The IP Multimedia Subsystem (IMS) is a standardized framework developed by 3GPP to support multimedia services such as voice, video calls, and messaging over IP-based networks. It is the backbone of Voice over LTE (VoLTE), enabling the following key advantages:
- HD Voice Quality : Crystal-clear audio quality and more reliable calls.
- Faster Call Setup :VoLTE connects calls in ~2 seconds compared to 4-6 seconds in 2G/3G.
- Improved Battery Life : No need for devices to switch to 2G/3G for voice calls.
IMS was once viewed as a complex and costly framework. However, the adoption of VoLTE transformed its reputation, showcasing IMS as an enabler of modern voice and multimedia services. By shifting from traditional circuit-switched voice technology in 2G/3G to all-IP LTE networks, VoLTE delivers superior call quality, faster setup times, and the ability to seamlessly handle both voice and video calls using the same mobile number…
How IMS Enables VoLTE:
- Seamless Integration: IMS operates separately from the LTE core but connects via the SGi interface through the Packet Gateway (PGW).
- SIP Protocol: IMS utilizes Session Initiation Protocol (SIP) to manage call setup, control, and termination.
- All-IP Technology: Unlike circuit-switched 2G/3G systems, IMS provides reliable, fast communication over IP networks.
A Brief History of VoLTE
IMS faced initial resistance due to its perceived complexity. In 2009, leading telecom operators and manufacturers like AT&T, Verizon, Nokia, and Alcatel-Lucent collaborated on the “One Voice” initiative, aiming to standardize VoLTE. GSMA and 3GPP finalized this as the global standard.
The first VoLTE trials began in 2012, and by 2014, SingTel Singapore became the first to offer commercial VoLTE services, enabling high-quality voice and video calls over 4G networks.
Deep-Dive Into IMS Core
Want to understand how IMS processes VoLTE calls step-by-step?
Download the guide for a detailed walkthrough and examples… 
IMS Core & VoLTE Calls (Alali Khalaf).pdf (1.7 MB)
LinkedIn: