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Virtual memory-mapped communication (VMMC) was developed out of the need for a basic multicomputer communication mechanism with extremely low latency and high bandwidth. This is achieved by allowing applications to transfer data directly between two virtual memory address spaces over the network. The basic mechanism is designed to efficiently support applications and common communication models such as message passing, shared memory, RPC, and client-server.
Experience with implementing connection-oriented communication using VMMC exposed some deficiencies in the VMMC model. VMMC-2 was designed to overcome those deficiencies. VMMC-2 extends VMMC with three mechanisms: a user-managed TLB mechanism for address translation which enables user libraries to dynamically manage the amount of pinned space and requires only driver support from many operating systems, a transfer redirection mechanism which allows to avoid a copy on the receiver's side, and a reliable communication protocol at the data link layer which allows to avoid a copy on the sender's side.
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