User`s guide

Configuration through the web interface
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Connection settings
The Connection settings configure how the Digi device connects to an iDigi server. These settings
include information about communication between Digi device and iDigi server, and the
connection methods used by the various interfaces on the system.
About device-initiated and server-initiated iDigi connections
Digi devices can be configured to connect to and communicate with an iDigi server through
device-initiated or server-initiated connections. To illustrate how both types of connections work,
here is a configuration scenario featuring Digi devices communicating over a cellular network with
a remote management server running in the home office.
Addresses for Digi devices can be publicly known, or private and dynamic, or handled through
Network Address Translation (NAT). NAT reduces the need for a large amount of publicly known
IP addresses by creating a separation between publicly known and privately known IP addresses.
NAT allows a single device, such as a router, to act as an agent between a public network, such as
the Internet or a wireless network, and a private, or local, network. This means that only one
unique IP address is needed to represent an entire group of computers. Addresses handled through
NAT can access the rest of “the world,” but “the world” cannot access them.
In a device-initiated iDigi connection, the Digi device attempts to connect to the network, and will
continue attempts to reach the iDigi server to establish the connection. To maintain the connection,
the Digi device sends keep-alive messages over the connection. The frequency with which keep-
alive messages are sent is configurable. An advantage of device--initiated iDigi connections is that
they can be used in any cellular network, whether public or private IP addresses are used, or even if
NAT is used. A disadvantage is that you can be charged for the Digi device sending the keep-
alives, depending on your cellular/mobile service plan.
A server-initiated iDigi connection works the opposite way. The iDigi server opens a TCP
connection, and the Digi device must be listening for the connection to the iDigi server to occur.
An advantage of server-initiated iDigi connections is that you are not charged for sending the keep-
alive bytes that are used in device-initiated connections. A disadvantage is that there is no way of
knowing whether the devices displayed in the device list at the iDigi server are offline or
connected. The device list shows all the devices as disconnected until the iDigi server does
something to interact with them. In addition, server-initiated connections cannot be used if Digi
devices have private IP addresses and are behind a NAT.
A paged connection is another form of a device-initiated connection. This type of connection is
initiated by an on-demand request, such as a Short Message (SM) received via a cellular modem
(from a mobile service provider). The request message may specify the iDigi server with which the
device should connect, or it may simply request that the device connect to the iDigi server that is
configured in the Paged iDigi Connection settings.