5G/NR - 无线电协议栈架构_5g无线协议栈
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在5G网络中，NR（New Radio）是指5G的无线接入技术。该技术包括一个分层的无线协议栈，用于在无线接口上进行通信。
这个协议栈包括以下几个主要的层级：
物理层（Physical Layer）：负责无线信号的调制、解调、编码和解码。它定义了无线传输的基本参数和方式，如调制方式、载波频率等。
MAC（Medium Access Control）层：负责无线接口上的数据分帧和调度。它控制无线资源的访问和分配，确保多个用户之间的公平共享和高效利用。
RLC（Radio Link Control）层：提供无线链路上的可靠数据传输和错误检测。它分为不同的模式，如确认模式（AM）、未确认模式（UM）和透明模式（TM）等，以满足不同的传输需求。
PDCP（Packet Data Convergence Protocol）层：确保无线接口上的数据传输的安全性和可靠性。它负责压缩和解压缩数据、加密和解密数据，并处理延迟等问题。
SDAP（Service Data Adaptation Protocol）位于PDCP层和IP层之间。
SDAP层的主要功能是为不同类型的业务流量提供适当的服务质量（QoS）标记和优化处理。它从上层协议（例如IP层）接收数据流，并根据业务要求为其分配适当的处理参数，如传输延迟、抖动和优先级等。然后，SDAP层与PDCP层进行交互，将标记的数据流传递给PDCP层。 PDCP层使用这些标记信息来有效地处理和传输数据流，确保满足其所需的服务质量。
IP（Internet Protocol）层：位于协议栈的最顶层，负责网络层的路由和数据传输。它为数据包分配IP地址，并将数据包路由到目标IP地址。
5G/NR - Radio Protocol Stack Architecture
Radio Protocol Stack Architecture
NR Radio Protocol Stack Architecture is almost same as LTE Radio Protocol Stack Architecture. If you are already familiar with LTE protocol stack or general concept of radio protocol stack, you would not need to spend too much time in reading this page. Just take a brief look at the various figures / diagrams shown in this page would be enough. If you are new to the concept of LTE/NR radio protocol stack, I would suggest you to go through this page whenever you have chance and try to form your own big picture.
I would not describe much details on each component of the protocol stack in this page. It is too much to describe everything in a single page. The purpose of this page is to provide you with some big picture or intuitive understanding of the radio protocol stack. Most of the fundamental idea in this page comes from 3GPP 38.300.
As in LTE / WCDMA, NR radio protocol stack has two different stack depending on the type of data that is processed by the stack. If the data is Signaling message, it goes through the C-plane stack and if it is user data, it goes through U-Plane stack. Both U-Plane and C-Plane is made up of a common structure : PHY <-> MAC <-> RLC <-> PDCP, but the components sitting on top of PHY/MAC/RLC/PDCP gets different between C-Plane and U-Plane. In case of U-Plane, a layer called SDAP is sitting at the top of the radio stack and the SDP is connected to UPF (User Plane Function). In case of C-Plane, the two layers RRC and NAS are sitting at the top of the stack. NAS layer gets connected to AMF (Access and Mobility Management Function).
What I've mentioned can be described in a block diagram as shown below.
Now let's look just one step further into the protocol stack. Take a look at the L2 (layer 2) structure of the NR U-Plane radio protocol. The structure of L2 downlink stack can be illustrated as shown below. Except the new layer called SDAP, you would notice that the overall structure is almost identical to LTE L2 structure. NR support carrier aggregation from the beginning, data for each carrier is processed separately for each carrier in SDAP, PDCP, RLC and multiplexed/scheduled in the common MAC layer. This is also same as LTE Rel 10 or higher.
Following is L2 structure of NR U-Plane Uplink radio protocol. Basic structure is same as downlink structure except that Uplink does not support carrier aggregation.
