Design Issues for Server Modems

For modems designed for Basic servers, the most important additional design issues are:

• Support for V.90, as host side modems where possible, which requires an ISDN or other digital network connection.
  
  
• Support synchronous PPP, using V.8bis and V.80.
  
  
• Do not migrate the modem signaling function, for example, V.90 or V.34, into the system.

For SOHO Server modems, the most important design issues are:

• SOHO Server modems must support adaptive answering features: V.8, V.8bis, V.251.
  
  
• Full duplex voice strongly recommended, using V.253, to support small scale Interactive Voice Response.

For Enterprise Server modems, the most important design issues are:

• The NDIS 5.0 miniport interface is preferred.
  
  
• Fax is optional, not mandatory, because the most common solutions use separate hardware and drivers, on separate public network connections.

System includes modem communications device

Recommended

The following device options, as defined later in this chapter, can meet this requirement:

• Serial modem with V.34 and V.90 56K ITU capabilities, supporting server fax capabilities (two or more ports recommended)
  
  
• ISDN adapter
  
  
• ATM adapter
  
  
• ADSL adapter

Modem supports ITU-T V.250, Hayes-compatible command set

Required

ITU V.250 (formerly V.25 ter) is a superset of TIA-602. TIA-602 codifies the most common data modem commands and responses.

V.250 also includes two additional components:

• A standard format for extending the AT command set, with standard means for the system to test the range of supported values for each command. This format enables adaptive modem installation.
  
  
• Standard extensions for modem ID, port control, modulation control and reporting, error control, and data compression control and reporting. Use of these extensions can reduce or eliminate the need for data modem INF files.

The essential V.250 commands are the following:

• All basic modem commands from TIA-602
  
  
• Identification: +GMI, +GMM, +GMR
  
  
• Port control: +IPR, +ICF, +IFC, +Ilrr
  
  
• Modulation: +MS, +MR, +MA
  
  
• Error control: +ES, +ER, +EB, +ESR, +ETBM
  
  
• Data compression: +DS, +DR

The particular utility of the standard format is that it allows a future modem installer to adaptively install and use a modem with minimal need for INF minidrivers.

Data modem supports PCM (V.90) with V.42 and V.42bis protocol

Required

This is the minimum modem capability specified in this guide.

Data modem supports digital connection to support host-side V.90 operation

V.90 depends on a digital connection for the host-side modem to the public telephone network, typically using T1 or ISDN. Server modems should be designed for digital connection, to support host side V.90, where digital connections are available.

Fax modem supports 14.4 Kbps (V.17) with Class 1 (TIA-578-A) command set

Required

The following are recommended:

• Class 1.0 (ITU T.31) with +FAR support, which allows the hardware to perform adaptive carrier detection
  
  
• Class 2.0 (ITU T.32 or TIA-592) for server modems, which offloads the T.30 session protocol to the modem

Fax modem supports adaptive DATA/FAX call classification based on T.32 +FAA

Required

The adaptive DATA/FAX call classification must be based on the Class 2.0 +FAA command or equivalent proprietary +FAE command. This allows a server to handle remote access calls and inbound FAX calls on the same lines.

Windows NT 5.0 and future versions of Microsoft BackOffice® products will support Class 1.0 and Class 2.0 fax modems, and use adaptive call-classification support. To benefit from this support, modem vendors should extend their modem INFs to support the new registry keys needed to support these features, as defined in the MDK.

Data modem supports V.80 for synchronous access

Required

This standard provides a control plane for the modem and synchronous access to the data path—the foundation for third-party voice/data/video software, for example, H.324 and V.70. Modems that support V.80 must also include V.8bis signaling and V.251 as described in requirement #85, “Modem supports adaptive connection, V.25, V.8, and V.8bis call control signaling with V.251 modem commands.”

Modem supports adaptive connection, V.25, V.8, and V.8bis call control signaling with V.251 modem commands

Required

V.25 defines basic call-type selection, with an answer tone, a fax-calling tone, and a data-calling tone. V.8 defines advanced call-type selection, with complex information exchanged between terminals; V.8 is used in V.34, V.90, and some digital simultaneous voice/data (DSVD) implementations. V.8bis is required for standard multimedia modes, such as V.61 ASVD, V.70 DSVD, and H.324 video telephony, and to negotiate point-to-point synchronous PPP, supporting H.323.

V.251 enables the computer to participate in call control, allowing flexibility and a visual user interface, as well as saving modem complexity. V.251 requires DCE-controlled operation; in addition, DTE-controlled operation is recommended.

Modem supports blacklisted and delayed number clearing

Required where applicable

During certain international Post, Telephone, and Telegraph (PTT) certification processes, modems must support the blacklisted and delayed numbers feature. That means that when the modem fails to connect to a specific number for a certain number of times, the dialed number is stored in an internal list. Any subsequent automated dialing operation to this number is then either delayed for a time (delayed) or forbidden until some form of manual intervention occurs (blacklisted). The international certification processes specify that manual intervention using an external device is required in order to clear these numbers.

The modem should clear its blacklisted and delayed number tables if the associated handset goes off hook.

Modem supports TDD, meeting V.18-1996 with V.250 AT commands

Recommended

People with deafness or reduced hearing can use Telephone Device for the Deaf (TDD), also known as Text Telephones, to communicate over phone lines. The U.S. Americans with Disabilities Act (ADA) 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:

• Baudot: 45 or 50 bps Frequency-Shift-Keyed (FSK) and 5-bit Baudot coding
  
  
• ASCII: 300 bps Bell 103 and 7-bit ASCII coding
  
  
• European Deaf Telephone (EDT): 110 bps half-duplex V.21 and 7-bit coding
  
  
• Minitel: V.23 modems and 7-bit coding
  
  
• Modems and 7-bit coding
  
  
• DTMF: 2-digit or 3-digit character coding

The International Telecommunications Union (ITU) recommendation V.18 codifies how all 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.

Text Telephone capability should be included for the type of modem commonly used in the country of sale and use, for example, Baudot in the United States, Minitel in France, and so on.

Modem controller meets minimum requirements

Required

The following are minimum requirements for the modem controller, in addition to supporting V.250:

• Unimodem Diagnostics command, AT#UD
  
  
• Software-upgradable modem controller (upgradable ROM or Windows modem)
  
  
• AT command buffer of at least 60 characters
  
  
• Semicolon (;) character dial string modifier, unless prohibited by national regulations

Voice modem support is provided

Voice capability is recommended for SOHO server modems to support Interactive Voice Response and 3-way DATA/FAX/Voice call classification on the same phone lines. This support, if implemented, must meet the requirements documented in requirement #94, “Voice modem supports ITU V.253 (AT+V).”

Voice modem supports ITU V.253 (AT+V)

Required

TIA IS-101-1994, the Interim Standard for Voice DCE, has been superseded by TIA-695 and ITU V.253-1998.

Voice capability is not mandatory, but if support for voice modem is implemented in a server system, it must meet the following requirements:

• V.253 compliance
  
  
• Voice recording and playback (+VTX, +VRX)
  
  
• DTMF generation and detection during voice I/O
  
  
• Voice I/O support of 8-bit, 8-kHz PCM formats: unsigned linear, G.711 (A-law and u-law)
  
  
• Programmable gain control for all audio channels
  
  
• Speakerphone with automatic training (no user intervention)
  
  
• Voice I/O to the handset (for voice-only devices)
  
  
• Duplex voice, to support IP telephony and IVR
  
  
• Caller ID Detection and Reporting (+VCID)