Section 1 - Introduction to Networks

Section 1-

 Introduction to Networks -What is a Network?
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

A network is simply defined as something that connects things together for