Link connectivity on the Ecessa device is determined by combining local (physical) and remote connectivity.
At it's base is simply detecting whether or not there is a peer that it can communicate with on the other side of the cable. This is done automatically using Duplex Negotiation (by default this is set to Auto Negotiate on the Ecessa, but can be changed under the Services page) and ARP (Address Resolution Protocol) matching an IP address to a MAC address. Generally, this is all handled automatically and should not need to be configured except in particular cases.
The Ecessa device also tests for remote network availability through the use of "testpoints" which are configured for each WAN. The Testpoint settings are located on the WAN configuration page.
The device will attempt to send either TCP or ICMP (ICMP is default) messages to each testpoint, and will mark the testpoint as passing or failing depending on whether it receives a response. The timeout value can be modified per testpoint on the Basic WAN configuration page, which determines how long the device will wait for a response before assuming the test is a failure and retries. By default, the device will perform 3 tests to each testpoint and will expect at least 1 response back. It will continue this testing every few seconds to determine link connectivity. The Advanced WAN configuration page includes the settings for number of responses out of number of tests.
If all three testpoints do not respond to the messages being sent out, the Ecessa will automatically mark the line as DOWN and will stop sending traffic out that circuit until connectivity is restored.
Some customers may experience issues with "flapping" where the circuit repeatedly fails the testing but shortly after comes back up for a short amount of time before failing again. Adjusting the settings such as the amount of testing and the timeout value can alleviate the issue. The "Delayed Line Status Reporting" setting found on the Services configuration page, if enabled, will prevent traffic from going out a flapping WAN circuit until it has been up for the amount of time specified.
There is also an option to disable line testing entirely for a particular WAN from the Advanced WAN configuration page, but this will then assume that the line is always up and does no testing to check the actual status of the line. Additionally, WAN testing can be disabled globally from the Services page (de-selecting the Recovery & Redundancy setting).