6 May 2017

NATO "copy-and-paste" ...and errors

Computer-based editing can involve very frequent use of copy-and-paste operations but sometimes these operations can lead to significant errors. I came across a case by reading the Annex C to STANAG-4538 Ed.1, more precisely the Amendment 21. The problem arises in "TABLE 7.2.5.2-1. LDL actions", where is specified (litterally):
"Note: The LDL transmitter can send duplicate packets either as a result of missing an LDL_ACK PDU, or at the end of a datagram, in order to fill the (otherwise unused) packet positions of an LDL_DATA PDU. The LDL receiver is required to inspect the sequence number of each data packet received without errors, and to use the sequence numbers to identify and discard duplicate packets." (highlighted in Figure 1).
Fig. 1
This text is clearly a copy-and-paste from "TABLE 7.1.5.2-2. HDL actions", unless the the term HDL (Figure 2):
Fig. 2

Well, the statement "The LDL transmitter can send duplicate packets either [...] or at the end of a datagram, in order to fill the (otherwise unused) packet positions of an LDL_DATA PDU."  (Fig .1) is wrong since LDL protocol, contrary to HDL, does not provide 'packet positions' in its DATA PDU but rather one single packet at a time! (each HDL_DATA PDU is a sequence of 24, 12, 6, or 3 data packets, in which each packet is composed of 233 bytes of payload data; each LDL_DATA PDU is a single data packet composed of 32, 64, 96,..., 512 bytes of payload data).

It's an oversight that hopefully will be edited in the next edition :)