I think i am very slowly honing in on the problems.
Agreed. Your point about the grade of glass deserves additional mention. But a good part of the problem that you mentioned in your earliest post on this topic, I believe has to do with the local carriers not provisioning enough TDM girth, lambda punch and other forms of optoelectronics to the end users they serve, which is still very expensive to do for short distances due to the still-high cost of wdm and other network elements, and not with the grades of fiber that they are bringing into carrier hotels. I say this because, almost by definition, most of today's carrier hotels and colos are recently pieced together (some barely). As such, the local serving ILEC or FLEC would have brought recent-vintage fiber into these locations. But some, like you say, do contain the older stuff. And there is always the possibility that some older sections of fiber that happened to be available were spliced to these locations to meet need.
Some local fiber carriers now have as many as three or more different grades of glass in the street that they are actively supporting. Try administering that SLA, when the same carrier or ISP customer (or even one of the more advanced enterprise ones) has all three!
These are all relatively new, as things in the fiber world go, coming onto the scene since the early 1990s. Competing fiber vendors have been out-doing one another in terms of wavelengths supported, dispersion shift characteristics and other more esoteric parameters to the point that some of their fibers are not compatible with the same sets of opto-electronic interfacing (laser wavelengths) as others.
And when fiber sections are connected in tandem configurations (connected in series), care must be taken to ensure that sections can effectively convey traffic from one to the other over specified distances greater than, say, a couple of kilometers. I say this because fiber A may support one set of parameters, and fiber B may not, while supporting others.
But these considerations don't often come into play with individual end users' needs, where a fiber carrier brings in a section of glass to a typical customer. Often times, if the user isn't a carrier, whatever singlemode that is in place will often suffice, unless it happens to be one of the earliest singlemodes, or a vintage multimode fiber that was installed in the early eighties.
Most local exchange fiber that has been put in place since the late eighties and beyond, however, is at least of the grade that will support an OC48 for local exchange carrier (subscriber section) distances. Note, I said local exchange, implying that the distances to be supported are not severe. Even here, however, some older single mode fiber will strain to meet the OC48 speeds, like you say.
Corning has a good page that I'd like to refer this discussion to, if I can find it.
Here it is, from their quarterly Guide Lines publication, an article on Connectiv, which is an East Coast Fiber CLEC, that contains some good background with historical references on the selection criteria for various grades of single mode:
corningfiber.com
Corning's Guide Lines is an excellent publication written in easy to digest language, which I commend to all who are interested in fiber optics.
FAC |
