Switching performance features (public networks)

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As call processing features or even short service features called ( English supplementary services ) refers to a public telecommunications network in addition by the network made available to subscriber-related services beyond the simple connection and disconnection by the caller, the so-called A-subscriber , the called subscriber ( B-participant ) go out.

Within ISDN , the local exchanges provide numerous services that can be used, for example, via an ISDN telephone. Access to and management of services via keyboard , display and audible tones , the control information is a signaling method (eg DSS1 ) between terminal and switch replaced. Such services are also made available to subscribers with other terminals (e.g. analog). The services are then called up and managed using the corresponding signaling protocols for these connections.

Switching performance features of the public networks can be subdivided according to ITU-T I.250 according to their functionality. Although a classification was standardized only for ISDN service features, today performance features for analog and mobile connections as well as IP telephony are classified accordingly. Often, however, only a subset of the available service features is supported.

Subdivision of the performance characteristics

The following subdivision applies according to ITU-T I.250:

Number identification z. B .: MSN DDI CLIP CLIR COLP COLR MCID SUB
Call delivery z. B .: CT CFB CFNR CFU CD LH
Call completion z. B .: CW HOLD CCBS CCNR
Multi-participant z. B .: 3PTY CONF
User groups z. B .: CUG PNP
Advanced billing z. B .: AOC REV
Information service features z. B .: UUS

Further services

Further services outside of switching-oriented performance features are part of the superimposed intelligent network .

New services outside of the ITU-T -I.250 specification are increasingly emerging for IP telephony and can be divided into:

  • Multimedia services
  • personalized performance characteristics

Some service features can also be implemented in the terminal with the appropriate device technology (for example speed dialing or call diversion in the ISDN terminal), so that the exchange does not need to be involved. In this case one speaks of device-technical performance characteristics.

Performance characteristics and their description

The following features refer to the occurrence in the German-speaking area (Germany, Austria and Switzerland). Their use and provision depends on the respective network operator.

Transmission of the caller's number (CLIP)

CLIP (short for English Calling Line Identification Presentation ) is a feature for incoming calls and can be enabled only for this or disabled. With CLIP, the call number of the calling subscriber is transmitted to the called subscriber, unless this has already been restricted on the calling side (CLIR). If the person called then has a CLIP-capable device, the caller's number is displayed. If this terminal device has an address book with the option of saving names, the corresponding name can also be displayed.

The option of displaying the number of the called subscriber was originally only available for ISDN and has also been available in Germany for analog telephone connections since January 1998 ; in Switzerland since 2005. While the phone number is transmitted as digital information in the D channel on ISDN connections, the time between the first and second call signal is used to transmit the data on analog connections. A digital FSK signal in MDMF or SDMF coding according to the V.23 standard is used for this. However, the analog end device must be suitable for evaluating this signal (CLIP-capable).

CLIP is by some equipment manufacturers as CLID ( english Calling Line IDentification called).

Suppression of the caller's number (CLIR)

CLIR (short for English Calling Line Identification Restriction ) is a feature for outgoing calls and can be enabled only for this or disabled. With CLIR it is possible to suppress or restrict the transmission of your own number to the called subscriber. It is therefore also referred to as number suppression. It is only possible to a limited extent, since emergency call centers for the police , fire brigade and rescue services are excluded from it ( CLIRO ).

The phone numbers are generally transmitted in the telephone network. If a subscriber does not want his call number to be communicated to the called party, there is the option of calling number suppression (CLIR). As a result, the called B-subscriber can not identify the calling A-subscriber using his call number, even if he has activated CLIP. When CLIR is activated, the number is transmitted on the network side to the subscriber exchange of the called party, but is not transmitted to the called subscriber. It is also possible to activate call number suppression on a case-by-case basis (on analog telephones by tone dialing a key sequence preceding the call number; on ISDN telephones using the keypad function).

A distinction is made between the following types of number suppression:

  • Constant transmission of your own phone number
  • Case-by-case transmission with constant suppression
  • Case-by-case suppression with constant transmission
  • Constant suppression of the number transmission

Depending on the service provider, all or some of these versions are available.

Ignoring Calling Line Identification Blocking (CLIRO)

CLIRO (short for English Calling Line Identification Restriction Override ), partly as CLIRIGN (for Calling Line Identification Restriction Ignore called), is a feature for incoming calls and is generally only certain subscriber connections available. It must be activated in the end exchange of the called party. With CLIRO, an activated CLIR service of the caller is ignored and his call number is always transmitted to the called party. This service feature is available to emergency call centers of the police, fire brigade, medical emergency services and special security-relevant state connections.

Display of the called party's number (COLP)

COLP (short for English Connected Other Line Presentation ) is a feature for outgoing calls and can be enabled only for this or disabled. With COLP, the call number of the subscriber who accepts the call is requested from the caller and as a result transmitted backwards to the caller ( A subscriber ). This feature is useful for call diversion, for example: the caller is informed that he has not reached the connection he has dialed but has been diverted to another. However, the called party can use the COLR feature to suppress or at least restrict the function of COLP and thus prevent the determination of their own call number.

Suppression of the called party's number (COLR)

COLR (short for English Connected Line Restriction Other ) is a feature for incoming calls and can be enabled only for this or disabled. If COLR is activated, regardless of COLP on the calling side, the call number of the subscriber receiving the call is transmitted backwards in the telephone network, but it is not transmitted to the caller ( A subscriber ). This performance feature is useful, for example, with call diversion: The caller is not informed where the called party has diverted his telephone despite the activated COLP. This gives the called party the option of suppressing a possibly activated COLP service of the calling party to a limited extent and thus protecting their privacy.

Transmission of the name of the caller (CNIP)

CNIP (short for English Calling Name Identification Presentation ) is a feature for outgoing calls and can be enabled only for this or disabled. With activated CNIP, the name of the calling subscriber registered with the telecommunication service provider and the location are transmitted to the called subscriber in alphanumeric form. The display of the called subscriber with a CNIP-capable telephone then shows Max Mustermann, Berlin .

In Germany, CNIP is only very rarely (2014) offered by special telecommunications service providers.

Transmission of the caller's own number information (CLIP -no screening-)

CLIP -no screening- is a feature for outgoing calls and can only be activated or deactivated for these. In addition to the caller's network number ( English network provided ), a customer-specific call number ( English user provided, not screened ) specified by the caller himself can be sent to the called party. In this context, no screening means that the transmitted phone number does not have to be checked for correctness by the switching telephone network. It is subject to some restrictions, for example, according to Section 66k TKG, it can only be another number that the caller has the right to use. To ensure the service provider is not obliged to take responsibility for compliance with the restrictions the sole responsibility of the user, as it transmits this number ( English user provided ).

This performance feature is possible for ISDN system connections and IP-based system connections on the calling side and is only used for those on the incoming side (at least for German cell phone connections). With analog connections - provided CLIR has not been activated on the calling side - only the network-side number is transmitted to the caller, otherwise none.

For example, the caller can suppress his network-side call number using CLIR and send the call number of a value-added service to the called party.

In general, both phone numbers of the caller, the network-side and the customer-specific (if CLIP -no screening- activated), are transmitted in the public telephone network. However, activated services such as CLIP / CLIR / COLP on the respective subscriber side and the type of connection decide which call number is transmitted to the subscriber himself. Device-specific settings on the recipient side ultimately decide which number (or whether both) are displayed. However, if device-specific settings are not possible due to the type of connection (e.g. with an analog connection or because a network provider does not support these options), the display is also clearly defined for this performance feature.

Display of customer-specific number information of the called party (COLP -no screening-)

COLP -no screening- is a feature for accepted calls and can only be activated or deactivated for these. In addition to the network-side telephone number ( English network provided ) of the subscriber who accepts the call, a customer-specific telephone number ( English user provided, not screened ) specified by the caller himself can be sent to the caller. In this context, no screening means that the transmitted phone number is not checked for correctness by the switching telephone network; it can only be another number that the caller has the right to use. The service provider is obliged to ensure this, d. i.e., it may only be configurable by this.

This performance feature is only possible for ISDN connections on the accepting side and only applies to those on the calling side. For analog connections, if COLR has not been activated on the called party, only the network-side number is transmitted to the caller, otherwise none.

For example, a subscriber who accepts the call can suppress his network-side call number using COLR and another customer-specific call number, e.g. B. the switchboard of the call center or a service number , send to the caller.

The same applies to the display of the phone number as for CLIP -no screening- .

Callback on busy (CCBS)

With CCBS (short for English Completion of Calls to Busy Subscriber ) is a caller in a position a connection to automate a previously occupied target participants in the exchange. A caller who receives a busy tone from his target subscriber can activate this service via the keypad of his terminal device before hanging up the receiver . If the previously occupied target subscriber is free again (= he hangs up), the caller's terminal receives information about this from the exchange. The end device then signals to the caller with a special ring tone (the callback) that the destination subscriber is no longer busy. If the caller accepts this callback by picking up the telephone receiver , the destination subscriber will be called again by the exchange. CCBS cannot be used if the destination subscriber rejects the incoming call or the exchange of the destination subscriber does not support the service.

In the Deutsche Telekom network, in addition to tone dialing after the busy signaling, voice control has also been used to activate the callback since 2005 . The call-by-call / preselection provider selected for the previous dialing attempt is also taken into account when the connection is set up via callback.

However, CCBS is not to be confused with the (automatic) redial function of some devices regardless of the telecommunications network , in which, in the event of a busy tone, the calling device repeatedly calls the destination subscriber after a predetermined period of time until no more busy tone can be detected, i.e. the connection of the Target participant is free again.

Callback on no reply (CCNR)

With CCNR ( English abbreviation for Completion of Calls on No Reply ) a caller is able to automate the establishment of a connection to a destination subscriber who does not answer in the exchange. A caller whose target subscriber is free (the call is not answered) can activate this service via the keypad of his terminal device before hanging up the telephone receiver . The next time the target subscriber hangs up the phone, the caller's terminal receives this information through the exchange. It now signals to the caller with a special ringtone (the callback) that the target subscriber is available. If the caller accepts this callback by picking up the receiver, the switching center reconnects them to the desired subscriber.

Call waiting (CW)

When the feature call waiting ( English C all W aiting is enabled), the subscriber is a so-called during an existing connection, a further incoming call waiting tone signals. The participant who has been informed in this way then has the option of accepting, ignoring or rejecting this second conversation. In order to take the second call, the subscriber can end the first connection or put the first connection on hold with the consultation feature .

Hold, inquiry, toggle (HOLD)

The features hold, toggle and consultation are usually bundled by an exchange or telephone system as the feature call hold (HOLD).


A subscriber can use the hold performance feature to put an existing connection on hold . In this state, the other subscriber usually receives an announcement or music on hold.


With consultation , the possibility is referred to an existing connection, with the previously holding to establish a second connection has been brought into a waiting state by the same terminal or a call waiting receive week.


Brokering is a feature in which a subscriber can alternately switch back and forth between two active connections. Only the participants of the currently active connection can speak to one another. The waiting subscriber is held in the exchange or telephone system until the call is resumed .

Mediation in Office (ECT)

With the Explicit Call Transfer (ECT) an existing connection can be switched to another participant. A connection in the HOLD state is interconnected with the active connection, then both external participants are connected. However, the connection still runs through the switching center of the intermediary for a fee .

Tripartite Conference (3PTY)

With the service three-party conference ( English Three-Party Conference or Three-way calling ) can called a conference Convener participants, including the initiator, a simplified teleconference cause. Three participants can call each other at the same time, each with each other. The three-way conference is carried out by the exchange without the need for a conference call . Participants in a three-party conference must already be switched through in terms of switching before it can be initiated. This differs from the actual conference call with conference call, which offers and requires additional features.

For the initiator of a three-way conference, the difference is that the other two interlocutors must already be connected to him. They must either be on hold, or one on hold and the other on the active call. In some mobile networks, participants can also call waiting ( Call Waiting Include) into a three-party conference. However, in a three-party conference, the initiator can never include more than two other participants in the conference.

With ISDN connections, it would also be possible to set up a three-party conference using the equipment. However, two B-channels would be used for this (one would be required for each external conference participant) instead of just one, as is the case with the three-way conference call. Modern SIP telephones also have this technical service feature.

Multiple subscriber numbers (MSN) for multiple device connections

With MSN ( English acronym for Multiple Subscriber Number ) one can ISDN - basic access among multiple numbers to be reached. The MSNs can be flexibly allocated to the end devices. In Germany, the number of MSNs per ISDN multi-device connection is limited by the Federal Network Agency to a maximum of ten. The MSN is the part of the telephone number that follows the area code , also known as the area code.

Reconnecting on the bus (TP) for multi-device connection

With TP ( English abbreviation for Terminal Portability ) a call can be parked in the exchange and the ISDN terminal can be plugged into another ISDN socket within the S 0 bus of a basic connection .

Direct dialing (DDI) for system connection

DDI (abbreviation for English Direct Dialing In ) (also known as Direct Inward Dialing (DID) known) defines a number block , through the terminals of a telephone system can be selected directly.

Call forwarding (CF and CD)

About the feature call forwarding ( English Call Diversion ), an incoming call by the central office will be diverted to a specified phone number. No B-channels to the subscriber are used, i. That is, the switchover takes place directly in the exchange of the called party. The number of the original caller (A subscriber) is signaled for the forwarding destination, but also that of the originally called party (B subscriber). Within ISDN, such numbers can also be displayed at the forwarding destination, because they are always transmitted on the network side in German-speaking countries. However, this does not apply across national borders and in some cases is only possible to a limited extent across network boundaries, e.g. B. from the fixed network to certain mobile networks within Germany. Call diversion is the generic term for various types of call forwarding and call deflection services (CF or CD):

  • With CFU ( English abbreviation for Call Forwarding Unconditional ), the diversion is always immediate - call diversion immediately.
  • With CFB ( English abbreviation for Call Forwarding Busy , dt. Call forwarding when busy), forwarding only takes place when the destination subscriber is busy - call forwarding when busy.
  • With CFNR ( English abbreviation for Call Forwarding on No Reply ), the diversion only takes place if the target subscriber does not answer after a certain time (usually after approx. 15 seconds) - delayed call diversion.
  • With CFDDI ( English abbreviation for Call Forwarding Direct Dialing In ) call forwarding is completely configured and switched in the telephone network independently of the telephone system . This feature is used in Germany, for example, with a system connection without a connection line . CFDDI is a company-specific standard from Siemens, as this type of call forwarding has not been standardized internationally. Similar services can also be found at other manufacturers, e.g. B. as CFUWA ( CFU on directory number Without Access ) from Alcatel-Lucent.
  • With CFVM ( English abbreviation for Call Forwarding to Voice Mail ), call forwarding is configurable by the subscriber, time-dependent, immediately or, if the subscriber cannot be reached, to the subscriber's internal answering machine. This service is mainly used in cellular networks.
  • With CFP ( English abbreviation for Call Forwarding Parallel ), both telephones ring at the same time.
  • CD ( English abbreviation for Call Deflection , German call forwarding after call delivery (AWS-R)) or call diversion differs from the call forwarding services, since the forwarding is initiated here on a case-by-case basis (by call) and is not configured to a destination. Call diversion and call forwarding service features are summarized under the umbrella term Call Diversion .
  • CDO ( English abbreviation for Call Diversion Override ) allows the suppression of an activated call forwarding or call diversion. This service feature is normally not available to private lines.

Call forwarding is therefore a switching service feature, since the execution of the service is provided by the switching network. In contrast, this service is also available as a device-related performance feature. This usually means forwarding via the B-subscriber's terminal. If the forwarding destination is outside your own connection, two B-channels are used during the call. At the forwarding destination, it is not the original caller's number but that of the forwarding B-subscriber as the caller that is signaled.

Partial Rerouting (PR) is only available for ISDN extensions and must be configured and activated there. It can be activated for the CFU, CFNR and CFB and CD service features when the forwarding destination leads back into the public switching network. When forwarding, the connection established up to that point is broken down in sections within the ISDN extension so that no connection channels from the public switching network to the ISDN extension are occupied for the duration of a forwarded call.

Transfer (CT)

With the Call Transfer (CT) feature , a dial-up connection can be transferred to another terminal or dial-up connections can be interconnected. The processes are standardized in Recommendation ITU-T I.252.1.

Tariff information (AOC)

There are three options for transmitting tariff information:

  • During a connection (AOC-D), ( English Advice of Charge During Call )
  • At the end of a connection (AOC-E), ( English Advice of Charge at End of Call )
  • Before and possibly during a connection (AOC-S) (only available in a few ISDN networks)

see also: Advice of Charge

Identify (MCID)

MCID ( English acronym for Malicious Call Identification ) is a service feature for incoming calls and is intended for the identification of bell interferers, harassing callers and other offenses by phone call (colloquially called capture or capture circuit known). The called subscriber can arrange for the call data of an incoming call to be recorded in the network, even with and despite activated call number suppression . The call data contain the caller and the called number as well as the time and date. These data, issued by the telephone service provider, are recognized as evidence in court. MCID is available in the following versions:

  • Identification during an existing call by activation by the called party.
  • Identification within a certain time after the call has ended, requires activation by the called party within 30 seconds of the caller hanging up. Not possible if the called party hung up himself.
  • Identify before accepting a call (to identify so-called bell interferers). Usually this is still possible 20 seconds after the caller has hung up.
  • Automatic identification of all unanswered calls.
  • Automatic identification of all calls (answered and unanswered calls).

In Germany, the availability of this feature is required by law and its provision and use are defined in the Telecommunications Act (Germany) . It usually has to be requested from the telephone service provider. An interception circuit (or MCID) is usually only granted if a related criminal or civil law fact can be substantiated.

Section 101 TKG 2004: Notification of incoming connections regulates in detail:

  • Provision of an interception circuit and the acceptance of an application
  • Information about the established connections
  • Cross-network information
  • Informing the owner of the connection from which the identified connections originated
  • Data protection regulations

Subaddress (SUB)

Subaddress is a subscriber extension of the number beyond the public numbering plan . The service feature is only available to ISDN connections on the calling and called side. The additional addressing option can be used to address certain devices behind the ISDN subscriber interface, e.g. B. to activate an amplifier for an announcement or to start a PC program.

The service feature can only be activated by the network operator. Only the called subscriber needs this authorization. Participant-dependent activation or deactivation is not provided. SUB can be used in parallel with all other services and has no different characteristics.

If subscriber A wants to communicate subaddress information to subscriber B, he sets up the so-called called subaddress field in his call. This information is then transmitted transparently through the switching telephone network and subscriber B is also delivered with the appropriate authorization.

The maximum length of the subaddress is 20 bytes, so up to 40 telephone digits can be transmitted. These depend on the subscriber coding selected in each case.

Subscriber-to-subscriber signaling (UUS)

UUS (short for English user-to-user signaling ) are features that allow the signaling channel (the customer D channel for ISDN) own data between the subscribers to transfer. Three UUS features are defined:

  • UUS1: Data exchange during connection establishment and disconnection
  • UUS2: Data exchange while the connection is being established
  • UUS3: Data exchange during the connection duration

Priority or disaster authorization

The feature priority ( English Priority ) is a connection-specific service and provides the participants with a higher priority in the switching of calls to and from its local loop. This enables calls to be made even if individual exchanges or the entire telephone network are overloaded. This service is used, for example, by authorities with special sovereign or security tasks and by hospitals. It should ensure that they are able to act even in the event of a disaster and overloading of the telephone network. The performance feature is available in three different versions:

  • Priority in the event of a disaster: This service is only used in the event of a designated disaster. To do this, the exchange must be brought into the so-called disaster state so that these connections have a higher priority in the telephone exchange. The prioritization only affects the local exchange of the connection and does not apply to the subsequent or preceding exchange in the telephone network.
  • Priority in case of overload: Connections with this characteristic always have a higher priority to and from this connection. However, here, too, the priority only affects the local exchange of the connection and does not apply to subsequent or upstream switching in the telephone network. This priority treatment only has a noticeable effect in the event of an overload of the local exchange.
  • Priority with call number category: Connections with this characteristic have a priority that can be changed in the switching network at any time. It can be increased in the event of a disaster and then has priority over other priority services and levels. Here, a priority identifier (in the so-called number Category English calling party category transmit) and thus retains its assigned priority for the entire network. It is the premium version of the priority service feature. This priority also applies to calls to this connection and can already be recognized in the local exchange even by a caller without priority.

The priority connection feature is available for analog and ISDN connections. However, the service is usually not available for private connections. He needs a special commission from the state. The availability of the feature is required by law in Germany for the public telephone network.

Reject Unknown Callers (ACR)

If the Anonymous Call Rejection (ACR) service feature is activated , the connection request for incoming calls with withheld Calling Line Identification (CLIR) is rejected and not put through to the called party. The caller then receives an announcement from the exchange; in the Telekom network, for example, with the misleading text "The desired call partner is temporarily unavailable, please try again later.", in the case of Swisscom with the meaningful text "The Swisscom customer does not want calls with withheld numbers."

This service feature is not actively marketed by most telephone connection providers (every failed connection means lost revenue), but must be free of charge for all connections on request due to an EU directive and the transfer into German law ( Section 102 (1) sentence 2 TKG 2007) be activated, but initially without the initiation of administrative measures. This does not apply to subscriber connections of closed user groups.

Call Notification (MWI)

In mobile networks , but also in some fixed networks, there is a network-supplied by the service provider answering machine ( english voice mail system ). If calls are diverted to this VMS server due to the unavailability or unavailability of the called party, voice messages can be stored there for the called party. Together with the network-side answering machine, a subscriber generally also receives the MWI switching service ( English abbreviation for Message Wait Indication ). When a voice message is received, the VMS server transmits information about the subscriber or his or her network-side subscriber data. In terms of switching, the messages are transmitted using the TCAP protocol in the entire German-speaking area . In other countries, for example Italy, this can also be done by means of an automatic call to subscribers with an over-decade digit identification. How the network ultimately communicates the information to the subscriber can be very different and depends on the network and device characteristics:

  • When lifting the handset, the participant hears a special dial tone ( English stutter tone or MWI tone).
  • When lifting the handset, the subscriber hears a short announcement before the normal dial tone. The use of an announcement allows a fax machine to recognize a normal dial tone and still transmit a fax, especially when MWI is activated.
  • In addition to the announcement or MWI tone, the subscriber hears a short ringtone.
  • The subscriber receives a text message, mainly used with ISDN devices. Especially with ISDN devices, the MWI information can functionally be transmitted in the DSS1 protocol. The display (switch on LED or text message and / or ring tone) on the ISDN device itself is device-specific.
  • The subscriber's telephone device receives an FSK signal that turns on an LED on the telephone. This option can only be used with analog connections and is known as VMWI ( English Visual Message Wait Indication ).

Call notification via SMS is primarily used in mobile radio networks , since the necessary device-specific features are available on the subscriber side. However, this is not a switching-related performance feature, since the transmission is provided with the help of the SMS service alone.

Call info via SMS

In the German cellular networks, the network operators have been establishing the call info via SMS message from subscribers about missed calls since 2005 when the network-side answering machine is deactivated by the customer , whereby the unavailability announcement in this case is usually billed to the caller as a chargeable connection.


In the case of cellular networks, it is common to make calls and be available in foreign networks ( roaming ). The basis for this are agreements between the network operators.

See also

Web links

Literature and Sources

  1. ITU-T Q.737.1 Stage 3 description for additional information transfer supplementary services using Signaling System No. 7: User-to-user signaling (UUS)
  2. [1] Directive 2002/58 / EC of the European Parliament and of the Council of July 12, 2002 on the processing of personal data and the protection of privacy in electronic communications (data protection directive for electronic communications)
  3. Telecommunications Act in the currently applicable version.
  4. Network operators must offer anonymous call rejection free of charge. In: golem.de .