Re: [DESIGN RFC] wifi: Robust AV streaming Design Proposal for AP

[Ben Greear <greearb@candelatech.com>]

On 7/1/25 12:38, Ramanathan Choodamani wrote:
> 
> 
> On 6/24/2025 3:31 PM, Ben Greear wrote:
>> On 6/24/25 13:57, Ramanathan Choodamani wrote:
>>> ===================================
>>> Robust AV streaming protocols - QoS
>>> ===================================
>>>
>>> The Robust AV stream protocols are mobile centric protocols - meaning they
>>> are initiated by a non-AP STA to the AP. These protocols are implemented
>>> at the Access Point (AP) to classify packets sent to the non-AP STA which requests
>>> classification using action frames. The non-AP STA initiates Robust AV streaming
>>> action frames requesting for specific classification for the IP packets
>>> destined to the non-AP STA from the AP. These parameters can be negotiated by both
>>> AP and non-AP STA.
>>>
>>> Upon successful handshake, The AP classifies incoming individually addressed MSDUs
>>> (Mac Service Data Unit) based upon parameters provided by the non-AP STA or
>>> notifies the non-AP STA to transmit MSDUs with preferred parameters based upon
>>> what was exchanged.
>>>
>>> Robust AV streaming improves AV (Audio and Video) streaming performance when
>>> using IEEE Std 802.11 for consumer and enterprise applications.
>>>
>>> Let's look at the Robust AV streaming protocols which are implemented as a
>>> part of this design.
>>
>> Thank you for posting this and for the beautiful ascii diagrams!
>>
>> Since this will be poking netfilter rules into the kernel,
>> is there a good way to clean up all rules created by a previous
>> hostapd process in case hostapd crashes or is killed hard and
>> cannot do its own cleanup?  Maybe the rules could have some
>> special marking that is configurable per hostapd (or per AP or BSS or something)
>> so that a (re)started hostapd could clean up any leftovers from a
>> previous instance?
>>
> hostapd does its own cleanup (cleanup of stations and interfaces)
> when it receives SIGTERM.

hostapd could crash without being able to clean up, though.
So I think you need a way to query the kernel's state and
clean it up in this case.

> An nft chain is created for each AP netdev/interface.
> 
> The nft rule handle (stored in internal hostapd data structure) and
> nft chain metadata can be used to cleanup/flush the nft rules as part of the
> interface cleanup.
> 
>> And, is there a mechanism to clean up flows that a buggy non-AP STA
>> has requested but then forgot to terminate (like phone starts a video call,
>> requests some QoS, then forgets to tell AP that it is done with the call
>> and packets no longer need to be classified?)
>>
>> Thanks,
>> Ben
>>
> The scs objects of the stations will be cleaned up during the station
> disconnect (by the AP which is maintaining them).
> As part of this deletion, the nft rules are also deleted, using the
> stored nft rule handle.

A station may be long lived, and it may be bad at cleaning up
its sessions, so the AP may end up with a large amount of classification rules
that are not actually needed, possibly slowing down performance
and/or limiting other stations from being able to add their own
flows.

Can you add time duration and/or detect idle flows and clean them
up automatically on the AP?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com