Radio Bearer in LTE
In Long-Term Evolution (LTE) wireless communication, a “Radio Bearer” serves as a crucial link between the user equipment (UE) and the evolved NodeB (eNodeB), facilitating the exchange of data. Radio Bearers are classified into two main categories: Control Radio Bearers (CRBs) and Data Radio Bearers (DRBs).
CRBs are responsible for transmitting control information essential for network management, while DRBs handle user data transfer, ensuring efficient and reliable communication in LTE networks. These bearers play a pivotal role in optimizing resource allocation, managing quality of service (QoS), and enabling seamless connectivity for mobile devices in the LTE ecosystem.
There are 2 types of Radio Bearers (RB) in LTE:
- To carry signaling. There are called the SRB (Signaling Radio Bearer)
- To carry user data. There are associated with an EPS Bearer
In LA1.X, the maximum number of RB per UE is 4
The following types of Radio Bearer are defined:
- SRB1: RRC signaling with high priority
- SRB2: RRC signaling and NAS signaling (lower priority)
- Best Effort: also defined as the default EPS Bearer
- GBR: Radio Bearer with a guaranteed bit rate
- VoIP: Radio bearer to carry the VoIP
In LA1.X the following combination are supported:
- SRB1
- SRB1+SRB2+Best Effort
- SRB1+SRB2+Best Effort + GBR
- SRB1+SRB2+Best Effort + VoIP
- SRB1+SRB2+Best Effort + Best Effort
At the RRC connection, the eNodeB scheduler creates a context for the UE containing the UEBearerList. this list is limited to 4 per user in LA1.X
Each bearer is identified by the LCID (Logical Channel ID)
Each bearer is associated with QoS parameters like :
- Max bit rate and guaranteed bit rate
- VoIP or not
- H-ARQ usage
Default Bearer vs Dedicated Bearer
- A default bearer is bearer able to carry all kinds of traffic (no filter) without QoS. It is typically created during the attach procedure
- A dedicated bearer is a bearer to carry a specific data flow, identify by the TFT (Traffic Flow Template), with a given QoS.
- Example: Voice, streaming
- It can be established:
- During the Attach procedure (depending on the user profile)
- After the Attach procedure, on demand
The first type, known as Signaling Radio Bearers (SRB), is primarily responsible for carrying signaling information. Signaling information includes critical data for network management, control, and coordination. SRBs ensure that essential control messages, such as connection setup and network handovers, are reliably transmitted between the UE and the eNodeB, guaranteeing seamless communication and network operation. These bearers are vital for maintaining the integrity and stability of LTE networks.
The second type of Radio Bearers in LTE is associated with an Evolved Packet System (EPS) Bearer and is designed to carry user data. These bearers, commonly referred to as Data Radio Bearers (DRB), are responsible for transporting the actual user-generated information, such as voice calls, video streams, and internet data. DRBs play a pivotal role in ensuring that user data is transmitted efficiently and in accordance with quality of service (QoS) requirements. They are instrumental in optimizing resource allocation, bandwidth utilization, and prioritizing different types of data traffic to deliver a seamless and high-quality user experience.
Together, SRBs and DRBs form a comprehensive framework that underpins the reliable and efficient functioning of LTE networks, catering to both control and user data transfer needs.
What is a Radio Bearer in LTE?
A Radio Bearer in LTE is a logical connection between the User Equipment (UE) and the evolved NodeB (eNB) that carries user data over the radio interface. It is responsible for delivering data from the device to the network and vice versa, ensuring efficient use of the radio resources and maintaining quality of service (QoS) for different applications.
Key Functions of Radio Bearers
- Data Transport: A Radio Bearer transports user data over the radio interface, facilitating communication between the UE and the eNB. It is part of the end-to-end data path for a service.
- QoS Enforcement: Each Radio Bearer is associated with a QoS profile that defines the quality of service requirements, such as priority, packet delay, and throughput, to ensure optimal performance for specific applications (e.g., voice, video, data).
- Radio Resource Management: The Radio Bearer helps the network manage radio resources by ensuring that data is transmitted over the available channels efficiently and with minimal interference.
Types of Radio Bearers
- Signaling Radio Bearer: This bearer is used for control plane signaling between the UE and the eNB. It carries signaling messages like connection setup, handovers, and other network management data.
- Data Radio Bearer: These bearers are used for user plane traffic, which includes voice, video, and data services. Data bearers can be further classified based on the required QoS for the traffic (e.g., real-time voice calls or large data downloads).
How Radio Bearers Work
When a device connects to the LTE network, the eNB establishes a Radio Bearer to facilitate communication. The eNB assigns the appropriate QoS profile based on the type of service being used. For example, a high-priority, low-latency bearer is created for a voice call, while a bearer with higher bandwidth may be allocated for a video stream.
Why Radio Bearers Matter
Radio Bearers are essential for managing data transmission over the LTE network. By providing differentiated services with proper QoS, they ensure that applications work optimally, whether you’re making a call, streaming video, or browsing the web. Efficient management of Radio Bearers is critical for maintaining a seamless user experience, especially in high-demand scenarios.