Table Of Contents


Last Modified: February 7, 2020

Indicates the operational status of the interface (that is, communicating or not).

String Value Description
Down 0 The interface cannot transmit or receive frames (packets).
Up 1 The interface is ready to transmit and receive frames (packets).

This property corresponds to interface operational status as specified in IETF management standards such as RFC 2863 and RFC 8343.

Data type: datatype_icon

Long Name: Interface:Ethernet:Operational Status

Class: XNET Session

Permissions: Read

Interface state

The XNET interface Communicating state behaves differently for Ethernet compared to other XNET protocols, such as CAN. The OS stack provides a network interface, and the operating system brings its network interface to communicating state ("link up") at power on. The operating system keeps the interface in communicating state until it is powered off. Therefore, the Ethernet interface is communicating at its physical layer (PHY) before and after the existence of any XNET session.

XNET interface states have a limited context; they control the transfer of frames to/from the XNET endpoint and monitor paths, but they do not control the actual communicating state ("link up" or "link down") of the interface. The Operational Status property returns the actual communicating state of the interface.

As a consequence of this state behavior, it is possible to enable the time sync protocol prior to starting the XNET interface because the time sync protocol operates independently from the endpoint and monitor paths (like the OS stack).

Read behavior

Although the link is up prior to XNET interface start, if a frame is received prior to the initial XNET start and would normally be received by endpoint or monitor, XNET Read will not return the frame.

XNET Start discards all unread frames from the receive queue. XNET Stop has no effect on the receive queue, and link down/up events have no effect on the receive queue. If frames are received but not read, and your application stops the interface without restarting, XNET Read will return the previously received frames.

All unread frames are discarded from the receive queue when the XNET session is cleared.

Write behavior

When XNET Stop is invoked, or when the link goes down, pending frames in the XNET transmit queues are discarded.

XNET Write ignores the operational status of the link when the XNET interface is not running. If you invoke XNET Write prior to starting the XNET interface, the frame is queued regardless of the operational status. If the link is up when XNET Start is invoked, those queued frames are transmitted. If the link is down when XNET Start is invoked, those queued frames are discarded.

If you invoke XNET Write on a started XNET interface and the link is down, the frame is not queued and an error is returned. After the link comes back up, when you invoke XNET Write again, frames are queued for transmission (with no need to restart the XNET interface).

You can use XNET Wait (Transmit Complete) to ensure that frames are transmitted before you clear the XNET session.

Where This Property Is Available:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application

Recently Viewed Topics