This document describes how to resolve the fast busy problem in a Cisco
IP Phone when a caller gets a fast busy from the call forwarded number and the
forwarded call fails.
Cisco recommends that you have knowledge of these topics:
The information in this document is based on these software and
The information in this document is based on the Cisco Unified
Communication Manager 4.1(3).
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
Call Forward is used when a call is extended to an IP Phone, but it
goes unanswered because the called party is busy or unavailable. The forwarded
call can be directed to another telephone number or a voicemail number.
When a Cisco IP Phone is set to forward a call, the forwarded call does
not work, and the caller hears a busy or a engaged tone. This occurs for both
internal and external forwarded calls.
Call Forward fails because the Forward Loop Prevention is falsely
triggered due to a leak in the MaxForwardsToDn counter.
Forward Maximum Hop Count: The counter increments each
time a call is forwarded from that dialed number. Once the call is cleared or
connected, the counter is decremented. This logic detects and clears external
loops between CCM and PSTN, or CCM and another PBX.
Cisco CallManager terminates the call if the number of hops specified
in this parameter is exceeded and the final destination is unavailable (for
example, busy or not registered). If the number of hops specified in this
parameter is exceeded, the call is terminated. If a rush of calls come in at
the same time and are not answered, this count could increase and exceed the
maximum, and calls are terminated.
In order to resolve this problem, complete these steps to reset the
Go off hook on the phonethat has the high counter and register it to
Enter **##*30 from the dialpad in order to enable
the phone to accept the code.
Go off hook again on the same Cisco IP phone, and enter
**##*35 from the dialpad in order to clear the
Complete calls to the IP Phone in order to verify if the problem is