LBI (linked EPS bearer identifier)

In modern mobile communication networks, the use of Quality of Service (QoS) mechanisms is becoming increasingly important. QoS mechanisms ensure that mobile network operators can provide different levels of service quality to their customers based on their needs and the type of data traffic they generate. To provide QoS, mobile networks use different mechanisms, including the use of Evolved Packet System (EPS) bearers. EPS bearers are logical channels that carry data traffic between a User Equipment (UE) and the core network.

EPS bearers are identified by an EPS Bearer Identity (EBI), which is used by the network to differentiate between different bearers and their associated QoS characteristics. However, there are situations where multiple EPS bearers can be established between a UE and the core network, resulting in potential ambiguity in identifying the correct bearer for specific data traffic. To address this, the 3rd Generation Partnership Project (3GPP) has introduced the Linked EPS Bearer Identifier (LBI).

The LBI is a new concept introduced in the 3GPP Release 15 specification. It is an extension of the existing EBI concept and provides a unique identifier for a specific data flow, which is associated with a particular application or service. The LBI identifies the EPS bearer that is associated with the data flow, and it is used to ensure that the correct QoS is applied to the data flow.

The LBI is used in situations where a UE is communicating with multiple servers or applications, and each of them requires a different level of QoS. For example, a UE may be running a video streaming application and a file download application simultaneously. The video streaming application requires a high QoS to ensure that the video playback is smooth, while the file download application can use a lower QoS. Without the LBI, it would be difficult for the network to identify the correct EPS bearer for each data flow, resulting in potential QoS issues.

The LBI is allocated by the network and is associated with a specific data flow. It is carried in the Packet Data Protocol (PDP) context and is used by the network to route the data flow to the correct EPS bearer. The LBI is a 12-bit value, and it is assigned by the Serving Gateway (SGW) when a PDP context is established for the UE. The SGW allocates the LBI from a pool of available LBIs, and it ensures that each LBI is unique within the context of the PDP session.

When a UE sends a data packet to the network, it includes the LBI in the packet header. The network uses the LBI to identify the correct EPS bearer and apply the appropriate QoS characteristics. If the LBI is not included in the packet header, the network may not be able to identify the correct EPS bearer, and the data flow may be treated as a best-effort traffic flow, resulting in potential QoS issues.

The LBI is particularly useful in situations where a UE is communicating with multiple servers or applications, each with different QoS requirements. For example, a UE may be running a video conferencing application and a file transfer application simultaneously. The video conferencing application requires a high level of QoS to ensure that the video and audio quality is good, while the file transfer application can use a lower QoS. Without the LBI, the network may not be able to differentiate between the two data flows and may treat both of them as best-effort traffic, resulting in potential QoS issues.

The LBI also enables dynamic QoS management, which is particularly useful in situations where network conditions change rapidly. For example, if a UE is moving between different radio cells, the network may need to adjust the QoS characteristics of the EPS bearer to ensure that the UE continues to receive the appropriate QoS. With the LBI, the network can quickly identify the correct EPS bearer associated with a data flow and make the necessary QoS adjustments.

In addition to the above, the LBI also enables efficient network resource utilization. When a UE communicates with multiple servers or applications, each with different QoS requirements, the network needs to allocate resources accordingly. Without the LBI, the network may allocate resources based on the highest QoS requirement, resulting in potential resource waste. With the LBI, the network can allocate resources based on the QoS requirements of each data flow, resulting in more efficient resource utilization.

It is worth noting that the LBI is a network-side mechanism and is not visible to the UE or the application layer. The UE does not need to be aware of the LBI, and it does not need to perform any additional actions to use it. The LBI is transparent to the UE, and it is used by the network to provide the appropriate QoS for each data flow.

In conclusion, the Linked EPS Bearer Identifier (LBI) is an important mechanism introduced by the 3GPP to improve QoS management in mobile communication networks. The LBI provides a unique identifier for a specific data flow, which is associated with a particular application or service. It is used to ensure that the correct EPS bearer is used for each data flow and that the appropriate QoS characteristics are applied. The LBI enables dynamic QoS management, efficient network resource utilization, and is transparent to the UE and application layer. As mobile networks continue to evolve, the LBI will continue to play an important role in providing high-quality mobile services to users.