Radio Link Control Protocol Fundamentals and Features

Radio Link Control (RLC) is a protocol that plays a crucial role in wireless communication systems. It's responsible for managing data transfer between devices, ensuring reliable and efficient communication.

RLC is based on the concept of data segmentation, which involves breaking down large data packets into smaller, more manageable chunks. This allows for better error detection and correction, as well as improved data transfer rates.

RLC also includes a feature called Acknowledgment (ACK) and Negative Acknowledgment (NACK) mechanism, which ensures that data is correctly transmitted and received. If errors occur, the receiving device sends a NACK to the sender, who then retransmits the corrupted data.

RLC supports different data transfer modes, including Unacknowledged Data Transfer (UDT) and Acknowledged Data Transfer (ADT). UDT is used for applications that don't require error correction, while ADT is used for applications that require reliable data transfer.

Explore further: Global Alliance for Information and Communication Technologies and Development

The Radio Link Control (RLC) layer plays a crucial role in ensuring reliable data transfer over the air interface. RLC entities can be established in three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM).

RLC entities can perform various functions, including error correction through ARQ in AM mode. In TM and UM modes, a separate entity is used for transmission and reception, while in AM a single RLC entity performs both.

RLC entities receive RLC Service Data Units (SDUs) from the PDCP layer and send out RLC Protocol Data Units (PDUs) to the MAC layer. An RLC PDU contains an RLC header and the RLC SDU.

Here are the main functions of RLC entities:

RLC entities also perform other important functions, including segmentation and reassembly, concatenation, padding, and in-sequence delivery of upper layer PDUs.

The RLC (Radio Link Control) protocol is responsible for several key functions that ensure reliable and efficient data transfer over the air interface. One of its main functions is the transfer of upper layer PDU's, which involves breaking down large data packets into smaller ones for easier transmission.

RLC also performs error correction, which is crucial for maintaining data integrity. This is especially important over the air interface, where bit faults are common. In-sequence delivery of upper layer PDUs is another important function, which ensures that data packets are delivered in the correct order.

Additional reading: 5g Core Network Functions

RLC entities can be of three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). Each mode has its own specific set of logical channels, and the RLC sublayer can have multiple RLC entities, each of a specific mode.

Here are the main functions of RLC:

RLC entities can be established, re-established, or released, depending on the needs of the system. In TM mode, RLC entities are used for BCCH, PCCH, and CCCH channels, while in AM mode, they are used for DCCH channels.

In Wireshark, you can tweak your preference settings to customize your experience. The heuristic RLC over UDP framing setting is OFF by default, but you can try enabling it to see if it makes a difference.

This setting was moved to the Enabled Protocols window in Wireshark 2.0, so if you're running an earlier version, you won't see it there. The default setting for trying to reassemble SDUs is ON, which means you'll get the most out of Wireshark's capabilities.

If you choose to see RLC headers only, the default setting is OFF, so you won't see them by default.

Take a look at this: 5g Network T Mobile

Radio Link Control (RLC) modes are designed to handle different types of data transmission efficiently. There are three main modes: Transparent Mode, Unacknowledged Mode, and Acknowledged Mode.

Transparent Mode is suitable for carrying voice data, as it doesn't segment or reassemble RLC Service Data Units (SDUs), and no RLC headers are added. This mode is also reliable for carrying voice data.

Unacknowledged Mode is used for streaming traffic, where segmentation and reassembly of RLC SDUs occur, and RLC headers are added. However, no delivery guarantees are provided in this mode.

In Acknowledged Mode, segmentation and reassembly of RLC SDUs also occur, and RLC headers are added. This mode provides reliable in-sequence delivery service, making it suitable for carrying TCP traffic.

Here's a summary of the three modes:

NoStreaming trafficAcknowledged ModeYes

YesTCP traffic

In Transparent Mode, if segmentation is configured by upper layers and a RLC SDU is larger than the TMD PDU size, the transmitting TM RLC entity segments RLC SDUs to fit the TMD PDU size without adding RLC headers. All the TMD PDUs carrying one RLC SDU are sent in the same Transmission Time Interval (TTI), and no segment from another RLC SDU is sent in that TTI.

The RLC dissector can call the IP handle for data traffic and the RRC dissector for control messages. This allows for a more efficient and organized process.

The MAC-LTE dissector can call the RLC-LTE dissector for specific types of traffic. This is controlled by preferences, which can be customized to suit different needs.

RLC-LTE can call PDCP-LTE for SRB channels, or LTE_RRC for CCCH channels. This is a key aspect of the protocol dependencies in LTE networks.

Here are some key protocol dependencies to keep in mind:

Wireshark is a powerful tool for analyzing Radio Link Control (RLC) data, and it's fully functional for RLC-LTE.

The RLC-LTE dissector in Wireshark can read RLC-LTE frames from two sources: DCT2000 log files, or using the UDP format defined in packet-rlc-lte.h.

To decode RLC-LTE frames sent in UDP format, you'll need to enable rlc-lte-udp in Wireshark.

The LTE RLC stats window is available from the Telephony menu, and it's a useful tool for finding channels where problems are happening and setting display filters.

You can also access these statistics from the command line using tshark with the option -z rlc-lte,stats.

Additionally, the RLC Time/Sequence graph is available from the Telephony menu in Wireshark.

Wireshark is a powerful tool for analyzing network traffic, and it offers some great features for working with LTE data. The RLC-LTE dissector is fully functional, allowing you to read RLC-LTE frames from DCT2000 log files or using the UDP format defined in packet-rlc-lte.h.

One of the key benefits of using Wireshark is the ability to decode RLC-LTE frames, which can be sent in UDP format using a BSD-licensed program. This program provides an example of how to send RLC-LTE frames in this format, and you'll need to enable rlc-lte-udp to decode these frames.

Wireshark also offers an LTE RLC stats window, available from the Telephony menu. This can be useful for finding channels where problems are happening, and setting appropriate display filters.

The same statistics are available from tshark, using the option -z rlc-lte,stats. This can be a convenient way to access the same information without having to use Wireshark.

Wireshark's RLC Time/Sequence graph is also available from the Telephony menu, providing a visual representation of the data.

For another approach, see: Charging Data Record

Wireshark's display filter is a powerful tool for analyzing network traffic. You can use it to show only the RLC based traffic, which can be a huge time-saver when troubleshooting issues.

To access the display filter, you can refer to the display filter reference for a complete list of RLC display filter fields.

To show only the RLC based traffic, simply use the display filter fields available in Wireshark.

One of the most useful features of the display filter is that it allows you to show only the RLC-LTE based traffic, which can be especially helpful when analyzing LTE networks.

The display filter reference is a great resource to learn more about the available fields and how to use them.

By using the display filter, you can narrow down your analysis to specific types of traffic, making it easier to identify problems and optimize your network.

Here are some examples of display filter fields you can use:

Keep in mind that the display filter is just one of the many tools available in Wireshark for analyzing network traffic.

Wireshark is an incredibly powerful tool for analyzing network traffic, and one of the key aspects of understanding how it works is looking at example traffic.

Wireshark can decode a wide range of protocols, including the 3GPP TS 36.322 Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link Control (RLC) protocol specification.

The 3GPP TS 36.322 protocol is used in wireless communication systems, and it's essential to understand how it works when analyzing example traffic.

Wireshark can also generate and send frames using the supported UDP framing format, which is a key aspect of understanding how data is transmitted over the network.

Here are some examples of protocols and programs that can be used to generate and send frames:

5G NR Layer 2 is built on the same foundation as LTE, with the Radio Link Control (RLC) playing a crucial role in data transmission. The RLC has three main modes of operation: Transparent Mode (TM), Un-Acknowledge Mode (UM), and Acknowledge Mode (AM).

Each mode serves different logical channels, with TM and UM having separate RLC entities for transmission and reception side functionalities, while AM has a single RLC entity that handles both.

In TM mode, there is no processing of RLC data, only buffering until scheduling is done, then the PDU is transmitted. The RLC input data is identical to the RLC output.

In UM mode, the RLC entity does more functions compared to TM, but there is no feedback mechanism. UM mode is used for logical channels that don't require acknowledgement.

AM mode is similar to UM, but with the added functionality of ACK/NACK, which includes a re-transmission buffer and a PDU control procedure to provide feedback on received RLC PDUs.

The three modes are used for different logical channels, and each mode has its own unique characteristics and functionalities. Here's a quick summary of the modes and their functionalities:

The Radio Link Control (RLC) model is made up of several key components. At its core is the RLC sublayer, which is responsible for segmentation and reassembly of data.

The RLC sublayer has three main functions: segmentation and reassembly, transfer of user data, and SDU discard. These functions work together to ensure that data is properly handled and transmitted.

Segmentation and reassembly is the process of breaking down large data units into smaller segments, which are then reassembled at the receiving end. This is a crucial step in ensuring that data is transmitted efficiently.

The RLC sublayer also handles the transfer of user data, which is the actual data being transmitted between devices. This is the core purpose of the RLC model.

SDU discard is a function of the RLC sublayer that handles situations where data cannot be successfully transmitted. In these cases, the RLC sublayer will discard the data to prevent it from causing errors or conflicts.

Here are the three main functions of the RLC sublayer in a list format: