Installation guide

9
LAN Mode
RFC-1483, bridged Ethernet over ATM, is supported in the LAN driver. This protocol provides LLC
encapsulation for carrying network interconnect traffic over a single ATM AAL5 Virtual Connection. LLC
encapsulation is desirable when it is not practical to have a separate VC for each carried protocol, such as
with an ATM network that only supports Permanent Virtual Circuits (PVCs). The provided NDIS 5
drivers automatically establish a “connection-less” call using the defined PVC, and encapsulate Ethernet
bridged frames.
WAN Mode
RFC-2364, PPP over ATM, is supported in the WAN driver. Point-to-Point Protocol provides a method of
transporting multi-protocol packets over point-to-point links. Point-to-point links allow for services such as
Link Control Protocol, Network-layer Control Protocol, and authentication. The PPP over ATM standard
brings these point-to-point services to the ATM network where they are not inherently supported. The
provided NDIS 5 drivers accept an empty dial string on a specific “link” or PVC from Windows Dial-up
Networking to establish a call, and encapsulate PPP frames.
User selection of WAN or LAN mode can be done manually via the provided control panel. However,
auto-configuration is supported with the provided installation wizard, so that the protocol mode is selected
properly without user intervention.
Host Software
The host software NDIS mini-port driver provided implements the ATM Adaptation Layer 5 (AAL5),
which is composed of two sub-layers:
1) The Segmentation and Reassembly (SAR) layer, and
2) The Convergence Sub-layer (CS). The AAL5 protocol
provides virtual connections, which offer error detection, but not error correction, between end stations
attached to the same network.
The SAR sub-layer transmitter segments the higher layer information into a size suitable for the payload of
the ATM cells of a virtual connection. The receiver reassembles the contents of the cells of a virtual
connection into data units to be delivered to higher layers. During periods of no data transmission, the
device set, and not the host software driver, performs idle cell insertion and deletion, thus unloading this
task from the host PC and unburdening the USB with unnecessary traffic.
The Convergence Sub-layer performs message identification and clock recovery. Additionally, the CS of
the AAL converts the user service information coming from the upper layer into a protocol data unit (PDU),
and also carry out the opposite process at the receiver.
Unspecified Bit Rate (UBR) service is supported. It allows a connection to be established without
specifying the bandwidth expected from the connection. The network makes no guarantees for UBR service:
it establishes the route but does not commit bandwidth. UBR can be used for applications that have no
delivery constraints and do their own error and flow control. Examples of potential uses or UBR are e-mail
and file transfer, as neither application has real-time characteristics.