[cisco-voip] changing behaviour of un-registered phone

[Ted Nugent]

CFUR in SRND 4.2
http://www.cisco.com/univercd/cc/td/doc/product/voice/c_callmg/4_2/srnd4_2/uc4_2/42dialpl.htm


Cisco Unified CallManager 4.2 introduces the Call
Forward Unregistered (CFUR) feature as a way to
reroute calls placed to a temporarily unregistered
destination phone. The configuration of CFUR consists
of two main elements:

•Destination selection

When the DN is unregistered, calls can be rerouted to
either of the following destinations:

–Voicemail

Calls can be sent to voicemail by selecting the
voicemail checkbox and configuring the CFUR calling
search space to contain the partition of the voicemail
pilot number.

–A directory number used to reach the phone through
the PSTN

This approach is preferred when a phone is located
within a site whose WAN link is down. If the site is
equipped with Survivable Remote Site Telephony, the
phone (and its co-located PSTN gateway) will
re-register with the co-located SRST router. The phone
is then able to receive calls placed to its PSTN DID
number.

In this case, the appropriate CFUR destination is the
corresponding PSTN DID number of the original
destination DN. Configure this PSTN DID in the
destination field, along with applicable access codes
and prefixes (for example, 9 1 415 555 1234).

•Calling search space

Cisco Unified CallManager attempts to route the call
to the configured destination number by using the
called DN's CFUR calling search space. The CFUR
calling search space is configured on the target phone
and is used by all devices calling the unregistered
phone. This means that all calling devices will use
the same combination of route pattern, route list,
route group, and gateway to place the call, and that
all CFUR calls to a given unregistered device will be
routed through the same unique gateway regardless of
where the calling phone is located. Cisco recommends
that you select a centralized gateway as the egress
point to the PSTN for CFUR calls and that you
configure the CFUR calling search space to route calls
to the CFUR destination to this centralized gateway.

The Call Forward Unregistered functionality can result
in telephony routing loops if a phone is unregistered
while the gateway associated with the phone's DID
number is still under control of Cisco Unified
CallManager, as is the case if a phone is simply
disconnected from the network. In such a case, the
initial call to the phone would prompt the system to
attempt a first CFUR call to the phone's DID through
the PSTN. The resulting incoming PSTN call would in
turn trigger another CFUR attempt to reach the same
phone's DN, triggering yet another CFUR call from the
central PSTN gateway through the PSTN. This cycle
could repeat itself until system resources are
exhausted.

The new service parameter
MaximumForwardUnRegisteredHopsToDn controls the
maximum number of CFUR calls that are allowed for a DN
at the same time. The default value of 0 means the
counter is disabled. If any DNs are configured to
reroute CFUR calls through the PSTN, loop prevention
is required. Configuring this service parameter to a
value of 1 would stop CFUR attempts as soon as a
single call is placed through the CFUR mechanism. This
setting would also allow only one call to be forwarded
to voicemail, if CFUR is so configured. Configuring
this service parameter to a value of 2 would allow for
up to two simultaneous callers to reach the voicemail
of a DN whose CFUR setting is configured for
voicemail, while also limiting potential loops to two
for DNs whose CFUR configuration sends calls through
the PSTN.

Note Extension Mobility DNs should not be configured
to send Call Forward Unregistered calls to the PSTN
DID associated with the DN. The DNs of Extension
Mobility profiles in the logged-out state are deemed
to be unregistered, therefore any calls to the PSTN
DID number of a logged-out DN would trigger a routing
loop. To ensure that calls made to Extension Mobility
DNs in the logged-out state are sent to voicemail,
ensure that their corresponding Call Forward
Unregistered parameters are configured to send calls
to voicemail. 
--- Lelio Fulgenzi <lelio at uoguelph.ca> wrote:

> I recall a while back there was some changes to the
> behaviour of an unregistered phone. The default I
> believe is to send it to the CFNA configured of the
> phone. I'd like to be able to route a number of
> phones if they are not registered but I want to read
> more about it to see what the caveats are.
> 
> 
>
--------------------------------------------------------------------------------
> Lelio Fulgenzi, B.A.     Network Analyst (CCS)
> University of Guelph     Guelph, Ontario     N1G 2W1
> (519) 824-4120 x56354     (519) 767-1060 FAX 
>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Sanity First : Number of days with less than
> 50 messages in my inbox at the end of the day:   
> buffer overrun>
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