Cellular Digital Packet Data (CDPD) systems offer one of
the most advanced means of wireless data transmission technology. Generally
used as a tool for business, CDPD holds promises for improving law enforcement
communications and operations. As technologies improve, CDPD may represent a
major step toward making our nation a wireless information society. While
CDPD technology is more complex than most of us care
to understand. In this age of information, no one needs to be reminded of
speed but also accuracy in the storage, retrieval and transmission of data. The
CDPD network is a little one year old and already is proving to be a hot
digital enhancement to the existing phone network. CDPD transmits digital
packet data at 19.2 Kbps, using idle times between cellular voice calls on the
cellular telephone network.
CDPD technology represents a way for law enforcement
agencies to improve how they manage their communications and information
systems. For over a decade, agencies around the world have been experimenting
with placing Mobile Data Terminals(MDT) in their vehicles to enhance officer
safety and efficiency.
Early MDT's transmits their information using radio modems. In this case data could be lost in transmission during bad weather or when mobile units are not properly located in relation to transmission towers. More recently MDT's have transmitted data using analog cellular telephone modems. This shift represented an improvement in mobile data communications, but systems still had flaw which limited their utility.
Since the mid-1990, computer manufacturers and the telecommunication industry have been experimenting with the use of digital cellular telecommunications as a wireless means to transmit data. The result of their effort is CDPD systems. These systems allow users to transmit data with a higher degree of accuracy, few service interruptions, and strong security. In addition CDPD technology represents a way for law enforcement agencies to improve how they manage their communications and information systems. This results in the capacity for mobile users to enjoy almost instantaneous access to information.
1. WHAT IS CDPD?
CDPD is a specification for supporting wireless access to
the Internet and other public packet-switched networks. Data transmitted on the
CDPD systems travel several times faster than data send using analog networks.
Cellular telephones and modem providers that offer CDPD
support make it possible for mobile users to get access to the Internet at up
to 19.2 Kbps. Because CDPD is an open specification that remains to the layered
structure of the Open Systems Interconnection (OSI) model, it has the ability
to be extended in the future. CDPD supports both the Internet's Connectionless
Network Protocol (CLNP).
CDPD also supports IP multicast (one-to-many) service. With multicast, a company can periodically broadcast updates to sales and service people on the road or a news subscription service can transmit its issues as they are published. It will also support the next level of IP, IPV6. With CDPD we can assigned our very own address. With this address, we can virtually always connected to our host without having to keep a constant connection.
There are currently two methods for sending data over
cellular networks: cellular digital packet data (CDPD) and cellular
switched-circuit data (CSCD). Each has distinct advantages depending on the
type of application, amount of data to send or receive and geographic coverage
needs.
CDPD is currently available to roughly 50 percent of the
population base. Two methods to transmit data are used, depending upon the
service provider's network architecture. Some providers have radio channels
dedicated to data transmission installed at existing voice cellular sites.
Others use voice cellular channels and interleave data messages within the
unused portion of voice radio signals. To use a CDPD data service, users
require a laptop computer, a connector cable and a CDPD radio modem. Radio
modems come in a PC-card format or connect to the user device with a serial
cable.
Regardless of the method used, messages are broken up into
discrete packets of data and transmitted continuously over the network.
Messages are then "reassembled" into the original message at the
receiving device. This technology supports roaming and is especially attractive
for multicast (e.g., one-to-many) service, allowing updates to be periodically
broadcast to all users. Users log on once per day to register on the network.
Messages and transmissions automatically locate them. Major CDPD providers
generally have roaming agreements to allow users to access the service when
outside their home coverage area. For the mobile users, CDPD's support for
packet switching means that a persistent link isn’t needed. The same broadcast
channel can be shared among a number of users at the same time. The user's
recognizes the packets intended for its user. As data such as e-mail arrives,
it is forwarded immediately to the user without a circuit connection having to
be established. There is circuit switched version, called CS CDPD that can be
used where traffic is expected to be heavy enough to warrant a dedicated
connection. As a tool for transmitting data CDPD utilizes digital
networks. Placing data, conversions, photographs, and multimedia into digital
form and transmitting the information through a network with a large bandwidth
permits more information to be sent more quickly with greater clarity. Thus,
data send using CDPD is received in a quick, secure, and accurate fashion. Data
send using CDPD systems is less likely to be lost between senders and receivers
due to the position of mobile units, weather conditions, or other anomalies.
CDPD is an overlay to the existing cellular network, which
enables users to transmit packets of data over the cellular network using a
portable computing device and a CDPD modem. CDPD offers a high-speed,
high-capacity, low-cost system with the greatest possible coverage.
Additionally data is encrypted for security. CDPD air link Transmission has a 19,200 bps raw data rate.
The Raven is a rugged, full duplex Cellular Digital Packet
Data (CDPD) modem that provides wireless transport capabilities for fixed and
mobile applications. The Raven is an efficient and secures wireless packet data
technology that is ideal for un-tethered applications. The CDPD Raven is
ideally suited for all fixed and mobile Industrial and Commercial Applications,
including Telemetry, SCADA, Public Safety, Dispatch, Field Service, Financial
Transaction Processing, and Security. The Raven's embedded TCP/IP stack enables
virtually any type of remote device to access the CDPD network.
The Raven is currently installed with many different types
of Remote Terminal Units (RTUs), which perform remote metering, and monitoring
functions in the oil, gas, and water industries. The CDPD Raven can be a
low-cost replacement for existing landline, private radio and circuit-switched
cellular installations.
