Cellular Digital Packet Data

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.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 transmissions have a 19,200 bps raw data rate.

Working Of CDPD

To effectively integrate voice and data traffic on the cellular system without degrading the level of service provided to the voice customer, the CDPD network implements a technique called channel hopping. The way this works is that when a CDPD mobile data unit desires to initiate data transmission, it will check for availability of a cellular channel. Once an available channel is located, the data link is established. As long as the assigned cellular channel is not needed for voice communications, the mobile data unit can continue to transmit data packet bursts on it. However, if a cellular voice customer initiates voice communication, it will take priority over the data transmission.

About

Cellular Digital Packet Data (CDPD) systems offer what is currently 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.

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 flaws which limited their utility.

Intermediate System (IS)

  The IS is a router and an off-the-shelf device. The IS routes the data through the IP and the CLNP network. The Intermediate System is a standard IP router with the primary responsibility of relaying data packets. It consists of the off-the-shelf commercially available router equipment, such as manufactured by Wellfleet. Most ISs are unaware of mobility.

Fixed-End System (F-Es)

          The F-ES is whatever network environment/resource the User is attempting to make available to mobile access via CDPD. The F-ES is the final destination of the message sent from an M-ES. The Fixed-End System receives the data and processes it appropriately. The F-ES can be one of many stationary-computing devices, such as a host computer, a UNIX workstation, an online information service, or another Mobile-End System. CDPD subscribers administrate external F-ES.

 Mobile Data Intermediate System (Md-Is)

The MD-IS keeps track of an M-ES’s location and routes data packets to and from the CDPD Network and the M-ES appropriately. In addition, the MD-IS is responsible for validating an M-ES on the network, and exchanging the encryption keys with the M-ES that allows for secure transmission of data over the air link. It is responsible for IP routing.

Mobile Data Base Station (Mdbs)

MDBS is located at the cell site. It acts as a relay station between M-ES and MD-IS systems. The MDBS relays packets of data to the MD-IS (Mobile Data Intermediate System) located at the MTSO (Mobile Telephone Switching Office).

Abstract

 Cellular Digital Packet Data (CDPD) is a specification for supporting wireless access to the internet and other public data networks. CDPD transmits digital packet data at 19.2 Kbps, using idle times between cellular voice calls on the cellular telephone network. CDPD technology represent a way for law enforcement agencies to improve how they manage their communications and information system.

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 secure wireless packet data technology that is ideal for un-tethered applications. 

Conclusion

The wireless networks we have now are not perfect. They are slow and vulnerable compared to wired networks, and exist as a community of devices - laptops, PDAs, and mobile phones -- that we can only hope will one day be integrated into a single, lightweight, easily portable unit. Still, it is already easy to see the advantages of wireless.