Computer Networks Chapter 1 (Lecture Notes)

• Star Topology

  • Each device has a dedicated point-to-point link only to a central controller, usually called a hub
  • No direct traffic and link between devices
  • Less expensive
  • Easy to install and reconfigure
  • Robustness
  • Single point of failure
• ACM


  1967
• Physical Layer

  • Physical characteristics of interfaces and media
  • Representation of bits
  • Data rate
  • Synchronization of bits
  • Line configuration (point-to-point or multipoint)
  • Physical topology (mesh, star, ring or bus)
  • Transmission mode (simplex, half-duplex or duplex)
• Data Link Layer

  • Framing
  • Physical addressing
  • Flow control
  • Error control
  • Access control
• Physical layer


  Responsible for movements of individual bits from one hop (node) to the next
• Functions of physical layer

  • Physical characteristics of interfaces and media
  • Representation of bits
  • Data rate
  • Synchronization of bits
  • Line configuration (point-to-point or multipoint)
  • Physical topology (mesh, star, ring or bus)
  • Transmission mode (simplex, half-duplex or duplex)
• Data link layer


  Responsible for moving frames from one hop (node) to the next
• Functions of data link layer

  • Framing
  • Physical addressing
  • Flow control
  • Error control
  • Access control
• Hop-to-hop delivery is handled by the data link layer
• The frame contains physical addresses in the header, which are the only addresses needed at the data link level
• Network layer


  Responsible for the delivery of individual packets from the source host to the destination host
• Functions of network layer

  • Logical addressing
  • Routing
• Source-to-destination delivery is handled by the network layer
• Network (logical) addresses are used for universal communications that are independent of physical network
• Transport layer


  Responsible for the delivery of a message from one process to another
• Functions of transport layer

  • Port addressing
  • Segmentation and reassembly
  • Connection control (Connection-oriented or connection-less)
  • Flow control
  • Error control
• Segmentation and reassembly is handled by the transport layer
• The transport layer ensures reliable process-to-process delivery of a message
• Session layer


  Responsible for dialog control and synchronization
• Functions of session layer

  • Dialog control
  • Synchronization (checkpoints)
• Presentation layer


  Responsible for translation, compression, and encryption
• Functions of presentation layer


  • Translation (EBCDIC-coded text file to ASCII-coded file)
  • Encryption and Decryption
  • Compression
• Application layer


  Responsible for providing services to the user
• Functions of application layer

  • Network virtual terminal (Remote log-in)
  • File transfer and access
  • Mail services
  • Directory services (Distributed Database)
  • Accessing the World Wide Web
• The OSI model has 7 layers, while the TCP/IP model has 4 layers
• The physical and data link layers in the TCP/IP model correspond to the same layers in the OSI model
• The network layer in the TCP/IP model corresponds to the network layer in the OSI model

  
• The transport layer in the TCP/IP model corresponds to the transport layer in the OSI model
• The application layer in the TCP/IP model corresponds to the session, presentation, and application layers in the OSI model
• Physical address

  Imprinted on the NIC, 48-bit (6-byte) address written as 12 hexadecimal digits separated by colons
• Physical addresses change from hop to hop
• Logical address


  IP addresses are 32-bit addresses that uniquely define a host, necessary for universal communications independent of physical network
• Logical addresses usually remain the same, while physical addresses change from hop to hop
• Port address

  16-bit address represented by one decimal number ranging from 0-65535, used to choose a process among multiple processes on the destination host
• Port addresses, like logical addresses, usually remain the same while physical addresses change from hop to hop