This section summarizes requirements for ATM hardware.
The NDIS 5.0 extensions provide kernel-mode NDIS 5.0 client drivers with direct access to connection-oriented media such as ATM. The new architecture for Windows NT extends native ATM support to Windows Sockets 2.0 (WinSock), Telephony API (TAPI), and applications based on Microsoft DirectShow™ by providing system-level components that map the applicable WinSock, TAPI, and DirectShow APIs to NDIS 5.0, extending direct ATM access to user-mode applications.
ATM is not required for any of the server classes. If an ATM adapter is designed for operation under Windows NT in the server system, it must meet the requirements defined in this section. For more details about the following requirements, see “ATM Layer Specification” in ATM User-Network Interface Specification, Version 3.1. This specification also includes references to other relevant specifications.
Required
The following network device requirements must be met:
Required
The VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier) ranges supported by the adapter affect the maximum number of simultaneous connections supported on a system.
This affects the applicability of the adapter to ATM applications such as LAN Emulation, where at least one dedicated virtual channel is created between each pair of communicating ATM hosts.
| System type | Simultaneous connections |
| Client (ATM adapter) | 64 or more |
| Client (Integrated ATM/ADSL-adapter) | 16 or more |
| Server | 2048 or more |
A sample driver is provided in the Windows NT DDK to guide developers in properly supporting resources to meet this requirement.
| Windows NT Server | Enterprise Edition | Small Business Server | |
| Basic Server: | Recommended | Required | Recommended |
| Enterprise: | Recommended | Required | Recommended |
| SOHO: | Recommended | Required | Recommended |
The ATM adapter should support the constant bit rate (CBR), variable bit rate (VBR), available bit rate (ABR), and unspecified bit rate (UBR) service types as defined by the ATM Forum.
Required
UBR is used by default for standard ATM services such as LAN Emulation and IP over ATM. In addition, PPP is a widely used model for residential network access and UBR is used by default for PPP over ATM virtual circuits. Therefore, it is required that ATM adapters support the UBR service type.
Required
Support for at least two simultaneously active VBR or CBR connections is required for basic ATM signaling and management.
Support for additional VBR/CBR connections is needed for ATM adapters that support multimedia or other traffic that demands Quality of Service (QoS). These are listed in the following table.
| System type | Simultaneous active VBR/CBR connections |
| Client | 6 |
| Server | 500 |
Required
The ATM adapter must support and enforce all the traffic-shaping rules specified for each service type it supports, including CBR, VBR, ABR, and UBR.
Note: This includes enforcement of peak cell rate on UBR virtual circuits.
Required
ATM adapters will be used to connect router, remote access, and content servers to the public ATM network. High-speed residential broadband access networks such as ADSL and cable modem will use an ATM virtual circuit from home or small office computers to connect directly to these servers. When the Windows Dial-Up Networking UI is used to connect from a home or small business computer to a remote router or server, a PPP link is established over an ATM virtual circuit.
The service type used on this PPP over ATM virtual circuit is unspecified bit rate (UBR). When creating the UBR virtual circuit, Windows will request upstream and downstream line rates, or Peak Cell Rates (PCR), equal to the upstream and downstream line rates provisioned for the user. Windows uses the ATM Interim Local Management Interface (ILMI) protocol to obtain information, such as getting the user’s provisioned line rates from the public network.
To avoid packet loss and ensure efficient network utilization, it is critical that all ATM, integrated ATM/ADSL adapters, or ATM/cable modem adapters enforce requested PCR on UBR virtual circuits.
Because any ATM adapter might be installed in a server to which clients connect through the public network, this requirement applies to all ATM adapters.
Required
When connected to a residential broadband network, ATM adapters must restrict the aggregate transmission rate across all active virtual circuits so that it does not exceed the provisioned upstream bandwidth of the residential broadband network.
All integrated ATM/ADSL and ATM/cable modem adapters must support aggregate shaping of upstream bandwidth according to the provisioned upstream bandwidth or the trained bandwidth, whichever is lower. Some implementations can support rate adaptation, and lower than provisioned rates may be negotiated due to poor line conditions. All 25-Mbps ATM adapters must support this as well, because any 25-Mbps ATM adapter could be used to connect by way of an external ADSL modem to an ADSL network. This support is optional for ATM adapters with line rates higher than 25 Mbps.
The Windows ATM Call Manager uses ILMI to query the public network to discover the provisioned maximum line rates for incoming and outgoing traffic. The Call Manager then uses the OID_GEN_CO_LINK_SPEED NDIS request (in SET mode) to set the line rate for both incoming and outgoing traffic. The adapter must shape the aggregate of ATM traffic within these incoming and outgoing rates.
Required
Operation and maintenance (OAM) is needed for diagnostics. This capability is required for a server system. At minimum, the ATM adapter must respond to received F4 and F5 loopback OAM cells. Support for other layers, F1–F3 is optional.
Required
This feature is needed for large packets. This capability is required for server systems, but is recommended for client systems.