What is Radio Resource Control (RRC)?
We know that in mobile communication, radio resource management is a very important link. First, let me introduce what is radio resource control (RRC).
The mobile phone and the network communicate with each other through the wireless channel and exchange a large amount of information with each other. Therefore, the two parties need a control mechanism to exchange configuration information and reach an agreement. This control mechanism is RRC, that is, radio resource control. We can understand it as a terminal UE A common language for communicating with the network. This language enables the network and the user terminal UE to cooperate tacitly.
In 5G, the main services and functions of the RRC sublayer include:
- broadcast system information related to AS and NAS;
- Paging initiated by 5GC or NG-RAN;
- Establish, maintain and release RRC connection between UE and NG-RAN, including:
Addition, modification and release of carrier aggregation;
- Add, modify and release dual connectivity within NR or between E-UTRA and NR.
Security features include key management;
-Establishment, configuration, maintenance and release of Signaling Radio Bearer (SRB) and Data Radio Bearer (DRB);
- Mobile features include:
- Handover and message transfer;
- UE cell selection and reselection and control of cell selection and reselection;
- Inter-RAT mobility.
-QoS management function;
-UE measurement report and control report;
- Detection and recovery of radio link failures;
- NAS transmits NAS messages to/from UE.
Compared with 4G (LTE) RRC, do you think there are any similarities and differences?
1. Protocol Architecture
From the perspective of the organizational structure of the RRC protocol, 5G (NR) is very similar to the protocol. The names of the specific chapters are still almost the same, and the key elements are still RRC connection establishment, RRC reconfiguration, authentication, encryption, bearer establishment, etc. Some of these information elements are slightly different because 4G parameters and 5G equivalents are required in some places.
2. Wireless measurement
Measurement configuration in 5G(NR) networks is still done in the same way as measurement objects and report configuration, and the actual measurement instructions that bind them together still exist. Events A1 to A6 and B1+B2 look very familiar and serve the same purpose as in LTE.
3. System message
MIBs and SIBs also serve the same purpose, but they are handled slightly differently. While MIB and SIB1 are always broadcast periodically, all other SIBs do not necessarily have to be broadcast , but can be requested by a terminal (UE) after it connects to a cell. If the cells will actually be configured this way or they will be broadcast as well.
4. RRC-Inactive
This is an RRC state that does not exist in 4G (LTE), and it is located between the RRC-Idle and RRC-Connected states. In this state, the terminal (UE) is allowed to release the radio bearer, but at the same time, the signaling connection from the user to the core network and the user data tunnel are reserved. This will be used a lot in 5G(NR) networks, as today's core network connections in the modern smartphone world are often set up and torn down, while many applications run in the background, they need to be kept alive to keep their TCP connections open state.
5. Counter Check ( Counter Check )
This is already defined in 4G (LTE). The specification states that networks can use the process to check how much data a device thinks has transmitted so far, which is then compared to counters based on the same network. This allows detection of packet insertion attacks. The spec doesn't say if and how this process is actually used, but I still find it interesting that someone took the time to specify this.
Three states of 5G radio resource control
RRC supports three states on 5G NR, RRC_IDLE, RRC_INACTIVE, RRC_CONNECTED . Yes, 5G is not the same as 3G/4G. Compared with 4GLTE, there are only two RRC states of RRC IDLE and RRCCONNECTED. 5G NR introduces a new state—— RRC INACTIVE.
Why does 5G introduce the RRC INACTIVE state?
The reason is simple, in order to reduce signaling and power consumption. 5G is geared toward the Internet of Everything, and it needs to connect a large number of battery-powered terminals. The battery life of these terminals needs to be maintained for 5-10 years, otherwise the maintenance cost will be too high. At the same time, mission-critical IoT requires ultra-low latency. When a task is triggered, the first data packet must be quickly transmitted to the network or terminal. In addition, under the large-scale Internet of Things, a large number of devices transmit a small amount of data sporadically, which will bring excessive signaling overhead.
On the one hand, it is necessary to reduce the power consumption of user equipment, on the other hand, it is necessary to quickly access, reduce the delay, and at the same time reduce the signaling overhead. It is necessary to take into account the three (there are so many requirements for 5G), and 5G introduces the RRC INACTIVE state.
In the RRC INACTIVE state, the terminal is in a power-saving "sleep" state, but it has to be on standby at any time, so it still retains part of the RAN context (security context, UE capability information, etc.), always keeps connected to the network, and can pass similar The paging message is quickly transferred from the RRC INACTIVE state to the RRC CONNECTED state, and the amount of signaling is reduced.
It should be pointed out that for the RRC state, 3GPP is still continuing to study so far, that is, the above FFS (to be studied in the future), that is, whether the network is always configured with a RAN-based notification area under RRC_INACTIVE, and if it is determined that it is not always configured based on RAN In the notification area, continue to study UE behavior in the future to achieve the goal.
The figure below shows the network status transition between 5G and 4G networks.
These three states are characterized as follows:
RRC_IDLE (idle mode):
PLMN selection;
broadcast system information;
Cell reselection mobility;
Paging for mobile terminated data is initiated by 5GC;
Paging in the mobile terminated data area is managed by 5GC;
DRX configured by NAS for CN paging.
RRC_INACTIVE deactivation mode :
PLMN selection;
broadcast system information;
Cell reselection mobility;
Paging is initiated by NG-RAN (RAN paging);
RAN based notification area (RNA) managed by NG-RAN;
RAN paging DRX configured by NG-RAN;
Establish 5GC-NG-RAN connection for UE (including control plane/user plane);
UE AS messages are stored in NG-RAN and UE;
The NG-RAN knows the RNA to which the UE belongs.
RRC_CONNECTED (connected mode) :
Establish 5GC-NG-RAN connection for UE (including control plane/user plane);
UE AS messages are stored in NG-RAN and UE;
NG-RAN knows the cell to which the UE belongs;
transmit unicast data to or from UE;
The network controls mobility, including metering.
Well, this is the brief introduction to 5G radio resource control. Then there are some similarities and differences between the 5G and 4G RRC (Radio Resource Control) protocols.
Here are some differences and similarities between them.
Different score
1. Goal: Both 5G and 4G are mobile communication technologies designed to provide wireless communication services. Their RRC protocols are used to control functions such as radio resource allocation, power control, and mobility management.
2. Architecture: There are certain differences between the network architectures of 5G and 4G. 4G adopts a layered structure, including radio access network (RAN) and core network (CN). 5G adopts a cloud-native architecture, in which the boundaries between RAN and controller (RAN-C) and core network (CN) are blurred. This means that the 5G RRC protocol may involve more interfaces and protocols.
3. Spectrum efficiency: Compared with 4G, 5G has higher spectrum efficiency, which is mainly realized through higher modulation and coding technology, better channel utilization and resource allocation algorithm. This leads to the 5G RRC protocol requiring more advanced algorithms and mechanisms to achieve higher performance.
4. Features: The 5G RRC protocol has lower delay, greater capacity and wider coverage, which is mainly due to the design of 5G for massive MIMO (Massive MIMO), beamforming (Beamforming) And the application of new scheduling/resource allocation algorithms.
5. Functionality: Both protocols need to handle functions in mobility management, wireless connectivity management, power control, resource allocation, etc. However, the RRC protocol of 5G also supports more functions, such as low-latency communication, large-scale Internet of Things connection, etc.
6. Security: 5G's RRC protocol is more challenging in terms of security, and strengthens the requirements for identity authentication, data encryption, and terminal device security to deal with more complex network security threats.
the difference
1. Frequency bands: 4G primarily operates on LTE frequency bands (e.g. 700 MHz, 2.6 GHz, etc.), while 5G operates on higher frequency bands (e.g. millimeter wave bands). Therefore, the 5G RRC protocol requires a greater degree of spectrum planning and management.
2. Management division: The 5G RRC protocol introduces a new concept of management division, which divides wireless resources into Cells and Service Areas to support finer resource control, capacity management, and interference coordination.
3. Configurability : The 5G RRC protocol provides more flexible configuration options, which can be customized for different application scenarios to meet different business needs.
To sum up, although the RRC protocols of 5G and 4G have some commonalities, they are different in terms of architecture, spectrum utilization, functions, and security, mainly due to the goal of 5G to further improve wireless communication performance and capabilities.
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