Echelon OpenLDV User Manual download pdf (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

ONWORKS 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.

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