Multichannel adaptive routing for intensive data packet flows transmission: SpaceWire networks and protocols, long paper

摘要

In many networks there is a necessity to transmit data packets flows, the intensity of which exceeds the throughput of one channel SpaceWire, GigaSpaceWire, SpaceFibre. This flow can be a packet flow from a single source to a single destination, for example, from a camera to a monitor. Also, a packet flow can include packets from different sources to different destinations that goes via two neighboring routers. An example is transmission of packets between two routers located on the boundaries of neighboring regions. The packets, belonging to one flow can have almost same length (transmission of uncompressed video), or quite different length (transmission of compressed video, transmission of packets with different content between two regions). The adaptive routing can be used for transmission of such packet flows. This mechanism includes in SpaceWire standard. A set of alternative output ports (a group of ports) can be determined in routing table for the logical (or regional address). Any output port from this group (if connection for this port is established and port is not occupied by other packet) may be used for transmission of packet with this address. Thus, the summary throughput of all ports belongs to the group can be used for transmission of data packets with this address. However, the possibility of parallel transmission of packets from this flow to different output ports belongs to the group is required for effective utilization of this summary throughput. If the length of packets may be different or if the quantity of input ports for considered flows is not equal to the quantity of output ports in the group, the router should include special mechanisms to ensure efficient parallel transmission of packets to all ports belongs to the group. Adaptive routing for intensive data flows transmission can be implemented not only in SpaceWire/GigaSpaceWire networks, but also in SpaceFibre networks. We consider the specific of its implementation taking into account the features of data link layer (virtual channels with a fairly large buffers, retry mechanism) In this paper we discuss possible implementations of these mechanisms for SpaceWire, GigaSpaceWire and SpaceFibre, estimate achievable bandwidth utilization of port's group, the overhead of the implementation of these mechanisms for packets flows with different characteristics. A side effect of adaptive routing is a possible mismatch of the order in which packets are sent to the network form the source and the order of their receipt by destination. We evaluate the packet's window size that required in the destination node for recovery order of packets and the associated delays. The ports of router belonging to the same group may be connected to one or several different routers (according to the standard). In the first case all packets from the flow will be transmitted via one chain of routers (via one path via network). In the second case, they will be transmitted through the network in different ways. The reordering of packets is possible in both cases. However, in the first case, the mechanisms, that prevent the packets reordering, can be implement in routers. But its implementation can lead to decrease of throughput utilization, to additional hardware costs and to increase of packet's transmission time. In the paper we estimate these overheads for data packets flows with different parameters.