DUAL provides a new format for amateur radio packet transmission that has less header overhead than AX.25 and is more `user-friendly' to higher-layer protocols such as IP. DUAL provides up to eight packet formats for each upper layer protocol, allowing packet transmission to be tailored to the link environment that will be used.
For the transmission of TCP/IP packets, the header compression scheme used in Compressed SLIP has been altered to work in a broadcast environment. Overall, there is an 83%decrease in header size when using DUAL to transmit TCP/IP packets, compared with TCP/IP transmission over AX.25.
We have implemented a basic DUAL layer in the BSD Network Stack in FreeBSD. The implementation is robust and confirms out protocol design. As yet, we have not completed our implementation to our satisfaction, nor tested DUAL in a real amateur packet radio environment, although we intend to achieve both in a few months. A future paper will describe our results.