free5GC：第五代行動網路之核心網路開發及架構

1G Wireless Networks

• Early 1980s
• Analog radio technologies and circuit-switched transmission and networking technologies.
• Main service: circuit-switched voice
• Lack the ability to support roaming（漫遊）between different network operators.
• Three main 1G radio system standards:
  • Advanced Mobile Phone Systems (AMPS)
    • 類比式行動電話系統，北美貝爾實驗室
  • Total Access Communications Services (TACS)
  • Nordic Mobile Telephone (NMT)
    • 北歐行動電話服務

Circuit Switching

• Dedicated communication path between two stations.
  • 當一個人在使用某個線路時，其他人就無法使用該線路。
• A channel on each physical link.
• Most common example is the telephone network.

Operation

1. Circuit establishment
   • Channel capacity must be reserved between each pair of node.
2. Information transfer
3. Circuit disconnect

Example:

• Public telephone
• Private Branch Exchange（PBX，專用交換機）

2G Wireless Networks

• Emerged in the early 1990s.
• Digital signal processing and transmission technologies.
  • increased radio capacity and spectrum utilization, enhanced voice quality, reduced power consumption, etc.
• Standards for core networks
• In addition to circuit-switched voice, enabled the first waves of mobile data and mobile Internet services.

2G Systems in North America

• RAN (Radio Access Network)
  • IS-136: Time Division Multiple Access (TDMA)
  • IS-95: Code Division Multiple Access (CDMA)
• Core Network (CN)
  • IS-41: support roaming between different network operators.

2G Systems in Europe

• GSM (Global System for Mobile communications)
  • RAN and core network
• Radio frequencies
  • 900 MHz and 1800 MHz in Europe
  • 800 MHz and 1900 MHz in the United States
• Services
  • circuit-switched voice
  • 9.6 Kbps circuit-switched symmetric channel as a data connection to access the Internet

2G Systems in Japan

• PDC (Personal Digital Cellular) network
• Services
  • circuit-switched voice
  • data services over 9.6 Kbps radio channels

Generic 2G Architecture

• PSTN: Public Switched Telephone Network，公用交換電話網路
• MSC: Mobile Switching Center，移動交換中心
• VLR: Visitor Location Register，拜訪位置暫存器
• HLR: Home Location Register，歸屬位置暫存器
• BS: Base Station，基站

2.5G Wireless Networks

• Provide higher radio system capabilities and per-user data rates than 2G systems, but do not yet achieve all the capabilities promised by 3G systems
• General Packet Radio Services (GPRS)
  • provide a packet-switched core network as an extension to GSM core networks
  • provides data rates of 56–114 kbit/sec
• Enhanced Data Rates for Global GSM Evolution (EDGE)
  • provide advanced modulation and channel coding techniques to increase the data rates of GSM radio systems

3G Wireless Networks

• Significantly increase radio system capacities and per-user data rates over 2G systems
• Support IP-based data, voice and multimedia services
• Enhance quality-of-service (QoS) support
• Improve interoperability

Packet Switching

• Data are transmitted in blocks, called packets.
• Long message is broken up into a series packets.
• Packet (1518 byte)
  • header (18 byte): control information
  • payload (1500 byte): data
  • 乙太網路的標準 MTU (Maximum Transmission Unit) 為 1500 bytes。
• At each switching node, the packet is received, stored, and passed on to the next node.

Use for Packets

Third-Generation Partnership Project (3GPP)

• 3G core networks will evolve the GSM core network platform to support circuit-switched mobile services and to evolve the GPRS core network platform to support packet-switched services.
• 3G radio access technologies will be based on the Universal Terrestrial Radio Access Networks (UTRANs) that use Wideband-CDMA (WCDMA) radio technologies.

Third-Generation Partnership Project 2 (3GPP2)

• 3G core networks will evolve the IS-41 core network to support circuit-switched mobile services and define a new packet core network architecture that leverages capabilities provided by the IS-41 core network to support IP services.
• 3G radio access technologies will be based on cdma2000 radio technologies.

3GPP Specifications

• 從 3G 時代創立，但直到現在還持續制定標準（即將邁入 6G）
• Release: a set of Technical Specifications (TS) and Technical Reports (TR)
• Freeze: content can only be revised in case a correction is needed
  • 將標準確定下來，只接受一些必要的修正
• Release 99 (R99) – 3G
  • Freeze March 2000
  • focus on a new RAN based on WCDMA
  • emphasize the interworking and backward compatibility with GSM
• Release 4 (R4)
  • freeze March 2001
  • a minor release with some enhancements to R99
  • IP transport was introduced into the core network
• Release 5 (R5)
  • freeze June 2002
  • major changes in the core network based on IP protocols
  • phase 1 of the IP Multimedia Subsystem (IMS)
  • IP transport in the UTRAN
    
• Release 6 (R6)
  • freeze March 2005
  • IMS phase 2
  • harmonization of IMS in 3GPP and 3GPP2
  • interoperability of UMTS and WLAN
    • session continuity
  • multimedia broadcast and multicast
• Release 7 (R7)
  • Functional freeze date including stable protocols: March 2008 (closed: September 2014)
• Release 8 (R8) – 4G
  • Functional freeze date including stable protocols: March 2009
  • Introduction of LTE

Gateway GPRS Support Node (GGSN)

GGSN 與 SGSN 相當於網際網路中網路層的 IP（負責 routing）。

• GPRS (General Packet Radio Service)
• Packet routing and forwarding center: all user packets to and from a mobile in a PLMN will be sent first to a GGSN (refer to as the mobile’s serving GGSN)
• Route and mobility management: maintain a route to the SGSN that is currently serving a mobile and uses the route to exchange the user traffic with the SGSN

Serving GPRS Support Node (SGSN)

• Access control
• Location management: track the locations of mobiles; may report the location information to the HLR
• Route management: maintain and relay user traffic between the mobile and the GGSN
• Paging: initiating paging to idle mobiles
• Interface with service control platforms: contact point with CAMEL (Customized Applications for Mobile Enhanced Logic)

Information Servers

• 3G
• Shared by CS and PS domains
• Home Subscriber Server (HSS)
  • master logical database
  • maintain user subscription information to control network services
  • Home Location Registrar (HLR): main component of HSS which maintains users’ identities, locations, and service subscription information
• Authentication Center (AuC)
  • maintain information to authenticate each user and to encrypt the communication
  • accessed by the HSS
• Equipment Identity Register (EIR)
  • maintain IMEIs of the subscribers

User Packet Routing and Transport

• Inside the PS CN domain, IP is the main protocol for transporting user packets between network nods.
• IP is used for routing between GGSNs.
• Routing of user packets between SGSN and GGSN is based on GPRS-specific protocols and procedures.

IP Address

• IP address represents both ID and location of a host
  • A specific IP address can only be used in a specific IP subnet
• IP routing can be done by just looking at the netid
  • A router does not need to maintain a table for all hosts

Tunneling Protocols in IP

IP隧道 - 維基百科

• IP in IP, RFC 1853, RFC 2003
• Minimal Encapsulation within IP, RFC 2004
• Generic Routing Encapsulation (GRE), RFC 2784, RFC 2890

不同組織制定標準的格式範例

• IETF (Internet Engineering Task Force)：RFC 791 (IP)、RFC 2460 (IPv6)
• IEEE (Internet Engineering Task Force)：802.11

Package Routing

• GGSN acts as a central point for routing of all user packets.
• User packets are tunneled between RNC (Radio Network Controller) and SGSN, between SGSN and GGSN, and between two SGSNs.
  • GPRS Tunneling Protocol (GTP): routing and mobility management
• Host-specific routes are used to forward user packets between a mobile and a GGSN.
  • maintain an individual routing entry as part of a PDP context for every mobile terminal that has an active PDP context

3GPP packet-switched domain

Evolution of standards for wide-area radio systems

3.5G

• 3GPP High-Speed Packet Access (HSPA)
• 3GPP2 Evolution - Data Optimized (EV-DO)

High-Speed Packet Access (HSPA)

• High-Speed Downlink Packet Access (HSDPA)
  • down-link speeds of 1.8, 3.6, 7.2 and 14.4 Mbits/s
• High-Speed Uplink Packet Access (HSUPA)
  • up-link speeds up to 5.76 Mbit/s
• HSPA+
  • up to 84 Mbit/s on the downlink
  • up to 22 Mbit/s on the uplink
  • MIMO

3GPP2 EV-DO

• Evolution - Data Optimized (EV-DO) is a marketing term that is used when referring to the 3GPP2 “HRPD” (High Rate Packet Data) standards, and “eHRPD” (Evolved High rate Packet Data) standards.
• HRPD is the cdma2000 technology for packet transmission as specified in the 3GPP2 C.S0024-A v3.0 cdma2000 High Rate Packet Data (HRPD) Air Interface Specification (also published as the TIA/EIA 856 standard)
• The eHRPD network provides a Radio Access Network (RAN) that supports an evolved mode of operation and provides an IP environment that supports attachment to multiple Packet Data Networks (PDNs) via the 3GPP Evolved Packet Core (EPC).
  • 3GPP2 X.S0057, 3GPP2 A.S0022, 3GPP2 C.P0087

4G

• Two 4G candidate systems are commercially deployed:
  • the Mobile WiMAX standard
    • first used in South Korea in 2007
  • the first-release Long Term Evolution (LTE) standard
    • in Oslo, Norway and Stockholm, Sweden since 2009

3GPP Architecture (Release 8)

• 3GPP Evolved Packet System (EPS)
  • Radio Side (LTE – Long Term Evolution)
    • Evolved-UTRAN (E-UTRAN)
  • Network Side (SAE – System Architecture Evolution)
    • Evolved Packet Core (EPC)
• 3GPP Release 8 is the first release of the SAE
  • Packet-switched core network only for voice, data, video, and other multimedia traffic
  • Roaming between 3GPP, non-3GPP (trusted and non-trusted), and fixed access networks
  • Designed to optimize network performance

Comparison with 3G

• Packet-switched only core network
• Simplified architecture/Flat architecture
• Separation of control plane and user plane
• Packets are routed through S-GW for intra E-UTRAN mobility
• Roaming between 3GPP, non-3GPP (trusted and non-trusted), and fixed access networks

EPS Architecture

1-5G基站是如何起名的？NR，gNB，en-gNB，ng-eNB，EN-DC，NE-DC，NGEN-DC，NG-RAN…_nr基站是什么意思-CSDN博客

• UE (user equipment)
• eNodeB (Evolved Node B, E-UTRAN Node B)
• MME (Mobility Management Entity)
• HSS (Home Subscriber Server)
• S-GW (Serving Gateway)
• P-GW (PDN Gateway)
  • PDN (Packet Data Network)
• PCRF (Policy and Charging Rule Function)

3GPP SAE Architecture – R8

(simplified)

Home Subscriber Server (HSS)

• A central database that contains information about all the network operator’s subscribers
• The components of LTE carried forward from UMTS and GSM

Policy and Charging Rules Function (PCRF)

• PCRF is the policy and charging control element.
  • See TS 23.203 for details.
• The PCRF terminates the Rx interface and the Gx interface.

Mobility Management Entity (MME)

• In control plane
• Subscriber management
• Session management
• Security procedures
• Location management: location tracking, location update

Serving Gateway (S-GW)

• Interface between E-UTRAN and core network
• Packets are routed through S-GW for intra E-UTRAN mobility

Packet Data Network (PDN) Gateway (P-GW)

• Anchor point for packets to external PDN
• Policy enforcement
• Packet filtering
• Charging

E-UTRAN Architecture – R8

E-UTRAN

• Only eNodeB in E-UTRAN: support all L1 and L2 features
  • The functions of RNC are distributed between eNodeB, MME, S-GW.
• X2 interface: minimize packet loss due to mobility

eNodeB

• Modulation and de-modulation
• Channel coding and de-coding
• Radio resource control
• Radio mobility management
• L2 protocol

Architecture Migration

5G

• More and more applications
• Lower and lower latency
  • End-to-End (E2E) latency < 5ms
  • Air latency < 1ms
• More and more data transmitted
• Not just smartphones anymore

1G to 4G

Mainly used by human beings:

• 1G and 2G were about voice
• 3G was about data
• 4G is about video
• 5G will be about intelligent networks that can handle billions of connected devices while remaining stable and operational.

Next Generation Mobile Networks (NGMN) Alliance

• Mobile telecommunications association of mobile operators, vendors, manufacturers and research institutes.
• Its objective is to ensure the successful commercial launch of future mobile broadband networks.
• It complements and supports standards organizations (ex: 3GPP, IEEE) by providing a coherent view of what mobile operators require.

NGMN 5G Requirements

White paper by NGMN (Next Generation Mobile Networks)

NGMN 5G vision

• Faster data rate: 1 ~ 10 Gbps
  • Download HD videos in seconds, AR, VR
• Lower end-to end latency: 1 ~ 10ms
  • Autonomous driving, Tactile Internet（觸覺互聯網）, Interactive applications
• Higher user mobility: > 500km/h
  • High Speed Train
• Broadband access in dense areas
  • HD video/photo sharing in stadium
• Ultra-reliable communications
  • E-health, Remote surgery, Drones
• Massive machine type communications
  • Smart grid, Smart transportation, Industrial 4.0 (Internet of Things)

What’s wrong with the current 4G core network?

功能與硬體綁定

• High cost
• Not flexible
• Limit innovation

解決方法：Softwarization and Virtualization

Network Function Virtualization (NFV)

把功能虛擬化，不會受到硬體限制

• Virtualized Network Functions (VNFs)

Network Slicing

Benefits of Softwarization

• Rapid innovation
  • Innovation at software speed
  • Can do experiments
  • Standards will follow software deployments
  • Open up network innovation to great minds around the world
• Flexibility
  • Deploy services according to geography
  • Deploy services according to user characteristics
  • Dynamically route packets to its particular network slice

Evolution of Cellular Networks

• 1G to 4G: linear evolution
• 4G to 5G: disruptive evolution

Features of 3GPP releases

• R8: 4G
  • All IP core network, the System Architecture Evolution (SAE)
  • Support of LTE and other 3GPP accesses, support of non-3GPP accesses, inter-system mobility, Single Radio Voice Call Continuity (SRVCC), CS fallback.
  • Earthquake and Tsunami Warning System (ETWS).
  • Support of Home Node B / Home eNode B.
• R9:
  • LCS (location services) control plane for EPS.
  • Support of IMS emergency calls over GPRS and EPS
  • Enhancements to Home Node B / Home eNode B
  • Public Warning System (PWS)
• R10:
  • Network improvements for machine-type communications.
  • Various offload mechanisms (LIPA, SIPTO, IFOM)
• R11:
  • Further improvements for machine-type communications.
  • Further improvements to LIPA and SIPTO.
  • Single Radio Video Call Continuity (vSRVCC)
• R12:
  • LIPA Mobility and SIPTO at the Local Network
• R13:
  • a Dedicated Core (DECOR)
• R14:
  • Control and User Plane Separation of EPC nodes (CUPS)
  • Enhancements of Dedicated Core Networks selection mechanism (eDecor)

Dedicated Core Networks (DCNs)

• One or more DCNs within a PLMN, with each core network dedicated for specific type of subscriber
• DCN selection is based on subscription information and operator configuration
  • Don’t need to modify UEs

eDECOR

• UE assistance information that facilitates the DCN Selection
  • to reduce the need for DECOR reroute
  • DCN-ID
    • The UE provides the DCN-ID to RAN at registration to a new location in the network
    • RAN selects serving node (MME or SGSN) based on the DCN-ID

(e)DECOR Specs

• 3GPP TS 23.707 - Architecture enhancements for dedicated core networks; Stage 2
• 3GPP TS 23.711 - Enhancements of Dedicated Core Networks selection mechanism

Control and User Plane Separation (CUPS)

• Control and User Plane Separation of EPC nodes (CUPS)
• Aligned with the MEC, Mobile Edge Computing ETSI ISG (Industry Specification Group)
• The user plane functions can be placed flexibly (e.g. centrally or closer to the RAN) while the control plane functions could still remain centralized and continue to support the interfaces to the other network entities (like MME, PCRF, Charging Systems).

Benefits of CUPS

• Reducing latency on application service
  • e.g. by selecting User Plane nodes which are closer to the RAN or more appropriate for the intended UE usage type without increasing the number of control plane nodes
• Supporting increase of data traffic
  • by enabling to add user plane nodes without changing the number of SGW-C, PGW-C and TDF-C in the network
• Locating and Scaling the CP (Control Plan) and UP (User Plan) resources of the EPC nodes independently
• Independent evolution of the CP and UP functions
• Enabling Software Defined Networking (SDN) to deliver user plane data more efficiently

CUPS introduces 3 new interfaces, Sxa, Sxb and Sxc between the CP and UP functions of the SGW, PGW and TDF respectively.

Protocol Stack

Packet Forwarding Control Protocol (PFCP)

• 3GPP assessed candidate protocols such as OpenFlow, FoRCES, Diameter, IETF DMM FPC and 3GPP native protocol.
• 3GPP decided to define a 3GPP native protocol with TLV(type-length-value/tag-length-value) encoded messages over UDP/IP, called Packet Forwarding Control Plane (PFCP) protocol, for the Sxa, Sxb and Sxc interfaces.

3GPP specifications for 5G

• R15: - 5G
  • the first set of 5G standards - including new work as well as the maturing of the LTE-Advanced Pro specifications.
• R16:
  • an initial full 3GPP 5G system to its completion; still on going …

5G Architecture – R15

• Non-Standalone (NSA)
  • Use 4G EPC as the core network
• Use 4G EPC as the core network
  • the first set of 5G standards
  • Service Based Architecture (SBA)

Non-Standalone Type 3/3a

• 5G UE 連到 gNB，控制訊息透過 Xx 傳到 eNB
• 3a 的 gNB 連到 EPC，可以減少 gNB 的負擔

System Architecture of 5G Phase 1 - Standalone

• Specifications
  • TS 23.501: System Architecture for the 5G System; Stage 2
  • TS 23.502: Procedures for the 5G System; Stage 2
  • TS 23.503: Policy and Charging Control Framework for the 5G System; Stage 2
• Features
  • Service Based Architecture (SBA)
  • Network Slicing

Service Based Architecture (SBA)

• Elements are defined as network functions that offer their services via interfaces of a common framework.
• Network repository functions (NRF) allows every network function to discover the services offered by other network functions.

3GPP R15 SBA (1/2)

• UPF 聽 SMF 指揮

EPC vs. 5GC

• EPC
  • PCRF (Policy and Charging Rules Function)
  • HSS (Home Subscriber Server)
  • MME (Mobility Management Entity)
  • S/PGW (Serving Gateway/PDN Gateway)

5G NF (Network Function)

• Authentication Server Function (AUSF)
  • With a fronted interface, AUSF is dedicated to authentication processing.
• Access and Mobility Management Function (AMF)
  • AMF the node that manages all UE related functions.
  • THE EPC functionally of MME, S-GW-C & P-GW-C has been allocated sothat all access and mobility functionality is done by AMF.
• Data Network (DN), e.g. operator services, Internet access or 3rd party services
• Unstructured Data Storage Function (UDSF)
• Network Exposure Function (NEF)
• Network Repository Function (NRF)
• Network Slice Selection Function (NSSF)
• Policy Control Function (PCF)
  • With a fronted interface, PCF supports unified policy framework to govern network behavior.
• Session Management Function (SMF)
  • SMF provides the functionalities of MME, S-GW-C & P-GW-C in EPC that are not covered by AMF.
  • It takes care of session management such as session establishment, modify and release, including tunnel maintain between UPF and AN node, UE IP address allocation & management.
• Unified Data Management (UDM)
• Unified Data Repository (UDR)
• User Plane Function (UPF)
• Application Function (AF)
• User Equipment (UE)
• (Radio) Access Network ((R)AN)
• 5G-Equipment Identity Register (5G-EIR)
• Security Edge Protection Proxy (SEPP)
• Network Data Analytics Function (NWDAF)

Access and Mobility Management Function (AMF)

• 主要大腦
• Termination of RAN CP interface (N2).
• Termination of NAS (N1), NAS ciphering and integrity protection.
• Registration (login) management.
• Connection management.
• Reachability management.
• Mobility Management.
  • 透過與基地台的訊號強度來計算移動距離
• Provide transport for SM messages between UE and SMF.
• Access Authentication.
• Access Authorization.
• Access Accounting.
  • 上面三個稱作 3A
• It interacts with the AUSF and the UE, receives the intermediate key that was established as a result of the UE authentication process.

Session Management Function (SMF)

• Session Management e.g. Session establishment, modify and release, including tunnel maintain between UPF and AN node.
• UE IP address allocation & management (including optional Authorization).
• DHCPv4 (server and client) and DHCPv6 (server and client) functions.
• Configures traffic steering at UPF to route traffic to proper destination.
• Termination of interfaces towards Policy control functions.
• Charging data collection and support of charging interfaces.
• Control and coordination of charging data collection at UPF.
• Termination of SM parts of NAS messages.
• Downlink Data Notification.
• Initiator of AN specific SM information, sent via AMF over N2 to AN.
• Determine SSC mode of a session.

Policy Control Function (PCF)

• Supports unified policy framework to govern network behaviour.
• Provides policy rules to Control Plane function(s) to enforce them.
• Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR).

Network Repository Function (NRF)

• Service discovery function
  • Service Registration/De-Registration
  • Service update
• Maintains the NF profile of available NF instances and their supported services
• Support Network slicing
  • PLMN-level
  • Shared-slice level
  • Slice-specific level
• NF profile of a NF instance (refer to Clause 6.2.6 of TS 23.501)
  • NF instance ID
  • NF type
  • PLMN ID
  • Network slice related Identifier(s), e.g. S-NSSAI, NSI ID
  • FQDN or IP address of NF
  • NF capacity information
  • …

5G SBI

• Namf: Service-based interface exhibited by AMF.
• Nsmf: Service-based interface exhibited by SMF.
• Nnef: Service-based interface exhibited by NEF.
• Npcf: Service-based interface exhibited by PCF.
• Nudm: Service-based interface exhibited by UDM.
• Naf: Service-based interface exhibited by AF.
• Nnrf: Service-based interface exhibited by NRF.
• Nnssf: Service-based interface exhibited by NSSF.
• Nausf: Service-based interface exhibited by AUSF.
• Nudr: Service-based interface exhibited by UDR.
• Nudsf: Service-based interface exhibited by UDSF.
• N5g-eir: Service-based interface exhibited by 5G-EIR.
• Nnwdaf: Service-based interface exhibited by NWDAF.

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• Two types of SBI:
  • Request – Response
  • Subscribe – Notify
• The Implementation is decided:
  • OpenAPI
  • RestFul API
  • HTTP/2
  • JSON

Service-based Behavior among Network Functions

• Request (Consumer)-Response (Producer)
  • One to one between NFs
  • One-time response from Producer to Consumer within a certain time
    
    
• Subscribe (Consumer)-Notify (Producer)
  • Multiple NFs may subscribe to the Same CP NF
  • Periodic updates/event-trigger update
  • Potential implementation
    • Separate Request/Response
    • Part of another NF service operation
    • Registration as notification endpoint to Network Repository Function (NRF)
      
      

Partial Steps Replaced with Service-based Operations in 5G Procedures

Three Key 5G Use Cases

• eMBB (enhanced Mobile Broadband)
  • initial phase of 5G Non-Standalone (NSA) deployments
• URLLC (Ultra Reliable Low Latency Communications)
• mMTC (massive Machine Type Communications)

Network Slicing in 5G Core Network (5GC)

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Transformation of Traditional Networking Paradigms to SDN/NFV/Cloud-enabled 5G

Network Evolution enabled by SDN/NFV

Examples of 5G Network Slices