80 7 HYBRID NETWORKS 7.1 TERRESTRIAL PACKET/SATELLITE Trucking company Boyle Transport makes it crystal clear: you should be able to pick a radio or cellular based system for regional service and satellite for long haul, but be able to use the same provider. 1 This is the goal of most hybrid offerings, though satellite may well be avoided in favor of an alternative technique such as circuit switched cellular. 7.1.1 AMSC/ARDIS Multimode System In March 1990 Rockwell announced that it was developing a satellite-based vehicle location and two-way data system. 2 Rockwells plan was to lease L-band capacity from AMSC, which was leasing time from InMarSat. Rockwell concentrated on the vehicular terminals and communications hardware. It began to develop a new control center for switching data between customers headquarters and their vehicles. Rockwell saw its competition as OmniTRACS (then only ∼ 7500 units) and Geostar (now defunct). Rockwells perceived edge were its customers, who had already installed 80,000 TripMasters. Since Rockwells product was not yet ready (indeed, it was still debating whether or not Loran-C was the best way to go), it purchased the first two years devices from Canadian Aeronautics (CAL). The plan was to resell each unit for $3500; its own device was estimated to be ∼ $2500. This was markedly cheaper than the $4000$5000 charged by Geostar and OmniTRACS. However, the Rockwell airtime costs were estimated to be $50$60 per month, quite a bit more than the $35$45 charged by Geostar and OmniTRACS. 3 The Wireless Data Handbook, Fourth Edition. James F. DeRose Copyright © 1999 John Wiley & Sons, Inc. ISBNs: 0-471-31651-2 (Hardback); 0-471-22458-8 (Electronic) As with many acts of bravado, the world did not accommodate itself to Rockwells goals. After long delays, Rockwell finally had the Pro2000 product in April 1993for $4000. The airtime price was $60 for 15,000 bytes ($4 per kilobyte). 4 Rockwells device sold slowly: 3000 units over six months. Meanwhile, OmniTRACS acceptances began to accelerate, climbing a steep hill. In October 1994 after OmniTRACS had reached 90,000 subscribers, Rockwell announced the first multimode device: the Pro2000SL. This unit contained a Motorola radio modem for communication over ARDIS. The price was $4495. There were also airtime pricing adjustments: $40 per 20,000 bytes per month. Each additional kilobyte was $1.65 during peak times (7:00 AM to 7:00 PM Central Time) 5 ; the nonpeak kilobyte charge was $0.75. Prior to the multimode system announcement, Rockwell had tested in a 100 mile radius of its Cedar Rapids plant using an ARDIS hand-held device. The conclusion was that about half the traffic would flow via satellite. This guess permitted new customers such as Umthun Trucking (400 units) to calculate an 18-month payback. But when using an external antenna mounted high in a truck, the device began picking up ARDIS well outside the expected range of coverage. Instead of half the traffic to ARDIS, 70 ± 5% of the messages flowed via the terrestrial source, which must have made Umthun happy! However, it did not please Rockwell; the business was sold to AMSC at year-end 1996. AMSC, in turn, purchased ARDIS on March 31, 1998, and announced its intent to leverage an integrated terrestrial/satellite network to advance its leadership in wireless data services. 6 7.1.2 BSWD/Norcom On November 10, 1992, ARDIS and Sears began a field test with 150 service technicians. After years of the most grueling network-independent application development work, the number of technicians had expanded to 7000 by December 1997. Sears, like most major corporations, is loath to be dependent upon a single vendor. In September 1996 BSWD approached Sears with a proposal to provide service in areas thinly covered by ARDIS. Unfortunately, BSWDs terrestrial coverage was not that hot in those sectors either. Its strategic network approach, which uses circuit switched cellular when the packet coverage is unavailable, was rejected by Sears as too expensive, insufficiently reliable, and lacking adequate nationwide coverage. 7 BSWD, taking a leaf from ARDIS book, then began work on terrestrial/satellite hybrid device. The network chosen was Norcom, a subsidiary of Telenor, which leases Ku/L-band time on AMSCs satellites. The key advantage is that the Norcom design uses an X.25 call setup protocol, resulting in a short response time, typically 35 seconds. ARDIS bid the Rockwell multimode solution, of course, but in its 1996 incarnation it was a polled device. This produced a design that could have a 510 minutes latency, unacceptable to Sears. BSWD/Norcom are installing the last 5000 Sears devices using their hybrid approach. 7.1 TERRESTRIAL PACKET/SATELLITE 81 Note that the technician does not walk around interchanging data with a GEOS. When the hybrid device is out of the cradle, there is no wireless connectivity. Only when it is returned to the cradle can communication with the satellite begin. 7.2 TERRESTRIAL PACKET/CIRCUIT SWITCHED CELLULAR This combination depends upon having a modem capable of operating on either packet or circuit switched networks, which is not so unusual. However, the modem must also be capable of automatically detecting when one of the services is unavailable. Typically the modems are designed to listen for packet first. The modem will then select the alternative service, sometimes in the middle of a transaction. The key advantages for the customer are increased coverage (often at higher airtime cost), without manual intervention or changes to the user application. Application transparency requires network enhancement to hide the message source from the user host. The notion is wonderfully attractive; customer acceptance has been disappointing. 7.2.1 CS-CDPD The CS-CDPD design was pioneered by GTE Mobile, Hughes Electronics, and the now-departed PCSI in early 1995. In this implementation a device operating on CDPD continually tests the field strength of the CDPD signals. If they begin to fade, a special circuit switched uplink protocol is dialed that can make a connection in about 3 secondsa delay often not noticed by the user. The dialing plan can be complex, including the use of 800 numbers when out of range of GTE Mobile coverage. In the spring of 1996, in cooperation with GTE Mobile, TranSettlements Network Services announced a wireless communications system for less-than-truckload (LTL) carriers. 8 The Tracker was intended to serve the pickup and delivery application; all emphasis is on telephone handset functions. TranSettlements began testing the PCSI PalPhone in the fourth quarter of 1996 with Silver Eagle (30 units) of Portland and Cal Pak of Hayward. 9 Beta testing was essentially complete on January 31 10 and the price list was placed on the Web. 11 However, the production roll-out failed. The many problems, not the least of which was the demise of PCSI, were best summarized in May 1998 by TranSettlements: our initial customers (in a decision made concurrently with TranSettlements) have had to discontinue use of the Tracker P&D system, as problems with CDPD reliability, interoperability, and lack of warranty for the hardware have greatly increased the overhead necessary to support the service. 12 7.2.2 BSWD Strategic Network On October 31, 1995, BSWD (then RAM) announced 13 the first segment of its strategic network: connection to the circuit switched cellular and public switched telephone (PSTN) network. 82 HYBRID NETWORKS CS-CDPD operates on the same 800-MHz cellular channels whether in packet or circuit mode. BSWDs Mobitex network operates in the 900-MHz band. Not only is the band allocation different, so is the channel width. CS-CDPD operates in 30-kHz wide channels; BSWD operates in 12.5-kHz wide channels. A single, inexpensive radio simply will not bridge this gap. Thus, the BSWD implementation requires two radios that operate on two completely independent networks. A single, special-purpose modeminitially, the NovaLink GoAnywherewas the bridging unit. Conceptually, the system looked as shown in Figure 7-1. Note that the modem was capable of dialing in over conventional landline networks, bypassing radio altogether. A small problem: The GoAnywhere modem never shipped. REFERENCES 1. M. Boyle, Director of Marketing & Information Resources, T.F. Boyle Transponation, Traffic World , 7-22-96. 2. Mobile Data Report , 3-12-90. 3. Mobile Data Report , 3-26-90. 4. En Route Technology , 3-15-93. 5. En Route Technology , 3-27-95. 6. AMSC press release, 3-31-98. 7. Wireless & Mobility , Mar. 1998. 8. Logistics Technology News , 11-8-96. Figure 7-1 BSWD strategic network. REFERENCES 83 9. Traffic World , 12-9-96. 10. Communications Today , 1-31-97. 11. www.itsc.state.md.us/info/EDI/chart/trans.html. 12. E. Fannin, TranSettlements, correspondence to J. F. DeRose, 5-5-98. 13. RAM Analyst & Media Conference , 10-31-95. 84 HYBRID NETWORKS