Voice Traffic

Is there a rule-of-thumb for calculating number of CO lines(N) needed given the number of extensions (E).

I am aware of Erlang but want an estimation, not exact calculations.

Thanks,

Marcel Riley

Reply to
Marcel Riley
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Sorry no help from me, but I am interested in any good answers you get. It depends so much on what kind of business, how many people need to really make or receive calls, and the 25-50% of calls that are personal. I have been in the business for over 25 years and have seen no more than cut and try solutions.

TerryS

TerryS

Reply to
TerryS

Marcel, that's a good question and the answer is (of course) "It depends".

There are a lot of factors - what sort of business are you in, do you work across multiple time zones or are you making pretty much local area calls, what sort of mixture of incoming -vs- outgoing calls do you have. If you have a lot of people who spend their day on th ephone (collections, purchasing, call centers, etc.) you'll need more trunking than something like the manufacturing business we're in.

Just as an example the switch I manage covers about 5,500 telephones in a manufacturing environment. We've got about 284 trunks on 12 PRIs, some dedicated to Toll-Free (in), LD and international (out) and some for local (2-way DIDs and LD overflow) and we seem to manage fine. Actually, that level of trunking gives me about 10% capacity headroom during the daily busy hour.

I believe that extra headroom is worth the money, too. I'd rather have a few to many trunks than have the President complain that his wife gets busy signals when calling!

Reply to
Al Gillis

<<SNIP>>

Like Mr. Gillis says, "it all depends." A general rule of thumb is to plan for 8 stations per trunk for general office usage, but you may even try 10 to one if there isn't a lot of traffic in/out of the business. If you overtrunk on the front end, then reducing the number of trunks leaves you with some excess hardware. If you undertrunk, then you may have to buy additional hardware to support the additional trunks.

It is usually cheaper to buy the trunk cards on the front end of the purchase - the incremental cost is a whole lot less - than it is to add a trunk card or two after the fact. The costs associated with bring a trunk on-line at system startup is a whole lot less than doing it after the fact.

Rodgers Platt

Reply to
Justin Time

And I just rememberd another reason to overtrunk just a little on a new system. On one of my first cutovers (back when I was a pup) we figured out the trunk quantities EXACTLY (or so we thought). When the system was placed in service there were busy signals galore for those who tried to call outside. It took a week or so to get more trunks, but during that initial period people formed their opinions of our work. For years afterward the nay-sayers would cite those busy signals as clear evidence that the new system was junk... "It never worked right from the very first day" they'd say. From that I learned to overtrunk initially and then cut back, if necessary, after a month or so. Adequate (or excess) trunks gives the gripers one less thing to shoot at!

Al

Reply to
Al Gillis

Good thing! Real world application of Erlang formulae produces only a "best guess" estimation.

You were looking for something a bit less than "best", in the quality of your guesswork, I guess? :)

Reply to
Hammond of Texas

Another advantage to over trunking up front is it makes you look like a bit of a hero. First of all everyone's happy and no one complains of any trunk congestion, secondly when it's time to put the nose to the grindstone to hammer out next year's budget, you can cut some of your excess trunking and save a few bux.

The actual ratio of trunks to stations is a bit of a logarithmic function. The fewer number of stations you have, the higher the ratio of trunks to stations needs to be. Example, in a small business with say only 10 or so employees, you could easily need 3 or even 4 trunks, a ratio of 2½ to 1. By contrast, with a large enterprise operation with 5000 employees, you could possibly get by with 250 trunks (a ratio of 20:1), but again, "it depends". The "depends" is what type of business you're in.

Reply to
wdg

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