Communications Model

Source -> Transmitter -> Transmission System -> Receiver -> Destination

• Point to point communication is not usually practical
  • devices are too far apart
  • large set of devices needed
• Solution is a communications network

Wide Area Network

• Large geographical area
• Rely in part on common carrier circuits
• Enabling technologies
  • Circuit switching
    • dedicated communications path established for duration of the conversation
  • Packet switching
    • data sent out of sequence
    • small chunks of data at a time

Data Flow

• Simplex, unidirectional
• Half-duplex, bidirectional one-at-a-time
• Full-duplex, bidirectional all the time

Host vs Node

Every single device that has an IP address and that is able to consume or produce data in the network is called a host.

Every device is a node but intermediate nodes allow you to transfer and manage data, ex. router, switch, hub, bridge.

Line configuration

• Point-to-point: physical connections between two hosts shared by two devices only
• Multipoint: physical connections between two or more devices.

Network Topologies

The arrangement of the elements (links, nodes, etc.) of a communication network.

4 main types: mesh, star, bus, ring.

Classification of Computer Networks

Local Area Networks

• smaller scope, building or small campus
• usually owned by same organization as attached devices
• data rates are high
• usually broadcast systems
• Wireless LAN
• uses Bus or Ring broadcast networks

Metropolitan Area Network (MAN)

• uses Junction box, and multiple wires connected to houses in neighborhood

Wide Area Networks (WAN)

• relations between hosts on LANs and the subnet

Protocol Architecture

• Protocol: a set of technical rules about how information should be transmitted and received using computers
• task broken into subtasks
• implemented separately in layers in stack
• functions needed in both systems
• peer layers communicate
• two standards
  • OSI reference Model
  • TCP/IP

Key elements of a Protocol

• Syntax
  • data formats
  • signal levels
• Semantics
  • control information
  • error handling
• Timing
  • speed matching
  • sequencing

OSI - The Model

• a layer Model
• each layer performs a subset of the required communication functions
• each layer relies on the lower layer to perform more primitive functions
• each layer provides services to the next higher layer
• changes in one layer should not require changes in other layers

TCP/IP

Has Application, Transport, Network/Internet, Data link and Physical layers

• Physical layer: controls the transmission, encodes data into signals
• Data link: responsible for communication inside the local area network, also responsible for error control
• Network: routing plus sending packets to other networks
• Transport: reliable delivery of data (TCP only)
• Application: suports all the different user applications, ex. HTTPS, MTP, FTP, SSH