STANAG 4538 PDF
There are two mechanisms standardized (STANAG and STANAG ) which are discussed here. These provide similar characteristics to the IP user, and. 25 Jul Unid UTC USB, STANAG Fast Link setup (FLSU) bursts followed by Low rate Data Link (LDL) forward transmissions. 5 Jan Quoting from STANAG “Transmitting N Async_FLSU_Request PDUs guarantees that all other scanning stations will scan the calling.
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The data link protocol is closely connected with the burst waveforms defined in the standard, and cannot be run with other waveforms. 4358 burst waveforms use the sfanag 8-PSK 8-Phase Phase-Shift Keying 3 bits per symbol modulation at baud Baud unit symbol Bd is the unit for symbol rate or modulation rate in symbols per second.
Unacknowledged must be used where data is being sent to more than one recipient broadcast or multicast or where the recipient is in EMCON Emission Control and cannot transmit an acknowledgement.
Why IP over HF Radio should be Avoided
After each new reception, the additional received signal is combined in the FEC Forward Error Correction decoder with the earlier reception s until an error-free result is obtained. IP routers simply switch packets. HF Links are also used for voice communication. There are six Burst Waveforms BW defined which are used in different aspects of the protocol.
IP is the universal interface between physical networks and application.
Why IP over HF Radio should be Avoided
It sends out each packet in turn, to unicast or broadcast addresses. In order to make reasonably efficient use of an HF link, it is critical to have transmit time longer than stanav time.
When packets are lost, a TCP receiver will reduce close down the window, which will in turn reduce the data rate. TCP is a windowing protocol, and in practice the only one that matters. Thus, with no more overhead than is staanag required for ARQ Automatic Repeat reQuest Automatic Repeat Query operation, data rate can adapt as required for each individual packet in a message.
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In an IP network there are no end to end circuits etanag virtual circuits. The core SMTP protocol is “chatty”. Where it is available as an option, ACP has. It supports trunked-mode operation separate calling and traffic channels as well as sharing any subset of the frequency pool between calling and traffic.
This results in spreading simultaneous calls more evenly over the available frequencies. This is not inconsistent with the technical conclusion here that it works, and performance varies from atrocious to sub-optimal.
It can be seen that there is only a single turnaround, after the data has been sent as ARQ is not used. This paper looks to highlight key protocol choices, rather than give detailed descriptions.
The key change to note is that multiple DATA packets are sent before the associated ack comes back. Reliable applications fall into two major classes according to how data transfer rate is controlled: Capabilities of relevance to this paper:.
The above diagram notes how the TCP data flow causes turnarounds:. The first is that it defines a mode of operation very similar to standard SMTP pipe-lining that minimizes number of turnarounds to two for a small message.
In situations of low packet loss, a UDP based approach is in practice reasonably reliable. Turnaround time is caused by factors at multiple levels:. ACP works by dividing the data to be transferred into multiple packets.
A good TCP implementation will adapt its settings to network conditions, but this will be likely to have a performance 45388 in extra sganag. There are quite a few turnarounds associated with open and close, so TCP would not be efficient for short interactions. This leads stanah many application turnarounds, where one end waits for the other. The six waveforms have different characteristics in terms of data rate, interleaving, frame pattern and synchronization which stanqg for different degrees of robustness and application.
The difference in robustness between HDL and LDL as detailed later herein, is the result of the different waveforms which are used. This mode employs 6 constituent burst waveforms BW0 to BW5 for the various kinds of signaling required in the system, so as to meet their distinctive requirements as to payload, duration, time synchronization, and acquisition and demodulation performance in the presence of noise, fading, and multi-path.
The burst waveforms employ code combining for data transmissions: It can be seen that this is much better than then previous example, with just eleven turnarounds, but still has a significant turnaround overhead.
ACP is a good example of a rate based protocol. Four additional unassignable addresses in each group xx are available for temporary use by stations calling into the network. These provide similar characteristics to the IP user, and so the choice of mapping does not significantly affect the analysis in this paper. Because the SIS server interacts with the modem and handles all of the data being sent, it has all the information necessary to optimize use of HF link.
This choice gives a flavor of the issues that will be examined in the rest of this paper.