EPS Bearer Types And Its Composition
EPS Bearer Types
As each EPS bearer is able to provide only one definition of QoS, and users may use multiple services and the UE might have multiple EPS bearers in use and each offering various levels of QoS to various services. For instance, a person could be using a browser and also engaged in VoIP calls. This could require two distinct levels of QoS, the need for two EPS bearers with one bearer for each of the different traffic flows. In addition, signaling is necessary to provide the services, and this could require the use of a third EPS bearer.
In all cases, LTE will always assign the default bearer of EPS. The bearer is defined and allocated once the UE is registered successfully in the system. The information about the context of bearer identities along with QCI information for default bearers is kept in the EPC until the UE is registered. However, when the UE is in idle mode, the default bearer remains inactive. In this situation, there aren’t any allocated resources in the EPS bearer in the air interface, or in the E-UTRAN.
An EPS is the union that a radio bearer via the air interface as well as an S1 bearer, and the S5/S8 bearer. Each bearer is described in a slightly different manner and the binding between these bearers is available at every node. Particularly, the connection between the radio bearer that is on the S1 interface as well as an air bearer in the S1 interface that is present in the eNB, is the E-RAB (E-UTRAN Radio Access Bearer). The E-RAB then is bound by an S5/S8 bearer inside the S-GW, and the combination of these two bearers is a bearer for EPS.
When an EPS has been identified, the packets that are related to that EPS bearer should be recognized and mapped. This is done through the TFT (Traffic Template for Flows) Template) functions described by the UE for uplink traffic flow and in the PDN-GW to handle downlink traffic flows. The TFT used by an EPS can identify packets related to a specific service by using TCP as well as UDP ports or DiffServ code indicates.
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