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Re: [STDS-802-11-TGBE] Discussions on tentative reassociation



Hi Guogang,

 

There are two mainly issues on your proposal, one is on STA side, as you confirmed, STA need to keep two copies of AP info, Key info and so on, it will be more complicated compared to current design. On the other hand, it not allowed to set up two links with ESS through two different APs(current and target AP) in current design. Because it will cause a lot of management issue if ESS system found the STA archor on two different APs.  We may let the current AP sent deauth/disconnect to the STAs if found the STA set up another link with target AP.

 

On the other hand, both current AP and target AP will have the STA’s data structure in MAC layer in this moment. That’s to say, MLD STA may have two links with the mesh network(or ESS system) in model 1, it will bring a lot of management issues from the system perspective.

[Guogang Huang] After the target AP MLD sends DS-STA-NOTIFY.request primitive to DS, the DS will deliver the MSDU addressed to this non-AP MLD to the target AP MLD, rather than the current AP MLD. Because the STA-AP routing info is updated.

à<Jay> No, not such a simple logic as you said, STA-AP routing may switch back to the current AP if the link is still alive.

 

 

 

Thanks

 

Best Regards

 

Jay Yang

 

From: huangguogang <huangguogang1@xxxxxxxxxx>
Sent: 2020
730 9:44
To: Yang, Zhijie (NSB - CN/Shanghai) <zhijie.yang@xxxxxxxxxxxxxxx>; STDS-802-11-TGBE@xxxxxxxxxxxxxxxxx
Subject:
答复: Discussions on tentative reassociation

 

Hi Jay Yang,

 

Thank you for your discussion. Please see the response inline. If you have further comments or questions, please let me know.

 

 

Regards

Guogang Huang

Huawei Technologies Co.,Ltd.

 

发件人: Yang, Zhijie (NSB - CN/Shanghai) [mailto:zhijie.yang@xxxxxxxxxxxxxxx]
发送时间: 2020730 7:05
收件人: huangguogang <huangguogang1@xxxxxxxxxx>
主题: RE: Discussions on tentative reassociation

 

Hi Guanggang,

 

There are mainly two different roaming models, I don’t know which one you prefer in your contribution.

 

      cid:image001.png@01D6663F.CC129130                                   cid:image003.png@01D6663F.CC129130

 

[Guogang Huang] I only consider the Model 1 in my contribution.

 

 

In Slide 6:

 

Then the STA can negotiate with the new AP to set up the correct conditions for data connectivity, while still using the old AP for data connectivity

 

I remember 11be STA can’t set up connection with two different MLD APs at the same time, I’m afraid your thought will beak this principle.  

 

[Guogang Huang] The reason that the STA only can associate with one AP is that the DS need to know “which AP is serving this STA”.  The answer to this question needs to be unique. When successfully exchanging Association Request/Response with Status code SUCCESS, the AP will send DS-STA-NOTIFY.request primitive to the DS. If the target AP doesn’t send this primitive to the DS, the STA still associate with the current AP. Because the STA-AP routing info isn’t updated. I also mentioned it in slide 4.

 

In Silde 14.

 

From the diagram, I guess it’s not 11R fast roaming case since I see 4-way handshake happened with the target AP MLD. Correct?

[Guogang Huang] Yes, it is the BSS transition using PMK caching, rather than  fast BSS transition. The fast BSS transition is shown in slide 15.

 

In this case, STA need to keep two copies of PTK,GTK and even IP address with two different MLD APs. IP address is not always the same especially in model2.

[Guogang Huang] Yes, the STA can maintain two copies of PTK and GTK. For the Model 1 mentioned, I’m pretty sure that the IP Address will not changed. Otherwise, all the upper layer connections need to be re-setup.

 

 I think your proposal is to get more DL traffic from current AP MLD, how do you consider the UL traffic in this moment?  It’s too complicated on STA side compared to current design.

[Guogang Huang] Note that the STA cannot receive DL traffic from the current AP MLD and transmit the uplink traffic to the target AP MLD simultaneously. What I mean is that after the STA sends a frame to trigger AP to send DS-STA-NOTIFY.request primitive, the data connection will completely switch from the current AP MLD to the target AP MLD. I think you misunderstood my proposal.

 

On the other hand, both current AP and target AP will have the STA’s data structure in MAC layer in this moment. That’s to say, MLD STA may have two links with the mesh network(or ESS system) in model 1, it will bring a lot of management issues from the system perspective.

[Guogang Huang] After the target AP MLD sends DS-STA-NOTIFY.request primitive to DS, the DS will deliver the MSDU addressed to this non-AP MLD to the target AP MLD, rather than the current AP MLD. Because the STA-AP routing info is updated.

 

I also mentioned that traffic switch issue in the call. For model 1, It’s necessary to give the AC a clear signal of the archor AP of the STA so that the AC knows which ethernet port is used for the DL traffic delivery for STA.  What’s your opinion in the two links case?

[Guogang Huang] The non-collocated MLD is pretty complicated. I didn’t touch this topic.

 

 

 

Note: Two links case diagram as bellow, it doesn’t mean STA MLD have two links with same AP MLD.

cid:image005.png@01D6663F.CC129130

 

 

 

Thanks

 

Best Regards

 

Jay Yang

 

From: huangguogang <huangguogang1@xxxxxxxxxx>
Sent: 2020
730 0:31
To: Yang, Zhijie (NSB - CN/Shanghai) <
zhijie.yang@xxxxxxxxxxxxxxx>
Subject: Discussions on tentative reassociation

 

Hi Zhijie Yang,

 

Thank you for your comments. Maybe I miss something during the call. If you have comments or questions, please send email to me.

 

 

Regards

Guogang Huang

 

 


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