Communication Types

While all MPI interprocess communication (including MPI-1 and MPI-2) can be supported by a single, suitably powerful mechanism such as active messages, the MPI communication semantics described above suggest four separate types of communication operations. These are:
1. Two-party, point-to-point communication. This is the classic send-receive operation. This typically involves coordination between the sender and the receiver, handling such items as flow control, rendezvous messaging, and eager message delivery. Many low-latency implementations of this kind of communication rely on polling to advance the communication (make progress in MPI terms). Others may use a separate thread or an interrupt-driven mechanism (or a hybrid of both polling and non-polling). Because MPI semantics support nonblocking communication of arbitrary message sizes, any low-level support for communication in MPI must provide nonblocking, point-to-point communication. This is most easily accomplished if the low-level communications is also nonblocking.
2. Communication that has the property of local-completion. That is, a communication operation that must complete independently of any explicit action by the target (destination) process. This is required in MPI-1 for the implementation of MPI_Cancel (in the send case in most implementations) and is useful for MPI_Abort. In MPI-2, local completion is also needed for passive target remote memory access (RMA) operations. This kind of communication is typically implemented through the use of active messages or remote service requests (without polling).
3. Communication for active-target RMA. In MPI, active target RMA operations include remote put, get, and accumulate. These operations are completed by either an MPI_Win_fence call made by all processes in the MPI window object or by the combination of MPI_Win_complete and MPI_Win_wait at the origin (process that initiating a put, get, or accumulate) and target (process containing the memory accessed by a put, get, or accumulate) processes. This form is similar to the two-party, point-to-point communication because it can be implemented by using a pure polling interface. This communication form is separated from the point-to-point mode because the hardware in some systems allows some of the active-target RMA operations to be implemented directly by hardware or low-level software.
4. Communication for passive-target RMA. These operations must complete locally. If these operations must be implemented by communicating with an agent at the remote process, then some form of non-polling agent is required, such as an interrupt-driven active message or a separate communication thread. As in case three, this communication form is separated from case 2 (local completion for MPI-1) because the hardware in some systems allows passive target RMA operations to be implemented directly. We expect some systems to provide an extensive set of operations (e.g., direct access to memory on an SMP through a shared memory segment), others to provide more limited access (e.g., remote DMA through special network support), and others to be implemented on top of a non-polling communication layer such as active messages. The ADI design is intended to provide a common set of entry points independent of the capabilities of the underlying system.

communication skill

Communication

The aim of the Communication qualification is to encourage learners to develop and demonstrate their speaking, listening, reading and writing skills (including the use of images) for different purposes. Communication is about developing the ability of learners to select and apply skills in ways that are appropriate to their particular context, audience and situation. Techniques (for example in reading and writing) are essential, but so too are the skills of application, such as making decisions about the relevance and quality of information.

Communication Skills:_
Regardless of what business you are in – a large corporation, a small company, or even a home-based business – effective communication skills are essential for success.

The articles in this section of Mind Tools help you to understand effective communication, and then show you how to communicate your message in the best possible way. After completing this section, you should have a better understanding of how to communicate effectively – to individuals and groups, via spoken communications, written communications, and even electronic communications.

These include other important sections that help you be the best you can be, courses, book reviews, additional resources and more. Take a look around this Communications Skills section of the Mind Tools web site, and then take the time to view other sections, all researched and written by the Mind Tools staff who share a strong commitment to helping you achieve lifelong success and happiness.