This section provides PC 98 requirements and recommendations for wireless and cellular modems.
18. Wireless support implemented for modems
Recommended
There is a variety of wireless modems and look-alike modems. These include the common types: North American analog cellular, global system for mobile communications (GSM) and other digital cellular systems, cellular digital packet data (CDPD), and so on. However, there are several other types, such as the Ricochet modem from Metricom.
Windows has registry keys that support analog cellular modems. Windows also supports data access in GSM and other wireless modem types. Participants in the Mobile Data Initiative are developing extensions for other services on digital cellular modems, as described in the following item.
For all wireless and cellular modems, the commands in TIA-678 are recommended. The +WS-46 command, which selects the wide area network (WAN), is required.
19. Digital cellular phone support is implemented for modems
Recommended
Digital cellular support is not a requirement, but if implemented, the following appropriate digital cellular control standards must be supported:
Unlike wireline data modems, these devices are not required to support V.34 signaling; it is not available. 9600 bps capability is required; higher speeds are recommended where available. Class 1.0 fax support is available on some of these devices, but it is not required; the error rates with transparent modem faxes are often very high.
Cellular telephone systems are widely deployed in the industrialized world and are now being deployed internationally. In North America, analog cellular systems (TIA-553) are currently predominant, although two types of digital cellular systems can also be deployed: code division multiplexed access (CDMA, TIA IS-95) and time division multiplexed access (TDMA, IS-136).
In Europe and the rest of the world, the GSM digital cellular system is widely deployed. In Europe, the infrastructure for data, fax, and short messaging is now in place.
For all three digital cellular systems, the system design has been extended to offer data, fax, voice, and short messaging service (SMS) to mobile users. In all cases, a modem pool is added to the ground stations, where connection is made to the PSTN. Access to the logical serial ports of these modems is made using the digital error-controlled radio link to the equipped mobile phone and is exposed on a serial port or associated PC Card.
Digital cellular communications equipment should default to using error correction on the radio link. For example, for GSM 7.07, the modem should initialize to +CBST=,,1 (which selects a “nontransparent” air interface).
The AT command sets for these digital cellular phone systems are contained in the following standards.
StandardCommand set
GSM 7.07GSM system: data, fax, voice
GSM 7.05GSM SMS
TIA IS-99North American CDMA: data and fax
TIA IS-135North American TDMA: data and fax
The TIA-678 +WS46 command has codes to indicate which system the modem is capable of. For example, the following values, quoted from Table 4 of the standard, are useful.
ValueSystem
1 Public telephone network (that is, a normal wireline modem)
4 Cellular Digital Packet Data (CDPD)
7 TIA-553 analog cellular system
10 Metricom Ricochet network
12 GSM digital cellular system
13 TIA IS-95 CDMA digital cellular
14 TIA IS-136 TDMA digital cellular (“PCS”)