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 and Windows NT extends native ATM support to Windows Sockets 2.0 (WinSock) and DirectShow-based applications by providing system-level components that map the applicable WinSock and DirectShow APIs to NDIS 5.0, extending direct ATM access to user-mode applications.
If ATM is included in a PC 98 system or is specifically designed for Windows or Windows NT, it must meet the requirements outlined in this chapter. For basic requirements for Plug and Play, power management, and driver support, see the “PC 98 Design for Network Communications” section later in this chapter. For more details about the following requirements, please refer to Section 3, “ATM Layer Specification,” in ATM User-Network Interface Specification, Version 3.1.
24. ATM adapter meets PC 98 network adapter requirements
Required
The following requirements must be met as defined in the “System Requirements for Network Communications” section earlier in this chapter:
25. ATM adapter supports a minimum number of active connections
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 VC is created between each pair of communicating ATM hosts.
| System type | Simultaneous connections |
| Client | 64 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.
26. ATM adapter supports all service types defined by the ATM Forum
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.
27. ATM adapter supports a minimum number of simultaneously active rt-VBR/nrt-VBR/CBR connections
Required
Support for at least two simultaneously active rt-VBR/nrt-VBR/CBR connections is required for basic applications, such as LAN Emulation (where “rt” stands for real time and “nrt” stands for non-real time). The two simultaneous active connections can be any combination of two from the three service types: rt-VBR, nrt-VBR, and CBR.
Support for additional CBR/rt-VBR connections is required for ATM adapters that support multimedia or other traffic that demands QOS. These are listed in the following table.
| System type | Simultaneous active rt-VBR/nrt-VBR/CBR connections |
| Client | 6 |
| Server | 500 |
28. ATM adapter supports traffic shaping
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. For example, this includes enforcement of peak cell rate on a UBR virtual circuit.
If the ATM adapter is connected to residential broadband networks—either directly or using external devices such as an ADSL modem or cable modem—there are additional traffic shaping requirements that restrict the total transmission rate of all active virtual circuits not to exceed the upstream bandwidth of the residential broadband network.
To support these types of connections with possibly limited throughput or asymmetric speeds, the adapter must enforce traffic shaping of all (aggregated) ATM traffic on the line, based on maximum line rate and peak cell rate (PCR) for outgoing traffic. This rate normally will be read from the adapter and reported to NDIS. However, a new requirement is that NDIS must also be able to write a lower rate back to the adapter, which shall then shape the aggregate of all ATM traffic to this indicated PCR.
29. ATM adapter supports external clocking
Required
Recommended: ATM adapter supports both internal and external (default) clocking.
Usually adapters can derive their transmit clocks from the switch’s Sonet frames (external clocking). Internal clocking is useful for diagnostics (connect Tx to Rx, and so on).
30. ATM adapter supports OAM
Recommended
Operation and maintenance (OAM) is needed for diagnostics.
This capability is recommended for Client systems, but is required for a Server system (layers F1–F5).
31. ATM adapter supports buffer chaining (Tx + Rx)
Recommended
This feature is needed for large packets.
This capability is recommended for Client systems, but is required for a Server system.