Dell PowerConnect 7048P User Manual - Page 163

NSF and VoIP Figure 8-13 shows how NSF maintains existing voice calls during a Management Unit failure. Assume the top unit is the Management Unit. When the Management Unit 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 the Management Unit restart. Figure 8-13. NSF and VoIP Phone A Phone B LAG Managing a Switch Stack 163