本网存在大量national roaming的用户，当这些用户从漫游网回到本网LTE的时候发起TAU时QCI为7（继承漫游网配置），TAU成功后本网EPC发起ERABModifyRequest（因为本网的默认承载QCI6）.
但是根据S1 trace，eNB收到ERABModifyRequest之后直接拒绝了修改ERAB，Response给EPC告知ERABModify Failure子原因 Radio Network - Cause unspecified.
5.3.5.8 Radio Configuration involving full configuration option
The UE shall:
1> release/ clear all current dedicated radio configurations except the C-RNTI, the security configuration and the PDCP, RLC, logical channel configurations for the RBs and the logged measurement configuration;
NOTE 1: Radio configuration is not just the resource configuration but includes other configurations like MeasConfig and OtherConfig.
1> if the RRCConnectionReconfiguration message includes the mobilityControlInfo:
2> release/ clear all current common radio configurations;
2> use the default values specified in 9.2.5 for timer T310, T311 and constant N310, N311;
1> else:
2> use values for timers T301, T310, T311 and constants N310, N311, as included in ue-TimersAndConstants received in SystemInformationBlockType2;
1> apply the default physical channel configuration as specified in 9.2.4;
1> apply the default semi-persistent scheduling configuration as specified in 9.2.3;
1> apply the default MAC main configuration as specified in 9.2.2;
1> for each srb-Identity value included in the srb-ToAddModList (SRB reconfiguration):
2> apply the specified configuration defined in 9.1.2 for the corresponding SRB;
2> apply the corresponding default RLC configuration for the SRB specified in 9.2.1.1 for SRB1 or in 9.2.1.2 for SRB2;
2> apply the corresponding default logical channel configuration for the SRB as specified in 9.2.1.1 for SRB1 or in 9.2.1.2 for SRB2;
NOTE 2: This is to get the SRBs (SRB1 and SRB2 for handover and SRB2 for reconfiguration after reestablishment) to a known state from which the reconfiguration message can do further configuration.
1> for each eps-BearerIdentity value included in the drb-ToAddModList that is part of the current UE configuration:
2> release the PDCP entity;
2> release the RLC entity or entities;
2> release the DTCH logical channel;
2> release the drb-identity;
NOTE 3: This will retain the eps-bearerIdentity but remove the DRBs including drb-identity of these bearers from the current UE configuration and trigger the setup of the DRBs within the AS in Section 5.3.10.3 using the new configuration. The eps-bearerIdentity acts as the anchor for associating the released and re-setup DRB.
1> for each eps-BearerIdentity value that is part of the current UE configuration but not part of the drb-ToAddModList:
2> perform DRB release as specified in 5.3.10.2;
