Centrex ( central office exchange service ) is a service from local telephone companies in the United Stated in which up-to-date phone facilities at the phone company`s central ( local ) office are offered to business users so that they don’t need to purchase their own facilities. The Centrex service effectively partitions part of its own centralized capabilities among its business customers. The costumer is spared the expense oh having to keep up with fast-moving technology changes ( for example, having to continually update their private branch exchange infrastructure ) and the phone company has a new set of services to sell.

Centrex is the generic name of telecommunication services, similar to Private Branch Exchange ( PBX ), offered by an operating company that uses the capabilities of a public switching system. The idea of Centrex service is to integrate features normally associated with a Private Branch Exchange ( PBX ) based telecommunication system. This allows for a flexible environment to support the communication requirements of a business customer.

In many cases, Centrex has now replaced the private branch exchange. Effectively, the central office has become a huge branch exchange for all of its local customers. In most cases, Centrex ( which is sold by different names in different localities ) provides customers with as much if not more control over the services they have than PBX did. In some cases, the phone company places Centrex equipment on the customer premises.

Typical Centrex service includes direct inward dialing ( Direct inward Dialing ), sharing of the same system among multiple company locations, and self-managed line allocation and cost-accounting monitoring.

1.1 Who can use Centrex

Centrex service for the grouping of station lines associated with a business, or other entities that have common telecommunication interests, e.g. Universities, Airlines All stations associated with a Centrex group share common attributes.

1.2 The Centrex Group

A Centrex group exist of subscribes, PBX-lines in a public switch, that have been grouped by the administration. For each Centrex Group EWSD provided the following basic features:

restrictions to provide or to deny access to call handling features.
a special dialling plan shared by all members of the group
group specific intercept treatments
special billing for calls within the Centrex Group
group specific control parameters
group specific traffic measurements with the ability to send traffic measurement data to the DSB:ISDN serving as attendant console for further processing
group specific collection of detailed call information with the ability to send this call data to the DSB:ISDN serving as attendant console for further processing.

A Centrex group may be spread over more than one central office. A station at the local office may call a station at one of the other offices- named „ remote station „ – using the centrex group`s dialling planning plan.

1.2.1 The Centrex Stations

The Station lines associated with the Centrex group may either be regular subscriber lines, ISDN BA lines connected to DSB:ISDN`s serving as attendant consoles, or may be members of a multi line hunt group ( MLGH ) that have direct appearance on the switch. The Regular subscriber lines are considered to be standard analog ( rotary or push bottom ) or ISDN BA subscriber lines ( CCITT bluebook Standard, connected to EWSD via LTGB and DLU. Customer premises equipment ( CPE ) is connected to EWSD like a standard analog subscriber, also via LTGB and DLU.

Analog PBX`s without DID are connected to EWSD via DLU. Digital PABX`s with DID are considered to be connected to EWSD via LTGB, digital interface unit ( DIU ) and / or PCM links. An ISDN PABX with or without DID may be connected via LTGB and DLU as a BA in Terminology: Throughout this document, the term PBX is used for analog PBX`s without DID, digital PABX`s with DID, and ISDN PABX`s with or without DID. This is in accordance with the craft interface. The Centrex station is generated by adding the Centrex attribute to either a subscriber directory number, to the directory number of a CPE line, or the pilot directory number of a MLHG or PBX. All lines of a MLHG or PBX are per definition also member of the Centrex group.

1.2.1.1 Centrex Intercom Numbers

Centrex stations based on local office subscribers have a public directory number as well as a Centrex group internal number assigned, the intercom number. Centrex stations based on a MLHG must have at least on public DN – the Pilot DN – and may have an All lines of a MLHG may have an individual public directory number – the line service number – and, whenever they have one, they also may have an intercom number. A DID:PABX – digital or ISDN – cannot have an intercom number assigned to the PABX. A PBX without DID may have an intercom number assigned. The intercom number is specific to the Centrex group dialling plan.

1.2.1.2 Centrex Subscriber Features:

A Centrex subscriber station in general may have all of the features offered to a non-Centrex subscriber, if not provided by Centrex features. For each Centrex station EWSD provides the option to assign restrictions to originate calls to outside the Centrex group or to receive calls from outside the group or the attendant special call handling capabilities.

1.2.1.3 Centrex MLHG Features

MLHG features are special hunting mechanism, and optionally, the queuing functionally may be associated with the MLHG.

1.2.1.4 Centrex PBX Features

Call handling capabilities for PBX`s are restricted to the routing of the Centrex group dialling plan. Features are not supported.

1.2.1.5 Centrex Attend Service

An Attendant of the Centrex group may be a normal Centrex subscriber ( Basic Attendant )or may be equipped with a personal computer ( DSB:ISDN ) connected as an ISDN basic access to the central office. All attendants must be configured as members of Centrex attendant groups controlled by the Call Distribution System ( CDS . As an option, for these attendant groups queuing mechanism may be provided. With exceptions, an attendant has most of the features of Centrex Station available. If equipped with the DSB:ISDN, additional Attendant features are available.

1.2.1.6 Attendant Console Features are

Call control features, comprising functions to support calls and features, which require attendant assistances,

Administrative abilities, consisting of the capacity to receive group specific data from the central office and store these data for further processing at the DSB:ISDN.

Post processing capabilities for data received from the central office and data management functions for the attendant’s internal database.

Operation and maintenance capabilities, comprising abilities to configure the Centrex group and stations to the needs of the customer. Terminology Throughout this document, the terms incoming call and outgoing call are always used with respect to the local Centrex group respectively the local Centrex station.

2 CENTREX GROUP FEATURES

2.1 Local intercom Dialling

Local intercom dialling refers to the translation and routing performed between CENTREX stations located within one local end office. When dialling an intercom number from a CENTREX station, the local end office translates an intercom number to a location within the end office ( the CENTREX Call Type is set to `local Intercom`) and terminates the call. When a CENTREX group is split over more than one area code of a local end office, administration software translates the area code as well as the directory number to terminate to the correct CENTREX station. There is no impact to call processing in this case.

Calls originated by Shared Attendant to the user CENTREX groups are established as local intercom calls.

2.2 Remote Operation Intercom Dialling

For a CENTREX Business group resides in more than one local end office ( ISUP- signalling) the translation and routing function provides Remote Operation intercom dialling. Each office must define the own CENTREX group numbering plan. Since this arrangement splits the numbering plan, care must be take when reproducing a CENTREX group numbering plan across end offices so that intercom dialling, and feature access codes remain transparent to the user location. In order to complete a call to a remote CENTREX station, translation and routing provides a public network number, and the CENTREX Call type is set to „ remote intercom“ The call is then routed over a public network trunk ( ISUP ) for termination in the remote end office. “Fehler! Verweisquelle konnte nicht gefunden werden.” Is an example how a centrex business group may be split over more than one End Office.

Implementation: Remote Intercom translation relies on the NEWCODE parameter of the CR DEST MML command for creating the public network address of the Remote numbers. For Remote Intercom codes the centrex translator is set up with a pointer to a „newcode“ destination data ( DEADA ) element. Associated with this newcode destination, a POTS code point ( CPT ) previously entered will define the public network address of the remote intercom number connected in the remote exchange. Remote Intercom number can be set up in the centrex translator to correspond to Public Directory Number Blocks ( allowing for more digits to be dialled after the remote intercom number ) , an individual Public Directory Number, an Attend public directory number, or a public directory number of a Costumer Premise Equipment.

2.2.1 Public Network

Is the Network outside a centrex group. So if you want to set a call out of the Centrex group you need to call the Access code for external calls first ( like „0“ ) After this you can call fahter depending on your restriction for Citywide, Countrywide or Worldwide Calls.

2.2.2 Call Distribution System

If a call coming to your Attend the System checks if it is an incoming, outgoing or any kind of intercepted call. Depending on the way the call comes in the subscriber is connected to a special Attendant. The system can also select an Attendant depending on the way of intercept. ( Busy, No Work, .... )

2.2.3 Paging

By using the Access Code for Paging ( Request ) you reach the Costumer Permisess Equipment ( CPE ) and enter the number of the Person you want to call. The CPE sends the signal to the pager of the user you what to reach. After the user dials the access code for Pickup CPE, he gets connected to you by the CPE.

2.2.4 Centrex Call Pick Up

The Call pick up feature allows a customer to answer a call, which has been terminated to another Directory Number on another station. There are two variants of the Call Pick Up feature:

2.2.4.1 Directed Call pick Up with No Barge In

The Directed Call Pick Up ( DPN ) feature allows pick up of a call to a specific station by dialling an access code and the Directory number of that station. If the Call is already answered the customer’s Call pick Up attempt will be rejected. „ No Barge In „ means, that a break into an established connection is not possible. Call waiting requests to analog subscriber cannot be answered with Directed Call Pick up.

2.2.4.2 Group Call Pick Up

With the Group Call Pick Up feature subgroups within the centrex group, call pick up groups, can be created. To pick up a ringing station of his pick up group, the user just dials an access code an no specific DN. If more than one station of his group is ringing he will get the longest ringing call within this Pick Up Group. Up to eight calls can wait simultaneously in a Pick Up Group to be answered, that means, only the first eight calls can be picked up. Call waiting requests to analog subscriber will not be inserted in the pick up list and so cannot be answered with group call pick up.

2.3 Location Dialling

As a means of including existing PBX equipment within the centrex dialling plan, or replacing PBX equipment while maintaining the existing inter-PBX dialling plan, EWSD provides the centrex dialling plan feature of Location Dialling. Location refers to identifying each PBX location with a digit sequence. As an example, a PBX station at location A would first dial 77 then possibly an extension code to reach a PBX station at location B. Than translation and routing function provides a public number translation of any location digits dialled. The extension number is appended to the public number translation to form the complete number of called party.

Centrex provides the administrable option for call processing and billing, to handle a location call as:

A Intra centrex group call ( group call type = local intercom ), even if the location is not number of the own centrex group ( shared Attendant ), or
A Remote centrex group call ( centrex call type = remote intercom ), if the location is located in a remote switch and in the same BGID, or
An external call ( centrex call type = external call ) or quasi remote call, even if the location is not included into the same business group as the originating centrex station ( external) , or even if the location is within the same switch as the originating centrex station, and is also a member of the same centrex complex group.

This means, that the administrable option always overrides the centrex call type derived from the centrex group membership and the dialled digits, and the call charges ( without external calls ) will be added to the appropriate centrex intercom counters ( in case of PPM ), respectively the intercom flag will be set in the AMA ticket. For external calls the pulses will be added. A centrex subscriber is required to have the proper CATCOD assigned in order to have dial access to a location.

2.4 AWC Area Wide Centrex

Area Wide Centrex is a service that provides the ability to enclose local centrex groups, speed over different exchanges of public telecommunication network, within one privat network. The basic idea of AWC is to limit the coordination and administration effort of the centrex dialling plan ( compared to AWC on a remote and location dialling plan base ). This is carried out with a combination of centrex and the intelligen network ( In ) feature virtual privat network ( VPN ). The VPN service allows public network operators to provide privat network features, e.g. privat numbering plan ( PNP ) and screening capabilities, using the existing public network infrastructure. VPn is typical unused to interconnected geographically distributed centrex groups and PBX`s.

2.5 Subscriber Controlled Inputs for:

2.5.1 Centrex call Forwarding

The Call Forwarding feature allows the user to forward calls terminating to his station, under certain conditions to another station, the Call forward destination. The feature can be activated and deactivated by the subscriber. Calls from this call forward destination ( inside the centrex group ) can reach the base station.

In compliance with the following existing Call forwarding features for non-centrex subscribers

Call Forwarding unconditional ( CFU )
Call Forwarding Busy ( or Busy Line ) ( CFB )
Call Forwarding Don’t Answer ( CFNR )

can be entered and activated for centrex station. Only one call at a timecan be forwarded for analog stations, for ISDN one call per B-channel can be forwarded simultaneously. All three features can be active simultaneously. If more than one fature is active CFU takes precedence over CFB and CFNR. The „ Busy“ and „“No Reply“ condition cannot occour at the same time for analog subscribers. Additional restrictions can be assigned to centrex stations. They apply only if one or more of the Call Forwarding features CFU, CFB, CFNR is active. The restrictions are:

2.5.1.1 Call Forwarding Within Group only

This is a restriction on all variants of call forwarding. When the subscriber activates call forwarding ( via SCI ), the forwarded-to intercom number is checked to see if the translation result is a local or remote intercom number. If it is not, then Call Forwarding is not allowed.

2.5.1.2 Call Forwarding Incoming only

This restriction for CFU only allows forwarding POTS-calls or calls outside of the same business/sub business group i.e. Calls from within the same centrex business/sub business group will be handled just as the line has no Call Forwarding feature assigned.

2.5.1.3 Call Forwarding Busy Line Incoming Only

Only POTS-calls or call outside of the same business/sub business group to the centrex group are to be forwarded to tha call forward destination, when the called party is busy. Calls from within the same centrex business/sub business group will be receive busy treatment.

2.5.1.4 Call Forwarding Don’t answer incoming only

Only POTS-calls or calls outside of the same business/sub business group to the centrex group will be forwarded if the base station does not answer in a specified time period. Calls from within the same centrex business/subsides group will be rung as long as the answer supervision timer is not exceeded.

2.5.2 Centrex Call Waiting

In all of its variants the Call waiting ( CW ) feature informs a busy station user that another call is waiting. For an analog subscriber this is indicated by a tone that dialled busy party of the existing connection my hear.

The busy analog subscriber may:

Go on hook and will be rung from the new partner or
May put his original partner on hold and answer the new call or
May release his original partner and answer the new call or
May release the new call without answer or
May ignore the waiting call

2.5.3 Centrex Call Pick Up

The Call pick up feature allows a customer to answer a call which has been terminated to another Directory Number station.

There are two variants of the Call pick Up feature:

2.5.3.1 Directed Call Pick Up with No Barge In

The directed Call pick Up ( DPN ) feature allows pick up of a call specific station by dialling an access code and directory number of that station. If the call is already answered the customer’s Call pick Up attempt will be rejected. „ No Barge In „ means, that a break into an established connection is not possible. Call waiting requests to analog subscriber cannot be answered with Directed call pick Up.

2.5.3.2 Group Call pick Up

With the Group call pick up feature subs group within the centrex group, call pick up groups, can be created. To pick up a ringing station of his pick up group, the user just dials an access code and no specific DN. If more than one station of his group is ringing he will get the longest ringing call within this Pick Up Group. Up to eight calls can wait simultaneously in a pick up Group to be answered, that means, only the first eight callas can be picked up. Call waiting requests to analog subscriber will not be inserted in the pick up list and so cannot be answered with Group Call Pick Up.

2.5.4 Centrex Abbreviated Dialling and Shared Abbreviated Dialling

This feature provides a subscriber to dial selected numbers using a 1 or 2 digits short number instead of the normally required number of digits. This is accomplished through the assignment of abbreviated codes to the frequently called directory numbers or access in an abbreviated dialling list. Maximum length of a stored number may be 23 digits.

The feature is available to Centrex subscribers Attendants, centrex MLHG, members of centrex MLHG, and PBX`s. Note, that Non-centrex rotary subscribers do only have access to one abbreviated list.

An abbreviated dialling list may be shared by several members of a centrex group, if all members belong to the same local area code. Only the owner of such a shared list may have the authorization to update the list. The abbreviated directory number can be placed into the list by input of the central offices operator or, if the owner has the authorization to update the list, by subscriber controlled input at the owners terminal. The stored long number may be an access code, an intercom code, a public network directory number or an appropriate combination of the above. After dialling of the abbreviated dialling code the user may dial additional parts of the directory number. The type of the abbreviated dialling list may be:

· 1 digit ( 5 DN or 10 DN ), starting with abbreviation number 0 or

· 2 digit (10 DN up to 100 DN in steps of 10 ), starting with abbreviation number 00, 10, 20, etc.

A centrex station may own or share at most one list of type 1-digit and one list of type 2-digit simultaneously. To avoid blocking of a set abbreviated dialling numbers by ambiguity with an access or an intercom code within the centrex dialling plan, access codes for abbreviated dialling usage are provided.

2.5.5 Centrex Do Not Disturb

The Do Not Disturb features routes calls destined to the centrex subscriber either to a special Do Not Disturb announcement or to a special tone. It is activated/deactivited by the subscriber. The feature will be overridden by the „ Attendant Emergecy Override „ feature

2.6 Distinctive ringing & call waiting

Depending on call types there are five ( 1 standard and 4 enhanced ) ringing cadences and call waiting tone sequences in order to audible indicate the kind of actuall call to the termination station. There are following call types relevant for this feature:

Data Privacy call,
Call Forwarding,
CCBS Recall,
Operator call,
Intercom ( remote & local ), quasi remote external call

The kind of ringing cadences or call waiting tone sequences is project specific dependent on prefence table.

2.7 Intercepts

Intercepts occur uif there is a problem or no permission connecting a call. Depending on the Intercept, the The intercept treatment can be:

An announcement,
Music,
tone,
a public network operator, or
attendant connection

2.8 Traffic Measurements

In addition to the usual traffic measurements for POTS, ISDN subscribers, and PBX`s , CENTREX specific traffic, measurements are provided.

The following types of counters are recorded for CENTREX:

Basic Counts on centrex group level
Attendant control on centrex group level
Feature counts on centrex group level
Remote intercom, location dialling and area wide centrex counts on centrex group level
Counts on MLHG/PBX level 1
Counts on Queue level 2
Surveillance counts for MDR data transmissions to the CPE
Surveillance counts for traffic data transmissions to the CPE
Counts over all centrex Groups

A subset of the traffic measurement data for a centrex group maybe provided to the costumer on a centrex group basis, if requested by the individual customer. This feature requires that least ( and most ) one attendantconsule position is assigned in the database to receive the traffic data. The customer may use the traffic data for network surveillance and as an input to network engineering studies. Only a subset of these counters is to be sent to the customer premises. The other counts are to be collected for analyses by the telephone company.

2.9 Music for Held and Delayed Connections

The centrex group may choose one out of 10 „ music „ announcements available within EWSD, delivered by an announcement device such as OCANEQ or DAS, to make waiting nicer.

2.10 Night Service

This feature allows the attendant group to shut down for a time period at the customer request. With exception of dial through request, camp-on-recalls, and intercepted calls Calls are redirected to the night service number. Calls to an attendant group that has the night service activated are redirected to the night service station. The night service station may be a specific attendant ( and there a message )

2.11 Night Service Call Pick Up ( NSCPU )

This feature ( in some documentation also called: Trunk Answer Station ) allows any station within the centrex group to pick up calls to the night service station dialling a specific feature access code. The NSCPU feature only works when the night service station is a local centrex station, call forwarding is not active for that station, and the subscriber invoking NSCPU has the CAT code authority. NSCPU feature works like directed call pick up all types of calls to he night service station, regardless if night service is active or not.

3 Centrex Line Features

3.1 Semi/fully restricted

Line feature semi restricted inhibits calls to the outside of the business/sub business group to a external station. Another station can be reaches via:

Call transfer all Calls
Call Transfer Outside
Call forwarding

If the station is fully restricted, the call can not even been transfered by attendant except direct Emergency Calls.

3.2 Call Forwarding incoming only

This feature is the same as Call forwarding but only for incoming calls. Internal calls will go through

3.3 Centrex Call Waiting

In all of its variants the Call Waiting ( CW ) feature informs a busy station user that another call is waiting. For an analog subscriber this is indicated by a tone that the dialled busy party of the existing connection may hear.

The busy analog subscriber may:

Go on hook and will be rung from the new partner on
May put has original partner on hold and answer the new call or
May realease his orginal partner and answer the new call or
May realease the new call without answer or may ignore the waiting call.

Only one call at a time may wait on busy analog subscriber. For a ISDN subscriber more calls may wait. The number of possible waiting cals per ISDN Basic Access is an defined by the network Determined User Busy Threshold value. Every additional call will get busy treatment. There are three types of the Call waiting feature:

Call waiting Terminating,
Call waiting originating,
Dial Call Waiting

Further on, the Cancel Call waiting feature is provided for analog subscribers

3.3.1 Call Waiting Originating ( CWO )

Call waiting originating ( CWO ) service allows an originating centrex subscriber with the feature to wait on a busy subscriber in the same business/subbusiness group and within the same switch, even if the terminating subscriber does not have a Call Waiting feauture.

3.3.2 Call Waiting Terminating ( CWT )

This is the standard from the Call Waiting feature. The centrex subscriber which has this feature provided, will ne notified on waiting calls, regardless, if the origin of this call is within the centrex business/subbusiness group or outside.

3.3.3 Dial Call Waiting ( DCW )

The difference to CWO is that Dial Call Waiting ( DCW ) is activated with an access code before the Call. The feature is active only for that single call set up. DCW has a higher priority than Call Forwarding at the B-side.

3.4 Call Waiting Incoming Only ( CWIO )

This is restriction that can be assigned to a station that has the CWT feature. The centrex station whic has CWIO restriction will be notified only for calls from outside the centrex business/subbusiness group ( quasi remote, external ). Calls from within the group ( local, remote ) will get normal busy treatment.

3.5 Prevent call waiting

A station has call waitingassigned may activate Prevent call waiting ( cancle call waiting CCW ) before call, Any call waiting indication will then be suppessed for the next call.

3.6 Three Way Calling Including Call Hold and Three Party Conference

With this feature you are able to call two other station and build a conference so that three user can talk with each other. Standard Three Way Calling ( TWC ) is available for centrex lines with the same user procedures as POTS. For ISDN the TWC feature consist of the ETSI Call Hold Service and the Three Party Conference Service. Both service are based on zhe Hold / Retrieve functions.

3.7 Voice Data Protection

With activation of the Voice Data Protection feature the analog user may inhibit interruptions of his connections due to in band signals directed to his stations cauesd by other features to allow an uninterrupted connection. The feature can be activated / deactivated by the user. This feature is nor applicable for ISDN.

3.8 Call Transfer

The Call transfer feature enables a user ( controller ) to transfer any established call to another station ( add on patry ). The user may be the originating or the terminating side of the established call. Is is nor possible to transfer two terminating calls to a centrex station. The feature is based on Three Way Calling feature for analog subscribers and for ISDN subscribers, if stimulus protocol is used. For ISDN subscribers the feature may also be invoked via functional protocol. In this case, the Call Transfer from an ETSI Three Party Call is not allowed. The Call Transfer is possible network wide if:

The controller is a centrex subscriber or Attendant,
At least the one of both partners is the number of the same Business Group as the controller

Remark: In case of a POTS-call or a calöl from different business group as controller is only possible to the targets which are reachable with the translated result remote local intercom.

3.8.1 B-side Call Transfer Individual All Calls

This is the standard from of the B-side Call Transfer feature. All external calls terminating to the centrex station can be transfered to any other line of the same centrex business group like controller and calls from any line of the same centrex Business group like controller can be transferred to a destination outside the Business group or to POTS. The exceptions are that external calls can not be transferred to a flly resctricted terminating station and calls from a fully restricted orginating station can be tranferred to the targets which are reachable with the translated result remote or local intercom.

This feature allows B-side controller station to transfer a call to the Add-on Party in 3 different call states. The Call to the Add-on Party may:

Have been answered
Be placed into a queue ( dealyed announcements are applied ), or
Still be ringing

3.8.2 A-side Call Transfer Individual All Calls

This feature allows a station who is the controller to originate both calls . Tha Call state of both calls must be answered , Call Transfer in ringing state or into queue is not posiible. Two of the Call Transfer restrictions listed for the B-side CALL Transfer do also apply for Centrex stations that have the A-side Call transfer authorization. Either the first or the second call leg is reachable with the translation result local or remote intercom.

3.8.2.1 Call Transfer Internal Only

The Transfer is allowed only if the other call leg is placed in the same business/subbisness group.

3.8.2.2 Call Transfer Outside

The other call leg must be placed in the same business/subbusiness group.

3.8.3 Ringing State

If a Call is transfered to a station that is not picked up ( ringing ) the call is tranfered in ringing state.

3.9 Group Call Pick Up

With the Group Call pick up feature subgroups within the centrex groups, can be created. To pick up a ringing station of his pick up group, the user just dials an access code and no specefic code and no specific DN. If more than one station of his group is ringing he will get the longest ringing call within this Pick Up Group. Up to eight calls can wait simultaneously in a Pick Up Group to be answered, that means, only the first eight calls can be picked up. Call waiting requestest to analog subscriber will not be inserted in the pick up list and so cannot be answered with group Call pick Up.

3.10 Directed Call Pick Up

The Directed Call Pick Up ( DPN ) feature allows pick up of a call to specific station by dialling an access code and the Directory number of that station. If the call is already answered the customer`s Call pick up attempt will be rejected. Call waiting requests to analog subscriber cannot be answered with Directed Call pick Up.

3.11 Abbreviated Dilalling and Shared Abbreviated Dialling

This feature provides a subsciber to dial selected directory numbers using a 1 or 2 digits short number instead of the normally required number of digits. This is accomplished through the assignment of abbreviated codes to the frequently called directory numbers or access codes in an abbreviated dialling list. Maxiumum length of a stored number may be 23 digits. The feature is available to centrex subscribers Attendants, centrex MLGH, members of centrex MLHG, and PBX`s. Note, that Non-centrex rotary subscribers do only have access to one abbreviated dialling list.

The abbreviated directory number ( DN ) can be placed into the list by input of the central offices operator or, if the owner has the authorization to update the list, by subscribers controlled input at the owners terminal. The stored long number may be an access code, an intercom, a public network directory number or an appropriate combination of the abover. After dialling of the abbreviated dialling code the user may dial addtional parts of the directory number.

3.11.1 Per Line

A centrex station may own or share at most one list of type 1-digits and one list of type 2-digit simultaneously. To avid the blcoking of a set of abbreviated dialling numbers by

Ambiguity with an access or an intercom code within the centrex dialling plan, access codes for abbreviated dialling usage are provided.

3.11.2 For a Group

An abbreviated list may be shared by several members of a centrex group, if all members belong to the same local area code. Only the owner shared list may have the authorization to update the list.

4 Centrex MAC features

4.1 Calltype Fature

Tha Calltype is the type of call how the call comes to the MAC ( Multifunctional Attendant Console ) like forwarded, intercepted, direct, ...

4.2 Attendant Camp On

If the subscriber does not have the permission for call waiting, the attendant can camp on a cal, give him the right for call waiting for one call.

4.3 Dial Trough Attendant

The Dial Trough Attendant ( DTA ) fature allows members of the same business group who are not fully restricted originating ( usually semi restricted ) to established calls terminating outside of the business group via the attendant.

4.3.1 With/without identification

Depending on the option of the attendant gropu the B-party numer is displayed to the attendant or not ( identified or not )

4.3.2 With Attendant answer

An attendant presented with a Dial Trugh Attendant call has the option to do or not answer the call and allow the dial trough attendant attempt.

4.4 Attendant Emergency Override

Attendant Emergency Override allows an attendant to extand a call to a station belonging to the same business group that has either assigned or activated respectively terminating restriction or redirection features.

These features are:

( non centrex specific ) Requested Suspension Terminating
( Fully Restricted terminating Station
( non centrex specific ) do not disturb
( non centrex specific ) all variants of call Forwarding

None of the Call forwarding variations will take place when the attendant attempts to terminate to a station via emergency Override.

The basic attendant has to dial a special access code to activate AEO. No authorization for using this feature is necessary.

4.5 Message Detail Recording

This feature is only possible with the Multifuctional Attendat Console. MDR offers detailed information about a call.

The details are:

The calling number
The called number
Call duration
Date and time
Charge units
Zone