Cabletron Systems Netlink FRX8000, User Manual

Page: 149 / 468

Chapter 11
Configuring SNA
The SNA PAD function allows an SNA host to connect via an FRX8000 or N7000
HPAD to up to 16 TPAD devices (e.g., cluster controllers). HPAD and TPAD(s) can
be in the same or separate FRX8000 nodes.
Using QLLC (Qualified Logical Link Control), the host can connect directly to the
X.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 or
remote connection over frame relay (via RFC1490) or X.25 (via QLLC) between two
SNA devices, one attached to a LAN and the other attached to either another LAN or
a frame relay-compliant SNA/APPN device. Each SNA host and terminal accessing
the 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 SNA
device and its network-access node, rather than passing them across the network. This
allows 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. Note
that the LANs shown are all Token Ring. The same examples can be presented with
Ethernet LANs.
Figure 11-1 SDLC and LLC2 Examples
1
PUs
SDLC
Frame Relay or X.25
Host
PUs
Host
PUs
Frame Relay PVC
Router
Host
FRX 1
FRX 2
FRX 1 FRX 2
FRX
2
3
4
PUs
SDLC
FRX
FEP
HOST