13-4940-00251 Commend SIP Doorpho ne
Resiliency
The following table lists the scenarios of resilience supported by this de vice 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 docum ent for
recommendations.
The various scenarios are described below. The scenario names are a con venience for
understanding this section of the configuration guide.
Scenario 1: Resiliency is achieved by utilizing the ability of DNS servers to pr ovide
multiple IP addresses against a single FQDN. This is generally achieved b y using DNS
SRV or A records. This scenario requires nothing from a SIP Endpoint exce pt that it
supports standard DNS behavior.
Scenario 2: The device has inherent knowledge of the primary and secondar y 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 r eturns to primary
ICP and when this occurs. This scenario has some dependency on user acti on in order
to detect a failure, especially if configured with a long registration exp iry 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, exc ept 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 f uture requests.
The intent of this scenario is to provide much faster failure detection b y the device. This
will allow devices to failover to their alternate ICP muc h more quickly, and much more
unnoticeably. (If the device can detect a failure of the primary ICP, and ca n failover
immediately, the chance that the user even notices a lack of service falls dram atically.)
Scenario 4: The device will support a new SIP header designed specifical ly 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 t he potential
servers and which server the UA must use.