As an IT/telecom professional, you are likely to have a good understanding about the theory and principles of voice and data. You understand the trends driving the convergence of voice and data, are familiar with how VoIP works, know the pros and cons surrounding net neutrality, stay current with regulatory and political issues, know how "free" conference calling companies stay in business, take advantage of wireless, etc.
However, even if you are an expert, at some point in time, you will need to discuss/explain voice, data and wireless principles to your colleagues who are non-technical (financial, executive, administrative, operations personnel). This may be difficult to do, as we tend to assume others have some basic technical knowledge and we fall into using "insider" jargon, terms, acronyms -- any of which will immediately confuse and throw off our audience. How can we explain what voice and data is in a manner that others can easily understand? After all, your effectiveness is largely based on your ability to communicate your points to others.
The intent of this, and subsequent No Jitter articles, is to help you "demystify" technical concepts to non-technical colleagues, customers, clients, etc. Each article in this series covers a couple of topics, and tries to explain these in non-technical terms. While the examples and analogies may not always be 100% applicable, they should provide some perspective (i.e. highlight the differences/advantages).
ANALOG
Remember the two cans and string trick? You pierce a hole in each can and tie a string between the cans. Drawing the string taut, one person talks into a can and the other person can hear what is being said.
This works because the speaker's voice is captured/concentrated in the can. The voice waves are converted into vibrations on the string, and the vibrations are transmitted down the string to the other can, where it is converted back to voice waves. The string/vibration is an example of analog transmission. Early voice calls were placed using analog lines (albeit via another medium, not strings).
THE PROBLEM -- While analog calls work, you quickly run into a problem as you add more users. Having two people talk with one analog path is simple. However, if you now wish to talk to a third person at a different location, you can add another line to that desk. Now to add a fourth person, you would string another point-to-point line to a fourth desk. What happens when you add a fifth, sixth, 20th, 100th, 234th person? Do you have 234 individual and separate point-to-point lines? What about the person at a second site?
In a community of 234 people, you would need to string 233 additional lines. The third person would require an additional 232 individual, point-to-point lines. You can see this problem quickly becoming untenable, with an eventual end result of 27,495 individual point-to-point lines. A solution needs to be identified.
SWITCH
The answer to this problem is a switch. Just as a railroad yard uses a switch to send trains down the right track, a switch is used to handle voice calls. In the above example of 234 users, instead of 27,495 individual lines, you have 234 lines going to a single device, a switch. This device will take a call from one user (e.g. #23) and switch the call to another user (e.g. #193).
Of course, this describes the basic workings of your company's PBX. At a site with 234 people you would assign an extension number to each person. When they place a call to another person, they use their extension number. The extension number you enter tells the switch (PBX) what line to ring.
While your office uses a switch to route calls within your facility, your PBX also has dedicated lines connected to a larger switch connected to the PSTN. Your local public switch allows you to call others in your immediate community (local area). And your local public switch is connected to other switches around the country and world, allowing you to place calls anywhere (i.e. intrastate, interstate, international).
THE PROBLEM -- With the increasing demand for voice calls, the ability to add more lines across the country (and world) becomes very expensive. Is there a way to put more calls on the same line? Yes. The answer is multiplexing.
MULTIPLEXING
When you hear multiplex, the first thing that may come to mind is your local theater (the Regal, AMC, Cinemark, Carmike, etc). At the Regal 12, there are 12 screens at one place. Instead of having 12 theaters (with 12 ticket sellers, 12 concession stands, 12 projectionists, etc.), the facility is able to put all this under one theater, thus reducing the need for staffing, space, parking, etc.
In general, multiplexing is the ability to gain more efficient utilization of a limited resource. In IT/telecom, multiplexing is the simultaneous transmission of two or more trains of signals or messages over a single channel.
A real world analogy is carpooling. The "simultaneous transmission of two or more trains of signals or messages" is equal to two or more people. "Over a single channel" means one vehicle. Just as carpooling is trying to get more people from point A to Point B over a one-lane car pool highway, the same principle applies.
In IT/telecom multiplexing, the objective is to carry more calls over a single channel (line). And just as there are variations of car pools (cars, vans, buses), there are variations of telecom multiplexing (time division multiplexing, statistical multiplexing, etc.).
In the next No Jitter article, we will discuss the advantages of digital versus analog.
"SCTC Perspectives" is written by members of the Society of Communications Technology Consultants, an international organization of independent information and communication technology professionals serving clients in all business sectors and government worldwide.
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