Describe 802.11 HE Information Elements

0:01[AUDIO LOGO] Welcome to describe 802.11 high efficiency or HT information elements. Well, if you are working your way through this course sequentially, we took a look at the HT information elements. We then took a look at VHT information elements. And now it's time to look at high efficiency, which came to us with 802.11ax. Now 802.11ax or Wi-Fi 6, it brought a lot of new technologies. It's got the ability to deploy OFDMA, for example. We have BSS coloring in here now.

0:31And so we've got all of these technologies that whether they're at the PHY layer or the MAC layer that are going to define for us new ways of operation. And so we need to the ability to specify these capabilities. And so once again, we're going to find that we have two different types of information elements. We have the capabilities information element. And we have the operation information element. The capabilities information element is interesting. First and foremost, we're going to find is we're actually out of IDs, which is a little bit funny. We had 1 byte in there for information element IDs. We've been getting closer and closer to 255, which is the max value with 1 byte.

1:06And we're here. We're out of IDs. So we're going to see how exactly we get around that now with these new information elements. So that's the first step. As far as the capabilities are concerned though, that's going to get divided up into PHY and MAC fields where we're describing different capabilities at the two different layers. Now from there, we'll take a look at the operation elements. And this is where we're going to see some of these other concepts come together. Ultimately, we've got six different fields inside the operation element, three of which are mandatory. And we'll take a video to make sure we go through all of those in depth.

1:37We'll actually pull up the spec as well. And make sure that we see this because there's a lot of flags in here. A little bit more than we probably are going to-- it's going to be more useful to pull up the spec and see them than it is to draw them all out on the chalkboard. Let's put it that way. So we'll pull up the spec and take a look at some of these different flags. But then we also have to worry about the three optional fields afterwards. One of which is specifying all kinds of information if we are deploying this into 6 gigahertz. And so it's interesting because we don't necessarily expect to get all this information elements depending on the band.

2:08If I'm in the 6 gigahertz or even the 2.4 gigahertz band, I don't expect to get VHT because that's only designed to work with 5 gigahertz. But with 6 gigahertz and HT-- I'm sorry. With 802.11ax and HT, we operate on all of the bands, whether it's 2.4, or 5, or 6. We can expect to see these information elements regardless of which band we happen to be scanning in our Wi-Fi networks. Let's go ahead and dive in and explore these different information elements. And hopefully have a little bit of fun doing so. With that, I will see you in the next video.

0:00[AUDIO LOGO] Well, we've covered VHT capabilities and VHT operations. So it's time for us to elevate our conversation now to Wi-Fi 6 or 802.11ax or ultimately the high efficiency PHY. Let's dive in. Well, once again, we are going to start with the capabilities element. But before we dive into the details, we need to keep a few things in mind as it relates to HE. First of all, even if we're sending HE, we are going to need to be backward compatible and talk about the previous technologies.

0:31So we will be sending the HT, VHT, and HE all at the same time. Now, keep in mind what we said about VHT only being applicable to 5 gigahertz. And that is the case. But we also are only going to apply HT to 2.4 and 5. So as we diagram this out, we realize HE is going to go to all three of the potential bands. We start to see our alignment here as far as what's happening within each band. So in 2.4, we're going to send HT and HE, in 5 gigahertz, we'll send all, and in 6 gigahertz, it's only going to be our HE.

1:03And so at that point, we are only going to send the HE capabilities element, at least at the time of this video. I'm sure we're going to find that when Wi-Fi 7 comes out that we will have a new information element to be sending at that point. But for now, within the context of Wi-Fi 6 being the most recent version, this is where we're at. Now, we also have some bad news that we need to get out of the way with, which is that we've always had these element IDs that are included inside of our elements. And the element ID is 1 byte in length. Well, 1 byte gives us 256 values between 0 and 255, and we've actually exhausted all of these at the time of coming out with high efficiency.

1:42And so we need a new structure. And the way we're going to do this is we're going to use what we call element ID extensions now. The element ID extension is going to be used when the element ID is set to 255. So if the ID is 255, then we will look for an extension, which is another 1 byte field after the length. And so as we start to draw out our element here, we will start to break this down. But at the very beginning, we're going to have our ID, and the ID will be 255.

2:12255 means we want to look here to find out what the actual ID is at that point. So we're skipping over the length, so we need to diagram that. So we've got the length here. And our length here is actually going to be variable, and we'll see why here in a little bit. Now, next up is another 1 byte field. This would be the extended ID. And in our case, the extended ID is going to be 35 for the HE capabilities element. So just keep in mind, if we see an ID of 255, that means that that's not actually the ID. We need to look at another header right here to find out what the true ID is, and that will help us to distinguish the capabilities element from other elements that are also using the extended version.

2:52Now, the rest of the element is broken down into four different subfields. The first two are going to play off layer 2 and layer 1. We have the HE MAC capability subfield, and then we're going to have the HE PHY capability subfield. Now, the MAC capability subfield is going to be 6 bytes in length, whereas the PHY is going to be 11 bytes. So this is not drawn to scale. Keep in mind that the PHY capability is almost twice as long as the MAC capabilities. The third subfield is going to be where we talk about our MCS and our NSS set.

3:25And so this is going to feel a little bit familiar after all of our other conversations regarding listing out the MCS rates that we support as well as the Number of Spatial Streams, which is what NSS stands for. And this is going to be variable in length. This is either going to be 4 or 8 or possibly 12 bytes, and we'll see why here in a little bit. Now, the last subfield is something we call the PHY Packet Extension or PPE threshold. And sometimes this is abbreviated as PPET. But either way, this is going to be variable length. And so when we consider the fact that this is variable length as well as our MCS and NSS set, subfield is variable.

4:00This is why we can't really predict exactly how long this capabilities element is going to be. We'll start off by taking a look at the HE MAC capabilities information subfield. This subfield is 6 bytes in length, which means we have a total of 48 bits in here. And those 48 bits are divided up among 37 different flags. This is a whole lot of information inside of this one subfield, and we're going to be talking about anything pertaining to the MAC layer of our high efficiency operation. And so when we look at this, we're going to see that we've got things such as our target wake time parameters in here.

4:34We've got our A-MSDU as well as our A-MPDU parameters in here as well and many other flags. Now, rather than detailing all of this out on the chalkboard, let's go and flip over and take a look at the actual spec. So as we see here, we've got all of these different bits laid out as far as whether or not we have single bit fields or subfields such as these first ones relating to HTC as well as target wake time. But we've also got multi-bit fields. So we've got 2 bits for dynamic fragmentation support, for example. As we scroll down, we're going to find that we've got this listed out for all of our 48 bits, so 0 through 47 down here.

5:12And so there's just so many different flags in here. But we can open up the spec, for example, and we can go right to the section where it describes all of the different flags. So here we've got them listed out in a block diagram. But as we scroll down, we can actually see what exactly each one of these subfields does. So we mentioned dynamic fragmentation support that says it indicates the level of dynamic fragmentation, and then it actually gives us the listing of all four of the options. Because remember, that particular subfield had 2 bits in there, and as a result, we have four different options here.

5:45Furthermore, when we're going through the spec, which is something we should probably do when we're studying for wireless exams to really understand what's happening from time to time, we can follow this as a hyperlink to say, OK, well, this is set 1 or set to 1 if the station supports level 1 dynamic fragmentation. OK, that doesn't tell me much until I click on this. And now it tells me a little bit more about dynamic fragmentation here. And so from here, we can just go back to where we were. And we can, again, understand that there are just a lot of flags in here, and we're not going to take the time to break them all down, but it is important for us to understand that for the most part, what we're talking about here is anything related to high efficiency that has to do with layer 2 and not so much with layer 1.

6:30If we want to understand layer 1 parameters, we're going to have to go into the next subfield. And in this case, the next subfield is our PHY capabilities information. Now, the PHY capabilities information is, once again, 11 bytes in length, and it's going to include features such as channel width. That's going to be something that we actually spend a little bit of time on here. We'll take a look at that in the spec here in a moment, as well as our multi-user MIMO configuration. We've got to worry about our spatial streams, and transmit beamforming is a big part of this as well.

7:01There are all kinds of parameters in here that have to do with the physical layer of our HE operation. So once again, we have a block diagram that tells us all of the different subfields that are within the HE PHY capabilities information field. So this is 11 bytes in length. That means 88 bits. So we have everything from bit 0 here at the top all the way to the bottom where we should see bit 87, and that's what we see. So we do see some reserved bits in here this time. But either way, this is going to address things from a layer 1 perspective.

7:31So we do start off with the supported channel width set. We need to understand whether we support 20 or 40 or 80 or 160 or 80 plus 80 megahertz. We've also got things in here related to multi-user MIMO. We've got our single user and multi-user beamformers and beamformees. We've talked about that actually with regards to VHT. And then as we scroll down here, we do see an important one right here in the middle, bit 55. This is a single bit that says whether that PPE thresholds field is present.

8:01That field is not only variable in length. It could be as low as 0 bytes, meaning we're not even including it. And so if this is a zero, this means we're not including that final field. But if it's a one, that means that we can expect to find data there at the end of this information element. And so there's all kinds of information embedded within here. And once more, if we want to know a little bit more information in the spec, we can keep scrolling down, and we do start to see some information here. Now, this supported channel width set, this is really interesting when we get to high efficiency because the interpretation of this field is going to depend on whether we're in the 2.4 gigahertz band or in the 5 or 6 gigahertz bands.

8:42And so as we can imagine, 2.4 gigahertz, yeah, it's not a great idea, but it does support 40 megahertz. There is enough bandwidth for that, but there is not enough bandwidth for 80 or 160, so we don't even see 80 or 160 show up in this particular section. So if we're in 2.4 gigahertz, the bits are not ever going to enable 80 or 160. Whereas in the 5 gigahertz or 6 gigahertz range, yeah, now we can actually activate 80 and 160 and that 80 plus 80 configuration.

9:12And from here, once again, we can always scroll down and continue to look at these different sections and read and figure out a little bit more information about not only what they mean, that would be the description field here, but then also what are we setting our bits to and what that ends up doing. So let's get back to the whiteboard and talk about this third section. This is going to be where we talk about our MCS data rates as well as the number of spatial streams. And this should be pretty familiar to us at this point, other than we understand there's a couple of changes here.

9:42For example, we have new data rates that we should address. But as far as the number of spatial streams are concerned, well, that hasn't changed. We can still only support a maximum of eight. But we do need to specify our MCS rates that we support on a per spatial stream basis. So the way we're going to do this should, again, feel a little familiar. We are going to have a receive section, and then we're going to have a transmit section. The receive section is going to be 2 bytes, the transmit section is going to be 2 bytes, and that gives us 16 bits each. Now, the way we're going to break this down is we're going to deliver 2 bits to each spatial stream.

10:15So spatial stream 1, for example, might be designated as 10, spatial stream 2 might be designated as 10. Maybe we do that for 3 as well, and then for 4, we designate this as 11. And so at this point, we just need to understand what these different values mean. I mean, what's a 0 mean versus a 1 and a 2 and a 3? So let's go ahead and diagram these out. So we've got these rates, and once again, we have 2 bits to represent the rates that we support. Now just like before, a 0 is just going to mean that we support the bare minimum, and those requirements don't actually change relative to HT and VHT.

10:51We need to support MCS rates between 0 and 7. And then from there, though, we do change things a little bit because again, we've got new rates. VHT had 10 rates, so we supported between 0 and 9. HE, however, adds two more, and we support between 0 and 11. So how are we going to do this when we still only have 2 bits? Well, the way we do this is we have a 1 represent a range of rates between 0 and 9, and then 2 is going to represent the range from 0 to 11.

11:23And so with VHT, we recall that we stepped from 7 to 8 to 9 in this fashion. But naturally, unless we add more bits to the equation here, we can't do that. We're going to have to take larger steps, and that's exactly what we do. Now, a 3 is going to mean just like what it did before, which is to say that we do not support this particular spatial stream. So we look at what I listed out over here, we have a 2, a 2, a 2, and a 3. And so when we look at our key down here, we see that ultimately spatial streams 1, 2, and 3 all support all of the MCS data rates, whereas spatial stream 4 is not supported.

11:58Now, do keep in mind that I'm going to have to list this out for all the other spatial streams as well. So I've got 5, 6, 7, and 8. And if I don't support spatial stream 4, then these are probably all unsupported as well. So each of these is going to be listed as a binary 11, which is the equivalent of 3. Now with transmit, I'm going to do the same thing. I'm going to have to say spatial stream 1 is 10 and then 2 and 3 and 4 and 5 and 6 and 7 and 8. And this is why we need 2 bytes or 16 bits for both the receive and the transmit.

12:28And so adding 2 and 2 together, this is why we see that 4 is an option here for our MCS and NSS set. So then we have to ask, well, where does this 8 and 12 come from? Well, HE actually allows for us to have a different configuration here for our larger channel sizes. In other words, we could have a completely different set for 160 megahertz. If we do, then we're going to need 4 bytes for this. We're going to have to list everything out in here as it pertains to 160 megahertz, assuming that it's different than what we support on the lower channel width sizes.

13:00And so that's where we get another 4 bytes and why we could have 8 bytes here. But then we do have another one to talk about, which is that 80 plus 80. We might have yet another configuration for 80 plus 80, and that's going to need its own 4 bytes. So this is where we get 12 from potentially. So whether it's 4 or 8 or 12, we're doing the same thing. We're just repeating it either a single time or possibly two times or maybe even three times. Now last up is this PPE threshold. And remember, not only is it variable in length, but it is actually optional. We might not even include this inside of our capabilities element.

13:32If we are going to include it, then there's that bit here inside of our PHY capabilities information field that's going to tell us that yes, indeed PPE threshold is being included. Now, remember, PPE stands for PHY Packet Extension, and this has to do with the padding of our HE PPDUs. The interesting thing about this is this is defined on a per spatial stream basis. It can also be defined on a per resource unit basis. And so this is why it's variable in length, and therefore we can't really predict exactly how long this capabilities element is going to be unless we just outright say that it's not going to be included.

14:08Now naturally, if a wireless device is building these capabilities element to in order to transmit it, at that point, we could add up R6 and R11 and maybe just say that we're going to use the same rates for everything. And so we're just going to have 4 bytes in there. And so that would add up to 21 bytes in total for our length. But naturally, we do need to account for the fact that MCS and NSS set is variable in length as well as PPE threshold when it comes to the capabilities element. So the HE capabilities element is going to use an extension ID of 35.

14:38And again, the extension ID is an important part of this. The ID itself is 255 because we've run out of element IDs. And so we're going to use this concept where if it's 255, I'm going to pay attention to the field that's after a length. And that ID is what's going to be 35. And keep in mind, that length is variable with the HE capabilities element. Now, we have two primary subfields that we really zeroed in on. That would be the MAC and the PHY capabilities. This is where we really talk about all of the different capabilities that we might have within the system and really specifying whether we have them or not.

15:11And we took a look at that through the spec itself to see that there are just tons and tons of flags in there. And so naturally, we shouldn't expect to have to memorize this for any particular exam we're hoping to take. It's really more a matter of, do we know where to go in reference to this as well as just how this breaks down and just understanding that there's a section for MAC and a section for PHY. Now the MCS and the NSS set that's very similar to what we've talked about before. But naturally, it can also be applied to the channel width, and this is where it becomes variable in nature, and we have that optional PPE thresholds field at the end as well.

15:44I hope that has been informative for you, and I'd like to thank you for viewing.

0:00[AUDIO LOGO] Well, the HE operation element is pretty long as well, and so we're going to break this conversation into two parts. We're going to start by talking about the mandatory fields that must be included within the information element, and there are three of them. And then we find that there are three other fields that are going to be optional, and we'll talk about those in the next video. Let's go ahead and see how exactly this element breaks down, and we'll dive into the details of those first three fields. So let's start to break this information element down.

0:30First of all, we have our ID. And just like before with the capabilities element, this ID is going to be 255, meaning we're going to have to check for the extension ID here coming up. Now, the length is going to be variable in nature once again. As we mentioned, we've got three mandatory fields and we have three optional fields. And so we'll take a look at those here coming up as well. But for now, we're going to focus in on the mandatory fields here in this video. Now, even though it's variable in nature, we do know that it's going to be a minimum of 6 bytes and it can be a maximum of 15 bytes depending on the inclusion of those optional fields.

1:03Now, after this, we have our extension ID. And our extension ID is going to be 36. So our capabilities element was 35 and now our operation element is 36. Now, from here we have six different fields. And once again, the first three are going to be mandatory. The first one is going to be called the HE operation parameters. And this field is going to be three bytes in length. As we might imagine from the name, this field is going to contain a lot of the different options that we have available to us as far as HE is concerned. Now, the next field is one byte in length.

1:35And this is going to have to do with BSS color. We call it BSS color is included in a lot of our messaging to help us understand whether we are hearing a message from a station inside our own BSS or if it's a station from a remote BSS. And having different colors on our BSS's are what helps us to identify that. Now, the next and last mandatory field is going to be the basic HE MCS and NSS set. And this is going to be two bytes in length. Once again, based on the name, this is going to include the actual operational configuration for the MCS and NSS set that we just talked about in the capabilities conversation.

2:13So what's left here? We've got these three other optional fields that we might end up seeing. The first one is going to be called VHT operation information. And this is going to have to do with the fact that sometimes we're sending HE out into a five gigahertz space without VHT information. And if that's the case, we're going to need to include that here. So this is three bytes if we include it. It's 0 bytes if we don't. So there is no variability to this field or any of the other optional fields. The next one is an interesting one.

2:44We call this the max cohosted BSS indicator. And that's going to be one byte in length. We'll talk about the details of this field here coming up. Now lastly, if we are sending this into the six gigahertz space, then we're going to need the field here at the end, which is six gigahertz operation information. So this is going to include information that we need from a six gigahertz perspective. And if we do include this, this is five bytes in length. So we can see here by looking at the mandatory fields, here these first three, this is where we can say that at a minimum it has to be six bytes in length because that's what the first three fields come out to.

3:21Now, these last three fields, these are the optional ones, and they come out to nine bytes. Just keep in mind, though, that we don't have to include all of them or none of them. We might actually pick and choose. We might send the six gigahertz out one. We might send the VHT out another. And so in the end, it's unlikely we'll ever hit 15 bytes, especially since VHT is really designed for the five gigahertz space, and six gigahertz is naturally designed for the six gigahertz one. But either way, we understand that this is the structure of the element, and we need to understand which of these are mandatory and which of these are optional.

3:54So let's start by zooming in on the HE operation parameters. Once again, this is three bytes. So it's 24 bits. And we're going to break this down into eight different subfields. Now, rather than listing them all out here on the chalkboard, I'm going to actually pull up the 802.11ax spec. And this is something that I would recommend everyone do is to go out to that IEEE and download this. This is something that actually at the time of this video, the IEEE has made several of their key specifications available for free. And so you can see if that's still available.

4:25If not, it might come at a small cost. But either way, if you do want to follow along, the HE operation element is listed at 9.4.2.249. And so run a quick search against that number, and it should pull up the HE operation element. So let's go and pull up the spec here, and we do see this 9.4.2.249. This is where we start to talk about the HE operation element. In fact, right away we see a block diagram of the various fields we. Do see the three mandatory fields here as well as the three optional fields, and it does give the indicator of how many bytes are in each.

4:57Now, as we scroll down here, we get a block diagram of the HE operation parameters field, which is what we want to break down and start to talk about. So let's start here with the default PE duration. This is a duration that ties to our high efficiency trigger based PPDUs. And this is going to give us a value that is multiplied by four microseconds. So we are given a duration there as far as how exactly we are to send those PPDUs. Now once again, when we're reading the spec, we actually see a small paragraph here that describes that as well as a hyperlink that if we want to click on that, we can go and learn a little bit more information about what exactly is happening there.

5:32But either way, we're just going to go ahead and move on. And we're going to talk about target wake time. This subfield is a single bit. And this is simply going to tell us whether or not target wake time is required. So a 1 means it's required. A 0 means it is not. And keep in mind, again, this is an operation element. And so we're describing the operation of the BSS. And so stations are going to need to abide by this. Do they support target wake time when they're trying to join the BSS or do they not support it? The next step is this transmit opportunity duration for the RTS threshold.

6:03This is actually 10 bits in length. And this is another duration field. And so this is going to be multiplied by 32 microseconds based on whatever value is inside of there. A station that wants to use RTS and CTS has to transmit for at a minimum, the amount of time expressed inside of this subfield. And so if we have a very large amount of time specified, that means that we can't actually use an RTS in order to send something unless we have a bunch of information stored up that we can send. And so to be clear, this is a minimum threshold, not a maximum threshold.

6:35We're not saying how much time you can spend. We're saying if you're going to use RTS to create a transmit opportunity, you have to have enough data based on the amount of, well, really based on this duration that we've set, the value multiplied by 32 microseconds. And by the way, if all of these are set to 1 where we have a 1023 in here, that means that we cannot use RTS at all. Now, next up we have an important flag here that's going to tell us whether or not we have this optional field included. So I know it's off the screen up there, but that's the VHT operation information field, and that's one of the optional ones.

7:10That's why we say it's either 0 or 3 bytes. In fact, we have another one of these here, the six gigahertz at the end, the 0 or 5 that we mentioned. And this bit right here tells us whether that one is included. Any station receiving this information element needs to understand which fields are included, which aren't, and these single bit flags are how we end up doing that. Now, we're not quite done yet, because we have a third optional field up there. And that's going to be tied to the cohosted BSS flag. However, this cohosted by this flag also is going to tell us whether or not we are using this functionality.

7:43We'll talk about this in a little bit more detail later, but ultimately what we're saying is that we can have multiple access points managing a single BSS. It's a feature we don't talk about very often, but it's technically possible using high efficiency. Now, the last one here, this extended range single user, that is one of our four different PPDU types. We've talked about this as it relates to high efficiency throughout the course. Ultimately what we're saying here is, can the access point receive extended range single user PPDUs?

8:13And then at the end here, we have a reserved field. And so the last six bits inside of our HE operation parameters, those are simply reserved at least at the time of this video. So that is the HE operation parameters field. Let's go ahead and scroll down and take a look at BSS color. BSS color is a single byte and so we don't have a whole lot here, but we'll go ahead and walk through this. So remember the concept of BSS color is that usually I've got non-overlapping cells here that are running on the same channel. So let's say we're running channel 44 in each one of these cells.

8:45But naturally, wireless, it goes a lot further than we like to think and goes well beyond our cell boundaries, especially when we have a station that's out here that's connecting in. Well, in the end, it's not too far away from the next cell over. And so we've got a lot of communications that are going back and forth between these. And if a station here at the edge is hearing something coming in from another station in that BSS, the one that's far away, well, at this point, it has no choice but to wait because somebody else is communicating.

9:16But if we have different colors assigned, and colors are ultimately a numerical value not an actual color, so if we've got numeric values of 32 and 67 in here, well, at this point I know that because this message is marked with 67 that I probably don't need to wait, because that person is communicating closer to their access point than I am, and chances are it's not going to cause interference. So that's the idea of BSS color. And so as we diagram this out, the first thing and most important part is the color itself, which is a six bit field.

9:49And so our colors can range between 0 and 63 based on these six bits. Now, next we do have the concept of a partial BSS color. It's an option within the configuration of BSS colors. And whether or not it's enabled, that particular option is right here as a single bit flag. And lastly, we do have this option of BSS color being disabled. Keep in mind if it says disabled here, that means that a 1 means that it's true, meaning that BSS color is disabled, whereas a 0 is saying that it is actually enabled.

10:19And so that's it. That's all that's in the BSS color information field. Again, it's only a single byte. So we only had eight bits to worry about. Now let's look back to the chalkboard here to see where we're at. We've got the HE operation parameters covered. We covered the BSS color. Let's go and talk about this basic MCS and NSS for high efficiency. As we have pointed out a couple of times, this is an operation element, and so we're no longer talking about capabilities. We're talking about how the BSS is actually configured. At this point, we've in theory got an access point managing a BSS with a bunch of stations here inside.

10:54And part of the operation element, as we've talked about with HT and VHT, is to let everybody know all of the different MCS rates that are actually enabled inside of this BSS. And this is going to be based on the existing stations. Because if an existing station doesn't support a particular MCS value, then we're going to need to avoid using that data rate, especially if somebody has a broadcast or multicast message to send out into the wireless space. Now, it doesn't happen too often. Most of our communications are unidirectional between an access point and a station.

11:27But just in case something like that does happen, everybody needs to know whether certain rates are supported or not. And so ultimately, we're going to do here what we've already done several times. We're going to take two bytes, which is really 16 bits, and we're going to divide those up among the spatial streams. So spatial stream one is going to list out those four different options. So maybe spatial stream one is listed as a two here. Or maybe spatial stream two is listed as a one. We have less functionality here. Maybe spatial stream three is listed as a 0 and so on and so forth.

11:58And so we just need to understand what everybody out there supports. Now, these values are the same as what we've talked about. 0 is going to be between 0 and 7. 1 from an HE perspective is going to be between 0 and 9. 2 will be 0 to 11. And 3 means that we are not supporting this particular spatial stream. So again, the way that we architect this is very similar. However, in this case, we're not advertising capability. The access point isn't saying what it's capable of doing. It's saying what the BSS is capable of doing based on the stations that have associated to the access point.

12:31So this HE operation element has an extended ID of 36, which by the way, means that its element ID is 255. And then the length is going to range between 6 bytes and somewhere up towards 15. Again, we probably aren't ever going to see it hit 15. But at the same time, we understand that some of these fields might be included, some of them might not. And so it's important for us to recognize that there are three mandatory fields as well as three optional fields. The first three fields are the mandatory ones. And in that first field, we actually have bits that tell us whether or not any of those other fields have been included in this information element.

13:06And so the last three are the optional fields. Now, the mandatory fields that we're talking about, we have the HE parameters to start with, the operation parameters. We've got the BSS color. It's only one byte. And most of that byte is just providing the BSS color itself, which is six bits. And then we have to describe the MCS rates as well as the number of spatial streams, and we use our two bits per spatial stream in order to describe that and broadcast out what the configuration is for the BSS based on the stations that have associated. I hope this has been informative for you, and I'd like to thank you for viewing.

0:00(light music) Alright, we have covered the mandatory fields that show up inside of the HE operation information element. Let's go ahead and now unpack those three optional fields that may or may not be included. So we've covered those mandatory fields. Let's dive into these optional ones. The VHT operational info. This is an interesting one, because we've actually already talked about this specific field. This field exists inside of the VHT operation element, and the reason why we're duplicating this is because there could be a scenario where we are sending out the HE operation element and we don't have the VHT operation element.

0:41If we don't have the VHT operation element, then we're not going to have the VHT operation information that shows up inside of it. And so this is the scenario. We don't have this element, and therefore we need to include this information here inside the HE operation element. So as mentioned, this is three bytes, which is 24 bits. And if we go back and take a look at the conversation we had earlier about this field, we'll find it's the same size and it has the same flags. This is primarily going to have to do with our channel configuration. So we recall we started with channel width.

1:12We had one byte dedicated to this, and then this is where we have that center frequency zero and center frequency one concept, where each of these is going to describe the center frequency, especially when we have that 80 plus 80 configuration, and each one of these is a one byte field. So this is where we get our three bytes from. If you want more information, then be sure to go back and review the video where we discussed the VHT operation element, 'cause we go into this in much more depth. Now, next up, we have this one byte max co-hosted BSSID indicator field. This is a rather interesting conversation, because high efficiency allows for us to have this concept of a co-hosted BSS.

1:50The co-hosted BSS has multiple access points, but they share a lot of the properties that normally belong to a single access point, such as the BSSID. Now, what this field is saying is we're listing out the max number of co-hosted BSSIDs that we can have. However, this doesn't just follow a straight number, we're not talking about between zero and 255, this is actually an exponential number. And so it follows the formula where it's two to the power of whatever value we have in here. And so keep in mind that this is one byte, and therefore we would expect that we could have this between two to the zero and two to the seventh power.

2:27However, there is a limit of eight on here, and so I'm not exactly sure why they architected it the way they did; however, for the time being, the maximum value we can have in this field is three. So technically, it's not zero to seven, it's going to be zero to three in the exponent, which is why we can land between one, technically, to two to the zero power and eight different BSSIDs, all co-hosting a single BSS. So last, let's talk about the six gigahertz field, what we call the six gigahertz operation information. This field is five bytes in length, and what we're going to find is it's actually carved up into five separate one byte subfields.

3:03We'll go through each one of these. First of all, we are going to list out the primary channel. The primary channel is simply going to tell us, well, just what it sounds like, the primary channel that we're operating on in this scenario. And this is pretty straightforward; we're simply going to list the ID inside of the subfield. Now, next, we have a subfield called control. This control subfield actually has quite a bit going on within it. First of all, we have two bits that are dedicated to the channel width. We're going to specify either a zero, meaning that it's a 20 megahertz channel, a one, meaning it's a 40 megahertz channel width, two is 80, and three is 160, or possibly that 80 plus 80 configuration.

3:44Next, we're gonna have a flag, a single bit flag that has to do with duplicate beacons, whether we're sending duplicate beacons out across multiple spatial streams. Then we have three bits dedicated to what is called the regulatory info. This provides information about whether we're talking about indoor or standard operation. We recall that when we talked about six gigahertz, we had that low power indoor concept, we have standard power, and so we're going to describe what's happening here; however, keep in mind that this is always going to be tied back to the regulatory domain.

4:15So for example, in the United States, if I see a zero in this field, this means that we're doing low power indoor. If I see a one in this field, this means we're doing standard power. In the United States, as of the time of this video, these are the only two options that we have available to us. We may recall that other regulatory domains have a very low power option, and so these bits are going to mean something different, depending on the regulatory domain that we're operating under. Now, an important part about all of this is we don't actually provide the domain inside of these three bits; the domain is provided in a different information element.

4:52And so we have to reference that other information element to figure out what domain we're in in order to understand what these bits are. If I find out I'm in the US and there's a one in this field, I know it stands for standard power, but if I happen to be operating in a different country, a one might mean something completely different. And so this is going to, again, be relative to the regulatory domain that I'm operating within. Now, lastly, there are two more bits in here, but those bits are reserved. Next, let me clear up part of the chalkboard here so we can continue this conversation, 'cause we still have three more one byte subfields to cover.

5:23The next one up is going to actually feel pretty familiar, we just listed this concept out. We have the channel center frequency segment zero, which would be our third subfield within this six gigahertz operation information field, and then fourth up we have the channel center frequency segment one. So once again, this is going to provide the center frequency for the channel that is in use. The first one, segment zero, this is going to be the primary channel. And if we're talking about a 160 megahertz or an 80 plus 80, this is actually going to be the primary 80 megahertz channel, in this case.

5:59Now, if we do have one of these larger channel widths, we need to know what the secondary 80 megahertz center frequency is, and that's what this down here is for. And so this is especially going to be relevant with 80 plus 80, 'cause we need to know where that secondary channel is, and so that information is carried in here. Now, lastly, there's only one more subfield to talk about, and it is number five; it is the minimum data rate. This one is fairly straightforward. It is going to express the minimum data rate supported by this particular device, and this is going to be expressed in megabits per second.

6:30And so that's where we get our five bytes from. And as you can imagine, the six gigahertz operational info field, this is only going to be included if we're transmitting into the six gigahertz space. So this concludes our conversation around the AT operation element. The operation element has the three mandatory fields that we just talked about before, but now here we've talked about the optional field. So we have VHT operation, we have the co-hosted BSSID, the max number of those, and then the six gigahertz operation information. So all three of those, again, in total, we can add up to nine bytes in here, but it's, we're not gonna find a situation where we're using all three at once.

7:07Either way, the VHT operation field, keep in mind that that's tied back to whether we're including the VHT operation information element. If we are not, then we need to actually include some of that information in our transmissions, and so this operation field is actually going to reflect exactly how the previous field is architected, and it includes the same information, like we discussed. Now, we talked about the six gigahertz as well quite a bit. If we're in the six gigahertz band, we're going to send it out. It's got all of our channel information in there, it's got a whole bunch of other important pieces, like the channel ID and such that are going to pertain to six gigahertz operation.

7:44I hope this has been informative for you, and I'd like to thank you for viewing.

0:00[AUDIO LOGO] We have reached the end of another skill, it's time to review what we've learned with a quiz. First up out of four questions. What can cause the HE-MCS and NSS Set to consume eight or 12 bytes relative to the four bytes that it normally would consume otherwise? So WPA has nothing to do with this. Yeah, saying more than four spatial streams, but we are already accounting for all eight of those spatial streams in the four bytes.

0:34And so that's not going to affect things either. C is going to be our answer here. Remember four bytes is going to be used assuming that all of our channel would support the exact same in data rates. However, our 160 megahertz channels might actually support different data rates. And so at this point, we would add four bytes, where the second four bytes addresses 160, and the original four bytes now address the 20, 40, and 80 megahertz. Now that said, we might actually need another four byte set to account for the 80 plus 80 configuration.

1:05At this point, we would have a total of 12 bytes in here because we'd have three different configurations. So these are only required if we have different configurations at the different channel widths. This is why it could truly be four bytes originally, or it could be eight, or it could be 12, depending on our needs. Either way, C is going to be our answer. Question two. What is the length of each of these fields and the HE operation element? So we should definitely have a sense of how this information element is constructed.

1:39Now, I did us the favor of listing them in order from start to finish. And so all we really need to do is remember how long each of these can be. So the HE Operation parameters, this is a three-byte field and it's going to have a lot of the various flags in there that pertain to operation outside of the other corner cases like, BSS, and MCS, and number of spacial streams. Now the BSS Color Information, this is just a single byte. And the BSS color is six bits of those eight bits. And so for the most part, we don't need a whole lot of information around BSS color.

2:09Next up we have this MCS and number of spatial streams set. This is classically going to be two bytes from an operations perspective because we don't need to list receive and transmit, and we don't need to list this for different channels potentially. And as a result, we really only need 16 bits in total, which is the two bytes. VHT Operation Information, this again is just a repeat of-- when we covered this with VHT, and so this is going to be a three byte field, in the way that we discussed. The Max Co-Hosted BSSID Indicator, this is only a single-byte.

2:40We're not going to need a whole lot of information in here. In fact, we can't even use the entire range of that byte because we recall that we're restricted in the amount of the number that we can specify here. Now lastly, the 6 Gigahertz. This is actually a big one. This is the biggest one of all of these, we have five bytes here. And remember this consists of five separate one-byte subfields. So we didn't have this memorize, that's probably not the biggest deal. But at the same time, again, we should have a sense of where all the information is going when it comes to how especially one of these information elements is constructed.

3:13Question three. When is the VHT Operation Information field included in the HE Operation Element? Well, this one's pretty straightforward. Remember we have a situation potentially, where the HE Operation element is included, and the VHT is not. If that's the case, then we need to include of some of this information at least inside of our HE Operation element. And so, A is the answer here, it's when the VHT Operation element at least is missing.

3:45And at that point, again, we're going to import as it were one of these particular fields. So this field, the VHT Operation Information field that shows up both in the VHT Operation element, but also in our HE Operation element as an optional field, in case we need it. Last question. And it's a little bit of a review of the last several skills. What are the IDs used for each of these information elements?

4:16So every one of our information elements has what we call an "element ID." The element ID is going to tell us what type of element this is, because we don't have a solid structure out there for which elements should be included, in which order. So starting all the way at the beginning with HT Capabilities, this was 45 as an ID. In HT Operation, it's unfortunately not sequential, this was a 61. So those are two of the harder ones to remember, because the other ones actually do build on each other. For example VHT Capabilities, this is 191.

4:47And VHT Operation is 192. Now lastly, when it comes to HE Capabilities, we actually go smaller here. We start with 35 for capabilities, and 36 for operation. Just keep in mind that these are actually extended IDs. Meaning that the actual ID, the element ID field is going to be populated with 255 or both of these information elements. And so we should absolutely keep in mind that 255 is going to be in the actual element ID field. But we should understand that 35 and 36 are what's going to show up in the extended ID field.

5:19And by the way, when we map this out, this field is actually going to be separated by the length field here in the middle. So we've got the element ID here, and then we've got the extended ID over here on the right. So the length is going to be in the middle. However, that's fine, because we know that if 255 is listed here, then we're going to read the length and then we're going to get the actual extended ID at that point in the field that follows. Now lastly, we have SSID here at the bottom. Remember we said that this information element is the one that has the honor of having element ID of zero.

5:51And I suppose that's just because SSIDs are such a foundational part of all of this that they were given the first information element ID. And remember those are going to be included, especially in our probe requests, and responses, and beacons. So with that, our review of this skill and even some previous skills is over. If you find you couldn't quite identify all of the answers to some of these questions, then be sure to go back and review the materials. Whatever it takes to seal off those knowledge gaps. Otherwise, congratulations on completing Describe 802.11 HE Information Elements. I hope this has been informative for you.

6:22And I'd like to thank you for viewing.