Specifications

Sierra Wireless, Inc. CDPD Primer
2130006 Rev 1.0 Page 18
4.2. Services: CDPD Network Services
When a cellular carrier constructs a CDPD network, it provides a number of services to provide
security, enable easy connection to the Internet, permit roaming, track usage, maintain accounting
information, and prevent unauthorized access.
4.2.1. Domain Name Server
As on the Internet as a whole, the Domain Name Server (DNS) system translates human-readable
host names into numerical IP addresses in the network. A CDPD network requires its own DNS
both to simplify Internet access for clients using that system and to allow incoming packets to find
their proper destinations.
4.2.2. Subscriber Location Service
Subscriber Location Service tracks the location of a CDPD subscriber and reports the location to
the appropriate application. This is not as precise as a global positioning system (GPS) location,
but only as specific as the cell sector of the device in question. Nevertheless, this service can be
useful, for example, in tracking delivery vehicles for more efficient dispatching.
4.2.3. Mobility Management Service
Mobility Management Service manages network roaming and tracks the location of each CDPD
subscriber, as well as keeping the serving MD-IS informed of that location down to the specific
cell site. In a traditional data network, the endpoints of the data connections remain in the same
physical location, and routing of data between these system endpoints is not a problem. However,
in a wireless mobile data network, the endpoints of the data connections can be located anywhere
in the network coverage area, and the location of these endpoints can change over time.
Like voice cellular networks, CDPD supports roaming. CDPD devices have a home subdomain
(or, in some cases, more than one—see section 5.1.1), usually the home city of the subscriber. For
example, you may live in Las Vegas and your CDPD modem may have been activated with a
CDPD carrier there.
You may travel from a subdomain registered as your home area to a new serving area. The CDPD
network’s Mobility Management Service handles the routing of packets for all visiting M-ESs in
its serving area. If you have pre-arranged with your service provider, you can obtain service in
another area served by that carrier, or even in an area supported by another service provider—so
your CDPD modem can roam outside its home subdomain anywhere that CDPD service is
available.
The home area is that in which the CDPD subscriber has registered their device with a CDPD
service provider. If the subscriber travels to another area, the mobility management services
maintain information about their current serving area. If data is destined for that subscriber in
their new location, the mobility management services at the home area forward the data to the
subscriber in their new location.
Mobility management services in the new serving area regularly notify the subscriber’s home-area
CDPD network of the subscriber’s new location. Therefore, a CDPD subscriber can travel
throughout the country and still obtain CDPD network services. The subscriber in the CDPD
network appears to have a seamless data connection as they change their location within the
network coverage area. The mobility management services that provide this seamless coverage
are transparent to the CDPD subscriber. See section 5.2.1 for more detail on mobility
management.