NAS uses the international X25 Interactive Terminal Interface (ITI) transport protocol to support start/stop ASCII TTY terminals (including PCs). ITI terminals can establish sessions with VTAM applications, with EP based applications or with the Comm-Pro CCU console subsystem. The path through NCP to VTAM may use VIRTUAL=YES programmed SNA resources controlled by Comm-Pro NCP Network Extension Option (NEO) code or NCP virtual line resources controlled by NTO and accessed by the PP04/VLSW package.
Comm-Pro NEO code provides ASCII TTY to PU Type 1 conversion for ITI terminals and is a functional replacement for IBM's Network Packet Switching Interface (NPSI) program product.
The host access method may initiate ITI calls using a DIAL CCW on the EP path or a CONNOUT PIU on the NCP/NEO path. ASCII TTY to 2741 code conversion is available to network ITI terminals on the EP path. Low speed ITI traffic is multiplexed across the X25 access lines. Terminal type and speed recognition is performed by network terminal PAD's. This information is passed to NAS in the CALL REQUEST packet for proper session establishment. Application switching occurs at call connect time based on a system select character entered by the terminal operator. Access to SNA hosts is provided by NEO code which converts ASCII TTY code and protocol to SNA 3767 PU Type 1.