7 Interworking classifications

29.0073GPPGeneral requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

7.1 Service interworking

Service interworking is required when the Teleservices at the calling and called terminals are different. No service interworking, except for facsimile group 3 (Teleservice 61 or 62 interworking with standard facsimile group 3 service), has been identified as a requirement of the PLMN system for PSTN/ISDN network based services.

7.2 Network interworking

Network interworking is required whenever a PLMN and a non‑PLMN together are involved to provide an end to end connection and may be required in instances of PLMN to PLMN connections.

The concept of Bearer Services was developed for the ISDN and has been extended to the PLMN. A bearer service is defined (in 3GPP TS 22.001) as.

A type of telecommunication service that provides the capability for the transmission of signals between user‑network interfaces.

Bearer services are described by a number of attributes, where an attribute is defined as a specified characteristic of an object or element whose values distinguish that object or element from others.

For the purpose of the present document, a PSTN is assumed to provide a bearer service which equates to an ISDN 3,1 kHz audio bearer service.

Refer to 3GPP TS 22.002 for complete list of bearer services. Refer to 3GPP TS 24.008 for coding of Bearer Capabilities. Refer to 3GPP TS 27.001 for the allowed combinations of parameter value settings.

Table 3: Bearer Service Interworking

Bearer service category in PLMN	Bearer Service in PLMN	Bearer service in ISDN	Service in PSTN
Circuit mode unstructured with unrestricted digital capability	Asynchronous Data general
Transparent and Non-transparent		Cct mode structured	Not Applicable
Circuit mode unstructured with unrestricted digital capability Transparent	Synchronous Data general	64 kbit/s unrestricted
3,1 kHz Audio Ex PLMN	Asynchronous Data general
Transparent and Non‑transparent		Cct Mode	Cct Mode
3,1 kHz Audio Ex PLMN	Synchronous Data general	3,1 kHz Audio	3,1 kHz Audio
Transparent

Table 4: Network interworking of Teleservices

Teleservice in PLMN	Lower layer capabilities addressed in the PLMN Bearer Capabilities IE	Bearer service in ISDN	Service in PSTN
Telephony	Unstructured with speech capability	Speech or Cct mode	Cct Mode
Emergency calls	Unstructured with speech capability	3,1 kHz audio	3,1 kHz audio
Alternate speech/ facsimile group 3	Data Cct duplex synchronous (A/Gb mode) / asynchronous (UTRAN Iu mode) access alternate speech group 3 fax	Cct mode 3,1 kHz audio	Cct mode 3,1 kHz audio
Automatic Facsimile group 3	Data Cct duplex synchronous (A/Gb mode) / asynchronous (UTRAN Iu mode) access group 3 fax	Cct mode 3,1 kHz audio

This table does not identify any relationship between Teleservices in the PLMN with those in the ISDN/PSTN, it is merely to identify the interworking of the lower network layers of that teleservice with the network layers i.e. bearer service in the ISDN/PSTN.

7.3 Signalling interworking

See 3GPP TS 49.003[31].

7.4 Numbering

See 3GPP TS 23.003[35]

7.5 Supplementary service interworking

For general aspects of supplementary services refer to 3GPP TS 22.004[34] and 23.011[37].

Not every supplementary service may be used in combination with each basic service. The applicability of each supplementary service for a basic service is defined in 3GPP TS 22.004[34].