Network

Overview

A protocol is a set of common behaviors communicated by using a common language. A protocol suite is a collection of related protocols. The reference model for the protocol suite is the design that specifies how various protocols of a protocol suite relate to each other and divide up tasks to be accomplished.

Multiplexing

Multiplexing is a method by which multiple data signals are combined into one signal over a shared medium. Demultiplexing is the reverse process, in which the original channels are extracted on the receiver end.

Protocol multiplexing allows multiple different protocols to coexist on the same infrastructure, as well as multiple instantiations of the same protocol object to be used simultaneously without confusion.

Telecommunications

A telecommunications network is a group of nodes interconnected by telecommunications links used to exchange messages between the nodes. A telecommunication link is any communication channel that connects two or more devices for the purpose of data transmission.

A connection-oriented network is one in which "per-flow" state is established prior to the exchange of data. This is done using a signaling protocol that supports connection establishment, clearing, and status information.

In a connection-oriented packet network, each packet would contain an index into a state table held on each switch. Such a table would contain information on the next switch along the path for the packet.

In constrast, a connectionless network uses datagrams, a special type of packet in which all the identifying information for the source and final destination resides inside the packet itself.

Circuit Switching

Circuit switching is a method of implementing a telecommunications network in which two nodes establish a circuit through the network before the nodes may communicate.

Message Switching

Message switching is a method of implementing a telecommunications network in which messages are routed to a destination, in their entirety, one hop at a time.

Packet Switching

Packet switching is a method of implementing a telecommunications network in which data is broken into short messages (i.e. packets), that are transmitted over a digital network.

Virtual circuits are used to transport data between two nodes over a packet switching network once a connection is established between them.

Layering

Layering refers to the hierarchical structure and separation of responsibilities used to approach networking-related protocol suites. The most frequently cited layering model is OSI.

When an object, called a protocol data unit (PDU), at one layer is carried by a lower layer, it is said to be encapsulated by the next layer down.

Tunneling

Tunneling refers to the encapsulation of lower-layer (or equal-layer) traffic in higher- (or equal-layer traffic) to establish virtual links. In essense, it is an inversion of the strict layering. For example, IPv4 can be used to wrap Ethernet frames. These can be received by another machine which unwraps the IPv4 payload and passes it to a virtual Ethernet adapter.