Sun Microsystems SunLink SNA 9.1 PU2.1, Руководство по настройке

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SNA Concepts C-3
C
The cluster controllers control the input and output of attached devices, such
as display stations and printers. A 3174 or 3274 Control Unit is an example of a
cluster controller. The Sun PU2.1 SNA Server emulates a cluster controller with
attached devices.
The cluster controllers connect to the SNA network through a data link
connection to a Physical Unit Type 4 (PU4) device. The physical unit can be an
IBM communications controller, a specially configured cluster controller, or a
host with an integrated communications adapter.
SNA supports the following types of data link connections:
•
Telecommunications lines
- The cluster controller can be connected to the
communications controller by using telephone lines. The Synchronous Data
Link Control (SDLC) protocol controls the transmission of data across the
data link. The data link can be a switched line (such as a dial-up line) or a
non-switched line (such as a private, dedicated line). The data link can
support many stations (multi-point line) or two stations (point-to-point
line).
•
X.25 packet-switched data networks (PSDNs) - The cluster controller and
the communications controller can be connected over X.25 PSDNs by using
X.25 virtual circuits (VCs). The Qualified Logical Link Control (QLLC)
protocol controls the transmission of data across the VC. The
communications controller, through the NCP Packet Switched Interface
(NPSI), provides the X.25 interface. Like SDLC, QLLC supports both
switched and non-switched connections. Switched connections are provided
by X.25 Switched Virtual Circuits (SVCs). Non-switched connections are
provided by X.25 Permanent Virtual Circuits (PVCs). Unlike SDLC, QLLC
supports only point-to-point connections.
•
IBM Token Ring local area network - IBM Token Ring networking consists
of two data link control sublayers: Logical Link Control (LLC) and Medium
Access Control (MAC). LLC and MAC (802.5) control the transmission of
data across the local area network. The network can have a data rate of
either 4 million bits per second (4 Mb/s) or 16 Mb/s. The networks can be
interconnected using either repeaters or bridges and source routing.
Multiple cluster controllers, or Downstream Physical Units (DSPUs), can
attach to the IBM Token Ring and communicate with the host either directly
though a communications controller or indirectly through a specially
configured cluster controller (3174 Establishment Controller with the 3270
Gateway feature). Attaching the DSPUs through the communications
controller requires the NCP/Token Ring Interconnection (NTRI).