Avaya 5900 Series Installing Manual page 52

Switch installation
Redundant cascade stacking
The 5900 Series switches allow a stack of up to eight units in a 5900 Series stack. If any single unit
fails or if a cable is accidently disconnected, other units in the stack remain operational without
interruption.
In addition to increasing bandwidth, the software uses the cables to provide two paths between
units. If one path breaks the data travels over the remaining path with half the normal inter-switch
bandwidth.
The following diagram shows an example of how a stack configuration reacts to a failed connection
in the stack configuration. In the illustrated example, the following occurs:
• Unit 3 becomes non-operational due to a unit failure, cable disconnection, or a loss of power.
• Units 2 and 4, directly upstream and downstream from Unit 3, sense the loss of link signals
from unit 3. The software causes all the data to traverse the remaining path.
• The Cascade Down LED for Unit 2 and the Cascade Up LED for Unit 4 turn amber to indicate
an error has been detected.
• The remaining stack units continue to be connected.
There are four internal ports for two Cascade links. Internal ports 1 and 2 are associated with
Cascade-Down link and internal ports 3 and 4 are associated with Cascade-Up link. When viewing
the event log after a stack port goes down, use the following information to help determine the
problem:
• Message Stack port 1 DOWN or Stack port 2 DOWN means Cascade-Down link is down.
• Message Stack port 1 UP or Stack port 2 UP means Cascade-Down link is up.
• Message Stack port 3 DOWN or Stack port 4 DOWN means Cascade-Up link is down.
• Message Stack port 3 UP or Stack port 4 UP means Cascade-Up link is up.
September 2017 Installing Avaya ERS 5900 Series
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