What is NAS and RRC?

According to 3GPP TS 36.331, the RRC protocol includes the following main functions:

• Broadcast of system information:
  • NAS common information
  • Information applicable for UEs in RRC_IDLE, e.g., cell (re-)selection parameters, neighboring cell information and information (also) applicable for UEs in RRC_CONNECTED, e.g., common channel configuration information.
  • ETWS notification
• RRC connection control:
  • Paging
  • Establishment/modification/release of RRC connection, including assignment/modification of UE identity (C-RNTI), establishment/ modification/ release of SRB1 and SRB2, access class barring
  • Initial security activation, i.e., initial configuration of AS integrity protection (SRBs) and AS ciphering (SRBs, DRBs)
  • RRC connection mobility including intra-frequency and inter-frequency handover, associated security handling, i.e., key/ algorithm change, specification of RRC context information transferred between network nodes
  • Establishment/ modification/ release of RBs carrying user data (DRBs)
  • Radio configuration control including assignment/ modification of ARQ configuration, HARQ configuration, DRX configuration
  • QoS control including assignment/ modification of semi-persistent scheduling (SPS) configuration information for DL and UL, assignment/ modification of parameters for UL rate control in the UE, i.e., allocation of a priority and a prioritized bit rate (PBR) for each RB
  • Recovery from radio link failure
• Inter-RAT mobility including security activation, transfer of RRC context information
• Measurement configuration and reporting:
  • Establishment/modification/release of measurements (e.g., intra-frequency, inter-frequency and inter- RAT measurements)
  • Setup and release of measurement gaps
  • Measurement reporting
  • Other functions including transfer of dedicated NAS information and non-3GPP dedicated information, transfer of UE radio access capability information, support for E-UTRAN sharing (multiple PLMN identities)
  • Generic protocol error handling
  • Support of self-configuration and self-optimization

NOTE: Random access is specified entirely in the MAC including initial transmission power estimation.

Figure 1 :  RRC States (from 3GPP TS 36.331)

Signaling Radio Bearers (SRB) are defined as Radio bearers that are used only to transmit RRC and NAS messages. SRB’s are classified into three types:

Signaling Radio Bearer 0 (SRB0): RRC message using CCCH logical channel. Signaling Radio Bearer 1 (SRB1): is for transmitting NAS messages over DCCH logical channel.

Signaling Radio Bearer 2 (SRB2): is for high priority RRC messages. Transmitted over DCCH logical channel.

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Expectations for high-definition video content and cloud services on 5G networks will require huge increases in data transmission speeds. Users will expect high-throughput services to be available any time, anywhere.

5G networks will need to keep up with their users, whether those users are at home or on the go. That means extending high-quality coverage to users traveling in cars, high speed trains, and even airplanes.

New use cases mean that 5G networks will be transmitting and receiving even more data from even more devices. Compared to 2010, the new generation of mobile networks will need to support one thousand times the amount of traffic.

The Internet of Things and M2M communication are already creating a sharp increase in the number of connected terminals. Stadiums, events, dense urban areas, and disaster response will also require networks to support access on a massive scale.

5. Latency and Reliability

Developments in AR, VR, and M2M will enable new services for medical applications and real-time control of remote devices. For mobile networks to support these types of applications, they must achieve extremely low latency and maximum reliability.

Making IoT devices viable means reducing the volume and complexity of required signaling as much as possible. Simplifying signaling protocols will make devices cheaper and significantly extend their battery life.

The Radio Resource Control (RRC) protocol is used in UMTS, LTE and 5G on the Air interface. It is a layer 3 (Network Layer) protocol used between UE and Base Station. This protocol is specified by 3GPP in TS 25.331[2] for UMTS, in TS 36.331 [3] for LTE and in TS 38.331[4] for 5G New Radio. RRC messages are transported via the PDCP-Protocol.

The major functions of the RRC protocol include connection establishment and release functions, broadcast of system information, radio bearer establishment, reconfiguration and release, RRC connection mobility procedures, paging notification and release and outer loop power control.[5] By means of the signalling functions the RRC configures the user and control planes according to the network status and allows for Radio Resource Management strategies to be implemented.[6]

The operation of the RRC is guided by a state machine which defines certain specific states that a UE may be present in. The different states in this state machine have different amounts of radio resources associated with them and these are the resources that the UE may use when it is present in a given specific state.[6][7] Since different amounts of resources are available at different states the quality of the service that the user experiences and the energy consumption of the UE are influenced by this state machine.[7]

RRC inactivity timers

The configuration of RRC inactivity timers in a W-CDMA network has considerable impact on the battery life of a phone when a packet data connection is open.[8]

The RRC idle mode (no connection) has the lowest energy consumption. The states in the RRC connected mode, in order of decreasing power consumption, are CELL_DCH (Dedicated Channel), CELL_FACH (Forward Access Channel), CELL_PCH (Cell Paging Channel) and URA_PCH (URA Paging Channel). The power consumption in the CELL_FACH is roughly 50 percent of that in CELL_DCH, and the PCH states use about 1-2 percent of the power consumption of the CELL_DCH state.[8]

The transitions to lower energy consuming states occur when inactivity timers trigger. The T1 timer controls transition from DCH to FACH, the T2 timer controls transition from FACH to PCH, and the T3 timer controls transition from PCH to idle.[8]

Different operators have different configurations for the inactivity timers, which leads to differences in energy consumption.[9] Another factor is that not all operators use the PCH states.[8]

See also

• Radio Resource Management
• Mobility management
• Radio Network Controller
• UMTS
• WCDMA

References

1. ^ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 24 November 2021.
2. ^ 3GPP TS 25.331 Radio Resource Control (RRC); Protocol specification
3. ^ 3GPP TS 36.331 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification
4. ^ 3GPP TS 38.331 NR; Radio Resource Control (RRC); Protocol specification
5. ^ UMTS RRC Protocol specification (version 12.4.0 Release 12) (PDF), European Telecommunications Standards Institute, February 2015
6. ^ a b Pe´rez-Romero, Jordi (2005). Radio Resource Management Strategies in UMTS. John Wiley & Sons Ltd. p. 103. ISBN 0470022779. Retrieved 10 April 2015.
7. ^ a b Qian, Feng (November 2010). "Characterizing Radio Resource Allocation for 3G Networks" (PDF). Proceedings of the 10th ACM SIGCOMM conference on Internet measurement. Melbourne, Australia: ACM. pp. 137–150.
8. ^ a b c d Henry Haverinen, Jonne Siren and Pasi Eronen (April 2007). "Energy Consumption of Always-On Applications in WCDMA Networks" (PDF). In Proceedings of the 65th Semi-Annual IEEE Vehicular Technology Conference. Dublin, Ireland.
9. ^ L. de Bruynseels, “Tuning Inactivity Timer Settings in UMTS”, white paper, Commsquare Ltd., 2005

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