WORMHOLE ROUTING

Here packets are further subdivided into Flits.

Flit buffers are used in the hardware routes attached to nodes.

The transmission from the source node to the destination node is done through a sequence of routes.

All the flits in same packet is transmitted in order as inseparable companions in a pipelined fashion.

Only the header flit knows where where the packet is going . All the data flits must follow the header flit. The flit from different packets cannot be mixed up.

Pipelining of successive flits in a packet is done asynchronously using a hand shaking protocol.

A path ( a 1-bit ready/request (R/A)) line is used between adjacent routers.

When the receiver router 'D' is ready is recieve a flit, it pulls the R/A line low.

When the sending router 'S' is ready it raises the line high and transmit the flit 'i' through the channel.

While the flit is being recieved by 'D', the R/A line is kept high.After the flit is removed from 'D''s buffer (i.e. transmiited to the next buffer), the cycle repeats itself fot the transmission of the next flit 'i+1' until the entire packet is transmitted

The communication latency TSF for a wormhole routing is given by
                 
                                              Twh= (L/W)+(F/W) *D


                                   where F is the flit length

                                    L i the packet  length

                                    W is the channel bandwidth

                                     D is distance