You may here us refer to a term called "QCI" in our discussions about data plans, throughput, and priorities when using various SIM cards and plans. Let's dive into what QCI levels are and how they affect your mobile experience.
Quality of Service Class Identifier (QCI) levels are an integral part of how mobile networks manage and prioritize different types of data traffic, ensuring that critical services receive appropriate levels of performance. These levels are particularly relevant in the context of LTE (Long Term Evolution) and 5G networks. In the U.S., major carriers like Verizon, AT&T, T-Mobile, and others utilize QCI levels to optimize traffic flow and meet the varying needs of different services.
How QCI Works:
QCI is essentially a set of predefined values that determine how traffic is prioritized on the network. Each QCI value corresponds to a specific quality of service (QoS) class, defining parameters like latency, packet loss, and error rates. QCI levels ensure that the network can differentiate between different types of traffic, such as voice calls, streaming video, browsing, and background applications, each having different network performance requirements.
There are two key categories of traffic based on QCI:
- Guaranteed Bit Rate (GBR) QCIs: Used for services that require a dedicated portion of network bandwidth to meet minimum data transmission rates (e.g., voice over LTE or VoLTE).
- Non-Guaranteed Bit Rate (Non-GBR) QCIs: Used for services that can tolerate fluctuations in bandwidth (e.g., web browsing or background apps).
Common QCI Levels in U.S. Mobile Networks:
Each QCI is associated with a different service. Below are some standard QCI levels typically observed in U.S. mobile networks:
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QCI 1:
- Service: VoLTE (Voice over LTE)
- Type: GBR
- Priority: High priority, low latency
- Use case: Voice calls over LTE, which require reliable, low-latency communication.
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QCI 5:
- Service: IMS (IP Multimedia Subsystem) signaling
- Type: Non-GBR
- Priority: High priority, ensuring that call setup and messaging through IMS can proceed quickly.
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QCI 6:
- Service: Real-time video streaming or conversational video (like video calls)
- Type: GBR
- Priority: Lower priority than VoLTE but still requiring minimal latency.
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QCI 7:
- Service: Streaming services, background data
- Type: Non-GBR
- Priority: Lower than QCI 6 but still optimized for continuous data flow with a bit of flexibility
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QCI 8 or 9:
- Service: Standard mobile internet traffic, such as browsing, social media, and app usage.
- Type: Non-GBR
- Priority: Lower than QCI 1, 6, or 7 but sufficient for most typical internet services. QCI 9 is the default for general internet traffic.
U.S. Carrier Implementations:
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Verizon: As one of the largest U.S. carriers, Verizon places a strong focus on VoLTE services with QCI 1 and prioritizes this traffic during times of network congestion. Standard internet traffic, especially on 5G, tends to fall under QCI 9.
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AT&T: AT&T also uses QCI levels to optimize VoLTE and video services, especially with increasing adoption of 5G. Their focus is on maintaining quality voice services with QCI 1 and ensuring low-latency video services with QCI 6 for 4G and 5G users.
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T-Mobile: T-Mobile, particularly in the 5G era, uses a similar approach to the other carriers, prioritizing VoLTE with QCI 1 and default internet traffic under QCI 9. They heavily optimize the network for consumer streaming and other services.
For a detailed look at the US carriers, their plans, and the QCI levels they represent, Reddit has a great post from u/Ethrem that is regularly updated with current carrier QCI categorizations.
5G and QCI:
In 5G networks, an extension of QCI called 5QI (5G QoS Identifier) comes into play, maintaining the same principles but with further granularity. It allows even more sophisticated traffic management, enabling ultra-reliable low-latency communications (URLLC), massive machine-type communications (mMTC), and enhanced mobile broadband (eMBB), which are critical for 5G use cases like autonomous driving, industrial IoT, and immersive AR/VR applications.