Technical: More About Connectivity

Latency Workarounds

ISDN has a latency of about 10 ms. Its throughput may be twice that of a modem, but its latency is ten times better, and that's the key reason why browsing the Web over an ISDN link feels faster than over a modem.

One reason standard modems have such poor latency is that they don't know what you're doing with your computer, or why. An external modem is usually connected through a serial port, and all it sees is an unstructured stream of bytes coming down the serial port.

Ironically, the much-maligned Apple GeoPort Telecom Adapter may solve this problem. The Apple GeoPort Telecom Adapter connects your computer to a telephone line, but it's not a modem. Instead, all modem functions are performed by software running on the Mac. The main reason for the criticism is that this extra software takes up memory and slows down the Mac, but in theory it "could" offer an advantage no external modem could match. When you use the GeoPort Telecom Adapter, the modem software is running on the same CPU as your TCP/IP software and your Web browser, so it could know exactly what you are doing. When your Web browser sends a TCP packet, the GeoPort modem software doesn't have to mimic the behaviour of current modems. It could take that packet, encode it, and send it over the telephone line immediately, with almost zero latency.

Sending 36 bytes of data, a typical game-sized packet, over an Apple GeoPort Telecom Adapter running at 28.8 Kbps could take as little as 10 ms, making it as fast as ISDN, and ten times faster than the best modem you can buy today. For less than the price of a typical modem, the GeoPort Telecom Adapter could give you Web browsing performance close to that of ISDN. Even better, people who already own Apple GeoPort Telecom Adapters would need only a software upgrade.

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