User guide

Chapter 3. InfiniBand technology 35
Figure 3-2 InfiniBand physical link
3.2 InfiniBand protocols
InfiniBand supports a number of upper-layer protocols (ULPs) that enable InfiniBand to be
exploited by different types of software with different requirements and objectives.
3.2.1 Internet Protocol over InfiniBand
Internet Protocol over InfiniBand (IPoIB) is the lowest-level existing network interface that is
provided on InfiniBand. IPoIB supports a wide variety of industry-standard applications,
middleware, and operating systems. Any communications protocol that is layered on top of IP
(in other words, anything that communicates using IP-based protocols such as TCP/IP or
UDP/IP), can be transported over InfiniBand through the IPoIB interface.
3.2.2 Sockets Direct Protocol
Sockets Direct Protocol (SDP) provides a legacy interface somewhat higher up the protocol
stack. For applications written to a TCP sockets interface, there is no need to implement all of
the TCP and IP protocol layers in order to communicate over InfiniBand. The SDP protocol
provides an
asynchronous sockets interface through which applications and middleware can
communicate without needing to understand that there might be no TCP or IP protocol layers
underneath.
The difference between synchronous sockets and asynchronous sockets is small, but it is
critically important to SDP. It involves the details of how application software is programmed
to request communications and how it issues the request (a call to the sockets interface).
Synchronous sockets calls from an application require that upon return from the call, the
requested communications have completed, and any data buffers involved are no longer
needed and can be reused immediately. Asynchronous sockets can (and generally do)
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