There are two classes of ISDN adapters: (1) parallel bus devices, supported by NDIS WAN drivers, and (2) serial port devices, supported by Unimodem with INFs. This section addresses serial ISDN modems.
For a general discussion of ISDN and a list of requirements related to parallel bus devices, see the “Network Communications” chapter in Part 4 of this guide.
ISDN modems share the following features:
ISDN modems also share the following differences from wireline PSTN modems:
20. ISDN modem supports required command set
| Required |
An ISDN modem must support basic AT commands (TIA-602, which is a subset of ITU V.25ter). Also, commands to set the switch type and SPID for user selection or if auto-detection fails must be included. This can be implemented in the device or in the communications driver.
21. ISDN modem supports auto-SPID detection algorithms and standard SPID format
Required
An ISDN modem must include commands or means to support software-based automatic switch type and SPID detection using the algorithms as defined by the National ISDN User’s Forum (NIUF) in 1997 Version of National ISDN Basic Rate Interface Terminal Equipment Generic Guidelines. This eliminates the need for the end user to enter the SPIDs.
An ISDN modem must include commands or means to support software-based automatic switch type and SPID detection using the algorithms defined by NIUF. This eliminates the need for the end user to enter the SPIDs and enhances the Plug and Play experience for users.
This requirement applies only in the United States.
22. ISDN modem supports CHAP in firmware if B channels are not exposed
Required
Recommended: Support MS-CHAP.
If the ISDN modem implements support for multilink point-to-point protocol (PPP), it must also support Challenge Handshake Authentication Protocol (CHAP). Supporting multilink PPP on an ISDN modem requires the devices to authenticate the second call themselves.
The remote access server uses CHAP to negotiate the most secure form of encrypted authentication supported by both server and client.
23. ISDN modem exposes both B channels
Recommended
ISDN modems should expose both B channels so that they can support the multilink PPP stack.
External ISDN modems should be on port fast enough to expose the full bandwidth of both B channels, that is, USB. Providing two separate COM-port cables is not an acceptable solution.
24. ISDN modem supports multilink PPP
Recommended
Multilink PPP as defined in RFC 1717 combines several ISDN B channels to increase the bandwidth of PPP links.
Windows and Windows NT operating systems include support for multilink PPP. When using ISDN modems that appear as modems to the operating system, multilink PPP must be implemented in the device. This is because Windows cannot see both B channels of the ISDN connection unless each B channel is exposed as a COM port.
See also the “ISDN modem supports CHAP in firmware if B channels are not exposed” requirement earlier in this section.
This recommendation is for ISDN modems only. Internal ISDN devices with NDIS WAN miniport drivers benefit from the built-in multilink support provided by the remote access services of the operating system, and therefore do not need to provide multilink PPP support.
25. ISDN modem supports asynchronous-to-synchronous conversion
Required
These types of ISDN devices are treated as modems, not as internal ISDN devices supported using NDIS WAN miniports. In the external case, the primary implication is that the operating system will send byte-level PPP (also known as asynchronous PPP). In the NDIS WAN case, the implication is that the operating system will send bit-level PPP (also known as synchronous PPP).
Because ISDN is a synchronous service and an ISDN modem connects to an asynchronous port on the PC, the device must provide some means of converting asynchronous data to synchronous data.
26. ISDN modem uses high-speed port
Recommended
Because of speed limitations inherent in a PC’s COM ports, the connection for ISDN modems should be high-speed, such as USB.
27. ISDN driver supports switch detection
Recommended
The driver can attempt to determine the switch type based on the directory number, or it can use other proprietary solutions to determine the switch type. This enhances the Plug and Play experience for users.
28. ISDN driver supports unattended installation, with limitations
Required
ISDN devices must be capable of being installed without user intervention. The exception is specific ISDN parameters, which must be acquired from the equipment being connected to. Dependent parameters include SPIDs and switch-type IDs.