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I have HW with networking
1
HOMEWORK1
Total points: 30 must work individually
INSTRUCTIONS
a) Use the PP presentation: “Introduction to Telecommunications” and the “OSI model” as your main source of information when answering the questions in this HW.
b) THEN if you want to complement your answer with a material found in a web source feel free to do it. However, beware that “copy and paste “is not allowed but you can summarize the information on the web and REFER THE SOURCE appropriately.
c) Multiple choice questions can be answered by doing a detailed reading of the PP presentation. (In the end, quiz one and possibly the final, will test your understanding of the PP presentation NOT necessarily the web sources you have found)
d) Beware that unless you have a lot of experience in the telecomm field there are MANY web source materials not well explained. You might get more confused with the concepts by using the web as your main source instead of the PP presentation.
e)
PLEASE BE SURE TO READ THE PLAGIARISM SECTION ON THE SYLLABUS, IT WILL NOT BE EXCUSES
.
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1. Go to
http://www.mediacomcommunication.com/internet?cid=tsellint
a. What is the “SPEED” or “TRANSFER RATE” (if can be known from the advertisement) of each one of the 3 different promotions? (explain please) (1/2 point)
b. What is the BANDWIDTH (If it can be known) of each one the three different promotions? (1/2 Point) (explain please)
c. What is the CAPACITY of each one of the three different promotions? (1/2 point) (explain please)
d) Why is the main reason the download speed is typically different from the upload speed? (1/2 point) (explain please)
2. Read the Following sources (3 points)
a. PowerPoint presentation “Intro to telecomm”
b.
c.
http://fiberbit.com.tw/differences-between-baseband-and-broadband-transmission/
Submit 200 to 250 words integrated summary (An integrated summary is NOT a summary of the three sources separately, but a ONE you do AFTER reading the three sources, condensate in ONE). The quality of your summary will give you the points. BEWARE of PLAGIARISM, must be in your own words, there will be no excuses.
3. If a cable (MEDIUM) has been adapted to have a fmin = 0.5 GHz and fmax= 2 GHZ, (G is for GIGA). Which of the following statements are NOT correct?
a. It is possible to change the BW of the media if we change the coding and modulation technique.
b. A signal with BW = 1 GHZ will be severely attenuated when transmitted by this medium
c. The BW of the media can’t be calculated however, the capacity and the speed are easily calculated.
d. The BW can’t be increased by improving equalization and by reducing the noise on the line.
e. A signal of 5,000 KHZ will have no problem moving along this cable
Briefly ( i.e. ~ 50 words) explain the choices that you believe are NOT CORRECT and why. No explanation NO credit! (if more than one answer is NOT correct you tell me which ones are right and why… PLEASE Only explain the one(s) that is (are) NOT CORRECT) (4 points)
4. Make a 200 to 250 summary about the following link (Own Words please or heavy penalties) (2 points)
http://www.differencebetween.com/difference-between-encoding-and-vs-modulation/
5. 4.Which of the following statements (or statement is) are NOT CORRECT about Signal to noise ratio (S/N) or Carrier to Noise (C/N) (4 points)
a. We must increase both, the signal and the noise power so there is no need for an equalizer.
b. The lower the Signal-to-Noise ratio the worst it is for telecomm.
c. When the signal has low power and the noise has high power, the C/N (S/N) ratio is low.
d. C/N ratio is better when we diminish the noise power so the signal can be better differentiated
e. C/N ratio could not be calculated or controlled at all because the average noise and the signal level can’t be measured.
f. C/N ratio is directly proportional to the BW of the media and then directly proportional to the media Capacity.
Briefly explain the NOT correct choices only (Even if you have the correct choice, if your explanation is not technically correct no credit)
5. Which of the following statements are correct? (if any) (2 points)
a. Broadband can’t transmit Voice, Video and Data at the same time
b. Baseband can transmit Voice, Video and Data at the same time
c. Broadband can divide the channel in many phase slots so it can transmit different signals in different phases of the wave.
d. Baseband is capable of transmitting voice, data and video however it must divide the BW is different frequencies to allow the transmission.
e. Broadband and baseband use FDM and TDM respectively to transmit signals.
Briefly explain your choices (Please explain only the correct statements only …. if the explanation is not technically sound no credit)
6. If 5000 equal signals are transmitted in 50 seconds. The Period (In seconds or milliseconds) and frequency (in KHertz) of each signals is____ (Show your calculations or no credit) (1 point)
a. T= 1 second and 0.1 KHz
b. T = 0.01 milliseconds and 0.01 KHz
c. T= 0.01 milliseconds and 100 KHz
d. T= 0.01 seconds and 10 KHz
e. None of the above
7. Which of the following factors do(es) not affect the “transfer rate” in a connection (1 point)
a. The receiver’s ability to receive the data
b. The transmitter’s ability to put data on the media
c. The amount of or machines connected to the server demanding data (i.e. The server you are downloading from)
d. The noise of the media involved in the connection
e. The size of the file transmitter
Briefly explain your choice(s) (choices with not sound or correct explanation no credit)
8. A synchronous transmission uses the sequence “1100100100100100000000000” to synchronize the equipment and the sequence “0011011011011011111111111” to let the equipment know the transmission has ended. In this transmission line 10,000 bits of information are transmitted at once (NOT including the above sequences which are added for sync purposes) what is the efficiency of this synchronous transmission channel assuming there is no noise? Explain, show your calculations (2 points) give your efficiency in percentage with 4 digits’ precision (i.e. 90.9193%)
9. Your transmitter can transmit up to 5 Gigabits/second, your receiver can receive up to 7 Gigabits/second and the Capacity of the channel is 10 Gigabits/second. Which of the following statements are wrong IF any? (Assume there is no noise, and when one change is mentioned, assume the other parameters are maintained the same)
a. Changing the transmitter to a one capable of transmitting 7 Gigabits/second will increase the Bandwidth of the channel.
b. Changing the receiver to a one capable of receiving 15 Gigabits/second will increase the speed of the channel to 15 Gigabits/second.
c. If another media with capacity 15 Gigabit/second is used this will ensure to increment the BW to 15 Gigabits/second.
d. Changing the transmitter to a one capable of transmitting 10 Gbits/second will optimize the transmission from beginning to end.
e. Changing ALL (transmitter, receiver and media) to 10 gigabits/second in capacity will ensure the Bandwidth is 10 GHZ per second.
(5 points) Briefly explain your WRONG choices only (no sound explanation for your choices no credit)
10. Prepare a 400-hundred-word summary (in your own words) of the following link (a couple of figures can be inserted as fare as you explain tem in your own words) (4 points)
Again, I will stress to read the plagiarism policy in the Syllabus before submitting, you can’t claim ignorance or that “it is your first time” or that it is your first semester. This is valid for ANY of the above questions too.
http://www.newport.com/Fiber-Optic-Basics/978863/1033/content.aspx
TEC5313
Advanced Data Telecommunication
Eastern Illinois University
Introduction to Telecommunications
By: Dr. Rigoberto Chinchilla
(Updated JAN 2018)
Introduction
The basic telecommunication LINK structure Typically is composed of:
Emitter (Antenna, Light emitter/receptor, etc.)
Path (medium) (Fiber Optic, Open Space, Copper, Coax Cable)
Receiver (Antenna, Light emitter/receptor, etc.)
Communications Channel
Signal Bandwidth
In order to
data faster, a signal has to vary more quickly.
Channel Bandwidth
A channel or medium has an inherent limit on how fast the signals it passes can vary in frequency
Limits how tightly input pulses can be packed
Transmission Impairments
Signal attenuation
Signal distortion
Spurious noise
Interference from other signals
Limits accuracy of measurements on received signal
Transmitted Signal
Received Signal
Receiver
Communication channel
Transmitter
*
How good is a channel?
Performance: What is the maximum reliable transmission speed?
Speed: Bit rate, R bps
Reliability: Bit error rate, BER=10-k
Where “k” is an indication of how many times one bit is in error per amount of bits transmitted
i.e. 1 errored Bit every 1000000 10-6
Cost: What is the cost of alternatives at a given level of performance?
Wired vs. wireless?
Electronic vs. optical?
Standard A vs. standard B?
MODEMS
In order to transmit information over a medium for long distances, it is typically necessary to change/adapt the frequency of the signal.
For short distances (i.e. Computer to printer) sometimes the above is not necessary as far as the coding (how ones and zeros are represented electrically or optically) is consistent on both sides.
Why?
Why Do we need to Modify the signal?
Voice frequency signals (even if they are transformed to electrical/optical pulses) ARE NOT compatible with the frequencies the telecommunication media (Copper, coax, fiber, Open space) can transport.
Although the open space is pretty good for your voice, if you shout, it will not go much farther than maybe ¼ of mile in the best conditions, therefore we need frequencies that can travel over long distances.
Therefore, we need to ADAPT the signal to the media, the ADAPTERS are called MODEMS.
MODEM
MODULATION: Is the process that changes the shape and/or the frequency of the signal in the transmitter.
The signal MUST be changed according to a specific pattern (frequency adaptation) that should be able to
Travel over the media
Be understood at reception
DEMODULATION: Is the process of recuperating the original signal after a modulation process
MODEMS
Typically a MODEM (modulator/demodulator) is used in the transmitter and in the receiver so the transmission can go in both directions
The MODEMS at each side traditionally are named as part of the TRANSMITTER and RECEIVER
Meaning…Sometimes you don’t see them depicted in the diagrams
What is a “carrier”
Every time the MODEM adapts the signal to the media somehow it changes the original frequency of the signal (i.e. voice signal) to a NEW frequency.
This NEW frequency (called carrier) is capable to move perfectly to the media “Carrying” the original signal within
NOTE: Sometimes we call “carriers” to those companies (VERIZON, AT&T) who carry the signals of the phones. Ultimately that is exactly what they are doing : !providing a carrier” for our communications needs
Attenuation
As an electrical signal travels through a cable, it becomes weaker due to the resistance offered by the cable to the flow of electrons or light.(remember….. other electrons are “living there!” )
The “weakness” of the signal is called attenuation and it refers to the reduction in POWER (This translates in amplitude loss) of a transmitted signal.
Attenuation
A second source of attenuation which is not related with the loss of power due to cable is related with the signal frequency.
Not all frequencies can be transported at the same level within a medium, some frequencies are more attenuated than others due to bandwidth limitations.
When signals are close to the bandwidth limits tend to have more attenuation respect to signals close to the bandwidth center
Attenuation
The attenuation effect in general can be corrected by amplifying the signal. These amplifiers are called “repeaters”
Most of the time is not practical to insert amplifiers in the transmission line ( Although, if you see bulky boxes hanging there in the cables , these are typically amplifiers and equalizers.)
The power of the signal has to be high enough to be recognized at the receiver.
3.*
Attenuation
A loss of energy through a medium due to the resistance of the medium.
Amplifiers are used to amplify the signal to compensate the loss.
*
3.*
Decibel
To measure the relative strengths
Of two signals, or
One signal at two different points
P1 and P2 are the powers of a signal at point 1 and 2, respectively.
Note:
The decibel is
negative if a signal is attenuated and
Positive if a signal is amplified
Example
Suppose a signal travels through a transmission medium and its power is reduced to one-half. This means that P2 is (1/2)P1. In this case, the attenuation (loss of power) can be calculated as
A loss of 3 dB (–3 dB) is equivalent to losing one-half the power.
3.*
*
Decibel Concept
In telecommunications, signals are attenuated by noise and other factors. The decibel represents the attenuation of a signal
Attenuation = 10 *Log10 (Power received/Power transmitted)
As an Example if a Signal was sent with a power of 5 watts and was received with a power of 3 wats then the attenuation is
Attenuation = 10* log 10 (3/5) = 10 log 10 (0.6)
= 10* (-0.22) = -2.2 Decibels
The negative sign means a loss of power
Notice : When a Signal does not lose power the result is zero decibels , zero decibels means no Loss of power in telecommunications
Attenuation = 10* log 10 (5/5) = 10 log 10 (1)
= 10* 0 = 0 Decibels
Example
A signal travels through an amplifier, and its power is increased 10 times. This means that P2 = 10P1 . In this case, the amplification (gain of power) can be calculated as
3.*
*
One reason that engineers use the decibel to measure the changes in the strength of a signal is that decibel numbers can be added (or subtracted) when we are measuring several points (cascading) instead of just two. In Figure 3.27 a signal travels from point 1 to point 4. In this case, the decibel value can be calculated as
3.*
*
Distortion
Different to attenuation, distortion is the effect of changing the shape of the signal by a random pattern.
The changes in the shape of the signal are due mainly to “noise”. (noise is random).
Noise can come from internal sources like electrons moving randomly while the signals is passing the media or EXTERNAL natural or man-made sources
Noise and distortion are the variables ALWAYS present in ANY telecommunication application, they can only be reduced not eliminated.
Emerging technologies (Amplifiers, equalizers and modern coding techniques) can ONLY diminish the noise. However, the noise can be reduced to a level that it is difficult to detect.
Equalization
Equalization is the process by which the effect of distortion is compensated.
Now a days it is relatively easier because we have only to reconstruct the shape of a “1” (i.e. +5 volts) or a “zero” (i.e. -5 volts) An Equalizer is the device used to do that
The transmitter modem shapes the original form of 1’s and 0’s . (Although the bulky boxes hanging lines between poles (equalizers/amplifiers) reshape the distorted /diminished original signals.
Note that equalization (fixing the shape) perform a different task that amplification (increasing the power)
Bit Error Rate (BER)
Is the measurement of how many bits are not recognized as they were sent.
Meaning a zero was recognized as a one and vice versa
The main sources of error are Noise and Distortion (always present !)
BER =
[(Number bits received with error) / (Number of bits transmitted)] *100
The result will be a percentage
Carrier to Noise Ratio (C/N)
(Sometimes called Signal to Noise ratio S/N)
Under noise conditions (always!) you need the signal level much more higher than the noise level
The “carrier” is the frequency that modulates the signal or the signal within the medium
If the carrier (Signal) level is high and the noise level is low the C/N (S/N) ratio is high (The ideal condition)
Modulation Techniques
Amplitude Modulation: (AM) : Can be done is several ways as far as it is consistent on both sides
The binary signal (“0” or “1”)
A “1” typically means presence of signal in a time interval (i.e. +5 Volts)
A “0” Typically means no signal present in a time interval (i.e. = zero volts
The binary Signal (“0” or “1”)
Sometimes a “1” means a positive signal and a “0” means a negative signal (i.e. +5volts =1 and -5volts =“0”)
The binary Signal (“0” or “1”)
Sometimes “1” = zero volts and “-1” = – 5volts
Modern modulators
Modern modulators (AM, FM, PHASE etc.) make modulation and encoding a unified process
However we should not forget the fact that encoding is to decide how to represent a one and a zero and modulation is the process of adapting the signal frequency to the media.
Encoding
Please read this brief article which describes the difference between coding (encoding) and modulation (part of the exam)
http://www.differencebetween.com/difference-between-encoding-and-vs-modulation/
Encoding DOES NOT depend on which modulation technique will be used.
Modulation Techniques
Amplitude Modulation: (AM)
AM refers to the fact that we will differentiate a “1” from a “0” exclusively on the signal amplitude (level) only
For example a “1” = +5 volts and a “0” = +3 Volts
AMPLITUDE SHIFT KEYING (ASK): Is the name of Amplitude Modulation in the context of digital technologies.
Modulation techniques
Frequency Modulation:
Here instead of sending a “1” or a zero as in AM modulation (amplitude of voltage) wemight send a constant AMPLITUDE signal but TWO different frequencies
One frequency (f1) is present when a “one” is transmitted and another frequency (f2) is present when a “zero” is transmitted.
FSK: Frequency Shift Keying is called in the digital technologies context
Modems and Routers
Routers are devices used to route information over the internet, however routers need modems to transport the information over the lines. A router is considered a computer (in the big picture) or a Data Transmission Equipment (DTE) a modem is considered a Data Communication equipment (DCE)
Routers and Modems
At your home the Cable Company typically provides the MODEM (DCE) and you buy the router (i.e. At Walmart) and you connect them to have an internet connection or the telecom company might provide both upon your contract with them.
Many times Routers and modems are incorporated in just one box…here is how it works
Frequencies within a Digital signal
A digital Signal looks like a “train” of “ones” and “zeroes” as follows
Although they look like just positive voltage (“1”) and no voltage (“0”) every digital signal is composed of many frequencies.
Fundamentals of “1” and “0”
A “1” typically is a positive voltage signal
A “0” in this picture is a negative voltage
Notice that the bottom signals begin to look like a squares when the two signal on the top are added , showing the concept of frequency components in a “square” signal.
Frequency Concepts
In practice, an electromagnetic signal is made up of many frequencies (has sinus components; one is the fundamental frequency, others are multiples)
Spectrum – range of frequencies a signal contains.
Bandwidth – signal’s width of the spectrum.
Any media has a limited bandwidth => limited data rate!
*
Wavelength
Distance occupied by one cycle
Distance between two points of corresponding phase in two consecutive cycles
Assuming signal velocity v
= vT
f = v
c = 3*108 ms-1 (speed of light in free space)
Frequency Concept
In practice, an electromagnetic
signal is made up of many
frequencies (has sinus components; one is the fundamental frequency, others are multiples.
Spectrum – range of frequencies a signal contains.
Bandwidth – signal’s width of the spectrum.
dc Component (continuous component) – component with zero frequency.
Any media has a limited bandwidth => limited data rate!!!
*
Wavelength
Distance occupied by one cycle
Distance between two points of corresponding phase in two consecutive cycles
Assuming signal velocity v
= vT
f = v
c = 3*108 ms-1 (speed of light in free space)
Analog and Digital signals
Why digital signals are so popular now ?
It is generally less expensive to make digital equipment
Digital signals are less vulnerable to errors caused by interference (noise)
We know that there are only TWO choices A “1” or a “0” (analog signals have infinite number of choices !)
Advantages of Analog signals
Analog signals can be easily multiplexed
Analog signals are less vulnerable to the attenuation problem due to distance (they can travel farther without becoming too weak for reliable transmission)
Do not confuse the Bandwidth(BW) of the signal with the Bandwidth of the media
Every SIGNAL to be transmitted over the media has a BW (range of frequency of the SIGNAL)
Every Media has a BW or Range of frequencies that can pass (or transported over the media)
The BW of the MEDIA should be COMPATIBLE with the BW of the SIGNAL otherwise the signal will NOT pass over the media (it will be severely attenuated)
Or at LEAST MOST of the MAIN frequency components (The components who allow to identify the shape of the signal properly) of the SIGNAL should be able to pass over the BW of the media
How the frequency of a signal is calculated?
Frequency : Is the number of signals that can be transmitted in ONE second
The more signals (up and down changes) are transmitted the higher the frequency. In the following picture if the TOTAL time shown is ONE second, the highest frequency signal will be the one at the bottom.
How the frequency of a signal is calculated?
To measure how many signals are transmitted, the easiest way is to count either the TOTAL number of peaks in the whole one second snapshot or the number of valleys in the whole one second snapshot. As an Example the GREEN signal has approximately 6 signals transmitted in a second (assume the snapshot is for exactly ONE second). : 6 signals / 1 sec
EACH of the SIX SIGNAL take a period ( “T”) of 0.166666 seconds
Frequency in HERTZ is simply = 1/T = 6 HERTZ !!! , So HERTZ is the number of signals or SYMBOLS (BAUDS) transmitted in ONE second !
Can you see why the bottom (pink) signal has a frequency of 15 hertz and a period of T = 0.067 seconds (approx.)
What is a phase ?
Phase is just a delay of a wave (i.e. sinusoidal) respect to a reference wave.
As an Example , we can use the red sinusoid as an indication of a “1” and the blue one as an indication of a “zero” , based on the delay (phase shift).
Modulation Techniques
Phase Modulation:
A phase “p1” is present when a “one” is transmitted and a phase “p2” is present when a “zero” is transmitted (see previous slide)
PSK: Phase shift keying is called within digital technologies
Modern Modulation Techniques
The above three modulation techniques are the BASIS for modern modulation techniques.
Now a days a combination of Amplitude, Phase and frequency is used when modulating a signal
The objective is to pack more ones and zeros in every BAUD. (symbol transmitted)
Advanced Modulation techniques
There are more advanced techniques for modulating (adapting a signal to the media) a signal
These advanced techniques use a combination of the previous basic techniques in order to put more information in a signal and optimize medium capacity
Transmission Modes
SIMPLEX: The communication goes ALWAYS in one direction.
T.V. Broadcast
Radio Broadcast
HALF DUPLEX: The channel can transmit OR receive but not at the same time
Typical Telephone conversation
Internet “chatting”
Transmission Modes
FULL DUPLEX: Information can travel in both directions simultaneously
INTERNET
Most High-speed links between machines
Most equipment in the data telecomm field now a days is full duplex
Bits/sec vs. Bauds/sec
The amount of bits transmitted in a second is the instant speed of data (bits/second)
When we transmit with ASK, FSK, or PSK we can transmit one or more bits per symbol
A BAUD (symbol) CAN pack many bits on it !!!
Symbols (bauds)/second
CAPACITY: is defined by how many bits per second a media can transmit under PERFECT conditions.
Each symbol may represent different amount of bits
1 Symbol 2 bits
1 symbol 4 bits
1 symbol 8 bits
The important point is we can “pack” many bits in one symbol or BAUD
BAUD/second versus BITS/second
If I agree with you that every time I tell you by phone
“YES” this means = “11111111” and
“NO” means “00000000” THEN
I am transmitting MANY bits (8) with shorter SYMBOLS (YES and NO)
How about is we agree that “y” = “11111111” and “n” = “00000000” ?
In this case I am transmitting the SAME 8 bits with less symbols (Y and N)
Bits/sec vs Baud/sec
Symbols (bauds) per second vs. Bits/second
One symbol may be transmitted over a line that may represent more than one bit
Example:
1 volt = 0000
1.5 volts = 0001
2 volts = 0010
2.5 volts = 0011
etc
Media Bandwidth Concept
Any media is limited in its capacity to transmit frequencies
BANDWIDTH DEFINITION/CALCULATION:
(Minimum Frequency allowed by the media) subtracted from (Max. Frequency allowed by the media ) Or
BW = fmax- fmin
Bandwidth is in HERTZ (Hertz is represented as number of variations/second or BAUDS/sec)
BW as we will visualize it in this course
In this course we will assume that the BW of a media can be visualized as a RECTANGLE limited by a minimum frequency and a maximum frequency.
In other words we will visualize BW (for exam and Homework purposes) as a SQUARE (blue)
frequencies INSIDE the square will NOT be attenuated at all
Frequenc8es OUTSIDE the square will be completely attenuated
BW …REAL picture
In reality the BW of a media is not a “perfect Square” is more like bell shaped and it attenuates some frequencies more than others.
The frequencies close to the center of the shape are lightly attenuated and the frequencies close to the borders of the shape are greatly attenuated.
BW is defined (in reality) as the signals that can pass over the media with less than 3 DB of attenuation (-3DB) or signal frequency components that have not loss 50% of their power.
HOWEVER , for THIS course purposes we will imagine the BW of the MEDIA as a perfect SQUARE FILTER , that attenuates completely the frequencies of the signal when the frequencies are outside the box and let pass the signals when its frequencies are inside the box defined by fmax and fmin
BW Illustration
The following figure illustrates how BW is defined (Hertz) , in the peak the signals are not attenuated (central frequency) however near the borders (- 3 DB line) the signal are attenuated to a point that might become indistinguishable. The peak is ZERO decibels
More formal definition of BW
“ Is the difference between frequencies at the extremes of the central frequency , when the signal has been attenuated 3 decibels”
HOWEVER for this course , we will assume that the frequencies outside f1 and f2 will be completely attenuated and the frequencies inside f1 and f2 will be passed without attenuation (see previous figures) and BW = f2-f1 for a perfect square filter.
A little bit of history of the “bandwidth” concept and current misconception
Originally (in the old modem technologies of the 60’s and 70’s) one symbol (hertz) per second was one bit per second, so it was no NUMERICAL difference between Bandwidth and the number of bits per second transmitted
1 analog symbol sent = 1 bit send (“0” or “1”) so
ORIGINALLY (50’s , 60’s and even 70’s) if you say that a BW was 1000 Hertz it meant 1000 bits per second
A little bit of history of the “bandwidth” concept and current misconception
However with the improvement of coding/modulation many bits begun to be packed in ONE symbol , then the BW in hertz was NOT the SAME than the number of bits send
THE BW (in HERTZ) can’t change …is an inherent property of the media , every media has a CONSTANT BW . For example Copper has a BW in Hertz that could NOT change, Coaxial Cable has a BW (in hertz that you can’t change)
What it can be done is to pack more bits in each symbol so NOW BW (in Hertz) is NOT equal to the number of bits per second we send.
CAPACITY DEFINITION
Capacity is a measurement derived from complex formulas (theoretical out of the scope of this course) that translates the particular coding/modulation technique and the BW available in a THEORETICAL value how many bits per second can be transmitted
Example
MEDIA BW (fmax-fmin) CAPACITY (from formula)
COAX 3,000,000 Hertz 50,000 bits/second
COPPER 2200 Hertz 8000 bits/second
BW (in Hertz) NOT equal to capacity (bits/second)
BUT many technicians kept calling (70’s 80’s) “digital bandwidth” to the capacity (Bits per second) then in the daily activities they dropped the word “digital” and kept saying “Bandwidth” (erroneously) instead of CAPACITY
That is why this term is NOT properly used today by the general public.
BW (in Hertz) NOT equal to capacity (bits/second)
HOWEVER, if you are well trained in telecommunications, every time you mention “BANDWIDTH” you should think and speak!!! In terms of frequencies and every time you mention “bits/second” you should think in terms of CAPACITY.
CAPACITY DEFINITION (con’t)
Therefore, CAPACITY is a theoretical VALUE, formula derived and is amount of bits per second that a media can theoretically transport based on an SPECIFIC modulation/coding technique.
If we change the modulation/coding technique the CAPACITY (bits/second) might change but NOT the BW (in hertz)
The formula for deriving capacity assumes IDEAL conditions: NO NOISE, PERFECT COMPUTERS, PERFECT SERVERS etc.
Bandwidth Concept
Generally ,the more frequency a media can handle the more SYMBOLS per second is possible to transmit over the media.
– Therefore if a BAUD (Symbol) represents many bits , the more BW , the more number of bits can be transmitted per second
The higher the BW (HERTZ) of a media the more changes per second is capable to transmit
This implies more bauds (symbols) per second can be transmitted or more bits per second (depends on the transmission technique used)
Summary: Bandwidth vs Capacity
Bandwidth: is in frequency Units (HERTZ)
Capacity: is in bits/second. (Theoretical maximum)
Bandwidth NOT EQUAL to Capacity, and terms are used WRONGLY interchangeable today (after this course you will not do that…hopefully )
CAPACITY (in Bits /second) is directly proportional to BW (in HERTZ) , meaning the MORE BW (in Hertz) the MORE CAPACITY a media possess for a PARTICULAR coding/modulation technique.
Transfer rate or speed concept
Speed (transfer rate): In bits/second is a fraction of the total capacity and it is the REAL amount of bits/second we receive in a connection and it is an instantaneous value (can’t be predicted precisely)
Transfer rate (speed) is what we got in real life and it will ALWAYS be less than the Capacity , the transfer rate is less than the capacity because
Noise losses/retransmissions
Loaded servers not ready for the demands of our connection
Your computer limitations etc.
Transfer rate (“speed”)
Transfer rate is an instant measurement of the amount of information transmitted in bits/sec , for example you might be paying an INTERNET service of 15 Mbits/sec (theoretical capacity)
However when you download anything from the internet you probably will never be even close to half of what you are paying
“popular culture” confuses all these terms
The ideal setting is to achieve a transfer rate as close to the capacity
Bandwidth vs. Capacity
Bandwidth: is in frequency (hertz) Units
(Freqmax-Freqmin): hertz
Capacity: is in bits/second. (Ideal maximum)
Speed or transfer rate (bits/second): Always less than the capacity (the real transmission which can vary every instant upon different conditions)
Bandwidth NOT EQUAL to Capacity
NOTICE that even your textbook sometimes does not uses this concept properly.
BW vs. Capacity vs. Transfer rate
Why these terms are confused ?
Bandwidth is typically directly proportional to the capacity: The more Bandwidth IN HERTZ the media has, in general, the more Capacity in “bits per second” can be achieved.
It is easier for the common public to confuse all these terms as one. (Although they are very different!)
Bandwidth concept Misunderstood
The expression:
“We offer you a bandwidth of 15 Mbps”
It is NOT technically correct but it might be acceptable as far you understand the proportionality”
Another reason is that non-technical people seems to understand better the concept of “bits/second” that the concept of “HERTZ”.
Ultimately people is more interested in “bits/second” and not in “Hertz”
How companies advertise the above concepts?
Typically a company will NEVER mention Hertz when selling a service (for Obvious reasons)
Internet providers typically use the Phrase
“Speeds up to 10 Megabits/second” (or 100 Megabits per second etc.)
What this means is: “Your transfer rate will vary from nothing to a maximum of 10 Megabits/second” (Meaning “The Capacity is 10 Megabits/second if you are lucky” or “Under perfect conditions (never!) you will reach a transfer rate equal to the capacity”
Bandwidth is NOT a Bit accelerator!
The fact that a company offers an specific capacity (for example 1 Gbps) DOES NOT mean that we will reach that speed every time the media is used.
What means is :
You have a “pipe” theoretically capable of transport 1 Gigabps. Good luck!
you will be achieving some partial “transfer rate”.
Bandwidth is NOT necessarily a bit accelerator!
The transfer rate (“speed”) you can reach over the media depends mainly of:
The capacity of the media
The capacity of the transmitter to “fill” the media (the “pipe”) at its maximum
The capacity of the receiver to “accept” these amount of bits per second
The amount of other users using the same connection (i.e. Satellite or intercontinental optical fiber)
Noise conditions (or quality of the connection)
Take a closer look at this table and be sure you understand the difference among BW, Capacity and Transfer rate
MEDIA BW (HERTZ) Fmax-Fmin CAN’T CHANGE CODING /MODULATION TECHNIQUE Capacity : form formula that uses the two previous columns Transfer rate
Can’t be guaranteed or predicted ,
COAX 3,000,000 HZ Technique “A” 30,000,0000 bits/second Variable upon Instant conditions
COAX 3,000,000 HZ Technique “B” 40,000,000 bits/second Variable upon Instant conditions
COPPER 2200 HZ Technique “C” 5000 bits/second Variable upon Instant conditions
COPPER 2200 HZ Technique “D” 7500 bits/second Variable upon Instant conditions
FIBER OPTIC 50,000,000 HZ Technique “F” 40*109 bits /second Variable upon Instant conditions
FIBER OPTIC 50, 000,000 HZ Technique “G” 60*109 bits /second
Variable upon Instant conditions
More about Capacity vs Transfer rate (I)
EVERY internet provider Typically sells CAPACITY when announcing their product .(TV, Internet etc.) or as an example they might say “with speeds up to 15 Gbps” meaning the transfer rate MIGHT reach the capacity of 15 Gbps in theory
In other words your internet provider sells the MAXIMUM theoretical amount of BITS/SECOND that can be transferred if ALL is perfect like:
NO NOISE
Capacity o the Internet server you are visiting : Always available and as fast as the capacity of your computer
Capacity of your computer to fill the pipe: As fast as the capacity of your internet provider.
THE provider gives you that capacity ONLY between your computer and your internet provider main equipment, after that your internet provider may share “BW pipes” differently.
More about Capacity vs Transfer rate (II)
As you might suspect THESE factors, are not always perfect, this makes IMPOSSIBLE to reach the capacity (bits/sec) of what they are selling you .
This is a COMMERCIAL TRICK allowed by the government
Basically you will have to connect at 3 a.m.(when NOBODY else is connected) PLUS you have to have NO noise + your computer should be so fast to fill the CAPACITY they are selling to you+ The server you are downloading should serve a very few people (or no one) and be fast enough to fill the capacity promised
THEN ….you might reach the capacity advertised !
More about Capacity vs Transfer rate (III)
EVEN if the internet provider mention “Bandwidth ” or “speed ” they are wrong !!!! Transfer rate (speed) can’t be guaranteed because it depends on the conditions of the line in that very moment.
Speed could not be sold or guaranteed because the speed depends of so many factors (NOISE, Speed of your computer, speed of the server you are visiting etc.) . This is easy to test from your home, for example try to download a huge file and see if the file downloads at a constant speed.
What you will see that the speed (transfer rate) is changing by the second (constantly) meaning the conditions in the connection are constantly changing , also you will see in your download that you will NEVER reach the capacity they offered you when you contract your internet provider
Analogy…When you buy a new car ….
You buy MANY things in the market the same way , for example when you buy a new car, the dealer tells you the IDEAL CONSUMPTION (miles/per gallon)…meaning consumption in the car LABORATORY testing facility.
ONCE you buy a car , you have to drive the car in traffic, with loopholes, you might not be a good driver etc. etc. making your car almost always make LESS consumption (miles per gallon) than the ideal label of the car , but they sell to you the ideal consumption (if everything is perfect…including the driver!)
Capacity (bits/second) is the same (is the IDEAL label for your connection) however REALITY makes your connection less than the ideal they have sold to you.(Transfer rate in bits/second !!)
Capacity Concept Analogy
Bandwidth Concept Analogy
We can think of a “Capacity” as a pipe with an hydraulic capacity of “X” liters/sec.
If you input “Y” liter/sec you will have “Y” liter/sec as an output. (Y
Bandwidth “pipe”
SIGNAL Bandwidth
Each SIGNAL also has its own BW, however the BW of the SIGNAL is not necessarily the (and generally is not !) similar to the BW of the Media.
Theoretically the Signal BW is infinite, although is typically defined by a subtraction of frequencies as the BW of the media
Meaning the higher and lower components are not quite essential to distinguish the signal
The Key is to match the SIGNAL(S) BW with the MEDIA BW we will put the signals through
Modem helps with that !!!
In this course, unless specified when we mention “bandwidth” we will be referring to the MEDIA BW
Transmission methods
Asynchronous serial data transmission: Each character is transmitted individually and consists of four parts:
One or more start bits
The data bits
A parity bit
One or more stop bits
Asynchronous transmission
Data are transmitted one character at a time, where each character is five to eight bits in length (utile data). See ASCII code…
Timing or synchronization must only be maintained within each character; the receiver has the opportunity to resynchronize at the beginning of each new character
Idle state Start bit 5 to 8 data bits 1-2 Stop bits Idle or next
(+ 1 parity bit – eventually) Start bit
*
Synchronous
Asynchronous Transmission
The receiving interface must know how many bits there are to a character in order to determine where the current character ends and when to start looking for the next start bit.
Asynchronous transmission
The best way to think “asynchronous” is to understand that there is NO TIME pattern BETWEEN each transmitted character
In other words you can send a character the next second and the second character in 10 seconds and the third character in 3 seconds and so on
The receiver will be “patiently” collecting the information until the whole word is transmitted
Asynchronous transmission
It does not matter if you send characters not synchronized with an specific time, the “start” bit, the “stop” bit will always indicate the receiver when to start to identify the information
Asynchronous therefore is associated with unpredictability in time between information.
Asynchronous transmission
Disadvantages: Because the unpredictability, the need of extra bits between small pieces of information give the method a typical 70% of efficiency
Example 1: 1 stop bit, 1 start bit, 1 parity bit, 7 bits of information. (7/10)
Example 2: 1 start bit, 2 stop bits,1 parity bit, 8 bits of information (8/12)
Advantages of Async Transmission
Pretty simple
Async: Used when devices are close or for short messages.
A Router that is being programmed in a room
A Switch
Our Routers in 4411 will be accessed initially using async lines through the “console port”
A printer connected to a home computer
What is parity?
It is a SIMPLE or SIMPLISTIC way to track errors in a transmission of small amounts of bits.
Parity can be “ODD” or “EVEN” which might mean the quantity of ones(“1’s) transmitted.
I.E. If we transmit 5 ones and 2 zeros of information, then the parity bit will indicate let’s say “ODD” number of ones in the transmission side. Meaning the receiver must receive and odd number of ones.
However , if TWO “1’s” are in error (and are interpreted as zeros) no error will be caught ! That is why is simplistic! However, it works fine most of the time because it is done with very short messages and at very short distances (i.e. Computer to printer)
Synchronous Transmission
A serial bit stream is sent over the line without start or stop bits to synchronize the bits in each character
The characters follow one another immediately rather than coming at random intervals as in asynchronous transmission.
Synchronous transmission
Works with blocks of bits (characters)
Inter-clock synchronization:
auxiliary clock line
synchronization at the block level => extra flag and control fields => data structure of frame
Flag fields (synchronization) fields: special bit sequences or sync characters; denoted as preamble-header and trailer
Flag Control Data field Control Flag
Field field field field
Synchronous transmission
The entire block of data is synchronized with a unique code which, when recognized, tells the receiver where a character begins
As in the asynchronous technique, the receiver must know the number of bits of a character
Synchronous transmission
A clock in each side must be synchronized in order to understand when each bit starts and stops
The synchronization is done with an initial bit stream like “110011001010101010”
The efficiency in this case reach typical values up to 95% to 98 %.
Synchronous transmission
Example: “11001100101010101010” to synchronize and “00110011010101010101” to indicate the end of transmission of a “chunk” of 10,000 bits of information
Efficiency of 10,000/10,040 which is approximately 99%
Routers use Synchronous transmission in their serial ports
Advantages/Disadvantages
IS pretty clear that Synchronous transmission is more efficient
Is the most used method now a days
Disadvantages:
Difficult to achieve in noisy environments
Expensive equipment
Expensive software routines
Synchronization may be a serious problem
Multiplexing
Multiplexing means the use of one facility to handle several separate but similar operation simultaneously
In Telecommunications it means the use of one telecommunication link to handle several channels of voice, data or video.
Multiplexing
To multiplex means to divide the link into “slots”, with each division containing information from a separate source
The slots can be divided in time (TDM) or frequency (FDM).
Time Division Multiplexing (TDM)
TDM can be compared to a switch that rapidly samples a number of lines
These samples are sent across the data link, then routed back to their original sequence by another switch at the receiver
“Baseband” technologies use TDM as a main technique to transmit data, voice and video
TDM multiplexer
Frequency Division Multiplexing (FDM)
In FDM Each transmission is assigned its own individual frequency, allowing simultaneous transmission of many data streams over a single line
The receiver contains demodulators, each looking for a particular frequency
Cable companies use FDM to transmit the video channels and offer other services as INTERNET and telephone (BROADBAND)
FDM Multiplexer
FDM multiplexer
Baseband Vs. Broadband
Baseband transmission means that the signal to be transmitted has ALL the BW of the media (only transmit one signal at a time in any direction over the cable!)
In general the base band signal is not modulated (modified) in certain protocols like the Ethernet protocol
Baseband is used mostly to transmit digital signals and is used by most computer networks
So baseband can transmit only ONE signal at a time
Broadband
Broadband divides the capacity of a link in two or more channels, each of which can carry a different signal
All channels can send simultaneously
Satellite, DSL, Wireless technologies, cable TV etc are examples of applications using broadband media
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TEC5313
Advanced Telecommunications
Eastern Illinois University
The OSI Model
By: Dr. Rigoberto Chinchilla
Network Design Goals
Connectivity: Everybody regardless of “status” or localization must be connected
Reliable performance: Is critical that the organization can operate competitively without interruptions
Robustness of the connection
Few errors in transmission
Network Design Goals
Management Control: The network must have troubleshooting specialized tools for network analysis.
These tools are key to the installation, performance and maintenance of the network
Scalability:
The ability to grow the network easily +
The fact that growth does not affect efficiency (It does not make sense to grow easily when growing increments problems)
The Layered Model
For a complex, multivendor internetwork to operate , its devices must be able to communicate with each other
The networking industry uses a model: The OSI model- that provides guidelines for efficient telecommunications
The separation of networking functions is called LAYERING
A general model of Communications
Learning about Networking is EASIER when you start with theory and concepts and THEN move on to more concrete aspects of implementation/practice.
As network PROFESSIONALS, you need to learn of how networks communicate BEFORE designing, building, and maintaining network
Complexity
The network communication process is complex :
The data , in form of ELECTRIC signals, MUST travel across media (The modem plays an important role !)
The destination ID should be correct, The Sender ID should be correct and the PROTOCOLS used in each layer should be perfectly understood on both ends
The data needs to be converted BACK to its original form in order to be understood by the recipient.
Chunking is the way to go !
A message (right before to be sent) is “chunked” in many pieces in order to handle the whole message better
The first “chunking” occurs at OSI level 5
The chunks at this level are called “dialog units”. These are “virtual chunks” divided logically by content (i.e. a bank transaction should be though as a UNIT, because must be have integrity and must be complete)
So in level 5 we are not “chunking” information by the size in bits (as in the next levels) but by the message unity
The “chunks” from level 5 (Dialog Units) are sent to OSI level 4 in order to be further classified/tagged and rebuild and are called “segments” once in level 4.
Chunking is the way to go !
Once in level 4 , the dialog units are divided in many pieces (based on a maximum number of bits) to prepare them for transmission.
Each piece in level 4 (Called “Segment”) is “prepared” for transmission by
Specifying the protocol to be used (i.e. TCP or UDP)
The type of error correction algorithms to be used
Sequence of each segment (because it must be reassembled once reach the other side).
The PORT at which the segment is directed etc. (port in level 4 context means application like http, telnet, ping etc.)
Once ready is sent to level 3
Chunking is the way to go !
Beware that AFTER the dialog units are “chunked” to form Segments , these segments GROW in size because all of the above information has been added.
At level 3 We will have to ADD more information to the SEGMENT , therefore on level 3 a PACKET will be build which will be BIGGER than the segment because we need to add more information.
The generic NAME of the chunks is PDUs (protocol data units)
SEGMENT : is the level 4 PDU
PACKET: Is the LEVEL 3 PDU
Chunking is the way to go !
THE PROCESS OF ADDING MORE INFORMATION WHILE THE “CHUNK” IS MOVING DOWN FROM LEVEL 4 THEN TO LEVEL 3 THEN TO LEVEL 2 IS CALLED
“ENCAPSULATION”
Encapsulation
The first reason what is called “encapsulation” is because the new information added is appended at the beginning and at the end of the chunk (typically) when moving from level 4 to level 3 to level 2 to level 1. Giving the sense you are adding extra stuff on both sides.
The second reason is called “encapsulation” is because the information in level 4 is NOT understood in level 3 , and the “stuff” send to level 2 from level 3 is NOT understood by level 2 !
So EACH level handles the information coming from the upper level as “data” …. level 3 does not have idea that level 4 added some extra stuff and handle ALL what level 4 sends as “data”
Encapsulation
Because “stuff” (important information) is passed/added from one level to another level and the next level does not understand what is passed from the previous level , the generic unit that is passed is known as “PDU” Protocol data unit.
For Example from level 3 to level 2 a PDU is passed (in this case the PDU passed from level 3 to level 2 is a packet)
Chunking is the way to go !
The segments are sent to OSI level 3 to be further processed and are called “Packets” or “Datagrams”
In level 3 , MORE stuff have to be added like
IP address of Origin
IP address of destination
Packet sequence
Length of the packet (they could be of different length)
Some Flags (bits either in the “0” or “1” position) to indicate special conditions (like Urgency or priority)
Pretty much the Routing information is added in level 3 .
Chunking is the way to go !
The Packets are then sent to OSI level 2 to be further processed (adding MORE stuff) and are called “frames”
The PACKET is THEN FILLED with more stuff like
ETHERNET addresses (sender and receiver)
FRAME ERROR algorithms etc.
In summary FRAMES are build so the information can travel on SWITCHES for long distances and/or in Local Area Networks (LANS)
Chunking is the way to go !
Finally the “frames” have to be reprocessed to form BITS ! First in the form of “1” and “0’s” in SOFTWARE form THEN formed in ELECTRICAL or OPTICAL pulses can be put in to the media using the right modulation technique, Coding /decoding etc.
The Frames then are ultimately decomposed in bits and then transformed to voltage, electricity, light etc. so they can travel as bits over the media.
Chunking
A One page word document for example of 5000 bytes (~40,000 bits) is typically divided in many chunks of 1500 bits
Each little chunk is processed by adding a sequential number, a destination an origin and some other information, so EACH chunk will grow from lets say 1500 bits to a bigger amount of bits when going down through the OSI levels (Upon the protocol used)
Chunks of Information are the key !
Before data can be send across networks as electrical/optical pulses, it first MUST be broken in manageable chunks
The data that travel across the network is not the original information, instead is The original information codified !
The GENERIC and TECHNICAL NAME of a CHUNK at any level is called “PDU” or Protocol Data Unit.
Why all of this ?
Why not to send the info without all these “complications”?
Well……. believe or not the “Explosion” in telecommunications technologies of the last three decades has been due to this “chunking model” ! Combined with
Huge amounts of BW (better and more optical fiber)
Powerful processors, better coding platforms cheap memory and smaller electronic components.
Why all of this ?
Well … the “chunks” (packets if routers are used or Frames and cells if switches are used) MIGHT NOT (typically they don’t ) travel over the same path and they do not even reach the destination in the sequential order they were created! (that is why they have to have a sequence number)
The above has proven to be the MOST efficient way we know to send/receive information
Until someone else figures out the new telecommunication generation, so far NOBODY has figured out a better or more efficient way !
Advantages of “chunking”
Computers on networks can take turns sending “chunks”, and one computer with a large amount of data to transmit will not monopolize the network’s bandwidth
If network is disrupted and a chunk is lost, only that small amount of data, rather than the entire file, must be retransmitted
Typically, “chunks” can take different paths to the destination (even if they come from the same source!). So if one path becomes congested they can take an alternative one
What is a protocol ?
Is a common set of rules and languages that should be followed by the parties involved
In Telecommunications means that the networks should restrict themselves to follow the “rules” and the “control signals” (language)
PROTOCOL: “ A set of rules that determine the format and transmission of data”
There are different protocols in telecommunications depending of the function they are performing
Who rules the protocols ?
OSI (International Organization for Standardization)
TCP
IP
DECNET, SNA
IETF (Internet Engineering task force)
Internet drafts (how the internet should evolve, behaves etc)
RFC
Implementations of Domain Name Servers (DNS)
Specifications on Network Address Translations (NAT)
IEEE
The 802 Project (created February of 1980) this regulates the 802.x protocols
THE OSI 7 layer model (Each layer has its own protocols)
Why a layered model ?
To divide the interrelated aspect of network operation into less complex elements
To define standards interfaces for “plug and play” compatibility and multivendor integration
To enable engineers to specialize design and development effort on modular functions
Why use a layered model?
To promote symmetry in the different internetwork modular functions so they interoperate
To prevent changes in one area from affecting other areas so each area can evolve more quickly
To divide the complexity of internetworking into discrete, more easily learned operation subsets
The “peer to peer” principle
“Each layer of a transmitting system uses its own protocol to communicate with its peer layer in the receiving system”
Each layer’s protocol exchanges information, called protocol data units (PDU’s), between layers
The encapsulation principle
Each layer of the OSI model depends on the service function of the layer below it
To provide service, the lower layer uses encapsulation to put the PDU from the upper layer into its data field
The lower layer can add whatever headers and trailers it will use to perform its functions
7-Layer OSI Reference Model
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Network
Layer
Application
Application
Data Link
Layer
Physical
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Communicating End Systems
One or More Network Nodes
End-to-End Protocols
THE ROUTER way to communicate between TWO different networks
NOTICE from the PREVIOUS SLIDE how the ROUTER WORKS:
FIRST: It takes the Ones and zeroes in electrical form and convert them to a software form (LEVEL 1)
SECOND : It REBUILDS the FRAME (LEVEL 2)
THIRD: Takes away the stuff added in level 2 until finds the PACKET
FOUR: Reads from the PACKET (Among other things) WHERE it has to send it, Meaning which port of the router has to output that information.
FIVE: ONCE it knows where to send the packet, it has to REBUILD the FRAME to its original state (it might change the ETEHERNET ADDRESS)
SIX : It has to decompose the FRAME in bits again and THEN put the info in
Electrical/optical form to travel through the media toward another router.
Encapsulation steps
Build the data
Package data from end-to-end transport
Append network address in header
Append local address in the data-link header
Convert to bits for transmission.
OSI layers and encapsulation
Application Processes
The Upper layers : Application Layer(7)
The application layer (Layer 7) of the OSI model is the closest (interface) to the user
It provides network services, such as file access printing, to the user’s application :TELNET and HTTP
Rather than provide services to other OSI layers, provides services to applications OUTSIDE the OSI model
The Upper layers : Application Layer(7)
The application layer decides:
What “applications” need services ?
Word processing programs
Bank terminal programs
Spreadsheet programs
Web pages and databases
LEVEL 7 is called the “HUMAN-MACHINE” Interface level
Application layer
The application layer is the closest to the end user when interacting with software applications such as sending and receiving e-mail over a network
The application layer deals with data packets from client-server applications, domain name servers and network applications by examining the following elements:
Client/server
Domain name system
E-mail
Telnet
FTP, TFTP, HTTP
Layer 7 Responsibilities
Synchronizing cooperating applications between the user and the OSI model.
Establishing agreement on procedures for error recovery between the USER and the layer 7
What are “Layer 8 problems” : IS a Code between telecomm-computer people to describe that the problem is the human in front of the machine. (kind of joke )
OSI Upper layers
Layer 6: Presentation Layer
Layer 6 presents data in a form that the receiving device can understand what the sending device is saying.
Two people talking different languages will not work !
Functions:
Data Formatting
Data Encryption
Data Compression
Presentation Layer Tasks
Determines how graphic images, sound, and movies are presented
Provides encryption of data
Compresses text
Converts graphic images into bit streams so that they can be transmitted across a network
Presentation Layer Functions and Standards (layer 6)
Presentation Layer Functions
Layer 6
Imagine two dissimilar systems, the first system uses Extended Binary Coded Decimal Interchange Code (EBCDIC) to represent characters on the screen.
The Second system uses ASCII for the same function.
Layer 6 provides the translation between these two different types of codes
File Formats used in layer 6
File formats
ASCII(7 bits code character) Contains simple character data and lack of any sophisticated formatting commands, such a boldface or underline (i.e. NOTEPAD)
EBCDIC is an 8 bit code character used in mainframes
Pictures, Music, and Movies
Data Encryption (Layer 6)
An encryption key is used to encrypt the data at its source and then to decrypt the data at its destination.
Encrypted data is called cipher text; unencrypted text is called clear text.
Data Compression (Layer 6)
Presentation layer (6)
The presentation layer provides code formatting and conversion services
Code formatting ensures that applications have a meaningful information to process
If necessary, the presentation layer translates between multiple data representation formats for text, data, audio, video, and graphics
Session Layer (5)
The session layer establishes , manages, and terminates communication sessions between applications.
Essentially, the session layer coordinates service request and responses that occurs when applications communicate between different hosts.
Session Layer (5)
As an Example a BANK transaction has to be treated in very specific DIALOG UNITS , it generally decompose the “message” (bank transaction) in very specific parts that has to be EXACTLY completed (re-assembled) by the application.
Layer 5: dialog control
The session layer establishes, manages, and terminates sessions between APPLICATION layer protocols:
Starting
Stopping
Synchronizing/Re-synchronizing
The session layer coordinates applications as they interact on two communication hosts
Dialog Separation
Layer 5: dialog control
Communication between two computers involves many mini-conversations, thus ensuring that the two computers can communicate effectively
One requirement of theses mini-conversations is that each host plays dual roles:
Requesting service, like a client
Replying with service, like a server
Determining which role they are playing at any given moment is part of dialog control
Layer 5: dialog separation
Dialog separation is the ORDERLY initiation, termination, and management of communication in which a transaction is tracked through completion
A transaction is defined as an atomic or indivisible unit of work- That is, it is a unit of work that either must fully complete or must be rolled back to some known state, as through it never began.
Example: A bank withdrawal
At the “Time Axis, t = checkpoint,” the host A session layer sends a synchronization message to host B, at which time both hosts perform the following routine:
Back up the particular files
Save the network settings
Save the clock settings
Make note of the endpoint in the conversation
Dialog Separation
Layer 5 Protocols
Layer 5: The session Layer
The session layer allows two applications to synchronize their communications and exchange of data
This layer breaks the communication between two systems into dialog units and provides major and minor synchronization points during that communication
Example: A large distributed database transaction among multiple systems might use session layer protocols to ensure that a transaction either is completed fully or is “rolled back” to a know checkpoint on all systems
COMPUTER engineers vs Electrical Engineers
Until the 90’s (approx.) COMPUTER and or software ENGINEERS used to deal with the upper three levels of the OSI model. Electrical/telecomm Engineers used to deal with the LOWER four Levels.
MOST schools now in the world have united as “Electrical and computer Engineering Schools” because in the 2000’s BOTH engineers and technologist has to deal with the seven levels.
OSI Lower layers Typical protocols
Transport Layer
The transport layer defines end-to-end connectivity between host applications (not user applications)
Establish end-to-end operations, it constitutes a logical connection between the endpoints of the internetwork
Send segments from one end to another end host: As the transport layer sends its segments, it can also ensure data integrity through the use of check sum calculations on the data
Provides flow control mechanisms
Provides data reliability
Transport Layer
Transfers data end-to-end from process in a machine to process in another machine
Reliable stream transfer or quick-and-simple single-block transfer
Port numbers enable
virtual multiplexing
Message segmentation and reassembly
Connection setup, maintenance, and release
Transport
Layer
Network
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Communication Network
OSI layers
15.bin
Encapsulation Picture
Network Layer (Layer 3)
Transfers packets across multiple links and/or multiple networks
Addressing must scale to large networks
Nodes jointly execute routing algorithm to determine paths across the network
Forwarding transfers packet across a node
Congestion control to deal with traffic surges
Connection setup, maintenance, and teardown when connection-based
Network Layer
“Is in charge of decide where to go and what will be the road to take” (uses the TCP and UDP as the most “famous” protocols.)
This function is performed by a router
Routers understand an International accepted addressing scheme (INTERNET) to decide where to go.
Routers understand a local accepted addressing scheme too (INTRANET) to decide where to go
Router role in data communications
Routers Understand IP addressees
IP Address : Unique identifier of a computer in the world (If it is connected to the internet) : example: 205.218.6.5
IP addresses can also be used even if the computers are not connected to the internet for building private WAN and LAN networks
IP addresses and Networks
Each SEPARATE network MUST have a different set of IP addresses as an example
THE MASK (something we will explain in detail later) of a network ,tells how many IP addresses are assigned to a network
A network with 4 IP addresses has a mask 255.255.255.252
A network with 8 IP addresses has a mask of 255.255.255.248
A network with 16 IP addresses has a mask of 255.255.255.240
A network with 32 IP addresses has a mask of 255.255.255.224
The mask ONLY tells the maximum number of computer devices that can be connected in a network NOT how many are connected in reality
The maximum number of computer devices that can be connected in a network are the number of IP addresses assigned MINUS two
IP addresses and Networks
The rule of thumb (for now) will be as follows (PLEASE use this for your LAB 1 exam)
A network with 1 or 2 computer devices needs 4 IP addresses (mask 255.255.255.252)
A network with more than 2 and less or equal than 6 needs 8 IP addresses (mask 255.255.255.248)
A network with more than 6 computer devices and less or equal than 14 computer devices needs 16 addresses (mask 255.255.255.240)
A network with more than 14 computer devices and less or equal than 30 computer devices needs 32 IP addresses (mask 255.255.255.224)
Once a Portion of IP addresses has been assigned to a particular network, their IP addresses can NOT be used in a different network , even if the first network is not using them
Router role in data communications
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Network Layer
The most famous (and used) addressing schema is called IPv4 used by the IP protocol
IPv4 Uses an address and a mask
Address: 205.218.7.1 (example)
Mask: 255.255.255. 248 (Example)
The mask tells HOW MANY IP addresses are assigned to a network which gives and indication of how many computers are (or can be connected) within a particular network
Another popular protocol used to be “IPX” by Novell networks (Pretty much out of phase now)
The Data Link Layer (2)
It provides the transit of data across a physical link
It typically work with FRAMES
The data link layer is concerned with physical addresses (i.e. Ethernet card or NIC card)
“0055.2EA4.8883.4231” (Ethernet address)
It figures out when to send BITS to the media (through a modem !) , controls error detection at the frame level
Data Link Layer
Transfers frames across direct connections
Groups bits into frames
Detection of bit errors; Retransmission of frames
Activation, maintenance, & deactivation of data link connections
Medium access control for local area networks
Flow control
Data Link
Layer
Physical
Layer
Data Link
Layer
Physical
Layer
frames
bits
Data Link Layer devices
The devices which process frames are called SWITCHES , because they can understand the CONTENTS of the frames and move them accordingly.
Switches have MULTIPLE ports. A switch which just one port is called a “Bridge”.
HUBS preceded switches they send frames to all devices of a network (broadcast) meaning the HUB only amplifies and transmit blindly (WITHOUT knowing the content of the Frame) Hubs are considered level 1 devices (like an amplifier /transmitter)
The Physical layer (1)
Defines the electrical and mechanical specifications of the communication equipment
Defines the rules for activating, maintaining and deactivating the PHYSICAL devices in telecomm systems
Works with electricity and hard devices like modems, Multiplexer, satellites etc.
Physical Layer
Transfers bits across link
Definition & specification of the physical aspects of a communications link
Mechanical: cable, plugs, pins…
Electrical/optical: modulation, signal strength, voltage levels, bit times, …
functional/procedural: how to activate, maintain, and deactivate physical links…
Twisted-pair cable, coaxial cable optical fiber, radio, infrared, …
What Kind of “Stuff” is done in LAYER 1 ?
MODULATION
DEMODULATION
AMPLIFICATION
Equalization (for distortion)
MULTIPLEXING
CODING (or ENCODING)
MEDIA: Antennas, Optical Fiber, Coaxial Cable, Copper Cable etc.)
De-Encapsulation (at the final destination)
When the remote device receives a sequence of BITS at LEVEL 1 and passes them to the data link layer
At level 2, The data link layer reassembles the FRAME
The FRAME is sent to level 3 and opened to find the packet.
The PACKET is open again to find the segment
And so forth ……
OSI layers and encapsulation
The TCP/IP model (Internet Model)
The INTERNET model was created originally by the department of defense (DoD) in the 70’s just with four layers
Application
Transport
Internet
Network
The TCP/IP original model
The TCP/IP model (Internet Model)
In the DoD Internet model an “APPLICATION” means a NETWORK application like FTP, TFTP,DNS etc.
In the OSI model context an APPLICATION means modern software at the level 7
So we have to be careful of the context and meaning of “application”
Emphasis in TEC 5313: Levels 1,2,3,4
Problems with Using IP Addresses
The Domain Name system
So far thousands of top-level domains exists on the Internet
.us United states
.uk United Kingdom
.edu Education
.org Non-profit sites
The DNS server
The DNS server is a device on a network that responds to request from clients to translate a domain name into the associated IP address
If a local DNS server is capable of translating a domain name into its associated IP address, it does so and returns the result to the client
If it can not translate the address, it passes the request up to the next higher- level DNS server on the system, which then tries to translate the address
If the DNS at this level is not capable to returns positive results to the clients sends a request to the next higher level server and so on
If the name can not be found , then it is considered an error and an error message is returned
Network Applications
DNS Function
E-Mail Messages
We select a network application based on the type of network we need to accomplish
Each application program type is associated with its own application protocol
WWW using HTTP (Chrome, explorer)
Remote access programs using TELNET
E-mail Programs supporting the POP3 application layer protocol
Application Layer Examples
Telnet – provides the capability to remotely access another computer
File Transfer Protocol – download or upload files
Hypertext Transfer Protocol – works with the World Wide Web
Network Security Services
Integrity Service: information received from network has not been altered during transmission
Authentication Service: the receiver can authenticate that information came from purported sender
Privacy Service: information is readable only by intended recipient
In applications that require network security, integrity & authentication essential; privacy not always justified
Why is important the OSI model ?
In a few words and very personal words (I have been involved in this are for 30 years)
I have never know a good data telecom engineer who does not understand the OSI model
I have known hundreds of people working in telecommunications , most of the ones who struggle to do a good job, do NOT understand the OSI model
NO understanding of the OSI model Probably you will not progress too much in this field
