10.5 Shared Memory Communications - Direct Memory Access 10.5.1 SMC-D overview 10.5.2 Planning for SMC-D configuration 10.5.3 Configuring SMC-D This section describes the configuration of the Shared Memory Communiction - Direct  Memory Access (SMC-D) connections on an IBM z14 ZR1.  SMC-D is a protocol that allows TCP socket applications to transparently use Internal Shared  Memory (ISM). ISM is a virtual channel that is similar to IQD for HiperSockets. A virtual  adapter is created in each z/OS LPAR and by using the SMC protocol, the memory is logically  shared. The virtual network is provided by firmware.  SMC-R requires a TCP/IP connection and preserves the entire network infrastructure.  SMC-D is also a “hybrid” solution. It uses a TCP connection to establish the SMC-D  connection. The TCP path can be through an OSA-Express port or HiperSockets connection.  A TCP option (called SMCD) controls switching from TCP to “out of band” SMC-D. The  SMC-D information is exchanged within the TCP data stream. Socket application data is  exchanged through ISM (write operations). The TCP connection remains established to  control the SMC-D connection. For more information about SMC-D, see  IBM z14 Technical Guide , SG24-8451, and  IBM  z/OS V2R2 Communications Server TCP/IP Implementation Volume 1 , SG24-8360. For more information about planning considerations for SMC-D, see “Shared Memory  Communications - RDMA” on page 22. For more information about configuring an SMC-D connection by using HCD, see 15.2.2,  “Defining an ISM PCIe function” on page 372. From an operational standpoint, SMC-D is similar to SMC-R. However, SMC-D uses direct  memory access (DMA) instead of an RDMA. It also uses a virtual PCI adapter that is called  ISM rather than an RNIC. The ISM interfaces are associated with IP interfaces (for example,  HiperSockets or OSA-Express) and are dynamically created, automatically started and  stopped, and auto-discovered.  SMC-D over ISM does not use QP technology like SMC-R. Therefore, links and Link Groups  that are based on QPs (or other hardware constructs) are not applicable to ISM. SMC-D  protocol features a design concept of a “logical point-to-point connection” called an SMC-D  link.  Note:  The SMC-D information in the  netstat  command displays is related to ISM link  information (not Link Groups). 10.5.4 SMC-D management Chapter 10. Specialized features  261