Wormhole Switching

The term wormhole switching is sometimes confused with cut-through switching but they are different in the sense that cut-through flow control assigns channel bandwidth and buffers on packet level, while wormhole flow control allocates them on flit level. The wormhole system is actually quite similar to multiprotocol label switching (MPLS) and asynchronous transfer mode (ATM) forwarding except that the cells are not placed in queues.

The characteristics of wormhole switching system include:

• Large network packets are divided into small flits, which are directed along the route via conflict-free VCT switching. The transmission of different packets is not freely multiplexed over a single physical channel.
• Every router is assigned small buffers of one to a few flits.
• The header flit defines the network path for all the other flits in the network pipeline.
• The buffer sequence and links that are already occupied by a given packet of flits constitutes the wormhole system. Typically, the length of the network path is measured in accordance to the number of flits in a single packet.
• If the output channel is busy, the entire flits chain - including the header – can become stuck blocking communication via the transmission path.

The key advantages of wormhole switching include:

• Working with small, cheap, simple and comparatively fast routers
• Employing only input buffering
• Efficiency of flow controls in using the buffers as compared to cut-through; requires only few flit buffers
• Throughput is snowballing because it does not buffer the entire network packet to move toward the next node.
• Bandwidth and channel allocation are generally decoupled.

Disadvantages of wormhole switching include:

• Blocks resources in cases of stuck network pipelines
• Prone to deadlock