Computer Networks and Communications

Posted on Sep 5, 2024 in Computers

Circuit Switching

Circuit switching establishes a dedicated communications channel between two stations. Resources are reserved for transmission, and the switching network is for the circuit’s exclusive use during the connection. The transmission is transparent because, once connected, it seems as if the devices are directly connected. Phases:

  1. Establishment of the circuit
  2. Data Transfer
  3. Disconnecting the circuit

Four Points to Highlight in Circuit Switching

  • Circuit switching occurs at the physical level.
  • Before communication, stations must reserve resources to use during communication.
  • Data transfer between two stations is done in packets (signal transfer at the physical level).
  • There is no address for data transfer. Of course, there is an end-to-end address used during the establishment phase.

Packet Switching

Packet switching consists of a “mesh” interconnection provided by telecommunications services, through which packets travel from source to destination. There is no allocation of resources for a packet, meaning there is no reserved bandwidth on links and no planned processing time for each package.

Datagram Networks

A datagram is a separate package fragment with sufficient information to be independently addressed. The structure is a datagram header and data. Datagrams are independent and can arrive out of order and with different delays. The switching of datagrams belongs to the network level. Another name is a non-connection-oriented network because there is no establishment or release phase. Data is sent without the receiver’s confirmation; the sender doesn’t care if the receiver is listening or not.

In a Datagram Network

  • Routing tables store the destination addresses and output ports for forwarding. The routing tables are dynamic and are updated regularly.
  • Destination Address: When the switch receives the packet, it examines this address and checks the routing table to find the corresponding output port to forward the packet.
  • Delay: Although there is no establishment and release phase, each packet may experience a delay on a switch before being forwarded. Furthermore, since not all packets of a message necessarily travel through the same switches, the delay is not uniform for a message’s packets.

Fiber Optics

Fiber optic cables are composed of an inner core of glass or plastic surrounded by cladding and enclosed within an outer sheath. Fiber optic cables carry the data signal in the form of light. The signal is spread through the inner core by reflection. Fiber optic transmissions are becoming increasingly popular due to their resistance to noise, low attenuation, and high bandwidth. Its disadvantages are the unidirectional propagation of light and cost. They are used in backbone networks, cable TV networks, and fast Ethernet networks.

Propagation Rates in Wireless Communication

Wireless data is transmitted through surface spreading, spread across the sky, and line-of-sight propagation. Wireless waves can be classified as radio waves, microwaves, or infrared. Radio waves are omnidirectional; microwaves are unidirectional. Microwaves are used for mobile phones, satellite communications, and wireless local area networks.

Microwave

Waves with frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. When transmitting from a microwave antenna, you can focus very precisely. This means that the source and receiving antennas must be aligned.

Types of Microwave Antennas Used

Microwave antennas are traditionally unidirectional antennas that send signals in one direction. Two types of antennas are used for communication via microwave: dishes and horns. Microwaves are used in unicast communications, including mobile phones, satellite networks, and wireless networks.

Infrared Wavelengths

Infrared waves are used for short-range communication, such as between a PC and a peripheral. They can also be used for internal LANs. Key Facts:

  • Direct reflection.
  • Utilization of transducers that modulate noncoherent infrared light.
  • They must be aligned or have a direct reflection.
  • They cannot cross obstacles.
  • Speed of installation; it is unnecessary to have a permit.
  • Unable to establish links in open media due to changing weather conditions, which can act as obstacles.

Explain the Reasons for the Use of Switching and What the Switches Are

They are used because sometimes it is impossible to connect multiple computers or devices point-to-point due to cost, extension, or because many teams are not logical.

  • A switched network is a series of interconnected nodes called switches.
  • Switches are devices capable of establishing temporary connections between two or more devices hooked to the switch.
  • Traditionally, there have been three major switching methods: circuit switching, packet switching, and message switching.