IT 300 - Modern Telecommunications - CH1
What is a transducer?
a device that converts one form of energy to another) such as a microphone, we can convert mechanical speech into electrical signals. can convert acoustic to electrical
ALL frequencies can be represented by
a sinusoidal waveform (either sine or cosine)
any electrical signal emits -
an electromagnetic (EM signal) which goes through the air, allows for things like radio
resistance is measured
in ohms
Layer 6 (Presentation Layer):
Provides information on how data should be presented (ex., .jpg, .tiff, .gif, ASCII, Unicode, .mpg, etc.)
Layer 7 (Application Layer):
User applications (ex., .doc, .xls, .xml, telnet, ftp, .ppt, etc.)
carrier frequency wave
An electrical voice grade signal with a frequency bandwidth of 3100 Hz, is used to modulate
Link:
Communications path between two nodes (a circuit will be comprised of one or more links).
"Right-Hand- Rule"
Current flowing through a conductive wire creates an E-M field that rotates in a circular fashion around the conductor. Basically you take your right hand, use the thumb to point in the direction of the current, and the fingers will point in the direction of the circulation of the EM wave.
What is the relationship between frequency and the time period of a sinusoidal wave?
There is an inverse relationship between frequency and the time period of a sinusoidal wave: frequency=1/T, where T is the period of the wave in seconds (i.e., the time in seconds that it takes for a wave to complete one full cycle before repeating itself).
An electrical signal carries
information using changes in current and voltage over conductive mediums.
attenuation
radiated power in the form of an e-m wave tends to spread
electric and magnetic fields are separated by
90 degrees
Dedicated Circuit:
: Dedicated circuits are distinct, physical circuits dedicated to directly connecting devices across a network
a signal wave
A carrier wave that has been modulated by an information or message wave, is called
the difference between "frequency" and "frequency bandwidth"
A frequency is a discrete value that can be represented by a sinusoidal waveform (ex., a tuning fork). However, most signals that contain information will be comprised a many frequencies, not just a single one. As an example, our voices are comprised of many frequencies of varying amplitudes between 100 Hz to about 8000Hz.
Who was the internet created by?
ARPANET, advanced research project agency, because of the cold war.
what is communications
Communications is the exchange of information between communicating entities in the form of data, images, video, audio, etc.
Layer 4 (Transport Layer):**
Enables the existence of multiple communication links between nodes and ensures that data is transmitted and received by the intended applications (ex., TCP, UDP, etc.) - once the packets have been delivered to the computer or server, the transport layer establishes the connection link between the source and destination - ensures the quality of the data - provides data delivered to the computer to the proper application
Circuit:
End-to-end communications path between two or more points. May consists of one or more links.
Full Mesh Network
Every node in the network is connected to every other node in the network. Expensive and complex! But extremely reliable because of much redundancy.
Partial Mesh Network
Every node is NOT connected to every other node. Problem with first example is if central node goes down, whole network goes down. Second is more reliable.
What are some of the ways we communicate electronically?
Ex. , PSTN, Internet, Satellites, CATV, AM and FM radio, Cellular Phones, etc.
Diagram of a sinusoidal wave
Figure 1 shows the sine wave, or signal, represented in the time domain where the x-axis represents time in seconds, and the y-axis is amplitude (e.g., power, voltage, etc.). In this figure, we selected a sine wave, however, we could have easily selected a cosine wave to represent our waveform.
How are telecommunications shaping the way societies function?
Get news from all over the world, access to vast quantities of data, virtual realities, e-commerce, social networking, e-learning, global awareness, exchange of ideas, advances in innovation.
Virtual Circuits:
Logical circuits that provide connectivity to users. Unlike switched circuits, many users can share the same physical circuit simultaneously
Layer 5 (Session Layer):
Manages communication sessions between hosts (ex., NetMeeting, etc.)
Layer 2 (Data Link Layer):**
Node-to-node communications. Information exists in logical digital format (1's and 0's) and is framed into symbols, and exchanged over a common network (ex., Ethernet, Token Ring, PPP, FR, ATM, etc.) here we can exchange data over a common network. you can communicate between computer to computer, etc.
Channel:
One way communications path between transmitter and receiver (two channels are typically assigned for full-duplex communications).
power density at distance
PD = PD/(4piDl^2)
Switched Circuits:
Physical circuits that are allocated to users when needed. Circuit switching provides physical connectivity for the duration of a specific call.
Layer 1 (Physical Layer): **
Physical interface/medium where information is exchanged in the form of electrical signals, optical and electromagnetic energy (hardware, transmission medium, interface specifications, etc.) - these are just signals, not at the data yet, no logical data
What makes up a network and how do you communicate through a network?
Physical links (guided and unguided) are connected together by nodes Nodes can be switches (OSI Layer 2) or routers (OSI Layer 3) Networks can be "full mesh" or "partial mesh" networks
how do you communicate through a network?
Physical links (guided and unguided) are connected together by nodes
Layer 3 (Network Layer): **
Provides an end-to-end transmission capability to transport data from source to destination over disparate Layer 2 networks. (ex., IP, etc.) facilitates exchanges between different source networks.
telecommunications?
Telecommunication is generally defined as communications over a large distance
What is the difference between a sine and cosine wave?
The difference between a sine wave and cosine wave is that they are 90 degrees, or π/2 radians, apart.
What is modulated?
The electrical current produced by the microphone varies proportionally with speech waves entering the microphone, and is said to be "modulated" by speech.
How do you determine how many trunks are needed for the amount of nodes in a network in a full mesh network?
X = [N(N-1)]/2 X = number of trunks N = number of nodes in network
we speak -
acoustically
Acoustic Sound Waves
are pressure waves through a medium such as the atmosphere for water.
carrier
carries the information by superimposing (modulating) the information signal onto the carrier waveform
full duplex communication
cell phones are an example, talk and receive at the same time. has two channels on each call, transmit and recieve
information captured in a wire is captured as
changes in voltage and currents
communications systems typically use what type of signals?
combination of electrical, EM, and optical
simplex communications
communication flows in one direction - from source to destination - like television
In 1821, Michael Faraday
discovered that as electrical current flowed through a wire, it produced energy (later termed electromagnetic energy) that continuously rotated around the wire.
central frequency
frequency of carrier and an associated frequency bandwidth
wavelength is measured
from peak to peak, how long until wave repeats itself again
time domain
how the amplitude of the signal varies with time
optical frequencies are
immune from emi because they use photons and have a neutral charge. transmit greater amounts of info because this is at such a high frequency range there are a lot of state changes between the carrier itself. used in fiber optics. the higher the frequency the more information can be represented.
A signal carries
information (ex., voice, image, video, data, etc.).
An electromagnetic (E-M) signal carries
information through unguided medium such as air or a vacuum.
"bandwidth
is also referred to as "capacity" which is measured in bits per second (bps) vice Hertz.
what is the osi model?
model developed by the International Organization for Standardization (ISO) provides a conceptual, layered architecture for data communications. used to figure out the best protocols and interfaces to communicate.
What is a longitudinal wave?
ones in which the oscillations are parallel in the direction of wave propagation or travel)
wave-particle duality
optical signals act as a wave and a particle at times
the power of the e-m signal is
proportional to the square of the electric voltage field component P = V^2/R
optical frequencies
reside between the infrared to ultraviolet spectrum
Signals encounters _______from the wire medium, as well as components within the communications path.
resistance (Ohms)
What is the formula that represents an electrical signal or EM wave?
sine wave formula where A, amplitude, or strength, of the signal (e.g., typically voltage or power) f, frequency of the signal in cycle per second (one cycle per second equals one Hertz (Hz)) t, time in seconds o with line, phase angle of the signal which represents the angle (typically in degrees or radians) of the start of the wave from a reference point (t=0 seconds). Note: π radians = 180 degrees
What must happen for human speech to be transmitted via electrical wires or radio transmitters?
the mechanical or acoustic waves must be converted into electrical signals. As these electrical signals travel through wired medium or antenna, EM waves are produced and emitted.
power factor
the power that you receive is going to be multiplied by the power factor, which tells you how efficient your circuit is - may be greater if system is efficient
acoustic waves vs electrical and electromagnetic waves
the real difference is that acoustic waves depend on molecules and are slightly different in their propagation - longitudinal propagation - vs electrical traverse propagation method
phase angle
the shift of a wave in radians from a reference point of 0
radio frequencies are vulnerable
to EM interference, EMI
What is a electromechanical (EM) wave?
used in electronic telecommunications systems are said to be transverse vice longitudinal (i.e., traverse waves consist of oscillations that are perpendicular to the direction of wave propagation).
what are the agreements between two communicating entities?
usually protocols and interface standards
An electrical signal is represented by
voltage (volts) and current (amperage)
amplitude can be in
volts, power, watts
power density
watts/meter^2 signal strength over distance
carrier frequency =
what the receiver is tuned into
are transducers required?
yes, because if we have an electrical signal and you want to put it in an optical system, you need a way to transduce the electrical signal into an optical signal. an electrical is nothing but electrons, but optical is photons
radar bands
bands broken up into letters in the frequency spectrum, these were used in world war II by frequency operators
what is frequency domain?
how the signal varies with frequency
frequency is
speed of light in a vacuum divided by wavelength in meters
the electrical field strength is proportionate to
the current going through the wire
one period is
until the wave repeats itself again
ohms law
v= current x resistance
Packet Switched:
Logical connections in which information in the form of data packets, do not necessarily following the same physical paths through a network.
What does the modulated electrical current that travels through the wire produce?
an EM wave or field, which is proportional to the modulated electrical signal. It is this EM field that enables radio frequency (RF) transmission from transmitter to receiver via unguided medium (e.g., air).
signal wave
carrier that has been modulated by information
need enough power to
overcome the resistance of the line
power
signal strength, V * current
half duplex communications
travel in both directions, but only one at a time, ex walkie talkie
