Second Lecture DCN386

Week 1 Second Lecture
DCN386

Next Question,

What is analog transmission and how does it work? (5 mark essay question)

In the history of communications, two important technologies their was analog at the beginning then their was digital, for week 6 you have to figure out why digital is good and analog is not, in fact analog transmission in Canada is non-existent, its making a come back through fibre-optic technologies, it uses analog.

What does the word analog mean?
Analogous it means that something is the same as, but not identical, visualize is two objects such as two different color markers red and blue, they are analogous, we are going to reinvent the telephone go back 120 years and reinvent the telephone, when people use analog transmission that means they are sending information through a phone company service,
What do you need to invent a telephone?
We need a power source, we need a circuit, we have a power source and a complete circuit of electricity will flow down the circuit,

Drawing of a circular wire with flowing electricity, its 60 ohms per-second, now were going to send the power through the circuit, but we want to modify the wave and change it in such a way to reflect the sounds you make when you talk into the phone, you voice which is a wave of sound is being transmitted through the receiver, how do we do this it is very simple, we are going to have a tiny container, in the container we are going to put a magical compound, a semi-conducting compound Carbon, which is a semi-conducting compound, in between the carbon we are going to put a membrane of some sort, carbon has a magical trick when it is compress it conducts electricity better, membrane is a wire and the sound will be analogous to the sounds that you make, we now have invented a telephone, the theory is as simple as that, at the other end of the circuit, there is a speaker as this goes round it vibrates the cord and you can listen to the sound on the other end.

What does this have to do with datacom….nothing at all, but for the longest period of time in Canada, all computers needed to make sound….modems made the sound for the computer, modems would take data, and change a beautiful even pattern to represent a 1 or 0 bit, that is all modems do, now we are going to invent modems,

If he gave us ten bucks and went to a garage sale u can buy enough equipment to make one,
Modem processes two different sounds 1’s and 0’s the receiving modem knows the differences in the sounds and will re-create 1’s and 0’s and process the information.

Ever see a old fashion volt metre? It is basically a little box connect to a circuit to both sides it swings it will be negative or positive, find one of the devices take it apart and put the arrow thing into a shoe box, you attach the voltmeter to the serial port to your personal computer, the same that you stuck your port into, to talk to another computer…..how does the computer send it out to the box….analog or digital?….digital of course, even when data is being send over the serial port, drawn 0100001, carry an ASCII chart with you, show your ASCII chart to everyone!, that binary was an A key theirs a special interrupt called INT14 and it will send the process through the cable in a series of pulses, in pulses some are positive and some are negative, back to our arrow, are little arrow goes up and down when transmitting data, we invented a modem with a wire attached to a bell at the other side, when the pulses go through the wire it will hit the bell on the other side and it will make thebell Ding Dong representing 1 0 1 0 1 0, all you have to do is invent a device on the other end to read the 10101’s and re-creates to make the sounds, modems create sounds, the sounds are interrupted by other modems…digital data that is re-created….modems……remember the noise when you got the number wrong, and the operator was in ur modem….i tripped out to that lol YO THEIRS A VOICE IN MY MODEM….picked up the phone…couldn’t connect to battle.net

The first modem was the Bell 102 , Miracle new technology, first modem beautiful thing it ran at 300bps, how many characters could it send in a minute? Before we talk about how this works we are going to talk about

Analog telephones, for years telephone engineers studied people normal conversational sounds, they realized human beings can make very low sounds, some people have high voice, but for ordinary conversation it was discovered if you have a frequency range…what does that mean….low and high waves, the lower the frequency the further you can send the signal, the higher the shorter the distance you can send it without being amplified.

200hz and 3400hz is a standard range sound can travel at a distance, your LAN phone filters out everything 4000hz, hertz, Who was the inventor Dead German Guy, created the cycles per second which are hertz.
How can you prove that the lower the frequency the further the higher the shorter?
He drew a wave with a whale under it, can a whale can swim 100 kilo at 100 hrs because it has very low frequency, if you have a sparrow if you immerse him into the sea water the sparrow will not be able to swim because it has a high frequency sound, when you talk all sound you see it in that range…

Modems learned how to make sound between this range, and they operated in the telephone network, modems work by a simple process, first when they talk to other modems they both send down a carrier wave, this is a very fixed amplitude ,fixed frequency, it will be modified to represent 1’s and 0’s how many ways can you modify a wave, how many can you do this,

How many ways can you change it?
You can change its amplitude, you can increase or decrease the voltage which is basically called its amplitude, another way you can change it is some instance in time radically changes the frequency this is called frequency change,

If it wanted to change the amplitude it would have to have different amplitude levels, theirs an increase of voltage to send bits, all modems have used frequency and amplitude , modern modems use phase change,

We have to understand amplitude, frequency and phase changing,

We went back to the 200hz 3400hz restrictions sound can travel on a telephone line we sent down 300hz, because it went down 300hz it achieved 300bps, modems like computers, their has been pressure on the line, just on computer manufacture and producing its products, the pressure has been to make modems faster, that has been the challenge for the 45-50 years, given the primitive technology how could you double the speed,
Why is it called a bell modem, when he was a kid and datacom was being invented no one made modem except bell, when you order a analog for data, a bell modem came, so how do we get from 300 to 600 bits for second, simple you send the a carrier wave 600hz, u have 600hz, and 1200hz, the oldest modem went to 56000bps how is this possible that has a maximum carrier wave of 3400hz max,

How is this possible?
With our primitive concept of only two different changes, someone wanted to develop a 24000bps came up with a place to send 2 bits every time the carrier wave was changed, 24000bps modem (drawn) inside the modem their was a buffer, a memory stick very small, the modems receiving is not sending them immediately, 01000010 (represents b). In the modems memory the modem it is going to analyze the character and break it into two bit pieces, now two bits can only be arranged four different ways, which means our new technology modem is going to need four different ways, its going to analyze the frequency it knows what the carrier frequency is, it is going have the ability to send it depending the two bits see how easy it is we are going to keep to 1200 hertz, every time we change it we are going to send two bits which is 24000bits per-second, now we need a 48000bps modem, this actually happen someone increased the frequency to 16000hz and send 3 bits, if you have 3 bits how many frequencies would you need, f8 we would need eight different frequency, carrier wave 16000 hertz every time we send it represents 3 bits, we got ourselves up to 48000 bits per-second, now we need a 9600 bits per-second we are going to send 3bits increase the frequency 48000 hertz send 4 bits , if you have four bits how many different ways can you send the data, this is where technology hit to the wall, 16 frequencies traveling down the line became very difficult, not understandable through the transmission, their was a new way, modern70% of the poor people in the world are using modem, and that technology has a limit, quadrature amplitude multitude, QAM for short, it applied a very unique method for modifying carrier method, uses two completely different attempts simultaneously they do phase changing, (know -amplitude frequency and phase changing,,) a normal wave through a line and what if the information went half round stopped and went around again, it would be very unique or it could do a change at 180 you can tell the difference, or it can do a change 280, or now not change at all, we have four different phase changes so we simply make up a rule, look at the 8 bits of the modem and analyze each 4 bits, for the first four bits from the right we are going to do a phase change for 90 degrees and we are going to do a phase change to 90 degrees to increase, and we are going to 90 degrees and leave the amplitude alone, we are going to do a phase change 180 we have four different phase changes with two different amplitudes, giving him, we have the ability 4 bits using QAM, this gives us max of 96000’s bps, QAM is used by the way using to fibre-optics,

What was the best modem ever invented?

56kb was not a true modem….Explain Why?

The last great true modem was the V34 modem a pure modem it was the modem that pushed to the limit of the carrier wave, the CW was 3400 hertz, but it could send every time it changed a CW, how many bits does it need to change the carrier wave, 256 different way’s to change the carrier wave, go into and type V34 specification the last true modem, how intelligent was it, it was very intelligent, once connect 3400 maximum, if the smart little V34 modem was getting a lot of errors it would send the a signal to the other modem and cut down the CW 2400, 1600, 1000…..Errors, 50% datacom studies 50% of the deal is the detection and handling of data errors, 50% is involved how does it detect errors….

The Bank Machine, what if you asked for $100 and their was a few bit errors, computers can not tolerate 1 bit, this is a catastrophe, just one bit.

BREAK

What’s Question 3,
What is digital technology and how does it work? Essay!

What does it mean to digitize something?

When you digitize you are turning something into a number.

The technology we are going to talk about its going to be a binary number, all it is, is turning information into numbers, before 1980, phone companies around the world started replacing analog technology with digital technology, 1980 Bell Canada Banner 100% Digital, in their backbone network its 100% percent digital, the phone from your hose to the bell office is analog, we are be talking about digital for the rest of the course for the next 13 weeks
A simple question…
When you talk on your telephone and it does to the Bell office it turns ur voice into numbers

How does it do this, some device turns ur voice into number, from your house theirs a telephone cable that goes under ground to the closest Bell telephone office connected to a computer a special process computer, it directs your phone call, and turn you voice into boring binary numbers how are you going ti invent digital technology, at the end of the line, think voltmeter it is going to listen to the sounds and the volt meter will pass info to a microchip, its only about $15 bucks, technology is deceptively simple, here what the phone companies did before 1980, they started looking at this at the 1940’s and not complete until the 80’s,
Story of Shannon, knew mathematics, turned his mind on this question, if you want to send digital representation on human voice how many bits per second will it take to represent a human voice, Shannon law was very simple , drawing of a sound wave, long wave, the volts meter will take sample readings, 0.1 Volt 0.2 Volt, 5 Volts, all are sample and each time its getting a number their number Decimal Numbers, the volt metre passes the values to micro chip and it is converted to an 8bit binary number, it becomes a next sample 2.0 volts. How can u represent minuet, the first bit of an 8 bit sample represents –negative or +plus value, these numbers get transmitted through a series of pulses through copper wire, the trick Shannon realized, how many sample per second should you take, so that the voice at the other end sound legible, the Sample Rate, what was it that he came up with, remember the sample wave 4000hertz, the sample rate should be twice the maximum rate 8000 samples per second each sample results in an 8 bit value which means data is travelling down the line, each sample is 8 bits, their for when talking you are talking to someone it is 64000bps, precision is vital in digital technology, this is how it works the tricky part, we are not going to far about today, digital technology is not simple as pulses there is many ways but we will look at 6 ways from this course,

stressing telephone companies around the world, in the middle (Company to you is seen as digital to analog….analog to digital is seen as you to the phone company)

The physical circuit between phone companies T1 circuit…..what does that mean what is a T1….it is a standard in North America called Multiplexing …means putting numerous signals up on 1 wire, very simple, next week, in Canada each T1 circuit can handle 24 simultaneous voice conversation, 24x64,000bps (digital signals)

The really important issue, by week 6 he wants a nice statement to this questions….

Why digital is good and why is analog is not?
Why did the world go digital?
Why do signal diminish?….all electronic signals diminish all signals, because this happens in fibre-optics all signals suffer from the same fact of nature they must come to an end, this is attenuation, which is unavailable, only way to combat this is to send you wire to 0 degrees Calvin, attenuation happens, now ask yourself how can you talk to your girlfriend in Vancouver every 15 cables bell has installed is Amplified, taking a diminishing signal and creates new signals, the trouble with this technique, but we want computer to send data to Vancouver which is a different problem, attenuation is avoidable, but there are several things we call them Noise, the worse culprit is fluorescent light, we place one of these lights to phone line they give of electro magnetic field and when placed near a phone line you get crackles on the line, now when someone is on the phone and you hear crackles a computer cant tell if its happening, here is the worse part amplifiers don’t know the difference either so an amplify the signal will amplify the crack and fluorescent is one way, solar flares introducing the crackles, bit errors worse thing in the universe next to windows,

Digital signals are getting attenuation which happens to digital signal, we are going to run a digital line through the fluorescent line and get crackles, but here is the answer
Why digital good?
When digital technology is introduced, phone companies did not install plain simple amplifiers, they used Repeaters, a repeaters is very different then a amplifiers it looks at the pulse can see if its decayed and makes a brand new decayed pulse Positive or Negative and if it doesn’t know what it is it will filter it out, efficient, making you signal clean and free!

Why 56kbps Not a true modem?
If your ISP still have analog transmission between the isp and the closest bell office the 56kb will not go over something……if your isp puts in a digital service such as a t1 circuit between the isp and the bell office and you install a V90 modem 56000bps at ur house and you put it on a analog line, ur isp is a digital service, analog to digital the technology for doing this is inpercise, analog digital conversion introduces problems, not a perfect technology yet, when you turn on ur V90 modem it realizes its on an analog circuit the modem degrades it self and become a V34 36000bps, when you turn on the other modem and it sees its on a digital it will continue to run at maximum 56000bps it will send 56000bps and you modem at you end will go 28000s, now if you wanted it both ways you have to phone bell telephone and disconnect the circuit and reconnect a digital home service, which will mean it will have to install a new cable and you willge ta service to ISDN, its over priced and will solve your modem problem.

How do you get ready for week 6 you go on google words like
Analog Transmission – Compliment QAM how
Digital Transmission

Digital Good Analog Bad