The HiperSockets MPC group

For a specific IQD CHPID, VTAM® builds a single HiperSockets™ MPC group, using the subchannel devices associated with that IQD CHPID. VTAM requests up to 10 devices from the I/O subsystem if they are defined to the CHPID being initialized, regardless of how many will be required for the number of TCP/IP stacks to be used in the LPAR. VTAM requires two subchannel devices for the read and write control devices, and 1 to 8 devices for data devices, one device for each of up to 8 TCP/IP stacks.

Therefore, to build the MPC group, there must be a minimum of 3 subchannel devices defined (within HCD) and associated with the same IQD CHPID. The maximum number of subchannel devices that VTAM will use is 10 (supporting 8 data devices or 8 TCP/IP stacks) per LPAR or MVS™ image. The subchannel devices must be configured for the LPAR and online prior to when the TCP/IP stack is initialized. Generally, the number of HiperSockets subchannel devices you should configure to HCD per LPAR is:

					2 	 (read / write control devices)
				+	N	 (where N = number of TCP/IP stacks)
				-----------------
					N+2 	(total subchannel devices per LPAR)
Example (LPAR 1 starts two TCP/IP stacks and both stacks use HiperSockets):

		 -  define 4 subchannel devices on the same IQD CHPID 
		 -  where 2 are used for read / write control and 2 data devices are available

Tip: The HCD configuration is the only way to control the number of devices that VTAM uses for HiperSockets.

The first TCP/IP stack within the LPAR to initialize dynamic XCF support (DYNAMICXCF) causes the IUTIQDIO HiperSockets MPC group to be dynamically created. The first TCP/IP stack within the LPAR to initialize a user-defined HiperSockets device (TRLE IUTIQDxx) causes the IUTIQDnn HiperSockets MPC group to be dynamically created.

Each TCP/IP stack can then start the HiperSockets device, and each stack is assigned a unique (dedicated) subchannel data device from the IUTIQDIO or IUTIQDnn MPC group.

Guideline: Configure the IQD CHPIDs using CHPIDs x'F0' through x'FF' (but any valid CHPID value x'00' through x'FF' can be configured as TYPE = IQD). See z/OS HCD Planning and Using HCD for additional details.