Implementing Shared Lines and Hunt Groups

Although it is widely used, the term hunt group seems to mean different things to different people and in different contexts. It's a general term that covers the distribution of calls among a group of phones. In this chapter, the term call coverage refers to the general concept of call distribution across phones. This helps avoid confusion with the Cisco CME CLI command ephone-hunt. The ephone-hunt command is used to configure a specific kind of call coverage that involves sequential selection among a group of selected phone lines.

Many other types of call coverage are addressed with other commands, combinations of commands, and configurations. Examples include the use of shared lines, overlay-dn, call forwarding, secondary ephone-dn numbers, and combinations of these.

This section describes a number of different types of call coverage:

• Simple sequential ringing of a selected set of phone lines
• Ringing of multiple phone lines at the same time, referred to here as parallel hunting
• Call forwarding from one line to another using call forward on busy or no-answer
• Combination sequences that involve sequential ringing of multiple phone lines, referred to here as sequential parallel hunting

Notice that all these refer to ringing phone lines, not phones. Calls are sequenced through an ordered set of phone lines. Which phones ring depends on the binding of the lines to the phones. Each line can be bound to multiple phones.

The following sections discuss several types of call coverage.

Cisco IOS Voice Dial Peer Hunting

A good place to start a discussion of call coverage for Cisco CME is to look at the voice dial peer hunting mechanism that is a standard component of the Cisco IOS voice infrastructure. Dial peers have a very large number of configuration options. The most basic options are related to matching a telephone number and directing the call to a specific voice port or VoIP destination. More advanced options relate to number manipulation (using translation rules or translation profiles), application selection (including custom TCL scripts), protocol options (such as fax relay and dual-tone multifrequency [DTMF] relay), voice codec selection, and caller ID manipulation and restriction.

Some dial peer operations relate to selecting a dial peer associated with the call's originator (incoming dial peer matching) and selecting a dial peer associated with the call destination (outgoing dial peer matching). Multiple parameters can affect the selection of the incoming and outgoing dial peers, but the primary matching criteria are the called and calling party numbers.

Describing all the dial peer options in detail is outside the scope of this book; however, numerous books deal with this subject in more depth, including the following:

• Deploying Cisco Voice over IP Solutions by Jonathan Davidson (Cisco Press, 2001).
• Cisco Voice over Frame Relay, ATM, and IP, edited by Steve McQuerry, Kelly McGrew, and Stephen Foy (Cisco Press, 2001).

This section provides a simplified overview of dial peers to provide a basic understanding of some of the options that apply to call coveragespecifically, dial peer hunting. Example 5-5 shows two basic dial peers.

Example 5-5. Two Basic Dial Peers

router#show running-config dial-peer voice 100 pots destination-pattern 1001 port 1/0/0 dial-peer voice 200 voip destination-pattern 20.. session target ipv4:10.0.4.2

The first dial peer (dial peer 100) is a POTS dial peer. This type of dial peer is used to reference a local telephony voice port connected to the router.

The second dial peer (dial peer 200) is a VoIP dial peer used to reference a remote telephony device accessed via IP, usually across a WAN data link.

Both dial peers have a destination-pattern parameter. This associates a telephone number or range of telephone numbers with the dial peer. In the VoIP dial peer, you can see that the destination pattern contains the wildcard character "." (to match any digit). In this example, the destination-pattern 20.. command matches telephone numbers in the range 2000 to 2099.

Both dial peers associate a destination device with the phone number selected by the destination pattern. In the POTS dial peer case, the destination is a physical voice port on the router designated as port 1/0/0. Your router's exact port numbering may vary by router type and voice interface type, but the basic numbering structure is slot/card/port.

In the VoIP dial peer case, the destination is an IP address, as indicated by the session target ipv4:10.0.4.2 parameter.

In Example 5-5, you can see how a dial peer is used to associate a telephone number (or range) with a destination, either a voice port or an IP address.

The dial peer hunting function comes into play when you create two or more dial peers that match the same telephone number but reference different destination devices. You can set many parameters to adjust the order in which matching dial peers are selected. The default behavior is called longest match. For longest match, the dial peer that most exactly matches the telephone number is preferred. A longest match selects the destination pattern that matches the desired number using the fewest "." wildcard characters. The best kind of longest match is an exact match, where no wildcards are used and the destination pattern and telephone number match literally and exactly. This is often the case with POTS dial peers, where you assign a specific phone number to a specific port.

Example 5-6 shows a dial peer configuration that illustrates some of the matching capabilities.

Example 5-6. Simple Dial Peers

router#show running-config dial-peer voice 101 pots destination-pattern 2001 port 1/0/0 dial-peer voice 102 pots destination-pattern 2007 port 1/0/1 dial-peer voice 200 voip destination-pattern 20.. session target ipv4:10.0.4.2

In Example 5-6, two POTS dial peers associate the phone numbers 2001 and 2007 to (local) voice ports 1/0/0 and 1/0/1. All other numbers in the 2000 to 2099 range are associated with the VoIP dial peer and are resolved somewhere in the VoIP space. This configuration provides a simplified way of indicating that the numbers 2001 and 2007 are local numbers. The remaining numbers in the range 2000 to 2099specifically, 2002 to 2006 and 2008 to 2099are remote and can be accessed via VoIP.

As a result of the longest-match rule, a call to 2001 selects POTS dial peer voice 101 in preference to VoIP dial peer 200. This is because the destination pattern for dial peer 101 has an exact match to the called number 2001, whereas VoIP dial peer 200 uses "." wildcard digits to match 2001.

Example 5-7 shows a more complex configuration.

Example 5-7. More Complex Dial Peers

router#show running-config dial-peer voice 101 pots destination-pattern 2001 preference 1 port 1/0/0 dial-peer voice 102 pots destination-pattern 2001 preference 2 port 1/0/1 dial-peer voice 200 voip destination-pattern 20.. session target ipv4:10.0.4.2

In Example 5-7, you can see that the two POTS dial peers now both have the same number. Because both dial peers provide an exact match to the number 2001, the longest-match criteria cannot distinguish between them. You also see that the dial peers now have an extra parameter, preference. The preference command is used to define a specific preference order for selecting the dial peers. The call to 2001 goes to the dial peer with the lowest preference value. The default preference value is 0.

In Example 5-7, when an incoming call to 2001 arrives, it first goes to POTS dial peer 101 with preference 1. Only if the port 1/0/0 associated with this dial peer is busy does the dial peer matching process hunt to the second dial peer 102 (preference 2). This provides the first basic mode of call coverage hunting: dial peer hunt on busy.

You may notice that there is a potential problem with the dial peer hunt-on-busy arrangement in this example: What if the second port is also busy? If ports 1/0/0 and 1/0/1 are both busy, the dial peer hunting mechanism takes the call to the next best available match. The next best match in this example is the VoIP dial peer 200. This dial peer matches the 2001 number, because it has a wildcard-based match range that spans the entire range 2000 to 2099. This range includes the number 2001.

In most cases, you do not want the call to hunt on busy into the VoIP dial peer, because (in this example) there is no resolution for the number 2001 in the VoIP space. If a call to 2001 gets routed to the VoIP destination, the call will fail with a cause code (returned by the remote VoIP system) indicating that the number 2001 does not exist. This condition returns a fast-busy tone (number not in service) indication to the caller. This is not the correct behavior. What is needed is to return a simple user busy tone indication to the caller.

You can solve this problem by adding the dial peer option huntstop, as shown in Example 5-8.

Example 5-8. Huntstop in a Dial Peer

router#show running-config dial-peer voice 101 pots destination-pattern 2001 preference 1 port 1/0/0 dial-peer voice 102 pots destination-pattern 2001 preference 2 huntstop port 1/0/1 dial-peer voice 200 voip destination-pattern 20.. session target ipv4:10.0.4.2

The huntstop command option tells the dial peer hunting mechanism not to try to find any further dial peer matches. Instead, the dial peer hunting stops at the dial peer containing the huntstop command. If no available voice port is found, it returns a busy tone to the caller.

Example 5-9 shows another variation using dial peers to manage call coverage.

Example 5-9. Dial Peer Variation

router#show running-config dial-peer voice 101 pots destination-pattern 2001 preference 1 port 1/0/0 dial-peer voice 102 pots destination-pattern 2001 preference 2 huntstop port 1/0/1 dial-peer voice 102 pots destination-pattern 2007 huntstop port 1/0/1

In Example 5-9, port 1/0/1 can be accessed by dialing 2001 or 2007. A call to 2001 first tries port 1/0/0. If this port is busy, it hunts to port 1/0/1. A call to 2007 goes directly to port 1/0/1.

Note that the default for the huntstop parameter under dial peer is for huntstop to be disabled. As you will see later (in the section "Cisco IOS Voice Dial Peer Hunting"), the default for huntstop when applied to the ephone-dn configuration is for huntstop to be enabled.

Ephone-dn Dial Peers and Voice Ports

The preceding section provided an overview of dial peers as used by the generic Cisco IOS voice infrastructure software. This section shows how Cisco CME uses dial peers to enable routing of calls to IP phones. The Cisco CME CLI configuration of IP phones and IP phone lines does not directly include dial peers or (virtual) voice ports. Instead, the dial peer and virtual voice port resources used by Cisco CME are hidden inside the ephone-dn command. This simplifies the configuration steps needed to create an IP phone line. It avoids the manual process of creating POTS dial peers to bind phone numbers to virtual voice ports.

Here is the original ephone-dn command from the beginning of this chapter, modified with a user name added and a specific dial peer preference included:

ephone-dn 4 number 1001 name John Smith preference 1

This ephone-dn command generates the configuration subelements shown in Example 5-10.

Example 5-10. Ephone-dn Subelements

router#show running-config dial-peer voice 20004 pots destination-pattern 1001 preference 1 huntstop port 50/0/4 voice-port 50/0/4 station-id number 1001 station-id name John Smith

The ephone-dn command is more compact and saves you from entering some information twice, such as the number 1001. The station-id commands (under the voice-port command) set the caller ID properties (name and number) for the IP phone line. This establishes the calling party name and number for calls originated by the ephone-dn. Note that the dial peer destination pattern by itself is not a good way to set the caller ID information. This is because in the general case, you can have multiple POTS dial peers that reference the same voice port. Because each dial peer can specify a different destination pattern phone number for the voice port, you can see that attempting to imply the caller ID calling party number from the dial peer creates ambiguity. With multiple dial peers for the same voice port, determining which dial peer to choose to represent the calling party number is difficult. There are specific rules for incoming dial peer selection that select the calling party number from the dial peers, but these are outside the scope of this chapter. The dial peer destination pattern is used as the calling party number for calls from the voice port only if the station-id command is omitted from the voice port configuration. As you can see, the ephone-dn configuration takes care of this detail for you.

Note the presence of the huntstop command in the generated dial peer in Example 5-10. This is discussed in the section "Cisco IOS Voice Dial Peer Hunting."

Also note the (virtual) voice port numbering 50/0/4. The numbering convention varies by router type, but it's typically slot/card/port. The value 50 was arbitrarily chosen as the virtual "slot" number for the virtual voice ports just to avoid contention with the routers' physical network module slots. Currently, no routers (that support Cisco CME) have 50 physical slots, so there's no confusion with physical hardware slot numbers. The middle card number value is always 0. The port number, 4 in this example, matches the ephone-dn tag value (as in ephone-dn 4). The dial peer tag numbering (20004) is not significant, but it usually has some correlation to the ephone-dn tag number, which is 4 in this example.

The only place that the virtual voice port port number is significant is in the binding of the ephone-dn dial peer to the virtual voice port. In most cases, you never need to be aware of the virtual voice port port numbers in your Cisco CME system.

If you execute the IOS command show running-config, you see only the ephone-dn commands you have entered, not the dial peer and virtual voice port commands. This is because the ephone-dn command automatically manages these subcommands for you, and there is no need for these to take up space in the router configuration. However, you can see the ephone-dn generated dial peers and virtual voice ports using the Cisco IOS commands show dial-peer summary and show voice-port summary.

The important point for you to understand here is that the dial peer and voice port configurations created by the ephone-dn do exist in the router configuration, even though they are not included in the output of show running-config. This point helps you understand how the Cisco CME configuration interacts with any general Cisco IOS voice infrastructure configuration that is included in your router, as well as for troubleshooting Cisco CME (covered in Part IV, "Maintenance and Troubleshooting").

Ephone-dn Secondary Number

The ephone-dn secondary number allows you to associate a second phone number with the same IP phone line. You can use this to create a simple hunt-on-busy configuration. This allows you to use the dial peer hunt-on-busy mechanism to make a call roll over from one line to another, even when the lines have different primary phone numbers. Example 5-11 shows an example.

Example 5-11. Ephone-dn Secondary Number

router#show running-config ephone-dn 4 number 1001 secondary 1007 name John Smith preference 1 secondary 2

This ephone-dn command generates the configuration subelements shown in Example 5-12.

Example 5-12. Ephone-dn Subelements

router#show running-config dial-peer voice 20004 pots destination-pattern 1001 preference 1 huntstop port 50/0/4 dial-peer voice 30004 pots destination-pattern 1007 preference 2 huntstop port 50/0/4 voice-port 50/0/4 station-id number 1001 station-id name John Smith

If you compare this with the earlier Example 5-7, you can begin to see how the ephone-dn command can leverage the IOS voice infrastructure dial peer hunting mechanism to provide simple call coverage. The configuration in this example causes incoming calls to both 1001 and 1007 to be routed to the IP phone line created by the ephone-dn 4 command, provided that no other dial peer elements in the system preempt the call routing path with a destination pattern match that has a lower numeric preference value.

Example 5-13 shows how you can use the ephone-dn secondary number to create dial peers that provide a simple form of call coverage.

Example 5-13. Ephone-dn Secondary Number

router#show running-config ephone-dn 4 number 1001 secondary 1007 name John Smith no huntstop preference 1 secondary 2 ephone-dn 5 number 1007 secondary 1001 name Jane Smith no huntstop preference 1 secondary 2

Example 5-14 shows the dial peers and voice port configurations that these commands generate.

Example 5-14. Ephone-dn Subelements

router#show running-config dial-peer voice 20004 pots destination-pattern 1001 preference 1 no huntstop port 50/0/4 dial-peer voice 30004 pots destination-pattern 1007 preference 2 no huntstop port 50/0/4 dial-peer voice 20005 pots destination-pattern 1007 preference 1 no huntstop port 50/0/5 dial-peer voice 30005 pots destination-pattern 1001 preference 2 no huntstop port 50/0/4 voice-port 50/0/4 station-id number 1001 station-id name John Smith voice-port 50/0/5 station-id number 1007 station-id name Jane Smith

With the configuration in Example 5-14, you can see that an incoming call to 1001 first goes to dial peer 20004 (preference 1) and tries virtual voice port 50/0/4 (for ephone-dn 4). If this port is busy, the call hunts on busy from dial peer 20004 to dial peer 30005 (preference 2) and tries virtual voice port 50/0/5 (for ephone-dn 5). In a similar manner, you can see that a call to 1007 first goes to ephone-dn 5 and then hunts to ephone-dn 4.

The dial peer hunting mechanism works only for hunt on busy. It does not provide hunting on no-answer timeout.

Note the use of the no huntstop command under ephone-dn. Without having this command present, the dial peer hunting stops at the first dial peer it reaches. The literal command text for no huntstop does not actually appear in the dial peers if you examine them using the show dial-peer Cisco IOS commands. This is because no huntstop is the default configuration for a dial peer, and default configuration items normally are not included in the IOS show running-config command display output. The no huntstop text is included in the preceding dial peer examples for clarity only. The no huntstop command is required under ephone-dn. This is needed to turn off the default ephone-dn configuration, which has huntstop enabled by default.

Using Call Forwarding for Call Coverage

In the examples of dial peer matching, you saw how calls can be distributed over a number of ephone-dn IP phone lines without changing the called number for the call. You can also use call forwarding to provide simple forms of call coverage. Cisco CME supports call forwarding for busy, no-answer, and unconditional (or call-forward all). When you use call forwarding to provide call coverage, the called number for the call changes. This can affect what is displayed on the IP phone receiving the forwarded call and entry into voice mail. Example 5-15 shows an example of a call forwarding configuration.

Example 5-15. Call Forwarding

router#show running-config ephone-dn 4 dual-line number 1001 name John Smith call-forward busy 1007 call-forward noan 1007 timeout 20 ephone-dn 5 dual-line number 1007 name Jane Smith call-forward busy 1001 call-forward noan 1001 timeout 20

In Example 5-15, you can see that John and Jane's phones are set to call forward on busy or no-answer (noan) to each other's phone. There's an issue with this configuration, because it potentially creates an infinite forwarding loop. If neither phone is answered, the call is repeatedly forwarded back and forth between the two phones until the caller hangs up.

You can limit the number of times the call forwarding loop is traversed by setting the max-redirect command under telephony-services. The max-redirect command has a range of 5 to 20 and a default value of five. This is a global command and limits call forwarding system-wide.

Using Shared Lines for Call Coverage

The previous examples showed you how to use the Cisco IOS voice infrastructure dial peer hunting mechanism to control the routing distribution of incoming calls across more than one line (virtual voice port). These examples assume that each different IP phone line is associated with a different IP phone. In this section, you learn how to distribute calls between multiple phones using only a single IP phone line. Example 5-16 uses a simple shared-line configuration to move a call between phones by dynamically moving the line ownership between phones instead of moving the call between lines.

Example 5-16. Shared-Line Configuration

router#show running-config ephone-dn 1 number 1001 name John Smith ephone-dn 2 number 1002 name Jane Smith ephone-dn 3 number 5001 preference 1 no huntstop name SalesLine1 ephone-dn 4 number 5001 preference 2 name SalesLine2 ephone 12 mac-address 000d.1234.0efc button 1:1 2:3 3:4 ephone 15 mac-address 000d.5678.0dcf button 1:2 2:3 3:4

Example 5-16 shows two IP phones. Ephone 12 belongs to John Smith and has John's personal phone line on button 1 (button 1:1). Ephone 15 belongs to Jane Smith and has Jane's personal phone line on button 1 (button 1:2). Note that the personal line on button 1 is the default line that's selected for outgoing calls when the phone's handset is taken off-hook (you can change this with the auto-line command).

Both phones have ephone-dns 3 and 4 associated with buttons 2 and 3. Ephone-dns 3 and 4 both have the same telephone number5001. The ephone-dns are set up so that the first call to the sales line goes to ephone-dn 3. If ephone-dn 3 is busy, a second incoming call will dial peer hunt on busy to ephone-dn 4.

Both ephone-dns 3 and 4 are present on both IP phones so that calls to either ephone-dn ring both IP phones. John and Jane can see at a glance which lines are in use.

Either John or Jane's phone can answer the first incoming call to 5001 SalesLine1. The second call rolls over to 5001 SalesLine2 and also goes to both phones. The phone that is busy with the first call sees the second call as call waiting (and hears a call waiting beep, which can be disabled). The other phone rings.

Furthermore, John can place his call on hold. This makes the call fully visible to Jane because it is on a shared line, and she can pick up the call simply by pressing the corresponding line button on her phone. Note that in this case of shared line pickup on hold, the call does not change lines. Rather, the active ownership of the line moves between the phones. The call stays on the same line throughout the call.

Using Overlay-dn

The preceding section described a simple two-by-two arrangement in which two phones share two IP phone lines. This type of arrangement can be expanded to, say, four lines shared by eight phones. However, there is a limit on how far you can go with this arrangement. A Cisco 7960 IP Phone has only six line buttons, so the maximum number of lines that it can directly share is six. If you also consider that the line buttons on a Cisco 7960 IP Phone can also be configured for speed dial or other uses, such as personal extensions and intercoms, you can see that it's fairly easy to run out of buttons.

The Cisco CME overlay-dn configuration provides a way around the physical button limit for many cases.

Example 5-17 shows an alternative arrangement for John and Jane's phones that provides a simple example of an overlay-dn configuration.

Example 5-17. Overlay-dns

router#show running-config ephone-dn 1 number 1001 name John Smith ephone-dn 2 number 1002 name Jane Smith ephone-dn 3 number 5001 preference 1 no huntstop name SalesLine1 ephone-dn 4 number 5001 preference 2 name SalesLine2 ephone 12 mac-address 000d.1234.0efc button 1:1 2o3,4 ephone 15 mac-address 000d.5678.0dcf button 1:2 2o3,4

The only thing that is different about this configuration relative to Example 5-16 is the button command button 1:1 2o3,4.

To configure a button for overlay use, you simply replace the colon button:dn separator with the letter o, for overlay. Following the o separator, you provide a list of two to ten ephone-dn tag numbers. You must have at least two ephone-dns in the overlay set to use the o separator.

You can see that this configuration uses only two buttons instead of the three buttons used originally. This leaves the additional buttons available for use as speed dial buttons, for example. Alternatively, you can use a lower-cost IP phone, such as the Cisco 7940 IP Phone, which has only two buttons instead of the six buttons of a Cisco 7960 IP Phone.

An overlay-dn arrangement works as a multiplexor. This works in a similar way to an old-fashioned printer-sharer device that allows multiple PCs to drive a shared printer.

When an incoming call arrives on one of the ephone-dns in the IP phone's button overlay set, the ephone-dn with the ringing call is multiplexed onto the appropriate button. At any time, only one ephone-dn in the overlay set is actively bound to the IP phone. When all ephone-dns in the overlay set are idle, the first ephone-dn in the set is the one that is actively bound to the phone. You can see this multiplexing activity using the show ephone command (examples of this are provided later in this book).

The ephone-dn is multiplexed into the active slot for the button when it needs to be used, as shown in Figure 5-2.

Figure 5-2. Overlay-dn Multiplexes Multiple Lines to a Single Button

When an outgoing call is attempted on a button that is configured for an overlay, the first available idle ephone-dn in the overlay set is selected based on the left-to-right order of the ephone-dn tags used in the phone's button overlay command.

The one drawback of the overlay-dn configuration is that you cannot perform the shared-line pickup on hold operation described in Example 5-16. Also, overlay-dn lines do not provide call waiting indication when multiple calls are present in the overlay set. This is because with ten lines mapped to a single button, the number of waiting calls can be rather large and generate too many interruptions.

When you use the overlay-dn configuration in a shared-line configuration (as in this example), it is recommended that you have at least as many lines in the overlay set as there are phones sharing. If there are more phones than lines in the shared-line overlay, when all ephone-dns are in use, you can get situations where there is no available ephone-dn to multiplex onto a phone. There is no specific harm in this situation, except the user confusion that may result when a user presses the line button and does not get dial tone (because no line is available).

An IP phone can have as many overlay sets as it has buttons. Each overlay set on each button on each IP phone can contain a unique set of ephone-dn tags. If you apply a ten-way overlay set to each of the six buttons on a 7960 IP Phone, 60 ephone-dns can be associated to the phone.

You can use an overlay-dn to support multiple lines, even on a phone such as the Cisco 7912 IP Phone, which normally is considered a single-line phone. The key difference between a single-line phone with a six-way overlay and a six-button phone with one ephone-dn per button is in the ability to see and navigate between calls. With a six-way overlay onto a single-line phone, you can see the status of only one line at a time. You also have no direct choice over which of the six lines is being used. The overlay multiplex mechanism makes the choice for you. With a six-button phone, you can see all the calls at once, and select between them by pressing the line button for the call you want.

The section "Using Overlay to Overcome Phone Button Count Limits" has more information on using overlays.

Called Name Display for Overlay Extensions

In most cases, when you overlay multiple extensions onto a single button, the set of extensions included in the overlay set is usually closely related, so you often don't need to distinguish between the individual extensions in an overlay set. But if you assign multiple unrelated extensions to the same phone button using an overlay, the phone user needs to know which extension is being called.

Cisco CME 3.2 introduced the called-name dialed number identification service (DNIS) to address this problem. This uses the command service dnis overlay (set under telephony-service). If this command is active, an incoming call on the (hidden) second through last members of the overlay set displays the extension name that is being called on the bottom line of the Cisco IP phone display. This name is set using the name command in the ephone-dn extension configuration. This allows the phone user to see at a glance which extension is ringing and allows the phone user to answer the call with a greeting appropriate to the specific extension. When the first (primary) extension in the overlay set is called, no name display appears, because the identity of the first extension line is implicitly indicated by the extension number display next to the phone line button itself.

Another thing to note about overlays is that if you put an overlay call on hold, the phone displays the extension number of the specific extension from the overlay set. This is useful if you want to perform a call on-hold extension pickup using the phone's pickup softkey.

Called Name Display for Non-Overlay Extensions

If you want to see the called name in cases where you are not using an overlay, you can use the service dnis dir-lookup command (under telephony-service). This command is useful when you are taking calls from the PSTN using a digital PRI trunk configured to receive calls for a large block of numbers and where each number is associated with a separate person or company.

For example, consider a doctor's answering service, where an agent may be taking messages for a group of 30 different doctors and where each doctor has a different answering service phone number for patients. In this simple example, assume that all the phone numbers are part of a specific block of numbers, say 555-0500 to 555-0529.

It's easy to set up a single Cisco CME extension to accept these calls using the "." wildcard character as part of the extension number:

ephone-dn 20 number 55505..

This takes care of routing the call to the right place, but it doesn't tell you which specific number is being called. To display the called name (for example, Dr. Smith for calls to 555-0500 or Dr. Jones for calls to 555-0501), you enable the service dnis dir-lookup command and configure the phone number-to-name associations that you want using the directory entry command as follows:

telephony-service service dnis dir-lookup directory entry 1 5550500 name Dr. Smith directory entry 2 5550501 name Dr. Jones

You can create a list of up to 100 directory entries to be used in this way. With this configuration, an incoming call to 555-0500 rings ephone-dn 20 and displays Dr. Smith, whereas a call to 555-0501 displays Dr. Jones. This allows the agent who answers the call to greet the caller with "Dr. Smith's answering service" or "Dr. Jones's answering service," as appropriate.

The ephone-hunt Command

The ephone-hunt command gives you a simple way to configure a sequential call group based on a list of extension numbers. You can configure up to ten ephone-hunt groups in a Cisco CME system (as of CME 3.0). Each ephone-hunt group can contain a list of up to ten extension numbers. Note that you should make sure that the global max-redirect limit set for your system (under telephony-service) is higher than the maximum number of internal forwards needed by your hunt groups.

You can choose from three ephone-hunt modes:

• Sequential mode This gives a simple ordered list of extension numbers. Each extension number in the list is tried in turn, always starting from the beginning of the list. If the end of the list is reached without finding an available number, the call is forwarded to a number configured as a final destination.
• Peer mode This gives a circular list of extension numbers. The starting point in the list for a new call is set by the last number tried for the preceding call. Because the list is circular, you have to set a parameter to limit how many times a call can be sequenced from one extension to the next. This value has to be less than the global call forwarding hop count limit set for the entire Cisco CME system by the max-redirect command. You have to do this to avoid an infinite hunting loop. You control it by setting the maximum number of hops for the call in the ephone-hunt command's subcommands. As soon as the maximum number of hops has been reached, the call is forwarded to the number defined as the final destination for the hunt group.
• Longest idle This also gives a circular list of extension numbers. The starting point in the list for a new call is set by the number that has been on-hook for the longest period of time. Again, because the list is circular, you have to set a parameter to limit how many times a call can be sequenced from one extension to the next. As soon as the maximum number of hops has been reached, the call is forwarded to the number defined as the final destination for the hunt group. The longest idle option was introduced in Cisco CME 3.2.

Example 5-18 provides a configuration for these modes.

Example 5-18. ephone-hunt Command

router#show running-config ephone-hunt 1 sequential pilot 5001 list 1001, 1003, 1007, 1008 final 6001 preference 1 timeout 15 ephone-hunt 2 peer (or longest-idle) pilot 5002 list 1002, 1003, 1008, 1009 final 6002 hops 3 preference 1 timeout 15

If you look at the two ephone-hunt commands in Example 5-18, you can see that some of the extension numbers are present in both ephone-hunt lists. This illustrates one of the advantages of ephone-hunt. In the previous examples, hunting to the IP phone ephone-dn lines is based on binding telephone numbers directly to the ephone-dns themselves. Because you can directly bind only two numbers per ephone-dn (the primary and secondary numbers), you are limited in how many simultaneous ways you can route calls to the ephone-dn.

In Example 5-13, you saw how both phones could be called using the numbers 1001 and 1007. This was done using the ephone-dn secondary number of the individual ephone-dns. You cannot add a third phone using this technique.

Example 5-17, which uses an overlay-dn, allows for greater expansion, but at the expense of consuming additional ephone-dns (at about 50 KB of memory per ephone-dn).

The other issue with using hunt numbers directly associated with the ephone-dns is that the call hunting path goes directly through each ephone-dn. This means that if you set any type of call forwarding on the ephone-dn (forward all, on busy, or no-answer), this forwarding affects the call hunt path too.

This is not true when you use the ephone-hunt command. You can set call forwarding on the individual ephone-dn without affecting the call hunt path defined by the ephone-hunt list.

When you use the ephone-hunt command and enter a list of numbers, here's what happens:

• The system searches for all ephone-dn entries that have primary numbers that match the ephone-hunt list.
• For each ephone-dn that matches, the ephone-dn builds an additional dial peer. This dial peer has a number that's derived from the ephone-hunt pilot number plus the relative position of the matched number in the ephone-hunt list. The dial peer also includes the virtual voice port number from the matching ephone-dn.

When you configure call forwarding under ephone-dn, the call forwarding information is inserted into the dial peers that are directly bound to the ephone-dn. The call forwarding information is not included in the dial peers created by the ephone-hunt command.

You also notice that the ephone-hunt command lets you set a preference value. As you might expect, this is a dial peer preference. The dial peer preference is inserted into the dial peer that is created by ephone-hunt to match the ephone-hunt pilot number.

For the ephone-hunt configuration examples shown, at least five dial peers are created. One dial peer is created for the pilot number. One dial peer is created for each ephone-dn that is found that matches one of the numbers in the list. If multiple ephone-dns match the individual numbers in the list, each of those ephone-dns causes the creation of an additional dial peer.

Here is a description of what you see for ephone-hunt 1 in Example 5-18:

• The pilot number creates a dial peer with destination pattern 5001. This dial peer has call forward all set to the first dial peer in the hunt list.
• The first member of the list creates a dial peer with destination pattern A5001A0001. This dial peer contains the virtual voice port number of the ephone-dn that has 1001 as its primary number. This dial peer has call-forward busy and call-forward no-answer set to the next ephone-hunt dial peer. The call-forward timeout value is set by the timeout subcommand under ephone-hunt.
• The second member of the list creates a dial peer with destination pattern A5001A0002. This dial peer contains the virtual voice port number of the ephone-dn that has 1003 as its primary number. This dial peer has call-forward busy and call-forward no-answer set to the next ephone-hunt dial peer.
• The third member of the list creates a dial peer with destination pattern A5001A0003. This dial peer contains the virtual voice port number of the ephone-dn that has 1007 as its primary number. This dial peer has call-forward busy and call-forward no-answer set to the next ephone-hunt dial peer.
• The fourth and final member of the list creates a dial peer with destination pattern A5001A0004. This dial peer contains the virtual voice port number of the ephone-dn that has 1008 as its primary number. This dial peer has call-forward busy and call-forward no-answer set to the number defined as the final destination for the ephone-hunt.

The digit A in the destination pattern is the DTMF digit A from the extended set of DTMF digits A to D. The digits A to D are routable digits within the Cisco IOS voice infrastructure software and can be used just like the digits 0 to 9 and *. The digit # is often used as a dial digit string terminator.

You can view all the dial peers created by the ephone-hunt command using the Cisco IOS command show dial-peer voice summary. Example 5-19 shows the dial peers associated with ephone-hunt 1 in Example 5-18.

Example 5-19. Ephone-hunt 1 Dial Peers

router#show dial-peer voice summary TAG TYPE ADMIN OPER DEST-PATTERN PREF SESS-TARGET 20051 pots up up 1001 0 50/0/1 20053 pots up up 1003 0 50/0/3 20057 pots up up 1007 0 50/0/7 20058 pots up up 1008 0 50/0/8 20069 pots up up A5001A000 1 50/0/1 20070 pots up up 5001 1 50/0/1 20071 pots up up A5001A001 1 50/0/3 20072 pots up up A5001A002 1 50/0/7 20073 pots up up A5001A003 1 50/0/8

The SESS-TARGET column shows the virtual voice port numbers that correspond to ephone-dns 1, 3, 7, and 8.

Using Ephone-dn Dual Line

The several previous call coverage examples included ephone-dns configured in the default single-line mode. This helps keep the examples relatively simple. If you use ephone-dn dual-line mode, you should consider how you want to treat call waiting calls.

When you create an ephone-dn configured as dual line, you provide the ephone-dn with a virtual voice port that has two subchannels so that it can accept two simultaneous calls. This operates in a similar manner to an ISDN BRI voice port that has two bearer channels. By default, for a dual-line ephone-dn, when the first subchannel is busy with an active call, a second call is routed onto the second channel.

This behavior is usually not wanted in a hunt group. You normally want the second call to go to the next member of the hunt group instead of being present as a waiting call on the first member.

If you configure the ephone-dn as a single line, you don't need to worry about this behavior. In this case, no second channel exists, so there is no choice but for the second call to go to the next hunt group member.

To prevent the presentation of call waiting calls in a hunt group situation, you should use the command huntstop channel. This command can be used independently of, and in addition to, the plain huntstop command. The huntstop channel command prevents incoming calls from hunting on busy from the first virtual voice port channel to the second channel. It does not affect hunting between dial peers. It influences channel hunting only within the voice port. The huntstop channel command can be used in any dual-line ephone-dn. Its use is not restricted to ephone-hunt.

The effect of the huntstop channel command is to prevent incoming calls from reaching the second channel of a dual-line ephone-dn. This effectively reserves the second channel for outgoing calls from the ephone-dn. This can be used to guarantee the availability of the second channel to support the second call instance required for features such as three-party conference and call transfer with consultation.

If you use ephone-dn configured as dual line within a hunt group situation, it is recommended that you also use the huntstop channel command, as shown in Example 5-20.

Example 5-20. huntstop channel Command

router#show running-config ephone-dn 1 dual-line number 1001 huntstop channel ephone-dn 3 dual-line number 1003 huntstop channel ephone-dn 7 dual-line number 1007 huntstop channel ephone-dn 8 dual-line number 1008 huntstop channel ephone-hunt 1 sequential pilot 5001 list 1001, 1003, 1007, 1008 final 6001 preference 1 timeout 15

Hunting Chains

Cisco CME provides a flexible set of mechanisms to support call coverage. These mechanisms are based on creating dial peers that are linked using hunt-on-busy arrangements and call forwarding.

The ephone-hunt command includes the option to set a final destination to forward calls to, when all hunt group members are busy. The number you forward to is itself resolved by another dial peer somewhere in the system. There is no restriction on the nature of the dial peer this number is linked to. The dial peer selection for the final number is based on the normal Cisco IOS voice infrastructure rules, taking into consideration criteria such as longest match and dial peer preference.

You can set the final destination of one ephone-hunt group to be the pilot number of a second ephone-hunt. The only restriction to consider is that the total number of times a call is forwarded cannot exceed the maximum set by the max-redirect command (under telephony-service). This has an allowed range of 5 to 20. You must count the internal forwarding hops included in each ephone-hunt when you figure the forwarding limit.

Also note that there is no restriction on the ephone-dn configuration matched by the ephone-hunt list. The ephone-dns matched to the ephone-hunt list can be part of more complex configurations. For example, you can use shared lines and overlay-dn as matches for the ephone-hunt list. This lets you create some very complex call coverage arrangements, including arrangements that perform sequential-parallel hunting, in which different groups of phones ring in a defined linear or circular sequence.

One final point here is that setting call-forward all for an ephone-dn that is part of a hunt group does not break the hunt group forwarding sequence. This is because the call-forward all is applied only to the ephone-dn's main dial peer, not to the subsidiary dial peers that are generated by the ephone-hunt command. To temporarily remove a phone from a hunt group, you simply put the phone into Do-Not-Disturb mode (the Cisco CME 3.2 DND feature).

Immediate Diversion of Calls to Voice Mail

In earlier sections, you saw the use of the call-forward busy and call-forward noan (no answer) commands to control call forwarding of calls for busy and no-answer extensions. In many cases, the number the call is forwarded to is the pilot number for a voice mail system.

Cisco CME 3.2 and later allows the person receiving a call to cause the incoming call to be forwarded immediately without having to wait for the no-answer timer to expire. (This is applicable only on Cisco IP phones that have softkeys.) When an incoming call is presented, the phone user sees two softkeys: answer and DND (Do Not Disturb). If the user's phone has call-forward no-answer configured, pressing the DND softkey causes the incoming call to be forwarded immediately to the number configured for call-forward no-answer (typically the voice mail number).

If no call-forward no-answer is configured for the extension, pressing the DND key simply mutes the phone's ringer until the call is cancelled (by the caller hanging up). The ringer mute DND action is temporary and applies only to the current call when used in the manner described. The phone can also be placed in a permanent muted ringer state by pressing the DND softkey while the phone is in the idle state. This allows the phone user to screen incoming calls, because the phone display is still active and shows the caller ID for incoming calls. If a phone user wants to avoid all incoming calls, you can use the cfwdall (call forward all) softkey to set up unconditional forwarding of incoming calls to voice mail (or another extension). In this case, there is no indication of incoming calls on the user's phone.

Call Coverage Summary

This section has described a wide array of techniques for providing call coverage solutions. You can use the dial peer hunting mechanisms provided by the Cisco IOS voice infrastructure features. You can use call forwarding. You can use the ephone-hunt mechanism. You also have the option of using overlay-dn. You may combine several of these options to produce complex call coverage paths.