LTE core network also called EPC in SAE is responsible for the complete control of the UE and the creation of media. The main logical nodes LTE EPC are:
• PDN Gateway (P-GW)
• Serving Gateway (S-GW)
• Mobility Management Entity (MME)
PCRF of LTE Core Network
The political control and charging rules is responsible for control policy making, as well as flow control functionality based charging enforcement function Control Policy (PCEF), which is the P-GW.PCRF provides QoS authorization (QoS class identifier [QCI] and bit rates), which decides how a particular data stream will be treated PCEF and ensure that it is in accordance with the user’s subscription profile.
HSS of LTE Core Network
Home Subscriber Server database subscription includes SAE users such as EPS subscribed QoS profile, as well as any restrictions on access for roaming. He also holds information on PDNs which users can connect. This could be in the form of an access point name (APN) (which is a label according to DNS naming conventions describing the access point PDN) or PDN address (indicating the subscriber’s IP address (es)). In addition HSS has dynamic information such as the identity of the MME user is already logged in or registered. HSS can also integrate, authentication center (AUC), which generates vectors authentication keys and security.
P-GW of LTE Core Network
PDN Gateway is responsible for allocating IP UE and the application QoS and flow based charging in accordance with the PCRF. It is responsible for filtering user downlink IP packets in different QoS-based carriers. This is done based on traffic patterns (TFTs) .P-GW performs application QoS guaranteed bit rate (GBR) bearers. It also serves as the anchor for mobility for interworking with non-3GPP technologies such as CDMA2000 and WiMAX networks.
S-GW of LTE Core Network
All user IP packets are transferred via Gateway service, which serves as the local mobility anchor data carriers if the UE moves between eNodeBs. It retains also information carriers when the UE is at rest (known as the “EPS Connection Management – IDLE” [ECM-IDLE]) and buffers downlink data temporarily while the MME initiates paging UE to restore carriers. In addition, S-GW performs certain administrative functions in the visited network, such as the collection of information load (ie the amount of data sent or received by the user) and lawful intercept. It also serves as a mobility anchor for interworking with other 3GPP technologies such as packet radio service (GPRS) and UMTS.
MME of LTE Core Network
Mobility Management Entity (MME) is a control node that processes the signaling between the UE and CN. Protocols running between the UE and CN are known as Non-Access Stratum (NAS) protocols.
Work Details of LTE Core Network Nodes PCRF, HSS, P-GW, S-GW, and MME in LTE
The LTE core network comprises several key nodes that perform different functions to ensure efficient service delivery, user mobility, and data routing. These nodes work together to handle tasks like authentication, session management, quality of service (QoS), and data forwarding. Below are the roles and responsibilities of the main core network nodes:
- PCRF (Policy and Charging Rules Function): The PCRF is responsible for managing the policies that govern user traffic. It determines the appropriate QoS parameters based on the user’s subscription, network load, and service type (e.g., video, voice, data). PCRF ensures that services are delivered according to user-specific policies and charges them accordingly. It works closely with the Serving Gateway (SGW) and the Packet Gateway (PGW) to enforce these policies for traffic management and billing.
- HSS (Home Subscriber Server): The HSS is a central database that contains subscriber-related information, such as user authentication credentials, service profiles, and roaming permissions. It supports functions like user authentication, authorization, and mobility management by providing the necessary data to other network elements like the MME (Mobility Management Entity). The HSS ensures that only authorized users can access the network and helps maintain user profile consistency during handovers.
- P-GW (Packet Gateway): The P-GW serves as the gateway between the LTE network and external IP networks (e.g., the internet). It is responsible for assigning IP addresses to the User Equipment (UE) and routing user data between the eNodeB and external networks. Additionally, the P-GW enforces QoS policies by managing traffic and ensures that data flows are handled in accordance with the rules set by the PCRF. It also collects usage data for billing purposes.
- S-GW (Serving Gateway): The SGW acts as a data forwarding node between the eNodeB and the core network. It routes user data to/from the P-GW and maintains the bearers for active user sessions. The SGW is responsible for user data forwarding in both the downlink and uplink directions, mobility management during handovers, and tunnel establishment between the eNodeB and the P-GW. It also performs packet routing and forwarding functions for users moving between different eNodeBs.
- MME (Mobility Management Entity): The MME handles the control plane signaling for the LTE network. It is responsible for tasks such as user authentication, bearer management, session establishment, mobility management (e.g., handovers), and the security procedures for protecting user data. The MME interacts with the HSS for authentication and authorization, and it also communicates with the SGW and PGW to establish, modify, and release bearers for active user sessions.
In summary, these core network nodes work together to provide a seamless LTE experience, ensuring that users are authenticated, their data is efficiently routed, and their sessions are managed securely and with the appropriate QoS. The separation of control and user planes between these elements allows for a scalable and efficient system that can handle large numbers of users and diverse traffic demands.