OSA configuration considerations

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IOCP supports the definition of open systems adapter (OSA) channels. OSA channels use either the Queued Direct I/O (QDIO) architecture, non-QDIO architectures, Enhanced Queued Direct I/O (EQDIO) architecture, or (based on how they are defined in IOCP) they operate as one of the following:
  • An OSA-ICC
  • An OSA for NCP
  • An OSA for a zBX data network
  • An OSA for a zBX management network
The following table summarizes the connectivity the various channels provide and the channel path type to use to define the channel types to the I/O subsystem.
Table 1. Summary of connectivity
Channel type Channel path type Connectivity the channel type provides
OSA QDIO OSD All LAN protocols supported by the OSA features that use QDIO architecture
OSA non-QDIO OSE All LAN protocols supported by the OSA features that use non-QDIO architectures
OSA EQDIO OSH All LAN protocols supported by the OSA features that use EQDIO architecture (these are Network Express features)
OSA-ICC OSC TN3270E emulators and 3215 data streams
OSA for NCP OSN CDLC protocol from an operating system image and QDIO architecture from a CCL image. An OSA channel in the CCL image provides LAN connectivity.
OSA zBX network management OSM All LAN protocols supported by the OSA features that use QDIO architecture
OSA zBX data management OSX All LAN protocols supported by the OSA features that use QDIO architecture

Like ESCON and FICON channel paths, you must define a control unit and devices for an OSC, OSD, OSE, OSH, OSM, OSN, or OSX channel path even though no control unit or devices exist outside of the IOCDS definitions. For OSD, OSE, OSH, OSM, and OSX channel paths, device numbers are used by software applications (for example, VTAM®) to communicate with networks through an OSD, OSE, OSH, OSM, or OSX channel path. For OSC channel paths, device numbers are necessary to configure a TN3270E emulator session or 3215 data stream. For OSN channel paths, device numbers are necessary for an operating system image to communicate with a CCL image. They also allow the operating system image to communicate with a LAN connected to the CCL image.

For further information about OSD, OSE, OSH, and OSN configuration requirements for client server applications, see Open Systems Adapter-Express Customer's Guide and Reference. For further information about OSC configuration requirements, see Open Systems Adapter-Express Integrated Console Controller User's Guide, SA22-7990.

Devices assigned to OSA channel paths are associated with a LAN port and each application using the OSA channel card. A maximum number of OSA valid subchannels can be defined on OSD, OSM, OSN, and OSX channels or used on OSE channels. An OSA valid subchannel is an OSD, OSE, OSM, OSN, or OSX device with a unit address in the range 00-FD. The OSAD device with unit address FE (OSD, OSE, OSM, OSN, or OSX only), used by the OSA Support Facility, is excluded from the maximum. Likewise, a maximum number of valid subchannels can be used on OSC channels. A valid subchannel for an OSC device can have any unit address in the range 00-FC. Also, a maximum number of valid subchannels can be used on OSH channels. A valid subchannel for an OSH device can have any unit address in the range 00-FE.

Valid subchannels are devices that are defined to a logical partition and permitted for use by the logical partition. Valid subchannels are calculated as follows:
  • For unshared channel paths, each device defined in IOCP represents a single valid subchannel.
  • For shared channel paths, each device defined in IOCP represents multiple valid subchannels based on the total number of logical partitions (LPs) in its device candidate list.

For example, with a maximum of 480 valid subchannels for an OSD channel path with priority specification enabled, if your configuration has 10 LPs and an OSD channel path is shared by all 10 LPs, each device assigned to the shared OSD channel path has a device candidate list that defaults to all 10 LPs. This design allows you to define a maximum of 48 devices per LP for a total of 480 valid subchannels on the channel path. However, if you specify device candidate lists of 5 LPs for each device on the channel path, this design allows you to define a maximum of 96 devices per LP for a total of 480 valid subchannels.

TCP/IP assigns each OSA device on an OSD or OSX channel path four outbound queues, each of which has a unique priority. These priorities allow the prioritization of outbound work based on TCP/IP Type of Service (TOS) settings. If you choose not to use the priorities for a channel, the channel can support four times as many devices where each device has a single outbound queue with a single priority. Specify the CHPARM keyword for the OSD, OSM, or OSX channel path with bit 6 of the CHPARM value on (CHPARM=02) to disable priority specification and support a maximum of 1920 OSA valid subchannels (640 TCP/IP stacks). Otherwise, an OSD or OSX channel path has priority specification enabled and supports a maximum of 480 OSA valid subchannels (160 TCP/IP stacks). OSM channel paths default to disabled priority queuing. The only valid definition for OSM is CHPARM=02 (or omitting the CHPARM keyword). Disabling priority specification is transparent to host policies and applications that set or affect the setting of the TOS byte. For additional information about QDIO priority queuing and how it relates to TOS and quality of service for Internet Protocol networks, see the z/OS® Communications Server IP Configuration Guide, SC31-8775.

TCP/IP assigns each OSA device on an OSH channel path a single outbound queue and a single priority.

Use of a feature in the OSA family has the following considerations:
  • For all OSA configurations except OSH:
    • For each OSA device on an OSD, OSE, OSM, or OSX channel path, specify UNIT=OSA on the IODEVICE statement.
    • Unit address FF is not allowed.
    • The OSA feature using QDIO architecture uses the I/O device definitions and unit addresses in your IOCDS.
    • A maximum of 480 OSA valid subchannels (160 TCP/IP stacks) can be defined on an OSD or OSX channel path when priority specification is enabled (CHPARM=00).
    • A maximum of 1920 OSA valid subchannels (640 TCP/IP stacks) can be defined on an OSD channel path on an OSA-Express2 or later feature, and on an OSM or OSX channel path on an OSA-Express3 or later feature when priority specification is disabled (CHPARM=02).
  • For OSA configurations using the OSA support facility:
    • Define a device with unit address FE for every OSD, OSE, or OSN channel path managed by the OSA Support Facility, and specify UNIT=OSAD on the IODEVICE statement. For an OSD, OSM, or OSX channel path, the control unit assigned to this device must either have a CUADD keyword value of zero or have the CUADD keyword omitted. Otherwise, the device is unusable.
    • A maximum of 240 OSA valid subchannels can be used on an OSE channel path even though IOCP allows you to define more than this number. The OSA Support Facility manages this maximum.
  • For OSE configurations not using the OSA support facility:
    • An OSA channel card port configured as an OSE channel path has unit addresses 00-01 associated with it when not using the OSA Support Facility.
    • Only a single logical partition (LP) can use the OSE channel path. To ensure that the channel path can only be used by a single LP, do one of the following actions:
      • Define the channel path as dedicated or reconfigurable.
      • Define the channel path as shared but give it access to only one LP or define both OSA devices with the same, single LP in their device candidate lists.
      • Define the channel path as shared and devices without device candidate lists but either configure or activate host TCP/IP profiles for the OSA devices in only a single LP. At any time, only a single LP can have a host TCP/IP profile active for the OSA devices.
  • For OSC configurations:
    • A maximum of 120 valid subchannels can be used on an OSC channel path even though IOCP allows you to define more than this number. The Support Element manages this maximum when sessions are configured under Advanced Facilities..
    • Unit address FE is not allowed.
    • The OSC channel must be installed and defined as OSC and must be configured on the Support Element using the Advanced Facilities window before TN3270E emulator sessions or 3215 data streams can be used. Under Advanced Facilities, select either Panel Configuration Options or Manual Configuration Options to configure each session you want to use. Each session corresponds to a single valid subchannel and you can configure a maximum of 120 sessions.
    • You can use an OSC channel path for either TN3270E emulator sessions or 3215 data streams but not both. Only TPF supports 3215 data streams, and some CPCs require an RPQ be installed. Specify the CHPARM keyword for the OSC channel path with bit 1 of the CHPARM value on (CHPARM=40) to use 3215 data streams with TPF. Otherwise, the OSC channel path supports TN3270E emulator sessions.
  • For OSH configurations:
    • An OSH channel path is associated with a single port on a Network Express card. Each port has a unique PCHID.
    • An OSH CHPID and NETH functions can co-exist on the same PCHID.
    • For each device on an OSH channel path, HCD requires you specify UNIT=OSA on the IODEVICE statement when migrating the IOCP source file into HCD.
    • The OSA feature using EQDIO architecture uses the I/O device definitions and unit addresses in your IOCDS.
    • Unit address FF is not allowed.
    • A maximum of 256 valid subchannels can be defined on an OSH channel path.
  • For OSN configurations:
    • For each OSA device on an OSN channel, you must specify UNIT=OSN or UNIT=3745 on the IODEVICE statement.
    • A maximum of 480 OSN valid subchannels and 180 3745 valid subchannels can be defined on an OSN channel path.
    • To reduce the number of valid subchannels, use the device candidate list to restrict the OSN devices to CCL images and the 3745 devices to operating system images.