North Korea is a major user of HF radio for diplomatic communications. Their network is very prolific, and uses a proprietary ARQ modem to carry over numerous messages every day to embassies around the world, on many shortwave links through an elaborate system of relays. Most North Korean embassies worldwide can be found on the network.

The current modem was introduced in late 2003, and at present is the only mode used. Previously, hand-sent Morse code, 50Bd/1000Hz RTTY, and a proprietary 150Bd/300Bd/600Bd/1200Bd BPSK modem were used at various times.

Traffic

Messages sent are almost exclusively 5-figure group ciphertexts. A small percentage of traffic consists of Korean language cleartexts, which include official foreign ministry statements, news articles of foreign outlets (translated to Korean), and visa applicant contact details.

An example 5-figure group message, along with its binary header represented in hex:

F8000000 19 00 01 11 3701 2C01 5500 0000 00
47547 27997 50675 45783 77046 01247 54723 19203 64656 48260
99665 86520 86646 00281 13600 44673 16760 14653 92766 42564
66832 38756 17156 89639 68102 23711 29045 91764 65853 74547
61171 06681 22221 33108 55812 17173 58397 21035 53662 96625
58259 05798 18234 78397 42021 02904 10215 82904 47777 81503
60744 68245 81733 29413 32575 99090 10808 69865 56438 53251
93652 14389 57865 36519 10504 57757 76740 69832 01816 55480
54470 99769 39457 34484 25947 97438 05638 29333 33949 92143
39311 47547 27997 50675 14009 0

For more details, see the full descriptions of the DPRK-ARQ protocol and message format.

Scheduling

Contacts with embassies follow a fixed daily schedule, subject to occasional modifications. Links between pairs of stations usually take place twice a day in daytime. In case of highly urgent traffic, stations may be called to operate overtime.