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Routing and Addressing
Published in Rui Valadas, OSPF and IS-IS, 2019
The information exchanged between hosts is carried in chunks of bits called packets. Packets are routed from source to destination through the networking infrastructure, which is formed by a mesh of switching equipment and physical communication media. The switching equipment transfers packets from ingoing to outgoing interfaces according to forwarding tables, and using the store-and-forward mode of operation. Store-and-forward operation means that a packet only starts being transmitted by the outgoing interface, after being completely received by the ingoing interface. Switching equipment are usually differentiated based on the type of addressing information used to make forwarding decisions. The figure shows two types of switching equipment: IP routers and Ethernet switches.
Parallel and high-performance systems
Published in Joseph D. Dumas, Computer Architecture, 2016
Store and forward routing is a data transfer approach that has been in use in networks (most notably the Internet) for many years. In a system using this type of routing, messages are sent as one or more packets (which are typically of a fixed size). When a message is sent from one node to another, the nodes may (if we are fortunate) be directly connected, but in most cases the packets will have to pass through one or more intermediate nodes on their way from the originating node to the destination. To facilitate this, each node has FIFO storage buffers the size of a packet. As a message packet traverses the network, at each intermediate node the entire packet is received and assembled in one of these buffers before being retransmitted to the next node in the direction of the destination (as determined by the particular routing protocol being used). Packets are treated as fundamental units of information; at any given time, a packet is either stored (completely buffered) in one node or in the process of being forwarded (transmitted) from one node to a neighboring node; thus, this method is referred to as store and forward routing. When store and forward routing is used, a packet is never dispersed over multiple nodes, regardless of how many hops must be traversed between the sending and receiving nodes. This approach simplifies the process of communication, but delays can be substantial when the sending and receiving nodes are widely separated.
Asynchronous Networks-on-Chip
Published in Wei Song, Guangda Zhang, Asynchronous On-Chip Networks and Fault-Tolerant Techniques, 2022
As shown in Figure 3.6b, the router in a store-and-forward network starts to transmit a packet only when all its flits are received. Since packet A arrives before packet B, the output port Cout is first allocated to A but it is only utilized at the fifth clock cycle when all parts of packet A are received. Consequently, packet B is temporarily stored in buffers and is transmitted when packet A is transmitted. The idea of store-and-forward is straightforward but it leads to long packet transmission latency and waste of resources. In this example, the output port Cout is allocated but not utilized for three clock cycles.
A study of multistage interconnection networks operating with wormhole routing and equipped with multi-lane storage
Published in International Journal of Parallel, Emergent and Distributed Systems, 2021
In a store-and-forward routing mechanism, the buffers of intermediate nodes must be large enough to store packets before they are retransmitted. In all cases in which packets encounter blocking or errors, they must be automatically saved [12,13]. Under this circumstance, the minimum space required is equivalent to the space occupied by at least a packet. In contrast, the proposed MIN operates with a wormhole routing mechanism. In a wormhole switching forwarding method, a packet can be considered as a number of flits [14,15].