Networking standards and the OSI model

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Networking standards and the OSI model
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Contents of lecture

• Organizations that set standards for networking
• OSI model layers
• Communication of systems through OSI model
• Data frames

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Standards

• Standards are documented agreements containing
  technical specifications or other precise
  criteria that stipulate how a particular product
  or service should be designed or performed

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Networking standards organizations

• American National Standards Institute (ANSI)
• Electronics Industry Alliance (EIA)
• Institute of Electrical and Electronic Engineers
  (IEEE)
• International Organisation for Standardization
  (ISO)
• International Telecommunication Union (ITU)

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Networking Standards Organizations

• ANSI
• Industry and government representatives
• Determine standards for the electronics industry
  in addition to other fields
• EIA
• Composed of representatives from electronics
  manufacturing firms across the USA

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Networking Standards Organizations

• IEEE
• International society of engineering
  professionals
• Promotes development and education in the
  electrical engineering and computer science
  fields
• ISO
• Collection of standards organizations
• Goal is to establish international technological
  standards to facilitate global information
  exchange and free-trade

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Networking Standards Organizations

• ITU
• United Nations agency that regulates
  international telecommunications
• Assists developing countries

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OSI Model

• Open Systems Interconnection Model (OSI model)
• Model for understanding and developing
  computer-to-computer communications
• Reference protocol model
• Developed in the 1980s by ISO
• Divides network architecture into seven layers
• Each layer has its own functions
• Together the layers ensure that data are
  delivered in readable, error-free and properly
  sequenced format

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Seven Layers of OSI model
Application
Presentation
Session
Transport
Network
Data Link
Physical
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Seven Layers of OSI Model Physical Layer

• Relates to the physical networking media
• Translates all data received from upper layers
  into signals to be transmitted on a transmission
  medium
• Determines signaling method (I.e. broadband or
  baseband)
• Specifies topology of transmission media
• Sets data transmission rate
• Monitors data error rates
• Controls functional interface, e.g. pin layout,
  connector type

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Some devices operating at the physical level in
networks

• NICs
• Transceivers
• Repeaters
• Hubs

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Seven Layers of OSI model Data Link Layer

• Divided into two sub-layers
• Logical Link Control
• Common interface, reliability and flow control
  services (supervises packet links between nodes)
• Media Access Control

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Data Link Layer (cont.)

• - Establishes and controls the physical path of
  communication to the next network node
• - Data coming from upper protocols are divided
  into logical chunks called frames
• - Adds physical (MAC) address to data frames
• - Responsible for sending receiving and checking
  data frames between nodes
• - Responsible for controlling media access

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Data Frames

• Simplified data frame

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What is a MAC address?

• MAC Media Access Control
• MAC address physical address, usually assigned at
  the factory
• 12 digit hexadecimal number, e.g.
  0757AC1FB276
• Unique for each manufacturer, e.g. 3Com Ethernet
  NICs start with 00608C and Intel NICs start with
  00AA00.
• Used by devices to direct packets to other
  devices

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Methods of Media Access

• Data link layer prescribes the method of media
  access
• - Contention control (every station has equal
  chance at transmission)
• Token passing
• Polling

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What is a logical topology?

• The logical topology relates to the way packets
  move through a network
• The Data Link Layer dictates the logical topology
  of the network
• Where the physical topology dictates the way the
  cables are laid out, the logical topology
  dictates the way data flows

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Devices operating at the Data Link Layer

• Connectivity devices, e.g.
• Bridges
• Switches
• These devices decode frames and use the
  connectivity information to direct information
  intelligently from sender to receiver

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Bridges

• Similar to repeater but it can interpret the data
  that it retransmits
• Bridges analyze incoming frames and make
  decisions on how to direct them to their
  destinations
• They read MAC address information, then decide on
  whether to forward the frame to another segment
  on the network

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Bridges (cont.)
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Switches (Also called switching hubs)

• Subdivide a network into smaller logical pieces
• Can interpret MAC address information
• Resemble multi-port bridges

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Switches (cont)
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Seven Layers of OSI model Network Layer

• - Translations of network (logical) addresses
  into their physical counterparts
• - Decisions on how to route data from sender to
  receiver

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Network layer (cont.)

• Routing deciding which path the data takes
• Static routing vs. dynamic routing

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Network layer (cont.)

• Network layer compensates for disparities in the
  capabilities of devices related to
  sending/receiving of data
• Segmentation vs. Reassembly

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Devices operating at network level

• Routers
• - Routers assist in organizing large networks in
  terms of logical network segments
• Brouters
• - Functions as a bridge on the data link MAC
  sub-layer and as a router on the network layer

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Seven Layers of OSI Model Transport Layer

• - Ensures that data are transferred between
  points reliably, in the correct sequence and
  without errors
• - Flow control
• Gauging the appropriate rate of data
  transmission
• - Sequencing
• Assigning a placeholder to each piece of a data
  block
• - Acknowledgment (ACK)
• Response that confirms to sender that its frame
  was received
• - Breaks long packets into the maximum length
  that the network type can handle
• - Establishes the level of error checking

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Seven Layers of OSI model Session Layer

• - Establishes and maintains communication
  between two nodes on the network
• - Session refers to a connection for data
  exchange between two parties
• - Security authentication, acknowledgement,
  connection release take place in this layer

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Seven Layers of OSI model Presentation layer

• Translates between the application and the
  network, e.g. character set conversion,
  encryption, etc.

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Seven Layers of OSI Model Application Layer

• Provides interface to the software enabling
  programs to use network devices
• Defines interaction between network services
  (applications) and the network
• Services functioning at application layer include
  file, print and messaging services

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Applying the OSI model

• Communications between two systems

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Data transformation
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Frame types

• Ethernet vs Token Ring

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Frame types

• Ethernet

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Frame types

• Token Ring

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IEEE 802 series standards

• Covers physical aspects of networks