Chapter 3 Notes

Chapter 3 Notes

After Reading this Chapter and Completing the Exercises you will be able to:

Explain the bus, ring, and star networking topologies and describe the advantages and disadvantages of each.
Draw a basic network diagram.
Describe the advantages and disadvantages of various types of network media:
- thick and thin coaxial cable
- shielded and unshielded twisted-pair cable
- fiber-optic cable
Discuss the advantages and disadvantages of wireless network media.
Compare the costs of different network media and understand implementation considerations.

Network Topologies

Two components:

Physical layout of the cable

Logical path followed by network packets sent on the cable

There are three main topologies:

Bus

Ring

Star

Before selecting the best topology for an installation, ask these questions:

What applications will be used on the network?

What types of hosts and file servers are to be connected?

Will the network be connected to other networks?

Will the network have mission-critical applications?

Is data transmission speed important?

What network security is needed?

What is the anticipated growth in the use of the network?

The applications intended to be used on a network influence the umber and frequency of packets to be transmitted. This is known as network traffic.
Whether other networks will be connected to the network also affects the topology used. The network topology for a small business that will never use more than 4 computers is different of that will be connected throughout a college campus.
A network used for a company’s payroll is mission critical, therefore a topology should be used with alternate routes for the transmission of packets.

Bus Topology

Consists of running cable from one PC or file server to the next.
Nodes are connected to segment of cable in the logical shape of a line, with a terminator at each end.
This design works well for small networks.
It is also relatively inexpensive to implement.
Managing a bus topology can be expensive.

It is difficult to isolate a single malfunctioning node or cable segment and associated connectors.

Can be over congested with network traffic.

Advantages	Disadvantages

Works well for small networks	Management costs often too high
Inexpensive to implement on small scale	Difficult to isolate a malfunctioning node or cable segment and associated connectors
Requires less cable	Possible for defective node to take down the entire network
Easy to add another workstation	Subject to congestion from network traffic

Ring Topology

Continuous path for data, with no logical beginning or ending point, and no terminators.
Shaped in a ring or circle, with nodes connected around the ring.
Easier to manage.
Handles traffic better than a bus topology.

Advantages	Disadvantages

Easier to manage than a bus	Requires more network cable and equipment at the start
Easier to locate node and cable problems	Not as many equipment options as for a bus
Good over long distances	Not as widely used a bus topology
Very reliable
Handles high volume traffic well

Star Topology

The shape of a star.
Oldest communications design method.
Consists of multiple nodes connected to a central hub.
Most popular.

Advantages	Disadvantages

Easier to manage than a bus	Susceptible to a single point failure at the Hub
Easier to locate node and cable problems	Requires more network cable at the start-up than a bus
Easier to expand than a bus or ring, especially for enterprise networking
More equipment options
Well suited for expansion into high-speed networking

Bus-Star Layouts

Modern networks combine the logical communications of a bus with the physical layout of a star.
In this topology, each ray radiating from the center of the star is like a separate logical bus statement, but with only one or two computers attached.
Multiple hubs can be connected to expand the network in many directions.
Connection between hubs is called backbone.

Advantages	Disadvantages

Easier to manage than the traditional bus design	Susceptible to a single point of failure (the hub)
Easier to locate node and cable problems than the traditional bus design	Requires more network cable at the start-up than a bus
Many options for expansion
Well suited for expansion into high-speed networking
Many equipment options
No exposed terminators

Communications Media

What binds a network together.

Thick coaxial cable

Thin coaxial cable

Shielded twisted-pair cable

Unshielded twisted-pair cable

Fiber-optic cable

Wireless technologies

When choosing the best media, consider this:

Data transfer speed

Use in specific network topologies

Distance requirements

Cable and cable component costs

Additional network equipment that is required

Ease of installation

Immunity to interference from outside sources

Upgrade options

Coaxial Cable

Thick Coaxial Cable

It is made up of:

Copper center

Conductor insulation

Aluminum Sleeve

PVC or Teflon jacket

Expensive to buy and install.

Durable and reliable, with great resistance to signal interference.

Thin Coaxial Cable

It is made up of:

Copper center

Conductor insulation

Aluminum Sleeve

PVC or Teflon jacket

Thinner than other coax cable.

Easier and cheaper to install than thick coax.

Twisted-Pair Cable

A flexible communications cable that contains pairs of insulated copper wires twisted together for reduction of EMI and RFI and covered with an outer insulating jacket.
Shielded Twisted-Pair Cabling

Reduces interruption of the communication signal caused by RFI and EMI.

Braided shielding is used for indoor wire.

Corrugated shielding is used for outside wire.

Unshielded Twisted Pair Cable

Most frequently used in network cabling.

Low cost and easy installation.

Twisted-Pair as Defined in the EIA/TIA-568 Specifications for Horizontal and Backbone Cable	Shielding	Maximum Transition Rate
IBM Type 1A	Shielded	4 Mbps
IBM Type 2A	Shielded	4 Mbps
Category 3	Unshielded	16 Mbps
Category 4	Unshielded	20 Mbps
Category 5	Unshielded	100 Mbps

Fiber-Optic Cable

A central glass cylinder encased in a glass tube called cladding.
Signal transmission along the inside fibers is accomplished using infrared, or in some cases, visible light.
A fat pipe is a fiber-optic cable used on a network backbone for high-speed communications.
Attenuation is the amount of the signal that is lost as the signal travels through the communications medium.
The power budget for optical-fiber cable communications is the difference between the transmitted power and the receiver sensitivity, measured in decibels. It is the minimum transmitter power and receiver sensitivity needed for a signal to be sent and received in tact.
Comes in two modes:

single-mode which is used for long distance communications

multi-mode which is for shorter distances

Wireless Technologies

Radio Waves

High frequencies

One or multiple directions, but a short distance

Good for line-of sight transmissions

Infrared

Inexpensive

Hard to intercept signal.

Light sources can cause interference.

Microwave

Terrestrial

Signal is transmitted between two directional antennas shaped like dishes.

Must have FCC license due to high frequency transmissions.

Satellite

Signal is transmitted from one dish to satellite, then to another dish.

Good for long distance networking.

Need to own a satellite or lease the service from a company.

	Radio	Infrared	Microwave
Advantages	An inexpensive alternative where cabling cannot be installed An option for portable communications Usually no licensing requirements	An inexpensive alternative where cabling is not easily installed Signal difficult to secret interception	An alternative to cabling, such as across long distances
Disadvantages	May not be feasible when high-speed communications are needed Subject to interference from military, amateur radio, and cell phones Subject to interference from natural obstacles	May not be feasible when high-speed communications are needed Subject to interference from light sources Does not go through walls	May not be feasible when high-speed communications are needed Expensive to install and maintain Subject to interference from bad weather, EMI, and atmospheric conditions

Evaluating Cost

Consider distance.
Consider speed needed.
Consider maintenance.
Consider installation costs.