22.0013GPPPrinciples of circuit telecommunication services supported by a Public Land Mobile Network (PLMN)Release 17TS
When an UE wishes to start a call and there is no existing radio connection, it requests a signalling channel. When such a signalling channel has been allocated to the UE, the UE can transfer the call set-up information.
A traffic channel may be allocated at any time before the network informs the UE that the remote user has answered.
For a call to be set up, certain information needs to be sent by the UE to the network, defining the call. This information may be provided as default by the MS, it may be derived from the SIM/USIM or be entered by the user either directly into the UE or from a DTE by using the DTE/DCE Interface.
The following information is sent. Where necessary, default values will generally be inserted by the UE if not directly specified by the user. The Teleservice Emergency Calls are set up using a special procedure not using the fields described in this clause (except for the Bearer Capability).
D.2.1 Called Party Address
This is the address of the called party, generally as defined in 3GPP TS 23.003 , using the TON/NPI specified below
D.2.2 Calling/Called Party Sub-address
This is the sub-address of the calling/called party, as defined in 3GPP TS 23.003 , in order to provide interworking with ISDN. This is described in more detail in ETS 300 059. Support and use of these fields are optional.
D.2.3 Type of Number
This indicates the format of the called party address. The selection procedure is given in 3GPP TS 22.030 . The following Types of Number are commonly used:
– International Format;
– Open Format ("Unknown");
D.2.4 Number Plan Indicator
This indicates the number plan of the called party address. Either of the following number plans may be the "default", depending on the contents of the Called Party Address (see 3GPP TS 22.030 ):
– ISDN/Telephony E.164;
Alternatively, one of these number plans may be specified if appropriate:
– data network X.121;
– telex network F.69;
– National Numbering Plan;
– Private Numbering Plan.
D.2.5 Bearer Capability
This is used to define the type of call to be set up (telephony, data, rate etc.) For most applications, the UE will use a set of default conditions, generally on the assumption of a telephony call, unless otherwise set. These may be overridden by the user (or DTE via the DTE/DCE Interface) if desired except for the determination of the channel mode (full or half rate, speech codec conversion).
The UE shall indicate to the network its channel mode capability in terms of the data channels and the speech codec versions supported.
The network decides which mode to use on the basis of the requested bearer or teleservice, the available network resources and the channel mode capability of the UE:
– for the "alternate" and "followed-by" services, the same principle applies (with the exception of TS61, where a Full Rate or an Enhanced Full Rate channel shall be provided);
– for the full set of parameters and values, refer to 3GPP TS 24.008 ;
– for data services see the 3GPP TS 27 series.
Lower Layer Compatibility and Higher Layer Compatibility Information Elements may also be included.
D.2.6 Calling Line Indication Restriction Override
If the user wishes to override the calling line identification restriction, he may indicate this on a per-call basis as described in 3GPP TS 22.030  and 3GPP TS 22.081 .
D.2.7 Action of the Network on Call Set-up
On receipt of the call set-up message, the network shall attempt to connect the call. However, if insufficient information has been provided by the UE to indicate the exact Bearer Capability requirements (e.g. due to missing or optional values or for rate adaptation for data), the network may insert the missing information, if this is possible, and the call set-up shall proceed using the new information. If the call set-up is unsuccessful, the network shall notify the UE of the cause.