data carried rather than the physical destination. The virtual link ID is a 16-bit unsigned integer value that follows a constant 32-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. BAG rate BAG stands for bandwidth allocation gap, this is one of the main features of the AFDX protocol. This is the maximum rate data can be sent, and it is guaranteed to be sent at that interval. When setting the BAG rate for each VL, care must be taken so there will be enough bandwidth for other VL's and the total speed cannot exceed 100 Mbit/s. Switching of virtual links Each switch has filtering, policing, and forwarding functions that should be able to process at least 4096 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 of 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