Yes, that's the Litespan alright. I didn't know that the DSC unit retained their name, tho.
Litespans are a favorite among telco engineers and outside plant operations staff. I've come across several situations using them in recent months (although they have been around for a while), where they were housed in CEVs and quansut huts.
The construction guys refer to them as "pair gain" No, not the company Pair Gain, but the engineering term which connotes the advantage of their use, as a function of ratio of virtual pairs that are gained through the use of multiplexing.
In days of copper T1 circuits --which were the original backbones that fed DLCs (and still do to this day in certain areas) along with microwave radio in other instances, the pair gain was often cited as 12:1. That is, twenty-four two-wire circuits supported by two two-wire circuits, or 24:2, or 12:1.
Today, the term "pair gain" gets lost to the abundance of channels that are derived from a single pair of fibers. Often 672 voice circuits to an STS-1 or T3, or 8,064 to an OC-12 (twelve T3s).
Nowadays, new cable routes that extend into the far reaches of a CO's serving area don't incorporate copper, especially those which are now supported by optical Digital Loop Carrier systems such as Litespan, or the AFCI line of DLCs, or Marconi, and others.
The fact that the cable spans do not include copper often puts a crimp into the backup (disaster recovery) strategies of businesses who often request a certain number of their services be delivered over copper lines, all the way back to the central office. These are connected directly to the Class 5 switch and consequently survive ordinary power outages because of the central office battery and generator backup that is used to keep their switches operational during those periods.
These services are ordered over the copper lines just in case there is a catastrophic SONET failure or a power outage knocking out everything else. Of course, if the only thing feeding an area is fiber, as in the case I began to discuss above, then this strategy is not a feasible one for backup, even if they use a digital loop carrier system such as Litespan whose outputs include copper pairs that emulate regular central office lines.
Despite this obvious conflict, what the telco will often offer instead of copper lines to the CO is a couple of copper-based circuits which originate at the CEV (actually, emanating from the Litespan or equivalent) which, in turn, is really supported from the CO by nothing but fiber!!
Two things are wrong with this. First, if the SONET ring fails or if it is otherwise rendered useless, then the Litespan is rendered useless, too, becuase the Litespan depends on fiber for its voice and data traffic. In all fairness, tho, this could actually be a useful alternative, i.e., one that offers a minimal level of voice service during telco related outages, if the fiber problem is a result of an optical mux failure at the customer premises.
SONETs are not supposed to fail, right? But neither was the Titanic supposed to sink. Talk to a controller of a large corporation and you will find that they use the latter form of logic, and probably rightfully so.
Secondly, the life expectancy of the CEC UPS, which is supported by commercial power under normal operating conditions, is rated for only several hours of use, although some of them are also equipped with generators. But most are not. And the higher the load those UPSes have to support, the less time they have to live.
Of course, customers have the option of ordering a "special assembly" copper build going all the way back to the central office if they wish, or to the nearest cross-connect box that it comes into contact with that is connected to the CO. But such an option can cost tens, even hundreds of thousands of dollars.
Recommendation? The same as I recommended for powerline loss contingency for the proposed FTTH lifeline services: Take the copper lines if they're available --and use them for fax and modem dial up connection during normal times, just make sure you know where they are if you ever really need them for voice-- and keep your cellular/pcs phones charged. Also, have a cigarette lighter power adapter handy just in case your cell phone battery runs down, if you do not have generator on location. And oh yes, make sure you always have enough gasoline in your tank to see you through the night.
FAC |
