Its been a long time since I've posted anything. Time to get back to it.
I want to start concentrating on talking about optical test equipment. One of the more complex test sets is the OTDR -- Optical Time Domain Reflectometer (what a mouthfull!) -- a test instrument that will graph out the characteristics of an optical fiber to which it is connected. It is not difficult to use (these days, anyway), but it is difficult to truly understand what it is doing, how it operates, and how you can use this powerful tool to troubleshoot and maintain fiber. Hopefully I'll be able to make it all a bit more clear.
I came across an old (1986 vintage) VHS video tape in my home office a while ago. It was a training video on an OTDR. I digitized it and created an MP4 video of the tape. Here is the YouTube link to this video on how to use a Laser Precision Corporation TD-9950 OTDR. This OTDR was produced in the late 1980s by Laser Precision in its Utica, NY, factory location. I was employed by LP from 1991 thru 2006 (through some name changes and consolidations... GN Nettest, NetTest, Anritsu...). We've come a long way since then as far as the technology in producing these instruments. But the specifications of the instrument and how to interpret the "trace" remains the same.
Watch this space. I will post a little booklet I started writing back in about 1992 called "Understanding OTDRs," That was version 1. I'm up to version 18 now as I've made many changes to keep up with changing technology and the improvements in the OTDRs specs and methods of use. I'll also post links to other educational sites that might help you understand the in-depth technology of fiber optics testing.
Wednesday, March 20, 2013
Monday, October 10, 2011
Topics to come...
In time I plan to pick up the pace a bit and post some more. For now I will throw out a few topics I plan to talk about. If anyone has suggestions, just post 'em in Comments. In no particular order, here are some subjects:
- Analog vs. digital;
- Digitizing voice;
- Modulation types;
- Transmission media overview: copper, fiber, & wireless;
- Testing the media;
- Testing the message;
- Testing the equipment;
- Focus on fiber testing;
- ...more...
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| The Electromagnetic Spectrum |
Friday, June 24, 2011
The Fundamentals
Tele = from a distance
Communications = sending/transferring information
Telecommunications (or Telecom for short) is a very generic term for communicating over a distance. This may be one-way (example: watching TV) or two-way (ex: phone call).
The very basic aspect of telecom is known as "POTS" or Plain Old Telephone Service (or Plan Ordinary Telephone Service). First patented & promoted by Alexander Graham Bell in the late 1800s, it has grown into a complex world-wide network. POTS is still around today and is probably the most common interconnection between people. In the US, the vast majority of people have acess to a telephone, with most having telephone service where they live.
Basic POTS means you have a telephone that is connected to two thin, insulated metal wires twisted together (a "twisted pair") running through the walls to some point outside the residence. The telephone converts your voice into an electrical current that is modulated by the various frequencies in your speech and put onto the wires. This modulation is analog in nature and varies the electrical current with the intensity (strength) and pitch (frequency) of your voice.
That twisted pair (or simply a "pair" in common telco-speak) is then connected in some way to another set of wires that leads back to the telephone company (more generically, the "service provider"). In its simplest form, pairs from a group of telephone customers, or "subscribers," runs out to a single point from each customer premise (house, apartment, or other type of residence). From this single congregation point (a plastic "pedestal" or metal cabinet), these pairs are bundled together to form a larger cable that is buried or hung on poles that goes for some miles back to the Service Provider's (SP) facility. For telephone companies, this facility is known as a "Central Office" or CO. From the CO, these pairs -- each of which lead to a single subscriber -- are connected to electronic equipment known as "switches" which can connect one pair to any other pair coming in to it. Modern switches are computer-controlled electronic devices which provide not only the connection to other subscribers, but also provide services such as Caller ID (CID), voice mail, special ringing tones, and many other special features. There are many switches in a CO, depending on how many subscribers are in the area. The switches in a CO are all connected to each other so calling between the subscribers in the area served by that CO is accomplished simply by connecting one line to another.
To complete a call outside of the serving CO, there is another cable or set of cables that connects the various COs in a Service Provider's area. These are called "trunks" or "interoffice cables." Rather than having large bundles of pairs, these trunk lines carry "multiplexed" phone calls, with one twisted pair carrying 24 or more calls simultaneously by combining the signals from individual pairs in digital form. More on digitizing and multiplexing in a different section.
For some images on what a Central Office looks like, check out this link: http://davewhitmore.net/Images/central_office.htm
Stay tuned for more...
Communications = sending/transferring information
Telecommunications (or Telecom for short) is a very generic term for communicating over a distance. This may be one-way (example: watching TV) or two-way (ex: phone call).
The very basic aspect of telecom is known as "POTS" or Plain Old Telephone Service (or Plan Ordinary Telephone Service). First patented & promoted by Alexander Graham Bell in the late 1800s, it has grown into a complex world-wide network. POTS is still around today and is probably the most common interconnection between people. In the US, the vast majority of people have acess to a telephone, with most having telephone service where they live.
Basic POTS means you have a telephone that is connected to two thin, insulated metal wires twisted together (a "twisted pair") running through the walls to some point outside the residence. The telephone converts your voice into an electrical current that is modulated by the various frequencies in your speech and put onto the wires. This modulation is analog in nature and varies the electrical current with the intensity (strength) and pitch (frequency) of your voice.
That twisted pair (or simply a "pair" in common telco-speak) is then connected in some way to another set of wires that leads back to the telephone company (more generically, the "service provider"). In its simplest form, pairs from a group of telephone customers, or "subscribers," runs out to a single point from each customer premise (house, apartment, or other type of residence). From this single congregation point (a plastic "pedestal" or metal cabinet), these pairs are bundled together to form a larger cable that is buried or hung on poles that goes for some miles back to the Service Provider's (SP) facility. For telephone companies, this facility is known as a "Central Office" or CO. From the CO, these pairs -- each of which lead to a single subscriber -- are connected to electronic equipment known as "switches" which can connect one pair to any other pair coming in to it. Modern switches are computer-controlled electronic devices which provide not only the connection to other subscribers, but also provide services such as Caller ID (CID), voice mail, special ringing tones, and many other special features. There are many switches in a CO, depending on how many subscribers are in the area. The switches in a CO are all connected to each other so calling between the subscribers in the area served by that CO is accomplished simply by connecting one line to another.
To complete a call outside of the serving CO, there is another cable or set of cables that connects the various COs in a Service Provider's area. These are called "trunks" or "interoffice cables." Rather than having large bundles of pairs, these trunk lines carry "multiplexed" phone calls, with one twisted pair carrying 24 or more calls simultaneously by combining the signals from individual pairs in digital form. More on digitizing and multiplexing in a different section.
For some images on what a Central Office looks like, check out this link: http://davewhitmore.net/Images/central_office.htm
A typical telco pedestal.
Stay tuned for more...
Introduction to the blog
Having been in the telecom industry for a few years I continue to run across folks who want or need to know a bit more than what most people know about the telephone, video, mobile phone, and internet/data functions they use on a regular basis. If you are interested in learning more about this industry, perhaps this blog may help you to understand a little more about this extremely complex and ever-changing business.
I will try to make this not only a high-level view of the industry, but also one which does not assume you know much of the background. Hopefully I won't use terms that I don't immediately describe or define on first use. Although I am an engineer by schooling, I have made a living so far selling products into the telecom industry and providing technical support and training on the products I sell. I understand these products well enough to train users on them, but I am by no means the end-all expert. I will assume that the reader knows little or nothing about the subjects as I go along. This will not be a brand-specific or "salesy" in any way. I want it to be generic as possible, but will use examples of brands as needed to help to explain things.
I am aiming this at newcomers, or for people who are considering doing business in the telecom industry and want to understand it better. Feel free to comment and ask questions. Point out any errors I make or expand on the topics.
Here we go...
I will try to make this not only a high-level view of the industry, but also one which does not assume you know much of the background. Hopefully I won't use terms that I don't immediately describe or define on first use. Although I am an engineer by schooling, I have made a living so far selling products into the telecom industry and providing technical support and training on the products I sell. I understand these products well enough to train users on them, but I am by no means the end-all expert. I will assume that the reader knows little or nothing about the subjects as I go along. This will not be a brand-specific or "salesy" in any way. I want it to be generic as possible, but will use examples of brands as needed to help to explain things.
I am aiming this at newcomers, or for people who are considering doing business in the telecom industry and want to understand it better. Feel free to comment and ask questions. Point out any errors I make or expand on the topics.
Here we go...
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