Basic Services

All activities that may be done in the GSM network, such as establishing a voice call, establishing
a data call, sending a short message, etc., are classified as basic services. In order for a subscriber
to use a GSM basic service, she must have a subscription to that service.3 The handling of a basic
2 GSM subscribers may program their MSISDN into the phone; this has, however, no significance for the
network.
3 Exceptions are Tele Service 12 (emergency call establishment) and Tele Service 23 (Cell Broadcast).
Subscribers do not need a subscription to these Tele Services to use them.

service is fully standardized. Hence, a subscriber may use a basic service in any GSM network
she roams to, provided that that basic service is supported in that network. The HLR will send
a list of subscribed basic services to the MSC/VLR, during registration. When a GSM subscriber
initiates a call, the MS supplies the serving MSC with a set of parameters describing the circuit-
switched connection that is requested. These parameters are the bearer capability (BC), low-layer
compatibility (LLC) and high-layer compatibility (HLC), as will be described below. The MSC
uses the BC, LLC and HLC to derive the basic service for this call. The rules for deriving the basic
service from LLC, HLC and BC are specified in GSM TS 09.07 [55]. The MSC then checks whether
the subscriber has a subscription to the requested basic service, i.e. whether the subscription data
in the VLR contains that basic service. If the service is not subscribed to, then the MSC disallows
the call. The basic service is not transported over ISUP.
When a CAMEL service is invoked, the MSC reports the requested basic service to the SCP. The
SCP may use the indication of the requested basic service for call service processing. Examples
include:
• video calls may be charged at a higher rate than speech calls;
• for data calls and fax calls, the CAMEL service shall not play any announcements or tones.
Basic services are divided into two groups: tele services and bearer services.

1.5.1 Tele Services
Table 1.1 provides an overview of the available tele services (TS); see also GSM TS 02.03 [3].

1.5.2 Bearer Services
Table 1.2 provides an overview of the available bearer services (BS). The two bearer service groups
are sub-divided into a variety of bearer services with different characteristics. Refer to GSM

Circuit Bearer Description
Bearer capability, low-layer compatibility and high-layer compatibility are descriptors of a circuit-
switched (CS) connection. When a GSM subscriber initiates a call, the BC, LLC and HLC are
transported from MS to MSC over DTAP. The MSC includes the parameters in the ISUP signal to
the destination. These parameters are also reported to the SCP during CAMEL service invocation.
That enables a CAMEL service to adapt the service logic processing to the type of call. Figure 1.8
shows the relation between LLC, HLC and BC on the DTAP and the corresponding parameters
on ISUP.

Table 1.1 Tele services
Tele service Description Comment
11 Telephony This TS represents the normal speech call
12 Emergency calls The emergency call uses the characteristics of telephony
(TS11), but may be established without subscription
and bypasses various checks in the MS and in the MSC
21 Short message MT This TS relates to receiving an SMS. This TS is not sent
to the MSC/VLR. When an SMS is sent to the
subscriber, the HLR checks whether the destination
subscriber has a subscription to TS 21
22 Short message MO This TS relates to the sending of an SMS
23 Cell broadcast This TS relates to the capability of an SMS that is sent as
a broadcast SMS
61 Alternate speech and fax
group 3
This TS relates to the capability to establish a speech and
fax (group 3) call
62 Automatic fax group 3 This TS relates to the capability to establish a fax (group
3) call
91 Voice group call This TS relates to the capability to participate in a group
call as specified in GSM TS 03.68 [35]
92 Voice broadcast This TS relates to the capability to receive a voice
broadcast as specified in GSM TS 03.68 [35]
Table 1.2 Bearer services
Tele service Description Comment
20 Asynchronous data
bearer services
May be used for asynchronous services from 300 bit/s
to 64 kbit/s.
30 Synchronous data
bearer services
May be used for synchronous services from 1.2 to
64 kbit/s. This BS may be used, amongst other things,
for multimedia services such as video telephony.4
MSC
ISUP
(ITU-T Q.763)
DTAP
(GSM TS 04.08)
Low layer compatibility
High layer compatibility
Bearer capability
Access transport [low layer compatibility]
User teleservice information
User service information
Figure 1.8 Transfer of LLC, HLC and BC through DTAP and ISUP
• Low-layer compatibility – the LLC is transported transparently between the calling entity and
called entity; it may be used by the respective entities to adapt codecs for interworking purposes.
LLC describes mainly characteristics related to the data transfer.
4 3GPP Rel-7 may include a dedicated bearer service for video telephony.


High-layer compatibility – the HLC is also transported transparently between the calling entity
and called entity; it is used to describe the requested service, such as telephony, Fax, video
telephony, etc.
• Bearer capability – the BC describes the characteristics of the 64 kbit/s circuit requested for
the call.
1.6 Supplementary Services
Supplementary services (SS) in GSM are a means of enriching the user experience. An SS may,
for example, forward a call in the case of no reply from the called party, bar certain outgoing or
incoming calls, show the number of the calling party to the called party, etc. In order to use an
SS, a GSM user needs a subscription to that SS. The subscription to supplementary services is
contained in the HLR and is sent to the MSC/VLR during registration. The supplementary services
are fully standardized. A GSM subscriber can therefore use her supplementary services in any GSM
network, provided that the network supports these supplementary services, and have the same user
experience.
Table 1.3 GSM supplementary services
SS group Supplementary services GSM TS
Line identification Calling line identification presentation (CLIP) 02.81 [13]
Calling line identification restriction (CLIR)
Connected line presentation (COLP)
Connected line restriction (COLR)
Name identification Calling name presentation (CNAP) 02.96 [24]
Call forwarding Call forwarding – unconditional (CFU) 02.82 [14],
Call forwarding – busy (CFB)
Call forwarding – no reply (CFNRY)
Call forwarding – not reachable (CFNRC)
Call deflection (CD) 02.72 [11]
Call offering Explicit call transfer (ECT) 02.91 [22]
Call completion Call waiting (CW) 02.83 [15],
Call hold (CH)
Call completion to busy subscriber (CCBS) 02.93 [23],
Multi-call (MC) 22.135 [69]a
Multi-party Multi-party call (MPTY) 02.84 [16]
Community of interest Closed user group (CUG) 02.85 [17]
Charging Advice of charge – information (AOCI) 02.86 [18]
Advice of charge – charge (AOCC)
Additional information transfer User-to-user signalling – service 1 (UUS1) 02.87 [19]
User-to-user signalling – service 2 (UUS2)
User-to-user signalling – service 3 (UUS3)
Call barring Barring of all outgoing calls (BAOC) 02.88 [20]
Barring of outgoing international calls (BOIC)
Barring of outgoing international calls except to the
home country (BOIC-exHc)
Barring of all incoming calls (BAIC)
Barring of all incoming calls when roaming
(BICROAM)
Call priority enhanced multi-level precedence and pre-emption
(eMLPP)
02.67 [10]