Introduction

The current Amateur Link Protocol, AX.25 [WB4JFI 84], has many deficiencies. This paper proposes a new Link Protocol called DUAL which attempts to address these deficiencies. DUAL - An Unreliable Amateur Link Format is not a replacement for AX.25 - it does not have all of AX.25's functionality. However, DUAL is designed to be a flexible method for transporting higher-level network packets. If required, AX.25 functionality can be added to DUAL as a Network layer protocol.

DUAL attempts to:

• Allow the transportation of packets from many types of higher-layer protocols, using link addresses that are suitable for these protocols instead of the standard amateur callsign,

• Provide a mechanism to broadcast the association between these link addresses and the callsign of the transmitting operator,

• Minimise the overhead of the Link layer, in terms of packet header size,

• Separate the Logical Link Control, Medium Access Control and Physical layers in a modular way, so that DUAL can be used independently of the Physical, MAC and higher layers desired.

The main reason behind the design of DUAL was to create a link layer that was better suited for the transmission of TCP/IP packets across amateur radio [Kahn 77] than the existing protocol. Although the design has been generalised to allow many other protocols, a large proportion of this document covers TCP/IP transmission over DUAL.