Technical: More About Connectivity

Send Less Data

Another way to cope with limited bandwidth is to write programs that take care not to waste bandwidth. For example, to reduce packet size, wherever possible Bolo (my interactive network tank game) uses bytes instead of 16-bit or 32-bit words.

For many kinds of interactive software like games, it's not important to carry a lot of data. What's important is that when the little bits of data are delivered, they are delivered quickly. Bolo was originally developed running over serial ports at 4800 bps and could support eight players that way. Over 28.8 Kbps modems it can barely support two players with acceptable response time. Why? A direct-connect serial port at 4800 bps has a latency of 2 ms. A 28.8 Kbps baud modem has a latency of 100 ms, 50 times worse than the 4800 bps serial connection.

Software can cope with limited bandwidth by sending less data. If a program doesn't have enough bandwidth to send high-resolution pictures, it could use a lower resolution. If a program doesn't have enough bandwidth to send colour images, it could send black- and-white images, or images with dramatically reduced colour detail (which is what NTSC television does). If there isn't enough bandwidth to send 30 frames per second, the software could send 15 fps, 5 fps, or fewer.

These trade-offs aren't pleasant, but they are possible. You can pay for more bandwidth or send less data to stay within your limited available bandwidth. However, if the latency is not good enough to meet your needs you don't have the same option. Running multiple circuits in parallel won't improve latency, and sending less data won't help either.

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