Wireless Communications and Mobile Computers

Editors’ Note: John Jerney, a software developer and free-lance writer specializing in network and communications technologies, develops software for both PenPoint and Windows for Pen Computing. While John covers some material that we have presented in previous issues, he provides some additional details as well as a valuable perspective on the recent AT&T/GO announcement. He can be contacted at P.O. Box 160098, Cupertino, CA 95016.

One of the goals usually associated with the new field of pen computing is to make the technology as easy and accessible as a pad of paper and a pen. However, as people begin to use these new computers, a number of new requirements become evident. These include integrating portable computers into existing networks and gaining access to data and resources that are available on desktop computers.

At the Pen Expo held June 1-4, 1992 (Santa Clara, CA), a number of interesting wireless communication technologies were presented. Wireless communications can take several forms. In this article, I’ll examine two radio frequency (RF) data networks — ARDIS and RAM Mobile Data — along with an infrared solution by Photonics Corp, all of which have been previously covered in this newsletter. I’ll also examine the announcement concerning the development relationship between GO Corp. and AT&T Microelectronics.

Like their wire-based cousins, wireless networks rely on two models of connectivity: circuit-switched and packet-switched. Circuit-switched networks establish a connection between the communicating stations and maintain it for the duration of the data exchange. This method of connectivity is used by the phone system and is well suited for voice communication, however it can be adapted for data exchange as well. Charges are based on the connection time, independent of the amount of data exchanged.

Packet-switched networks break the data into chunks called packets. Each packet is individually addressed and transmitted to the destination station. This method is similar to the handling of mail by the postal service and is frequently referred to as a datagram service. Charges are calculated by the number of packets sent, not the time used to transmit the data across the network.

Circuit-switched networks have the disadvantage of requiring an orderly connection setup and teardown, but once the connection is established, data transfer can occur with minimum overhead. This makes circuit-switched networks particularly suitable for the transfer of large data files. In contrast, packet-switched networks introduce a noticeable overhead because each packet must be individually addressed and delivered. However, since no connections need to be established and maintained (and charged for), packet-switching is ideal for short bursty traffic such as an interactive terminal session, or the exchange of regular-sized (1-2 KB) electronic mail messages. An important consideration for people using the wireless networks in several locations across the nation is known as “nationwide roaming.” Seamless nationwide roaming permits users to access the wireless network automatically in all supported metropolitan areas. This is done by associating network addresses with users, not locations. The network determines the users in any region and permits them to access the network immediately upon entering a new area.

RF Communications

Two radio frequency data networks were described at a session focusing on the connectivity issues for pen computers: ARDIS and RAM Mobile Data. Both are metropolitan area services that use a packet-switching technology to exchange data between mobile stations.

ARDIS (Advanced Radio Data Information Service) is a joint venture between Motorola and IBM. Motorola developed the packet switching network under contract to IBM for use by IBM’s field service technicians. Support was initially provided within major metropolitan areas, however, since the service was expanded for public use in 1990, the number of regions has grown to over 300, many more than its competitors.

Regions supported by ARDIS are known as Metropolitan Statistical Areas (MSA) and most MSAs rely on single 4800-baud channels based on proprietary communication protocols. The RF modems used to access the ARDIS network are supplied by Motorola. While ARDIS provides very high quality in-building service, it does not support seamless nationwide roaming.

The maximum packet size in the ARDIS network is 256 bytes long. ARDIS charges 4 cents for each 100 characters transmitted and includes a minimum monthly charge of $32. ARDIS’ most significant competitor is RAM Mobile Data, which is a joint venture between RAM Broadcasting Corp. and Bell South Enterprises Inc. and began operations in February 1991. The number of MSAs supported is less than 50 — however, unlike the ARDIS network, each MSA has between 10 and 30 channels for communication. This translates to a greater amount of data transfer within a particular region.

The RAM Mobile Data Network uses a technology known as Mobitex which provides the packet-switched wireless network. Mobitex is becoming an international standard with networks deployed in several countries including the United States, Canada, the United Kingdom, Sweden, Norway, and Finland. The equipment used by the Mobitex system is supplied by Ericsson, the giant Swedish multinational communications firm. Mobitex permits seamless nationwide roaming and uses packet protocols that are publicly available, permitting multiple vendors to supply modems and terminals, including Gandalf, Kustom, Telxon, and Husky.

Pen computers can exchange data on the network using the Mobidem Portable Wireless Modem supplied by Ericsson GE Mobile Communications Inc. The Mobidem is an external 8 kbps packet radio modem that weighs 1 pound and attaches to the RS-232 serial port of the pen computer. The cost of using the RAM Mobile Data Network is $15-$30 per month plus the packet charges. The packet charges vary depending on the number of characters in the packet. These rates range from 3 cents for a single character to 12.5 cents for 488 to 512 characters per packet.

Infrared Communications

Photonics Corporation (Campbell, CA) was on hand to present its Infrared Transceiver, a part of a family of products known as COLLABORATE. It will provide wireless connectivity for both GO Corp.’s PenPoint and Microsoft Corp.’s Windows for Pen Computing.

The transceiver can be used in three types of settings: collaborative computing among several mobile computer users in a room, communications between mobile and desktop computers, and collaborative access points used to reach a LAN within a building.

The Infrared Transceiver employs a method of diffuse infrared transmission that doesn’t require it to be directly pointed or operated on a line-of-sight basis. Instead, light is bounced off the walls of the room making it very difficult to block the signal.

The unit measures 2-x-2 inches and has a small window that allows data to be transmitted and received. The unit is also available to OEMs, enabling the technology to be integrated directly into the motherboard or a proprietary internal slot of a pen-based computer. Photonics states that commercial release is scheduled for first quarter 1993.

Photonics claims that the Infrared Transceiver requires a small amount of power, thereby minimizing its effect on the already precious battery power in notebook and pen computers. During their own tests, they found that the unit is idle approximately 90 percent of the time, receives data 9% of the time, and transmits during the remaining 1 percent. Through the use of power management, they are able to reduce the power requirements during the idle states.

A typical use of the Infrared Transceiver would be to establish a troublefree connection with a regular wire-based local area network. In addition to COLLABORATIVE Port, a parallel port adapter for portable computers, Photonics will supply an ISA or EISA PC adapter known as COLLABORATIVE PC that has a tethered transceiver for use in a desktop workstation. COLLABORATIVE Access will also be available to permit a direct connection to the network. These units can be placed on a ceiling and link the infrared front-end to a wired 10-BaseT (unshielded twisted pair Ethernet) connection in the access unit. This enables the mobile unit to gain access to the wired local area network. To enhance connectivity to industry standard networks, Photonics will provide drivers for Novell NetWare, Microsoft LAN Manager, and TCP/IP-based networks.

The Infrared Transceiver operates at a speed of 1 Mbps and uses a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) system to provide the media access to the network. Media access techniques reside in the data link layer of the OSI Reference Model, and are important because they control the station’s access to the shared network medium (the wire or the wireless signal). Media access methods control who can communicate over the channel at a given time, preventing every station from transmitting data at the same time.

The transceiver uses a light emitting diode (LED) to produce the light signal. LEDs are safe and have the additional advantage of not being susceptible to electromagnetic or radio frequency interference. Another advantage of using light is that unlike radio transmission, no national agency requires a license for data transmission. This allows the system to be used freely throughout the world. In comparison, radio frequencies are tightly controlled and allocated.

Photonics says that it plans to introduce an Infrared Transceiver as a PCMCIA (Personal Computer Memory Card International Association) card in second quarter 1993. The card will come in two versions. The first is called Type II, and will feature a tethered connection to the Infrared Transceiver. The second version is called Type IIe and will feature the entire unit on the PCMCIA card.

Personal Communicators

In the months following the Pen Expo, several announcements concerning wireless communications have been made. I believe one deserves special attention. In a glimpse of the future, AT&T Microelectronics (AT&T-ME) and GO Corp. announced at the Mobile ’92 Conference on July 13, 1992, that they are forming a development relationship to create an open platform for what they identify as the “personal communicator” market. The alliance plans to optimize GO’s PenPoint operating system to work with AT&T-ME’s new line of RISC microprocessors, code-named Hobbit.

The Hobbit is a 3.3 volt RISC processor designed to integrate well with digital signal processing (DSP) modules. It was designed and developed at AT&T Bell Labs, and uses an architecture known as CRISP (C-Language Rational Instruction Set Processor). The Hobbit is designed to support fast context switching, fast response to interrupts, and low activity on the system bus. These features will permit personal communicators to operate in an environment that can have a user taking notes on screen, while the system is sending, receiving, or processing communication messages.

GO’s PenPoint is well-suited as the operating system and interface to a new line of wireless communicators. The architecture was designed to support the model of asynchronous communications (through its deferred input/output architecture), along with intermittent connections that are frequently the operating conditions for mobile computers. Moving PenPoint to the Hobbit architecture chiefly involves modifying the Machine Interface Layer (MIL) that decouples the operating system from the underlying hardware.

The personal communicators will focus on sending and receiving voice, data, handwriting, fax, images, and in the future, full-motion video. Personal communicators will include support for connecting to AT&T’s long distance telephone network and exchanging electronic mail using AT&T’s EasyLink electronic mail network. In their marketing literature, GO and AT&T-ME present a sketchy overview of several hypothetical products. These include devices such as the Tablet Communicator, the Office Phone-Pad, and the Travel Companion which integrate pen-based input with interpersonal voice, mail, and fax communications. Each of these devices rely on a standard RJ-11 connection to the phone network. More interesting are the wireless products envisioned. These include:

• The CellPad, a folding notepad-sized device that integrates a cellular phone. Using a DSP, the system will send and receive voice messages, and can act as a mobile answering machine. The InBox and OutBox features of PenPoint will permit email and fax messages to be sent and received.

• The NotePhone, a small unit that will combine a cellular phone with a screen to display information and capture electronic ink. The form will be similar to present flip-open cellular phones. In place of the conventional keypad, users will be able to use the screen to place calls and review voice mail. Notes that are written on the screen can be sent though a wireless electronic mail network. Consideration has also been given to receiving pager information on the screen.

• The PowerPhone, a desk unit with a removable tablet and built-in thermal printer. The unit will contain a cellular phone, and will support email, fax, and voice messaging. The base unit itself can be directly attached to the wired phone network.

• Video FlipPhone, projected for the year 2000, this device is envisioned to have a wireless phone and a touch screen that will display a caller on the screen enabling a personal video conference. The unit will also incorporate a voice recognition system. Perhaps in anticipation of the recent FCC ruling to allow Regional Bell Operating Companies (RBOCs) to transmit television programming over the phone system, the description of the Video FlipPhone includes a reference to watching a ballgame on the small screen.

In its marketing literature, AT&T Microelectronics and GO talk about the importance of establishing both local and wide-area wireless connections. In the list, they include references to both infrared and packet radio networks (such as ARDIS and RAM Mobile Data), however no timetable has been supplied concerning any personal communicator products and options.

Everyone interested in pen computing knows about GO, but who exactly is AT&T Microelectronics? As you might expect, AT&T-ME is a multibillion dollar business unit of AT&T, and one of six units in the AT&T Network Systems Group. AT&T-ME designs and manufactures electronic and photonic components for both AT&T and other telecommunications companies. The products they develop include digital signal processors, 3.3 volt ASICs (Application Specific Integrated Circuits), laser and LED subsystems, and the first V.32 modem chip set.

AT&T-ME has three design centers in the United States: Allentown PA, Reading PA, and Sunnyvale CA. AT&T-ME recently formed the new Personal Communication Systems (PCS) business unit, located in Sunnyvale, which will design and manufacture personal communicators.

What Does All This Mean?

Standalone mobile computers will become as desirable in the ’90s as standalone PCs did in the ’80s. Today, the fastest growing segment of the computer industry is network computing. Connecting mobile computers to existing LANs and enterprise networks will become a major field and products such as the Photonics Infrared Transceiver will play a key role in providing this link.

However, now that powerful computers have broken their desktop bounds, the opportunity for truly revolutionary communications is at hand. This will extend the model of computer-to-computer communications as we know it today to interpersonal communications, where everything and everyone is reachable. And because people will have powerful information retrieval and processing devices on hand at all times, the much used phrase of “anywhere, anytime” will be expanded to include “anything.”

Certainly one of the prerequisites for this new paradigm is a solid, ubiquitous wireless communications infrastructure. RF data networks such as ARDIS and RAM Mobile Data are the important early innovators. In addition to the network, mobile computers must be designed and built to support the style of computing that wireless communications will bring.

With the AT&T-ME and GO announcement coming after what seems like an avalanche of announcements from most every other vendor, this announcement can be viewed as either an important signal, or simply another me-too announcement. I think the former is correct. GO has demonstrated a clear commitment to developing a truly mobile architecture centered around its pen-based notebook model. This announcement also signifies that a company with the strength and presence of AT&T sees PenPoint as a powerful vehicle for delivering advanced communications devices to millions of mobile professionals.

In view of IBM’s newly expressed interest in expanding its efforts to bring pen-based technologies into the OS/2 fold, this alliance is a timely one for GO. Likewise for AT&T, the selection of PenPoint brings a degree of concreteness to its vision for personal communicators.