Introducing Dial Plans (Identifying Dial Plan Characteristics) (Cisco Voice over IP (CVOICE)) Part 2

PSTN Dial Plan Requirements

A PSTN dial plan has three key requirements:

■ Inbound call routing: Incoming calls from the PSTN need to be routed correctly to their final destination, which might be a directly attached phone, including endpoints that are handled by Cisco Unified Communications Manager or Cisco Unified Communications Manager Express. This inbound call routing also includes digit manipulation to ensure that the incoming Dialed Number Identification Service (DNIS), that is, the incoming called number, matches the pattern expected by the final destination.

■ Outbound call routing: Outgoing calls to the PSTN need to be routed to the voice interfaces of the gateway—for example, a T1/E1 or a Foreign Exchange Office (FXO) connection. As with inbound calls, outbound calls might also require digit manipulation to modify the DNIS according to the PSTN requirements. This outbound call routing usually includes stripping of any PSTN access code that might be included in the original called number.

■Correct PSTN Automatic Number Identification (ANI) presentation:  An often-neglected aspect is the correct ANI presentation for both inbound and outbound PSTN calls. The ANI for inbound PSTN calls is often left untouched, which might have a negative impact on the end user’s experience. The calling number that is presented to the end user should include the PSTN access code and any other identifiers required by the PSTN to successfully place a call using that ANI—for example, using the missed calls directory.

Inbound PSTN Call Example

Figure 6-4 shows a call flow for an inbound call.

Figure 6-4 Inbound PSTN Calls

A site consists of an H.323 gateway that is controlled by Cisco Unified Communications Manager. The DID range of the PSTN trunk is 4085552XXX, and phones use the extension range 2XXX. Here is the process the inbound call goes through:

1. A PSTN user places a call to 14085552001; that is, to Phone1-1.

2. The call setup is received by the gateway with a DNIS of 4085552001.

3. The gateway modifies the DNIS to 2001, the extension of Phone1-1, and routes the call to the voice port created when the IP phone registered with UCME.

4. The phone rings.

Outbound PSTN Call Example

Figure 6-5 shows a call flow for an outbound call.

A site consists of an H.323 gateway and a Cisco Unified Communications Manager server. The DNIS that Cisco Unified Communications Manager sends to the gateway includes the PSTN access code 9, and the ANI is the 4-digit extension of the phone. The process of the outbound call is as follows:

1. Using Phone1-1 with the extension 0151, a user places a call to 9 1 512 555-0101.

2. The gateway accepts the call and modifies the DNIS to 1 512 555-0101, stripping off PSTN access code 9. The gateway also modifies the ANI to 408 555-0151 by prefixing the area code and local code to the 4-digit extension.

Figure 6-5 Outbound PSTN Calls

3. The gateway sends out a Q.931 setup message to the PSTN with an ANI of 4085550151.

4. The PSTN subscriber telephone at 512 555-0101 rings.

ISDN Dial Plan Requirements

When you are using ISDN trunks, additional requirements might exist:

■ Correct PSTN inbound ANI presentation depending on TON: Some ISDN networks present the inbound ANI as the shortest dialable number combined with the type of number (TON). This treatment of the ANI raises an issue because simply prefixing the PSTN access code might not result in an ANI that can be called back. The potential problem can be solved by proper digit manipulation on gateways.

■ Correct PSTN outbound ANI presentation depending on TON: Some ISDN networks and PBXs might expect a certain numbering plan and TON for both DNIS and ANI. Using wrong flags might result in incomplete calls or wrong DNIS and ANI presentation. Again, digit manipulation can be used to solve these issues.

Inbound ISDN Call Example

Figure 6-6 shows a call flow for an inbound ISDN call.

A site consists of an H.323 gateway that is controlled by Cisco Unified Communications Manager Express. The DID range of the PSTN trunk is 408555XXXX, and phones use the extension range 01XX. The process of the inbound ISDN call is as follows:

1. A PSTN user in Chicago with the number 512 555-0101 dials 1 408 555-0101.

2. The gateway receives an ISDN setup message with the DNIS 4085550101 and the ANI 5125550101 TON National.

Figure 6-6 Inbound ISDN Call

3. Based on the ANI TON, the gateway prefixes 91 to the ANI (9 as the PSTN access code and 1 as the national identifier).

4. The call is routed to Phone 1-1, and the calling number is displayed: 915125550101. A user who misses the call can directly call back using the missed call directory without any modification.

Configuring PSTN Dial Plans

You can use the following steps to configure PSTN dial plans.

Step 1. Configure digit manipulation for PSTN calls.

Step 2. Configure digit manipulation for intersite calls.

Step 3. Configure dial peer matching.

PSTN Dial Plan Example

In the example illustrated in Figure 6-7, you are required to develop and implement a dial plan for your company.

The dial plan must meet network requirements as specified. The configuration scenario that is represented in this figure will be used throughout this procedure.

Dial Plan Requirements

Dial plan requirements are as follows:

■ San Jose site:

Cisco Unified Communications Manager Express on Router1 DID range 4085552XXX DN range 2XXX

Figure 6-7 PSTN Dial Plan Scenario

■ Austin site:

Cisco Unified Communications Manager Express on Router3 DID range 5125553XXX DN range 3XXX

■ Any intersite calls routed using the PSTN will require digit manipulation to change the dialed remote extension to a PSTN routable number (for example, 2001 to 14085552001).

Digit Manipulation for Inbound Calls

Examples 6-1 and 6-2 provide the configurations for Router1 and Router3, which perform digit manipulation for inbound calls.

Example 6-1 Digit Manipulation for Inbound Calls on Router1

Example 6-2 Digit Manipulation for Inbound Calls on Router3

The following describes the configuration applied to Router1 (which is similar to that of Router3):

Step 1. Voice translation rule 1 is used to modify the inbound called number to the actual directory number:

Step 2. The voice translation profile pstn-in is used to modify the incoming called and calling number:

Step 3. The voice translation profile pstn-in is bound to the voice port and will be used for any incoming call: