Network Addressing

Networking Basics: Network addressing 

Internet vs. local area network

When a group of computers are connected together within a relatively small area, it is referred to as a local area network (LAN). If a LAN is available only to certain people (such as employees of a company), it is called a private or internal network. The Internet is a public network because it is accessible to many users and computers from different networks. The network shown in Figure 6 is a LAN that can be used to connect to the Internet.

You can help to physically secure your small business LAN by configuring your hardware or software so that the router acts as a gateway to the Internet. A gateway is a combination of hardware and software that connects two different types of networks, for example a private network and a public network. There must be at least two network adapters installed on a gateway, one to connect to the Internet (ISP network adapter) and the other to connect to the private or local network (local network adapter), as shown.

End Devices and their Role on the Network

The network devices that people are most familiar with are called end devices. These devices form the interface between the human network and the underlying communication network. Some examples of end devices are:

Computers (work stations, laptops, file servers, web servers)

Network printers

VoIP phones

Security cameras

Mobile handheld devices (such as wireless barcode scanners, PDAs)

In the context of a network, end devices are referred to as hosts. A host device is either the source or destination of a message transmitted over the network. In order to distinguish one host from another, each host on a network is identified by an address. When a host initiates communication, it uses the address of the destination host to specify where the message should be sent. In modern networks, a host can act as a client, a server, or both. Software installed on the host determines which role it plays on the network. Servers are hosts that have software installed that enables them to provide information and services, like e-mail or web pages, to other hosts on the network. Clients are hosts that have software installed that enables them to request and display the information obtained from the server.

Intermediary Devices and their Role on the Network

In addition to the end devices that people are familiar with, networks rely on intermediary devices to provide connectivity and to work behind the scenes to ensure that data flows across the network. These devices connect the individual hosts to the network and can connect multiple individual networks to form an internetwork. Examples of intermediary network devices are:

Network Access Devices (Hubs, switches, and wireless access points)

Internetworking Devices (routers)

Communication Servers and Modems

Security Devices (firewalls)

The management of data as it flows through the network is also a role of the intermediary devices. These devices use the destination host address, in conjunction with information about the network interconnections, to determine the path that messages should take through the network. Processes running on the intermediary network devices perform these functions:

Regenerate and retransmit data signals

Maintain information about what pathways exist through the network and internetwork

Notify other devices of errors and communication failures

Direct data along alternate pathways when there is a link failure

Classify and direct messages according to QoS priorities

Permit or deny the flow of data, based on security settings

Network Media

Communication across a network is carried on a medium. The medium provides the channel over which the message travels from source to destination. Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are:

Metallic wires within cables

Glass or plastic fibers (fiber optic cable)

Wireless transmission

The signal encoding that must occur for the message to be transmitted is different for each media type. On metallic wires, the data is encoded into electrical impulses that match specific patterns. Fiber optic transmissions rely on pulses of light, within either infrared or visible light ranges. In wireless transmission, patterns of electromagnetic waves depict the various bit values. Different types of network media have different features and benefits. Not all network media has the same characteristics and is appropriate for the same purpose. Criteria for choosing a network media are:

The distance the media can successfully carry a signal.

The environment in which the media is to be installed.

The amount of data and the speed at which it must be transmitted.

The cost of the media and installation

LANs, WANs, and Internetworks

Local Area Networks

Networks infrastructures can vary greatly in terms of:

The size of the area covered

The number of users connected

The number and types of services available

An individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure, such as a single business, campus or region. This type of network is called a Local Area Network. A LAN is usually administered by a single organization. The administrative control that governs the security and access control policies are enforced on the network level.

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