Parallel Computer Architecture

7.2 Realizing Programming Models 483

the destination. The question then arises, how does the source determine that space

is again available for it? There must be some flow control information transmitted

back from the destination to the sender. This is a design issue that can be resolved

either by acknowledging each transaction or by coupling the acknowledgment with

the protocol at a higher level (for example, the reply indicates completion of pro-

cessing the request).

An alternative approach, common in reliable networks, is for the destination to

simply refuse to accept incoming transactions when its input buffer is full. Of

course, the dat ...