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In this lesson, we examine the bandwidth provided with Plain Ordinary Telephone Service, which is often referred to as the voiceband.
We’ll understand what the term "bandwidth" means, and how it is measured in the analog world.
Then, we'll look at the details of the voiceband, what frequencies it covers and why, and its limitations.
This free online telecom training course lesson is the introduction to the course.
The Voiceband is in both the CTNS Certification Package and the CTA Certification Package.
If you can't play flash, use the Puffin browser or watch Course 2201 Lesson 5 The Voiceband on youTube
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Sixteen online courses covering telecom, datacom and networking for non‑engineers from A-Z, plus the prestigious TCO Certified Telecommunications Analyst certification.
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These are the words that are displayed and spoken during the lesson. Get these notes for the whole course in the Certification Study Guide, available in print or eBook. Many people tell us a printed companion book enhances their learning!
If a tree falls in the forest and no-one is there to hear it, does it cause a sound? The answer depends on whether you believe sound is sound pressure waves – air molecules getting closer together then further apart; or if you believe sound is the sensation one gets in one's brain when one hears the sound pressure waves. Then, two points of view when designing the telephone system would be:
The difference between these two ideas is that the brain is a hugely complicated processing instrument, and we can play different stimuli at it and get the same response.
What choice did Alexander Graham Bell make?
Answer #2.
Based on testing human beings' ears, throats and brains, and some technical limitations, A. G. Bell decided to transmit all of the information in the frequency range between about 300 and 3300 Hz.
Hertz (Hz) is the unit for frequency, or changes per second.
This range or band of frequencies is called the voiceband.
The image is a representation of the voiceband, with frequency on the horizontal axis and amplitude or intensity on the vertical axis.
A simplified version of the image (contained within the lesson) shows any electricity vibrating at least 300 times per second and less often than 3300 times per second will be passed.
Any electricity vibrating less often than 300 times per second will be suppressed.
Similarly, any electricity vibrating more than 3300 times per second will be suppressed.
Only electricity vibrating within the band 300-3300 Hz will be transmitted.
The suppression of energy outside this frequency band 300-3300 Hz is implemented with simple electrical circuits called filters. There is a filter in the telephone and a filter in the switch in the CO.
For our purposes, the term bandwidth means capacity.
In the analog world, capacity is measured literally by the width of the available frequency band.
In this case, the width of this frequency band is 3300 – 300 = 3000 Hz, or 3 kHz for short.
This 3 kHz bandwidth is the capacity provided for ordinary telephone service.
The two wires that make up the loop are capable of supporting electricity vibrating more often than 3300 times per second – in fact, DSL technologies require electricity vibrating at frequencies measured in the millions of times per second.
The users' ears and brains are capable of detecting sound pressure waves vibrating more often than 3300 times per second – the human hearing range is traditionally thought to extend up to 20,000 Hz.
So why would the capacity a user is allowed to employ purposely limited to 3 kHz, even though the wires are capable of more than that, and the users are capable of more than that?
The answer is, as usual, money.
The more capacity a user is allowed to employ on the access circuit, the loop, the more capacity and hence money required to transmit the information across distance.
This narrow voiceband frequency range was chosen based on studying people's ears, throats and brains, to determine the minimum capacity necessary to meet the requirements.
Returning to the question of trees falling in the forest: the sound pressure waves at the far end are not reproduced exactly as they were at the near end; in fact, they are quite muffled and distorted, missing most of the higher frequencies.
The sound is reproduced just well enough so that the listener can recognize the speaker and understand what the speaker is saying, thus meeting the requirement to communicate information using speech and hearing.
We are interested in transmitting the minimum required to meet that objective since there is a direct relationship between the capacity a user can employ on the access circuit and the cost of transmitting the information long-distance.
Voiceband Filter
It turns out that the voiceband is not quite enough bandwidth to be able to understand everything the speaker is saying!
In particular, it is difficult to tell the difference between “S” and “F” over a telephone.
This is because the frequency of sound pressure wave that distinguishes “S” from “F” is above 3300 Hz… which is not transmitted over the phone system.
Thus, one has to say “S as in Sierra” and “F as in Foxtrot”.
One could also say things like “S as in Sea”, “A as in Are” and “E as in Eye” to liven things up.
If that doesn’t get the listener confused, there’s always “E as in Ewe”.
Alternate Phonetic Alphabet: "A as in ARE"...Lesson 1 is the Introduction to the Course.
Lesson 2 is a brief history lesson, beginning with the invention of the telephone. This will establish the concept of local telephone companies, access circuits and inter-city transmission.
Next, in Lesson 3, we will understand the fundamentals of the PSTN: customer premise and Central Office, loops, trunks, circuit switching and understand how a telephone call is connected end-to-end.
Then in Lesson 4, we will understand how information is represented on the local loop using analog techniques in traditional telephony, and just what exactly we mean by analog.
Lesson 5 is the question of fidelity: how faithfully the voice is reproduced at the far end, which is determined by the frequency bandwidth provided on the access, known as the voiceband. The lesson on the voiceband is available free on this page.
Lesson 6: The voiceband, loops, trunks and circuit-switching are all aspects of Plain Ordinary Telephone Service. We'll round out the discussion by understanding some of the other key aspects of POTS and related jargon and buzzwords like "twisted pair".
In Lesson 7, we will then look at an improvement on the address signaling mechanism for POTS that was called "touch tone", or more technically, DTMF.
Finally, in Lesson 8, we will understand in broad brushstrokes the control system for the telephone network, called SS7 in North America, and basic principles of call routing.
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Like Teracom's famous core training Course 101 "Telecom, Datacom and Networking for Non-Engineers", our very popular core training DVD-Video packages and the Telecom 101 textbook, the Certified Telecommunications Network Specialist Certification Package begins with the Public Switched Telephone Network, then a course on Wireless Telecommunications, followed by four courses covering IP telecommunications and IP telecom networks.
If you are interested only in IP telecommunications, the CIPTS: Certified IP Telecom Network Specialist package may be appropriate, as it skips the traditional telephony and wireless and goes directly to the IP telecommunications courses.
If your goal is to build a full, rounded knowledge of telecommunications, then understanding the history, structure and operation of the telephone network built over the past 135 years or more is the starting point for everything else.
We begin with a history lesson, understanding how and why telephone networks and the companies that provide them are organized into local access and inter-city transmission, or as we will see, Local Exchange Carriers (LECs) and Inter-Exchange Carriers (IXCs).
Then we will establish a basic model for the PSTN and understand its main components: Customer Premise, Central Office, loop, trunk, outside plant, circuit switching, attenuation, loop length, remotes, and why knowledge of the characteristics of the loop remains essential knowledge even though we are moving to Voice over IP.
Next, we'll cover aspects of telephony and Plain Ordinary Telephone Service, including analog, the voiceband, twisted pair, supervision and signaling including DTMF. The course is completed with an overview of SS7, the control system for the telephone network in the US and Canada.
On completion of this course, you will be able to draw a model of the Public Switched Telephone Network, identify and explain its components and technologies including:
In many parts of the world, particularly outside Canada, the US and Western Europe, the physical telephone network is wireless, as deploying radio transceivers is far cheaper than embarking on a new project to pull copper wires and/or fiber to every residence.
Most of this course is devoted to mobile wireless telecommunications. We begin with basic concepts and terminology including base stations and transceivers, mobile switches and backhaul, handoffs, cellular radio concepts and digital radio concepts.
Then, we cover spectrum-sharing technologies and their variations in chronological order: GSM/TDMA vs. CDMA for second generation, 1X vs. UMTS CDMA for third generation along with their data-optimized 1XEV-DO and HSPA, how Steve Jobs ended the standards wars with the iPhone and explaining the OFDM spectrum-sharing method of LTE for 4G.
This course is completed with a lesson on WiFi, or more precisely, 802.11 wireless LANs, and a lesson on satellite communications.
You'll gain a solid understanding of the key principles of wireless and mobile networks:
The remaining four courses in the CTNS package are on the "IP" telecommunications network and its three main enabling technologies: Ethernet, IP and MPLS, and beginning with the OSI model and its layers to establish a framework.
If you'd prefer to take just these four "IP" courses, check out the Certified IP Telecom Network Specialist package.
This course establishes a framework for all of the subsequent discussions: the OSI 7-Layer Reference Model, which identifies and divides the functions to be performed into groups called layers.
This framework is required to sort out the many functions that need to be performed, and to be able to discuss separate issues separately.
First, we'll define the term "protocol" and compare that to a standard. Then we'll define "layer" and how a layered architecture operates, and provide an overview of the name, purpose and function of each of the seven layers in the OSI model.
Then, we'll go back through the story more slowly, with one lesson for each of the layers, examining in greater detail the functions that have to be performed and giving examples of protocols and how and where they are used to implement particular layers.
The result is a protocol stack, one protocol on top of another on top of another to fulfill all of the required functions. To make this more understandable, this course ends with the famous FedEx Analogy illustrating the concepts using company-to-company communications, and an analogy of Babushka dolls to illustrate how the protocol headers are nested at the bits level.
On completion of this course, you will be able to:
On completion of this course, you will be able to explain:
MPLS and Carrier Networks is a comprehensive, up-to-date course on the networks companies like AT&T build and operate, how they are implemented, the services they offer, and how customers connect to the network.
The IP packets and routing of the previous course is one part of the story. Performance guarantees, and methods for quality of service, traffic management, aggregation and integration is another big part of the story, particularly once we leave the lab and venture into the real world and the business of telecommunications services.
We'll begin by establishing a basic model for a customer obtaining service from a provider, defining Customer Edge, Provider Edge, access and core, and a Service Level Agreement: traffic profile vs. transmission characteristics.
Next, we'll understand virtual circuits, a powerful tool used for traffic management and how they are implemented with MPLS, explaining the equipment, jargon and principles of operation.
Without bogging down on details, we’ll cut through buzzwords and marketing to demystify:
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DVD versionTeracom is an Accredited Training Partner of the Telecommunications Certification Organization, authorized to administer exams for TCO certifications on the myTeracom Learning Management System and award TCO Certifications.
TCO Certification is proof of your knowledge of telecom, datacom and networking fundamentals, jargon, buzzwords, technologies and solutions.
It's backed up with a Certificate suitable for framing - plus a personalized Letter of Reference / Letter of Introduction detailing the knowledge your TCO Certification represents and inviting the recipient to contact Teracom for verification.
You may list Teracom Training Institute as a reference on your résumé if desired.
Each course has a course exam, consisting of ten multiple-choice questions chosen at random from a pool and shuffled in order. Passing the course exams proves your knowledge of these topics and results in your certification as a Certified Telecommunications Network Specialist.
Your Certificate and Letter of Reference / Letter of Introduction will be immediately available for download from your Dashboard in the myTeracom Learning Management System. You may also order a signed and sealed Certificate by airmail.
Choosing the "Unlimited Plan" at registration allows you to repeat courses and/or exams at no additional charge – which means guaranteed to pass if you're willing to learn.
Alternatively, if you like this discounted package of courses, but don't need the certification – or don't feel like writing exams – no problem! Take the Telecom, Datacom and Networking for Non-Engineers course package, which includes the same courses as the CTNS certification package, without the certification exams.
One benefit of TCO certification is differentiating yourself from the rest of the crowd when applying for a job or angling for a promotion.
The knowledge you gain taking Teracom's Online Courses, confirmed with TCO Certification, is foundational knowledge in telecommunications, IP, networking and wireless: fundamental concepts, mainstream technologies, jargon, buzzwords, and the underlying ideas - and how it all fits together.
This type of knowledge and preparation makes you an ideal candidate to hire or promote to a task, as you will be able to build on your knowledge base to quickly get up to speed and work on a particular project - then have the versatility to work on subsequent projects.
TCO Certification will help demonstrate you have this skill... a desirable thought to have in your potential manager's mind.
Take advantage of these courses for individual learning, a team, or for an entire organization.
The scalable myTeracom Learning Management System can register and manage all of your people through their courses, lessons and exams, and generate management reports showing progress and scores with the click of a button.
For larger organizations, the courses and exams can also be licensed and deployed on an organization's internal LMS.
Teracom certification packages are an extremely cost-effective way of implementing consistent, comprehensive telecommunications and networking technology fundamentals training, ensuring that both existing resources and new hires are up to the same speed, with a common vocabulary, framework and knowledge base.
The course exams provide concrete measurements of competency in key knowledge areas. Management can view the progress and results of all team members and export the results to Excel with the click of a button.
These reports identify skills deficiencies and strengths, and provide tangible proof of return on investment and team readiness for reports to upper management.
What is the value of the CTNS certification? Click here to find out
