Sierra Wireless 20070914 - Manual (Page 86)

Data Communication and Host Modes
Rev 3.0B Feb.08 73
as subnet masks, routers, etc.) to each computer or device
without the need to set up each specifically or keep track of
what addresses have already been used.
In a default configuration, the PinPoint X acts as a DHCP host
to any device connected to its ports, providing that device with
an IP address which can be used to communicate on the
Internet. In Public Mode, that will be the IP address assigned
by the cellular network. In Private Mode, that will be the IP
address defined in *HOSTPRIVIP.
1. When the PinPoint X registers on the cellular network, it is
assigned an IP address from AT&T, let’s say A.B.C.D.
2. Acting as a DHCP server, in Public Mode, when the
PinPoint X receives a DHCP request from an Ethernet
device, it hands off the assigned address to the device and
sets up the default gateway address as A.B.C.1. If the
fourth octet is already a 1, it assigns A.B.C.2 as the router
address.
3. The PinPoint X also sends a /24 netmask (255.255.255.0 by
default) and sets up a static route which maps
192.168.13.31 (or the address configured with
*HOSTPEERIP if it is changed) to A.B.C.1 (or A.B.C.2 if
that was what the gateway address was given as).
Tip: When PPPoE is used with the PinPoint X, DHCP is not needed.
A tunnel is set up connecting a device (such as your computer or a
router) with the modem. The device will then simply use the MAC
address of the PinPoint X to send all outgoing packets.
Keepalive
Keepalive is used to test the connection to the cellular network
by pinging an IP address after a specified period of inactivity.
Keepalive is only recommended for users who have a remote
terminated modem that infrequently communicates to the
network or if you have experienced issues over time where the
modem can no longer be reached remotely.
When Keepalive pings the IP address, an acknowledgement
indicates there is an active connection to the network. If the
PinPoint X does not receive a response from the IP address, it
will make additional attempts according to a backoff algorithm
before determining the Internet connection is not functioning
properly. If it determines the connection is not functioning, the
modem will then attempt to reconnect to AT&T to reestablish
IP connectivity.