Cellular Digital Packet Data (CDPD) an IP-based wireless wide - area - network (WWAN) using idle spots in cellular channels not used by voice at any given time. CDPD technique, originally developed by IBM, allows data to hop from one idle channel to another idle channel. The CDPD network was deployed by cell carriers providing coverage to most of the U. S. Bell Atlantic boasted of 400 public safety (police) customers in mid - 1999.

A major issue with CDPD is a lack of national coverage by a single network. Large wireless network service suppliers, such as Cingular, AT&T, Bell Atlantic and Verizon have roaming agreements with carriers where they do not have coverage of their own.


CDPD Network Summary

Brief Description
  • CDPD is a wireless mobile packet data network, created as an overlay on the existing cellular network. It uses same frequency as cellular and utilizes "holes" in channels not being used for voice transmission at any given time.
  • Mobile End Station (M-ES), Mobile Data Base Station (MDBS), Mobile Data Intermediate System (MD-IS) and Fixed-End System (F-ES)
Frequency Bands
  • Same frequency as cellular
  • Currently in metropolitan areas, expected to match cellular coverage by 1996 year end
Capacity and Speed
  • Presently enough for the current set of users; carriers will upgrade based on demand. 19200 bps for data. However, because of voice priority and packetization, it is difficult to assume that you can effectively achieve 19200 as speed from user perspective.
Protocols Supported
  • TCP/IP. Other protocols supported through third-party gateways.
Most Suitable Applications
  • Short OLTP transaction-based and messaging, such as telemetry, credit authorization, e-mail based messaging, public safety, transportation, etc.
  • Long file transfer is NOT suitable for CDPD.
  • Prices under constant change at present time; expect them to be slightly below Motient and RAM initially for competitive reasons.
  • It is available now but in large metropolitan areas only.
  • Higher than cellular but some applications may need end-to-end encryption.
  • Potential of full nationwide coverage in future (1997)with seamless roaming within metropolitan areas;
  • Link speed of 19,200 bps can give good response times for OLTP-type short-message-length applications, if carriers have enough channel capacity.
  • Direct TCP/IP support means fewer application changes.
  • Support from RNA industry is coming quickly.
  • Voice priority means applications that are not "mobile-aware" could suffer from poor response time and disconnection.
  • Current level of coverage is not adequate for national applications. Limited coverage in rural areas.
  • Inter-operability between regional CDPD carriers has not been proven in production application environments.
  • Cannot transmit facsimiles directly to fax machines.
  • Emerging network - end-to-end systems-integration expertise is scarce