L.5 Use of circuit-switched domain

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

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

There is no CS domain in this access technology.

NOTE 1: If the UE sends an INVITE request including voice codecs which is not successful due to a failure from the lower layers indicating that access is barred for originating calls but not specific to CSFB (see 3GPP TS 24.301 [8J]) and if the CS domain is supported and available, the UE can attempt the voice call via the CS domain.

NOTE 2: If the UE has sent an INVITE request including voice codecs, receives a 500 (Server Internal Error) response to this INVITE request containing no Retry-After header field, including a Reason header field with a protocol value set to "FAILURE_CAUSE" including a cause value header field parameter set to "1" as specified in subclause 7.2A.18.12.2, a Response-Source header field with a "fe" header field parameter set to "<urn:3gpp:fe:p-cscf.orig>", and the UE is attached to both PS and CS domains, the UE can attempt the voice call via the CS domain, e.g. by initiating a service request for CS fallback (see 3GPP TS 24.301 [8J]).

Annex M (normative):
IP-Connectivity Access Network specific concepts when using cdma2000^® packet data subsystem to access IM CN subsystem