How does 4G support international roaming for mobile users?

International roaming in 4G networks allows mobile users to maintain connectivity and use mobile services when they travel outside their home network's coverage area.

Here's a technical breakdown of how 4G supports international roaming:

1. LTE Network Architecture:
   • Long-Term Evolution (LTE) is the technology behind 4G networks. It employs a packet-switched network architecture based on Internet Protocol (IP) for data transmission.
   • LTE networks consist of several components: User Equipment (UE), Evolved NodeB (eNodeB), Mobility Management Entity (MME), Serving Gateway (SGW), and Packet Data Network Gateway (PGW).
2. Subscriber Identity in 4G:
   • Each subscriber is uniquely identified in 4G using an International Mobile Subscriber Identity (IMSI). IMSI is stored on the Subscriber Identity Module (SIM) card in the user's device.
   • The IMSI contains information about the home network and the subscriber's identity.
3. Home Network and Visited Network:
   • When a mobile user travels abroad, they enter a different country with its own mobile network infrastructure.
   • The home network is the user's native network, while the visited network is the network in the foreign country where the user roams.
4. Authentication and Authorization:
   • When a 4G device enters a new network's coverage area, it initiates a process called Attach.
   • The device sends its IMSI to the visited network's eNodeB, which forwards it to the MME of the visited network.
   • The MME in the visited network communicates with the home network's Home Subscriber Server (HSS) using Diameter protocols to authenticate and authorize the subscriber.
   • The HSS verifies the subscriber's credentials and roaming profile. If approved, it sends the necessary information to the visited network to allow the user to access services.
5. Data Routing and Traffic Handling:
   • After authentication, the visited network assigns a local IP address to the user's device through the PGW.
   • Data traffic from the user's device is then routed through the visited network's infrastructure to the PGW, SGW, and eventually to the destination on the internet or the user's home network.
6. Billing and Charging:
   • Roaming agreements between home and visited networks involve intricate billing arrangements.
   • The visited network tracks the usage of the roaming subscriber and periodically exchanges charging data with the home network to ensure accurate billing.
7. Quality of Service (QoS) and Service Continuity:
   • 4G networks maintain QoS for roaming users by providing similar service levels as in the home network. This includes speed, latency, and other performance factors.
   • Handovers between different eNodeBs within the visited network ensure seamless connectivity as the user moves within the coverage area.