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In the Information Technology (IT) world, there are two basic types of networks:

  • Networks that exist in a relatively confined geographical area are referred to as local area networks (LANs).
  • Networks distributed over wider geographical areas are referred to as wide area networks (WANs).

There are several less-well-defined versions of these basic area network types, as described in this section.

In all of the following network types, two fundamental considerations must be in place to implement communications between the network’s devices: its physical or logical connection method (topology) and the rules governing its communication processes (or protocols). You must be able to link the network components together, and they must all use the same signal types and language.

Campus Area Networks or Corporate Area Networks (CANs)

Campus area networks or corporate area networks (CANs) are combinations of interconnected local area networks inside a limited geographical area.

Metropolitan Area Networks (MANs)

Metropolitan area networks (MANs) are widespread combinations of interconnected local area networks inside a medium-sized geographical area. This designation is applied to networks that operate between LANs and WANs and most likely connect different LANs to a WAN.

Wireless Local Area Networks (WLANs)

Wireless local area networks (WLANs) are local area networks of more than two devices that are connected by wireless radio communication methods. These networks may also interconnect through a wireless access point, which also attaches the LAN to a wide area network, such as the Internet.

Storage Area Networks (SANs)

Storage area networks (SANs) are a network of dedicated storage devices configured for the express purpose of providing consolidated data storage. These devices act in a transparent manner so that they appear to be an integral part of the network’s server(s).

The OSI Networking Model

Networks are complex, multifaceted structures that require a tremendous amount of interaction between computer designers, network equipment designers, operating system manufacturers, and networking application providers. Several initiatives have been put forward to provide models to serve as blueprints for these groups to follow in designing their products. While you should be aware that different hierarchical networking models exist, the most widely discussed initiative is the open systems interconnection (OSI) model put forward by the International Standards Organization.

The OSI model helps us conceptualize how data is handled between two networked systems. To do so, the OSI model divides the working flow of data into abstract layers. Although the layers are not literal in any sense, nor do they provide any actual barrier for product design, the layers do help people respect and understand the flow of how data gets managed.


The primary functions of the layers are summarized in the following sections.

Layer 1: Physical

This layer is concerned with the transmission media used to move data. Functions associated with this layer include moving the data onto the transmission media, providing electrical or light signals, the mechanical compatibility between the communications port and the media, and activation and deactivation of the physical connection.

Layer 2: Data Link

This layer involves controlling how the data is packaged and moved between communication points. At this layer, the data is formatted into frames suited for transmission. Components at this level also add error detection and correction functions to the frames, as well as media access protocols and specific information about transmission to specific nodes on the same network segment.

Layer 3: Network

Elements of the network layer are responsible for controlling the routing of data packets between different communication nodes, network segments, or media types. This includes multiplexing and demultiplexing signals as they pass from one media type to another, assembling and disassembling message packets, and establishing, maintaining, and terminating connections.

Layer 4: Transport

The transport-level components are responsible for providing an orderly end-to-end flow of data that includes sequencing of data packets and providing basic error-recovery functions and flow control.

Layer 5: Session

This layer of the model is dedicated to setting up and managing sessions between applications as well as providing parameters such as security. Activities conducted by components at this level include stopping and starting data transfers, controlling the flow of data between applications, and providing network failure recovery options. This layer deals with management of transmission security options such as authentication and tunneling protocols.

Layer 6: Presentation

The elements of this level are tasked with controlling how the data looks to the user at the destination end. Functions provided by components at this level include visually formatting and presenting data, dealing with data compression and encryption functions, and starting/stopping control of sessions.

Layer 7: Application

The highest level of abstraction for the OSI model is concerned with the network handling of data for end-user applications. Services such as email and the web browser are application examples where the application layer is functioning. At this level of the model, user IDs and passwords are authenticated, and user services are provided.

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