GSM System Services

Telecommunication Services

· Bearer services:
Bearer services are telecommunication services providing the capability of transmission of signals between access points (called user-network interfaces in ISDN). The bearer services describe what the network can offer (e.g. speech, data and fax).
· Teleservices
Teleservices are telecommunication services including terminal equipment functions, which provide communication between users according to protocols established by agreement between network operators. The teleservices are user end-to-end services (e.g. emergency call and short message service).
· Supplementary services
Supplementary Services modify or supplement a basic telecommunication service. Consequently, they cannot be offered to a customer as a stand-alone service. They must be offered together or in association with a basic telecommunication service. The same supplementary service may be applicable to a number of telecommunication services. Most supplementary services are directly inherited from a fixed network, with minor modifications (when needed) to adapt to mobility. Examples of supplementary services are calling line identification and call waiting.

Types of teleservices:
Currently three types of categories of teleservices are distinguished: Speech Transmission, Short Message Service and Facsimile Transmission.

Speech transmission:
There are two speech transmission teleservices:

· Teleservice 11 - Telephony
This service provides the transmission of speech information and audible tones of the PSTN/ISDN. Transparency for telephone signaling tones is provided.

· Teleservice 12 - Emergency Calls
The standardized access method throughout all GSM PLMNs is mandatory. In addition national emergency call numbers of PSTN/ISDN must be usable from a mobile station.

Short Message Service
Short Message Service (SMS) provides a means of sending messages of limited size to and from GSM MSs without the use of a voice channel. The provision of SMS makes use of a Service Center (SC), which acts as a store and forward center for short messages. The SC is considered to be outside of the PLMN. Three types of SMS are available: SMS MT/PP, SMS MO/PP and SMS CB.

· SMS MT/PP
Teleservice 21 - SMS MT/PP (Mobile Terminating Point to Point) is a Point-to-Point service that allows a short data message to be terminated to an MS. The originator of the short message can either be another mobile subscriber or a subscriber from a fixed network. In the latter case this is only possible if both ends support an application for this purpose.

· SMS-MO/PP
Teleservice 22 - SMS MO/PP (Mobile Originating Point to Point) is a Point-to-Point service that allows a short data message to be originated by an MS. The recipient of the short message can either be another mobile subscriber or a subscriber from a fixed network. This service provides the transmission of short message from a mobile station to an SMS SC.

The point-to-point services provided by GSM are similar to paging, but with many enhancements. For instance the network is informed whether the message has been received or not by the mobile station; messages can thus be kept in the network in case of delivery failure and be sent again when conditions improve. On the MS side the last received messages can be stored in a non-volatile memory. The message text is limited to a length of 160 characters.

· SMS-CB
Teleservice 23 - SMS CB (Cell Broadcast) is a teleservice that allows a number of unacknowledged general messages to be broadcast to all receivers within a particular area. Unlike the SMS-MO and SMS-MT services, the SMS-CB service can be received only on an idle MS. The Cell Broadcast (CB) messages are broadcast on the Cell Broadcast Channel (CBCH). The maximum length of each CB message is 93characters.

Supplementary Services
Both the mobile subscriber and network to control Supplementary Services can perform administrative functions. These functions include:

Supplementary services management:
Both the mobile subscriber and network to control Supplementary Services can perform administrative functions. These functions include:

Ø Provisioning. The service provider makes a service available for a subscriber.

Ø Invoking. The service required is invoked by the subscriber (for example by pressing a specific button) or automatically by the network or terminal as a result of a particular condition (e.g. calling number identification for each incoming call).

Line Identification Services:

· Calling line identification presentation (CLIP)
The CLIP service allows the called party to receive the line identity of the calling party. The network delivers the calling line identity to the called party at call set-up time, regardless of the terminal capacity to handle the information. The CLIP service may not be applicable if at least one of the two parties is not an ISDN or GSM PLMN subscriber (depends on national network specific rules).

· Calling line identification restriction (CLIR)
The CLIR service enables the calling party to restrict presentation of its line identity to the called party. For inter-network calls, when the CLIR service is invoked, the originating network provides the destination network with a notification that the line identity of the calling party is not allowed to be presented to the called party.

Normally CLIR takes precedence over CLIP. However, depending on national regulations, some networks may define categories of subscribers that have the ability to override the presentation restriction (CLIR) and have the calling line identity presented (e.g. the police).

· Connected line identification presentation (COLP)
The COLP service allows the calling party to receive the line identity of the connected party. This service is not a dialling check, but the calling subscriber receives the full connected line identity as used in a full ISDN/GSM environment, i.e including all the information necessary to unambiguously identity the connected party. The network delivers the connected line identity to the calling party regardless of the terminal capability to handle the information.
· Connected line identification restriction (COLR)
The COLR service allows the connected party to prevent presentation of its line identity to the calling party. The network automatically invokes the COLR service for each incoming call at set- up phase. When the COLR service is invoked, the destination network provides the originating network with a notification that the line identity of the connected party is not allowed to be presented to the calling party. This also applies to inter-network calls. Normally COLR takes precedence over COLP. However, depending on national regulations, some networks may define categories of subscribers that have the ability to override the presentation restriction (COLR) and have the connected line identity presented (e.g. the police).

Call Offering Services

· Call forwarding unconditional (CFU)
This service permits a called mobile subscriber to have the network send all incoming calls (or just those associated with a specific basic service group), addressed to its directory number, to another directory number. The ability of the served mobile subscriber (i.e. the `forwarding subscriber' or the `called subscriber') to originate calls is unaffected. If this service is activated, calls are forwarded no matter what the condition of the termination.

· Call forwarding on mobile subscriber busy (CFB)
This service permits a called mobile subscriber to have the network send all incoming calls (or just those associated with a specific basic service group) that reach a busy signal, to another directory number.

· Call forwarding on mobile subscriber not reachable (CFNRc)
This service permits a called mobile subscriber to have the network send all incoming calls (or just those associated with a specific Basic Service group), addressed to her directory number, but which is not reachable, to another directory number.

The ability of the served mobile subscriber to originate calls is unaffected. Call origination is affected if only the MS is de-registered, if there is radio congestion, or if the MS is being out of radio coverage. If this service is activated, a call is forwarded only if the MS is not reachable.

Call Completion Services

· Call waiting (CW)
The Call Waiting Service permits a mobile subscriber to be notified of an incoming call (as per basic call procedures), while the traffic channel is not available for the incoming call and the mobile subscriber is engaged in an active or held call. Subsequently, the subscriber can either accept, reject, or ignore the incoming call. The time the network will wait for a response of the mobile subscriber to the waiting call can be set to between 0.5 and 2 minutes, at the service provider's discretion.

· Call holding (HOLD)
The Call Holding Service allows a served mobile subscriber, who is provisioned with this supplementary service, to interrupt communication on an existing active call and then subsequently, if desired, re-establish communication. The traffic channel remains assigned to the mobile subscriber after the communication is interrupted to allow the origination or possible termination of other calls. The served mobile subscriber can only have one call on hold at a time.

If the served mobile subscriber has a call on hold and is not connected to an active call, she can either retrieve or disconnect the held call, or set up another call. She cannot receive a call, except when using the Call Waiting (CW) service. If the served mobile subscriber is connected to an active call and has another call on hold, the subscriber can alternate between the two calls, or disconnect the active call, the held call, or both calls. Again no new call can be accepted, except when using the CW service.

Multiparty Supplementary Services:

· Multi party service (MPTY)
This service provides a mobile subscriber with the ability to have a multi connection call, i.e. a simultaneous communication with more than one party.

A pre-condition for the MPTY service is that the served mobile subscriber is in control of one active call and one call on hold, both calls having been answered. In this situation the served mobile subscriber can request the network to begin the MPTY service. Once a MPTY call is active, remote parties may be added, disconnected or separated.

During a multi-party call, the served mobile subscriber is able to:
· Put the connection to multi-party on hold. The served mobile subscriber may make a new call (to a potential participant) or process a Call Waiting request. While the multi-party call is on hold, the remote parties in that call can still communicate with each other.
· Add another party, to which a private communication has been established previously (see above). By again invoking the MPTY service, the network joins the active call and the MPTY call on hold together, resulting in an active multi-party call again.
· Separate a remote party. Explicitly choose one remote party to have a private conversation with. This results in that remote party being removed from the multi-party call which is placed on hold, and the conversation between the served mobile subscriber and the designated remote party being a normal active call. Again, while on hold, the participants of the MPTY call can still communicate with each other. The separated party can be added again to the MPTY call or released.
· Disconnect the entire MPTY call or disconnect remote parties on a one at a time basis.

Community Of Interest Supplementary Services:

· Closed user group service (CUG)
The CUG service enables subscribers, connected to a PLMN and possibly also other networks, to form closed user groups (CUGs) to and from which access is restricted. A specific user may be a member of one or more CUGs. Members of a specific CUG can communicate among each other but not, in general, with users outside the group. The ability to set up emergency calls remains unaffected. CUG subscribers can originate calls outside the group and/or to receive calls from outside the group. CUG subscribers can restrict originating calls to other members of the CUG, or receiving calls from other members of the CUG.
Each subscriber may be a member of different CUGs.

The user can choose one of the following subscription options for each basic service group applied to the CUG service. Each option may be provisioned on a per basic service group basis, or for all basic services:
· CUG calls only
· CUG with incoming access, i.e. can also receive calls, which are not subject to CUG restrictions
· CUG with outgoing access, i.e. can also make calls, which are not subject to CUG restrictions
· CUG with incoming and outgoing access
A user may subscribe to one of two additional restrictions applying for each particular CUG:
· Incoming calls barred within a CUG
· Outgoing calls barred within a CUG

Charging Supplementary Services

· Advice of charge (information) (AOCI)
This service permits the mobile station to display an accurate estimate of the size of the bill, which will eventually be levied in the Home PLMN (HPLMN).

· Advice of charge (charging) (AOCC)
This service allows the mobile subscriber to indicate the charge that will be made for the use of telecommunication services. It is intended for applications where the user is generally not the subscriber but is known to the subscriber, and where the user pays the subscriber, rather than the Service Provider. The charge information is based as closely as possible on the charge that will belevied on the subscriber's bill in the Home PLMN (HPLMN).

Call Restriction Services

· Call restriction services
The Call Restriction supplementary services allow the possibility for a mobile subscriber to bar certain categories of outgoing or incoming calls at the subscriber's access. The group of Call Restriction Services includes two supplementary services:

Ø Barring outgoing calls
Ø Barring incoming calls

Types of calls barred
The mobile subscriber can select the categories of calls to be barred. The following categories are defined:
Ø All outgoing calls (BAOC)
Ø Outgoing international calls (BOIC)
Ø Outgoing international calls except those directed to the home PLMN country (BOIC- exHC)
Ø All incoming calls (BAIC)
Ø Incoming calls when roaming outside the home PLMN country (BIC-Roam)

Interworking Function (IWF):

· Manages communication between GSM and other networks
· May be implemented in MSC and MS
· Basically consists of transmission adaptation and protocol adaptation equipment
· Its role depends on type of user data and type of "other" network

The interface with external networks outside GSM may require a gateway for adaptation, the so-called Interworking Functions (IWF). The role of IWF may be more or less substantial depending on the type of user data and the network it interfaces with. It adapts the GSM transmission peculiarities to those of the partner network.

The term interworking describes interactions between networks, between end systems, or between parts, with the aim of providing an end-to-end communication. The interactions required rely on functions, which include converting physical and electrical states and mapping protocols, called Interworking Functions (IWFs).

IWF consists of transmission and protocol adaptation equipment. It enables interconnection with networks such as PSPDN (Packet Switched Public Data Network) or CSPDN (Circuit Switched Public Data Network), but it also exists when the partner network is simply a PSTN (Public Switched Telephone Network) or the ISDN (Integrated Services Digital Network). Interworking functions may be implemented together with the Mobile-services Switching Center (MSC) function, or they may be performed by separate equipment. On the user side the IWF function is normally built in into the mobile station.

Interworking classifications
Four levels of interworking are required in a GSM network:

· Network interworking, required whenever a PLMN and a non-PLMN together are involved in providing and end-to-end connection.

· Service interworking, required when the Teleservices at the calling and called terminals are different. An example is the GSM Teleservice 61 and 62 interworking with standard facsimile group 3 service.

· Signaling interworking. Existing call control signaling procedures are used between the PLMN and other types of network (e.g. Signaling System No. 7 (SS7) and ISDN User Part (ISUP)).

· Supplementary service interworking. Not every GSM supplementary service may be used in combination with each PSTN/ISDN service.