APN(Access Point Name) in LTE
APN stands for Access Point Name. This is a kind of Gateway (or Anchoring point) to which your UE (Mobile Phone) get attached to get access to the core network for most of the data service.
In this page, I will talk about APN with practical aspect and followings are the list of topics I will cover in this page.
- How APN is assinged ?
- Protocol aspect of APN assignment
- APN in S1AP
- UE Setting Aspect of APN Assignement
- Why sometimes UE does not specify APN name in PDN Connectivity Request ?
- Common Issues and Challenges for APN related issues
- Check List
How APN is assigned to UE ? Basically it gets assigned by network based on the request from the UE. So it is combination of UE setting(for request) and Network configuration. Since both parties get involved in APN assignment, frequently this APN assignment cause various issues espcially for testing the UE. (You would not see much of the problem with this for commericilized phone being used in real network since they are preconfigured to exactly match network requirement when you purchase it, but in many testing situation frequently you would see the case where the exact APN requirement on UE and network is not known. Some UE is pretty flexible/tolerant about the mismatched APN assignment from test equipment but some UE is very picky about the APN assignment from test equipment and shows various strange behavior when the assignment from network does not exactly match what it is expecting.
So when you are testing a UE (DUT) for most of the data service related test (e.g, IP throughput, Browsing, IMS etc), you have to consider both Protocol aspect of APN assingment and UE side APN setting.
Protocol aspect of APN assignment.
Typical process of APN assingment protocol is very simple. It happens in two steps as listed below.
i) UE -> NW : PDN Connectivity Request // Usually UE request PDN with a specific APN (or no specified APN)
ii) UE <- NW : Activate Default EPS Bearer Context Request // Network always specifies a specific APN
In reality, these two NAS message gets embedded in a little bit different RRC messages. Typically you may see following two types of RRC message carrying these NAS messages.
Case 1 : Assignment of default APN
In case of assignment of default APN, usually following two steps gets involved.
i) RRC : RRC Connection Setup Complete + NAS : Attach Request + ESM : PDN Connectivity Request
ii) RRC : RRC Connection Reconfiguration + NAS : Attach Accept + NAS : Activate Default EPS Bearer Context Req
< PDN Connectivity Request : Default APN >
NAS EPS session management messages: PDN connectivity request (0xd0)
0011 .... = PDN type: IPv4v6 (3)
.... 0001 = Request type: initial request (1)
ESM information transfer flag
1101 .... = Element ID: 0xd-
.... 000. = Spare bit(s): 0x00
.... ...1 = EIT (ESM information transfer): Security protected ESM information transfer required
Protocol Configuration Options
Element ID: 0x27
Length: 32
[Link direction: MS to network (0)]
1... .... = Extension: True
Configuration Protocol: PPP for use with IP PDP type or IP PDN type (0)
Protocol or Container ID: Internet Protocol Control Protocol (0x8021)
Length: 0x10 (16)
PPP IP Control Protocol
Code: Configuration Request (1)
Identifier: 0 (0x00)
Length: 16
Options: (12 bytes), Primary DNS Server IP Address, Secondary DNS Server IP Address
Primary DNS Server IP Address: 0.0.0.0
Type: Primary DNS Server IP Address (129)
Length: 6
Primary DNS Address: 0.0.0.0 (0.0.0.0)
Secondary DNS Server IP Address: 0.0.0.0
Type: Secondary DNS Server IP Address (131)
Length: 6
Secondary DNS Address: 0.0.0.0 (0.0.0.0)
Access Point Name // UE can specify a predefined name here.
// In case of default EPS bearer, it is common that the APN is not specified
Protocol or Container ID: DNS Server IPv4 Address Request (0x000d)
Length: 0x00 (0)
Protocol or Container ID: DNS Server IPv6 Address Request (0x0003)
Length: 0x00 (0)
Protocol or Container ID: IP address allocation via NAS signalling (0x000a)
Length: 0x00 (0)
Protocol or Container ID: IPv4 Link MTU Request (0x0010)
Length: 0x00 (0)
< Activate Default EPS Bearer Context Request : Default APN >
NAS EPS session management messages: Activate default EPS bearer context request (0xc1)
EPS quality of service
Length: 1
Quality of Service Class Identifier (QCI): QCI 9 (9)
Access Point Name
Length: 8
APN: internet // Network Assigns a specific APN Name
PDN address
Length: 13
0000 0... = Spare bit(s): 0x00
PDN type: IPv4v6 (3)
PDN IPv6 if id: 0000000000000001
PDN IPv4: 192.168.137.2 (192.168.137.2)
Protocol Configuration Options
Element ID: 0x27
Length: 8
[Link direction: Network to MS (1)]
1... .... = Extension: True
Configuration Protocol: PPP for use with IP PDP type or IP PDN type (0)
Protocol or Container ID: Internet Protocol Control Protocol (0x8021)
Length: 0x04 (4)
PPP IP Control Protocol
Code: Configuration Nak (3)
Identifier: 0 (0x00)
Length: 4
Case 2 : Assignment of additional APN
In case of assignment of additional APN after the default APN, usually following two steps gets involved.
i) RRC : ulinformationTransfer + ESM : PDN Connectivity Request
ii) RRC : RRC Connection Reconfiguration + NAS : Activate Default EPS Bearer Context Req
< PDN Connectivity Request : Additional APN >
NAS EPS session management messages: PDN connectivity request (0xd0)
0011 .... = PDN type: IPv4v6 (3)
.... 0001 = Request type: initial request (1)
Access Point Name
Element ID: 0x28
Length: 4
APN: ims // Usually UE request PDN with specific APN name
Protocol Configuration Options
Element ID: 0x27
Length: 41
[Link direction: MS to network (0)]
1... .... = Extension: True
Configuration Protocol: PPP for use with IP PDP type or IP PDN type (0)
Protocol or Container ID: Internet Protocol Control Protocol (0x8021)
Length: 0x10 (16)
PPP IP Control Protocol
Code: Configuration Request (1)
Identifier: 0 (0x00)
Length: 16
Options: (12 bytes), Primary DNS Server IP Address, Secondary DNS Server IP Address
Primary DNS Server IP Address: 0.0.0.0
Type: Primary DNS Server IP Address (129)
Length: 6
Primary DNS Address: 0.0.0.0 (0.0.0.0)
Secondary DNS Server IP Address: 0.0.0.0
Type: Secondary DNS Server IP Address (131)
Length: 6
Secondary DNS Address: 0.0.0.0 (0.0.0.0)
Protocol or Container ID: DNS Server IPv4 Address Request (0x000d)
Length: 0x00 (0)
Protocol or Container ID: DNS Server IPv6 Address Request (0x0003)
Length: 0x00 (0)
Protocol or Container ID: P-CSCF IPv6 Address Request (0x0001)
Length: 0x00 (0)
Protocol or Container ID: P-CSCF IPv4 Address Request (0x000c)
Length: 0x00 (0)
Protocol or Container ID: IP address allocation via NAS signalling (0x000a)
Length: 0x00 (0)
Protocol or Container ID: MS Support of Network Requested Bearer Control indicator (0x0005)
Length: 0x00 (0)
Protocol or Container ID: IPv4 Link MTU Request (0x0010)
Length: 0x00 (0)
< Activate Default EPS Bearer Context Req : Additional APN >
NAS EPS session management messages: Activate default EPS bearer context request (0xc1)
EPS quality of service
Length: 1
Quality of Service Class Identifier (QCI): QCI 9 (9)
Access Point Name
Length: 4
APN: ims // Network Allocate the specific APN Name. This may or may not be the same as UE requested
PDN address
Length: 13
0000 0... = Spare bit(s): 0x00
PDN type: IPv4v6 (3)
PDN IPv6 if id: 0000000000000011
PDN IPv4: 192.168.1.11 (192.168.1.11)
Linked TI - Transaction identifier
Element ID: 0x5d
Length: 1
0... .... = TI Flag: The message is sent from the side that originates the TI
TI value: 0x02 (2)
Quality Of Service - Negotiated QoS
Element ID: 0x30
Length: 14
00.. .... = Spare bit(s): 0
..10 0... = Quality of Service Delay class: Delay class 4 (best effort) (4)
.... .011 = Reliability class: Unacknowledged GTP/LLC, Ack RLC, Protected data (3)
1001 .... = Peak throughput: Up to 256 000 octet/s (9)
.... 0... = Spare bit(s): 0
.... .010 = Precedence class: Normal priority (2)
000. .... = Spare bit(s): 0
...0 1010 = Mean throughput: 100 000 octet/h (10)
100. .... = Traffic class: Background class (4)
...1 0... = Delivery order: Without delivery order ('no') (2)
.... .011 = Delivery of erroneous SDUs: Erroneous SDUs are not delivered('No') (3)
Maximum SDU size: 1500 octets (150)
Maximum bitrate for uplink: 64 kbps (64)
Maximum bitrate for downlink: 384 kbps (104)
0111 .... = Residual Bit Error Rate (BER): 1*10-5 (7)
.... 0100 = SDU error ratio: 1*10-4 (4)
0000 00.. = Transfer delay: Subscribed transfer delay/reserved (0)
.... ..00 = Traffic handling priority: Subscribed traffic handling priority/Reserved (0)
Guaranteed bitrate for uplink: 64 kbps (64)
Guaranteed bitrate for downlink: 568 kbps (127)
000. .... = Spare bit(s): 0
...0 .... = Signalling indication: Not optimised for signalling traffic
.... 0000 = Source statistics description: unknown (0)
Maximum bitrate for downlink (extended): Use the value indicated by the Maximum bit rate for downlink (0)
Guaranteed bitrate for downlink (extended): Use the value indicated by the Guaranteed bit rate for downlink (0)
LLC Service Access Point Identifier - Negotiated LLC SAPI
Element ID: 0x32
0000 .... = Spare bit(s): 0
.... 0011 = LLC SAPI: SAPI 3 (3)
Radio Priority
1000 .... = Element ID: 0x8-
Radio Priority (PDP or SMS): priority level 1 (highest) (1)
Protocol Configuration Options
Element ID: 0x27
Length: 72
[Link direction: Network to MS (1)]
1... .... = Extension: True
Configuration Protocol: PPP for use with IP PDP type or IP PDN type (0)
Protocol or Container ID: Internet Protocol Control Protocol (0x8021)
Length: 0x10 (16)
PPP IP Control Protocol
Code: Configuration Nak (3)
Identifier: 0 (0x00)
Length: 16
Options: (12 bytes), Primary DNS Server IP Address, Secondary DNS Server IP Address
Primary DNS Server IP Address: 10.211.64.87
Type: Primary DNS Server IP Address (129)
Length: 6
Primary DNS Address: 10.211.64.87 (10.211.64.87)
Secondary DNS Server IP Address: 10.211.64.87
Type: Secondary DNS Server IP Address (131)
Length: 6
Secondary DNS Address: 10.211.64.87 (10.211.64.87)
Protocol or Container ID: DNS Server IPv4 Address (0x000d)
Length: 0x04 (4)
IPv4: 10.211.64.87
Protocol or Container ID: DNS Server IPv6 Address (0x0003)
Length: 0x10 (16)
IPv6: 2001:0:0:1::2
Protocol or Container ID: P-CSCF IPv6 Address (0x0001)
Length: 0x10 (16)
IPv6: 2001:0:0:1::2
Protocol or Container ID: P-CSCF IPv4 Address (0x000c)
Length: 0x04 (4)
IPv4: 192.168.1.2
Followings are some of the message example going through S1AP that carries APN information.
< UplinkNASTransport >
S1 Application Protocol
S1AP-PDU: initiatingMessage (0)
initiatingMessage
procedureCode: id-uplinkNASTransport (13)
criticality: ignore (1)
value
UplinkNASTransport
protocolIEs: 5 items
Item 0: id-MME-UE-S1AP-ID
ProtocolIE-Field
id: id-MME-UE-S1AP-ID (0)
criticality: reject (0)
value
MME-UE-S1AP-ID: ....
Item 1: id-eNB-UE-S1AP-ID
ProtocolIE-Field
id: id-eNB-UE-S1AP-ID (8)
criticality: reject (0)
value
ENB-UE-S1AP-ID: 3
Item 2: id-NAS-PDU
ProtocolIE-Field
id: id-NAS-PDU (26)
criticality: reject (0)
value
NAS-PDU: 27a8ccdcee7e024eda2808016e05697370736e
Non-Access-Stratum (NAS)PDU
0010 .... = Security header type: Integrity protected and ciphered (2)
.... 0111 = Protocol discriminator: EPS mobility management messages (0x07)
Message authentication code: 0xa8ccdcee
Sequence number: 126
0000 .... = EPS bearer identity: No EPS bearer identity assigned (0)
.... 0010 = Protocol discriminator: EPS session management messages (0x02)
Procedure transaction identity: 78
NAS EPS session management messages: ESM information response (0xda)
Access Point Name
Element ID: 0x28
Length: 8
APN: testapn
Item 3: id-EUTRAN-CGI
ProtocolIE-Field
id: id-EUTRAN-CGI (100)
criticality: ignore (1)
value
EUTRAN-CGI
...
Item 4: id-TAI
ProtocolIE-Field
id: id-TAI (67)
criticality: ignore (1)
value
TAI
...
< InitialContextSetupRequest >
S1 Application Protocol
S1AP-PDU: initiatingMessage (0)
initiatingMessage
procedureCode: id-InitialContextSetup (9)
criticality: reject (0)
value
InitialContextSetupRequest
protocolIEs: 8 items
Item 0: id-MME-UE-S1AP-ID
ProtocolIE-Field
id: id-MME-UE-S1AP-ID (0)
criticality: reject (0)
value
MME-UE-S1AP-ID: ...
Item 1: id-eNB-UE-S1AP-ID
ProtocolIE-Field
id: id-eNB-UE-S1AP-ID (8)
criticality: reject (0)
value
ENB-UE-S1AP-ID: 3
Item 2: id-uEaggregateMaximumBitrate
ProtocolIE-Field
id: id-uEaggregateMaximumBitrate (66)
criticality: reject (0)
value
UEAggregateMaximumBitrate
uEaggregateMaximumBitRateDL: 201943030
uEaggregateMaximumBitRateUL: 201943030
Item 3: id-E-RABToBeSetupListCtxtSUReq
ProtocolIE-Field
id: id-E-RABToBeSetupListCtxtSUReq (24)
criticality: reject (0)
value
E-RABToBeSetupListCtxtSUReq: 1 item
Item 0: id-E-RABToBeSetupItemCtxtSUReq
ProtocolIE-SingleContainer
id: id-E-RABToBeSetupItemCtxtSUReq (52)
criticality: reject (0)
value
E-RABToBeSetupItemCtxtSUReq
e-RAB-ID: 5
e-RABlevelQoSParameters
qCI: 9
allocationRetentionPriority
priorityLevel: Unknown (12)
pre-emptionCapability: shall-not-trigger-pre-emption (0)
pre-emptionVulnerability: pre-emptable (1)
0... .... Extension Present Bit: False
transportLayerAddress: 0a9bb99c
transportLayerAddress(IPv4): xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx)
gTP-TEID: ...
nAS-PDU: ...
Non-Access-Stratum (NAS)PDU
0010 .... = Security header type:
Integrity protected and ciphered (2)
.... 0111 = Protocol discriminator:
EPS mobility management messages (0x07)
Message authentication code: 0x5e7a308b
Sequence number: 76
0000 .... = Security header type:
Plain NAS message, not security protected (0)
.... 0111 = Protocol discriminator:
EPS mobility management messages (0x07)
NAS EPS Mobility Management Message Type: Attach accept (0x42)
0000 .... = Spare half octet: 0
.... 0... = Spare bit(s): 0x00
.... .001 = Attach result: EPS only (1)
GPRS Timer - T3412 value
...
Tracking area identity list - TAI list
...
ESM message container
Length: 83
ESM message container contents: ...
0101 .... = EPS bearer identity:
EPS bearer identity value 5 (5)
.... 0010 = Protocol discriminator:
EPS session management messages (0x02)
Procedure transaction identity: 78
NAS EPS session management messages:
Activate default EPS bearer context request (0xc1)
EPS quality of service
Length: 1
Quality of Service Class Identifier (QCI): QCI 9 (9)
Access Point Name
Length: 8
APN: testapn
PDN address
Length: 5
0000 0... = Spare bit(s): 0x00
PDN type: IPv4 (1)
PDN IPv4: xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx)
APN aggregate maximum bit rate
Element ID: 0x5e
Length: 6
APN-AMBR for downlink : 8640 kbps
APN-AMBR for uplink : 8640 kbps
APN-AMBR for downlink (extended) : 44 Mbps
APN-AMBR for uplink (extended) : 44 Mbps
APN-AMBR for downlink (extended-2) : 256 Mbps
Total APN-AMBR for downlink : 308.640 Mbps
APN-AMBR for uplink (extended-2) : 256 Mbps
Total APN-AMBR for uplink : 308.640 Mbps
Protocol Configuration Options
....
EPS mobile identity - GUTI
Element ID: 0x50
Length: 11
.... 0... = odd/even indic: 0
.... .110 = Type of identity: GUTI (6)
Mobile Country Code (MCC): 001
Mobile Network Code (MNC): 01
MME Group ID: 32774
MME Code: 33
M-TMSI: 0xc071bb09
EMM cause
Element ID: 0x53
Cause: CS domain not available (18)
GPRS Timer - T3402 value
...
GPRS Timer - T3423 value
...
PLMN List - Equivalent PLMNs - 2 PLMNs
Element ID: 0x4a
Length: 6
PLMN[1] Mobile Country Code (MCC): 001
PLMN[2] Mobile Country Code (MCC): 01
EPS network feature support
Element ID: 0x64
Length: 1
....
Additional update result
1111 .... = Element ID: 0xf-
.... 00.. = Spare bit(s): 0x00
.... ..01 = AURV: CS Fallback not preferred (1)
Item 4: id-UESecurityCapabilities
ProtocolIE-Field
id: id-UESecurityCapabilities (107)
criticality: reject (0)
value
UESecurityCapabilities
..0. .... Extension Present Bit: False
encryptionAlgorithms: c000
...0 .... Extension Present Bit: False
integrityProtectionAlgorithms: c000
Item 5: id-SecurityKey
ProtocolIE-Field
id: id-SecurityKey (73)
criticality: reject (0)
value
SecurityKey: ... [bit length 256]
Item 6: id-HandoverRestrictionList
ProtocolIE-Field
id: id-HandoverRestrictionList (41)
criticality: ignore (1)
value
HandoverRestrictionList
servingPLMN: 131002
Mobile Country Code (MCC): 001
Mobile Network Code (MNC): 02
equivalentPLMNs: 2 items
Item 0
PLMNidentity: 134109
Mobile Country Code (MCC): 001
Mobile Network Code (MNC): 02
Item 1
PLMNidentity: 138107
Mobile Country Code (MCC): 001
Mobile Network Code (MNC): 02
Item 7: id-SubscriberProfileIDforRFP
ProtocolIE-Field
id: id-SubscriberProfileIDforRFP (106)
criticality: ignore (1)
value
SubscriberProfileIDforRFP: 1
UE Setting Aspect of APN Assignement
There is special settings on UE in which you can add or delete (define) your own APN. How you define these APN on UE side would change UE behavior drastically. So when it comes to testing, it is very important to configure UE side APN setting to match the equipment APN setting. But the problem is .. depending on UE, some UE gives you full control over the APN setting but some UE does not give you any control at all or gives you the limitted controlability.
Following is one example of APN settings that I configured for testing purpose. (Don't try to blindly copy this setting onto your UE and expect it to work with your test environment or in live network).
Why sometimes UE does not specify APN name in PDN Connectivity Request ?
Case 1 : UE does not want to send those information before Security is established
I think this is the most common case and happens most frequently for the default bearer setup. The PDN request is piggybacked in Attach Request which happens before 'Security Mode Command' procedure. That is, UE does not want to send this kind of information without any security protection. In this case, it is expected that UE send PDN Connectivity Request with ESM information transfer flat = 1. Then Network will send ESM Information Request afrer Security process is completed and then UE will notify APN name it wants to use in ESM Information Response message.
Message: Attach request
Protocol discriminator = 0x7 (EPS Mobility Management)
Security header = 0x1 (Integrity protected)
Auth code = 0xab180dd6
Sequence number = 0x0a
Protocol discriminator = 0x7 (EPS Mobility Management)
Security header = 0x0 (Plain NAS message, not security protected)
Message type = 0x41 (Attach request)
EPS attach type = 2 (combined EPS/IMSI attach)
NAS key set identifier:
...
Old GUTI or IMSI:
...
UE network capability:
...
ESM message container:
Protocol discriminator = 0x2 (EPS Session Management)
EPS bearer identity = 0
Procedure transaction identity = 68
Message type = 0xd0 (PDN connectivity request)
Request type = 1 (initial request)
PDN type = 3 (IPv4v6)
ESM information transfer flag = 1
NOTE : The meaning of ESM information transfer flag is specified in 3GPP 24.301-9.9.4.5 as follows :
The purpose of the ESM information transfer flag information element is to indicate whether ESM information, i.e. protocol configuration options or APN or both, is to be transferred security protected.
value 0 : security protected ESM information transfer not required
value 1 : security protected ESM information transfer required
Case 2 : Implying that UE doesn't care which APN the network assigns
I am not sure if this is explicitely allowed in terms of 3GPP, but I saw many cases where UE accept whatever APN the network assigns when UE does not specify APN name in PDN request.
Case 3 : Possible UE bug
I saw some cases where UE omit APN name in PDN request without setting ESM information transfer flag. In this case, some network may reject PDN request.
Common Issues and Challenges for APN related issues
One of the biggest issues about APN is that there is no strict rule, requirement clearly specified in 3GPP. A lot of detailed behavior is up to UE protocol stack implementation and requirement from Carriers. The most important factors is 'Matching between UE side expectation and NW side expectation'. The biggest problem is that it is very hard to find right person who has the clear information about this.
In my case, most of the issues that I come across with these problems are with UE maker/engineers who is working with application layer testing (e.g, IP throughput, IMS etc) and followings are the common situation that ends up with.
- Step i) I think we need to get clear understanding of UE side APN handling implementation and you need to talk to your radio protocol engineer about this.
- Step ii) (after a long time (at least several days) to get any feedback from radio protocol engineer). This protocol implmentation is implemented by chipset maker. We don't have much control over it. We need to talk to chipset maker for clear information.
- Step iii) (after even longer time to get any response from chipset vendor). Chipset maker says the APN configuration varies with each carrier (network operator). If you get clear problem description from Carrier, we may revise our stack to fix the problem.
- Step iv) (UE maker talks to Carriers and also takes a long time to get any feedback). Carrier says "We specified in our that we need this and this kind of APN and you have to make it work in any way. If you have any issues in the detailed protocol layer, it is your problem. We don't have any clear definition in terms of protocol sequence".
After the step iv), it goes back to step i) and after a couple of iteration with no productive progress, usually the verification engineer give up any further technical communication and try to rely on ad-hoc method as follows.
- Method 1) Keep changing UE side APN setup parameters until it work with a specific test equipment
- Method 2) Keep changing test equipment parameters until it work with a specific UE setting
Sometimes this kind of ad-hoc approach works but it can never be a perfect solution. Somebody use Method 1 and some other person use Method 2. So even for testing a same UE using the same equipment, if two different person performs the test final configuration on UE and equipment would be completely different. Also, in some UE you can use only method 1 due to equipment restriction and in some other cases you can use only method 2 due to UE side restriction. Therefore, none of them can be a generic solution.
To be honest, I don't think there would be any generic solution for this issue unless 3GPP put forward any clear requirement on it. For the time being, the most reasonable approach would be to create a clear requirement and check list of your own and coordinate everybody (chipset maker, UE maker and carrier) to follow the rules defined in the check list. Personally, I think Carrier (Network Operator) is at the best position to enforce this practice.
There is no right or wrong in many APN related issues (e.g, APN name). It is just a matter of a specific rule (set by developer or by network operator) and strictly following the rule. So the check list in this sections ask you about 'do you have this and this kind of rules of your own ?'
1. In what condition UE sets APN name in PDN Connectivity Request message ?
As I mentioned in Protocol aspect of APN assignment, in some case UE specifies APN name in some case and in some case UE does not specify it. The questions is 'in your UE, when it specify the APN name in PDN Connectivity Request ?'.
2. When UE does not specify APN name in its PDN Connectivity Request, what APN name the UE expects from Network in Activate Default EPS Bearer Context Req ?
Is any APN name OK ? or does it expect any specific APN name ?
3. If UE expect any specific APN name from the network in Activate Default EPS Bearer Context Req, where does the specific APN name come from ?
Is it from the requirement by network operator ? or is it from what you specified in UE APN setting ?
4. If UE send PDN Request with IP Type = IPv4v6 and Network allocates IPv4v6 in Activate Default EPS Bearer Context Req but RS(Router Solicitation)/RA(Router Advertisement) process failed, how UE should react ?
It would be desirable that UE gives up IPv6 setup process and just stick to IPv4, but I saw some UE retry the PDN request process until it gets RS/RA successful.
Note : Unlike APN name issues, there is relatively clear requirement specified in 3GPP. Refer to ESM Cause section for further information on this issue.