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APN(Access Point Name)
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.
How APN is assinged ?
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
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