to use of dedicated links
• Provides robust, Privacy and security.
• Easy fault identification and fault isolation.
• Disadvantages
• related to the amount of cabling and the number
  of I/O ports
• installation and reconfiguration are difficult
• because every device must be connected
• Space problem
• the sheer bulk of the wiring can be greater
• Expensive
• N-1 I/O ports/devices/cable

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Bus

• One long cable acts as a backbone to link all the
  device in the network (multipoint)
• Nodes are connected to the bus cable by drop
  lines and taps
• drop line
• A connection between the device and the main
  cable
• tap
• A connector to create a contact with the metallic
  core
• limit on the no. of taps and on the distance
  between taps
• Advantage
• easy installation, Less cabling than star type
• Disadvantage
• Difficult to reconfiguration and isolate fault
• A fault/break stops all transmission

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Hybrid topology
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2.3 Transmission mode
to define the direction of signal flow between
two linked devices
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2.3 Transmission mode

• Simplex
• unidirectional, as on a one-way street
• keyboard, monitor

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2.3 Transmission mode

• Half-Duplex
• each station can both transmit and receive, but
  not at the same time

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2.3 Transmission mode

• Full-Duplex
• both stations can transmit and receive
  simultaneously

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2.4 Categories of Networks

• three primary categories
• size, ownership, distance it cover, physical
  architecture

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2.4 Categories of Networks

• LAN(Local Area Networks)
• usually privately owned and links the devices in
  a single office, building or campus

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2.4 Categories of Networks

• LAN(Local Area Networks)
• Distinction
• Size ? Km
• Transmission tech.
• 10-100Mbps
• Low delay
• Very few errors
• Topology
• Bus, Ring, Star
• Ethernet IEEE 802.3
• Decentralized control
• At 10 to 100Mbps
• Transmit whenever
• If collide,
• just waits random time
• and tries again

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2.4 Categories of Networks

• Allocation in broadcast networks
• static allocation
• round robin algorithm (Token Ring/Bus)
• wastes channel capacity
• dynamic allocation
• centralized arbitration unit determines who
  goes next
• decentralized each machine decide for itself
  (CSMA/CD)

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2.4 Categories of Networks

• MAN(Metropolitan Area Networks)
• designed to extend over an entire city
• ex. DQDB, SMDS (Ch.13)

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2.4 Categories of Networks

• WAN(Wide Area networks)
• Provides long-distance transmission of data,
  voice, image, and video information over large
  geographical areas
• country, continent, the whole world

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2.4 Categories of Networks

• Classifying networks by scale

Figure 1.2 Classification of Interconnected
processors by scale
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2.5 Internetwork

• an interconnection of networks by the use of
  internetworking device(router and gateway)
• cf.
• internet an interconnection of networks
• Internet a specific worldwide network

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2.5 Internetwork

• Internetwork (internet)