NGAP (NG Application Protocol) in 5G-NR

Imagine a bustling orchestra, instruments playing in perfect harmony. Just like the conductor ensures seamless communication between sections, NGAP acts as the maestro in 5G networks, orchestrating communication between the core and radio access.

What is NGAP?

This specialized language, the NG Application Protocol, isn't your average chatter. It's the protocol designed specifically for 5G and beyond, enabling efficient and secure messaging between the heart of the network (core) and the frontline troops (radio access).

The NGAP architecture is built on the N2 interface, which connects the gNB (RAN) and the AMF (core network). This interface facilitates the exchange of control plane signaling messages. The NGAP architecture consists of the following layers:

Application layer: This layer contains the NGAP protocol entities, which are responsible for generating and processing NGAP messages.

Transport layer: This layer is responsible for the reliable delivery of NGAP messages between the gNB and the AMF. It typically uses the SCTP (Stream Control Transmission Protocol) protocol.

Security layer: This layer is responsible for providing security services for NGAP messages, such as authentication, integrity protection, and confidentiality. It typically uses the TLS (Transport Layer Security) protocol.

Why NGAP is important?

Think of 5G as a high-speed train whisking data packets around. NGAP ensures smooth boarding, seamless handovers between stations (cells), and efficient resource allocation, all while keeping everything secure. Without it, 5G's promises of ultra-fast speeds, ultra-low latency, and diverse services would be mere dreams.

How does NGAP work?

NGAP operates on a dedicated line, the N2 interface, connecting the radio access (gNB) and the core network (AMF). Imagine this as a dedicated communication channel for important updates and instructions. Through a series of procedures and messages, NGAP manages everything from user authentication to mobility and service activation.

The NGAP architecture also includes the following entities:

• gNB This is the base station in the 5G network. It is responsible for providing radio access to UEs (User Equipment).
• AMF (Access and Mobility Management Function): This is a core network entity that is responsible for managing the mobility of UEs and providing access to network services.
• UPF (User Plane Function): This is a core network entity that is responsible for forwarding user plane data between the gNB and the core network.

NGAP Features and Functionalities

NGAP, the Next Generation Application Protocol, serves as the essential language for communication between the core network and radio access network (RAN) in 5G.

Let's explore its key features and functionalities:

1.????? NAS Signaling:

Imagine it as the network's passport control. NGAP facilitates NAS (Non-Access Stratum) signaling, responsible for user authentication, mobility management, and bearer services management. This ensures secure access and seamless service experience across different radio access technologies.

2.????? Control Plane Separation:

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Think of it as dedicated lanes for traffic. NGAP maintains a clear separation between the control plane (signaling) and the user plane (data). This allows for efficient resource management and scalability, handling information flow without data traffic interference.

3.????? Security Mechanisms:

Like robust encryption in online banking. NGAP incorporates robust security measures like mutual authentication and integrity protection. This safeguards against cyber threats and ensures secure communication, protecting network integrity and user data.

4.????? Flexibility and Extensibility:

Think of it as a future-proof design. NGAP is designed to be flexible and adapt to emerging needs. Its modular architecture allows for easy integration of future enhancements and new services, paving the way for B5G evolution and unforeseen advancements.

5.????? User Equipment (UE) Management:

This is like managing passengers on a high-speed train. NGAP establishes and manages UE contexts, handling user authentication, registration, and mobility procedures. It ensures smooth onboarding, seamless handovers, and continuous connectivity as users move across the network.

6.????? Radio Resource Management:

Think of it as allocating seats efficiently. NGAP assists in allocating and managing radio resources for UEs, optimizing network performance and ensuring fair and optimal resource utilization for each connected device.

7.????? Service Management:

Imagine ordering different meals on a flight. NGAP enables the establishment and management of diverse services for UEs, facilitating data, voice, video, IoT connectivity, and even cutting-edge applications like AR/VR seamlessly.

8.????? Mobility Management:

Think of it as ensuring smooth transitions between stations. NGAP facilitates seamless handover between different RATs (radio access technologies) and gNBs (base stations), guaranteeing uninterrupted connectivity for users on the move, ensuring no dropped calls or service disruptions.

List of NGAP Elementary Procedures

NGAP operates through various elemental procedures, acting as the building blocks for information exchange between the core network and RAN. Here's a list of some key procedures:

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Class 1 Procedures (require a response):

• Initial Context Setup: Establishes the initial connection between a UE and the network, allowing service access.
• PDUSession Resource Setup/Modify/Release: Manages data connections for specific services (e.g., internet access, video call).
• Handover Preparation/Resource Allocation/Cancel: Ensures seamless handovers between different gNBs during movement.
• NG Reset: Resets the UE context on the network side, often used for network maintenance or troubleshooting.
• NG Setup: Establishes the initial connection between an gNB and the core network.
• Path Switch Request: Switches the data path for a UE between different gNBs for optimized performance.
• UE Context Modification: Updates UE information on the network side, like location or service access rights.
• UE Context Release: Releases the UE context, indicating the UE is no longer connected.

?Class 2 Procedures (no response required):

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• aMF Configuration Update: Informs the gNB about changes in AMF configuration that affect service delivery.
• Broadcast Session Setup/Modification/Release: Manages broadcast sessions for group communication services.
• Distribution Setup/Release: Establishes/terminates distribution of information to multiple UEs simultaneously.
• RAN Configuration Update: Updates gNB configuration with new parameters or settings.
• uEContextSuspend/Resume: Temporarily suspends or resumes UE context without terminating the connection.
• uERadioCapabilityIDMapping: Associates a UE's radio capability with its identifier.

NG Setup Procedure

?NG Setup procedure, described in clause 8.7.1 of 3GPP TS 38.413. It plays a crucial role in the 5G network by establishing the initial signaling connection between the gNB and the AMF.

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• Establishes the initial "handshake" between gNB and AMF, enabling them to exchange control plane signaling messages crucial for network operation.
• This connection is not UE-specific, meaning it's independent of any specific user equipment connected to the gNB. This allows the gNB to communicate with the AMF even before any UEs register.
• It lays the foundation for further procedures like UE registration, handover, and service activation.

NG Setup Request

?Imagine a new gNB (like a cell tower) joining the 5G network. It needs to introduce itself!

NGSetupRequest is the message it sends to say "Hello world!" It's like a gNB's business card, containing important information:

GlobalRANNodeID: This unique code identifies the gNB globally, like a passport for the network.

RANNodeName: Just like we have names, the gNB can have one too, for easier management.

• SupportedTAList: Think of these as areas the gNB covers, like a map showing where it can find and connect devices.
• DefaultPagingDRX: This fancy term basically says how often the gNB "checks its voicemail" for devices needing attention, saving power in the meantime.
• IfConfigured TAC Indication: Signals if the gNB provides specific configuration for optimized signaling towards certain Tracking Areas.
• UE Retention Information: Proposes retaining existing user connections, potentially speeding up service access.
• Extended RAN Node Name: Alternative, possibly more comprehensive, human-readable name for the gNB.
• NID within NPN Support: Indicates specific network slices (S-NSSAI) supported by the gNB for different Tracking Areas within a Non-Public Network (NPN).

NG Setup Response

?The NG Setup Response in 5G is like a reply "hi!" back from the core network to the gNB's initial introduction (NG Setup Request). It confirms the handshake and provides essential information for further communication.

• AMFName : This Information Element (IE) contains the name of the Access and Mobility Management Function (AMF)
• ServedGUAMIList : This IE enumerates the Globally Unique AMF ID (GUAMI) served by the AMF. The GUAMI comprises the PLMN Identity, AMF Region ID, AMF Set ID, and AMF Pointer, collectively forming a unique identifier for the AMF within the global 5G network.
• RelativeAMFCapacity : This IE denotes the relative capacity of the AMF, represented as a dimensionless value. It enables load balancing and priority management across various AMFs within the network.
• PLMNSupportList : This IE provides a list of the Public Land Mobile Networks (PLMNs) supported by the AMF, along with the available slices for each PLMN. Slice support is indicated through the s-NSSAI (Single Network Slice Selection Assistance Information), specifying the supported slice(s).

Initial UE Message

?The InitialUEMessage is a crucial message sent by your phone to the 5G core network, initiating your connection journey. Think of it as your phone's first "hello" to the network, containing everything it needs to introduce itself and start using services.

Downlink Nas Transport

• This message is sent by the AMF and is used for carrying NAS information over the NG interface.
• DownlinkNASTransport: A courier delivering messages (like registration or service requests) from the network to your phone.
• NAS Security Mode Command: Instructions carried by the courier, telling your phone and the network how to encrypt and protect their communication.

Uplink Nas Transport

The UplinkNASTransport message acts like a secure "express mail" in the 5G network, allowing your phone to send important information to the core network safely. This is crucial for:

• Service requests: Telling the network what services you want (e.g., data access, calls).
• Authentication: Confirming your identity to the network for secure access.
• Mobility management: Seamlessly switching between cell towers as you move.
• Session management: Setting up and maintaining your data connections.

InitialContextSetupRequest?

Think of it like setting up your "room" in the 5G hotel.

This message tells the gNodeB to get your room ("context") ready after you've checked in (authenticated).

• It includes instructions for both communication channels:
• User plane: Like your room phone for calls and data.
• Control plane: Like the hotel staff for managing your stay.
• Once set up, this "room" allows you to use all the 5G services you need!
• Essentially, it initiates the crucial step of configuring your connection inside the network, paving the way for smooth and secure communication

InitialContextSetupResponse

Think of accessing the 5G network like staying at a hotel. The InitialContextSetupRequest is like asking for a room, and the InitialContextSetupResponse is the confirmation that your room is ready with everything you need for a comfortable stay.

PDUSessionResourceSetupRequest

In the 5G network, the PDUSessionResourceSetupRequest (PDUSessionResourceSetupRequest) message is crucial for establishing data connections, similar to placing an order for dedicated communication channels. Let's break down its function:

Imagine you're setting up a virtual data tunnel for each online activity you want to do (e.g., streaming video, browsing the web). This message acts like your request form to the network, outlining your specific needs.

What it does:

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• Requests resource allocation: It tells the network to allocate resources on both the Uu interface (phone to cell tower) and the NG-U interface (cell tower to core network). These resources are like dedicated "lanes" on a highway, ensuring efficient data flow for each activity.
• Defines Quality of Service (QoS): It specifies the desired QoS for each data connection. This defines the "service level" for each activity, ensuring it receives the necessary priority, bandwidth, and delay characteristics (e.g., low latency for real-time gaming).
• Triggers Dedicated Radio Bearers (DRB) setup: It instructs the network to establish DRBs on the Uu interface. Think of these as dedicated "tunnels" connecting your phone to the cell tower, specifically carrying data for each activity.

Essentially, the PDUSessionResourceSetupRequest message initiates the process of configuring dedicated and optimized data channels for your various online activities within the 5G network.

PDUSessionResourceSetupResponse

PDUSessionResourceSetupResponse: Your Data Channels are Ready!

The PDUSessionResourceSetupResponse message serves as the confirmation from the network after you send a PDUSessionResourceSetupRequest in 5G. It's like receiving a confirmation email after placing an online order.

Key points:

• Indicates success: This message signifies that the network has successfully processed your request to set up data channels for your desired activities.
• Contains configuration details: It may include specific information about the allocated resources, such as:
• QoS parameters: Confirming the granted service levels for each data connection (e.g., guaranteed bandwidth, delay limits).
• DRB identifiers: Providing names for the dedicated "tunnels" established between your phone and the cell tower.
• Triggers further actions: This response often triggers subsequent messages for additional configuration and finalization of the data session setup process.

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