Radio Link Control (RLC) for LTE

This protocol sits between the MAC and PDCP layers in the LTE air interface (connecting an LTE UE with an eNodeB).

Protocol dependencies

The MAC-LTE dissector can call the RLC-LTE dissector for srb1 and srb2 (since it is known that these should be AM). For signalling PDUs, the RLC-LTE dissector can call PDCP-LTE for SRB channels, or LTE_RRC for CCCH channels. This is controlled by preferences (see below).

A UDP framing format for RLC-LTE has been defined (described in packet-rlc-lte.h, purely for use with Wireshark)

Example traffic

Wireshark

The RLC-LTE dissector is fully functional. There is support for reading RLC-LTE frames from:

• DCT2000 log files, or

• using the UDP format defined in packet-rlc-lte.h. This (BSD-licensed) program gives an example of how you might send RLC-LTE frames in this format. Note that you will need to enable rlc-lte-udp in order to decode these frames.

There is 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 -zrlc-lte,stats

Also available from the Telephony menu is an RLC Time/Sequence graph.

Preference Settings

• Do sequence analysis for AM channels. Can be done for either standalone RLC frames, or those found inside MAC frames. Default is OFF.
• Do sequence analysis for UM channels. Can be done for either standalone RLC frames, or those found inside MAC frames. Default is OFF.
• Call PDCP dissector for SRB PDUs. Default is OFF.
• Call RRC dissector for CCCH PDUs. Default is OFF.
• Try heuristic LTE-RLC framing over UDP. Default is OFF. Starting from Wireshark 2.0, heuristic activation is moved to Enabled Protocols window.
• May see RLC headers only. Default is OFF.
• Attempt SDU reassembly. Default if OFF. Will not currently work with out-of-order PDUs or resegmentation.

Example capture file

XXX - Add a simple example capture file to the SampleCaptures page and link from here (see below). Keep this file short, it's also a good idea to gzip it to make it even smaller, as Wireshark can open gzipped files automatically.

• SampleCaptures/PROTO.pcap

Display Filter

A complete list of RLC-LTE display filter fields can be found in the display filter reference

Show only the RLC-LTE based traffic:

 rlc-lte 

Capture Filter

You cannot directly filter RLC-LTE protocols while capturing.

External links

• 3GPP TS 36.322 Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link Control (RLC) protocol specification

• Example program that generates and sends frames using the supported UDP framing format

Discussion

It is recommended that you use current sources or a recent automated build for this and other LTE dissectors.

Imported from https://wiki.wireshark.org/RLC-LTE on 2020-08-11 23:23:59 UTC