29-01-2013, 02:31 PM
General Networking Concepts
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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.
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.
Network Reference Models
A computer network connects two or more devices together to share
information and services. Multiple networks connected together form an
internetwork.
Internetworking present challenges - interoperating between products from
different manufacturers requires consistent standards. Network reference
models were developed to address these challenges. A network reference
model serves as a blueprint, detailing how communication between network
devices should occur.
The two most recognized network reference models are:
• The Open Systems Interconnection (OSI) model
• The Department of Defense (DoD) model
Without the framework that network models provide, all network hardware
and software would have been proprietary. Organizations would have been
locked into a single vendor’s equipment, and global networks like the
Internet would have been impractical, if not impossible.
Network models are organized into layers, with each layer representing a
specific networking function. These functions are controlled by protocols,
which are rules that govern end-to-end communication between devices.
Protocols on one layer will interact with protocols on the layer above and
below it, forming a protocol suite or stack. The TCP/IP suite is the most
prevalent protocol suite, and is the foundation of the Internet.
OSI Reference Model
The Open Systems Interconnection (OSI) model was developed by the
International Organization for Standardization (ISO), and formalized in
1984. It provided the first framework governing how information should be
sent across a network.