38 Installation fundamentalsThe following diagram shows an example of how a stack configurationreacts to a failed connection in the stack configuration. In the illustratedexample, the following occurs:• Unit 3 becomes non-operational due to a unit failure, cabledisconnection, or a loss of power.• Units 2 and 4, directly upstream and downstream from Unit 3, sensethe loss of link signals from unit 3. The software causes all the data totraverse the remaining path.• The Cascade Down LED for Unit 2 and the Cascade Up LED for Unit 4turn amber to indicate an error has been detected.• The remaining stack units continue to be connected.There are 4 internal ports for two Cascade links. Internal ports 1 and 2are associated with Cascade-Down link and internal ports 3 and 4 areassociated with Cascade-Up link. When viewing the event log after astack port goes down, use the following information to help determine theproblem:• Message Stack port 1 DOWN or Stack port 2 DOWN meansCascade-Down link is down.• Message Stack port 1 UP or Stack port 2 UP meansCascade-Down link is down.• Message Stack port 3 DOWN or Stack port 4 DOWN meansCascade-Up link is down.• Message Stack port 3 UP or Stack port 4 UP means Cascade-Uplink is down.ERS 5000 Series InstallationNN47200-300 04.0313 April 2009Copyright © 2008–2009 Nortel Networks
