What is OSA Express?

OSA Express is a family of adapters, which provides direct mainframe-to-network attachment. The clients on the Local Area Networks (LANs) use this integrated hardware feature for direct connections. In ATM, Gigabit Ethernet (GbE), Fast Ethernet (FENET) and Token Ring(TR) LAN connection the OSA Express features are available. All these features use the IBM Queued Direct I/O (QDIO) architecture, for which neither Channel Control Words (CCWs) nor interrupts are needed and thus the TCP/IP data packet transmission gets accelerated.

The Channel Path Identifier (CHPID) for an OSA Express helps it to be identified in the hardware I/O configuration. During the installation the CHPID is assigned to an OSA. It is mandatory to provide the device numbers and unit address for each OSA Express CHPID and for that the Hardware Configuration Definition (HCD) or I/O Configuration Program (IOCP) are used.

Only the Images that are defined in the System Hardware I/O Configuration can share an OSA channel path per port. This allows access to a network port on the OSA to be shared by as many images as allowed on the system. When the OSA CHPID detects the packet destination, located in an image, that is also connected to the same OSA CHPID, the packet is simply routed to the destination. This phenomenon is called 'image-to-image' communication.

The supported CHPID types are:

•OSD CHPID type (QDIO mode)
QDIO is a signaling protocol that minimizes I/O interruptions. With the activation of QDIO data queues continuous and direct data exchange between the OSA-Express and the Host Operating System is initiated and remains active without the need for additional instructions to start the sub channel.

•OSE CHPID type (non-QDIO mode)
TCP/IP Passthru mode
In this mode the data is transferred between a host IP program, which has the OSA definition and clients on the Ethernet LAN and Token Ring LAN networks.

SNA mode
In an SNA mode the OSA is treated as an External Communications Adapter (XCA) by VTAM and the SNA function of Z/OS. An XCA can use either switched or non-switched lines of communication.

•OSN CHPID type (OSA NCP)
The connection between Channel Data Link Control (CDLC) protocol and the QDIO architecture on the Linux side is the main focus of an OSA for the Network Control Program (OSA NCP). The QDIO architecture runs Communications Controller for Linux (CCL). This is accomplished with OSA-Express2 and higher.

The OSN CHPID type does not support any additional network functions.

•OSX CHPID type (OSA zBX System z Blade Center Extension)
An OSA-Express3 or OSA-Express4S 10 Gigabit feature, configured as an OSX feature, provides connectivity between z196 or higher and the Intraensemble Data Network (IEDN) for application workloads.

•OSM CHPID type (OSA intranode management network)
An OSA-Express3 or OSA-Express4S 1000Base-T Ethernet, configured as OSM feature, provides connectivity between z196 or higher and the Intranode Management Network (INMN) for management related functions.

Few of the commonly available OSA-Express features are :

•OSA-Express Gigabit Ethernet LX
•OSA-Express Gigabit Ethernet SX
•OSA-Express 1000Base-T Ethernet
•OSA-Express Fast Ethernet and
•OSA-Express Token Ring

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