Making The Call With Two-Way Paging Building Pager Networks Two-wa y paging networks use spectrum in the 900-MHz band auctioned in 1995 by the FCC for what is called narrowband personal communications service (PCS). Licenses, which are local, regional or nationwide, consist of blocks of up to 50 KHz for transmission in every direction. Compared with the tens of megahertz auctioned for broadband PCS, this is a small amount of spectrum, and it limits message size and message volume. A nationwide narrowband PCS license can be a huge advantage for carriers. Unlike cellular licenses where nationwide coverage can be achieved only through cooperation among carriers, one paging carrier can serve the entire nation. Although the glamour of two-way paging is two-way messaging, the technology also lets carriers provide traditional one-way paging nationwide at a muc h lower cost to the carrier. Since the pager can register itself with the network, the network has to broadcast only in the area where the pager is located rather than across the entire coverage area. Compared to battery life with other wireless network devices, the pager's battery life is good. With typical use, you can expect about two weeks of use from one AA battery, far longer than the typical one day of use with cellular phones and wireless modems. SkyTel's network is based on Motorola's ReFLEX two-way paging technology (see "SkyTel Network Architecture," above). The system requires fewer transmitters than receivers because transmitters blast out messages at hundreds of watts, and receivers have to detect much fainter signals from the pagers, which transmit at just 1 watt. SkyTel's network, using a version of ReFLEX, called ReFLEX50, transmits to pagers a 25.6-Kbps signal in a 50-KHz channel comprising four subchannels of 6.4 Kbps, and receives from pagers a 9.6-Kbps signal in a 12.5-KHz channel. Ac tual data throughput is lower, since these signals include forward-error correction and other communications overhead. Motorola offers another version of ReFLEX, ReFLEX25, which uses a 25-KHz channel for transmitting one channel of up to 6.4 Kbps. Carriers intending to provide ReFLEX networks can purchase infrastructure elements from Motorola or Glenayre Technologies, a licensee of ReFLEX technology. Two-way pagers are available from Motorola and Wireless Access, which supplies the SkyWriter for SkyTel. An important element in SkyTel's architecture is that all messages pass through its network operations center (NOC). A two-way paging network configured this way is not a general-purpose WAN such as CDPD, where individual IP packets can originate from a host on the Internet and reach a mobile computer. Instead, the entire message must be formatted in a specific way and submitted to the NOC for delivery to the pager. It is a store-and-forward messaging system. Doing That Two-Way Thing Sk yTel provides considerable flexibility in sending and receiving messages. There are numerous ways to send messages. You can visit SkyTel's home page (www. skytel.com) and enter a message by filling in a form, or you can use SkyTel's QuickAccess software that runs on Microsoft Windows. Once you have composed a message, the software dials into SkyTel's NOC and transfers messages. The software also lets you check on the status of messages sent. Additionally, you can use the Telocator Message Entry (TME) protocol (to which SkyTel has added special extensions) to submit messages over dial-up or dedicated connections to SkyTel's NOC. SkyTel provides a developer's kit to develop applications that easily exchange messages with SkyTel's network. Every pager is assigned an e-mail address, so that you can address a pager as an Internet e-mail destination using a seven-digit ID, such as 1234567@skytel.com. It is also possible to use a cc:Mail client where the SkyTel network presents itself as a remote cc:Mail post of fice. Skytel also supports the Telocator Alphanumeric Protocol (TAP) to submit messages over a dial-up connection to SkyTel's NOC. The first three options let you attach a set of reply messages through which the recipient can scroll and select one for their reply. When sending a set of reply messages, you also can specify an address where the reply message should be sent. To originate a message from a pager, you can address the message to an Internet address, address the message to another SkyTel pager, reply to a message sent from SkyTel's QuickAccess software or reply to a message sent from SkyTel's Web site. You can expect similar options from other service providers once they begin offering service. To a large extent, these options will determine what applications are feasible for two-way networks.

Updated January 10, 1997