In a wireless communication system, is responsible for processing user data transmitted and the stream is referred to as user plane protocol; protocol is responsible for transmitting and processing system of coordination is called control plane signaling. Responsible for user plane as dock workers handling the control plane is equivalent to the commander, when two levels are not separated, both responsible for their own transportation and is responsible for directing, this situation is not conducive to large cargo handling, so after the division of independence, efficiency can be increase exponentially, in the LTE network, user and control plane are clearly separated.
1.2 interfaces and protocols
Interface node information refers to the interaction between the different network elements, each containing a different protocol interfaces, the interface used between network elements of the same language understood mutually perform information interaction, called interface protocol architecture interface protocol called protocol stack. There terrestrial interface and the air interface in LTE, there is also a corresponding protocol stack and corresponding protocol.
LTE data processing system is broken down into different protocol layers. Simply divided into three layers: physical layer, data link layer L2 and a network layer. Figure 1 illustrates the overall system transmission path LTE protocol architecture and user plane and control plane information and data flow. User data and signaling flow stream in the form of IP packets transmitted prior to transmission over the air interface, the IP packet will be processed by a plurality of protocol layer entities, an eNodeB after arrival, protocol layer after the reverse process, and then through the S1 / X2 interfaces are EPS entity different flow paths in each sub-layer protocol features and functions as follows:
Protocol 1.2.1 NAS (Non-Access Stratum protocol)
Information transmission process between the UE and the MME, the content delivery may be user information or control information (e.g., business establishment, release or the mobility management information). It is independent of the access information, the access only through signaling interaction layer between the UE and the MME to establish a signaling pathway, to thereby be able to process the non-access stratum signaling.
NAS layer functions as follows:
- Session Management: includes session establishment, modification, release and QoS negotiation
- User management: management including user data, and adhesion, detach
- Security Management: includes authentication and encryption between the user and the network initialization
- Billing
1.2.2 RRC layer (Radio Resource Control Layer)
RRC layer is to support the most critical signaling protocol between the terminal and the eNodeB multiple functions. RRC features include:
- System message of the NAS layer and the layer AS
- Paging function (performed by the PCCH logical channel)
- RRC connection establishment, maintenance and release, comprising a temporary identifier allocated between the UE and E-UTRAN, signaling radio bearer configuration
- Security features, including key management
- End radio bearer establishment, modification and release
- 移动性管理，包括UE测量报告，以及为了小区间和RAT间移动性进行的报告控制、小区间切换、UE小区选择与重选、切换过程中的RRC上下文传输等
- MBMS业务通知，以及MBMS业务无线承载的建立、修改与释放
- QoS管理功能
- UE测量上报及测量控制
- NAS消息的传输
- NAS消息的完整性保护
1.2.3 PDCP层（分组数据汇聚协议层）
负责执行头压缩以减少无线接口必须传送的比特流量。头压缩机制基于ROHC。在接收端，PDCP协议将负责执行解密及解压缩功能。对于一个终端每个无线承载有一个PDCP实体。一个PDCP实体是关联控制平面还是用户平面，主要取决于它为哪种无线承载携带数据。PDCP层在控制面对RRC和NAS层消息进行完整性校验，在用户面不进行完整性校验。
PDCP层功能
- IP包头压缩与解压缩
- 数据与信令的加密
- 信令的完整性保护。
1.2.4 RLC层（无线链路控制层）
参考：https://wenku.baidu.com/view/4415bb9381c758f5f71f673f.html