GSM Services

It is important to note that all the GSM services were not introduced since the appearance of GSM but they have been introduced in a regular way. The GSM Memorandum of Understanding (MoU) defined four classes for the introduction of the different GSM services:

• E1: introduced at the start of the service.
• E2: introduced at the end of 1991.
• Eh: introduced on availability of half-rate channels.
• A: these services are optional.

Three categories of services can be distinguished:

• Teleservices.
• Bearer services.
• Supplementary Services.

Teleservices

- Telephony (E1® Eh).

- Facsimile group 3 (E1).

- Emergency calls (E1® Eh).

- Teletex.

Short Message Services (E1, E2, A) Using these services, a message of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. If the mobile is powered off, the message is stored. With the SMS Cell Broadcast (SMS-CB), a message of a maximum of 93 characters can be broadcast to all mobiles in a certain geographical area.

- Fax mail. Thanks to this service, the subscriber can receive fax messages at any fax machine.

- Voice mail. This service corresponds to an answering machine.

Bearer Services

A bearer service is used for transporting user data. Some of the bearer services are listed below:

• Asynchronous and synchronous data, 300-9600 bps (E1).
• Alternate speech and data, 300-9600 bps (E1).
• Asynchronous PAD (packet-switched, packet assembler/dissembler) access, 300-9600 bps (E1).
• Synchronous dedicated packet data access, 2400-9600 bps (E2).

Supplementary Services

- Call Forwarding (E1). The subscriber can forward incoming calls to another number if the called mobile is busy (CFB), unreachable (CFNRc) or if there is no reply (CFNRy). Call forwarding can also be applied unconditionally (CFU).

- Call Barring. There are different types of `call barring' services:

• Barring of All Outgoing Calls, BAOC (E1).
• Barring of Outgoing International Calls, BOIC (E1).
• Barring of Outgoing International Calls except those directed toward the Home PLMN Country, BOIC-exHC (E1).
• Barring of All Incoming Calls, BAIC (E1)
• Barring of incoming calls when roaming (A).

- Call holds (E2) puts an active call on hold.

- Call Waiting, CW (E2) informs the user, during a conversation, about another incoming call. The user can answer, reject or ignore this incoming call.

- Advice of Charge, AoC (E2) provides the user with online charge information.

- Multiparty service (E2) Possibility of establishing a multiparty conversation.

- Closed User Group, CUG (A). It corresponds to a group of users with limited possibilities of calling (only the people of the group and certain numbers).

- Calling Line Identification Presentation, CLIP (A). It supplies the called user with the ISDN of the calling user.

- Calling Line Identification Restriction, CLIR (A). It enables the calling user to restrict the presentation.

- Connected Line identification Presentation, CoLP (A). It supplies the calling user with the directory number he gets if his call is forwarded.

- Connected Line identification Restriction, CoLR (A). It enables the called user to restrict the presentation.

- Operator determined barring (A).Restriction of different services and call types by the operator.

Conclusion

The aim of this paper was to give an overview of the GSM system and not to provide a complete and exhaustive guide.

As it is shown in this chapter, GSM is a very complex standard. It can be considered as the first serious attempt to fulfill the requirements for a universal personal communication system. GSM is then used as a basis for the development of the Universal Mobile Telecommunication System (UMTS).