By Peter Rysavy  Wide-Area Wireless Computing Profile of Wireless Networks In this section we profile the major wireless data networks available in the United States. After introducing each network, we characterize it in a table. Analog Cellular Systems Digital Cellular Systems and PCS Cellular Digital Packet Data ARDIS RAM Mobile Data Metricom Ricochet Paging (One way and two way) Enhanced Specialized Mobile Radio Satellite Analog Cellular Systems No wadays it is practical to send data over the analog cellular network. In the United States, this network is based on the Advanced Mobile Phone Service (AMPS) standard. Many new PC Card modems come equipped with cellular protocols and can be connected directly to a cellular telephone. The key issue is that the fixed-end modem at the other end of the connection needs to support the same cellular protocols as the PC Card modem. Cellular carriers are addressing this issue by installing modem pools that provide a gateway function between cellular and landline modem protocols. ITEM CHARACTERISTIC Service providers All cellular telephone companies. The FCC has licensed cellular spectrum to two operators in each geographic area. Coverage The best coverage of any wireless system. Nearly every metropolitan area in the United States, as well as major highways. Modem pool coverage more limited. Spectrum 50 MHz total shared between two carriers. Current markets Vertical market and horizontal markets. Value-added services Modem pools, sometimes also called *DATA service, which allow reliable data calls to fixed-end modems that do not support cellular protocols. Check with cellular provider for details as service details vary. Best applications Any application that uses modem communications where sessions are relatively short and tightly controlled by the application or monitored by the user. Batch-oriented data transfers are ideal such as uploading and downloading e-mail in bulk. Architecture Base stations connect to mobile switching centers which connect to the PSTN. Protocols Modem protocols optimized for cellular communications include ETC (Enhanced Throughput Cellular) from Paradyne, MNP10 and MNP10-EC (Enhanced Cellular) from Microcom, TXCEL (Throughput Accelerator, a waveshaping technology) from Celeritas, and EC 2 (Enhanced Cellular Control) from Motorola. Data throughput Typically 4,800 bps or 9,600 bps. 14,400 bps possible under ideal conditions. Future cellular protocols promise rates to 21,600 bps. Network latency (round trip time) Comparable to landline modem connections. Typically less than 100 milliseconds. Modem vendors Nearly all PC Card vendors support cellular protocols, many in their standard products. Note that each modem only supports certain makes and models of cellular telephones. Service pricing Usually same as cellular voice calls, about 30 cents per minute for home area calls and $1.00 per minute for roaming calls. More information See Cellular Data Communications Made Easy (article by Peter Rysavy in July 1, 1997, issue of Network Computing online) Digital Cellular Systems and PCS Digital cellular systems transmit information between the cellular telephone and base station in digital form, including encoded voice communications. PCS systems use the same technology as digital cellular, but occupy new higher frequency bands. Compared to analog cellular, digital cellular systems offer security through authentication and encryption, short message service (similar to paging), more flexible data services, a variety of value-added voice services (such as caller ID), longer battery life, higher capacity and ultimately lower cost of deployment per subscriber. Though data services have received lower priority than voice, many analysts believe that data traffic will exceed voice traffic within a decade. Data services will include both circuit-switched and packet-switched offerings. ITEM CHARACTERISTIC Service providers Cellular and PCS carriers, though not all yet offer data services. Principal technologies include IS-136 Time-Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), and IS-95 Code Division Multiple Access (CDMA). Coverage Eventually every metropolitan area in the United States, as well as major highways. Digital cellular and PCS coverage currently very fragmented. Spectrum 50-MHz analog cellular spectrum will eventually be all digital. PCS spectrum consists of 120 MHz in the 1.9 GHz band. Current markets Vertical market and horizontal markets. Value-added services None yet. Best applications Most modem-based applications, including faxing, should be compatible with circuit-switched data service. Any IP-based application should be compatible with the packet-switched data service. Architecture Base stations connect to Mobile Switching Centers which connect to the PSTN. Packet service will connect with the Internet. Protocols The radio link uses network specific protocols that provide reliable transfer of data. Data throughput Most initial circuit-switched data offerings will operate at 9,600 or 14,400 bps. Various schemes are being developed to offer data at rates of 28,800 bps or even 64,000 bps. Packet data rates will range from 9,600 bps to 64,000 bps. Network latency (round-trip time) Comparable to landline modem connections for circuit-switched data, slightly higher delays for packet-switched connections. Modem vendors Modems will typically be incorporated into cellular telephones, though for GSM phones, a separate PC Card is sometimes required. Service pricing Circuit data usually same as cellular voice calls, about 30 cents per minute for home area calls and $1.00 per minute for roaming calls. Digital cellular and PCS pricing plans are changing constantly, so check with the carrier. Packet data pricing not yet available. More information See Digital Cellular Networks; On the Road to PCS (by Peter Rysavy and Craig Mathias, Network Computing, February 15 1996). Cellular Digital Packet Data (CDPD) CDPD is an IP-based packet data technology that is deployed as an overlay to the analog cellular network. Packets of data are transmitted either over idle voice channels in some networks or over dedicated channels in other networks. Service, offered by cellular carriers, is available in most major cities in the United States and Canada. ITEM CHARACTERISTIC Service providers The principal providers in the United States include Ameritech, AT&T Wireless Services, Bell Atlantic-NYNEX, and GTE. Canadian providers include BC TEL Mobility and TELUS Mobility. Coverage Most major cities in the United States and Canada. Spectrum CDPD uses a shared 30-KHz analog-cellular channel. Carriers can add additional channels as demand increases. Current markets Mostly vertical at this time, though current emphasis is on developing horizontal and consumer markets. Value-added services Various information services will be available for CDPD capable smart phones. GoAmerica (GoAmerica) at www.goamerica.com Best applications Ones using short and bursty messages. Architecture Existing cellular base s tations are upgraded with communications equipment referred to as the Mobile Data Base Station (MD-BS). The MD-BS bypasses the rest of the cellular network and connects to a central routing function called the Mobile Data Intermediate System (MD-IS). The MD-IS routes IP traffic to value added networks, customer networks and the Internet. Protocols The mobile computer and the modem exchange IP datagrams using SLIP or PPP. The modem routes data to and from the MD-IS over a Mobile Data Link Protocol. Interconnections to other networks are through conventional routed IP connections. Data throughput 19,200 bps raw throughput. Actual throughput is 10 to 12 Kbps. Network latency (round trip time) Typically less than 1 second. Modem vendors Wireless modems available from INET, Motorola, Novatel, PCSI, Sierra Wireless and Uniden. Smart phones that combine a cellular telephone and CDPD modem available from Mitsubishi, PCSI and Samsung. Service pricing Approximately 10 cents per KB depending on pricing plan. More information www.cdpd.org for information about CDPD from the CDPD Forum. See Wireless Data Made to Order (by Peter Rysavy, Network Computing, March 15, 1996.) ARDIS ARDIS, a wireless WAN owned and operated by Motorola, was developed by Motorola and IBM in the early 1980s for IBM customer engineers. A number of networks around the world, operated by other carriers, are based on the underlying DataTAC technology. ITEM CHARACTERISTIC Service providers ARDIS (owned by Motorola) in the United States. Other carriers in foreign countries. Coverage Top 400 metropolitan areas in the United States serving 80 percent of the population and 90 percent of business locations. Spectrum Nationwide 25-KHz channel. Up to 6 channels available in some markets. Current markets Mostly vertical. Value-added services E-mail, Internet and fax gateways: Radiomail (Radiomail) at www.radiomail.net Interactive paging using the Inter@ctive pager from Research in Motion. Best applications Ones using short and bursty messages. Well-suited for character-based host/terminal session-oriented applications. Architecture Based on Motorola DataTAC technology. A hierarchical network where base stations connect to Area Communications Controllers that connect to Message Switches. Customers' fixed-end systems connect to Message Switches. Network offers excellent in building coverage. Protocols MDC-4800 and MDLAP used over the air. Networking protocols are unique to DataTAC. Fixed-end connections typically over X.25 links. Data throughput 4,800 bps raw throughput for MDC-4800 (nationwide coverage). Actual throughput about one half this rate. 19,200 bps raw throughput for RDLAP (limited coverage). Actual throughput about one half this rate. Network latency (round trip time) 4 to 10 seconds Modem vendors Motorola, IBM and Research in Motion. External, PC Card and OEM versions available. Service pricing Approximately 30 cents per KB depending on pricing plan. More information www.ardis.com for information about ARDIS. www.motorola.com for information about DataTAC technology (search on DataTAC in the home page). RAM Mobil e Data RAM Mobile Data is a joint venture between RAM Corporation and BellSouth. This wireless WAN is based on Mobitex technology which has been deployed in 17 countries worldwide. ITEM CHARACTERISTIC Service Providers RAM Mobile Data in the United States. Other carriers in foreign countries. Coverage Coverage extends to 93 percent of U.S. business population. Spectrum 10 to 30 12.5-KHz channels available per city. Current markets Mostly vertical. Increasing number of horizontal market applications becoming available. Value-added services E-mail, Internet and fax gateways: Radiomail (Radiomail) at www.radiomail.net Wynd Communications (Wynd-Mail) at www.wynd.net DTS Wireless (Zap-It) at www.dtswireless.com GoAmerica (GoAmerica) at www.goamerica.com Interactive paging using the Inter@ctive pager from Research in Motion. Best applications Ones using short and bursty messages. Architecture Based on Mobitex technology, controlled by the Mobitex Operators Association. A hierarchical network where base stations connect to local switches that connect to regional switches that connect to the main exchange. Customers' fixed-end systems connect to local switches. Protocols ROSI airlink protocol with GMSK modulation. Network layer called MPAK (Mobitex Packets). Fixed-end connections typically over X.25 links. Data throughput 8,000 bps raw throughput. Actual throughput is about one half this rate. Latency (round trip) 4 to 8 seconds Modem vendors Ericsson, IBM, Motorola, Research in Motion and US Robotics. External, PC Card and OEM versions available. Service pricing Approx. 25 to 30 cents per KB depending on pricing plan. More information www.ram-wireless.com for information about RAM Mobile Data Metricom Ricochet Metricom operates a packet data network using unlicensed bands. Service is oriented towards consumers, offering flat rate pricing for access to the Internet. Service is currently available only in a small number of geographic areas. ITEM CHARACTERISTIC Service Providers Metricom Coverage Metropolitan coverage in the San Francisco bay area, Seattle, and Washington DC. Coverage also available at various educational and corporate campuses. Spectrum Uses unlicensed Industrial Scientific and Medical (ISM) bands in the 902 to 928 MHz band. Other frequencies planned for future deployment. Current markets Mostly consumer and horizontal business markets. Value added services Standard account includes Internet access, newsgroups and an e-mail account. Additional services include: modem gateways through a service called Telephone modem access (TMA) and dial-in Internet access. Best applications Any Internet or modem-based application that operates reasonably at a maximum speed of 28.8 Kbps. Architecture Small base station equipment is attached to light poles throughout the coverage area. Base stations forward packets to other base stations eventually reaching a base station that has a fixed connection to the Metricom infrastructure. Protocols For Internet conn ections, PPP is used between the mobile computer and a router in the Metricom infrastructure to transport IP datagrams. Data throughput 100 Kbps raw channel throughput with up to 28.8 Kbps actual throughput. Metricom promises higher throughput for the future. Latency (round trip) Typically less than 1 second. Modem vendors Metricom Service pricing Approximately $30.00 per month for unlimited Internet access. More information http://www.metricom.com/ for information about Metricom. Paging (One way and two way) Though paging has not been the focus of our discussion above, it deserves a quick overview because paging networks allow certain types of data to be delivered in a very efficient and cost-effective manner. A variety of paging systems have been available over the last couple of decades, including ones that delivered single tones (effectively one bit of information), analog voice messages; numeric messages (most common today); and most recently alphanumeric messages. The most recent innovations in paging include two-way paging networks, such as SkyTel 2-Way (www.skytel.com), and digital voice messaging, such as PageNet's VoiceNow (www.pagenet.com). Paging systems are characterized by: Small device size, most pagers being smaller than other kinds of wireless modems. Long battery life, with an AAA battery providing weeks of service. Limited capacity, with 500 characters usually the maximum practical message size. High latency, with messages potentially taking minutes or longer to be delivered. Queuing through carrier message systems which store and forward messages. Paging applications cannot use conventional networking protocols and real -time connections on and end-to-end basis are not possible. One-way systems are not completely reliable, since there is no acknowledgment from the receiver. Paging companies design their systems for ninety percent or greater reliability. Two-way networks offer higher reliability and message storage while the pager is off our out of coverage. For more information, see Making the Call with Two-Way Paging , Peter Rysavy, Network Computing, January 15 1997. Enhanced Specialized Mobile Radio (ESMR) ESMR refers to new digital versions of Specialized Mobile Radio (SMR). SMR service, the precursor to ESMR, is provided by smaller operators offering dispatch types of services over relatively limited coverage areas. These service typically consists of "push to talk" analog voice communications used by the customers such as couriers, taxi fleets and construction companies. ESMR requires more expensive infrastructure than SMR, but once deployed can deliver more flexible services to more customers at lower cost. As a consequence, large ESMR operators such as Nextel have been buying out smaller SMR companies to deploy nationwide networks. The two largest ESMR companies in the United States are Nextel using a TDMA technology from Motorola called Integrated Dispatch Enhanced Network (iDEN) and Geotek, using technology based on frequency hopping spread spectrum. Nextel does not offer any data service, though it plans to do so in the future. Geotek (www.geotek.com) offers IP-based packet data operating at a raw throughput of 4,800 bps as part of an integrated dispatch solution. Satellite People have used satellites to communicate data for decades, though most communications involves fixed earth stations communicating with geostationary satellites. Only recently has it become practical to communicate data using mobile stations. Tod ay, the smallest such mobile terminal is about the size of a brief case, but that is about to change with the deployment of some half dozen different low earth orbiting (LEO) networks. These LEO networks use a larger number of satellites in orbits much closer to earth than geostationary systems. For example, Iridium will use 66 satellites at an altitude of 420 miles, compared to a typical geostationary system today that uses three satellites at an altitude of 22,300 miles. The shorter distances will substantially reduce time delays and the amount of power required for transmissions. Handheld satellite telephones will be possible for the first time. Most mobile satellite services will emphasize voice communications, usually as an extension of terrestrial voice networks. Telephones will look like today's cellular phones, and will be able to both connect to local cellular systems if available and automatically connect to a satellite in remote areas. Globalstar expects to charge about $1.00 per minute for voice and data communications. Since data services will use voice channels, data rates for these networks will fall in the range of 4,800 bps to 9,600 bps. Carriers will offer both circuit-switched and packet-switched data services, as well as paging. Initial satellites for some of these networks were launched in 1997, but full commercial service will not be available until late 1998 or 1999 for the first of these systems. Other satellite systems now on the drawing boards will not be deployed until the next millennium. Future wireless broadband services Filled with plans and grand ambitions, a large number of companies are investigating wireless broadband services. (A limited number have already been deployed.) These will offer data rates from ISDN speeds (64 Kbps) through to ATM rates (155 Mbps) and higher. Services include Mulichannel Multipoint Distribution Service (MMDS), for which spectrum is currently available, and Local Multipoint Distribution Ser vice (LDMS), for which extremely large blocks of spectrum in excess of 1 GHz will soon be auctioned, and next generation microwave systems that will apply cellular techniques to licensed microwave bands (e.g. 38 GHz) to optimize capacity. For the most part, providers are targeting these services for companies seeking high-speed Internet access or bypass of the local telephone company and are not targeting individual or mobile users. Another contender in this space will be broadband satellite services such as Teledesic whose major differentiating feature will be providing high-speed data services (to 2 Mbps) to fixed terminals anywhere in the world. Such service should prove attractive for developing nations or industrial operations in remote locations. In the mobile area, look to an international standards effort to develop third-generation cellular technology, called IMT-2000. Present digital cellular and PCS standards (CDMA, TDMA, GSM) are considered second-generation systems, with analog cellular being the first generation. The goal of IMT-2000 is to standardize on one technology worldwide by the year 2000, and to provide a mobile data rate of 144 Kbps, a portable data rate of 384 Kbps and an in-building fixed data rate of 2 Mbps. Given that second-generation networks are only now being deployed on a broad scale, third-generation systems will most likely not see the light of day until well into the next decade. Introduction Planning Protocols and Interfaces Hardware Wireless Middleware Profile of Wireless Networks Integration Updated September 30, 1997 Print This Page E-mail this URL