The peak usage times are usually between 11am and 1pm, then again in the evening between 6pm and 9pm. We take every step humanly possible to keep the give the peak times equal efficiency to off-peak, but increased usage can eventually slow the line by small increments. We update modems constantly to avoid slowness, but if enough users get online at once, service can slow. Again this is related to peak times, but IGC's service may be running at optimum speeds, while the next level provider we connect to is clogged. This will produce a similar effect.
Modems are a little tricky when it comes to speed.
There will be times that you will connect higher than your modem speed, especially if you have a 14.4k modem. Because our modems are 33.6kbs, this, or slightly below, will be the average speed. Much of your Internet service depends on your local phone lines. If they are cluttered with excess noise or static, the connection will be slower and have a tendency to break off at times. The only solution is call and complain to your local phone company.