What is a Network? by Barbara Jean Thompson

A network is a system of 2 or more computers that are linked to share resources, exchange files or allow electronic communications.

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Types of Networks:

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Most widely used:

LAN - Local Area Network

WAN - Wide Area Network

Also:

Metropolitan Area Networks (MAN), a Wireless LAN (WLAN), or a Wireless WAN (WWAN)

LAN - Local Area Network

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Usually used in a smaller area, confined to a building
Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others
Used in work stations, computer labs.
Can be connected by cables or wirelessly

WAN - Wide Area Network

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Connect networks in larger geographic areas, example: statewide
A WAN is more complicated than a LAN
It uses multiplexers, bridges, and routers to connect local and metropolitan networks to global communications networks like the Internet.
To a use a WAN will function like a LAN

School Network

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A school network is a LAN.

Advantages:

User access control

User credentials are centrally owned and managed

Can provide specific services to your network

More control

Disadvantages:

Can be expensive

Required maintenance

Network security must be provided but is expensive and

What is Network Protocol?

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Protocol is the communication between computers on the network.

OSI (Open Systems Interconnection) define 7 layers of networking protocols:

Physical
Data Link
Network
Transport
Session
Presentation
Application

4 Layers of Communication via the Internet

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Ethernet (Physical/Data Link Layers)
1. The physical layer of the network focuses on hardware elements, such as cables, repeaters, and network interface cards
2. Most common layer used at the physical level = cords, how to connect
3. Uses a twisted pair wire
4. Fast Ethernet, Gigabit Ethernet
5. Some old networks are still in operation due to the availability of Ethernet
IP/IPX (Network layer)
1. This layer is in charge of routing network messages (data) from one computer to another.
2. Networks using the IP and IPX protocols assign logical addresses (which are made up of the MAC address and the network address) to the devices on the network,
3. The network layer takes care of assigning the correct addresses (via IP or IPX) and then uses routers to send the data packets to other networks.
TCP/SPX (Transport Layer)
1. The transport layer is concerned with efficient and reliable transportation of the data packets from one network to another.
2. Example - a document, email.
3. TCP, paired with IP, is by far the most popular protocol at the transport level.
HTTP, FTP, TelNet, SMTP, DNS (combined Session/Presentation/ Application Layers)
1. Several protocols overlap the session, presentation, and application layers of networks.

Hardware

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File Network Server - A part of a LAN. The network operating system provides tools to share server resources and information for network users. Includes the fastest processors, a large amount of RAM, multiple large, fast hard drives, extra expansion slots and a fast network interface card(s).

Workstations - Computers that people use. They are configured with a network interface cared, networking software and appropriate cables.

Network Interface Cards - These provide the physical connection between the network and the computer workstation. It is an internal device and usually is sold with the computer. These determine the speed and performance of the network. The most widely used NIC is an Ethernet card and wireless adapters.

Switches - An Ethernet switch is a device that provides a central connection point for cables from a workstation or server.

Repeaters - These electrically amplify the signal to boost connectivity.

Bridges - These segment the large network into two smaller, more efficient networks. It monitors the traffic online and maintains optimum performance.

Routers - These are the traffic lights of the internet. They communicate with each other and allow access. They are network gateways.

Firewalls - Can be hardware or software. They provide protection to the network.

Network Cabling

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Unshielded Twisted Pair (UTP) Cable
- Varies from telephone grade wire to high speed cable
- Cheapest wire
- May be susceptible to radio and electrical frequency interference
Shielded Twisted Pair (STP) Cable
- Extends maximus distance of cables
- Is less susceptible to radio and electrical frequency interference
  - 3 Configurations
    - Each pair of wires is individually shielded with foil.
    - There is a foil or braid shield inside the jacket covering all wires (as a group).
    - There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).
Coaxial Cable
- Has a single copper conductor at its center
- Difficult to install
- Highly resistant to interference
Fiber Optic Cable
- Has a center that is made from glass or plastic fibers
- Surrounded by several layers of protection
- Transmits signals over much longer distances than coaxial or STP
Cable Installation Guides
- Always use more cable than you need. Leave plenty of slack.
- Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.
- Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.
- If it is necessary to run cable across the floor, cover the cable with cable protectors.
- Label both ends of each cable.
- Use cable ties (not tape) to keep cables in the same location together.
Wireless LANs
- Uses high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs
- Security can be an issue

Topology

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Definition: the way in which constituent parts are interrelated or arranged.

The Physical Topology of a Network:

The configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.

Software

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Network Operating System (NOS):

Coordinates the activities of multiple computers across a network. The network operating system acts as a director to keep the network running smoothly.

Peer to peer
Allows users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source.
Security is an issue.
Is decentralized.
Client/Server
Allows the network to centralize functions and applications in one or more dedicated file servers (See fig. 2). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location. UNIX/Linux and the Microsoft family of Windows Servers are examples of client/server network operating systems.
Expensive and requires maintenance.
If the server goes down the network ceases to exist.

NOS Software: Microsoft Windows Server, Macintosh OSX, UNIX/Linux

Vocab

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Linear Bus Topology

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Advantages -

Easy to connect a computer or peripheral to a linear bus.
Requires less cable length than a star topology.

Disadvantages -

Entire network shuts down if there is a break in the main cable.
Terminators are required at both ends of the backbone cable.
Difficult to identify the problem if the entire network shuts down.
Not meant to be used as a stand-alone solution in a large building.

Star Topology

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Advantages -

Easy to install and wire.
No disruptions to the network when connecting or removing devices.
Easy to detect faults and to remove parts.

Disadvantages -

Requires more cable length than a linear topology.
If the hub, switch, or concentrator fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of the hubs, etc.

Tree Topology

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Advantages -

Point-to-point wiring for individual segments.
Supported by several hardware and software venders.

Disadvantages -

Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.