• GSM Services

Objectives

On completion of this module you will be able to ...

• Explain what a service is in GSM.
• Classify and explain the various types of service.
• Describe the services' technical functionality from the network operators' and the customers' point of view.

Content

2.1	Classification
2.2	Bearer Services
2.3	Teleservices
2.4	Supplementary Services
2.4.1	Line Identification Services
2.4.2	Call Offering Services
2.4.3	Call Completion Services
2.4.4	Multi Party Supplementary Services
2.4.5	Closed User Groups (CUG)
2.4.6	Advice of Charge
2.4.7	Call Restriction Services
2.5	Value Added Services

2.1 Classification

The GSM services subdivide into the Bearer Services and the Teleservices. These base services are supplemented by the Supplementary Services. In addition, we have the Value Added Services.

The Bearer Services are telecommunication services that guarantee the transmission of signals between access points in telecommunication networks. They are used exclusively for transport and define the services a network can offer, for example data transmission between a corporate network and a mobile notebook, or data download from the web.

The Teleservices are telecommunication services as well as functions that enable communication between users, and are based on protocols agreed on by the network operators. Teleservices affect the final link in the communication process - the end user. They include telephone services, emergency calls, the Short Message Service, E-mail and fax.

Supplementary Services modify or add to the basic telecommunication services. They are only offered in combination with a Bearer Service or a Tele service. The same Supplementary Service can be applied to a range of Telecommunication Services. Most of these services have been inherited directly from fixed networks, with some concessions as regards their adjustment to the mobile radio network. Supplementary Services include e.g. line identification and call forwarding. Value-Added Services depend on the service provider or network operator they are supplied by. They are not predefined in specifications, and include e.g. reservation or information services.

Let's have a closer look at the services

2.2 Bearer Services

GSM specifies a huge variety of Bearer Services for data transmission. Bit rates between 300 and 9,600bps can be chosen according to data terminal equipment and the interference situation of the air interface. With HSCSD, the data rate may increase to 57.6 kbps.

All Bearer Services are handled as circuit-switched services between the mobile data equipment and the NSS requiring a permanent link between the involved components.

A converter, called Packet Assembler-Dis-assembler or PAD, is used to adapt these signals to the packet-switched mode in public data networks, e.g. the Internet. With GPRS, a total packet-switched transmission is provided between all data terminal equipment at a maximum bit rate of 171.2 kbps.

2.3 Teleservices

Teleservices provide voice and non-voice services. Voice services include normal speech telephony and emergency calls. Non-voice services include the Short Message Service, for example, that is the sending, receipt and broadcast of short messages.

Short messages can be received at any time, even during a call, and are transmitted over signalling channels. Whereas normal short messages are stored temporarily in the Short Message Service Center SMSC, with Cell Broadcast they are stored in the Base Station Controller BSC.

The fax services, also referred to as Group 3 facsimile, provide automatic fax service between a mobile fax and a fax machine within a PSTN, or between 2 mobile fax terminals, each with its own MSISDN at a maximum speed of 9.6 kbps.

2.4 Supplementary Services

Supplementary Services can be controlled by the subscriber as well as by the network. There are two groups of services.

First, there are those services which are provided by the service provider and made available to a customer.

Then there are the services which are invoked by a customer. The desired service is, for example, activated by a customer pressing a particular key, as is the case with line identification.

The supplementary services subdivide into several types.

2.4.1 Line Identification Services

The Line Identification Services include the Calling Line Identification Presentation (CLIP), that is the display of the caller's number on the called party's mobile station. The network transmits the call number at call set-up, provided that both parties are ISDN or GSM customers.

Using Calling Line Identification Restriction (CLIR), the calling party can restrict its call number, so it cannot be identified by the called party. An appropriate instruction is sent from the caller's network to the network of the recipient. Some networks allow particular user groups, such as the police, to identify a call number even if the CLIR service is activated.

In accordance with CLIP and CLIR, there is the Connected Line Identification Presentation, COLP, for identification of the called party by the caller, and Connected Line Identification Restriction, COLR, if the called party does not want to be identified by the caller. COLP and COLR come into play when the called party has diverted its number to another number.

2.4.2 Call Offering Services

Call Offering Services are services which allow a customer to forward incoming calls to other target numbers.

Call Forwarding Unconditional CFU ensures that all incoming calls are diverted to a number specified by the customer, independent of the conditions of the call.

Call Forwarding on mobile Subscriber Busy CFB diverts calls only if the called subscriber is making a call and the line is busy. Calls can also be diverted if the called party can't be reached - because it currently has no network access, because the phone is switched off, or because the call is not accepted.

Supported by the Optimal Routing Service SOR - a GSM Phase 2+ feature - calls are routed directly to the subscriber's current location. This service is based on the information provided by the called subscriber's home network. As an option, the network may permit or deny SOR on a per call basis. SOR has not yet been implemented.

2.4.3 Call Completion Services

Call Completion Services allow the customer to postpone incoming calls which he is currently not able to accept, as well as to hold calls while simultaneously making another call.

Call Waiting CW notifies the customer of an incoming call when no traffic channel is available, and the customer is engaged in an active or held call. The customer now has from half a minute to two minutes time to decide whether to accept, reject or ignore the postponed call.

The Call Holding Service HOLD permits the customer to interrupt communication on the active call for another call, without losing the connection to the first call. This is because the traffic channel remains assigned to the customer even after interruption of the active call, so he can resume the communication.

2.4.4 Multi Party Supplementary Services

Multi Party Services, also called conferencing services, allow the customer to communicate with more than one party simultaneously. The Multi Party Service can be initiated if a customer is in control of at least one active call and one call on hold. After it has been initiated, parties an be added, disconnected or separated. Thus the subscriber initiating the service can add more parties to the Multiparty Call and exclude others from conversation. At the same time, he can have a private conversation with another party, which the other participants cannot hear. During all this, the participants of the Multiparty Call can still communicate with each other.

2.4.5 Closed User Groups (CUG)

Closed User Group (CUG) gives a particular group of customers the opportunity to communicate with each other in PLMN or ISDN networks. The members of a Closed User Group can't communicate with subscribers outside the group. If desired, one or more subscribers in this group can be authorised to call subscribers outside, or to receive calls from them.

Emergency calls are not subject to the restrictions of this service.

2.4.6 Advice of Charge

The service Advice of Charge (AOC) is a supplementary service that allows a mobile subscriber who uses services to receive service-related billing details.

With Reverse Charging, on the other hand, a called subscriber can be charged for certain calls. For this purpose, each individual call is analyzed and evaluated. Reverse Charging is activated at request by the calling subscriber, and must be permitted by the called subscriber. At present, Reverse Charging is not implemented in GSM networks.

2.4.7 Call Restriction Services

There are basically two categories of Call Restriction Services: one refers to outgoing calls, and the other to incoming calls. The service offers several possibilities, such as:

• Barring all outgoing and incoming calls
• Barring all outgoing international calls

or

• Barring all incoming calls except those coming from the country of the home network.

The calls can be barred manually by the subscriber, or by network configuration.

2.5 Value Added Services

Value Added Services are supplied by the respective Service Provider or network operator, and can be transmitted either via a normal telephone call or via SMS. These services offer the supplier a further opportunity - apart from price - to attract customers.

• Value Added Services are, for example:
• Information on cultural events or traffic announcements via Cell Broadcast
• Reservation of a hotel, a flight or a hire car
• Help in the event of a car breakdown
• Information services
• Medical advice
• Ticket reservation
• Sports news
• Delivery services, like sending flowers to a particular person and many more.