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The CFUR feature is a way to reroute calls placed to a temporarily unregistered destination
phone. The configuration of CFUR consists of the two main elements of destination
selection and CSS, as shown in Figure 6-6. Choose Cisco Unified Communications
Manager Administration > Call Routing > Directory Number.
Figure 6-6 SRST Dial Plan Configuration of CFUR and CSS
When the directory number is unregistered, calls can be rerouted to the voice mail that
is associated with the extension or to a directory number that is used to reach the phone
through the PSTN. The latter approach is preferable when a phone is located within a site
whose WAN link is down. If the site is equipped with SRST, the phone (and its co-located
PSTN gateway) reregisters with the co-located SRST router. The phone then can receive
calls placed to its PSTN direct inward dialing (DID) number.
134 Chapter 6: Implementing Cisco Unified SRST and MGCP Fallback
In this case, the appropriate CFUR destination is the corresponding PSTN DID number of
the original destination directory number. Configure this PSTN DID in the destination field,
along with applicable access codes and prefixes. For this example, the number would be
9-1-481-555-0001.
CUCM attempts to route the call to the configured destination number using the CFUR CSS
of the called directory number. The CFUR CSS is configured on the target phone and is
used by all devices that are calling the unregistered phone. This means that all calling
devices 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 are routed through the
same unique gateway, regardless of where the calling phone is located. It is recommended
that you select a centralized gateway as the egress point to the PSTN for CFUR calls. You
also should configure the CFUR CSS to route calls that are intended for the CFUR
destination to this centralized gateway.
SRST Dial Plan: Max Forward UnRegistered
Hops to DN
The CUCM service parameter Max Forward UnRegistered Hops to DN reduces the
impact caused by CFUR routing loops, as shown in Figure 6-7. Choose CUCM
Administration > System > Service Parameter > Cisco CallManager.
Figure 6-7 SRST Dial Plan Configuration of Max Forward UnRegistered Hops to DN
This parameter specifies the maximum number of forward unregistered hops that are
allowed for a directory number at one time. It limits the number of times the call can be
forwarded because of the unregistered directory number when a forwarding loop occurs.
Use this count to stop forward loops for external calls that have been forwarded by CFUR,
SRST Dial Plan Components for Normal Mode Analogy 135
such as intercluster IP Phone calls and IP Phone-to-PSTN phone calls that are forwarded to
each other. CUCM terminates the call when the value that is specified in this parameter is
exceeded. The default 0 disables the counter but not the CFUR feature. The allowed range
is from 0 to 60.
MGCP Fallback and SRST Dial Plan Configuration
in the Cisco IOS Gateway
A dial plan in SRST mode, at a minimum, enables the remote-site users to place and receive
calls from the PSTN.
At least one dial peer needs to be configured to enable calls to and from the PSTN. The
destination pattern of that dial peer has to correspond to the PSTN access code (for example,
9T). The more elegant way is to configure several dedicated dial peers with destination
patterns that match the number patterns in a closed numbering plan, such as 91
(91 followed by ten dots).
In countries that have variable dial plans, the only destination pattern that is needed is 9T.
Because of the variable length of dialed numbers, the router waits for the interdigit timeout
(T302) or for a hash (#) sign to indicate the end of the dial string. Cisco Unified SRST
version 4.1 and Cisco Unified Communications Manager Express Release 4.1 do not
support the overlap sending feature to the PSTN. The receiving of ISDN overlap dialing
from PSTN is supported but has to be enabled on the interfaces. To shorten the wait time
for users after they complete the dial string, it is possible to reduce the interdigit timeout
from the SRST default of 10 seconds.
SRST Dial Plan Components for Normal
Mode Analogy
A good SRST dial plan is as close as possible between the dialing functionality in normal
mode and in SRST mode. The telephony service should have the same look and feel for the
user, regardless of the mode the system is in. For example, it would be an unacceptable
failover design if the remote user required an awareness of WAN link connectivity when he
dials his headquarters.
The numbers in the call lists (such as missed calls) must have the correct format (PSTN
access code plus PSTN phone number) to enable users to use the list entries for dialing. The
calling party ID of incoming calls from the PSTN needs to be modified by voice translation
profiles and voice translation rules.
136 Chapter 6: Implementing Cisco Unified SRST and MGCP Fallback
Abbreviated dialing between sites of the site code plus the extension number is possible in
SRST mode. Voice translation profiles have to be used to expand the called numbers to
PSTN format for intersite dialing.
If the calling privileges (which normally are controlled by the CUCM) have to be preserved
in SRST mode, class of restriction (COR) configuration must be used.
SRST Dial Plan Dial Peer Commands
The dial-peer command is the main component for configuring dial plans on Cisco IOS
routers, as shown in Example 6-8.
Example 6-8 Dial Peer Commands for an SRST Dial Plan
RemoteSite#configure terminal
RemoteSite(config)#dial-peer voice tag pots
RemoteSite(config-dial-peer)#destination-pattern [+]string[T]
R e m o t e S i t e ( c o n f i g - d i a l - p e e r )#port slot-number/port
You define a particular dial peer, specify the voice encapsulation method, and enter dial
peer configuration mode using the dial-peer voice command in global configuration mode.
The following list defines the keywords and parameters used in the configuration shown in
Example 6-8:
• The parameter tag specifies digits that define a particular dial peer. The range is from
1 to 2147483647.
• The keyword pots indicates that this is a plain old telephone service (POTS) peer. The
option voip also exists, indicating that this is a VoIP peer, but is not mentioned in
Example 6-8 because POTS dial peers are predominately used for SRST. POTS dial
peers contain a port, whereas VoIP dial peers contain a configured IP address.
• You specify either the prefix or the full E.164 telephone number to be used for a dial
peer using the destination-pattern command in dial peer configuration mode.
• The optional character + indicates that an E. 164 standard number follows.
SRST Dial Plan Dial Peer Commands 137
• The parameter string defines a series of digits that specify a pattern for the E. 164 or
private dialing plan telephone number. Valid entries are the digits 0 through 9, the
letters A through D, and the following special characters:
*
#
+
A
S
\
[]
0
• The optional control character T indicates that the destination-pattern value is a
variable-length dial string. Using this control character enables the router to wait until
all digits are received before routing the call.
• To associate a dial peer with a specific voice port, use the port command in dial peer
configuration mode.
• The parameter slot-number defines the number of the slot in the router in which the
voice interface card (VIC) is installed. Valid entries depend on the number of slots that
the router platform has.
• The parameter port defines the voice port number. Valid entries are 0 and 1.
Table 6-1 lists common classes of PSTN calls in the North American Numbering Plan
(NANP) and lists the pattern that is used for each class. An access code of 9 should be used
to indicate a PSTN call. The exception is 911, which should be configured with and without
the access code 9. The patterns outlined in Table 6-1 must be reachable in SRST mode.
138 Chapter 6: Implementing Cisco Unified SRST and MGCP Fallback
An access code of 9 typically is used to indicate a PSTN call; however, other access codes
such as 8 are also permissible.
The patterns in the table are the minimum number of patterns that need to be reachable in
SRST mode.
Example 6-9 provides a sample configuration of dial peers only, demonstrating outbound
dialing to the PSTN in an SRST router. This example is in the NANP, which also shows
local ten-digit dialing in area code 919. The configuration as written can be directly pasted
into a router.
Example 6-9 Dial Peer Example for an SRST Dial Plan
SRST Dial Plan Dial Peer Comman ds 139
NOTE This example does not contain any class of restriction (COR), which currently
allows all SRST registered phones to dial all numbers, including long-distance, 900, and
international, without any constraint. COR is discussed later in this chapter. In addition,
dial peers 3 and 4 do not require the forward-digits command, and are added only for
clarity.
140 Chapter 6: Implementing Cisco Unified SRST and MGCP Fallback
SRST Dial Plan Commands: Open Numbering Plans
Example 6-10 defines the configuration commands for open numbering plans in an SRST
dial plan.
Example 6-10 SRST Dial Plan Commands for an SRST Dial Plan
RemoteSite#configure terminal
RemoteSite(config)#interface s e r i a l 0 / 1 / 0 : 23
R e m o t e S i t e ( c o n f i g - i f ) # i s d n overlap-receiving [T302 ms]
R e m o t e S i t e ( c o n f i g - i f ) # e x i t
RemoteSite(config)#call-manager-fallback
RemoteSite(config-cm-fallback)#timeouts i n t e r d i g i t sec
RemoteSite(config- cm - f a l l b a c k)#dialplan-pattern tag pattern
extension-length length [extension-pattern extension-pattern] [no-reg]
The following list defines the commands, keywords, and parameters used in the
configuration shown in Example 6-10:
• To activate overlap receiving on ISDN interfaces, you use the isdn overlap-receiving
command in interface configuration mode. This command is applicable on BRI interfaces
or on the ISDN interface of El/Tl controllers in PRI mode.
• The optional parameter T302 defines how many milliseconds the T302 timer should
wait before expiring. Valid values for the ms argument range from 500 to 20000. The
default value is 10000 (10 seconds).
CAUTION Modifying the T302 parameter, when connected to public networks, might
disable the function. The T302 describes the interdigit timeout for all phones in the
CUCM cluster.
• Configure the timeout value to wait between dialed digits for all Cisco IP Phones that
are attached to a router using the timeouts interdigit command in call-managerfallback
configuration mode.
• The parameter sec defines the interdigit timeout duration, in seconds, for all Cisco IP
Phones. Valid entries are integers from 2 to 120.
• Create a global prefix that can be used to expand the extension numbers of inbound and
outbound calls into fully qualified E.164 numbers using the dialplan-pattern
command in call-manager-fallback configuration mode.
• The parameter tag is the unique identifier that is used before the telephone number. The
tag number is from 1 to 5.
SRST Dial Plan Commands: Open Numbering Plans 141
• The parameter pattern is the dial plan pattern, such as the area code, the prefix, and the
first one or two digits of the extension number, plus wildcard markers or dots (.) for the
remainder of the extension-number digits.
• The keyword extension-length sets the number of extension digits that will appear as
a caller ID followed by the parameter length, which is the number of extension digits.
The extension length must match the setting for IP Phones in CUCM mode. The range
is from 1 to 32.
• The optional keyword extension-pattern sets the leading digit pattern of an extension
number when the pattern is different from the leading digits defined in the pattern
variable of the E.164 telephone number. An example is when site codes are used. The
parameter extension-pattern that follows defines the leading digit pattern of the extension
number. It is composed of one or more digits and wildcard markers or dots (.)• For
example, 5,. would include extensions 500 to 599, and 5... would include extensions
5000 to 5999. The extension pattern configuration should match the mapping of internal
to external numbers in CUCM.
• The optional keyword no-reg prevents the E. 164 numbers in the dial peer from registering
with the gatekeeper.
Example 6-11 demonstrates the use of the dialplan-pattern command, which shows how
to create a dial plan pattern for directory numbers 500 to 599 that is mapped to a DID range
of 408-555-5000 to 5099. If the router receives an inbound call to 408-555-5044, the dial
plan pattern command is matched, and the extension of the called E. 164 number, 408-555-
5000, is changed to directory number 544. If an outbound calling party extension number
(544) matches the dial plan pattern, the calling-party extension is converted to the E.164
number 408-555-5044. The E.164 calling-party number appears as the caller ID.
Example 6-11 SRST Dial Plan Example for Mapping Directory Numbers
RemoteSite#configure terminal I
RemoteSite(config)#call-manager-fallback
RemoteSite(config-cm-fallback)#dialplan-pattern 1 40855550..
extension-length 3 extension-pattern 5..