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The Wired Local Loop/ Books on OSP?/ Link to a Digital Loop Carrier Tutorial / The Wireless Local Loop / Norman Rockwell and OSP (really neat) / Outside Plant -- A Woman's Experience/ Open wire picture

The Basic Elements of Outside Plant

A single wire does not run from your house to the central office. A communication path is maintained, instead, by a collection of wires and cable, mostly twisted pair, often in large bundles, that connects like a chain to different equipment. Let's take one common example.

We'll follow your phone line from your house to the nearest CO or central office. This example combines aerial and buried plant. Let's assume that you live in an older neighborhood in a medium sized town. The kind with telephone cable running through the neighborhood's backyards on poles.

1. Telephone wiring inside your house first connects to the telco's wire at the house protector or station protector. This is the demarcation point. Your wiring ends here and the telco wiring begins.


2. From here a drop wire containing several twisted pair goes to a pole closure, an aerial terminal or ready access terminal. Call it what you will, this is the termination of the subscriber's drop wire. Drop wires can be thirty feet long or thousands of feet in length. They contain several twisted pair, only the oldest drops containing a single twisted pair.

3. The customer's twisted pair is connected to binding posts within the enclosure. Depending on the enclosure, a wire representing your twisted pair may now be connected to the aerial cable servicing your neighborhood. This sort of enclosure is inline with the aerial cable and may serve as a connecting or splice point. Or, a wire from the back of the enclosure may run to a splice case nearby. This marries the enclosure's wire with the larger aerial cable that services your area.

4. This cable contains at least 50 pairs, commonly 100 or more. It's called distribution cable or aerial cable or F2 for being the secondary feeder cable. Several F2 cables may work their way back to the nearest SAI.

Click here for a picture of a standard aerial service terminal

And here's a picture of an aerial service terminal for fiber optic cable

5. These F2 cables go underground via conduit before connecting to the serving area interface. In some areas the feeder does not go underground but is carried directly by the poles to the Serving Area Interface, which is described next.

6. The SAI or serving area interface. A big terminal block. Called B-Boxes, cross-connect boxes and APs, or Access Points. Whatever! Those ubiquitous gray-green cabinets you see nearly everywhere. They are usually mounted on the ground but can also be located on poles. F2 cable pairs connect with F1 pairs at this point. It's here that the individual twisted pairs are terminated. F1 or main feeder cables then go underground in conduit, usually to the nearest central office or remote switch. Or first to transmission equipment like a multiplexer and then to the C.O.

Click here for a picture of a typical cross connect box.


elements of outside plant

Once your signal hits the telephone switch it gets converted from an analog signal to a digital one. Although exceptions may exist, all traffic in America between telephone switches is now digital. Only traffic in the local loop as described above remains analog, but, again, everything goes digital once it hits a switch.

Courtesy of Jade Clayton's Telecom Dictionary:

1.) Picture of a central office distribution frame

2.) Picture of a cable vault


If you want to know what those strange looking telco cabinets and housings are for, the ones you see around your neighborhood, go to Marconi's site and take a look at their product catalog. Great learning: plant.htm (link now dead)

Here's another good company site:

Outside plant specifications, both aerial and buried. Detailed info: (external link)

The following describes, extensively, inside building procedures for telecom. You should take a look. (external link)

A comment . . .

"The problem with OSP is that everyone forgets it's still the basic core for the majority of telephony. Some think that Digital is all there is -- but you still have to have the local loop F1 (fiber or copper) for the span line, the system, and the F2 distribution loop to the customer. Or people think wireless is all there is. All the latest technology is very important but it won't replace the local loop for decades to come. Maybe never really."

"My friends in OSP say that we are the forgotten children or the step-children. But the telephone company can't function without us. We are the working grunts however. While IOF (inter-office facilities), Switch, and Wireless think they are all of it, they actually have just one piece of the pie."

Our anonymous OSP authority. . .

Digital Loop Carrier Tutorial

This tutorial seems good. It starts out this way,

"This tutorial-level presentation OF Digitall loop carrier (DLC) technology is for both nontechnical readers and the technically versed who lack network applications experience. It describes DLC technology with a focus on the primary motivations for its development. Other topics include a comparison to channel bank technology, the organization of DLC technology in North America, and a comparison of universal digital loop carrier (UDLC) and integrated digital loop carrier (IDLC) technologies. The concluding topic illustrates a functional equivalence between DLC and fiber-in-the-loop technologies. Although three generations of DLC technology have brought an abundance of features and capabilities, this paper sticks to the basics to remain instructional. Discussion is limited to North American DLC technologies. . . ."

The link I had to this has now gone dead. Sigh. I hate this. Try going to this site and searching: (external link)

Books on OSP?

It is absolutely impossible to find books on OSP. I have one, Lee's, but it is quite dated. You'll be lucky to find any of the titles below. Try OSP Magazine instead. GTE also had a book or a series but I don't even have a title for it. This is all the information I have on these long out of print books, you may have to search Amazon, e-bay, and just to find one. Don't forget, though, this resource I mentioned above: (external link)


Outside Plant, Frank K. Lee. Quite dated. Far too much on open wire construction.

Available here, along with many other tutorial books and videos: (external link)

Outside Plant Construction: Cable Maintenance Methods, Bell System. I am not sure whether this is a series or not, I think so. See the title below which suggests that it is.

Handbook Of Outside Plant Engineering, AT&T.

Standard Outside Plant Construction Methods., Book 1, Section 1-- Pole line construction. Compiled, edited, and produced by Kellogg switchboard and supply co. Chicago, Kellogg switchboard and supply co. [c1945] 1 v. incl. illus, tables, diagrs. 11 1/2 x 18 1/2cm.

Outside plant magazine

Outside Plant Magazine (external link) is an excellent resource. Look for the numerous, helpful files in their back issue section. Many topics covered from an OSP point of view. Well worth checking out!

The Wireless Local Loop

Difficult paper but, hey, it's here. Special note: This is a Word document, almost one megabyte.

The Wired Local Loop/ Books on OSP?/ Link to a Digital Loop Carrier Tutorial / The Wireless Local Loop / Norman Rockwell and OSP (really neat) logo West Sacramento, California, USA. A Tom Farley production




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