Page 34 - From GMS to LTE

20 From GSM to LTE-Advanced Pro and 5G

Table 1.4 Supplementary services of a GSM network.

Supplementary
service Description

Call forward If this service is activated, a number can be configured to which all incoming
unconditional (CFU) calls are forwarded immediately [9]. This means that the mobile device will
not be notified of the incoming call even if it is switched on
Call forward busy This service allows a subscriber to define a number to which calls are
(CFB) forwarded if they are already engaged in a call when a second call comes in
Call forward no If this service is activated, it is possible to forward the call to a user‐defined
reply (CFNRY) number if the subscriber does not answer the call within a certain time. The
subscriber can change the number to which to forward the call as well as the
timeout value (e.g. 25 seconds)
Call forward not This service forwards the call if the mobile device is attached to the network
reachable (CFNR) but is not reachable momentarily (e.g. temporary loss of network coverage)
Barring of all This functionality can be activated by the network operator if, for example,
outgoing calls the subscriber has not paid their monthly invoice in time. It is also possible
(BAOC) for the network operator to allow the subscriber to change the state of this
feature together with a PIN (personal identification number) so that the
subscriber can lend the phone to another person for incoming calls only [10]
Barring of all Same functionality as provided by BAOC for incoming calls [10]
incoming calls
(BAIC)
Call waiting (CW) This feature allows signaling of an incoming call to a subscriber while they
are already engaged in another call [11]. The first call can then be put on
hold to allow the subscriber to accept the incoming call. The feature can be
activated or barred by the operator and switched on or off by the subscriber
Call hold (HOLD) This functionality is used to accept an incoming call during an already active
call or to start a second call [11]
Calling line If activated by the operator for a subscriber, the functionality allows the
identification switching center to forward the number of the caller
presentation (CLIP)
Calling line If allowed by the network, the caller can instruct the network not to show
identification their phone number to the called party
restriction (CLIR)
Connected line Shows the calling party the MSISDN to which a call is forwarded, if call
presentation (COLP) forwarding is active at the called party side
Connected line If COLR is activated at the called party, the calling party will not be notified
presentation of the MSISDN to which the call is forwarded
restriction (COLR)
Multiparty (MPTY) Allows subscribers to establish conference bridges with up to six subscribers [12]

1.6.4 The Authentication Center
Another important part of the HLR is the AuC. The AuC contains an individual key per
subscriber (Ki), which is a copy of the Ki on the SIM card of the subscriber. As the Ki is
secret, it is stored in the AuC and especially on the SIM card in a way that prevents it
from being read directly.