If you install a Cisco Unified CME system to replace an older telephony system that had an established telephone number plan, you can retain the old number plan. Cisco Unified CME supports flexible extension number lengths and can provide automatic conversion between extension dialing and E.164 public telephone number dialing.

When a router receives a voice call, it selects an outbound dial peer by comparing the called number (the full E.164 telephone number) in the call information with the number configured as the destination pattern for the POTS dial peer. The router then strips out the left-justified numbers corresponding to the destination pattern matching the called number. If you have configured a prefix, the prefix will be put in front of the remaining numbers, creating a dial string, which the router will then dial. If all numbers in the destination pattern are stripped-out, the user will receive (depending on the attached equipment) a dial tone.

A successful Cisco Unified CME system requires a telephone numbering plan that supports future expansion. The numbering plan also must not overlap or conflict with other numbers that are on the same VoIP network or are part of a centralized voice mail system.

Cisco Unified CME supports shared lines and multiple lines configured with the same extension number. This means that you can set up several phones to share an extension number to provide coverage for that number. You can also assign several line buttons on a single phone to the same extension number to create a small hunt group.

If you are configuring more than one Cisco Unified CME site, you need to decide how calls between the sites will be handled. Calls between Cisco Unified CME phones can be routed either through the PSTN or over VoIP. If you are routing calls over VoIP, you must decide among the following three choices:

• You can route calls using a global pool of fixed-length extension numbers. For example, all sites have unique extension numbers in the range 5000 to 5999, and routing is managed by a gatekeeper. If you select this method, assign a subrange of extension numbers to each site so that duplicate number assignment does not result. You will have to keep careful records of which Cisco Unified CME system is assigned which number range.

• You can route calls using a local extension number plus a special prefix for each Cisco Unified CME site. This choice allows you to use the same extension numbers at more than one site.

• You can use an E.164 PSTN phone number to route calls over VoIP between Cisco Unified CME sites. In this case, intersite callers use the PSTN area code and local prefix to route calls between Cisco Unified CME systems.

If you choose to have a gatekeeper route calls among multiple Cisco Unified CME systems, you may face additional restrictions on the extension number formats that you use. For example, you might be able to register only PSTN-formatted numbers with the gatekeeper. The gatekeeper might not allow the registration of duplicate telephone numbers in different Cisco Unified CME systems, but you might be able to overcome this limitation. Cisco Unified CME allows the selective registration of either 2- to 5-digit extension numbers or 7- to 10-digit PSTN numbers, so registering only PSTN numbers might prevent the gatekeeper from sensing duplicate extensions.

Mapping of public telephone numbers to internal extension numbers is not restricted to simple truncation of the digit string. Digit substitutions can be made by defining dial plan patterns to be matched. For information about dial plans, see Dial Plan Patterns. More sophisticated number manipulations can be managed with voice translation rules and voice translation profiles, which are described in the Voice Translation Rules and Profiles section.

In addition, your selection of a numbering scheme for phones that can be directly dialed from the PSTN is limited by your need to use the range of extensions that are assigned to you by the telephone company that provides your connection to the PSTN. For example, if your telephone company assigns you a range from 408 555-0100 to 408 555-0199, you may assign extension numbers only in the range 100 to 199 if those extensions are going to have Direct Inward Dialing (DID) access. For more information about DID, see Direct Inward Dialing Trunk Lines.

A dial plan pattern enables abbreviated extensions to be expanded into fully qualified E.164 numbers. Use dial plan patterns when configuring a network with multiple Cisco Unified CMEs to ensure that the appropriate calling number, extension or E.164 number, is provided to the target Cisco Unified CME, and appears on the phone display of the called phone. In networks that have a single router, you do not need to use dial plan patterns.

When you define a directory number for an SCCP phone, the Cisco Unified CME system automatically creates a POTS dial peer with the ephone-dn endpoint as a destination. For SIP phones connected directly into Cisco Unified CME, the dial peer is automatically created when the phone registers. By default, Cisco Unified CME creates a single POTS dial peer for each directory number.

For example, when the ephone-dn with the number 1001 was defined, the following POTS dial peer was automatically created for it:

  dial-peer voice 20001 pots
	  destination-pattern 1001
	  voice-port 50/0/2
	 

A dial plan pattern builds additional dial peers for the expanded numbers it creates. If a dialplan pattern is configured and it matches against a directory number, two POTS dial peers are created, one for the abbreviated number and one for the complete E.164 direct-dial telephone number.

For example, if you then define a dial plan pattern that 1001 will match, such as 40855500.., a second dial peer is created so that calls to both the 0001 and 4085550001 numbers are completed. In this example, the additional dial peer that is automatically created looks like the following:

 dial-peer voice 20002 pots
	 destination-pattern 40855510001
	 voice-port 50/0/2
	 

In networks with multiple routers, you may need to use dial plan patterns to expand extensions to E.164 numbers because local extension numbering schemes can overlap each other. Networks with multiple routers have authorities such as gatekeepers that route calls through the network. These authorities require E.164 numbers so that all numbers in the network are unique. Define dial plan patterns to expand extension numbers into unique E.164 numbers for registering with a gatekeeper. For more information on E.164 numbers, see E .164 Enhancements.

If multiple dial plan patterns are defined, the system matches extension numbers against the patterns in sequential order, starting with the lowest numbered dial plan pattern tag first. Once a pattern matches an extension number, the pattern is used to generate an expanded number. If additional patterns subsequently match the extension number, they are not used.

Direct Inward Dialing (DID), is a one-way incoming trunking mechanism, that allows an external caller to directly reach a specific extension without the call being served by an attendant or other intervention.

It is a service offered in which the last few (typically three or four) digits dialed by the caller are forwarded to the called party on a special DID trunk. For example, all the phone numbers from 555-0000 to 555-0999 could be assigned to a company with 20 DID trunks. When a caller dials any number in this range, the call is forwarded on any available trunk. If the caller dialed 555-0234, then the digits 2, 3, and 4 are forwarded. These DID trunks could be terminated on a PBX, so that the extension 234 gets the call without operator assistance. This makes it look as though 555-0234 and the other 999 lines all have direct outside lines, while only requiring 20 trunks to service the 1,000 telephone extensions. Using DID, a company can offer its customers individual phone numbers for each person or workstation within the company without requiring a physical line into the PBX for each possible connection. Compared to regular PBX service, DID saves the cost of a switchboard operator. Calls go through faster, and callers feel they are calling a person rather than a company.

Dial plan patterns are required to enable calls to DID numbers. When the PSTN connects a DID call for “4085550234” to the Cisco Unified CME system, it also forwards the extension digits “234” to allow the system to route the call.

Translation rules manipulate dialed numbers to conform to internal or external numbering schemes. Voice translation profiles allow you to group translation rules together and apply them to the following types of numbers:

• Called numbers (DNIS)

• Calling numbers (ANI)

• Redirected called numbers

• Redirected target numbers—These are transfer-to numbers and call-forwarding final destination numbers. Supported by SIP phones in Cisco Unified CME 4.1 and later versions.

After you define a set of translation rules and assign them to a translation profile, you can apply the rules to incoming and outgoing call legs to and from the Cisco Unified CME router based on the directory number. Translation rules can perform regular expression matches and replace substrings. A translation rule replaces a substring of the input number if the number matches the match pattern, number plan, and type present in the rule.

For configuration information, see Define Voice Translation Rules in Cisco CME 3.2 and Later Versions.

For examples of voice translation rules and profiles, see the Voice Translation Rules technical note and the Number Translation using Voice Translation Profiles technical note.

A secondary dial tone is available for Cisco Unified IP phones connected to Cisco Unified CME. From Cisco Unified CME Release 11.6 onwards, secondary dial tone is supported on both SIP phones and SCCP phones.

The secondary dial tone is generated when a phone user dials a predefined PSTN access prefix and terminates when additional digits are dialed. An example is when a secondary dial tone is heard after a PSTN access prefix, such as the number 9, is dialed to reach an outside line. For SIP phones, a dialplan file is downloaded when the phone restarts. This dialplan file will have the dialplan pattern configured. Based on this dialplan pattern, phone would collect the digits or play secondary dial tone if there is a comma (,) in the pattern. The call is placed from the phone, when there is matching pattern in the dialplan file. Also note that when this feature is enabled, KPML digit collection is disabled on SIP phones.

For configuration information, see Activate Secondary Dial Tone For SCCP Phones and Activate Secondary Dial Tone for SIP Phones.

Cisco Unified CME 8.5 allows you to present a phone number in + E.164 telephone numbering format. E.164 is an International Telecommunication Union (ITU-T) recommendation that defines the international public telecommunication numbering plan used in the PSTN and other data networks. E.164 defines the format of telephone numbers. A leading + E.164 telephone number can have a maximum of 15 digits and is usually written with a ‘+’ prefix defining the international access code. To dial such numbers from a normal fixed line phone, the appropriate international call prefix must be used.

The leading +E.164 number is unique number specified to a phone or a device. Callers from around the world dial the leading + E.164 phone number to reach a phone or a device without the need to know local or international prefix. The leading + E.164 feature also reduces the overall telephony configuration process by eliminating the need to further translate the telephone numbers.