What are Direct Interconnection Networks?

Direct Interconnection networks are used to connect different processing elements or different process memory. Interconnection networks are also known as multi-stage interconnection networks (or MINs), are high-speed computer networks.

Characteristics of Direct Interconnection Network

• Topology − It denotes how the nodes of a network are organized.

• Network Diameter − It is the minimum distance between the most distant nodes in a network. The distance is measured in terms of the multiple specific hops between any two nodes.

• Node degree − The number of edges linked with a node is known as node degree. If the edge carries information from the node, it is known as out-degree and if this carries information into the node it is known as in degree.

• Bisection Bandwidth − The number of edges needed to be cut to break a network into two halves is known as bisection bandwidth.

• Latency − It is the delay in sending the message between two nodes.

• Network throughput − It is an exhibitive measure of the message carrying capacity of a network. It is represented as the total number of messages the network can share per unit of time.

In an interconnection network, the traffic flow between nodes can be non-uniform and it can be possible that a specific pair of nodes manage a disproportionately huge amount of traffic. These are known as “hot spots.” The hot spot can act as a bottleneck and can degrade the implementation of the whole network.

• Hardware Cost − It defines the cost contained in the execution of an interconnection network. It contains the cost of switches, arbiter unit, connectors, arbitration unit, and interface logic.

• Blocking and Non-Blocking network − In non-blocking networks, the route from any free input node to any free output node can always be supported. Crossbar is an example of a non-blocking network. In a blocking network, concurrent route establishment between groups of nodes cannot be possible.

There may be situations where blocking can appear. Blocking defines the situation where one switch is needed to create more than one connection simultaneously and an end-to-end path cannot be created even if the input nodes and output nodes are free. An example of this is a blocking multistage network.

• Dimensionality of Interconnection Network − Dimensionality denotes the arrangement of nodes or processing components in an interconnection network. In single dimensional or linear network, nodes are linked linearly; in a two-dimensional network, the processing elements (PE’s) are arranged in a grid, and in a cube network they are arranged in a three-dimensional network.