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As an overlay to the existing analog cellular infrastructure, CDPD networks are easy and economical for carriers to set up and operate. Carriers estimate that it costs only 5% over the initial cost of a cell site to upgrade to CDPD. Cell sites typically cost about$1 million to set up, including the cost of real estate.
Per-User Pricing | ||
---|---|---|
Application | Bell Atlantic Mobile Systems | GTE Mobilnet |
Data base Inquiry | $23 to $27/month | $20 to $28/month, 25 sessions a day, 5 days a week |
Electronic Mail | $40 to $60/month | $45 to $60/month, 14 messages a day, 5 days a week |
Dispatch | $13 to $17/month | $10 to $20/month, 1 to 2 jobs per hour, 9 hours a day, 5 days a week |
Alarm Monitoring | $13 to $17/month | $10 to $20/month, 1 transaction per hour, 24 hours a day, 7 days a week |
Field Service | $23 to $27/month | $16 to $22/month, 20 transactions a day, 5 days a week |
Note: Estimated per-user prices are based on sample applications and usage figures. All prices subject to change without prior notice. |
Users are the beneficiaries of CDPDs resulting economies and efficiencies. For many applications, initial CDPD service pricing is competitive with that of the proprietary analog wireless services of ARDIS and RAM Mobile Data. Exhibit 1 indicates that CDPD is best suited for transaction-oriented applications. Although these services might prove too expensive for heavy database access, the use of intelligent agents can cut costs by minimizing connection time.
Because CDPD uses the existing voice-oriented cellular network and off-the-shelf hardware for implementation, it is cost-effective. There are, however, additional benefits to users besides economy. These benefits include:
Because CDPD allows the network to operate more efficiently by providing digital packet data over the voice network, carriers also realize maximum flexibility, simplified operations and maintenance, and cost savings. Carriers can offer enhanced messaging services such as multicast, cellular paging, and national short-text messaging. CDPD allows portable access to a variety of information services.
In effect, CDPD extends client/server-based applications from the LAN environment into the wireless arena. This extension provides nearly limitless possibilities for future wireless data services.
CDPD is not without its problems. Even though CDPD takes advantage of the existing circuit cellular voice infrastructure to send data at up to 19.2K b/s, existing cellular modems cannot be used on CDPD-based networks. Modems designed for CDPD networks are still larger and more expensive than those designed for circuit cellular.
CDPD-only modems cost about $500; modems that handle both CDPD and circuit cellular run about $1,000. When the cost of CDPD modems drops to the $200 range, expense will no longer be a barrier. Also, carriers are considering subsidizing the cost of Cellular Digital Packet Data modems, the way they currently do with cellular phones, when users sign up for service.
The CDPD specification defines all the components and communications protocols necessary to support mobile communications. Exhibit 2 shows the main elements of a CDPD network.
Exhibit 2. CDPD Network Architecture.
The backbone router, also known as the MD-IS, uses the location information derived from the mobile network location protocol to route data to the mobile units, which are referred to as M-ES. Information on the link between the backbone router and a MDBS is transmitted using a DLL protocol. Communications on the other side of the backbone router are handled using internationally recognized protocols. This ensures that standard, off-the-shelf systems can be used in the network infrastructure and that computer systems currently in use can be accessed by CDPD networks without modification.
The MDBS provides the relay between the cellular radio system and the digital data component of the CDPD network. The MDBS communicates with the mobile units through radio signals. Up to 16 mobile units in a sector can use the same cellular channel and communicate as if they were on a LAN. This communications technique is known as DSMA. After MDBS turns the cellular radio signal into digital data, it transmits the data stream to its backbone router, typically using frame relay, X.25, or the PPP.
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