This section defines requirements for basic hardware features.
2. Modem command set: TIA-602, "Hayes compatible"
| Required |
TIA-602 codifies the most common data modem.
Recommended: ITU V.25ter, which is a superset of TIA-602 with significant and useful improvements. It includes three new components:
The particular utility of the standard format is that it allows a future modem installer to adaptively install and use a modem without need for INF minidrivers.
3. Data modem: 28.8 Kbps (V.34-1994) with V.42 and V.42bis protocol
| Required |
Recommended: 33.6 Kbps (V.34-1996).
The dominant use of data modems now is connection to Internet service providers. Web browsing is bandwidth intensive, so the more available the better.
As part of the command set, the modem must have a distinct means for controlling the reporting of modem-to-modem protocols, so the modem can be forced to generate recognizable reports for modulation, error control, and data compression. Examples include the Wn command, the S95 register, the \Vn command, or the ITU V.25ter +MR, +ER, and +DR commands.
4. Synchronous access for data modems: V.80 or similar technique
| Recommended |
This recommendation can be implemented using V.80 or similar proprietary techniques that provide synchronous access to enable Videophone capabilities over PSTN. ITU V.80, a PC-to-modem protocol based on V.25ter, opens the door to support standard voice/data/video communication from PC software, at minimal cost to the modem maker. It also provides mechanisms to enhance the quality of service of Internet real-time multimedia services by defining standard means for multiplexing data and modem control messages on the same port at the same time, and providing synchronous access to the PC. V.80 includes the following components:
Note If implemented on both sides of a modem connection, V.80 can be used to increase the throughput of PPP or PPTP connections by 25 per cent (delete the start-stop bits). IETF is studying proposals to make use of V.80 for that purpose.
5. Fax modem: 14.4 Kbps (V.17) with Class 1 (TIA-578-A) command set
| Required |
Recommended: Class 1.0 (ITU T.31) with +FAR support, which allows the hardware to perform adaptive carrier detection.
Modems continue to be useful for fax communications, particularly for sending faxes and print-to-fax. The recent ITU version of this standard includes features for improved performance in the presence of echo delays. T.31 Annex B extends to support V.34 fax, but there are few V.34 fax machines available in 1996.
6. Telephone Device for the Deaf (TDD): V.18 with V.25ter command
| Recommended |
TDD is also known as Text Telephones. People who are hearing impaired use Text Telephones to communicate over phone lines with both hearing and hearing impaired persons. The U.S. Americans with Disabilities Act requires all businesses of a certain size or larger to have Text Telephone services available and to be able to receive calls from people using Text Telephones.
In North America and Europe, the following types of Text Telephones are used:
ITU recommendation V.18 codifies how all of these devices work and how to adaptively connect to all of them. ITU recommendation V.25ter contains AT commands for control of V.18 features in a modem.
It is recommended to include Text Telephone capability, for the type commonly used in the country of sale and use (for example, Baudot in the U.S., Minitel in France). ASCII (Bell 103), V.21, and V.23 modem capability are common in modems. Voice modems (IS-101 type) commonly contain the ability to do DTMF send and receive. Baudot and EDT can be implemented in software using voice modems and simple software signal processing. However, because the adaptive connection phase is difficult to implement in software, even on a voice modem, it is best to implement V.18 in the modem itself and expose that functionality to the PC using the V.25ter commands.