Visara LINCS Features - Manual (Page 51)

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Chapter 5. Host Connectivity
707021-001
During LINCS’ sub-area SNA operation, communication occurs between a primary logical
unit (PLU) and a secondary logical unit (SLU). The host contains the PLU, and the LINCS
node contains the SLUs. The SLU can be associated with a display terminal or printer.
Outbound data is data transmitted from the host to the LINCS node. Inbound data is data
transmitted from the LINCS node to the host. SNA Sessions
An SNA session is a logical connection between the host and the LINCS node. Three types of
sessions exist within the LINCS node:
• SSCP-PU
• SSCP-SLU
• PLU-SLU (known as LU-LU)
The host access method (VTAM, VTAME, TCAM) provides the System Services Control
Point (SSCP) facility that enables the host PLU to communicate with a LINCS’ SLU.
An SSCP-PU session occurs between the access method and the LINCS node’s physical unit
(PU). Its purpose is to open the physical link between the LINCS node and the host.
The SSCP-SLU session occurs between the access method and an SLU contained within the
LINCS node. Its purpose is to establish communication between the host and the SLU. The
SSCP-PU session must precede this session.
The LU-LU session occurs between the host PLU and an SLU contained in the LINCS node.
The SSCP-PU and SSCP-SLU sessions must precede this session. An LU-LU session is one
of four types:
• Type 1 - The SLU’s attached device is a printer whose datastream is an SNA character
string (SCS), or is specified by the Datastream Profile (DSP) of a Function Management
Header Type 1 (FMH-1).
• Type 2 - The SLU’s attached device is a display terminal whose datastream is in 3270
datastream compatibility (DSC) mode format.
• Type 3 - The SLU’s attached device is a printer whose datastream is in 3270 DSC mode
format.
• Type 6.2 - This LU originally was used to support the Central Site Change Management
feature. It now additionally is the native traffic scheme for APPN.
TCP/IP
TCP/IP Host Circuits are supported over Ethernet or Token Ring lines. To configure a TCP/IP
Host Circuit, enable TCP/IP on an Ethernet or Token Ring Line Options panel, and define a
TCP/IP Link Profile.
SNA Encapsulation
SNA may be encapsulated in TCP/IP using the Switch-to-Switch Protocol (SSP) described in
RFC 1434 for interoperability with IBM’s 6611 and other LINCS machines.
LINCS will connect any standard PU2.0 SNA DSPU to a TCP/IP-attached upstream node.
LINCS can also use TCP/IP to connect TCP/IP DSPUs to SNA hosts.