Atoms & ElectronsAll matter is composed of atoms. The Periodic Table of Elements lists all known types of atoms and their properties. The atom is comprised of: Electrons – Particles with a negative charge that orbit the nucleus Nucleus – The center part of the atom, composed of protons and neutrons Protons – Particles with a positive charge Neutrons – Particles with no charge (neutral)

Forces within an Atom

ESDLoosened electrons that stay in one place, without moving, and with a negative charge, are called static electricity. If these static electrons have an opportunity to jump to a conductor, this can lead to electrostatic discharge (ESD). ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment.

VoltageVoltage is sometimes referred to as electromotive force (EMF).

EMF is related to an electrical force, or pressure, that occurs when electrons and protons are separated.

Voltage can also be created in three other ways. The first is by friction, or static electricity. The second way is by magnetism, or electric generator. The last way that voltage can be created is by light, or solar cell.

Voltage is represented by the letter V, and sometimes by the letter E, for electromotive force.

The unit of measurement for voltage is volt (V).

Volt is defined as the amount of work, per unit charge, needed to separate the charges.

Resistance / ImpedanceThe materials through which current flows offer varying amounts of opposition, or resistance to the movement of the electrons.

The materials that offer very little, or no, resistance, are called conductors.

Those materials that do not allow the current to flow, or severely restrict its flow, are called insulators.

The letter R represents resistance. The unit of measurement for resistance is the ohm (). (Greek letter omega)

Semiconductors are materials where the amount of electricity they conduct can be precisely controlled.

CurrentElectrical current is the flow of charges created when electrons move.

In electrical circuits, the current is caused by a flow of free electrons.

When voltage, or electrical pressure, is applied and there is a path for the current, electrons move from the negative terminal along the path to the positive terminal. The negative terminal repels the electrons and the positive terminal attracts the electrons.

The letter “I” represents current. The unit of measurement for current is Ampere (Amp).

Amp is defined as the number of charges per second that pass by a point along a path.

More TermsGround typically means the zero volts level, when making electrical measurements.

The relationship among voltage (V), resistance(R), and current(I) is V=I*R. This is Ohm’s law.

Two ways in which current flows are Alternating Current (AC) and Direct Current (DC).

Alternating current (AC) and voltages vary over time by changing their polarity, or direction.

Direct Current (DC) always flows in the same direction and always has the same polarity.

Cable Specifications10BASE-T The T stands for twisted pair.

10BASE5 The 5 represents the fact that a signal can travel for approximately 500 meters 10BASE5 is often referred to as Thicknet.

10BASE2 The 2 represents the fact that a signal can travel for approximately 200 meters 10BASE2 is often referred to as Thinnet.

All 3 of these specifications refer to the speed of transmission at 10 Mbps and a type of transmission that is baseband, or digitally interpreted. Thinnet and Thicknet are actually a type of networks, while 10BASE2 & 10BASE5 are the types of cabling used in these networks.

Coaxial Cable

Unshielded Twisted Pair (UTP) Cable

Shielded Twisted Pair (UTP) Cable

Fiber Optic Cable

Fiber Optic ConnectorsConnectors are attached to the fiber ends so that the fibers can be connected to the ports on the transmitter and receiver.

The type of connector most commonly used with multimode fiber is the Subscriber Connector (SC connector). On single-mode fiber, the Straight Tip (ST) connector is frequently used

Fiber Optic Patch PanelsFiber patch panels similar to the patch panels used with copper cable. These panels increase the flexibility of an optical network by allowing quick changes to the connection of devices like switches or routers with various available fiber runs, or cable links.

Bending Too MuchBending the fiber in too tight a curve can change the incident angle of light rays striking the core-to-cladding boundary. Then the incident angle of the ray will become less than the critical angle for total internal reflection. Instead of reflecting around the bend, some light rays will refract into the cladding and be lost.

Fiber End Face Finishes

SplicingImproperly installed connectors, improper splices, or the splicing of two cables with different core sizes will dramatically reduce the strength of a light signal.

Wireless LAN Organizations and Standards

In cabled networks, IEEE is the prime issuer of standards for wireless networks. The standards have been created within the framework of the regulations created by the Federal Communications Commission (FCC).

A key technology contained within the 802.11 standard is Direct Sequence Spread Spectrum (DSSS).

Cellular Topology for Wireless

Authentication & AssociationWLAN authentication occurs at Layer 2. It is the process of authenticating the device not the user. Association, performed after authentication, is the state that permits a client to use the services of the AP to transfer data.

Authentication and Association types

Unauthenticated and Unassociated The node is disconnected from the network and not associated to an access point.

Authenticated and Unassociated The node has been authenticated on the network but has not yet associated with the access point.

Authenticated and Associated The node is connected to the network and able to transmit and receive data through the access point.

Methods of AuthenticationIEEE 802.11 lists two types of authentication processes.

The first authentication process is the open system. This is an open connectivity standard in which only the SSID must match. This may be used in a secure or non-secure environment although the ability of low level network ‘sniffers’ to discover the SSID of the WLAN is high.

The second process is the shared key. This process requires the use of Wireless Equivalency Protocol (WEP) encryption. WEP is a fairly simple algorithm using 64 and 128 bit keys.

The problem of unauthorized entry into WLANs is being addressed by a number of new security solution technologies.

Frequencies

SecurityA number of new security solutions and protocols, such as Virtual Private Networking (VPN) & Extensible Authentication Protocol (EAP) are emerging.

EAP-MD5 Challenge – Extensible Authentication Protocol is the earliest authentication type, which is very similar to CHAP password protection on a wired network.

LEAP (Cisco) – Lightweight Extensible Authentication Protocol is the type primarily used on Cisco WLAN access points. LEAP provides security during credential exchange, encrypts using dynamic WEP keys, and supports mutual authentication.

User authentication – Allows only authorized users to connect, send and receive data over the wireless network.

Encryption – Provides encryption services further protecting the data from intruders. Data authentication – Ensures the integrity of the data, authenticating source and destination devices.