Network Protocol Families

Network Protocol Families

There are two types of network services: connectionless and connection-oriented.

Connectionless-mode Network Service

A connectionless network service, or CLNS, is a type of communication service in which data packets are sent from a source to a destination without the need for a prior establishment of a dedicated connection or circuit. In a connectionless network, each data packet is treated independently, and routing decisions are made based on the destination address contained within each packet. Some key characteristics include:

  1. No Circuit Setup: In connectionless networks, there is no requirement to establish a dedicated circuit or connection path before data transmission begins. Unlike connection-oriented services, which involve a setup phase to create a dedicated path, connectionless services send data packets immediately without any prior arrangement.
  2. Requires the Destination at Each Node: Each data packet in a connectionless network contains destination addressing information (e.g., IP addresses or MAC addresses), allowing intermediary devices, such as routers or switches, to make routing decisions based solely on this information. Therefore, CLNS requires the destination at each node.
  3. Lack of State Information: Connectionless networks do not maintain state information at intermediary nodes. This means that routers or switches in the network do not need to keep track of ongoing connections or maintain specific session information for data packets. Each packet is processed in isolation.

Since CLNS requires the destination at each node, every data packet is essentially a datagram. Each datagram carries all information needed to be delivered even if some links/nodes fail.

Connection-Oriented Network Service

A Connection-Oriented Network Service, or CONS, is the other network layer protocol. In CONS, there is a virtual circuit over which all data will transit. Essentially, it is the opposite of CLNS.

  1. Circuit Setup Requirement: Unlike connectionless services, CONS necessitates the establishment of a circuit or path before any data transfer. This setup phase involves determining the route that the data packets will follow from the source to the destination.
  2. State Information: In CONS, intermediary nodes along the transmission path maintain state information about the established circuit. This information allows the network to efficiently route all subsequent data packets along the pre-established path without needing to determine the route for each packet.
  3. Routing Process: Only the initial run needs to route to find a path. Once this path is established and the circuit is set up, all the data packets follow this pre-defined path, making the routing process for subsequent packets simpler and more efficient.
  4. Congestion Control: CONS allows for more effective congestion control compared to connectionless services. By establishing a circuit initially, CONS can pre-reserve bandwidth or bitrate for the communication, ensuring a certain level of quality of service. This pre-reservation helps in managing congestion, as the network can allocate resources based on the known requirements of the circuit.

One caveat of CONS is that if any node along the path fails, the entire communication circuit may collapse. This is because the state information, which is crucial for the routing of the packets along the circuit, is lost or becomes invalid.