5G/NR - Network Architecture |
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NR Network Architecture / Network Interface - N1 / N1-Mode
N1 interface(Reference Point) indicates the connection between UE and AMF mainly for NAS layer signaling, but the exact role of N1 interface (reference point) is a little bit ambiguous to me.
According to 23.501-Figure 4.2.4-4, N1 reference point (labeled as '1') is indicated as follows. It seems obvious that N1 is the interface between UE and AMF, but there is no access network along N1. So I was wondering how UE can get access to AMF without access network.
With further looking at other parts of the document (like figures in section 23.501-4.2.8.2 and description at 23.501-5.3.3.1), it seems that N1 interface represent the interface as follows. At least for now, my understanding is as follows.
There is another statement from 24.501-3.1 writing the definition of N1 NAS signalling connection as follows. N1 NAS signalling connection: A peer to peer N1 mode connection between UE and AMF. An N1 NAS signalling connection is either the concatenation of an RRC connection via the Uu reference point and an NG connection via the N2 reference point for 3GPP access, or the concatenation of an IPsec tunnel via the NWu reference point and an NG connection via the N2 reference point for non-3GPP access.
In addition to N1 reference point/interface with the focus on physical connections in the overal network architecture, there is another term called N1 mode which is more focused on functional point of view (especially with the perspective of NAS signaling).
The formal definition of N1 mode is defined in 24.501-3.1 as follows N1 mode: A mode of a UE allowing access to the 5G core network via the 5G access network.
UE Usage state and N1 disable/enable
Following table is based on 24.501 - 4.3.3.1, 4.3.4.1 and 4.9. I changed the format for better / quictly to be used as a cheat sheet -:)
NOTE 1 > This timer based re-enable is suggested as an implementation option in 24.501 - 4.9.1
3GPP Statements on N1 interface/refernce point
For futher clarification and for those who would not agree with my interpretation -:), I quoted various descriptions directly from 3GPP document here.
Regarding the role N1 reference points, it is described as follows in 3GPP.
23.501 - 4.2.8.1 General Concepts to Support Non-3GPP Access
23.501 - 4.4.2.2 Reference point to support SMS over NAS
4.4.4.2 Reference point to support Location Services
23.501 - 5.2.5 Access control and barring
23.501 - 5.3.3.1 General
23.501 - 5.3.3.2.3 CM-CONNECTED state
23.501 - 5.6 Session Management
23.501 - 5.6.2 Interaction between AMF and SMF
23.501 - 8.2.2 Control Plane Protocol Stacks between the UE and the 5GC
UE Capability for N1mode Support
You can check whether UE support N1mode or not by NAS message as shown below. This message is from Amari Callbox log. You may take this as an indicator whether UE support SA or not.
Message: Registration request Protocol discriminator = 0x7e (5GS Mobility Management) Security header = 0x1 (Integrity protected) Auth code = 0xaab82c81 Sequence number = 0x0e Protocol discriminator = 0x7e (5GS Mobility Management) Security header = 0x0 (Plain 5GS NAS message, not security protected) Message type = 0x41 (Registration request) 5GS registration type: Follow-on request bit = 1 Value = 1 (initial registration) ngKSI: TSC = 0 NAS key set identifier = 6 5GS mobile identity: 5G-GUTI MCC = 001 MNC = 01 AMF Region ID = 128 AMF Set ID = 4 AMF Pointer = 1 5G-TMSI = 0x3b2df3b5 UE security capability: 0xf0 (5G-EA0=1, 128-5G-EA1=1, 128-5G-EA2=1, 128-5G-EA3=1, 5G-EA4=0, 5G-EA5=0, 5G-EA6=0, 5G-EA7=0) 0x70 (5G-IA0=0, 128-5G-IA1=1, 128-5G-IA2=1, 128-5G-IA3=1, 5G-IA4=0, 5G-IA5=0, 5G-IA6=0, 5G-IA7=0) 0xf0 (EEA0=1, 128-EEA1=1, 128-EEA2=1, 128-EEA3=1, EEA4=0, EEA5=0, EEA6=0, EEA7=0) 0x70 (EIA0=0, 128-EIA1=1, 128-EIA2=1, 128-EIA3=1, EIA4=0, EIA5=0, EIA6=0, EIA7=0) NAS message container: Protocol discriminator = 0x7e (5GS Mobility Management) Security header = 0x0 (Plain 5GS NAS message, not security protected) Message type = 0x41 (Registration request) 5GS registration type: Follow-on request bit = 1 Value = 1 (initial registration) ngKSI: TSC = 0 NAS key set identifier = 6 5GS mobile identity: 5G-GUTI MCC = 001 MNC = 01 AMF Region ID = 128 AMF Set ID = 4 AMF Pointer = 1 5G-TMSI = 0x3b2df3b5 5GMM capability: 0x03 (SGC=0, 5G-IPHC-CP CIoT=0, N3 data=0, 5G-CP CIoT=0, RestrictEC=0, LPP=0, HO attach=1, S1 mode=1) UE security capability: 0xf0 (5G-EA0=1, 128-5G-EA1=1, 128-5G-EA2=1, 128-5G-EA3=1, 5G-EA4=0, 5G-EA5=0, 5G-EA6=0, 5G-EA7=0) 0x70 (5G-IA0=0, 128-5G-IA1=1, 128-5G-IA2=1, 128-5G-IA3=1, 5G-IA4=0, 5G-IA5=0, 5G-IA6=0, 5G-IA7=0) 0xf0 (EEA0=1, 128-EEA1=1, 128-EEA2=1, 128-EEA3=1, EEA4=0, EEA5=0, EEA6=0, EEA7=0) 0x70 (EIA0=0, 128-EIA1=1, 128-EIA2=1, 128-EIA3=1, EIA4=0, EIA5=0, EIA6=0, EIA7=0) Requested NSSAI: S-NSSAI Length of S-NSSAI contents = 1 (SST) SST = 0x01 Last visited registered TAI: MCC = 001 MNC = 01 TAC = 0x000064 S1 UE network capability: 0xf0 (EEA0=1, 128-EEA1=1, 128-EEA2=1, 128-EEA3=1, EEA4=0, EEA5=0, EEA6=0, EEA7=0) 0x70 (EIA0=0, 128-EIA1=1, 128-EIA2=1, 128-EIA3=1, EIA4=0, EIA5=0, EIA6=0, EIA7=0) 0xc0 (UEA0=1, UEA1=1, UEA2=0, UEA3=0, UEA4=0, UEA5=0, UEA6=0, UEA7=0) 0x40 (UCS2=0, UIA1=1, UIA2=0, UIA3=0, UIA4=0, UIA5=0, UIA6=0, UIA7=0) 0x19 (ProSe-dd=0, ProSe=0, H.245-ASH=0, ACC-CSFB=1, LPP=1, LCS=0, 1xSRVCC=0, NF=1) 0x80 (ePCO=1, HC-CP CIoT=0, ERw/oPDN=0, S1-U data=0, UP CIoT=0, CP CIoT=0, ProSe-relay=0, ProSe-dc=0) 0xb0 (15 bearers=1, SGC=0, N1mode=1, DCNR=1, CP backoff=0, RestrictEC=0, V2X PC5=0, multipleDRB=0) UE's usage setting = 0x01 (Data centric) LADN indication: Length = 0 Data = Network slicing indication = 0x00 (DCNI=0, NSSCI=0) 5GS update type = 0x01 (EPS-PNB-CIoT=no additional information, 5GS-PNB-CIoT=no additional information, NG-RAN-RCU=0, SMS requested=1)
Message: Attach request
Protocol discriminator = 0x7 (EPS Mobility Management) Security header = 0x1 (Integrity protected) Auth code = 0x57498120 Sequence number = 0x0d 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: TSC = 0 NAS key set identifier = 0 Old GUTI or IMSI: MCC = 001 MNC = 01 MME Group ID = 32769 MME Code = 1 M-TMSI = 0x2f915853 UE network capability: 0xf0 (EEA0=1, 128-EEA1=1, 128-EEA2=1, 128-EEA3=1, EEA4=0, EEA5=0, EEA6=0, EEA7=0) 0x70 (EIA0=0, 128-EIA1=1, 128-EIA2=1, 128-EIA3=1, EIA4=0, EIA5=0, EIA6=0, EIA7=0) 0xc0 (UEA0=1, UEA1=1, UEA2=0, UEA3=0, UEA4=0, UEA5=0, UEA6=0, UEA7=0) 0x40 (UCS2=0, UIA1=1, UIA2=0, UIA3=0, UIA4=0, UIA5=0, UIA6=0, UIA7=0) 0x19 (ProSe-dd=0, ProSe=0, H.245-ASH=0, ACC-CSFB=1, LPP=1, LCS=0, 1xSRVCC=0, NF=1) 0x80 (ePCO=1, HC-CP CIoT=0, ERw/oPDN=0, S1-U data=0, UP CIoT=0, CP CIoT=0, ProSe-relay=0, ProSe-dc=0) 0xb0 (15 bearers=1, SGC=0, N1mode=1, DCNR=1, CP backoff=0, RestrictEC=0, V2X PC5=0, multipleDRB=0) ESM message container: Protocol discriminator = 0x2 (EPS Session Management) EPS bearer identity = 0 Procedure transaction identity = 23 Message type = 0xd0 (PDN connectivity request) Request type = 1 (initial request) PDN type = 3 (IPv4v6) ESM information transfer flag = 1 Last visited registered TAI: MCC = 001 MNC = 01 TAC = 0x0001 DRX parameter: Data = 0a 00 MS network capability: Length = 3 Data = e5 e0 3e Old location area identification: MCC = 001 MNC = 01 LAC = 0x0001 Mobile station classmark 2: Length = 3 Data = 57 58 a6 Mobile station classmark 3: Length = 12 Data = 60 14 04 e2 91 81 0f 1a 1e 50 00 00 Supported codecs: Length = 8 Data = 04 02 60 04 00 02 1f 02 Voice domain preference and UE's usage setting = 0x07 (IMS PS voice preferred, CS Voice as secondary, Data centric) Old GUTI type = 0 MS network feature support = 0x01 (MS supports the extended periodic timer in this domain) UE additional security capability: 0xf0 (5G-EA0=1, 128-5G-EA1=1, 128-5G-EA2=1, 128-5G-EA3=1, 5G-EA4=0, 5G-EA5=0, 5G-EA6=0, 5G-EA7=0) 0x00 (5G-EA8=0, 5G-EA9=0, 5G-EA10=0, 5G-EA11=0, 5G-EA12=0, 5G-EA13=0, 5G-EA14=0, 5G-EA15=0) 0x70 (5G-IA0=0, 128-5G-IA1=1, 128-5G-IA2=1, 128-5G-IA3=1, 5G-IA4=0, 5G-IA5=0, 5G-IA6=0, 5G-IA7=0) 0x00 (5G-IA8=0, 5G-IA9=0, 5G-IA10=0, 5G-IA11=0, 5G-IA12=0, 5G-IA13=0, 5G-IA14=0, 5G-IA15=0)
Reference
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