ARINC operates in such a way that its single transmitter communicates in a point-to-point connection, thus requiring a significant amount of wiring which amounts to added weight. Data are read in a round-robin sequence among the virtual links with data to transmit. However, total bandwidth cannot exceed the maximum available bandwidth on the network. However, the number sub-VLs that may be created in a single virtual link is limited to four. Retrieved May 28, Multiple switches can be bridged together in a cascaded star topology.
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In one abstraction, it is possible to visualise the VLs as an ARINC style network each with one source and one or more destinations. Virtual links are unidirectional logic paths from the source end-system to all of the destination end-systems.
The virtual link ID is a bit unsigned integer value that follows a constant bit field. The switches are designed to route an incoming frame from one, and only one, end system to a predetermined set of end systems. There can be one or more receiving end systems connected within each virtual link.
Each virtual link is allocated dedicated bandwidth [sum of all VL bandwidth allocation gap BAG rates x MTU ] with the total amount of bandwidth defined by the system integrator. However, total bandwidth cannot exceed the maximum available bandwidth on the network. Bi-directional communications must therefore require the specification of a complementary VL. Each VL is frozen in specification to ensure that the network has a designed maximum traffic, hence determinism.
Also the switch, having a VL configuration table loaded, can reject any erroneous data transmission that may otherwise swamp other branches of the network. Additionally, there can be sub-virtual links sub-VLs that are designed to carry less critical data. Sub-virtual links are assigned to a particular virtual link. Data are read in a round-robin sequence among the virtual links with data to transmit.
Also sub-virtual links do not provide guaranteed bandwidth or latency due to the buffering, but AFDX specifies that latency is measured from the traffic regulator function anyway. This is the maximum rate data can be sent, and it is guaranteed to be sent at that interval. Switching of virtual links[ edit ] Each switch has filtering, policing, and forwarding functions that should be able to process at least VLs. Therefore, in a network with multiple switches cascaded star topology , the total number of virtual links is nearly limitless.
There is no specified limit to the number of virtual links that can be handled by each end system, although this will be determined by the BAG rates and maximum frame size specified for each VL versus the Ethernet data rate.
However, the number sub-VLs that may be created in a single virtual link is limited to four. The switch must also be non-blocking at the data rates that are specified by the system integrator, and in practice this may mean that the switch shall have a switching capacity that is the sum of all of its physical ports. However, some features of a real AFDX switch may be missing, such as traffic policing and redundancy functions.
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