Best of the ISP-Lists

The User-to-Modem Ratio

Members of the ISP-Tech list discuss an issue that appears to be mathematical: The appropriate user-to-modem ratio for a small ISP. In fact, this is an eternally unanswered question that always provokes discussion.

[January 19, 2001]

On the ISP-Tech list in January, PJ asked,

"For those smaller ISPs at about five hundred customers, what is your modem-to-user ratio? We have trouble with busy signals when we get at 6:1. I know the big boys run higher than that, but what about those of you around my size?"

A number of respondents agreed that anything higher than 4:1 causes problems:

[MK noted] "Right now we are around 4:1. When we were at 6:1 we had users complaining about busy signals. Makes me wonder how some ISPs maintain an 8:1 or higher ratio!"

[EC added] "Back in the good old days, 10:1 was the magic number. Can you imagine the amount of complaints you would get now at that ratio? We're currently at 4:1. At 6:1 we also start getting complaints."

Others suggested that a ratio of 6:1 ought to be okay:

[RW advised] "6:1 is about right for the number of users. It seems you may have some bandwidth hogs."

[JY agreed] "Most ISPs of any size have idle timeout limits and session limits. We don't allow people to connect for over twelve hours straight, and idle timeouts are set to twenty minutes."

[JL added] "We impose a 3-hour session limit, and a 30-minute inactivity timer."

Still others countered that an even higher ratio should be fine:

[RS observed] "We are at about 7:1. We are giving busy signals, but not every day."

[JM added] "We are between 8:1 and 10:1. Some people get busy signals, and that's okay by me. We make no guarantees against busies, and in order to make money, 8:1 is the break even point."

[TN offered] "We need a 6:1 ratio from September until March. During the rest of the year we can easily get away with a 12:1 ratio or higher."

—End