Shared Memory Communications terms

The following terms apply to Shared Memory Communications (SMC). You can use this list as needed for brief descriptions when you are using other SMC information.

Associated ISM interface

An internal shared memory (ISM) interface that is associated with an Shared Memory Communications - Direct Memory Access (SMC-D) capable interface that has the same physical network ID.

Associated RNIC interface

An IBM® 10 GbE RoCE Express® interface that is associated with an Shared Memory Communications over Remote Direct Memory (SMC-R) capable interface that has the same physical network ID.

Direct memory buffer (DMB)

Local memory that is used to receive inbound data over an SMC-D link. The remote peer places TCP socket application data directly into the DMB that the local peer assigns to receive data for the TCP connection. The local peer then copies the data from the DMB into the receive buffer of the receiving socket application.

DMB element (DMBE)

The portion of a DMB that is associated with a specific TCP connection. Each DMB is partitioned into one or more DMBEs.

IBM 10 GbE RoCE Express feature or RoCE Express2 feature

A feature that enables Remote Direct Memory Access by managing low-level functions that the TCP/IP stack typically handles.

IBM 10 GbE RoCE Express interface

An interface that is dynamically created by TCP/IP that uses a particular port of an IBM 10 GbE RoCE Express feature.

IBM RoCE Express2 interface

An interface that is dynamically created by TCP/IP that uses a particular port of a 10 GbE or 25 GbE RoCE Express2 feature.

Internal path

The System z® internal PCIe infrastructure for "RoCE Express" features. The internal path of a "RoCE Express" feature is determined based on how the feature is plugged into the System z I/O drawers.

ISM device

The System z firmware that facilitates the use of internal shared memory for SMC-D processing. An ISM device is identified by a unique PCIe function ID (PFID) and a virtual channel ID (VCHID). An ISM device is configured in the hardware configuration definition (HCD) and is associated with a single physical network ID.

ISM interface

An interface that is dynamically created by TCP/IP to represent an ISM device for SMC-D capable interfaces with the same physical network ID.

Operating system images

Logical partitions (LPARs) or guest virtual machines that operate in the same central processor complex (CPC).

Physical channel ID (PCHID)

A 2-byte hexadecimal value that is used to uniquely define a RoCE Express feature.

PCIe function ID (PFID)

A value that represents the SMC device.

For SMC-R, the PFID value is configured on the SMCR parameter of the GLOBALCONFIG statement in the TCP/IP profile to identify a "RoCE Express" feature. The PFID represents a physical "RoCE Express" feature and must match a FID value configured in the hardware configuration definition (HCD) for the PCHID value that identifies the feature. When the "RoCE Express" feature is installed on a System z that supports a shared RoCE environment, the same physical feature can be shared with other operating system images, and multiple PFID values specified on the same GLOBALCONFIG statement can represent different ports on the same physical "RoCE Express" feature.

For SMC-D, the PFID value is obtained during ISM interface activation that identifies an ISM device. The PFID value matches an FID value that is configured in the HCD for the VCHID value that represents the ISM device.

Peripheral Component Interconnect Express (PCI Express, or PCIe)

A local bus that provides the high-speed data path between the processor and an SMC device. For SMC-R, the device is an attached "RoCE Express" feature. For SMC-D, the device is the ISM device.

Physical network ID (PNetID)

A value that is defined to uniquely identify your physical layer 2 LAN fabric or physical broadcast domain. You can use this value to logically associate the System z features, adapters, and ports to be physically connected to your network. You specify the PNetID in a single step within the hardware configuration definition (HCD), and all operating systems of all associated central processor complexes (CPCs) can dynamically learn and use this definition.

RDMA network interface card (RNIC)

A RoCE Express feature that enables Remote Direct Memory Access by managing low-level functions that are typically handled by the TCP/IP stack.

RDMA over Converged Ethernet (RoCE)

An InfiniBand Trade Association (IBTA) standard that enables Remote Direct Memory Access over Converged Ethernet.

Redundancy level

For an SMC-R link group, this value indicates the level to which z/OS® Communications Server can provide dynamic failover processing if there is a failure of an underlying "RoCE Express" interface or the associated network hardware.

Reliable connected queue pair (RC QP)

A logical connection between two virtual servers that enables that specific pair of servers to use RDMA communications between themselves.

Remote Direct Memory Access (RDMA)

A high-speed, low-latency network communications protocol in which data is transferred directly to the memory of a remote host with no involvement from the remote host processors or operating system.

Remote memory buffer (RMB)

Local memory that is used to receive inbound data over an SMC-R link. The remote peer places TCP socket application data directly into the RMB that the local peer assigns to receive data for the TCP connection. The local peer then copies the data from the RMB into the receive buffer of the receiving socket application.

Rendezvous processing

The sequence of TCP connection management flows that are required to establish SMC communications between two peers.

RMB element (RMBE)

The specific portion of an RMB that is associated with a specific TCP connection. Each RMB is partitioned into RMBEs.

RoCE environments

Depending on the level of hardware that is used, the 10 GbE RoCE Express feature operates in either a shared or a dedicated RoCE environment. A RoCE Express2 feature always operates in a shared RoCE environment.

Dedicated RoCE environment

A dedicated RoCE environment applies to an IBM zEnterprise® EC12 (zEC12) with driver 15, or an IBM zEnterprise BC12 (zBC12). In this environment, only a single operating system instance can use a physical 10 GbE RoCE Express feature. Multiple operating system instances cannot concurrently share the feature.

Shared RoCE environment

A shared RoCE environment applies to an IBM z13® (z13) or later system. In this environment, multiple operating system instances can concurrently use or share the same physical RoCE Express feature. With IBM z13 (z13) or later systems, the RoCE Express feature operates in a shared environment even if only one operating system instance is configured to use the feature.

RoCE Express

Generic term for either IBM 10 GbE RoCE Express, IBM 10 GbE RoCE Express2, or IBM 25 GbE RoCE Express2 feature.

RoCE Express2

Generic term for either IBM 10 GbE RoCE Express2 or IBM 25 GbE RoCE Express2 feature.

SMC-D link

A logical representation of communication between two virtual servers that use SMC-D protocols. The concept of an SMC-D link exists primarily for operational consistency with SMC-R processing.

SMC-R link

A logical point-to-point link between two virtual servers that is used for SMC-R communications.

SMC-R link group

A logical grouping of equal SMC-R links between two communicating peers.

Staging buffer

Memory that the TCP/IP stack allocates for outbound SMC-R data. Staging buffers are not associated with specific SMC-R links or link groups, and are used by all TCP connections that traverse SMC-R links on this stack. Only local applications access the staging buffer storage.

Virtual channel ID (VCHID)

A 2-byte hexadecimal value that is used to uniquely define an ISM device.