Introduction to Tandem X.25 Capabilities

X25AM Connectivity

Tandem X.25 Features and Capabilities

065307 Tandem Computers Incorporated 2–23

Connecting to SNA

Networks

To connect a Tandem system to an SNA network via a PSDN, you define the X25AM

subdevice for the Qualified Logical Link Control (QLLC) protocol . You must also use

the SNAX/XF product. The SNAX/XF process runs over the the X25AM line.

QLLC is a type of logical link defined by IBM to accommodate SNA adjacent-node

physical services, which are equivalent to SDLC functions such as XID, SNRM, TEST,

and DISC, when such nodes are connected through a PSDN. QLLC provides an

end-to-end control mechanism through the X.25 network.

When SNAX/XF is used with X25AM, the X.25 protocol becomes a delivery

mechanism for the SNA upper-layer protocols. The PSDN appears to SNA as one or

more SDLC links. X.25 switched virtual circuits (SVCs) appear as switched SDLC

links to the controlling SNA nodes. X.25 permanent virtual circuits (PVCs) appear as

SDLC leased lines.

SNAX/XF supports both primary and secondary switched and leased lines. A

Tandem SNAX/XF primary station functions as a type 5 node controlling one or more

type 2 node cluster controllers. See Figure 2-12.

Figure 2-12. Switched Primary SNAX/XF Station over X25AM

Tandem

NonStop System

Packet-Switched

Network

QLLC

X25AM

Application

SNAX/XF

X.25

IBM Cluster

Controllers

029

X.25

Note Remote SNA devices can call in to a Tandem system through the SNAX/XF process. However, a

Tandem system cannot establish a call out to remote SNA devices through SNAX/XF alone. The

Tandem system must communicate through SNAX/CM to initiate a call out to remote SNA devices.

SNAX/CM became available in a controlled release in June ‘92.