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13-4940-00251 Commend SIP Doorphone
Resiliency
The following table lists the scenarios of resilience supported by this device when
connected to the MCD 6.0 on the 3300 ICP.
Device Scenario 1 Scenario 2 Scenario 3 Scenario 4
Commend
doorphone
Not Supported Not Supported Not Supported
- No issues found - Issues found, cannot recommend use - Issues found
Note: Refer to list of device limitations and known issues later in the document for
recommendations.
The various scenarios are described below. The scenario names are a convenience for
understanding this section of the configuration guide.
Scenario 1: Resiliency is achieved by utilizing the ability of DNS servers to provide
multiple IP addresses against a single FQDN. This is generally achieved by using DNS
SRV or A records. This scenario requires nothing from a SIP Endpoint except that it
supports standard DNS behavior.
Scenario 2: The device has inherent knowledge of the primary and secondary 3300 ICPs
and will switch between them if a SIP request (REGISTER, INVITE, or SUBSCRIBE)
times out. Behavior will be characterized based on whether the device returns to primary
ICP and when this occurs. This scenario has some dependency on user action in order
to detect a failure, especially if configured with a long registration expiry time, so the
chance of a user experiencing a long delay making a call goes up.
Scenario 3: The behavior of the device is the same as that of scenario 2, except that the
device will “ping" the currently active server with an OPTIONS request. If the OPTIONS
request times out, the device will switch to the alternate server for all future requests.
The intent of this scenario is to provide much faster failure detection by the device. This
will allow devices to failover to their alternate ICP much more quickly, and much more
unnoticeably. (If the device can detect a failure of the primary ICP, and can failover
immediately, the chance that the user even notices a lack of service falls dramatically.)
Scenario 4: The device will support a new SIP header designed specifically for
resiliency. The P-Alternate-Server header must be included in a 200 OK or 301 Moved
Permanently response. This header will include data that designates the potential
servers and which server the UA must use.