Specifications

Chapter 4 Connecting with Direct Dial
Niagara Considerations
Niagara Release 2.3
Niagara Networking & Connectivity Guide Revised: May 22, 2002
4–5
Only a single connection between a host and a remote Niagara software component
can exist at one time. For example, if a JACE-4/5 has dialed a Web Supervisor to
deliver alarms, you cannot use JDE on the same connection to access a JACE.
Conversely, if the Web Supervisor runs the Admin Tool and dials into a JACE, the
JACE will not be able to deliver alarms to the Web Supervisor on the same
connection. These restrictions exist even if the GUI component (Admin Tool or JDE)
is running on the same PC as the Web Supervisor station. Therefore, if you are on a
user-initiated connection from the Web Supervisor to the JACE, alarms will queue in
the JACE station for delivery by a subsequent application-initiated connection. In
addition, any alarm acknowledgements processed on the Web Supervisor while
user-connected will also queue in the WS station until the station has a chance to
make an application-initiated connection. Polled archive requests will also queue
until the user on the Web Supervisor releases the manual connection.
In all cases, user-initiated connections have priority over application-initiated
connections. After each connection initiated by an application there is a period of
time (5 minutes) when application-initiated re-connects are prohibited. There is also
a maximum connect time (10 minutes) for application-initiated connections. After
this time expires, the connection will be terminated automatically. This prevents a
station rapidly generating alarms from monopolizing the modem and locking out
dial-in user access.
Note You cannot modify these parameters.
Design Considerations
You should note the following things about connecting Niagara hosts with direct dial:
• Connection between hosts using direct dial will be slower than connection on
a LAN/WAN.
• If the hosts will use long-distance to dial each other, it may be cheaper to
connect the hosts to local ISPs and connect through the Internet (see
“Connecting to an ISP,” page 5-1). Some factors to consider are:
– does each host have access to a local dial-in number to the ISP? Otherwise,
long distance charges for any non-local host will be a factor.
– will the JACEs be sending much data (archives and alarms)? If not,
connecting long distance briefly, even several times a day may be cheaper
than the ISP’s monthly fee.
• If you need frequent access to a remote host, consider connecting the host to
an ISP. An ISP-connected host is virtually always available. In addition, an
ISP-connected host does not have the same user- versus application-initiated
restriction. With an ISP-connected host, user and application data can travel
simultaneously.
• Support for ISDN, which provides faster dial-up connection, is available for
any Windows-based Niagara host, but is not available for JACE-4/5s.