Amateur Radio Digital Communications

Lore & Background

The use of TCP/IP on amateur radio began early in Internet history, preceding the public Internet by over a decade. In 1981, Hank Magnuski obtained the class A 44/8 netblock of 16.7 million IP addresses for amateur radio users worldwide, prior to Internet flag day on 1 January 1983 when ARPANET switched from NCP to TCP. The initial name used by Jon Postel in RFC 790 was the 'Amateur Radio Experiment Net'. Originally, the amateur link layer protocol AX.25 carried several competing higher level protocols, with TCP/IP a minority due to configuration complexity and high protocol overhead. One approach for VHF/UHF operation emerged as TCP/IP over ROSE (Radio Amateur Telecommunications Society 'RATS' Open Systems Environment, based on X.25). Within a few years the public Internet made these solutions obsolete; the ROSE system is now maintained by the Open Source FPAC Linux project.

The AMPRNet is connected by wireless links and Internet tunnels. Due to bandwidth limitations, 300 bit/s is normally used on HF, while VHF and UHF links are usually 1,200 bit/s to 9,600 bit/s. Mass-produced Wi-Fi equipment on 2.4 GHz and 5 GHz is now used on nearby amateur frequencies for faster links as HSMM or hinternet. Since it is based on IP, the AMPRNet supports the same transport and application protocols as the rest of the Internet, though there are regulatory restrictions on encryption and third-party traffic. The network is composed of subnets worldwide; portions have point-to-point radio links, while others are isolated. Geographically dispersed subnets can be connected using IP tunnels. As of October 2011, experimentation moved to dynamic configurations provided by peer-to-peer VPN systems such as n2n and ZeroTier.

Reader's Guide

The significance of Amateur Radio Digital Communications lies in its pioneering role in applying Internet protocols to radio, and its unexpected dual use as a major research resource. The 44/8 address block, originally allocated for amateur packet radio, became the basis for the UCSD network telescope starting in February 2001, which passively monitors Internet background noise and backscatter. This telescope recorded the spread of the Code Red II worm in July 2001 and has collected terabytes of data for security research. By December 2009, only about 1% of inbound traffic to the 44/8 network was legitimate amateur radio traffic, with the rest being background noise. The network's legacy includes the mirrorshades router at UCSD, which since the 1990s forwarded most packets within the 44/8 range via IP-in-IP encapsulation. The project has been funded by multiple agencies including the National Science Foundation, the Department of Homeland Security, and DARPA. In mid-2019, part of the IPv4 range was sold off due to IPv4 address exhaustion, reducing the available address space. The remaining addresses (44.0.0.0/9 for USA and 44.128.0.0/10 for the rest of the world) remain available to licensed amateur radio operators through volunteer coordinators.

Did You Know?

• The 44/8 address block was allocated in 1981, before the Internet flag day of 1 January 1983.
• The UCSD network telescope using 44/8 recorded the spread of the Code Red II worm on 15 July 2001.
• By December 2009, only about 1% of inbound traffic to 44/8 was legitimate amateur radio traffic.
• In mid-2019, part of the 44/8 IPv4 range was sold off due to IPv4 address exhaustion.