Visara LINCS Features - Manual (Page 70)

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LINCS Features
707021-001
If a class_name is used, this corresponds to the LINCS Class Name for a 3270 host. LINCS is
not case-sensitive for the class_name parameter.
Session Management System
Some of the problems associated with moving 3270 client platforms to a LAN environment
include:
- Less dependable server platforms than traditional coax controllers
- Training users on how to connect to multiple TN3270 servers so that when one is unavailable
due to the host link down, server down, or all sessions in use, another server can be accessed.
- Balancing the work load across multiple servers to get the best overall performance
- Knowing when a preferred host connection is available again after an outage
The Session Management System (SMS) of the LINCS/Gen C platform addresses these issues.
The LINCS SMS feature provides a system which manages TN3270 (and TELNET) client
connections to a pool of servers. SMS provides two main functions. One is to automatically
select which one of a pool of TN3270 servers will be approached with a session connection
based on the available number of sessions and connections at each server. The other function
is to provide redundancy. For example, if a particular server is down, SMS will select another
server to which the client can connect.
The SMS feature provides these functions by implementing a primitive Domain Name Server
which will provide domain name-to-IP address resolution for the TN3270 and TELNET clients.
Instead of a domain name representing one server, many servers will be represented by a
single domain name. The SMS domain server will return the IP address of the server which
has the most available sessions and connections and is operational. To determine session and
connection availability the SMS server will periodically poll, via TCP connections, a configured
list of servers.
Each SMS server, maintains contact with each of the TN3270 server platforms to keep
information on session availability up to date. Clients request the IP address of a TN3270
server using a configured domain name for the session that they desire. The primary SMS
server provides the IP address of the server with the most available active sessions to give. The
backup SMS server is approached only if the primary SMS server is unavailable.
Once the client is given an IP address to contact, it will attempt to establish a session with the
TN3270 server.
The SMS feature can be used along with the an existing DNS server or can be used in
environments where DNS is not already in use. When used in conjunction with an existing
DNS server, the SMS server is configured to control a sub-domain of the existing DNS. TN3270
clients are configured with the DNS server’s IP address, and the IP address of the back-up
DNS server, along with the fully-qualified domain name of the required TN3270 service. The
existing DNS server (and back-up DNS server) is configured to direct any requests to the new
sub-domain over to the SMS server. The SMS server responds back to the DNS server with a
resolved IP address. The DNS server in turn responds back to the requesting client. The DNS
server is not allowed to cache the resolved name, forcing the DNS server to always pass new
requests on to SMS.