LTE CSFB: Advantages and Disadvantages

This page explores the pros and cons of LTE CSFB (Circuit Switched Fallback).

CSFB stands for Circuit Switched Fallback, while LTE stands for Long Term Evolution.

Introduction: LTE is an all-IP network, so voice over LTE requires specific solutions. Two common options are using IMS (IP Multimedia Subsystem) or CSFB (Circuit Switched Fallback) to existing 2G/3G networks.

CSFB is a mechanism to “handover” voice calls to the circuit-switched (CS) domain of existing 2G/3G networks. This applies to both Mobile Originated Calls (MOC) and Mobile Terminated Calls (MTC).

Figure-1: LTE CSFB

LTE CSFB allows users to make or receive voice calls in an LTE network using existing 2G/3G circuit-switched networks.

Advantages of LTE CSFB

Here are the benefits of using LTE CSFB:

• Cost Savings: Reuses the existing 2G/3G CS domain, saving on investment costs for providing voice support in the LTE network.
• Seamless User Experience: End users don’t notice any difference in voice services, as the existing 2G/3G CS infrastructure is used.
• Emergency Call Support: Emergency calls are supported from the beginning of LTE network deployment.
• Consistent Charges: Call charges remain the same as those levied in 2G/3G networks.
• Legal Interception: Supports legal interception from the start.

Disadvantages of LTE CSFB

Here are the drawbacks of using LTE CSFB:

• Impact on Existing Equipment: Requires enhancements to existing equipment. For example, the SGW (Serving Gateway) needs upgrades. The PS (Packet Switched) session (i.e., data session) needs to be maintained when the UE (User Equipment) falls back to the 2G/3G CS domain. Proper handling is needed to prevent data session suspension or interruption.
• Increased Signaling: Additional signaling messages are generated to establish voice calls from LTE to the switched network (2G or 3G), which can increase network overhead.
• Call Setup Delay: The voice call setup time is longer in LTE compared to direct 2G/3G voice call establishment.
• Performance Impacts: The success rate of MTC calls can be affected by inaccurate mapping between TAI (Tracking Area Identity) and LAI (Location Area Identity). Accurate mapping improves the success rate.