7.7.28 MM Context

29.0603GPPGeneral Packet Radio Service (GPRS)GPRS Tunnelling Protocol (GTP) across the Gn and Gp interfaceRelease 17TS

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

The MM Context information element contains the Mobility Management, MS and security parameters that are necessary to transfer between SGSNs at the Inter SGSN Routeing Area Update procedure.

Security Mode indicates the type of security keys (GSM/UMTS) and Authentication Vectors (quintuplets/triplets) that are passed to the new SGSN.

Ciphering Key Sequence Number (CKSN) is described in 3GPP TS 24.008 [5]. Possible values are integers in the range [0; 6]. The value 7 is reserved. CKSN identifies Kc. During the Intersystem Change to 3G-SGSN, the KSI shall be assigned the value of CKSN.

Key Set Identifier (KSI) identifies CK and IK. During the Intersystem Change to 2G-SGSN, the CKSN shall be assigned the value of KSI.

Used Cipher indicates the GSM ciphering algorithm that is in use.

Kc is the GSM ciphering key of the GSM security context to be used by the new SGSN. This is the GSM security context agreed with the MS during the latest successful authentication procedure. Kc shall be present if GSM key is indicated in the Security Mode.

CK is the UMTS ciphering key of the UMTS security context to be used by the new SGSN. This is the UMTS security context agreed with the MS during the latest successful authentication procedure. CK shall be present if UMTS keys are indicated in the Security Mode.

IK is the UMTS integrity key of the UMTS security context to be used by the new SGSN. This is the UMTS security context agreed with the MS during the latest successful authentication procedure. IK shall be present if UMTS keys are indicated in the Security Mode.

The Triplet array contains triplets encoded as the value in the Authentication Triplet information element. The MM Context IE may contain a Triplet array if so indicated in the Security Mode. At most 5 Authentication Triplets may be included. The field ‘No of Vectors’ shall be set to the value ‘0’ if no Authentication Triplet is included (i.e. octets ’14 to m’ in Figure 40 are absent).

The Quintuplet array contains Quintuplets encoded as the value in the Authentication Quintuplet information element. The MM Context IE may contain a Quintuplet array if so indicated in the Security Mode. At most 5 Authentication Quintuplets may be included. The field ‘No of Vectors’ shall be set to the value ‘0’ if no Authentication Quintuplet is included (i.e. octets ’40 to m’ in Figure 41, octets ’16 to m’ in Figure 42, or octets ’40 to m’ in Figure 42A are absent). If the quintuplet array is present, the Quintuplet length field indicates its length.

The DRX parameter carries the DRX settings that the UE is using within the network.

MS Network Capability provides the network with information concerning aspects of the MS related to GPRS. MS Network Capability and MS Network Capability Length are coded as in the value part described in 3GPP TS 24.008 [5]. If MS Network Capability is not included, its Length field value shall be set to 0.

DRX parameter is coded as described in 3GPP TS 24.008 [5], the value part only.

The two octets Container Length holds the length of the Container, excluding the Container Length octets.

Container contains one or several optional information elements as described in the clause "Overview", from the clause "General message format and information elements coding" in 3GPP TS 24.008 [5]. For the definition of the IEI see table 47a, "IEIs for information elements used in the container". The IMEISV shall, if available, be included in the Container. The IMEISV is included in the Mobile identity IE. If Container is not included, its Length field value shall be set to 0. If the MS is emergency attached and the MS is UICCless or the IMSI is unauthenticated, the International Mobile Equipment Identity (IMEI) shall be used as the MS identity.

In Figures 41 and 42A,

– if the UGIPAI (Used GPRS integrity protection algorithm Indicator), bit 7 of octet 4, is set to 0, then bits 4 to 6 of octet 4 shall contain the Used GPRS integrity protection algorithm field, otherwise these bits shall be set to 1 and ignored by the receiver.

– the GUPII (GPRS User Plane Integrity Indicator), bit 8 of octet 4, shall be set to 0 if the subscriber profile indicated that user plane integrity protection is required and set to 1 otherwise.

NOTE: The encoding of the bits is not identical with GTPv2 as the spare bits are encoded differently.

If Length of Access Restriction Data is zero, then the field of Access Restriction Data shall not be present. The Access Restriction Data is composed of NRSRNA(NR as Secondary RAT Not Allowed). The presence of the Access Restriction Data in MM Context Information is optional.

NOTE: Including the Access Restriction Data when NRSRNA is provided allows optimized selection of SGW in case of handover from GSM/UTRAN to E-UTRAN.

Bits

Octets

Type = 129 (Decimal)

2-3

Length

Spare 1111

CKSN

Security Mode

No of Vectors

Used Cipher

6-13

14-m

Triplet [1..5]

(m+1)-(m+2)

DRX parameter

(m+3)

MS Network Capability Length

(m+4)-n

MS Network Capability

(n+1)-(n+2)

Container length

(n+3)-o

Container

o+1

Length of Access Restriction Data

o+2

Spare

NRSRNA

Figure 40: MM Context Information Element with GSM Key and Triplets

Bits

Octets

Type = 129 (Decimal)

2-3

Length

GUPII

UGIPAI

Used GPRS integrity protection algorithm

KSI

Security Mode

No of Vectors

Spare 111

6-21

22-37

38-39

Quintuplet Length

40-m

Quintuplet [1..5]

(m+1)-(m+2)

DRX parameter

(m+3)

MS Network Capability Length

(m+4)-n

MS Network Capability

(n+1)-(n+2)

Container length

(n+3)-o

Container

o+1

Length of Access Restriction Data

o+2

Spare

NRSRNA

Figure 41: MM Context Information Element with UMTS Keys and Quintuplets

Bits

Octets

Type = 129 (Decimal)

2-3

Length

Spare 1111

CKSN

Security Mode

No of Vectors

Used Cipher

6-13

14-15

Quintuplet Length

16-m

Quintuplet [1..5]

(m+1)-(m+2)

DRX parameter

(m+3)

MS Network Capability Length

(m+4)-n

MS Network Capability

n+1-n+2

Container length

n+3-o

Container

o+1

Length of Access Restriction Data

o+2

Spare

NRSRNA

Figure 42: MM Context Information Element with GSM Keys and UMTS Quintuplets

Bits

Octets

Type = 129 (Decimal)

2-3

Length

GUPII

UGIPAI

Used GPRS integrity protection algorithm

CKSN/KSI

Security Mode

No of Vectors

Used Cipher

6-21

22-37

38-39

Quintuplet Length

40-m

Quintuplet [1..5]

(m+1)-(m+2)

DRX parameter

(m+3)

MS Network Capability length

(m+4)-n

MS Network Capability

(n+1)-(n+2)

Container length

(n+3)-o

Container

o+1

Length of Access Restriction Data

o+2

Spare

NRSRNA

Figure 42A: MM Context Information Element with Used Cipher value,
UMTS Keys and Quintuplets

Table 46: Used Cipher Values

Cipher Algorithm	Value (Decimal)
No ciphering	0
GEA/1	1
GEA/2	2
GEA/3	3
GEA/4	4
GEA/5	5
GEA/6	6
GEA/7	7

Table 47: Security Mode Values

Security Type	Value (Decimal)
GSM key and triplets	1
GSM key and quintuplets	3
UMTS key and quintuplets	2
Used cipher value, UMTS Keys and Quintuplets	0

Table 47A: IEIs for information elements used in the container

IEI	Information element
0x23	Mobile identity

NOTE: In 3GPP TS 24.008 [5] the IEI definition is message dependent. The table is added to have a unique definition in the present document for the used IEI in the MMcontext.

Table 47B: Used GPRS integrity protection algorithm Values

Integrity protection Algorithm	Value (Decimal)
No integrity protection	0
spare	1
spare	2
spare	3
GIA4	4
GIA5	5
spare	6
spare	7