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VM/VTAM Communications Network Application
(VM/VCNA)
Inter User Communications
Vehicle (IUCV)
THE SNA Console Communications
Services (SNA CCS) REST OF VM/SP Virtual Machine CP Figure 26. SNA Virtual Console Support Interfaces
Functions
SNA CCS handles the following functions in support of the console, CMS, and full
screen mode environments for SNA terminals:
Connect VTAM service machine and Logical Units
Logon a Logical Unit
Request a read
Request a write Process an enter key Process a PAl key Process a P A2 key Process a P A3 key Process a PF key Process an Attention Interrupt Process a Cursor Back One Logoff a Logical Unit Process error conditions
Quiesce and Resume processing for a given logical unit
Sever a communications path
SNA Virtual Console Communication Services 181

Enabling SNA Terminals CP operator must issue the ENABLE SNA command. The SNA parameter on the
ENABLE command enables all SNA devices and has no effect on non-SNA
devices. The ENABLE ALL command enables both non-SNA and SNA devices.
In the multiple VT AM service machine environment, the operator may selectively
enable or disable any given VT AM service machine by using the userid option on
the ENABLE/DISABLE SNA command. The operator cannot enable and disable
individual logical units.
Establishing Communications Links
The VTAM service machine issues an IUCV CONNECT under two separate con­
ditions:
182 VM/SP System Programmer's Guide
VTAM Service Machine CONNECT
VM/VCNA issues a CONNECT via IUCV to establish an initial global con­
nection between VM/VCNA and SNA CCS. This CONNECT notifies SNA
CCS that a new VT AM service machine has logged on and is ready to service
logical units. If the VM/SP operator has issued the ENABLE SNA or ENA­
BLE ALL command, SNA CCS accepts the CONNECT, and authorizes
VM/VCNA to allow users to logon to SNA terminals. SNA CCS creates a VT AM Service Machine Block (VSMBLOK) for that VTAM service machine.
In a multiple VT AM service machine environment, the VSMBLOK allows
SNA CCS to associate the logged on SNA user with the correct VM/VTAM
Communications Network Application (VM/VCNA). See VM / SP Data Areas
and Control Block Logic, Volume 1 for a detailed description of the
VSMBLOK.
Logical Unit CONNECT
To logon to VM/SP, the SNA terminal user must first logon to VM/VCNA
running in the VTAM service machine. To logon to VM/VCNA, the user
issues the ACV /VT AM LOGON command. When logging on to VM/VCNA,
the terminal user may optionally specify the userid (or the userid and
password) of his virtual machine in the DATA portion of the ACF/VTAM
LOGON command. The following forms of the LOGON command are valid:
LOGON APPLID (VCNA)
LOGON APPLID (VCNA) DATA (userid [password])
If you specify VCNA in the APPLID field, ACF /VTAM queues a logon
request to VM/VCNA.
If no logon data (VM/SP userid and password) is specified, the system
writes a VM/370 logo to the terminal under the control of VM/VCNA.
From this point on, the user logs on to VM much the same as he does with
a local terminal. The attention interrupt generated when the user clears the
logo from the screen causes VM/VCNA to issue an IUCV CONNECT
SVC on behalf of the terminal. If 'SNA' is still enabled, CCS builds an
RDEVBLOK and a SNA Resource Block (SNARBLOK) and chains them
to the VSMBLOK built during the VM/VCNA connect described above.
This ties the user's control block (SNARBLOK) to the VTAM service