Setup & Configuration
HDE-VoIP Telephones
Page 9
6.3. Mitel Resiliency
The Mitel Resiliency filter allows for seamless failover between two Mitel SIP servers without user intervention.
The device supports two levels of resiliency: Bronze and Silver.
Bronze:
The device supports multiple DNS records for a single FQDN. If the device fails to register with one server via an IP
address associated with the FQDN’s DNS record, it will try other IP addresses given. Alternatively, the DNS server
can provide a single IP address for an FQDN if it is aware of the servers’ statuses.
Silver:
While idle, the device will attempt to register with the primary Mitel SIP server (“Primary SIP Server” in the device’s
configuration). If the device fails to register with this primary server at any point, it will register with the secondary
Mitel SIP server (“Backup SIP Server 1” in the device’s configuration). The device will maintain registration with the
secondary server, but will indefinitely attempt to re-register with the primary server. When the primary server comes
back online, the device will unregister with the secondary server and go back to registering with the primary server.
On first boot (or first registration), the time it takes for the device to failover to the secondary server is based on
timers in the SIP RFC. Once the device has successfully registered with a (any) server, the time it takes for the
device to failover to another server is based on the same timers as well as the SIP Re-registration Interval
specified in the device’s configuration. The device attempts to re-register with its SIP server at about 66% of the
specified interval, which should result in downtime of no more than 75% of the specified interval.
When the device sends a SIP INVITE request, the device will start a timer (“Invite Timeout” in the device’s
configuration). If the SIP INVITE exchange is not successfully completed before this timer expires, the call will be
aborted and the device will failover to the next server. The user will need to attempt the call again.