Thanks, Dennis. I found that Agilent training document quite rich in information, not only pertaining to the fundamentals of fiber optics, but to all of the popular IEEE and ANSI LAN protocols, as well.
I see what you mean about the url, btw. I was able to capture the url, but it times out after a spell. IOW, the url worked at first, but it soon expired.
While skimming through the doc, I came across the all-familiar "eye-pattern" which is usually displayed on a traditional time domain scope. I thought to myself, this evening, as I did numerous times over the years, how peculiar that Agilent, at this stage of the game, should still resort to a visual decode method of determining the suitability of a transmission medium. Just musing...
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As relates to the "loop" that the HFC technician was fashioning atop the pole, such constructs exist in basements, in main cross connect rooms, in cable vaults, and other locations. These are known variously, depending on which trade group installs them, as "service loops, and they do, in fact, allow for a reservoir of additional cable "slack" to be used in the event of a cable break, or as in the case which you witnessed, in the event of a pole being taken out on a Friday night by someone who's had too much to drink.
In commercial buildings where fiber is pulled from the central office, there will often be a wall- or ceiling- mounted fiber enclosure measuring something like 4' x 2' x 1' (sometimes called a Kaufman Box) very close to the entry point in the basement where such a service loop is provisioned.
At this point, if indoor outdoor cable is not used --and here, there are often fire and building code issues which focus on traveling flame issues-- the "outside" rated cable is spliced to the "indoor plenum" rated cable, the latter being the cable which is pulled up the riser. (Hi, GHowe!)
Here, the service loop allows for enough slack so that if a break occurs outside the building, say between the first manhole and the entry sleeve in the basement, some section of cable from within the building could be pulled back out into the street to the first manhole (where there could also be another service loop), or, conceivably, to a midway point where it would be spliced to repair the break. These basement service loops also come in handy on college campuses and industrial parks when backhoe operators and landscapers ignore utility markers.
Even where twisted pair Category x cabling is concerned, most installers of premises distribution systems will leave some extra cable "curled up," above in the ceiling, or below under raised floors in network centers (LAN rooms and server hotels) in the immediate proximity of the equipment cabinets, or racks in which they terminate. This is done to allow for ad hoc relocations of hardware enclosures within those rooms. Sometimes in large equipment rooms (the main cross-connect, or sometimes even in intermediate distribution closets), a service loop in the shape of a "figure 8" will appear mounted onto a plywood backboard, nice and neat like. Again, this allows for the eventuality of room reorganization, allowing for enough slack so that the cabling will "swing" to the new floor location of the equipment cabinet, or rack, when necessary without the need for pulling new cabling to every desk out on the floor.
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re: "..the similarity between copper and glass - in both cases, the signal in fact propagates in a dielectric material, and not "in the wires" as is often thought..
Are you referring to the "skin effect" which takes place at the higher frequencies, in the case of metallic conductors?
And in the case of fiber, it's dielectric to begin with, so I'm a little perplexed as to what you mean. Here, I've read in several places that a greater amount of optical signal travels the outer cladding of optical fibers than is often considered, as opposed to modal propagation in the core. I can't quantify that, although I'd have to think that this amount is minute. Is this what you are referring to in your statement when concerning fiber? Please explain.
FAC |
