BS/EN 4660-003-2019 pdf download.Aerospace series-Modular and Open Avionics Architectures Part 003 : Communications / Network.
4.3 Module Physical interface
The Module Physical Interface, defines the module connector interface which provides interconnection between the Common Functional Module and the network medium.
There are, however, additional properties that shall be defined by the System Designer, probably in a project-specific ‘System Design Specification’, that are network specific and therefore outside the scope of the. These properties define the Physical Layer of the network and the properties listed below shall be provided as a minimum in the case ofan optical network:
— Optical fibre geometry and mode of operation (multimode or single mode) — The MPI only specifies a fibre outer dimension.
— Wavelength division multiplexing or fiber ribbon interconnects.
— Optical fibre Numerical Aperture (Acceptance angle), Spectral Width and Index Profile. (Ideally the same optical fibre type should be used throughout the system to reduce optical losses).
— Number and arrangement of optical fibres within the optical contacts.
— Optical input sensitivities, optical output powers and maximum return loss.
The following parameters shall be separately defined for each sub-network:
Data rate The rate at which data information Is transferred.
Modulation — The method of encoding used to transfer the information.
Signalling rate — A measure of the rate at which the driving devices change state at the medium interface. This isa function of the data rate and the modulation scheme.
Bandwidth-Length product — The product of signalling rate and the maximum path length.
In the case of an optical implementation the following parameters shall also be defined for each sub-network:
Wavelength(s) — The range of optical wavelength(s) at which communications is performed. Power Budget — The optical signal characteristics for reliable communications (transmit and receive).
4.4 Optional Module Logical Interface
To enable interoperability between modules of a different type or between different implementations of the same CFM type, the Module Logical Interface (MU) is defined. This comprises two parts:
— The Module Logical Interface for Network Properties. This specifies the format, protocol, control and characteristics of the communication across the Network, between Network Interface Units (NIU) on different CFM.
— The Module Logical Interface for Communications. This defines the data presentation and Virtual Channel communications format between instances of the Communications Manager In the Operating System Layer through the MOS interface, as shown in Figure 2. These logical communications support:
— Module and System Initialisation;
— Module Resource Management;
— Time Management;
— Network Management.
The generic services available are defined in the MOAA Standard for Software EN 4660-005. but the
MLI specification will be required to specify the use of such calls and the parameters that are passed.
4.5 Optional MLI — Network Properties
4.5.1 General
The MLI Network Properties are not defined in the MOAA Standards. Therefore, for each system implementation that is based on the MOAA architecture definition, the designer shall define a set of MLI Network Properties. The following information provides an indication of the necessary content for this definition.
The definition of a new set of MLI Network Properties per project should be discouraged, since maximisation of LCC benefits from IMA is expected through the reuse of common components. The definition of the MLI Network Properties should consider factors concerned with evolution of technology and possible future communications requirements. In the following, the possible commonality between MLI Network Properties is considered.
4.52 Data Formats
4.5.2.1 General
Information/Destination Identification — The representation of the intended destination (e. g. process, processing element, module). May not be needed if resources are dedicated to the transfer.
Information Length — The amount of information being sent as a packet/block. May not be needed if always a fixed size or information delimiters are used.
Information Type — Indicates the structure of information in the frame.
Error Detection — The technique for detecting transfer errors. May not be needed if the underlying transfer service is sufficiently reliable or the user of the transfer takes responsibility for any unreliability.
Source Identification The representation of the providing source (e.g. process, processing element, module). May not be needed if resources are dedicated to the transfer.
4.5.3 Data Link properties
4.5.3.1 General
The MOS communications services defined in the MOAA Standard for CFM EN 4660-002 provide generic services to provide the software with a level of network Independence. However, the system designer must be aware that the characteristics of the overall system design are dependent on the characteristics of any particular network implementation. So the designer must take into account the implications of network choice on various system properties Including timeliness, reconfigurability, safety, security and fault management.
As in the case of changing a module, the contents of the blueprints will need to change if the network is changed, but as the network integrates the system, the impact on the system characteristics is greater. These characteristics may also be affected by a simple change In network topology (I. e. a change from point-to-point links to a broadcast bus, ring or switched network).
Therefore, the characteristics of a specific network implementation must be carefully defined, as they heavily influence the characteristics of the overall system. It should also be recognised that these characteristics cannot be associated with any specific component or layer in a communications model.
4.5.3.2 Required Characteristics
All the following characteristics are separately defined for each sub-network.
Bit Error Rate (BER) — The maximum rate at which bit errors can be expected to occur under tàultfree conditions.
Data Integrity — The probability of receiving corrupt data and accepting it as correct.BS/EN 4660-003-2019 pdf download.