All, Can I suggest we “pop up a level” on this discussion? I note that this all seems to have come from CID 3085, and the proposed resolution that currently includes the text, “An IRM is a random MAC address that is constructed from the locally administered address space. A non-AP STA should shall construct randomized IRMs according to IEEE Std 802-2014 and IEEE Std 802c-2017.” I _think_ the concern is whether or not this text should explicitly mention the AAI quadrant, from IEEE Std 802c-2017. Is that correct, that this whole discussion about the number of bits to be randomized, and the resulting probability analysis, comes down the question of whether we mention the AAI quadrant or not? Or, does someone have another concern that is embedded in this discussion? If that’s correct, and that is our concern (whether how to mention IEEE Std 802c-2017, and explicitly the AAI quadrant or not), then can I suggest that we should (can) defer to our baseline, and make this question of “how random does an IRM need to be?” match the same answers we already have for 802.11aq randomized MAC Addresses in general. Specifically, I would suggest that we modify the text quoted above (to become part of the CID 3085 resolution), to instead say something like: “An IRM is a random MAC address that is constructed from the locally administered address space. A non-AP STA should shall construct randomized IRMs according to the rules for constructing any randomized MAC address, per 12.2.10.” (And, this implies that we (TGbh) don’t need to get into the business of how these rules are framed – if there are any concerns with 802.11’s use of randomized MAC addresses, that can be addressed with comments on the 12.2.10 text.) Thoughts? Mark From: Harkins, Dan <daniel.harkins@xxxxxxx>
Sent: Monday, 3 June, 2024 14:54
To: STDS-802-11-TGBH@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11-TGBH] 46 or 44 bit IRMs Hi Graham, I don't believe that associating 3x a day makes it 44 days for a 0.5 probability of collision. If these STAs are associating 3x per day that means they are disassociating as well. They do not maintain their old MAC addresses for any period of time and a MAC address that is used by a STA at some slice of time is not fixed such that other STAs in their 3x per day associating will collide with it if they happen to choose it. We're talking about the probability of 2 STAs *simultaneously* choosing the same MAC address. If it's 9000 STAs then it doesn't matter if they associate once per day or 3x per day. If I chose a particular MAC address, disassociated, and then you came along later in the day and randomly selected the same MAC address it's not a collision. The fact we chose the same MAC address *at different times* does not matter. The odds are not 1 in 1747993 per association, they are 1 in 1747993 period. regards, Dan. -- "the object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." – Marcus Aurelius Dan is correct. The relationship between probability and odds is “1 in (1-P)/P”, which in this k=9000 case, the odds of a duplicate is 1 in 1747993 per association. If we say 1 association per day then this probability means once every 137 years there is a 50% chance of a duplicate (401448 Associations). But, as I tried to point out in my contribution (23/2148r1), this is not the whole story. Every time a STA associates to any AP in an ESS there is a chance of a duplicate, so if the STA associates 3 times a day, it comes down to a only 44 days for a 50% chance of a duplicate in the ESS, but this is 200 days for each AP in the ESS (5 APs in the ESS). Hopefully all is explained in my contribution where I have tried to explain all the formulas and their derivations. Hope this helps, Graham Hi Bob, I do not believe that means the 9001st will collide with one of the existing 9000. The probability for 9001 is basically the same. What it's saying is that the probability of any 2 STAs out of those 9000 (or 9001) randomly choosing the same MAC address is 0.000000575. It is certainly not 1. regards, Dan. -- "the object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." – Marcus Aurelius Graham,
This is what I use in calculating the probability of a collision:
Calculating Collision Probabilities
The accepted formula for calculating the probability of a collision
is:
P = 1 - e^({-k^2/(2n)})
P: Collision Probability
n: Total possible population
k: Actual population
Example:
n=2^46
k=9000
P= 5.7*10^-7
That is that the 9001th will collide with one of the existing 9000.
And if n=2^44
Then it would be 4x as likely. On 6/3/24 10:15, G Smith wrote: Hi Jay, I may not be the best person to answer this but basically the MAC address is made up of 48 bits. However, bit 0 in the 1st octet is the unicast/multicast bit, set to 0 for unicast. Bit 1 in the first octet is the global unique/locally administered bit. As was agreed for 11aq and in the baseline, all random MAC address must have this bit set to 1 so as to distinguish it from the unique assigned MAC address. Hence, we have 46 bits that IRM can set randomly. Then along came SLAP which uses the next two bits, b2 and b3 in the 1st octet to specify four quadrants: extended local (ELI), standard assigned (SAE), administratively assigned (AAI) and reserved. The proposal (by SA) is that the IRM should always be in the AAI quadrant so now we only have 44 bits that IRM can set to random. I calculated the effect of having just 44 bits versus 46 on the probabilities of duplicates. The results seem to indicate that it is still rare, but the chance of duplication is going to be at least 4 times worse with 44 bits than with 46 bits. Not sure if I answered you question but I did my best :>) Thanks Graham Hi Graham, What's the exactly requirement to define 44 bits for IRM? Or do you propose to use totally 46-bit for MAC address? I'm not sure I get your intention. If you want to refine the length of MAC address, we could discuss it in 802.11me group, but it's out of 11bh scope. I'm still confused on the gain of 46-bit MAC address compared with 48-bit MAC address, as SYSTEM always process information based on unit of BYTE, but not BIT. Thanks Best Regards Jay Yang (杨志杰) Original Subject: Re: [STDS-802-11-TGBH] 46 or 44 bit IRMs Antonio, I know it's "not for WLAN only." I said it's not being used in WLANs so the inference from that statement is that it must be for something other than WLAN. But without any advertisement of SLAP policy—remember, SLAP is not just "44 bits for random MACs", there are other policies enforced in other quadrants—the STA can only assume there is no SLAP policy being enforced in the ESS and, hence, is free to use all 46 bits to create a random MAC address. If we really want to bring SLAP into the TGbh draft we'll need to decide what IRM does for the 3 defined quadrants, not just assume 44 bits are always available. For instance, if the quadrant is "administratively assigned" then the STA can't just decide to use 44 bits for randomization because it's MAC is going to be assigned to it in a fashion that is entirely up to the administrator of the network. And in that case there is no need for IRM or Device ID, right? The STA is going to be identified by the MAC address it got administratively assigned. No need for TGbh! This is what is known as a "can of worms", something you don't want to open up. I really don't think we want to bring SLAP into the TGbh draft. regards, Dan. -- "the object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." – Marcus Aurelius Hi Dan, I do not want to go into endless discussions here but please remember SLAP is not for wlan only, it is to enable future use of the local space in 802 technologies. So there maybe an application of SLAP in the wired part connecting your ESS, and by using the 46 bits you are not allowing other technologies to use it. I think just going for 46 bits on the basis of wlan not using it right now, is a too wlan centric approach. Antonio
—
Antonio de la Oliva
Associate Professor, UC3M
Skype: aolivadelgado
Phone: +34916248803 Hi Graham, I get roughly the same numbers for "results" (slide 8) but I do not agree with your interpretation. There is a problem when two STAs try to use the same MAC address. That probability is very remote. Even if, as you assume, 80,000 STAs associating (note, I believe the record for simultaneous associations in a single ESS is closer to 30,000 but let's plan for the future) and each one associates 3 times per day that does not mean there will be 15.75 duplicates per day because these 80,000 STAs are not running through their random MACs simultaneously. The probability of 2 STAs using the same MAC at the same time if there are 80,000 STAs associating is still 0.000045. It's not 1 (which 15 duplicates per day would imply). And I agree with Mike. We can use all 46 bits for randomization. Nobody's doing the SLAP for 802.11 networks. regards, Dan. -- "the object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." – Marcus Aurelius Hi TGbh’s, At the Interim last week we discussed CID 3085 which proposed to define IRM as follows : " A MAC address selected randomly from among the Administratively Assigned local identifiers specified in IEEE Std 802 and used by a non-access point (non-AP) station (STA) to identify itself to a network." Using the AA designation means that the IRM would comprise 44 random bits as against 46 bits if we kept to the present “constructed from the locally administered address space”. I had previously uploaded, but never presented, 23/2148r0 which looked at the theoretical probabilities of IRM duplicates for ESSs up to 80,000 stations using IRMs of 46 random bits. I have now posted r1 where I have added the results for IRMs of 44 random bits. https://mentor.ieee.org/802.11/dcn/23/11-23-2148-01-00bh-probability-of-irm-duplicates.pptx The results are: For a busy ESS (network), with each STA associating 3 x per day, storing a high number of IRMs (80,000) For 46 random bits: – Each AP (40) in ESS has a duplicate every 2.54 days – Each STA only experiences a duplicate every 14 years. (i.e., Action frame exchange to get new IRM is a small overhead) Notes: Assumed 2000 STAs per AP For S1G (8000 STAs per AP), each AP has 1.57 duplicates per day. For 44 random bits: • Each AP in ESS has a duplicate 1.57 times per day (i.e., 4 times more frequently) • Each STA experiences a duplicate every 3.5 years. Note: For S1G (8000 STAs per AP), each AP has 6.3 duplicates per day I do not intend to ask Mark for time to present this as it would probably take up a lot of valuable time. I have included all the formulas and derivations I used, so those interested can check my analysis and results, and of course, I welcome comments. The results are what matters as I have provided above. Of course if anyone feels that my assumptions of the maximum size (80,000) ESS should be different, or each STA should on average associate more (or less) than 3x a day, please let me know and I will run the numbers accordingly. I leave it to the group to decide if the effect of reducing the random bits from 46 to 44 is significant enough that we could use it as a reason to stick with the “locally administered address space”, and not change to “selected randomly from among the Administratively Assigned local identifiers specified in IEEE Std 802.”? Thanks Graham To unsubscribe from the STDS-802-11-TGBH list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBH&A=1 To unsubscribe from the STDS-802-11-TGBH list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBH&A=1
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Robert Moskowitz
Owner
HTT Consulting
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There's no limit to what can be accomplished if it doesn't matter who gets the credit To unsubscribe from the STDS-802-11-TGBH list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBH&A=1 To unsubscribe from the STDS-802-11-TGBH list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBH&A=1 To unsubscribe from the STDS-802-11-TGBH list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBH&A=1
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