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Natureboy,

There are more variables associated with cable speed (throughput, actually) than there are with DSL speed. How much latency there is even within one ISP's network depends on how the ISP has provisioned their network. Between ISPs, there are generally more variables related to how the two networks are interconnected.

The interconnect may be more or less than 10 mbits. And throughput typically doesn't vary as much on a DSL connection as on a cable connection, because of differences in the way DSL and cable networks are built out.

Going to wireless, even from the same ISP, is likely to have the opposite effect from what you want. The chances that the interconnection of a wireless network is the same as the interconnection of a cable network are the same is very low.

You should look at the level of DSL service you have. Is it ADSL or SDSL? The "A" in ADSL stands for asymmetric, while the "S" in SDSL stands for symmetric. So an ADSL connection by design has more throughput in one direction, towards the customer, than the other, towards the ISP. SDSL, on the other hand, provides the same throughput in both directions. You should expect to see no more than about eighty percent of the rated speed of the connection because of overhead associated with the way DSL works.

The reduction in speed in the afternoon may be caused by a variety of factors other than overall load. For example, the sun may hit the telephone company's connector box in the afternoon and increase the resistance of a connection by heating.

You said you've already determined that the ping timing between the DSL-connected site and your central site doesn't vary as a function of the time of day. You might want to try the "ping" with a larger packet size. Some kinds of problems are sensitive to the size of the data packet.

The Microsoft "ping" command uses " -l (size) to vary the packet size. Try -l 1472. The times will increase because of the larger packet size, but they should be consistent. You can also use the "tracert" utility to determine the path taken between the remote and central sites. That will give you an idea how many routers are traversed.

You may also want to involve your DSL ISP in the problem. If you're paying for business-grade DSL, they should be willing to assist you in getting what you're paying for. They can check the DSL circuit for noise margins and evidence of other problems remotely, and typically at no cost.

Jim