请教关于Bearer Context数量的问题

hxp_hust

create session并不是只在开机就有，在协议上是这样说的
The Create Session Request message shall be sent on the S11 interface by the MME to the SGW, and on the S5/S8 interface by the SGW to the PGW as part of the procedures:
-        E-UTRAN Initial Attach
-        UE requested PDN connectivity
The message shall also be sent on S4 interface by the SGSN to the SGW, and on the S5/S8 interface by the SGW to the PGW as part of the procedures:
-        PDP Context Activation
The message shall also be sent on the S11 interface by the MME to the SGW as part of the procedures:
-        Tracking Area Update procedure with Serving GW change
-        S1/X2-based handover with SGW change
-        UTRAN Iu mode to E-UTRAN Inter RAT handover with SGW change
-        GERAN A/Gb mode to E-UTRAN Inter RAT handover with SGW change
-        3G Gn/Gp SGSN to MME combined hard handover and SRNS relocation procedure
-        Gn/Gp SGSN to MME Tracking Area Update procedure
and on the S4 interface by the SGSN to the SGW as part of the procedures:
-        Routing Area Update with MME interaction and with SGW change
-        Gn/Gp SGSN to S4 SGSN Routing Area Update
-        Inter SGSN Routeing Area Update Procedure and Combined Inter SGSN RA / LA Update using S4 with SGW change
-        Iu mode RA Update Procedure using S4 with SGW change
-        E-UTRAN to UTRAN Iu mode Inter RAT handover with SGW change
-        E-UTRAN to GERAN A/Gb mode Inter RAT handover with SGW change
-        Serving RNS relocation using S4 with SGW change
-        Combined hard handover and SRNS relocation using S4 with SGW change
-        Combined Cell / URA update and SRNS relocation using S4 with SGW change
-        Enhanced serving RNS relocation with SGW relocation
这个消息是用来建立默认承载的，在E-UTRAN Initial Attach和UE requested PDN connectivity会有这个消息，默认承载可以有多个，不同的PDN连接有不同的默认承载，同时在各种更新和切换中都会有这条消息，你看一下相关的流程（23.401）就知道了。