RR (Subradio resource management sublayer)

The Subradio Resource Management Sublayer (RR) is a component of the GSM (Global System for Mobile Communications) protocol stack. It operates at the air interface level and is responsible for managing the radio resources in a GSM network. The RR sublayer is situated between the Radio Link Control (RLC) sublayer and the Baseband sublayer.

The main objectives of the RR sublayer are to establish and maintain a reliable and efficient radio link between the mobile station (MS) and the base station (BS), perform handover procedures between cells, manage radio channels, and control the allocation and release of radio resources.

Let's delve into the key functions and mechanisms of the RR sublayer:

1. Radio Channel Management: The RR sublayer manages the allocation and release of radio channels for voice and data communication. It ensures that the available radio resources are efficiently utilized and optimally allocated to MSs based on their needs. The RR sublayer is responsible for initiating the establishment of a dedicated channel (e.g., Traffic Channel, TCH) when a call is made or data transfer is required.
2. Call Setup and Teardown: The RR sublayer handles the procedures for call setup and teardown. When a user initiates a call, the RR sublayer coordinates with other network entities to establish the necessary signaling and traffic channels between the MS and the BS. Similarly, during call termination, the RR sublayer manages the release of the allocated resources.
3. Handover Management: Handover refers to the process of transferring an ongoing call or data session from one cell to another without interrupting the communication. The RR sublayer is responsible for executing handover procedures, ensuring seamless transition, and maintaining the quality of the communication. It monitors various parameters such as signal strength, quality, and interference to decide when to initiate a handover.
4. Cell Selection and Reselection: The RR sublayer assists the MS in selecting the most suitable cell to camp on and establish a connection. It periodically measures signal strength and other network-related parameters to determine the quality of neighboring cells. Based on these measurements, the RR sublayer advises the MS to reselect a new cell if the current connection quality deteriorates or a better cell becomes available.
5. Power Control: The RR sublayer is involved in power control mechanisms to optimize the transmit power of the MS. It adjusts the MS's transmit power based on factors such as signal quality, interference, and distance to the BS. The objective is to maintain a balance between conserving battery power and ensuring sufficient signal strength for reliable communication.
6. Paging and Location Update: The RR sublayer handles the paging and location update procedures for the MS. It manages the registration process when a mobile station initially enters a new area or changes its location. It also handles paging requests from the network to locate the MS when there is an incoming call or message.
7. Ciphering and Deciphering: The RR sublayer is responsible for ensuring the confidentiality and integrity of user data during transmission. It manages the ciphering and deciphering of voice and data streams using encryption algorithms. This ensures that the information exchanged between the MS and the BS is protected from unauthorized access.

In summary, the RR sublayer of the GSM protocol stack plays a crucial role in managing radio resources and maintaining reliable communication between mobile stations and base stations. It handles various tasks such as radio channel management, call setup and teardown, handover procedures, cell selection and reselection, power control, paging, location update, and ciphering.