1.7 of the STANAG from March 1990 stated "The main body of this document is identical to the proposed Rev 1.7 of prEN 3910".
[1] Following this, several provisional, green-paper versions, prEN 3910 P1 & P2, were produced by working-group C2-GT9 of the Association Europeene des Constructeurs de Materiel Aerospatial (AECMA) (now ASD-STAN),[2] before its development also ceased in 1996-7 (following the withdrawal of the French delegation, who held the chair of AECMA C2-GT9 at the time).
As a result, the standard remains (as of Aug. 2013) in green paper form: the latest draft version is prEN3910-001 Issue P1, the front sheet of which states, 'This "Aerospace Series" Prestandard has been drawn up under the responsibility of AECMA (The European Association of Aerospace Industries).
[5] The incomplete nature of the standardization process (as of Aug. 2013) has not prevented at least two versions of STANAG 3910 being implemented: one for the Eurofighter Typhoon[6] and one for the Dassault Rafale.
The major difference between the transmissive and reflective star coupled fibre networks is that two fibres are needed with the transmissive star coupler to connect a line replaceable item (LRI), but with the reflective star, and a "Y" coupler internal to the LRI, only a single fibre is required: a "Y" coupler, is a three-port optical device that connects the simplex transmitter and simplex receiver to a single fibre that carries the optical signals transmitted and received by the LRI in opposite directions (half duplex).
However, while the use of the reflective star reduces the cabling in the aircraft, and thus weight, the excess losses involved in the use of the "Y" couplers and reflective star coupler makes meeting the power budget requirements, given a transmitter power and receiver sensitivity, more difficult.
Whilst it is explicitly stated that the LS buses may be a fibre optic equivalent to STANAG 3838, e.g. MIL-STD-1773, there are no known implementations of this approach.
Versions using an electrical HS channel require an additional active component, in the form of a "central repeater", with multi-tap collector and distributor lines (which use directional couplers to connect to the LRIs) and a buffer memory, to allow for small differences in data rates.
The standard and the electrical media slash sheet it contains specify a 100-ohm characteristic impedance cable for both collector and distributor lines.
However, the losses in the directional couplers, etc., especially for the RT furthest from the central repeater, and the limitations on dynamic range between the furthest (and most attenuated) and nearest (and least attenuated) RT, will limit the number of RTs operating to the standard that may be connected to the HS media.
With electrical media HS buses, the physical architecture is like that with 3838/1553B, save that the central repeater has to be at one end of each of the collector and distributor lines: the RT's connections to these lines work preferentially in one physical direction along the bus - hence directional couplers.
The use of optical media for the HS buses, e.g. in EFABus, has a significant effect on the physical architectures: it is not practical to implement linier T coupled bus architectures, where the bus is run around the platform (e.g. the aircraft), and each line replaceable item (LRI) connects, though a stub, at the nearest convenient point in its path.
3838/1553B BC-RT transfers are sent to a specific subaddress of the receiving and transmitting RTs by the STANAG 3910 bus controller (BC).
The standard does not indicate how the transmitting terminal is meant to know whether the receiving RT implements this feature or not; hence it may be assumed to be part of the system's design.
MIL-STD-1553E is, therefore, an attractive option for upgrading existing aircraft, etc., that use 1553B, because it should not involve any modification to the wiring or any RTs that are not required to take part in these high-speed transfers.
This may be related to the susceptibility of these additional high-speed transmissions to the specific routeing of the 1553 bus cables, and the exact placement of the couplers, BC, and RTs on different aircraft of a fleet, which may make it difficult to specify, in advance of an upgrade, precisely what additional capacity might be provided.
[9] In addition to 1553B, it also runs over coax, twisted pair, Power-Line Carrier, and existing ARINC 429 links.