Echelon OpenLDV - Manual (Page 15)

OpenLDV Programmer’s Guide 7
information about xDriver extensions, see Chapter 6, Extending xDriver,
on page 99.
Getting Started with the OpenLDV Driver
An OpenLDV application can use a Layer 2 network interface or a Layer 5
network interface:
• Layer 2 Network Interface – A network interface that communicates at
Layer 2 of the LonTalk protocol. This type of interface transports
LonTalk packets without processing them, and does not filter by network
address. It is typically used for applications that implement layers 3
through 7 of the LonTalk protocol, such as an LNS Server, and is also
used for protocol analyzers that log and display network traffic.
Implementing layers 3 through 7 on a Windows computer, rather than in
the Neuron core or other processor of a local network interface, can
provide significantly higher performance. For example, the LNS Server
includes an implementation of layers 3 through 7 that provides
significantly higher performance when used with a Layer 2 network
interface.
• Layer 5 Network Interface – A network interface that communicates at
Layer 5 of the LonTalk protocol. This type of interface transports
incoming LonTalk packets that are addressed to the network interface,
and transports outgoing packets that are addressed to other devices. It is
typically used for remote network interfaces (such as a SmartServer or an
i.LON network interface) because these interfaces typically implement
layers 3 through 5 on a high performance processor within the network
interface, and it allows an uplink session to be initiated when the host
receives a particular message addressed to it. This type of interface
requires handling of NI resources, such as reference IDs, at a software
layer above the OpenLDV layer. For example, the LNS Server manages
NI resources when used with a Layer 5 network interface.
A typical OpenLDV application uses Layer 5 interfaces so that it need not
implement layer 3-5.
You can use the L
ON W ORKS Interfaces application in the Windows Control Panel
to determine if your network interface provides a Layer 2 or Layer 5 image or
supports switching between Layer 2 and Layer 5:
• Echelon U10 and U20 USB Network Interfaces can operate as either a
Layer 2 or Layer 5 interface, switchable within an OpenLDV application
• Remote Network Interfaces (SmartServer or i.LON) can be configured to
operate as a Layer 5 interface or as a read-only Layer 2 interface (for use
with protocol analyzers, such as the LonScanner Protocol Analyzer)
• IP-852 devices always operate as Layer 2 interfaces, as defined by the
ISO/IEC 14908-4 standard
For PCC-10, PCLTA-20, or PCLTA-21 network interfaces, Table 1 on page 8 lists
the application image that you can select to operate at either Layer 2 or Layer 5,
as needed. See the documentation for your network interface for additional
information.