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Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

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IBM Wireless Modem for ARDIS

To interface with ARDIS, you can utilize the IBM Wireless Modem for ARDIS, which has a PCMCIA Type II form factor. This card can be installed internally in an IBM ThinkPad or externally with the optional External Battery Assist and tethered radio transceiver. The product also includes an external transceiver that you connect to the card via a cable. IBM also offers the modem in a form that fits into the floppy drive of a ThinkPad. The modem operates with a power output of 0.8 watts.

RAM Mobile Data

RAM Mobile Data is another alternative for wireless WAN connectivity. RAM covers the top 266 United States metropolitan areas plus airports and major transportation corridors. This includes more than 92 percent of the urban business population. RAM is committed to providing 100 percent coverage through RAM’s Strategic Network initiative. For example, a RAM user will be able to maintain connectivity through the use of circuit-switched cellular and satellite when traveling beyond RAM’s wireless WAN coverage area. In order to provide the Strategic Network, RAM has linked up with satellite service providers and telecommunications carriers to ensure a complete and seamless solution.

RAM Mobile Data utilizes Mobitex technology, which is an established and proven packet radio system for the transmission of data. Mobitex infrastructure was originally developed by L.M. Ericsson in 1983 in cooperation with Sweden’s Postal Telegraph and Telephone national communications authority. Mobitex today is seen as a de facto standard for packet-based wireless WANs. The Mobitex Operators Association (MOA) now manages Mobitex standards. There are currently 17 other wireless WANs throughout the world that use Mobitex technology, with more planned for 14 other countries.

RAM Mobile owns and operates its network and has licensed frequencies from the FCC with the 896–901 MHz and 935–940 MHz bands. RAM parcels these frequencies to give each metropolitan area up to 30 channels. Each channel supports a data transmission speed of 8 Kbps. RAM provides wireless connectivity to mobile users within specific service areas, then uses a regional switch to tie the service areas together.

The RAM Mobile Data network provides nationwide, transparent and seamless roaming. Subscribers do not have to manually intervene when moving from one service area to another. Each service area uses a different frequency, and the RAM modem automatically locates the best available channel and local switch. In addition, RAM does not charge fees for roaming.

RAM offers an e-mail service for sending and receiving messages with other RAM and Internet users. The service also enables you to utilize many other e-mail products. In fact, over 80% of all e-mail products have been RAM-enabled, meaning they will interface with the RAM wireless network. For example, Lotus cc:Mail, Microsoft Mail Remote for Windows, and Novell Groupwise support the RAM network.

IBM Wireless Modem for RAM

To interface with RAM Mobile’s network, you will need to obtain a compatible modem. IBM offers its Wireless Modem for RAM, which is housed in a PCMCIA Type III card. The modem operates from a self-contained battery and uses the portable computer’s battery for a continuous trickle-charge. The modem operates at 2 watts of output power and minimizes power consumption by using sleep and battery saving modes during operation. The IBM RAM modem was manufactured by Ericsson. The RAM card comes with ZAP-it software, which provides e-mail access to the Internet and fax capabilities.

Metricom

Another radio-based wireless WAN is Metricom’s Ricochet, which provides two-way multi-user data communications. For a relatively low price, Ricochet offers user throughput rates of 28.8 Mbps with unlimited data transmissions. The Ricochet network enables personal computer users to wirelessly access the Internet, America Online, Compuserve, and most other dial-up services from anywhere within a covered area.


NOTE:  

Although Ricochet’s current coverage is limited to the southern San Francisco area, Metricom is making large deals to expand their network. In 1995 Metricom agreed to form a joint venture with PepData, Inc., a subsidiary of Potomac Electric Power Company (PEPCO) of Washington, D.C., to deploy, own, and operate a wireless network providing data communications services to four million potential customers throughout the metropolitan D.C. area. As part of the joint venture agreement, Metricom is installing a network of poletop radios on street lights, power poles, and buildings to provide Metricom’s Ricochet wireless data communications service to residential, business, and governmental users. Metricom will supply the Ricochet technology, install the components, and operate the network.


The architecture of Ricochet is shown in figure 4.4. The concept is to use wireless access points and network radios (radio relays) on top of light poles and buildings approximately one half mile apart to facilitate connectivity between user appliances. The radios operate in the license-free (902-928 MHz) portion of the radio spectrum using frequency hopping spread spectrum modulation. Ricochet interfaces with the RS-232 port of a user appliance via Ricochet’s wireless radio modem, allowing it to work with any application that can interface with standard wireline modems. Ricochet implements standard AT modem command set as well as SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol) protocols for direct serial access to the Internet or any private TCP/IP-based LAN. The modem transmits the user’s data packets to the nearest poletop radio. The data packets then move through the mesh from poletop to poletop until they reach their final destination.


Figure 4.4  The architecture of Metricom’s Ricochet.


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