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Our Users' Dialup Connect Speeds

Our Dialup Lines

We have 32 dialup lines in a main hunt group (206-386-4199) and 5 lines in a second hunt group (206-654-7044).
the 32 line main hunt group (386-4199)
The first 18 lines are connected through Microcom 33.6 rack modems. The remaining lines are connected through 3-Com/USR Sportster 33.6 external modems. We get beyond the first 18 lines in evening hours between 18:00 and 23:00.
the 5 line hunt group (654-7044)
These are connected through 3-Com/USR Sportster 33.6 external modems.
We also have 3-Com/USR Sportster 14.4 externals which we use for backup and sometimes place near the end of the hunt group.

Connect Speeds

We very rarely see a connection at 33.6. The reason is that the quality of voice phone lines (POTS - plain old telephone service) will not support the maximum theoretical speed. About 50% of the connections are 32,200, and another 25% at speeds from 24,400 to 28,800. We see some connections as low as 19,200. The users on the other end of the 19,200 connections could have anything from 28.8 through 56K modems.

About 20% of our connections at 2400. 1200 connections are less common, about about 3% of calls. We do support down to 300 in case you want to fire up that old CP/M machine, but I've not seen a 300 baud connection.

Maximum Connect Speeds

Looking at the 19,200 connections, these apply equally to 28.8, 33.6 and 56K modems; there is no advantage or disadvantage to any of these speeds if your phone line won't connect faster. The modems could have been programmed to connect faster, but that would substantially reduce performance.

See (Modem Init. Strings) - Max Speed for more details.

The Microcom modems have an adjustment for throttling them back. This will increase throughput, but lower connect speeds by about 2400. We intend to do so but only after testing. I have a pretty clean phone line and will use file transfer speeds to measure this.

Commercial ISPs and manufacturers of modems for consumers have an incentive for seeking a higher speed. They are selling speed and the higher numbers look nice. Since we are trying to transfer data more efficiently, we can allow the modems to seek a more optimum connect speed.

Faster Connect Speeds

56K lines require a digital line at one end, which is at the ISP. Most of these use 56K modems, but the system works equally well with 33.6 modems. The user of course has an analog POTS line. While connect speeds in excess of 33.6 are often seen, it is likely that 33.6 or lower is optimal, so there is no advantage to using a 56K modem for such connecitons. (SCN does not have these digital lines.)


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Stan Protigal bk269_DELETE_THIS_TEXT@scn.org
http://www.scn.org/~bk269/

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