General Networking Concepts:-Section 1

                                                

Introduction to Networks

What is a Network?

A network is simply defined as something that connects things together for a specific purpose. The term network is used in a variety of contexts, including telephone, television, computer, or even people networks.

A computer network connects two or more devices together to share a nearly limitless range of information and services, including:

·        Documents

·        Email and messaging

·        Websites

·        Databases

·        Music

·        Printers and faxes

·        Telephony and videoconferencing

Protocols are rules that govern how devices communicate and share information across a network. Examples of protocols include:

·        IP – Internet Protocol

·        HTTP  - Hyper Text Transfer Protocol

·        SMTP – Simple Mail Transfer Protocol

Multiple protocols often work together to facilitate end-to-end network communication, forming protocol suites or stacks. Protocols are covered in great detail in other guides.

Network reference models were developed to allow products from different manufacturers to interoperate on a network. A network reference model serves as a blueprint, detailing standards for how protocol communication should occur.

The Open Systems Interconnect (OSI) and Department of Defense (DoD) models are the most widely recognized reference models. Both are covered in great detail in another guide.

Basic Network Types

Network types are often defined by function or size. The two most common categories of networks are:

·        LANs (Local Area Networks)

·        WANs (Wide Area Networks)

A LAN is generally a high-speed network that covers a small geographic area, usually contained within a single building or campus. A LAN is usually under the administrative control of a single organization. Ethernet is the most common LAN technology.

A WAN can be defined one of two ways. The book definition of a WAN is a network that spans large geographical locations, usually to connect multiple LANs. This is a general definition, and not always accurate.

A more practical definition of a WAN is a network that traverses a public or commercial carrier, using one of several WAN technologies. A WAN is often under the administrative control of several organizations (or providers), and does not necessarily need to span large geographical distances.

A MAN (Metropolitan Area Network) is another category of network, though the term is not prevalently used. A MAN is defined as a network that connects LAN’s across a city-wide geographic area.

An internetwork is a general term describing multiple networks connected together. The Internet is the largest and most well-known internetwork.

Some networks are categorized by their function, as opposed to their size. A SAN (Storage Area Network) provides systems with high-speed, lossless access to high-capacity storage devices.

A VPN (Virtual Private Network) allows for information to be securely sent across a public or unsecure network, such as the Internet. Common uses of a VPN are to connect branch offices or remote users to a main office.

Network Architectures

A host refers to any device that is connected to a network. A host can also be defined as any device assigned a network address.

A host can serve one or more functions:

·        A host can request data, often referred to as a client.

·        A host can provide data, often referred to as a server.

·        A host can both request and provide data, often referred to as a peer.

Because of these varying functions, multiple network architectures have been developed, including:

·        Peer-to-Peer

·        Client/Server

·        Mainframe/Terminal

In a basic peer-to-peer architecture, all hosts on the network can both request and provide data and services. For example, two Windows XP workstations configured to share files would be considered a peer-to-peer network.

Peer-to-peer networks are very simple to configure, yet this architecture presents several challenges. Data is difficult to manage and back-up, as it is spread across multiple devices. Security is equally problematic, as user accounts and permissions much be configured individually on each host.

In a client/server architecture, hosts are assigned specific roles. Clients request data and services stored on servers. An example of a client/server network would be Windows XP workstations accessing files off of a Windows 2003 server.

There are several advantages to the client/server architecture. Data and services are now centrally located on one or more servers, consolidating the management and security of that data. As a result, client/server networks can scale far larger than peer-to-peer networks.

One key disadvantage of the client/server architecture is that the server can present a single point of failure. This can be mitigated by adding redundancy at the server layer.

Network Architectures (continued)

In a mainframe/terminal architecture, a single device (the mainframe) stores all data and services for the network. This provides the same advantages as a client/server architecture – centralized management and security of data.

Additionally, the mainframe performs all processing functions for the dumb terminals that connect to the mainframe. The dumb terminals perform no processing whatsoever, but serve only as input and output devices into the mainframe.

In simpler terms, the mainframe handles all thinking for the dumb terminals. A dumb terminal typically consists of only a keyboard/mouse, a display, and an interface card into the network.

The traditional mainframe architecture is less prevalent now than in the early history of networking. However, the similar thin-client architecture has gained rapid popularity. A thin-client can be implemented as either a hardware device, or software running on top of another operating system (such as Windows or Linux).

Like dumb terminals, thin-clients require a centralized system to perform all (or most) processing functions. User sessions are spawned and managed completely within the server system.

Hardware thin-clients are generally inexpensive, with a small footprint and low power consumption. For environments with a large number of client devices, the thin-client architecture provides high scalability, with a lower total cost of ownership.

The two most common thin-client protocols are:

·        RDP (Remote Desktop Protocol) – developed by Microsoft

·        ICA (Independent Computer Architecture) – developed by Citrix