FRER MLO — IEEE 802.1CB Frame Replication and Elimination for Reliability over Wi-Fi 7 Multi-Link Operation

An OMNeT++ simulation framework implementing IEEE 802.1CB Frame Replication and Elimination for Reliability (FRER) on top of IEEE 802.11be (Wi-Fi 7) with Multi-Link Operation (MLO).

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Dependencies

Dependency	Version
OMNeT++	6.0.3
INET Framework	4.5.2
wifi-mlo-omnet	(see below)

MLO Base Framework

This project requires the MLO base framework as a linked OMNeT++ project:

https://github.com/tkn-tub/wifi-mlo-omnet

The Ieee8021CbStation and Ieee8021CbAccessPoint nodes extend MLOStation and MLOAccessPoint defined in that framework. Both projects must reside in the same OMNeT++ workspace and the MLO project (mlo) must be set as a referenced project in the build settings.

Building

This project is built using the OMNeT++ IDE (Eclipse-based):

1. Place this project folder, inet4.5/, and wifi-mlo-omnet/ side by side in your OMNeT++ workspace.
2. Import all three projects into the workspace.
3. Set project Makemake properties for this project:
   • Root: build mode (makemake), source location
   • simulations/ and src/: No makefile, C++ Source Folder
4. Add wifi-mlo-omnet as a referenced project under Project > Properties > Project References.
5. The MLO project should be set to library (static or shared) in its Makemake settings.
6. Build via Project > Build in the OMNeT++ IDE.

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Architecture

Design Overview

FRER is layered between the application and the MLO U-MAC. The Ieee8021rLayer (from INET) handles stream identification, replication, and duplicate elimination. The FRER-aware U-MAC steers each replicated member stream to a dedicated radio link. The 802.1CB layer is kept unmodified; compatibility with the MLO stack is handled entirely in the surrounding modules.

Application (UdpBasicApp / UdpSink)
          ↕
   Ieee8021rLayer   (stream identification, splitting, merging — INET)
          ↕
  Ieee8021CbUMac   (per-stream link steering — src/umac/)
       ↕                  ↕
   lmac[0]            lmac[1]        (per-link IEEE 802.11be — MLO framework)
   2.4 GHz             5 GHz

Uplink (STA → AP → STA): The sender replicates each FRER packet into k member streams, tags each copy with an R-TAG (IEEE 802.1r Redundancy Tag) carrying a sequence number, and routes each copy to a distinct radio link via the forwarding table. At the AP, the first arriving copy is decoded, merged, relayed, and then re-split into k member streams for the downlink. The second arriving copy is discarded by the stream merger. At the receiver, the first copy is accepted and the second is eliminated.

Modules

U-MAC (src/umac/)

• Ieee8021CbUMac — Extends the base UMac from the MLO framework. Implements FRER-aware packet routing:
  • No R-TAG present: packet has not yet passed through the 802.1CB pipeline — forwarded to the stream identifier for stream identification, sequence numbering, and splitting.
  • R-TAG present, stream identified: routes packet to the interface specified in forwardingTable.
  • R-TAG present, no stream: strips the R-TAG and forwards over the default interface (non-FRER frames).
  • At the AP on the downlink: converts StreamInd/SequenceNumberInd tags back to StreamReq/SequenceNumberReq so the 802.1CB layer can re-split the merged packet for downlink transmission over both links.

Relay (src/relay/)

• Ieee8021CbRelay — Extends INET's Ieee8021dRelay. Overrides lower-packet handling to preserve FRER-specific tags (StreamInd, SequenceNumberInd) when forwarding received frames, so that the U-MAC at the AP can identify and steer replicated streams correctly on the downlink.

L-MAC Portal (src/lmac/portal/)

• Ieee8021CbPortal — Extends INET's Ieee80211Portal. Overrides decapsulation to bridge the EPD/LPD header mismatch: the default WiFi LLC uses LPD-style framing, but FRER frames carry an EtherType-based R-TAG (EPD). The portal re-inserts the R-TAG into the reconstructed Ethernet frame and sets the required dispatch protocol tag so packets traverse the U-MAC correctly on the receive path.

Nodes (src/node/)

• Ieee8021CbStation — FRER-enabled Wi-Fi STA. Extends MLOStation with Ieee8021CbUMac and an Ieee8021rLayer for stream identification and duplicate elimination.
• Ieee8021CbAccessPoint — FRER-enabled Wi-Fi AP. Extends MLOAccessPoint with Ieee8021CbUMac, Ieee8021CbRelay, Ieee8021CbPortal (per-link portal), and an Ieee8021rLayer.

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Key Parameters

Parameter	Location	Description
umac.forwardingTable	U-MAC	Maps member stream names to outgoing interface names. E.g. {streamA1: "lmac0", streamA2: "lmac1"} routes each replica to a different link.
ieee8021r.policy.streamIdentifier.identifier.mapping	ieee8021r	Identifies application flows as named streams and enables sequence numbering. Supports flexible packet filter expressions (UDP/TCP ports, IP fields).
ieee8021r.policy.streamRelay.splitter.mapping	ieee8021r	Splits a stream into member streams (one per link). E.g. {streamA: ["streamA1", "streamA2"]}.
ieee8021r.policy.streamCoder.decoder.mapping	ieee8021r	Identifies member streams on the receive side by MAC address and receiving interface (interface-based matching is critical for MLO).
ieee8021r.policy.streamRelay.merger.mapping	ieee8021r	Merges member streams and eliminates duplicates (VRA-like SRF). E.g. {streamA1: "streamA", streamA2: "streamA"}. Set to empty target at the listener to remove R-TAGs.
ieee8021r.policy.streamRelay.merger.bufferSize	ieee8021r	VRA sequence window size. Must be set large (≥ 500; 10000 used in experiments) due to sequence number divergence from asymmetric link speeds and wireless retransmissions.
umac.defaultInterface	U-MAC	Default outgoing interface for non-FRER (SLO) packets.

Note on StreamRedundancyConfigurator: INET's built-in StreamRedundancyConfigurator cannot be used here because it enforces VLAN/PCP-based stream configuration, which does not apply to plain WiFi. All FRER mappings must be configured manually per node in omnetpp.ini.

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Simulation Scenarios

Scenarios are defined in simulations/omnetpp.ini. All configurations share a common [General] base: two MLO STAs and one MLO AP operating over 2.4 GHz (52 Mbit/s) and 5 GHz (130 Mbit/s) links, scalar radio propagation with log-normal shadowing, 15 s simulation time, and 10 repetitions.

Three MLO operating modes are compared across scenarios:

Mode	Description
FRER	Each packet is replicated and sent over both links; duplicate eliminated at receiver.
Link Aggregation	Frames distributed uniformly across links (RandomUMac from the base MLO project); no redundancy.
SLO	Single-link operation on the 2.4 GHz link only.

Configs

Config	Network	Description
SLO	BaseNetwork	Baseline: UDP traffic over a single link (default 2.4 GHz).
LinkAggregation	BaseNetwork	MLO without FRER: frames distributed randomly across both links.
FRER	BaseNetwork	Full FRER: each packet replicated over both links, duplicate eliminated at receiver. Failure scenarios (Scenarios 1–4 in the paper) are run under this config by enabling the ScenarioManager script (failure.xml).
Congestion	MixedNetwork	FRER flow coexists with background SLO traffic from additional MLOStation nodes. Network size is swept from 8 to 24 STAs.
Mobility	MixedNetwork	FRER under mobility: all nodes follow RandomWaypointMobility at 7–9 m/s across a 450 × 450 m area.

MixedNetwork extends BaseNetwork by adding arrays of plain MLOStation nodes (slo_sender_sta, slo_receiver_sta) as background traffic sources, parameterised by networkSize.

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Citation

If you use this framework in your research, please cite our paper:

@article{ergenc2026redundancy,
  author = {Ergen{\c{c}}, Do{\u{g}}analp and Reisinger, Tobias and Dressler, Falko},
  doi = {10.1016/j.comcom.2025.108373},
  title = {{Redundancy in WiFi 7: Combining Multi-link Operation with IEEE 802.1CB FRER}},
  journal = {Elsevier Computer Communications},
  issn = {0140-3664},
  publisher = {Elsevier},
  month = {2},
  volume = {247},
  year = {2026},
}

License

This project is licensed under the GNU Lesser General Public License v3.0 (LGPL-3.0). See LICENSE for details.