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Dealing with Busies

Busy signals are a turn-off to dail-up customers—and a business killer for ISPs. Here are some thoughts on keeping them under control.

[July 29, 1999]

In a thread on ISP-Tech in July of 1999, PJ wrote:

"We are running a 5:1 user-to-modem ratio and still experience some busy signals during peak hours at night. Over the past month, we've had about 55% of nights busy-free. The rest range from 5 to 45 minutes of busies. I'm looking for some kind of benchmark. If any of you tolerate busy signals, what is your standard?"

Three related issues emerged as the thread unfolded

• What's a viable modem-to-user ratio?
• Maximizing line usage by eliminating campers
• When should you add capacity?

Here's what respondents had to say:

Rolling ratios
[ RS wrote] "Right now, we run around 600 customers, keep the modem ratio at about 6:1, but still get busies every night from about 7 to 10 p.m. or a bit after. I don't think it would make a lot of difference here if we went 5:1, we'd still get busies."

[KM pointed out] "The more modems you have, the more you can stretch the ratio—to a point. We're running with 46 modems and about 310 users [6.7:1], and seeing about 10 minutes of busies once or twice a week."

[N wrote] "Our experience is that you have to keep it well below 5:1 for the first 1,500 customers. After that the number starts to go up. We're running 5.5:1 right now, and we've got no busies in sight."

[B agreed] "When we first started, our user-to-modem was about 4:1 with about 150 customers. Now we have about 1,100 users, and we keep ours at 7:1. We can go to about 8.2:1 before we start getting busies."

Optimizing line useage
[VB wrote] "User-to-line ratio is only one part of the equation; average line usage time is the other part. If users are just hopping on and off, you can run a much higher ratio than if they're hanging on for long periods. Watch the people that are camping. If you don't have some sort of idle policy, you should."

[N agreed] "We found it really helps to make sure you've got no campers and no multiple-line users that aren't paying for the extra line. We started brutally enforcing our 'one concurrent dialup' policy, and our busies dropped immediately."

[MS went farther] "We have a two hour session limit from 4 PM to 10 PM. Then you have to get off for 15 minutes. In fact, many of my customers have been 'acquired' from a cheaper provider because we don't allow 'camping.' I've lost a couple, but I've gained 10 or more for every one that left."

Adding capacity
[D asserted] "I think no busies are tolerable. Order more lines. When we are at 60 to 80 percent lines full consistantly, we order more lines. By the time the telco actually delivers, we really need them."

[KM agreed] "With almost 50 percent of your evenings seeing busies, I think you should have had more capacity ordered already. Our next PRI is ordered. The telco gave us an install date about three weeks after the order was placed. I would advise adding modems now."

[MS wrote] "I watch the traffic on my last line, and as long as it sees much lower use than the others I leave things alone. When it sees a lot of traffic, I add another line."

[JO added] "A rule of thumb that works for me is that when the number of calls on the last line is more than 10 percent of those on the first line, it's time to add more lines. If I let the number of calls on the last line get much over the 10 percent figure, I start getting customer complaints. I need to collect counts for at least a couple of weeks though to get a valid indication."

—End

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