Establishment sequence of each wireless bearer (SRB1, SRB2, DRB) when the RRC connection is established

Translated from http://bbs2.c114.net/home.php?mod=space&uid=918520&do=blog&id=4283 donnar of personal Space

    Radio Bearer (RB) is a series of protocol entities and configurations ENODEB for UE, including PDCP protocol entities, RLC protocol entities, Mac protocol entities, and PHY-assigned series of resources. RB is a channel for the UU interface to connect ENODEB and UE (including PHY, MAC, RLC, and PDCP), and any data transmitted on the UU interface must be RB. RB includes SRB and DRB,SRB are the channels that the system signaling messages actually transmit, and DRB is the channel that the user data actually transmits. SRB0 is the default bearer, and the host already exists when the UE is Rrc_idle. The
    RRC is the protocol entity that manages RB, which accomplishes the function of establishing, modifying and releasing RB through the interaction of RRC signaling. Popular speaking RRC connection refers to the UE and ENODEB established between the SRB1, because the standard provisions SRB0 is not required to establish, UE in the Rrc_idle state can obtain SRB0 configuration and resources, if necessary can be used directly. The process of business initiation in the system is through the SRB0 on the transmission signaling establishment SRB1,SRB1 after the establishment of the UE into the rrc_connected state, and then through the SRB1 transmission signaling set up SRB2 used to transmit the NAS signaling, using SRB1 transmission signaling set up DRB to transfer user data, In the business process through the SRB1 management; When the business is over, signaling transmitted on SRB1 can release all DRB and SRB, allowing the UE to enter the Rrc_idle state, the only resource that the UE can use when needed is SRB0, and it needs to be done after random access.
    rrcconnectionsetup messages are used to establish SRB1, wireless bearer SRB0, and the logical channel is CCCH,RLC-SAP is a TM. The
    rrcconnectionreconfiguration message is used to modify the RRC connection, the wireless-hosted SRB1, and the logical channel is DCCH,RLC-SAP is am.

RRC connections are established including the establishment of SRB1. E-utran completes the establishment of the RRC connection (build SRB1) before completing the S1 connection setup process, i.e. before receiving the UE context information from the EPC. As a result, as security will not be activated during the initial phase of the RRC connection.
When receiving the UE context from the EPC, E-utran uses the initial secure activation process to activate security (including encryption and integrity protection).
After the initial security activation process starts, E-utran initiates the establishment of SRB2 and DRB. These hosts are not established for SRB2 and Drb,e-utran until security is activated.

"Signaling Wireless Hosting" (SRB) is defined as the wireless Bearer (RB) that is used only for RRC and NAS message transmissions. More specifically, the following three types of SRB are defined:
-SRB0 for RRC messages, using CCCH logical channel;
-SRB1 is used for RRC messages (which may include NAS messages), and for NAS messages, SRB1 is established prior to SRB2, all using dcch logical channels;
-SRB2 for NAS messages, using DCCH logical channel. SRB2 is established after SRB1 and is always configured by E-utran after security activation.

Once security is activated, all RRC messages on SRB1 and SRB2, including those containing NAS or non-3GPP messages, are fully protected and encrypted by PDCP. NAS messages are built independently of each other using integrity protection and encryption.

Establishment sequence of each wireless bearer (SRB1, SRB2, DRB) when the RRC connection is established