Data Communications Fundamentals

• The fundamental problem of communication is reproducing a message selected at one point at another point, either exactly or approximately.

Data Communications

• Consists of a communication component including protocols, senders, receivers, messages, and transmission media.

Trends in Contemporary Data Communications:

• High and steady traffic growth
• Development of new services
• Advances in technology.
• Significant change in requirements, particularly the emergence of high-speed LANs.
• Increased corporate WAN needs
• Advances in digital electronics

A Communications Model

• Consists of a source system and destination system.
• SourceSystem
  • Generates data.
  • Converts data into transmittable signals via a transmitter.
• Transmission System
  • Carries data from the source to the destination.
• Destination System
  • Converts the received signal into data via a receiver.
  • Takes the incoming data as its destination.
• An example of this model is a workstation connected to a server via a modem and the public telephone network.

Communications Tasks

• Transmission system utilization and addressing.
• Interfacing and routing.
• Signal generation and recovery.
• Synchronization and message formatting.
• Exchange management and security.
• Error detection/correction and network management.
• Flow control.
• Key tasks performed in data communication systems include:
  • Efficient use of transmission facilities shared by communicating devices.
  • A device must interface with the transmission system.
  • Signal generation is required once an interface is established.
  • Synchronization between transmitter and receiver is needed to determine signal arrival and end.
  • Requirements for communication between parties are collected under exchange management.
  • Error detection and correction are necessary in circumstances where errors cannot be tolerated.
  • Flow control assures that sources do not overwhelm destinations.
  • Addressing and routing: a source system indicates the identity of the intended destination and chooses a specific route.
  • Recovery allows interrupted transactions to resume activity.
  • Message formatting involves an agreement between parties on the form of data to be exchanged.
  • Security measures are frequently needed in data communication systems.
  • Network management capabilities are needed to configure the system and monitor its status.

Data Communications Model

• Digital Bit Stream -> Analog Signal -> Analog Signal -> Digital Bit Stream.
• This goes from source to destination.

Transmission Medium

• Selection involves balancing business needs with carrier availability.

Networking

• Growth of computers is driving the need for interconnection.
• Rapid integration of voice, data, image, and video technologies is occurring.
• Two Broad Categories of Communications Networks:
  • Local Area Network (LAN)
  • Metropolitan Area Network (MAN)
  • Wide Area Network (WAN)

Wide Area Networks (WANs)

• Spans a large geographical area
• connects two or more LANs and MANs through public networks like the telephone system and the Internet.
• WANs connect through leased lines or satellites, relying on common carrier circuits.
• WANs have been implemented using technologies like:
  • Circuit Switching
  • Packet Switching
  • Frame Relay
  • Asynchronous Transfer Mode (ATM).

Circuit Switching

• Uses a dedicated communications path for the duration of the conversation, comprising a sequence of physical links with a dedicated logical channel.
• Eg. telephone network

Packet Switching

• Transmits data in small chunks (packets) without needing a dedicated communications path.
• Packets are passed between source and destination.
• For terminal-to-computer and computer-to-computer communications.

Frame Relay

• Packet switching systems have overhead to compensate for errors, frame relay provides high data rates and low error rates on modern WAN links.
• Modern systems are reliable
• Errors can be caught in the end system.
• Frame Relay provides higher speeds with reduced error control overhead.

Asynchronous Transfer Mode (ATM)

• The culmination of developments in circuit switching and packet switching.
• The evolution of frame relay involves fixed packet lengths with little overhead for error control.
• Anything from 10Mbps to Gbps
• It allows constant data rates using a packet switching technique with multiple virtual circuits.

Local Area Networks (LANs)

• Smaller scope is intended for buildings or small campuses.
• Usually owned by the same organization and have much higher data rates.
• Switched LANs, e.g., Ethernet and wireless LANs.

Metropolitan Area Networks (MANs)

• Act as a middle ground between LAN and WAN.
• Spanning a city or metro area with high-speed connections.
• A private or public network, characterized by high speed and a large area.