Modem Pools

One of the tangential benefits of ETC (Enhanced Throughput Cellular) design is that it works, albeit not at its best, when present in only one-half of a modem-to-modem connection. This is the theory behind a relatively new concept called modem pools. One of the reasons that so many cellular carriers are endorsing ETC is that it makes their services look that much better, but they're not stopping with appearance.

A modem pool is an array of modems, maintained by the cellular carrier, that provide error correction and signal-reliability enhancement without active participation or investment from the end user. The primary modem at the carrier accepts the mobile call and applies the appropriate error-correction technology (e.g., TX-Cell, MNP level 10, or ETC). The data is translated (if necessary) to a landline-based error-correction protocol (e.g., MNP level 2 or V.42) and is switched to a second modem back-to-back with the primary modem. The second modem switches the call to landlines and on to the call destination. The user sees only the results, which, with ETC, are good.

Primary Access (San Diego, CA) is the supplier of modem-pool hardware and software to the cellular industry. Primary's product is a single digital platform supporting many pairs of back-to-back modems. The modems themselves are DSP (digital signal processor) systems that are configurable via software. These platforms are interfaced on T1 lines that provide 24 channels and a cumulative bandwidth of 1.5 Mbps.

One of the carriers using this technology is NYNEX Mobile Communications (Orangeburg, NY). The company selected ETC because it delivers increased reliability for NYNEX services. It also increases the throughput of all data calls, resulting in increased customer satisfaction. Installing ETC in the network relieves corporate customers from the responsibility and cost of replacing or upgrading al l their modems. Finally, it gives the end user point-to-multipoint benefits, rather than the point-to-point benefits that are derived from any protocol required on both ends of a connection.

Jim Ducay, director of wireless data services for NYNEX, believes that ``Cellular can meet all of our customers' needs, both voice and data. One such need is wireless modem service, which we supply with ETC-protocol support in the network. The entire process is transparent to the customer, who only sees increased carrier reliability and throughput.'' While this system delivers benefits without customer investment, if the end user does have ETC installed on his or her end of the link, the benefits are greater.

Of the 15 cellular providers currently endorsing ETC, about half have implemented modem-pool technology in their systems. Most provide it as a value-added service to the customer at no cost. Some are even looking at the possibility of providing reduced-rate data-only services to their customer base.