gtps2m2uACF/SNA Data Communications Reference

NCP Support

In order to connect TPF to current level NCPs as a PU type 5, the TPF system must connect as a data host using exchange identification format 2 (XID) and use FID4 PIUs. In addition, the TPF system supports explicit route (ER) and virtual route (VR) protocols when using FID4. The TPF system supports ER0, VR0, and TP2 (transmission priority high) between TPF and a channel-attached SNI NCP.

Channel Contact

A channel contact procedure is implemented between TPF and channel-attached NCPs in SNA 4.2; that is, an explicit PU type 5 to PU type 4 session separate and distinct from the SSCP-PU.T4 session. This PU-PU session is analogous to the PU-PU sessions exists that is supported between NCPs, and is established and terminated using a formal channel protocol between the physical units. Such establishment and dis-establishment of PU-PU sessions is always initiated by the PU Type 5(TPF) at the direction of its SSCP (through CONTACT and DISCONTACT requests). This new procedure occurs as an integral part of the activation of a channel-attached NCP and is completely transparent to the network operator.

As part of the channel contact procedure, the 2 physical units exchange certain information using the XID Format 2 architected for PU-PU contact procedures. Among the information sent from TPF to the NCP is the channel transmission group (which will always be 1) and other items concerning the environment in which the 2 PUs agree to operate. Such information is supplied at PU generation (NCP generation for NCPs and when the resource definition is created for the TPF system). As a result of this, using certain parameters of the NCP's HOST macro changes.

INBFRS, the number of buffers allocated by an NCP to receive data from a host, and MAXBFRU, the number of buffers allocated by a host to receive data from an NCP, is sent to the NCP in the XID Format 2. TPF obtains the MAXBFRU value from the SNAKEY macro in CTK2.

The size of host buffers used to receive data from an NCP (formerly obtained by the NCP from UNITSZ) is sent to the NCP in the XID. The number of pad characters prefixing NCP transmissions to the host (formerly obtained by the NCP from BFRPAD) is always sent to the NCP as zero in the XID. TPF obtains the UNITSZ value from the SNAKEY macro value in CTK2.

For the case of a host subarea attempting channel contact for a subarea which the NCP already has active on another channel, the NCP normally rejects the XID. The host can prevent this rejection and force acceptance (with the consequent breaking of contact on that other channel) by setting a bit in the XID Format 2. TPF does not support a host backup over a different channel adapter. Since TPF is designed to keep the network up and running, the backup host connects on the same channel adapter with the same subarea and does not issue the channel contact to break the connection. Whenever possible TPF continues from the point of failure. However, when the failing host was not able to checkpoint the fact that the NCP had been in contact, TPF issues a channel contact with the bit set in the XID to allow acceptance of the channel contact.

XID Format 2 Sent by TPF

This section describes the format and contents of the XID format 2 command sent by TPF. The values TPF uses are shown. Values reserved or not used are not shown.

0  bits 0-3, Format of XID I-Field.
         X'2'  Format 2 (For T5 to T4 Node exchanges),
               bytes 0-41 are included.
 
   bits 4-7, Type of the XID-Sending Node.
         X'4'  Subarea node
 
1     Length, in binary, of variable-format XID I-field (bytes 0-41).
 
2-5   Node Identification
   bits 0-11,  BLOCK NUMBER: The IBM Product Number for TPF. TPF will
               set block number to X'000' to indicate a node
               identification that is not unique.
 
   bits 12-31, ID number: a binary value that, together with the block
         X'0'  number, identifies a specific station uniquely within a
               customer network installation. TPF does not support ID
               number and will set this field to zero (0).
 
6-p   Format 2 Continuation
6-7   Reserved
 
8         Characteristics of TPF node:
   bit  0, TG Status:
 
         0  TG inactive
 
   bit  1, multiple-link TG support:
         0  not supported
 
   bits 2-3 segment assembly capability:
         10 segments are assembled on a session basis.
 
   bits 4-7 reserved
 
9         FID types supported
   bit  0
         0  FID 0 not supported
 
   bit  1
         0  FID 1 not supported
 
   bits 2-3, Reserved
 
   bit  4
         1  FID 4 supported
 
   bits 5-7, Reserved
 
10        Reserved
 
11-12     Length in binary of maximum PIU XID sender can receive
         MAXBFRU*UNITSZ
 
13        Transmission Group Number (TGN)
         1
 
14-17     Subarea address of XID sender
 
18
 
   bit  0  Reserved
 
   bits 1-4 error status
 
   bits 5-7 Reserved
 
19        CONTACT or load status of XID sender
 
       00  CONTACT has been received by an XID command sender
20-27     IPL Load module name
 
       40....40  no information conveyed
 
28-29     Reserved
 
31        Number of buffers suggested by primary
       00 No suggestion made.
 
32-33     Number of Read command (MAXBFRU)
 
34-35     Number of Bytes allocated per Read (UNITSZ)
 
36        Number of pad bytes
       00 No pad
 
37
   bit 0   Reserved for primary
   bit 1   Reserved
   bit 2   1, accept XID if TG in contacted state on another channel
 
38-39     Reserved for primary
 
40-41     Reserved for primary

NCP Considerations

NCP can operate with TPF as a PU 5 SSCP, where FID4 PIUs are used. The old values for the MAXBFRU and UNITSZ parameters (13 and 106 respectively) can be used in TPF for FID4 support. However, MAXBFRU and UNITSZ can be increased to support larger message sizes in the network. The only necessary requirement is to ensure the class of service (COS) table pointed to on the NETWORK macro for the TPF network has entries for ISTVTCOS and the default entry that matches TPF's requirements.

The following items must be specified in an NCP gen to define a channel-attached TPF system as a PU Type 5:

Sample Definition for an NCP Gen with TPF Channel-Attached as a PU Type 5 Node

See Figure 88 for a sample definition for an NCP gen with TPF channel-attached as a PU Type 5 node.

Note:
This sample definition only shows the specified keywords that are required to define a PU Type 5 node. User-supplied keywords are not included here.

Figure 88. NCP Gen with TPF Channel-Attached as a PU Type 5 Node

**********************************************************************
*        BUILD MACRO FOR N30H521                                      * 00620003
*********************************************************************** 00630003
N30H521  BUILD MODEL=3745,                                             *
               SUBAREA=511,                                            *
               TYPGEN=NCP,                                             *
               BFRS=80,                                                *
               MAXSESS=1000,                                           *
               NEWNAME=N30H521,                                        *
               PUNAME=N30H521,                                         *
               NETID=VTAMNET,                                          *
               SALIMIT=1023,                                           *
               SLODOWN=12
**********************************************************************  01320003
*        HOSTS MACRO                                                 *  01330003
**********************************************************************  01340003
TPFBH    HOST INBFRS=4,             TPF INPUT BUFFERS                  *
               MAXBFRU=13,                                             *
               UNITSZ=106,          TPF UNIT SIZE                      *
               BFRPAD=0,            TPF  REQUIRES NO PAD               *
               NETID=TPFNET,                                           *
               SUBAREA=11
*                                                                       06280003
*********************************************************************** 21950003
*        GROUP MACRO FOR CHANNEL ADAPTERS                             * 21960003
*********************************************************************** 21970003
GR30CA   GROUP LNCTL=CA,                                               *
               CA=TYPE6,                                               *
               NCPCA=ACTIVE,                                           *
               NPACOLL=YES
*                                                                       23210003
***************************************                                 23220003
*    CHANNEL DEFINITION FOR VTAM PU5  *                                 23230003
***************************************                                 23240003
L30CA3   LINE ADDRESS=(10),                                            *
               CASDL=0,                                                *
               TRANSFR=52,                                             *
               DELAY=0,                                                *
               INBFRS=6,                                               *
               ISTATUS=INACTIVE,                                       *
               TIMEOUT=120
*                                                                       23320003
P30CA3   PU PUTYPE=5
*                                                                       23690003