Sockets Direct Protocol

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The Sockets Direct Protocol (SDP) is an InfiniBand specific protocol defined by the Software Working Group (SWG) of the InfiniBand Trade Association (IBTA). It defines a standard wire protocol over IBA fabric to support stream sockets (SOCK_STREAM) networking over IBA. SDP utilizes various InfiniBand features (such as remote DMA (RDMA), memory windows, solicited events etc.) for high-performance zero-copy data transfers. SDP is a pure wire-protocol level specification and does not go into any socket API or implementation specifics.

While IP-Over-IB (IPoIB) specifies a mapping of IP (both v4 & v6) protocols over IBA fabric and treats the IBA fabric simply as the link layer, SDP facilitates the direct mapping of stream connections to InfiniBand reliable connections (or virtual circuits).The IPoIB specification is currently being created and published by an IETF working group. The IPoIB specification will define the packet level format of IP packets on the IBA fabric, and describe the InfiniBand address resolution protocol (IBARP). Conceptually, the IPoIB driver in Linux will look like a network driver and will plug- in underneath the IP stack as any standard Linux network device. The IPoIB driver exposes a network device per IBA port (and partition) on the host system and these devices are used to assign (statically or dynamically - using protocols such as DHCP) IP addresses. The SDP stack simply makes use of these IP assignments for endpoint identifications.

Sockets Direct Protocol only deals with stream sockets, and if installed in a system, allows bypassing the OS resident TCP stack for stream connections between any endpoints on the IBA fabric. All other socket types (such as datagram, raw, packet etc.) are supported by the Linux IP stack and operate over the IPoIB link drivers. The IPoIB stack has no dependency on the SDP stack; however, the SDP stack depends on IPoIB drivers for local IP assignments and for IP address resolution.

Architecture of the SDP is shown below.

Nowadays latest linux kernel cosists of complete infiniband support(Red Hat Enterprise Linux Update 3).

Socket Direct Protocol inturn is a part of protocol stack namely openIB which is still under development.

For any queries visit www.openib.org[1]

To involve in development join the openIb mailing list at openib-general@openib.org[2]