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7.9 Least Cost Routing (for U.S. Only)

7.9.1 Introduction

This section explains the definitions and procedures used by the Hicom 150 E least cost routing (LCR) feature to control the path over which outgoing calls are routed to the public network.

The system analyzes each trunk call placed using least cost routing. If the digits are recognized, a reference route table is scanned for route-group choices. After the route group is selected, the availability of the route is checked against the time schedule. If the route group is available, the LCR class-of-service requirement assigned to the route group is compared to the LCR class of service associated with the dialing device. If the LCR class of service associated with the dialing device is equal to or greater than the route-group class of service, the toll-restriction tables are then checked for additional screening information.

The dialed call number is used as the criterion for the connection path to be used. The system can evaluate up to 24 digits of the digit sequence plus up to 9 field separators. The digit sequence that can be dialed can consist of up to 32 digits. The evaluation can be carried out both destination dependently and time dependently and in dependence on the station's LCR class of service (COS).

General Operating Principle

The system analyzes the number dialed to determine if the digits input are valid. If the digits are recognized, a reference route table is scanned for Route group choices. Once the Route group is selected, the availability of the route is checked against the time schedule. If the Route group is available, the LCR COS requirement assigned to the route group is compared to the LCR COS associated with the dialing device. If the LCR COS associated with the dialing station is equal to or greater than the route group COS, the Toll Restriction tables are checked for additional screening information. This process is repeated for every call using the system LCR application.

Figure 7-5 General LCR Flow (for U.S. Only)

A system-wide flag activates LCR via Hicom Assistant T or Hicom Assistant E Office.
When LCR is activated, the check is performed for every trunk seizure (except when dialing a trunk code).
If all the least expensive connection paths have been seized, LCR automatically switches to defined more expensive paths. The user can be signaled of this fact both visually and acoustically.
In the case of outgoing calls on the ISDN network, the dialed number continues to be displayed until the destination number information on the other party is received.
Digits can be transmitted either per digit or en-bloc, depending on the access method and the dial plan.
Once an account code is entered, it applies to the entire connection setup.
The allowed and denied lists are also used for LCR. The toll restriction check then refers to the digits dialed on the station without the trunk group code.

Configuration

For instructions on configuring least cost routing using Hicom Assistant E Office, refer to Section 8.34.1.
For instructions on configuring least cost routing using Hicom Assistant T, refer to Section 8.34.2.

7.9.2 Carrier Types

Since in many cases the individual carriers provide specific connections and conditions at different tariffs (with different signaling methods, when applicable), the least cost routing feature can be used for automatically selecting the most economical connection or most economical carrier for each outgoing telephone call.

The following carrier types and networks are available for implementing least cost routing (LCR):

AT&T
MCI
Sprint
Westinghouse
U.S. Government Federal Telephone System FTS-2000

Connections to the local exchange carrier (LEC) are toll-free. Connections to the inter-exchange carrier (IEC) are handled by the carriers listed above. The LEC has a default IEC that it uses for long distance calls unless the user selects another carrier. To select another carrier, the user must first dial the IECs Carrier Access Code (CAC) and Carrier Identification Code (CIC).

There are two different types of CIC numbering schemes: one for a 3-digit CIC and another for a 4-digit CIC. The four-digit code consists of the three-digit code preceded by the number 0. For example, the CIC for MCI is 222 or 0222.

The CAC for a three-digit CIC is 10, and the CAC for a four-digit CIC is 101.

7.9.3 Using Alternate Carriers

Alternate carriers may be connected to each trunk route group. The selection of the carrier is defined in the least cost routing outdial-rule section.

7.9.3.1 Carrier Access Methods Supported

Main Carrier

When seizing a trunk using the main carrier, the system can use en-bloc dialing or send single digits to the public network to set up the outgoing call. Note that this access method is used when routing calls over the public switching network.

MCL Single Stage

The system calls the selected carrier using a prefix and then dials the destination number. Digits are sent in the D channel when using ISDN service or as normal dialing when using analog service. This selection may be used in CorNet applications for advancing to public network facilities for overflow applications.

MCL Two Stage

The system calls the selected carrier using a prefix in this method as well. After a short synchronization phase, it sends a programmable authorization code and then the destination number using DTMF digits.

Corporate Network (CorNet)

When a corporate network (CN) method is used, the alternate network is connected directly to the Hicom 150 E. This can be seen as a company network. LCR determines the trunk group by analyzing the number the user has dialed and routes the call either over the CO trunk group or over the corporate network. This method allows both an open and closed numbering plan to be implemented by manipulation of digits.

Dial-In Control Server

The system calls the selected carrier using a prefix and calls a dial-in control server (DICS). The authorization code and the destination number are transmitted within the SUB address. Dialing information is sent in the D channel.

Primary Rate Interface

The choice of a carrier or of a calling service is encoded in the following information elements:

Network specific facility
Operator system access
Transit network selection

LCR Dial Plan

The dialed destination number serves as a criterion for the route group to be used. The system can evaluate up to 24 digits in the dialed sequence plus the routing code. The system evaluates and routes the call based on a time of day schedule and the station's least cost routing class of service.

Destination-Dependent Evaluation

The dialed digit sequence may be converted to a new digit sequence after evaluation, or it may be preceded by additional digits such as the carrier information of the destination.

7.9.4 LCR Time of Day Evaluation

The time table allows the system to evaluate the availability of a selected route according to a maximum of eight time zones. For each weekday, the number can be evaluated in hour:minute intervals throughout the day.

7.9.5 LCR Outdial Rules

The dialed number can be converted to any new digit sequence (up to 40 digits). The system can evaluate up to 514 digit sequences dialed from the station. Wildcards may be used in the LCR dial-plan table. The system supports 254 outdial rules for digit translation requirements as well.

7.9.6 Expensive Route Identification

If the first route selection in the route table is busy, the LCR function can advance to the next expensive path configured in the route group table. The system can notify the user of this with an audible signal, an optical signal, or both. Users can then decide whether they would like to use the assigned path or hang up.

7.9.7 Overflow Options

When the LCR function determines that the preferred trunk or tie-trunk group cannot be used, it can select an alternate trunk group within the selected route-group table.

7.9.8 LCR Class of Service

Up to 15 station-specific trunk classes of service are possible. The class of service setting controls access to the configured route groups in the LCR route-group table.

7.9.9 Carrier-Select Override

Carrier-select override (CSO) can be implemented using selective line seizure. In this case a connection can only be set up via the main carrier.

7.9.10 Handling of Numbers and Destinations and Trunk Group Access Codes

All numbers except internal station numbers are stored as an LCR digit string. All numbers dialed by a user are displayed without routing information. The dialed numbers remain displayed until answer supervision is received from the central office. If more than one trunk group access code is programmed for a trunk group, the first access code is the default.

If the number of the called party during an outgoing connection is also stored in the optiset caller list or if a callback is activated, the number dialed by the user is stored instead of the destination number sent by the system. In this case, the trunk group access code is also stored so that the system can recall the party from the caller list using the correct access code.

7.9.11 Correlation With Other Features

This section describes how the least cost routing application interacts with other system features

7.9.11.1 Station-Related Features

System speed-dialing call numbers must be prefixed with the LCR access codes for proper operation.
Station redial will insert the access code used for the original call.
Repertory dial keys to external destinations must have the LCR access code for proper operation.
Electronic notebook entries on optiset E memory telephones must include an LCR access code.
General call keys will be activated when the route is selected by the system.
Call keys will be activated when the route is selected by the system.
MUSAP keys may be used for external calling using the LCR access code.
DTMF tones may be input manually when answer supervision is received.
Toll restriction class of service is checked as part of the LCR analysis.

7.9.11.2 Trunk-Related Features

Basic rate ISDN trunks may be accessed by stations assigned CACH values or PDID values.
Verified forced account codes may be requested before a selected route group is accessed.
DTMF or rotary pulse dialing may be selected based on the outdial rule

Additional Information Concerning the Setup of Public Network Trunks

The class of service configured is valid on a locked terminal (code lock).
It is possible to send speed-dialing numbers after selecting the network.
If speed-dialing numbers are used without first selecting the network, the default network is used (carrier-select override).
When LCR is activated, no trunk group overflow is performed. An alternative route can be determined using the path table.
When LCR is activated, no digit repetition is performed; the routing tables are followed instead.
Message waiting and automatic callback follow the rules for LCR.
An account code entered by the user is valid for the whole connection, even if more than one route over different trunk groups was tried during connection setup.
In the case of connections via other network providers or carriers, the provider or carrier may not transmit the actual connection costs, i.e., it may send the Hicom 150 E only the charges to the dial-in node (such as a dial-in control server [Europe only]).

7.9.12 Routing Tables

The routing tables evaluate the digits that the user has dialed and determine the destination number to be dialed from the system. The digits may be changed (manipulated) during this process. Digit translation makes it possible to repeat, suppress, and add digits or convert digit sequences. It is also possible to insert an inter-digit pause and change the signaling method. A distinction is made between the routing tables discussed in the following sections.

7.9.13 LCR Dial Plan

In the case of external calls, the system checks each number dialed up to a total of 25 digits, including field separators and trunk-group access codes. The dial-plan entry is associated with a route group for the destination number and the system assigns this path to the station for setting up the connection.

The dial plan may be separated into unique fields for identification and configuration purposes using the outdial rules. Table 7-2 shows the numbers 4922000 and 14084922000 entered in the dial-plan table.

Table 7-2 Sample Entries in a Dial-Plan Table

Field 1 
 
Field 2 
 
Field 3 
 
Field 4 
 
Field 5 
492 
2000 
 
 
 
 
408 
492 
2000 
62659321 
Reset boards and port assignments stored in the system. 
 
 
 
 
 
 
 

The following entries are valid for the destination:
0 . . . 9
Allowed digits 
-
Field separator (maximum of 10 fields per dial-plan entry) 
C
Simulated dial tone (can be entered up to three times). This entry is also interpreted as a field separator. 
X
Any digit between 0 and 9 
N
Any digit between 2 and 9 
Z
One or more digits follow before end of dialing 
C
Simulated dial tone (can be entered up to three times) 
 
Notes: The character # within a dial string means end of dialing or signaling method changeover. For this reason, * and # are not valid entries. Outdial rules may be used to insert the * and # in the dial string to the public network. 
Do not confuse the dash (-) symbol in the destination field, which functions as a field separator, with the dash in the Route Table field, which functions as a call blocker (refer to Table 7-3). 

If Prime Line is used, no LCR is possible.

For the LCR dial plan to accurately select the route group, the dial-plan entries must be entered as follows.

Entries should be placed in ascending numeric order from 0 to 9. Specific dialed numbers must precede wildcard entries to prevent conflicts in matches with wildcard entries. Table 7-3 is an example of the suggested entry order.

Table 7-3 Sample Entries in a Dial-Plan Table

Entry No. 
Dialed Digits
(code + station no.) 
Route Table 
9C0Z 
9C011Z 
 
9C492-5001 
9CNXX-XXXX 
9C1-NXX-XXX-XXXX 
9C1-900-XXX-XXX 
-1  
9C1-976-123-3456 
-2  
... 
 
 
254 
 
 

1 In this example, the dash (-) blocks all 900 numbers from being dialed.

2 In this example, the dash (-) blocks only the specific number (976-123-3456) from being dialed.

The fields formed by the field separators "-" and "C" in the dial plan can be addressed selectively to repeat, suppress, exchange, or insert digits.

7.9.13.1 Rules for Creating LCR Dial Plan Entries

The first field should contain only a programmed trunk group access code. It must not contain any wildcards.
The wildcards N and X can occur more than once in any field except the first field.
The wildcard Z can occur only in the last field. It represents an undetermined number of suffix digits.
A digit sequence can be divided into a maximum of 10 fields.

7.9.14 Route Table

A route table contains up to 16 paths. Each path is described by a combination of the following:

Route group
Outdial rule
Trunk access
Time schedule plan
Code for an expensive path

Paths

The system contains 254 path tables, each with 16 paths. LCR evaluates the trunk access in hierarchical order.

Search Order

The system searches the path table from top to bottom. If the located path is busy, or if the station does not have the proper class of service, the system continues to the next path.

Outdial Rule

The outdial rule is described in Hicom Assistant E Office by its name, which can be up to 16 characters long, and by its index in system administration.

Carrier-Select Override

Users can deactivate automatic selection within the path by selecting a specific carrier (carrier-select override, CSO). For CSO to work, the requested carrier must be located in the dial plan and the path table assigned by the dial plan, and the user must have the required trunk access.

7.9.15 Time Table

To control LCR it may be necessary to configure up to eight time zones per day. These time zones are programmable for every day of the week. Each day begins at 12:00 a.m. Entering the end time in each of the columns delineates the time zones.

7.9.16 Outdial Rule Table

Table 7-4 is a sample outdial rule table. The outdial rule table determines the following:

The way the digits entered by the user are converted and dialed by the system
The route on which dialing will take place
The maximum amount of time the LCR function has to control dialing
Up to 254 outdial rules, each up to 40 characters long, can be defined.

Outdial rules are defined by the following parameters:

A: Repeat all remaining fields (transmit).
D (n): Dial a digit sequence (1 to 24 digits).
E (n): Repeat field (1 to 10) from dial plan.
M (n): Authorization code (1 to 16). This letter must not be in the final position.
P (n): Pause (1 to 60 times the system-wide pause unit)
S: Switch, changes signaling methods from DP to DTMF (with CONNECT, PROGRESS or CALL PROC with PI).
C: Access code
U: Use subaddress signaling method.
N (n): Network SFG (1 to 5) or Band Number (1)

Table 7-4 Sample Outdial Rule Table

Number 
Name 
Outdial Rule 
Type 
Dial All 
Main network provider 
Dial Fld 2 Then 3 
E2E3 
Main network provider 
Dial All _P_ D444 
AP1D444 
Main network provider 
Dial 4 Dial All 
D4DA 
Corporate network 
... 
 
 
 
254 
 
 
 

The outdial rules provide access to different carriers via digit translation. The outdial rules address the dial plan fields selectively for the following operations:

Repeating digits
Suppressing digits
Exchanging digits
Inserting digits
Inserting pauses
Switching the signaling method
Detecting a dial tone.

Using the A Parameter

The parameter A ensures that all subsequent digit fields are transmitted. The reference point is the last field indicator preceding A. The parameter A can occur more than once in the string and can be placed in any position. The AA combination has the same effect as A. The E1A combination is permitted only at the beginning of a string.

Using the D Parameter

The parameter D (n) can occur more than once in the string and can be placed in any position. The parameter D (n) can be surrounded by any other parameters. It should be no more than 25 characters long.

Using the E Parameter

The parameter E (n) can occur more than once in the string and can be placed in any position. The parameter E (n) can be arranged in any order, depending on n. A determining field can be addressed more than once, even consecutively. With the exception of the E1A combination, E (n) can be surrounded by any other parameters. The n can be any number between one and 10.

Using the M Parameter

The parameter M (n) can occur only once in the string. The parameter M (n) should not be placed in the final position in the string. The n can be any number between one and 16.

Using the P Parameter

The parameter P (n) can occur more than once in the string and can be placed in any position. The parameter P (n) can be surrounded by any other parameters. The pause length is n times the length of the system pause. The n can be any number between one and 60.

Using the S Parameter

The parameter S can occur only once in the string and should not be placed in the final position in the string. It cannot precede the C parameter.

Using the C Parameter

The parameter C can occur only once in the string. The digits following C are sent without dial pause. The parameter C is used for carrier access with single stage, two stage, DICS and PRI. It cannot be used after S.

Using the U Parameter

The parameter U can occur only once in the string. It should not be placed in the final position in the string. The subsequent characters are re-selected in INFO. The following parameters may not be used after U:

S
P
C
M

Using the N Parameter

The parameter N can occur only once in the string and should not be placed in the first position. The subsequent digits are the SFG or the band number, depending on the calling service.

Authorization Code

Up to 16 authorization codes with a maximum of 16 digits can be entered for accessing services from different carriers. The codes may be used for accessing special common carriers or adding additional digits to a dial string as part of the outdial rule.

Example: 53276543

One secure authorization code is provided (displayed as **********).

7.9.17 Operation

The system does not seize a trunk until it has completed the routing tables. To inform the user that the telephone is ready for dialing, you can insert a dial tone into the LCR dial plan using the letter C. The dialed digits are buffered until the system completes the routing tables. Only then is a connection set up.

The route table (1 to 254) is first determined via the dial plan on the basis of the dialed destination number. If the destination number is not found in the dial plan, the user receives a busy signal.

The route table for each route element describes the following:

The trunk group assigned to the path
The outdial rule
The trunk access needed for seizure
The required time plan
The code of an expensive path (warning tone)

The out-dial rule determines the outgoing dialing procedure for the selected trunk group. Selection may be unsuccessful for one of the following reasons:

Busy route group
Time-of-day restriction
LCR class-of-service restriction

In this case, another carrier can be selected via the alternative paths. You can configure an expensive-path warning tone to sound when an expensive carrier is selected.

The destination number that the user dialed is generally displayed until the requested party answers (ALERT or CONNECT). Then the destination number reached is displayed if available. The dialed destination number is stored in the station's redial memory.

Figure 7-6 shows a sample LCR flow diagram.

Figure 7-6 Sample LCR Flow Diagram (for U.S. Only)

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