3GPP 24.501 v20.0.0 — the document's own text

9.11.3.9 5GS tracking area identity list

Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).

The purpose of the 5GS tracking area identity list information element is to transfer a list of tracking areas from the network to the UE.

The coding of the information element allows combining different types of lists. The lists of type "00" and "01" allow a more compact encoding, when the different TAIs are sharing the PLMN identity.

The 5GS tracking area identity list information element is coded as shown in figure 9.11.3.8.1, figure 9.11.3.8.2, figure 9.11.3.9.3, figure 9.11.3.9.4 and table 9.11.3.9.1.

The 5GS tracking area identity list is a type 4 information element, with a minimum length of 9 octets and a maximum length of 114 octets. The list can contain a maximum of 16 different tracking area identities.

8	7	6	5	4	3	2	1
5GS tracking area identity list IEI	octet 1
Length of 5GS tracking area identity list contents	octet 2
Partial tracking area identity list 1	octet 3octet i
Partial tracking area identity list 2	octet i+1octet l
…	octet l+1octet m
Partial tracking area identity list p	octet m+1octet n

Figure 9.11.3.9.1: 5GS tracking area identity list information element

8	7	6	5
0Spare	Type of list	Number of elements	octet 1
MCC digit 2	MCC digit 1	octet 2
MNC digit 3	MCC digit 3	octet 3
MNC digit 2	MNC digit 1	octet 4
TAC 1	octet 5
TAC 1 (continued)	octet 6
TAC 1 (continued)	octet 7
…	…
…	…
TAC k	octet 3k+2*
TAC k (continued)	octet 3k+3*
TAC k (continued)	octet 3k+4*

Figure 9.11.3.9.2: Partial tracking area identity list – type of list = "00"

8	7	6	5
0Spare	Type of list	Number of elements	octet 1
MCC digit 2	MCC digit 1	octet 2
MNC digit 3	MCC digit 3	octet 3
MNC digit 2	MNC digit 1	octet 4
TAC 1	octet 5
TAC 1 (continued)	octet 6
TAC 1 (continued)	octet 7

Figure 9.11.3.9.3: Partial tracking area identity list – type of list = "01"

8	7	6	5
0Spare	Type of list	Number of elements	octet 1
MCC digit 2	MCC digit 1	octet 2
MNC digit 3	MCC digit 3	octet 3
MNC digit 2	MNC digit 1	octet 4
TAC 1	octet 5
TAC 1 (continued)	octet 6
TAC 1 (continued)	octet 7
MCC digit 2	MCC digit 1	octet 8*
MNC digit 3	MCC digit 3	octet 9*
MNC digit 2	MNC digit 1	octet 10*
TAC 2	octet 11*
TAC 2 (continued)	octet 12*
TAC 2 (continued)	octet 13*
…
…
MCC digit 2	MCC digit 1	octet 6k-4*
MNC digit 3	MCC digit 3	octet 6k-3*
MNC digit 2	MNC digit 1	octet 6k-2*
TAC k	octet 6k-1*
TAC k (continued)	octet 6k*
TAC k (continued)	octet 6k+1*

Figure 9.11.3.9.4: Partial tracking area identity list – type of list = "10"

Table 9.11.3.9.1: Tracking area identity list information element

Value part of the Tracking area identity list information element (octets 3 to n)

The value part of the Tracking area identity list information element consists of one or several partial tracking area identity lists. The length of each partial tracking area identity list can be determined from the 'type of list' field and the 'number of elements' field in the first octet of the partial tracking area identity list.
The UE shall store the complete list received. If more than 16 TAIs are included in this information element, the UE shall store the first 16 TAIs and ignore the remaining octets of the information element.


Partial tracking area identity list:

Type of list (octet 1)
Bits
7	6
0	0	list of TACs belonging to one PLMN or SNPN, with non-consecutive TAC values
0	1	list of TACs belonging to one PLMN or SNPN, with consecutive TAC values
1	0	list of TAIs belonging to different PLMNs (see NOTE)

All other values are reserved.

Number of elements (octet 1)
Bits
5	4	3	2	1
0	0	0	0	0	1 element
0	0	0	0	1	2 elements
0	0	0	1	0	3 elements
…
0	1	1	0	1	14 elements
0	1	1	1	0	15 elements
0	1	1	1	1	16 elements

All other values are unused and shall be interpreted as 16, if received by the UE.

Bit 8 of octet 1 is spare and shall be coded as zero.


For type of list = "00" and number of elements = k:

octet 2 to 4 contain the MCC+MNC, and
for j = 1, …, k:
octets 3j+2 to 3j+4 contain the TAC of the j-th TAI belonging to the partial list,

For type of list = "01" and number of elements = k:

octet 2 to 4 contain the MCC+MNC, and
octets 5 to 7 contain the TAC of the first TAI belonging to the partial list.
The TAC values of the other k-1 TAIs are TAC+1, TAC+2, …, TAC+k-1.

For type of list = "10" and number of elements = k:

for j = 1, …, k.
octets 6j-4 to 6j-2 contain the MCC+MNC, and
octets 6j-1 to 6j+1 contain the TAC of the j-th TAI belonging to the partial list.


MCC, Mobile country code

The MCC field is coded as in ITU-T Recommendation E.212 [42], annex A.

MNC, Mobile network code

The coding of this field is the responsibility of each administration but BCD coding shall be used. The MNC shall consist of 2 or 3 digits. If a network operator decides to use only two digits in the MNC, MNC digit 3 shall be coded as "1111".

TAC, Tracking area code

In the TAC field bit 8 of the first octet is the most significant bit and bit 1 of third octet the least significant bit.
The coding of the tracking area code is the responsibility of each administration. Coding using full hexadecimal representation may be used. The tracking area code consists of 3 octets.

NOTE: If the "list of TAIs belonging to different PLMNs" is used, the PLMNs included in the list need to be present in the list of "equivalent PLMNs". This type of list is not applicable in an SNPN.