7.7 SIP timers

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

The timers T1, T2, T4 A, B, C, D, E, F, G, H and I (defined in RFC 3261 [26]), timers L and M (defined in RFC 6026 [163]), and timer N (defined in RFC 6665 [28]) need modification in some cases to accommodate the delays introduced by the air interface processing and transmission delays. Table 7.7.1 shows recommended values for IM CN subsystem.

Table 7.7.1 lists in the first column, titled "SIP Timer" the timer names as defined in RFC 3261 [26] and RFC 6026 [163].

The second column, titled "value to be applied between IM CN subsystem elements" lists the values recommended for network elements e.g. P-CSCF, S-CSCF, MGCF, when communicating with each other i.e. when no air interface leg is included. These values are identical to those recommended by RFC 3261 [26], RFC 6026 [163], and RFC 6665 [28].

The third column, titled "value to be applied at the UE" lists the values recommended for the UE, when in normal operation the UE generates requests or responses containing a P-Access-Network-Info header field which included a value of "3GPP-GERAN","3GPP-UTRAN-FDD", "3GPP-UTRAN-TDD", "3GPP-E-UTRAN-FDD", "3GPP-E-UTRAN-TDD", "3GPP-E-UTRAN-ProSe-UNR", "3GPP-NR-FDD", "3GPP-NR-TDD", "3GPP-NR-U-FDD", "3GPP-NR-U-TDD", "3GPP-NR-SAT", "3GPP-NR-ProSe-L2UNR", "3GPP-NR-ProSe-L3UNR", "3GPP2-1X", "3GPP2-1X-HRPD", "3GPP2-UMB", "IEEE-802.11", "IEEE-802.11a", "IEEE-802.11b", "IEEE-802.11g", "IEEE-802.11n", "IEEE-802.11ac", or "DVB-RCS2". These are modified when compared to RFC 3261 [26] and RFC 6026 [163] to accommodate the air interface delays. In all other cases, the UE should use the values specified in RFC 3261 [26] or RFC 6026 [163] as indicated in the second column of table 7.7.1.

The fourth column, titled "value to be applied at the P-CSCF toward a UE" lists the values recommended for the P-CSCF when an air interface leg is traversed, and which are used on all SIP transactions on a specific security association where the security association was established using a REGISTER request containing a P-Access-Network-Info header field provided by the UE which included a value of "3GPP-GERAN","3GPP-UTRAN-FDD", "3GPP-UTRAN-TDD", "3GPP-E-UTRAN-FDD", "3GPP-E-UTRAN-TDD", "3GPP-E-UTRAN-ProSe-UNR", "3GPP-NR-FDD", "3GPP-NR-TDD", "3GPP-NR-U-FDD", "3GPP-NR-U-TDD", "3GPP-NR-SAT", "3GPP-NR-ProSe-L2UNR", "3GPP-NR-ProSe-L3UNR", "3GPP2-1X", "3GPP2-1X-HRPD", "3GPP2-UMB", "IEEE-802.11", "IEEE-802.11a", "IEEE-802.11b", "IEEE-802.11g", "IEEE-802.11n", "IEEE-802.11ac", or "DVB-RCS2". These are modified when compared to RFC 3261 [26] and RFC 6026 [163]. In all other cases, the P-CSCF should use the values specified in RFC 3261 [26] and RFC 6026 [163] as indicated in the second column of table 7.7.1.

The final column reflects the timer meaning as defined in RFC 3261 [26], RFC 6026 [163] or RFC 6665 [28].

Table 7.7.1: SIP timers

SIP Timer	Value to be applied between IM CN subsystem elements	Value to be applied at the UE	Value to be applied at the P-CSCF toward a UE	Meaning
T1	500ms default (see NOTE)	2s default	2s default	RTT estimate
T2	4s (see NOTE)	16s	16s	The maximum retransmit interval for non-INVITE requests and INVITE responses
T4	5s (see NOTE)	17s	17s	Maximum duration a message will remain in the network
Timer A	initially T1	initially T1	initially T1	INVITE request retransmit interval, for UDP only
Timer B	64*T1	64*T1	64*T1	INVITE transaction timeout timer
Timer C	> 3min	> 3 min	> 3 min	proxy INVITE transaction timeout
Timer D	> 32s for UDP	>128s	>128s	Wait time for response retransmits
Timer D	0s for TCP/SCTP	0s for TCP/SCTP	0s for TCP/SCTP	Wait time for response retransmits
Timer E	initially T1	initially T1	initially T1	non-INVITE request retransmit interval, UDP only
Timer F	64*T1	64*T1	64*T1	non-INVITE transaction timeout timer
Timer G	initially T1	initially T1	initially T1	INVITE response retransmit interval
Timer H	64*T1	64*T1	64*T1	Wait time for ACK receipt.
Timer I	T4 for UDP	T4 for UDP	T4 for UDP	Wait time for ACK retransmits
Timer I	0s for TCP/SCTP	0s for TCP/SCTP	0s for TCP/SCTP	Wait time for ACK retransmits
Timer J	64*T1 for UDP	64*T1 for UDP	64*T1 for UDP	Wait time for non-INVITE request retransmits
Timer J	0s for TCP/SCTP	0s for TCP/SCTP	0s for TCP/SCTP	Wait time for non-INVITE request retransmits
Timer K	T4 for UDP	T4 for UDP	T4 for UDP	Wait time for response retransmits
Timer K	0s for TCP/SCTP	0s for TCP/SCTP	0s for TCP/SCTP	Wait time for response retransmits
Timer L	64*T1	64*T1	64*T1	Wait time for accepted INVITE request retransmits
Timer M	64*T1	64*T1	64*T1	Wait time for retransmission of 2xx to INVITE or additional 2xx from other branches of a forked INVITE
Timer N	64*T1	64*T1	64*T1	Wait time for receipt of a NOTIFY request upon sending SUBSCRIBE
NOTE: As a network option, SIP T1 Timer’s value can be extended, along with the necessary modifications of T2 and T4 Timers’ values, to take into account the specificities of the supported services when the MRFC and the controlling AS are under the control of the same operator and the controlling AS knows, based on local configuration, that the MRFC implements a longer value of SIP T1 Timer.