4G/LTE - NAS

 

 

 

ESM Cause - #50, #51, #52

 

The purpose of the ESM cause information element is to indicate the reason why a session management request (e.g, PDN Connectivity Request) is rejected (e.g, PDN Connectivity Reject) or restricted (e.g, Activate default EPS bearer context request).

 

 

NAS Messages Carrying ESM Cause

 

There are roughly two type of NAS message that carry ESM Cause. One is Activate default EPS Bearer Request which is used to accept the IP that UE requested and another message is PDN Connectivity Reject which is used to reject the PDN that UE requested.

 

 

 

Meaning of the Cause defined in 3GPP

 

The details of ESM Cause is described in 24.301 B.1 Causes related to Nature of Request

 

#50, #51, #52 are as follows :

 

ESM Cause

Meaning

Description

50

PDN type IPv4 only allowed

Indicate that only PDN type IPv4 is allowed for the requested PDN Connectivity

51

PDN type IPv6 only allowed

Indicate that only PDN type IPv6 is allowed for the requested PDN Connectivity

52

Single Address Bearer only allowed

Indicate that the requested PDN connectivity is accepted with the restriction that only single IP version bearers are allowed

 

If you expend this table into more detailed cases, we can describe the cases as follows.

IP Type

Requested by UE

Network Capability/Assignment By Network

IP Type

Single Bearer (*)

ESM Cause

NAS Message

IPv4

IPv4

OFF

N/A

Activate Default EPS Bearer Context Request

IPv4

IPv4

ON

N/A

Activate Default EPS Bearer Context Request

IPv4

IPv6

OFF

#51

PDN Connectivity Reject

IPv4

IPv6

ON

#51

PDN Connectivity Reject

IPv4

IPv4v6

N/A

N/A

Activate Default EPS Bearer Context Request

IPv6

IPv4

OFF

#50

PDN Connectivity Reject

IPv6

IPv4

ON

#50

PDN Connectivity Reject

IPv6

IPv6

OFF

N/A

Activate Default EPS Bearer Context Request

IPv6

IPv6

ON

N/A

Activate Default EPS Bearer Context Request

IPv6

IPv4v6

N/A

N/A

Activate Default EPS Bearer Context Request

IPv4v6

IPv4

OFF

#50

Activate Default EPS Bearer Context Request

IPv4v6

IPv4

ON

#52

Activate Default EPS Bearer Context Request

IPv4v6

IPv6

OFF

#51

Activate Default EPS Bearer Context Request

IPv4v6

IPv6

ON

#52

Activate Default EPS Bearer Context Request

IPv4v6

IPv4v6

N/A

N/A

Activate Default EPS Bearer Context Request

Note (*) : "Single Bearer" indicate Network allows 'single address bearer only'.

 

Also, 24.301 6.2.2 IP address allocation via NAS signalling describes in detail as follows :

  • If the UE requests for PDN type IPv4v6, but Network allows IPv4 only or IPv6 only for the requested APN for various reason, the network shall override the PDN type requested by the UE to be limited to a single address PDN type (IPv4 or IPv6). In the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message sent to the UE, the network shall set the PDN type value to either "IPv4" or "IPv6" and the ESM cause value to #50 "PDN type IPv4 only allowed", or #51 "PDN type IPv6 only allowed", respectively. The UE shall not subsequently initiate another UE requested PDN connectivity procedure to the same APN to obtain a PDN type different from the one allowed by the network.
  • A UE, which is IPv6 and IPv4 capable and
    • has not been allocated an IP address for this APN, shall set the PDN type IE to IPv4v6.
    • has been allocated an IPv4 address for this APN and received the ESM cause #52 "single address bearers only allowed", and is requesting an IPv6 address, shall set the PDN type IE to IPv6
    • has been allocated an IPv6 address for this APN and received the ESM cause #52 "single address bearersonly allowed", and is requesting an IPv4 address, shall set the PDN type IE to IPv4.

 

 

Example 1 >

    i) UE Request IPv4 to Network that support IPv6 only

    ii) Network send PDN Connectivity Reject with ESM Cause 51

 

Step

Direction

Message

Comment

1

UE -> NW

RRC Connection Request

 

2

UE <- NW

RRC Connection Setup

 

3

UE -> NW

RRC Connection Setup Complete

+ Attach Request

+ PDN Connectivity Request

PDN Type value = IPv4

4

UE <-> NW

< Authentication >

 

5

UE <-> NW

< NAS Security >

 

6

UE <-> NW

< RRC Security >

 

7

UE <- NW

dlInformationTransfer

+Attach Reject

+PDN Connectivity Reject

ESM Cause =

       #51:PDN type IPv6 only allowed

8

UE <- NW

RRC Connection Release

 

 

 

Step 3 : RRC Connection Setup Complete + Attach Request + PDN Connectivity Request

 

UL-DCCH-Message

    message: c1 (0)

        c1: rrcConnectionSetupComplete (4)

            rrcConnectionSetupComplete

                rrc-TransactionIdentifier: 0

                criticalExtensions: c1 (0)

                    c1: rrcConnectionSetupComplete-r8 (0)

                        rrcConnectionSetupComplete-r8

                            selectedPLMN-Identity: 1

                            registeredMME

                                mmegi: 8001 [bit length 16, 1000 0000  0000 0001 decimal value 32769]

                                mmec: 00 [bit length 8, 0000 0000 decimal value 0]

                            dedicatedInfoNAS: 17824a8d76050741220bf61300148001000000000105e060...

                                Non-Access-Stratum (NAS)PDU

                                    .....

                                    EPS mobile identity

                                        .....

                                    UE network capability

                                        .....

                                    ESM message container

                                        Length: 33

                                        ESM message container contents:

                                                   0202d011d1271a8080211001000010810600000000830600...

                                            0000 .... = EPS bearer identity: No EPS bearer identity assigned (0)

                                            .... 0010 = Protocol discriminator:

                                                        EPS session management messages (0x02)

                                            Procedure transaction identity: 2

                                            NAS EPS session management messages: PDN connectivity request (0xd0)

                                            0001 .... = PDN type: IPv4 (1)

                                            .... 0001 = Request type: initial request (1)

                                            ESM information transfer flag

                                                ....

                                            Protocol Configuration Options

                                               .....

                                    Tracking area identity - Last visited registered TAI

                                        .....

                                    DRX Parameter

                                        .....

                                    MS Network Capability

                                        .....

    HEX : 20 20 80 01 00 65 17 82 4A 8D 76 05 07 41 22 0B F6 13 00 14 80 01 00 00 00 00 01 05 E0 60 C0 40 01 00 21 02 02 D0 11 D1 27 1A 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 00 0D 00 00 0A 00 52 13 00 14 00 01 5C 0A 00 31 03 E5 E0 3E 13 13 00 14 00 01 11 03 57 58 A6 40 08 04 02 60 00 00 02 1F 00 5D 01 02 E0

 

Step 7 : dlInformationTransfer+Attach Reject+PDN Connectivity Reject

DL-DCCH-Message

    message: c1 (0)

        c1: dlInformationTransfer (1)

            dlInformationTransfer

                rrc-TransactionIdentifier: 0

                criticalExtensions: c1 (0)

                    c1: dlInformationTransfer-r8 (0)

                        dlInformationTransfer-r8

                            dedicatedInfoType: dedicatedInfoNAS (0)

                                dedicatedInfoNAS: 27cf676073020744137800040202d133

                                    Non-Access-Stratum (NAS)PDU

                                        ....

                                        NAS EPS Mobility Management Message Type: Attach reject

                                        EMM cause

                                            Cause: ESM failure (19)

                                        ESM message container

                                            Element ID: 0x78

                                            Length: 4

                                            ESM message container contents: 0202d133

                                                ....

                                                Procedure transaction identity: 2

                                                NAS EPS session management messages:

                                                    PDN connectivity reject (0xd1)

                                                ESM cause

                                                    Cause: PDN type IPv6 only allowed (51)

    HEX : 08 00 81 3E 7B 3B 03 98 10 3A 20 9B C0 00 20 10 16 89 98