5G Network Architecture

5G Network Architecture:

Introduction:

            In this blog, we will see 5G network architecture nodes, their functionality and interfaces between different nodes. it is vary important to know about all the nodes and their functionality to understand the whole concept of 5G architecture.
Below description is taken from 3gpp TS.
 

In Detailed:

Core network service based architecture:
 






AMF: Access and Mobility Management Function:- 
             Like in LTE MME, In NR AMF provide the similar services to the access network and core network component. general functions of AMF are to provide the mobility management, Authentication management, NAS related management to UE and SMF selection types of services.

=>Termination point for RAN Control Plane interfaces (NG2).
=>UE Authentication and Access Security procedures.
=>Mobility Management (handover Reach-ability, Idle/Active Mode mobility state. handling)
=>Registration Area management.
=>Access Authorization including check of roaming rights; 
=>Session Management Function (SMF) selection
=>NAS(non access stratum) signaling including NAS Ciphering and Integrity protection, termination of MM NAS and forwarding of SM NAS (NG1).
=>AMF obtains information related to MM from UDM.
=>May include the Network Slice Selection Function (NSSF) 
=>Attach procedure without session management adopted in CIoT implemented in EPC is defined also in 5GCN (registration management procedure) 
=>User Plane (UP) selection and termination of NG4 interface (AMF has part of the MME and PGW functionality from EPC.


AUSF: services Authentication Server Function:  The main function of AUSF is to provide the services for Authentication procedure and communicate directly with UDM and AMF for accessing and providing the subscriber information.

=>Contains mainly the EAP authentication server functionality 
=>Storage for Keys (part of HSS from EPC) 
=>Obtains authentication vectors from UDM and achieves UE authentication. 72 NF Repository Function (NRF) 
=>Provides profiles of Network Function (NF) instances and their supported services within the network 
=>Service discovery function, maintains NF profile and available NF instances. (not present in EPC world) NRF offers to other NFs the following services: 
=>Nnrf_NFManagement 
=>Nnrf_NFDiscovery 
=>OAuth2 Authorization Core network functions 73 Core network functions Network Exposure Function (NEF) 
=>Provides security for services or AF accessing 5G Core nodes 
=>Seen as a proxy, or API aggregation point, or translator into the Core Network 
Policy Control Function (PCF) 

=>Expected to have similarities with the existing policy framework (4G PCRF) 
=>Updates to include the addition of 5G standardized mobility based policies (part of the PCRF functionality from EPC) 

 Session Management Function (SMF) :
=>DHCP functions 
=>Termination of NAS signaling related to session management 
=>Sending QoS/policy N2 information to the Access Network (AN) via AMF
=>Session Management information obtained from UDM 
=>DL data notification 
=>Selection and control of UP function 
=>Control part of policy enforcement and QoS. 
=>UE IP address allocation & management 
=>Policy and Offline/Online charging interface termination 
=>Policy enforcement control part 
=>Lawful intercept (CP and interface to LI System) Core network functions.

 Unified Data Management (UDM) :

=>Similar functionality as the HSS in Release 14 EPC User Data Convergence (UDC) concept: separates user information storage and management from the front end 
=>User Data Repository (UDR): storing and managing subscriber information processing and network policies 
=>The front-end section: Authentication Server Function (AUSF) for authentication processing and Policy Control Function (PCF). Core network functions 

 User Plane Function (UPF) :
=>Allows for numerous configurations which essential for latency reduction
=>Anchor point for Intra-/Inter-RAT mobility 
=>Packet routing and forwarding 
=>QoS handling for User Plane 
=>Packet inspection and PCC rule enforcement 
=>Lawful intercept (UP Collection) 
 Roaming interface (UP)
=>May integrate the FW and Network Address Translation (NAT) functions 
=>Traffic counting and reporting (UPF includes SGW and PGW functionalities) 

 Application Functions (AF) 
=>Services considered to be trusted by the operator
=>Can access Network Functions directly or via the NEF 
=>AF can use the PCF interface PCF for requesting a given QoS applied to an IP data flow (e.g., VoIP). 
=>Un-trusted or third-party AFs would access the Network Functions through the NEF (same as AF in EPC) Network Slice Selection Functions (NSSF) 
=>Selecting of the Network Slice instances to a UE.
=>Determining the AMF set to be used to serve the UE.
=>The Application Function (AF) can be a mutually authenticated third party. – Could be a specific 3rd party with a direct http2 interface or a inter-working gateway exposing alternative API’s to external applications. 
=>Enables applications to directly control Policy (reserve network resource, enforce SLAs), create network Slices, learn device capabilities and adapt service accordingly, invoke other VNF’s within the network… 
=>Can also subscribe to events and have direct understanding of how the network behaves in relation to the service delivered.
 Data Network (DN):


=> Services offered: Operator services, Internet access, 3rd party 
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TDD-UL-DL-slot Configuration


TDD Slot configuration:

5G provides a feature using which each symbol within a slot can either be used to schedule a Uplink packet (U) or Downlink packet(D) or Flexible (F). A symbol marked as Flexible means it can be used for either Uplink or Downlink as per requirement.


In NR, slot format configuration can be done in a static, semi-static or fully dynamic fashion. The configuration for Slot format would be broadcast from SIB1 or/and configured with the RRC Connection Reconfiguration message. The configuration of Static and semi-static for a slot is done using RRC while dynamic slot configuration is done using PDCCH DCI.

Note that if a slot configuration is not provided by the network through RRC messages, all the slots/symbols are considered as flexible by default.

Slot configuration via RRC consists of two parts. 
 1-  Providing UE with Cell-Specific Slot format Configuration (tdd-UL-DL-ConfigurationCommon)
 2-  Providing UE with dedicated Slot format configuration (tdd-UL-DL-ConfigurationDedicated)

1- :RRC: tdd-UL-DL-ConfigurationCommon
     In LTE TDD, there are 7 predefined patterns for UL and DL allocation in a radio frame. In 5G/NR, we don't have any predefined pattern. Instead, we can define the pattern in a much more flexible way using several parameters as shown below.
The IE tdd-UL-DL-ConfigurationCommon is either broadcasted within SIB1 or configured to the UE using dedicated RRC signaling.
When it is provided by RRC signaling then it is mandatory IE and when it is provided via SIB1, this IE is optional for TDD cells. 
 Structure of IE tdd-UL-DL-ConfigurationCommon:

   A reference SCS configuration µref  by referenceSubcarrierSpacing. at least one pattern is available. a pattern1 is mandatory and pattern2 is optional.    Both pattern1 and pattern2 contain the same parameters but usually of different values.

The configuration in pattern1 provides
- a slot configuration period of  P msec by dl-UL-TransmissionPeriodicity
- a number of slots  dslots with only downlink symbols by nrofDownlinkSlots
- a number of downlink symbols  dsym by nrofDownlinkSymbols
- a number of slots  uslots with only uplink symbols by nrofUplinkSlots
- a number of uplink symbols  usym by nrofUplinkSymbo

dl-UL-TransmissionPeriodicity (P)
µref(SCS)
0.5
all
0.625
3
1
all
1.25
2,3
2
all
2.5
1,2,3
5
all
10
all
All the configurations provided by pattern1 is used to conclude below mentioned points.

=> a slot configuration perio of P mesc.
=> It includes S = P X 2µ  
      For example, let P = 2.5 ms and µ = 3, in this case, there are 20 slots within the slot          configuration period.
=> Total S slots reserve, first dslots slots for downlink symbols and last uslots slots for              uplink symbols.
=> First dsym symbols within the slot immediately following the last full downlink slot and       last usym symbols in the slot preceding the first full uplink slot.
=> Consider the remaining symbols as flexible symbols. The flexible symbols can be configured for uplink and downlink symbols.
No. of flexible symbols = (S1 - dslots- uslots).14  - dsym - usym
    Note: The first symbol every 20/P period is a first symbol in an even frame.
Example:


RRC: tdd-UL-DL-ConfigurationDedicated:
The UE specific information to the slot configuration is necessary to help the network adjust DL/UL pattern based on the UE needs.
The network sends the UE-specific slot configuration using IE tdd-UL-DL-ConfigurationDedicated towards UE which further allocates the unallocated (flexible) slots and symbols.
The IE tdd-UL-DL- ConfigurationDedicated is optional. and if the network doesn’t configure this IE, the UE uses tdd-UL-DL-ConfigurationCommon IE alone to derive the slot configuration for transmission.
The configuration in tdd-UL-DL ConfigurationDedicated iE can overrides only flexible symbols per slot over the number of slots as provided by tdd-UL-DL- ConfigurationCommon that is this dedicated configuration can not change the slots/symbols which are already allocated for downlink and uplink via tdd-UL-DL-ConfigurationCommon IE.
The contents of tdd-UL-DL- ConfigurationDedicated IE are presented below;














The tdd-UL-DL-ConfigurationDedicated IE provides individual slot configuration(s) using slotSpecificConfigurationsToAddModList. Each slot configuration contains the following parameters ;
slotIndex identifies a slot within a slot configuration period given in tdd-UL-DL-configurationCommon IE.
symbols structure provides the direction (downlink or uplink) for the symbols within the slot that is being configured.
-      allDownlink indicates that all symbols in this slot are used for downlink symbols;
-      allUplink indicates that all symbols in this slot are used for uplink symbol;
-      explicit indicates explicitly how many symbols in the beginning and end of this slot are allocated to downlink and uplink, respectively.
-      nrofDownlinkSymbols is the number of consecutive downlink symbols in the beginning of the slot identified by the slot index.
-      nrofUplinkSymbols is the number of consecutive uplink symbols at the end of the slot identified by the slot index.
If nrofDownlinkSymbols IE is not provided, there are no downlink symbols in the slot and if nrofUplinkSymbols IE is not provided, there are no uplink symbols in the slot. The remaining symbols in the slot are the flexible symbol.
The following illustration shows how UE-specific slot configuration overrides flexible slots/symbols provided by the cell-specific configuration.







It is important to note that a symbol can only be flexible if and only if both UE and cell-specific slot configurations indicate that the respective symbol to be flexible.
Slot Formats:
Slot format table from TS (38.213 Table 11.1.1-1).
Symbol Number in a slot
Format
0
1
2
3
4
5
6
7
8
9
10
11
12
13
0
D
D
D
D
D
D
D
D
D
D
D
D
D
D
1
U
U
U
U
U
U
U
U
U
U
U
U
U
U
2
F
F
F
F
F
F
F
F
F
F
F
F
F
F
3
D
D
D
D
D
D
D
D
D
D
D
D
D
F
4
D
D
D
D
D
D
D
D
D
D
D
D
F
F
5
D
D
D
D
D
D
D
D
D
D
D
F
F
F
6
D
D
D
D
D
D
D
D
D
D
F
F
F
F
7
D
D
D
D
D
D
D
D
D
F
F
F
F
F
8
F
F
F
F
F
F
F
F
F
F
F
F
F
U
9
F
F
F
F
F
F
F
F
F
F
F
F
U
U
10
F
U
U
U
U
U
U
U
U
U
U
U
U
U
11
F
F
U
U
U
U
U
U
U
U
U
U
U
U
12
F
F
F
U
U
U
U
U
U
U
U
U
U
U
13
F
F
F
F
U
U
U
U
U
U
U
U
U
U
14
F
F
F
F
F
U
U
U
U
U
U
U
U
U
15
F
F
F
F
F
F
U
U
U
U
U
U
U
U
16
D
F
F
F
F
F
F
F
F
F
F
F
F
F
17
D
D
F
F
F
F
F
F
F
F
F
F
F
F
18
D
D
D
F
F
F
F
F
F
F
F
F
F
F
19
D
F
F
F
F
F
F
F
F
F
F
F
F
U
20
D
D
F
F
F
F
F
F
F
F
F
F
F
U
21
D
D
D
F
F
F
F
F
F
F
F
F
F
U
22
D
F
F
F
F
F
F
F
F
F
F
F
U
U
23
D
D
F
F
F
F
F
F
F
F
F
F
U
U
24
D
D
D
F
F
F
F
F
F
F
F
F
U
U
25
D
F
F
F
F
F
F
F
F
F
F
U
U
U
26
D
D
F
F
F
F
F
F
F
F
F
U
U
U
27
D
D
D
F
F
F
F
F
F
F
F
U
U
U
28
D
D
D
D
D
D
D
D
D
D
D
D
F
U
29
D
D
D
D
D
D
D
D
D
D
D
F
F
U
30
D
D
D
D
D
D
D
D
D
D
F
F
F
U
31
D
D
D
D
D
D
D
D
D
D
D
F
U
U
32
D
D
D
D
D
D
D
D
D
D
F
F
U
U
33
D
D
D
D
D
D
D
D
D
F
F
F
U
U
34
D
F
U
U
U
U
U
U
U
U
U
U
U
U
35
D
D
F
U
U
U
U
U
U
U
U
U
U
U
36
D
D
D
F
U
U
U
U
U
U
U
U
U
U
37
D
F
F
U
U
U
U
U
U
U
U
U
U
U
38
D
D
F
F
U
U
U
U
U
U
U
U
U
U
39
D
D
D
F
F
U
U
U
U
U
U
U
U
U
40
D
F
F
F
U
U
U
U
U
U
U
U
U
U
41
D
D
F
F
F
U
U
U
U
U
U
U
U
U
42
D
D
D
F
F
F
U
U
U
U
U
U
U
U
43
D
D
D
D
D
D
D
D
D
F
F
F
F
U
44
D
D
D
D
D
D
F
F
F
F
F
F
U
U
45
D
D
D
D
D
D
F
F
U
U
U
U
U
U
46
D
D
D
D
D
F
U
D
D
D
D
D
F
U
47
D
D
F
U
U
U
U
D
D
F
U
U
U
U
48
D
F
U
U
U
U
U
D
F
U
U
U
U
U
49
D
D
D
D
F
F
U
D
D
D
D
F
F
U
50
D
D
F
F
U
U
U
D
D
F
F
U
U
U
51
D
F
F
U
U
U
U
D
F
F
U
U
U
U
52
D
F
F
F
F
F
U
D
F
F
F
F
F
U
53
D
D
F
F
F
F
U
D
D
F
F
F
F
U
54
F
F
F
F
F
F
f
D
D
D
D
D
D
D
55
D
D
F
F
F
U
U
U
D
D
D
D
D
D
62-254
Reserved
255
UE determines the slot format for the slot based on tdd-UL-DL-ConfigurationCommon, or tdd-ULDL-
                                     D : Downlink, U : Uplink, F : Flexible    

What if TDD-UL-DL-ConfigCommon is not configure ?
        If a UE is not configured to monitor PDCCH for DCI format 2-0, for a set of symbols of a slot that are indicated as flexible by TDD-UL-DL-ConfigurationCommon or TDD-UL-DL-ConfigDedicated, or when TDD-UL-DL-ConfigurationCommon and TDD-UL-DL-ConfigDedicated are not provided to the UE

=> the UE receives PDSCH or CSI-RS in the set of symbols of the slot if the UE receives a corresponding indication by a DCI format 1_0, DCI format 1_1, or DCI format 0_1.


=> the UE transmits PUSCH, PUCCH, PRACH, or SRS in the set of symbols of the slot if the UE receives a corresponding indication by a DCI format 0_0, DCI format 0_1, DCI format 1_0, DCI format 1_1, or DCI format 2_3


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