Users Guide

284 Stacking
NSF and VoIP
Figure 8-13 shows how NSF maintains existing voice calls during a failure of
the management unit in the stack. Assume the top unit is the management
unit in the stack. When the management unit in the stack fails, the call from
phone A is immediately disconnected. The call from phone B continues. On
the uplink, the forwarding plane removes the failed LAG member and
continues using the remaining LAG member. If phone B has learned VLAN or
priority parameters through LLDP-MED, it continues to use those
parameters. The stack resumes sending LLDPDUs with MED TLVs once the
control plane restarts. Phone B may miss an LLDPDU from the stack, but
should not miss enough PDUs to revert its VLAN or priority, assuming the
administrator has not reduced the LLDPDU interval or hold count. If phone
B is receiving quality of service from policies installed in the hardware, those
policies are retained across a restart of the management unit in the stack.
Figure 8-13. NSF and VoIP