Computer Networks

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Computer Networks
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A History Lesson of Networking

• 1969 ARPANET, first packet switched network
  consist of UCLA, Stanford, UC Santa Barbara and
  Utah University
• 1971 first email program
• 1974 TCP/IP
• 1980s Local Area Networks (LANs)
• 1984 OSI Layer
• 1990s WWW / Internetworking

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Why Networking?

• Efficiency and Productivity
• Reliability
• Distributed Systems

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What Applications?

• Client/Server Business Applications
• Electronic Messaging
• Information Retrieval

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Network Classification by Area

• Wide Area Network
• Metropolitan Area Network
• Local Area Network
• Personal Area Network
• Ad Hoc Network

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Protocols

• Driving Force need for different proprietary
  networking system to communicate
• Protocol set of rules for acceptable behaviour
  (how communication should take place in)
• Specifically
• the set of rules used by communicating parties
  for that communication to be successful
• Suite of protocols cover all required behaviour
• Mostly implemented in Software
• Complexity demands that protocols are layered

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Advantages of Layering Protocols

• Dividing complex network operation into more
  manageable layers
• Defining the standard interface for the
  plug-and-play multi-vendor integration
• Facilitate Modular Engineering
• Simplifies Teaching and Learning

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ISO/OSI Reference Model

• ISO in 1984
• Open Systems Interconnect (OSI)
• A design guideline for network layering
• Abstract layers provide different services
• Defines 7 layers of service
• Each layer provides service to adjacent layers
• Each layer communicates with same layer in remote
  machine

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OSI Reference Model
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Layer 1 - Physical

• Physical Layer
• Move bits between devices
• Specifies voltage, wire speed, and pin out cables
• Passes data up to data link layer (and receives
  from data link layer)

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Layer 2 Data Link

• Data Link Layer
• Performs framing of bits, flow and error control
  but not correction
• Responsible for transmission of frames across the
  physical link
• Provide access to media using MAC address
• Passes data between physical and network layers

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• The Institute of Electrical and Electronics
  Engineers (IEEE) has subdivided the data link
  layer into two sublayers Logical Link Control
  (LLC) and Media Access Control (MAC).

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• The Logical Link Control (LLC) 802.2 sublayer is
  responsible for identifying Network Layer
  protocols and then encapsulating them. An LLC
  header tell the Data Link Layer what to do with
  the packet if a frame is coming. Also provide
  flow control and sequencing of control bits
• The Media Access Control (MAC) sublayer of the
  data link layer manages protocol access (logical
  topologies) to the physical network medium. The
  IEEE MAC specification defines MAC addresses,
  which enable multiple devices to uniquely
  identify one another at the data link layer. IEEE
  802.3 dan 802.5

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Layer 3 - Network

• Network Layer
• Passes data between data link and transport
  layers
• Responsible for routing data across a network,
  from source to destination using network-wide
  addressing
• Pass data between (separate) subnetworks
• Hides network topology from higher layers

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Layer 4 - Transport

• Transport Layer
• Passes data between network and session layers
• Provides reliable end-to-end delivery of data,
  including flow and error control of packets
• Fragmentation of large messages
• Quality of Service (QoS), usually with layer 3
• Last of the pure network layers

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Layer 5 - Session

• Session Layer
• Passes data between presentation and transport
  layers
• Responsible for managing network sessions (series
  of related data streams)
• Provides synchronization and scheduling

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Layer 6 - Presentation

• Presentation Layer
• Passes data between application and session
  layers
• Provides translation services for data to ensure
  applications are using compatible formats
• E.g. converting from ASCII to EBCDIC text
  representations

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Layer 7 - Application

• Application Layer
• Passes data to presentation layer (and receives
  from presentation layer)
• to and from the user!
• Communicates with remote applications
• Determines the user capability within the network

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Data Encapsulation
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Data Encapsulation
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OSI Layer vs. TCP/IP Layer
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FTP File Transfer Protocol HTTP Hypertext
Transfer Protocol WAP Wireless Application
Protocol SMTP Simple Mail Transfer Protocol
5-7
TCP
UDP
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IP
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1-2
e.g. IEEE 802.x
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Some Protocols in TCP/IP Suite
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Quiz

• Protocols
• What are they?
• Why do we layer protocols?
• ISO/OSI 7 layer reference model
• How does the OSI abstract services?
• How does data pass between layers (local/remote)?
• How does Internet stack relate to OSI?