What is the Difference Between GBR and Non-GBR in LTE?
In LTE (Long-Term Evolution) networks, the terms GBR (Guaranteed Bit Rate) and non-GBR are used to describe different types of QoS (Quality of Service) bearers that handle traffic with varying priority levels and service guarantees. Understanding the difference between GBR and non-GBR bearers is crucial in designing and optimizing LTE networks to support diverse services like voice, video, and data, each with specific performance requirements.
GBR (Guaranteed Bit Rate) Bearers
GBR bearers are used to provide a guaranteed minimum bit rate for specific types of traffic, ensuring that the data flow meets the required QoS levels for applications that need constant and predictable bandwidth. GBR is primarily used for applications that require a certain amount of resources to function effectively, such as real-time services like voice calls, video streaming, and VoIP (Voice over IP). These applications have stringent latency, jitter, and throughput requirements that cannot be compromised.
In an LTE network, GBR bearers are established with specific QoS parameters, including the guaranteed bit rate, which is the minimum bandwidth allocated for that bearer. This ensures that even if the network experiences congestion, the bearer will still receive enough resources to maintain the required performance levels. The GBR mechanism is part of the LTE’s QoS framework, which helps prioritize traffic based on its specific service requirements.
GBR bearers are created during the initial bearer setup procedure in the LTE attach process and are maintained for the duration of the session. The network is responsible for allocating resources to ensure that the GBR is met. If the demand for bandwidth exceeds the available resources, the network may take measures such as traffic shaping or congestion control to maintain the GBR for these high-priority services.
Non-GBR (Non-Guaranteed Bit Rate) Bearers
Non-GBR bearers, on the other hand, are used for applications that do not require a guaranteed minimum bit rate. These bearers are typically used for best-effort traffic, such as web browsing, file downloads, and email services, where a certain level of bandwidth is preferred, but the application can tolerate variable data rates. Non-GBR traffic is usually less time-sensitive and can be delayed or adjusted depending on network conditions, making it more flexible and less resource-intensive than GBR traffic.
Unlike GBR bearers, non-GBR bearers do not have strict bandwidth guarantees. The resources allocated to non-GBR bearers are dynamically adjusted based on the network’s load and the availability of spare capacity. When the network is under heavy load, non-GBR bearers may experience slower data rates or increased latency, as the network prioritizes GBR traffic. This makes non-GBR bearers suitable for applications where consistent performance is not critical, and occasional delays or variations in throughput are acceptable.
Non-GBR bearers are also established during the bearer setup process but are typically allocated with more flexible QoS parameters, such as maximum bit rate and priority. These parameters allow the network to optimize resource allocation based on current traffic conditions and the overall system load.
Key Differences Between GBR and Non-GBR
1. Bit Rate Guarantee
The primary difference between GBR and non-GBR bearers lies in the bit rate guarantee.
- GBR: A guaranteed bit rate is provided, ensuring that the traffic will receive a minimum amount of resources throughout the session. This is critical for applications requiring high, consistent throughput, such as voice and video communications.
- Non-GBR: No guaranteed bit rate is provided. Instead, traffic is served on a best-effort basis, with no assurance of a minimum bandwidth allocation. This is suitable for less time-sensitive applications like web browsing or file transfers.
2. Traffic Priority
GBR and non-GBR bearers also differ in terms of traffic priority.
- GBR: GBR bearers are prioritized in the network. They are typically allocated higher priority compared to non-GBR bearers, ensuring that critical services receive the necessary resources even under network congestion conditions.
- Non-GBR: Non-GBR bearers have lower priority and can be affected by network congestion, with traffic possibly experiencing delays or reduced throughput if GBR traffic demands more resources.
3. Use Cases and Applications
GBR and non-GBR bearers serve different use cases based on their requirements for consistent throughput and low latency.
- GBR: Used for real-time applications that require a stable and predictable bit rate, such as voice over LTE (VoLTE), video calls, IPTV, and online gaming. These applications are sensitive to latency and jitter, making a guaranteed bit rate crucial for maintaining service quality.
- Non-GBR: Used for data applications where intermittent delays are acceptable, such as web browsing, file downloads, social media access, and email. These applications are less time-sensitive and can tolerate variations in performance.
4. Resource Allocation and Network Efficiency
GBR and non-GBR bearers differ in how they allocate and use network resources.
- GBR: GBR bearers are allocated fixed resources based on the required bit rate, which can lead to inefficient use of network resources, especially when the bearer is not fully utilized. However, the guaranteed bit rate ensures that the service quality is maintained even during periods of high network congestion.
- Non-GBR: Non-GBR bearers offer more flexible resource allocation. Since these bearers are used for best-effort traffic, the network can dynamically allocate resources based on the overall network load and the availability of spare capacity, resulting in more efficient use of resources.
5. Impact of Network Congestion
The performance of GBR and non-GBR bearers is affected differently during periods of network congestion.
- GBR: GBR bearers are designed to maintain a consistent performance level, even under heavy congestion. If the network is overloaded, the system may take steps like traffic shaping, quality-of-service enforcement, or reallocation of resources to ensure that the guaranteed bit rate is upheld for critical services.
- Non-GBR: Non-GBR bearers are more likely to experience degradation in performance during periods of congestion. As the network prioritizes GBR traffic, non-GBR traffic may experience delays, lower throughput, or even packet loss if the network is heavily loaded.
6. Overhead and Complexity
From a network management perspective, GBR and non-GBR bearers introduce different levels of overhead and complexity in terms of resource management and scheduling.
- GBR: Managing GBR bearers requires a more sophisticated scheduling algorithm to ensure that the guaranteed bit rate is provided without violating the QoS requirements. This can introduce additional overhead in terms of signaling and resource management.
- Non-GBR: Non-GBR bearers are less complex to manage, as the network can dynamically adjust the resources allocated to these bearers based on current traffic demand, making them easier to handle in terms of signaling and resource optimization.
Conclusion
The distinction between GBR and non-GBR bearers in LTE networks plays a crucial role in determining the quality of service for different types of traffic. GBR bearers are essential for applications that require guaranteed performance, such as real-time voice and video communications, while non-GBR bearers are used for best-effort services where performance can vary without significant impact on the user experience. The choice between GBR and non-GBR bearers depends on the type of service, the required level of QoS, and the network’s ability to handle different traffic demands efficiently.