This article relies too much on references to primary sources. Please improve this by adding secondary or tertiary sources. This enables a clean separation between application and modem. The standard also defines two more layers, CAS which is intended to establish connections to other HF nodes and control the status of these connections, and DTS, which controls all the data manipulation for transmission slicing, directioning, timing There are two basic modes of transmission defined by this standard.
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This enables a clean separation between application and modem. It comprises: An HF Radio, which is an analogue device. An HF Modem, which converts from analogue to digital. Encryption optional. For a larger deployment, applications may be running on separate computers and connecting over a LAN.
We will contact you to arrange an evaluation. Why STANAG is needed It is useful to consider the key characteristics of HF Radio, which is sufficiently different to other systems that it becomes imperative to use a specially designed protocol.
Key characteristics are: Low bandwidth. HF Radio is slow, with bandwidth ranging from 75 to bits per second, with a typical rate of bits per second. HF transmission is subject to varying levels and types of noise and interference.
Variable bandwidth. This will result in varying bandwidth for the system using the modem. Simplex mode. An HF radio cannot detect incoming signals when it transmits, and so is not even half duplex. If more than one radio transmits at once, nothing gets through and none of the transmitting radios can detect the problem. HF Radio is a broadcast medium, and it is important to enable applications to use this in order to provide broadcast and multicast services. Receive only. Long turnaround time.
Turnaround time is the time taken for one radio to stop sending, and another radio to start. This can vary from a few seconds to a few tens of seconds. Interleaving is a technique commonly used to reduce the impact of burst noise, and this substantially increases turnaround time. To optimize throughput, a radio needs to transmit for a reasonably long period and then allow other radios to transmit.
To get reasonable utilization of the bandwidth, the transmit time needs to be quite a lot longer than the turnaround time. An HF modem provides a quite basic interface; essentially send OR receive data. This combination of requirements is quite unlike any other communications medium, and special protocols are needed to efficiently transmit data over HF.
The central service is called "Unit Data", where the application sends or receives a block of data, typically up to around 2 kBytes. There are two basic variants of Unit Data: Unreliable. Here the data is sent out, without any form of acknowledgement. This is used for broadcasting i. This is used for sending data to a single radio that is not in EMCON mode, and provides guaranteed delivery. Optional services associated with Reliable Unit Data are: Acknowledgement of Unit Data delivery to the sending application.
Delivery of multiple Unit Data blocks to the receiving application in the order they were sent. The Unit Data service provides a number of things to the application: Multiplexing.
It enables multiple applications to send and receive data at the same time. Flow Control. The STANAG server will provide flow control to the application, to control the amount of queued data that builds up.
Precedence handling. This is a vital feature for military applications. Unit Data gives a simple building block that can be used by a wide variety of applications, and is the key capability provided by STANAG to applications using it. This section does not attempt to fully explain how it works, but describes a few key features to help better understand its value. STANAG controls which radio is transmitting and seeks to organize data to minimize the number of turnarounds.
Where the maximum transmit time seconds can be used, this will give reasonable link utilization, for normal turnaround times. In order to minimize the number of turnarounds, sending of acknowledgements is delayed. A typical sequence with two radios might be: Radio 1 transmits to Radio 2 for seconds; it sends a number of DPDUs. As you can see this sequence makes efficient use of the link by minimizing turnarounds.
You can also see that in the event of retransmissions, that there can be considerable delays in data getting through. These delays could be reduced, but at the cost of less efficient link utilization. STANAG provides a number of management features, and one of the most interesting is remote modem control.
The optimum modem parameters e. Edition 1, and Edition 2 until recently known as Edition 1, Amendment 1 radios do not attempt to transmit when it is known that another radio is transmitting. When there is silence, if two radios start transmitting together, they conflict with each other and all data is lost. This causes problems when there are more than a few radios and traffic is high. It becomes inefficient and chaotic. In practice, Edition 1 is only useful for very small numbers or radios, or where radios transmit for a low percentage of total time.
Edition 3 should be used for most deployments with medium and large numbers of radios.. Isode Ltd.
STANAG 5066 Data Transfer Sublayer (S5066_DTS)
R&S®STANAG 5066 HF Radio Data Communication System