Chapter 11Configuring SNAThe SNA PAD function allows an SNA host to connect via an FRX8000 or N7000HPAD to up to 16 TPAD devices (e.g., cluster controllers). HPAD and TPAD(s) canbe in the same or separate FRX8000 nodes.Using QLLC (Qualified Logical Link Control), the host can connect directly to theX.25 network and the remote TPAD(s) without going through an HPAD.LLC2 (Logical Link Control type 2) support in the FRX8000 provides a local orremote connection over frame relay (via RFC1490) or X.25 (via QLLC) between twoSNA devices, one attached to a LAN and the other attached to either another LAN ora frame relay-compliant SNA/APPN device. Each SNA host and terminal accessingthe FRX8000—via SDLC, LLC2, frame relay, or X.25—will appear to a local LLC2-attached terminal or host as if it is directly connected to the local LAN.LLC2, defined by IEEE 802.2, provides exchange of control frames between an SNAdevice and its network-access node, rather than passing them across the network. Thisallows more efficient use of available bandwidth, and minimizes LLC2 session time.(A session is an exchange of poll and acknowledgment between devices.)The following figure shows some examples of SDLC and LLC2 configurations. Notethat the LANs shown are all Token Ring. The same examples can be presented withEthernet LANs.Figure 11-1 SDLC and LLC2 Examples1PUsSDLCFrame Relay or X.25HostPUsHostPUs Frame Relay PVCRouter HostFRX 1 FRX 2FRX 1 FRX 2FRX234PUsSDLCFRX FEPHOST
