gtps2m2u | ACF/SNA Data Communications Reference |
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.
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.
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 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:
See Figure 88 for a sample definition for an NCP gen with TPF channel-attached as a PU Type 5 node.
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