Understanding LTE Model Internals and Interfaces

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1581 Understanding LTE Model Internals and InterfacesEPS BearerActivation/Deactivation/Modification• Bearers can be activated, deactivated, and modified on-the-fly• Activation:• Activation begins at the higher layer (NAS)• Both the network-initiated and UE-initiated cases supported• Deactivation:• Bearer deactivation can begin at the NAS or radio level• In OPNET, bearer deactivation is supported for idle bearers, which starts at theradio level at the eNodeB• Bearers can also be preempted, in which case, they are torn down from thesystem in a similar way as the inactive bearers• Modification:• Modification of the bearer’s QoS parameters is defined at the higher layer in thestandard (NAS)• In OPNET, QoS parameters are not modified at the EPS or radio level, althoughbearer modification message is used when it is rejected at the setup• In lab 1, bearer modification will be achieved at the radio layerCONFIDENTIAL ─ RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2010 OPNET Technologies, Inc.18
1581 Understanding LTE Model Internals and InterfacesAdmission Control in LTE• Starts at the NAS layer of the UE or the core network• A chain of ESM and RRC messages needs to be exchanged• Applicable only for the GBR bearers• Non GBR bearers are admitted by default• A brief functional overview• The core communicates EPS ID and QoS parameters of the bearer to the eNodeB• eNodeB S1 translates the EPS information to the radio information (EPS_ID RB_ID) for the eNodeB AS• eNodeB AS uses a custom procedure to calculate if this GBR bearer should be admittedby looking at the available radio resources• If the bearer can be admitted, the eNodeB AS exchanges RRC messages with the UEAS• Else the NAS at the core is informed about the rejection of EPS bearer• ESM messages are created for the core to indicate that the radio part of the bearer isactive• Finally, the core network starts sending traffic mapped to this bearerCONFIDENTIAL ─ RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2010 OPNET Technologies, Inc.19
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