gtps2m2v | ACF/SNA Data Communications Reference |
With CTC support, TPF connects to an MVS/VTAM, VM/VTAM, or another TPF system. TPF appears to a remote host as a PU type 5 (T5) node using FID4 PIUs. TPF and the remote system exchange identification (XID) and establish sessions across a virtual route using the CTC connection.
TPF supports a CTC "priming" procedure that allows links (across devices that support the CTC architecture) to be activated without operator intervention. SNA restart places each attached CTC device in extended mode and ready state; this generates an asynchronous interrupt to the other side of the CTC adapter. The remote system initiates XID processing, if the link is pending active.
A channel contact procedure is implemented between TPF and channel-attached T5 nodes. In other words, there exists an explicit PU Type 5-to-PU Type 5 session. This PU-PU session is analogous to the PU-PU sessions supported between NCPs, and it is established using a formal channel protocol between the physical units.
As part of the channel contact procedure, the 2 physical units exchange information using the XID Format 2 architected for PU-PU contact procedures. Among the information sent from TPF to the T5 is the transmission group number and environmental characteristics under which the 2 nodes agree to operate. Such information is supplied at network generation (VTAM generation and when the resource definition is created for the TPF system).
The XID process for SNA CTC connection consists of the initiating host (X-side) sending an XID0 (XID format 2 with byte 19 set to 0) to the receiving host (Y-side). See XID Format 2 for detailed information about XID format 2. If the other host is not able to connect at this time, the operation times out and the initiating host will wait for the other host to activate the connection. XID0 is then allowed 30 seconds to complete.
If the other host is able to connect, it receives an attention interrupt from the write control (WCTL) CCW that began the initiating host's (X-side) channel program. The receiving host (Y-side) then issues its XID channel program, beginning with a sense command byte (SCB) CCW. The Y-side channel program consists of a read CCW for the X-side's XID0 and a write CCW for the Y-side's XID0.
TPF checks the XID returned by the remote node for any error status set (byte 18, bits 1-4) and if the value is non-zero, TPF terminates the channel contact procedure.
The side with the lower subarea will send XID7 (byte 19 set to 07) if it can accept the CTC connection. When the other side sends its XID7, the CONTACT procedure is complete and the explicit route operatives (ER.OPs) are exchanged. The CTC connection is now available for sessions, subject to the virtual route availability.
The transmission group (TG) number that TPF passes in the XID0 data is TG=0 (TG=ANY). If the remote system is VTAM, the TG number is specified in VTAM's PU definition. TPF requires that the TG number specified be a value of 1 or 2. If the remote system is TPF, then the system with the low subarea selects either TG=1 or TG=2.
When XID processing has completed, a completion message is then sent to the originating operator.
See Figure 89, Figure 90, and Figure 91 for illustrations of XID processing flows.
Figure 89. XID Processing Example 1. TPF is the low subarea.
Figure 90. XID Processing Example 2. TPF is the high subarea.
Figure 91. XID Processing Example 3. There are 2 links between TPF systems.
The following 2 parameters in the VTAM definition for the channel-attached major nodes must be correctly specified in order to attach to TPF. These parameters are sent to VTAM in the XID format 2.
The number of 4K read buffers used by TPF for a CTC connection is specified in the CTCRBFR operand of the SNAKEY macro. The number of 4K write buffers in a buffer pool is specified on the CTCWBFRS operand of the SNAKEY macro. The buffer pool is used to allocate buffers for CTC write operations. TPF dynamically allocates write buffers to match the VTAM MAXBFRU value discovered at XID time.
This section describes the format and contents of the XID format 2 information sent by TPF. The values used by TPF are shown in the following XID header data example. Values reserved or not used are not shown.
The following is an example of the header that precedes XID format 2 for CTC links.
Byte 0-1 Number of buffers transmitted XL2'0001' XID data occupies 1 4K buffer 2 Indicator byte 1....... XID transfer .1...... Error Indicator ..000000 Reserved 3 CTC format indicator XL1'01' New protocol used 4-5 Number of 4K pages in input buffer 6-7 Reserved
The following is an example of the XID format 2.
Byte 0 XID format and node type 0010.... Format 2 ....0101 Type 5 node 1 Length, in binary, of variable-format XID I-field 2-5 Node identification and ID number XL4'FFF00000' Block number x'FFF0' and ID number 0 6-7 Reserved 8 Characteristics of TPF node: 0....... TG status inactive .0...... Multiple link transmission group (TG) not supported ..10.... Segments reassembled on session basis ....0000 Reserved 9 FID types supported 0....... FID 0 not supported .0...... FID 1 not supported ..00.... Reserved ....1... FID 4 supported .....000 Reserved 10 Reserved 11-12 Length in binary of maximum PIU XID sender can receive X'0FF5' 4086 byte PIU 13 TG number X'00' TG0 (TG=ANY) X'01' TG1 X'02' TG2 14-17 Subarea address of XID sender 18 Error status 0....... Reserved .1000... XID parameters are incompatible .1001... Multi-link TG is incompatible .1010... TG number not defined .1100... Multi-link TG is not supported .....000 Reserved 19 CONTACT or load status of XID sender X'00' CONTACT has been received by an XID sender X'07' XID response sender is already loaded 20-27 IPL load module name XL8' ' No information conveyed 28-29 Reserved 30 DLC type X'03' System/370 to S370 31-36 Reserved
When multiple TPF processors are coupled together to share a common database, there are some important considerations to keep in mind: the IODEV addresses defined in SIP include all the SDAs for processors in the complex; that is, 1 SDA per TPF processor for each CTC connection to a VTAM or TPF host.
For SNA CTC connections between members of a loosely coupled complex, only CDRM-CDRM session and TPF/APPC sessions are supported.
Sessions can be established across a PU type 5 CTC connection using either a CDRM-CDRM session or a session between a Control LU (CLU) and the VTAM Logon Manager. When TPF connects to the subarea network, a CDRM-CDRM session is established. Then, an optional CLU session may be established with the Logon Manager. The CLU session is required if TPF/APPC sessions are to be brought up. In any case, there is a CTC configuration restriction on sessions that can be established: TPFs' subarea routing is limited to a single hop. (A hop is a link crossed on a path from 1 host or NCP subarea to another host or NCP subarea.) Therefore, the session partner must be in a host adjacent to TPF.