Transcript CCNA1 3.0-03 Networking Media

Atoms & Electrons
All 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
ESD
Loosened 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.
Voltage
Voltage 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 / Impedance
The 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.
Current
Electrical 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 Terms
Ground 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 Specifications
10BASE-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 Connectors
Connectors 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 Panels
Fiber 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 Much
Bending 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
Splicing
Improperly 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 & Association
WLAN 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 Authentication
IEEE 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
Security
A 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.