Sign in Subscribe

4g ims

Last updated on 


IMS stands for IP Multimedia Subsystem. It's an architectural framework for delivering multimedia services, such as voice, video, and messaging, over IP networks. The IMS architecture is particularly significant in 4G (LTE) and later networks to provide richer multimedia services beyond just basic voice and data.

Here's a technical breakdown of 4G IMS:

1. Basic Architecture:

The IMS architecture is divided into three main layers:

  • Service Layer (SL): This layer includes application servers and service platforms that offer various multimedia services like voice over LTE (VoLTE), video calling (ViLTE), Rich Communication Services (RCS), and more.
  • Control Layer (CL): This layer handles the session and connection control. It includes components like the Call Session Control Function (CSCF) entities:
    • Proxy-CSCF (P-CSCF): Sits at the edge of the IMS network and is the first point of contact for the user equipment (UE).
    • Interrogating-CSCF (I-CSCF): Routes the session request to the appropriate Serving-CSCF (S-CSCF).
    • Serving-CSCF (S-CSCF): Handles the session setup and teardown processes for the user.
  • Transport Layer (TL): This layer is responsible for transporting the user data and signaling between different IMS components. It uses the IP protocol for communication.

2. Key Components and Functionalities:

  • User Equipment (UE): Devices like smartphones, tablets, or other devices that initiate and receive IMS services.
  • Home Subscriber Server (HSS): It stores user-related data like user profiles, service subscription information, and authentication vectors.
  • Policy and Charging Rules Function (PCRF): It provides policy control and charging functionalities. It determines the QoS (Quality of Service) for each subscriber and enforces policies related to charging and data usage.
  • Media Resource Function (MRF): Provides media handling capabilities like transcoding, mixing, and processing for multimedia services.
  • Breakout Gateway Control Function (BGCF): It determines the breakout point for a session when it needs to interact with another network or service that is not part of the IMS.

3. VoLTE (Voice over LTE):

One of the most significant applications of IMS in 4G is VoLTE. Here's a simplified flow:

  • Registration: The UE registers with the IMS network, authenticating itself through the HSS.
  • Session Setup: When a user initiates a voice call, the IMS network sets up the session through the CSCF entities, ensuring QoS parameters like latency, jitter, and packet loss are maintained.
  • Media Handling: Media traffic (voice packets) is transported over the LTE network using the IP protocol, ensuring efficient use of resources and better voice quality.

4. Security:

IMS incorporates various security mechanisms to protect user data and services. These include:

  • Authentication and Authorization: Before accessing IMS services, the UE undergoes authentication using security mechanisms like AKAv1-MD5 (Authentication and Key Agreement version 1 with MD5 hashing).
  • Encryption: IMS ensures end-to-end encryption of voice and data traffic to prevent eavesdropping and unauthorized access.

5. Integration with Other Networks:

IMS allows seamless integration with other networks like PSTN (Public Switched Telephone Network), WLAN (Wireless Local Area Network), and more. The BGCF and other components facilitate this integration, enabling users to access services across different networks.