I wanted to start a thread to address comments that were made on 11-25/621 which describes a mechanism for Enhance Frame Processing for UHR. Based on the minutes related to this contribution from the Monday June 2 meeting, we wanted to introduce a discussion on these topics.
1. Encryption of an MSDU and duplication of traffic on multiple links.
In MLO as specified in TGbe, an MSDU is assigned an SN at the MLD which means that block ACK agreement needs to be managed at the MLD. At the same time, encryption is performed at the MLD which means an MPDU is created at the MLD and the PN is assigned at the MLD. This means that a block ACK agreement applies across all setup links and from a practical point of view, encryption of MPDUs is dependent on the BA window of MSDUs.
With enhanced frame processing, which is proposed as an optional feature that can be negotiated between a non-AP MLD and an AP MLD, PN assignment and encryption is performed on MSDUs at the MLD and the encrypted MSDUs are sent to affiliated STAs for transmission. Block ACK agreements are negotiated for each setup link. Each BA agreement can be tailored to the bandwidth of the link it was negotiated on.
In some of the seamless roaming proposals, there were features that were proposed to ensure that no frames were lost in the process of transition. One benefit of Enhanced Frame Processing is that during transition, an encrypted MSDU, identified by a PN, could be transmitted by the current AP MLD and target AP MLD simultaneously during the transmission (for a short period of time). This feature is used by the receiver to minimize packet loss and reduce any latency with frames received during the transmission. The PN would be used for duplicate detection. We don't see this as a key feature of the proposal since it introduces frame processing and transmission overhead, but its certainly is one that could be leveraged for some use cases.
2. AAD and header information for MSDUs vs MPDUs
For encapsulation today, the AAD for CCMP and GCMP include:
From the FC field: Protocol version, type, protected bits are used.
- Address 1-4
- QoS Control, Note that priority is assigned to an MSDU
All of this information is available for the MSDU. We are willing to discuss modifications to the AAD for enhanced frame processing but for the most part, we do not believe it needs to be modified.
3. How does replay detection work
Replay detection for Enhanced Frame Processing works exactly the same as it would for MLO today. PNs are assigned to each MSDU to be encapsulated, the transmitter and receiver negotiate the number of replay counters and the receiver updates the replay counter as it successfully receives an encrypted MSDU. At this time, we do not believe we need to modify the requirements for replay detection. Although it might be advantageous for the transmitter and receiver to negotiate a replay counter per TID for data frames.
4. Issues addressed with this proposal
We are willing to work with others to update this proposal to address any issues and provide suggested feature updates.
Thanks,
Mike. Arik, Stephen, and Oren