TPC, Operating Classes, and Channel Switching

TPC, Operating Classes, and Channel Switching Date:2012-03-04 Slide 1 Brian Hart, Cisco Systems

Executive Summary • This document considers a range of issues related to transmit power, channel identification and operating classes • Regulations are getting more complicated with mixtures of units. VHT Transmit Power Envelope does not even define units => add • Operating classes can be used to indicate band and bandwidth in 11k/s/v => update • Expressing 80+80 is especially problematic for 11k/s/v protocols • Operating classes can be used to indicate time/location/AP-state-dependent regulatory permissions that clients wouldn’t be aware of otherwise. Need to keep this mechanism in our back pocket for future spectrum around the world => update • VHT weakens channel switching and next-channel TPC => refresh • 11mb uses the Global Operating Table in two inconsistent modes, and there are arguments towards 802.11 rallying around the less well recognized mode => pick a winner • A few other related matters => fix • A high level description of proposed changes is provided for discussion and to sanity-check the direction of the normative text Brian Hart, Cisco Systems

Case Study: TPC is a broad UNII requirement in FCC Part 15 Part 15 has a subpart for UNII i.e. TPC • adv- • Ised • party • = • manu • i.e. • TPC • adv- • ised i.e. This is the clause that lets you know that the FBI can knock on the end-user’s door. For the manufacturer, the products had better be in compliance with Part 15 . For the end-user, hopefully there is a channel and/or a TPC level that avoids harmful interference , else no operation. See also KDB 789033 Which defines TX power, etc The AP has the right and the responsibilityto select the channels and the max TX power of the clients Which in turn refer us to more regulations 1 Which in turn refer us to more regulations in subpart A And further regulations in subpart C And which also refers us to other subparts 2 Brian Hart, Cisco Systems

Transmit Power Units (1/5) Background • The 5 GHz 802.11 protocol to report the rules from AP to client is contained in a mixture of Country string, Operating class table, Operating Class, Max TX power in Country element, VHT Transmit Power Envelope element, Power Constraint element and Extended Power Constraint element • All these fields and elements contain one value, so assume one set of units (conducted or EIRP or EIRP/MHz, etc) • Since Japan is EIRP/MHz, and USA tends to be conducted, etc, 11d defined the units of the Max TX power in the Subband Triplet in the Country element as “interpreted according to the regulations applicable for the domain identified by the Country string” • But regulators use a mixture of units • FCC 15.247 2.4 GHz rules: conductedPower < 30 dBm AND EIRP < 36 dBm; this rule is labeled “conducted output power” • FCC UNII-2 TX Power rules: conductedPower < min(24,11+10logB)dBm AND EIRP < min(30,17+10logB)dBm AND conductedPSD< 11dBm/MHz AND eirpPSD < 17dBm/MHz (where the rule text refers first to “conducted output power” but the eirpPSD rule is actually the most stringent) ; versus the FCC UNII-2 TPC rules which are plainly: EIRP < 27 dBm • FCC 15.247 2.4 GHz point-to-point rules: conductedPower + (antennaGain-6)/3 < 36 • Even if the AP ignores its general TPC requirements, sometimes the regulators impose specific TPC requirements on the AP, as master, and thence the BSS. Brian Hart, Cisco Systems

Transmit Power Units (2/5)Existing Headache • Specifically for 5.25-5.35 and 5.47-5.725 GHz: • FCC’s max power is generally written in terms of conducted power (to promote the use of smarter antennas), but the FCC’s TPC rules are written in terms of EIRP. • The 802.11 protocol puts the max power in the Country element (“interpreted according to the regulations applicable for the domain” so is conducted power) then subtracts away a power constraint. So, in the USA in these bands, an 802.11 AP is advertising a conducted power, to enforce an EIRP constraint. Worked example: • Say an AP chooses to advertize a 27 dBmEIRP. The AP has clients associated that are capable of high conducted power and EIRP. • The AP could assume all clients are 0 dBi and advertize say 27 dBm, but then a 27 dBm client with a 6 dBi antenna can pick a power that is actually 6 dB higher than the AP thought it was requesting! • Or the AP assumes all clients are 6 dBi and advertizes say 21 dBm, but then a 27 dBm client with a 0 dBi antenna is unnecessarily limited to 21 dBm! And can never know. And still a 9 dBi client is actually 3 dB higher than the AP thought it was requesting! • The Power Constraint really only “works” if a) a client can never exceed the lowest TPC limit on EIRP or maybe b) it interprets the power constraint as a reduction from its homologated limit – which is very different to the 802.11 language Brian Hart, Cisco Systems

Transmit Power Units (3/5)VHT Extensions • In VHT, we add VHT Transmit Power Envelope element and Extended Power Constraint, but are silent on their units (not even “interpreted according to the regulations applicable for the domain identified by the Country string”). We do have: • 8.4.2.164: The Maximum Transmit Power field defines the maximum transmit power limit of the transmission bandwidth defined by the VHT Transmit Power Envelope element. The Maximum Transmit Power field is an 8-bit 2's complement signed integer in the range of -64 dBm to 63.5 dBm with a 0.5 dB step. • 3.2: transmit power: The effective isotropic radiated power (EIRP) when referring to the operation of an orthogonal frequency division multiplexing (OFDM) physical layer (PHY) in a country where so regulated. • From the original author, “where so regulated” is intended to bind to country and so indicate “TX Power = EIRP in a country if the country regulates via EIRP”, so transmit power is undefined in a country that doesn’t regulate as EIRP. And many countries regulate using a variety of units (e.g. from the earlier slide, FCC uses a mixture of conducted, EIRP, conducted/MHz, EIRP/MHz) even in the same subpart. • In fact, in almost every usage of transmit power in 802.11, “transmit power” is followed by explanatory text: conducted/EIRP/interpreted according to the regs. • BTW, the Extended Power Constraint element does fulfill a regulatory role: 10.8.4: “The Local Power Constraint field of any transmitted Power Constraint element and Extended Power Constraint element shall be set to a value that allows the mitigation requirements to be satisfied in the current channel.” Brian Hart, Cisco Systems

Transmit Power Units (4/5) SolutionInclude units for VHT Transmit Power Envelope element • Where to put the units - open for discussion • To express a mixture of units – e.g. “conducted < X and EIRP < Y” – send 4 elements: VHT Transmit Power Envelope [conducted], Extended Power Constraint, VHT Transmit Power Envelope [EIRP], Extended Power Constraint • Which would be cleaner if we merged VHT Transmit Power Envelope and Extended Power Constraint into a single element Add a final tuple with channel center frequency segment = 201, and withunits in Segment Channel Width field. • Inefficient, not D2.0 compatible Partition into a 5 bit table for Segment Channel Width (with 0, 3, 5-31 reserved for future use) and 3 bits for units. Second segment is reserved. Efficient, not D2.0 compatible Insert new IE just for units. • D2.0 compatible but very inefficient Insert new octet for units. Efficient, not D2.0 compatible Brian Hart, Cisco Systems

Transmit Power Units (5/5) SolutionAddress other ambiguous uses of “transmit power” Brian Hart, Cisco Systems

80+80 affects a lot of 11d/11h/11k/11v fields/elements/frames • We created the problem, so we ought to fix it • We could pick the fields/elements/frames that we care about and only update them • Leads to a drawn out discussion • Simpler for a volunteer to just try to fix “everything” Brian Hart, Cisco Systems

Solution: Channel number identification (1/7) Brian Hart, Cisco Systems

Solution: Channel number identification (5/7) Slide 16 Brian Hart, Cisco Systems

Country element format • Country element in Beacons and Probe Responses is the only 802.11 mechanism by which an AP can alert clients to time/location/AP-state-dependent regulatory permissions that clients couldn’t be aware of otherwise (i.e. structured information that cannot be known at manufacturing time) • Need to keep this mechanism in our back pocket for future spectrum around the world => update • As we see above, Country element is pretty powerful already • Let look at how it works by example, and look for holes Brian Hart, Cisco Systems

How to use the Country element to express Operating Classes (if AP needs to specify time/loc/AP-state dependent rules that the client cannot know otherwise) 160 MHz BSS 160 or 80+80 MHz BSS 80+80 MHz BSS with TPC Brian Hart, Cisco Systems

How to use the Country element to express multiple Operating Classes 80 MHz BSS on ch155 • But, ch138 is a new problem. If there were time/location/AP-state dependent rules for ch138, some arising from UNII and some arising from 15.247, how can we express these both – given that this is now an “AND” relationship? • Solution: define First Channel = 224+1 to indicate that the permissions of the Operating Class are ANDed with the following operating triplet (versus “+80”, which denotes a frequency-domain bonding). The 225 operating triplet is sent first so legacy can’t interpret the earlier triplet as unANDed • See more details on this encoding in a later slide 80 MHz BSS on ch138 Brian Hart, Cisco Systems

How to use the Country element to deal with wide spectrum crossing multiple regulations 160 MHz BSS on ch155 • Similarly if there was a 160 MHz made up of a first 80 MHz of spectrum subject to one regulation and a second 80 MHz of spectrum subject to a second regulation (or the second 80 MHz of spectrum is subject to both regulations), then we should allow 160 MHz to be represented as “80” and “+80” (since an 80 MHz-only client would not be subject to any additional S80 rules • Idle thought: Reserve “Coverage Class” in new operating classes? Brian Hart, Cisco Systems

Channel Switch (1/4) • In VHT, we only allow the Wide Bandwidth Channel Switch element in the Channel Switch Announcement frame • Many devices sleep as much as possible - only wake up to send or to check the TIM element • If so, they will never see the Channel Switch Announcement frames • Solution: allow this element in Beacons, Probe Responses and the Extended Channel Switch Announcement frame (and more, as we shall see) Brian Hart, Cisco Systems

Channel Switch (2/4) • From earlier slides, the AP has a right and a responsibility to perform TPC • 802.11 has had some off-channel TPC, via regulatory triplets in the Country element (first channel, number of channels and a lowered maximum transmit power level). But we’re leading with the VHT Transmit Power Envelope element in 11ac rather than regulatory triplets, so 11acD2.0 APs have less off-channel transmit power control than they’re used to. • And the regulatory triplet mechanism is painfully inefficient – the AP sends a lot of octets in the beacon on the off-chance that it might switch to one of the channels a long time in the future. And it doesn’t express TX power units • Much better to associate the TPC with the channel switch (11af model also). • i.e. 11ac doesn’t have a way for the AP to change channel and power at the same time • The (Extended) Channel Switch Announcement frames/elements (or Beacon or Probe Response) do not include any TPC elements that refer to the next channel • A client doesn’t know the new permissions until it has reached the new channel and heard a Beacon or Probe Response from its AP • BUT, the Beacon is coming too late – high-power PPDUs could be transmitted for up to 1 beacon interval, and longer if the Beacon is lost to collisions. Brian Hart, Cisco Systems

Channel Switch (3/4) • As well, 11ac doesn’t have a way for the AP to change channel and operating class(es) at the same time • E.g. to move a BSS from UNII ch36 to ch149, and ensure that all capable clients adopt 15.247 not UNII rules at ch149 (for more power) • In Japan, a channel switch from say 5.15-5.25 GHz (using the Global Operating Class Table) to say 4.94-4.99 GHz (using the Japan Operating Class Table) is not possible, since the Operating Table identifier is present in the Country element but the Country element is not transmitted in the (Extended) Channel Switch Announcement frames/elements • Work needed to allow for a Operating Class Table change, or avoid this altogether • An AP on a school-bus making daily trips between Ciudad Juarez and El Paso (5000 students daily cross the border with Wi-Fi) should perform a Country switch and advertise reduced transmit powers in the Subband triplet – but the AP cannot include the Country element in any (Extended) Channel Switch Announcement frame/element Brian Hart, Cisco Systems

Channel Switch (4/4) Solution • In CSA and ECSA, optionally allow: • Wide Bandwidth Channel Switch element (already allowed in CSA) • VHT Transmit Power Envelope element • Extended Power Constraint element • Country element • All for the next channel • To Beacon and Probe Response, if a CSA or ECSA element is also present, allow a new optional wrapper element “Extended Extended Channel Switch Announcement” that optionally contains: • VHT Transmit Power Envelope element • Extended Power Constraint element • Country element • All for the next channel • (Wide Bandwidth Channel Switch element could be moved inside this wrapper element) Brian Hart, Cisco Systems

Operating Class Tables (1/4)Sharing Operating Class Tables • 11mb keeps the US/Europe/Japan countries tables and adds the global operating table • The selected Country table is indicated by the third octet of the Country string • i.e. “One table at a time” • But, the example in Annex E.1 actually reports operating classes from both the US and the global operating tables. • And 11mb keeps the operating class numbers in the country and global operating classes separate. • Let’s put a lot of weight on these two observations. • So explicitly selecting and reporting an operating table doesn’t seem to be as important. As long as we parsimoniously assign operating classes and aggressively deprecate unused redundant classes, then we can keep this that simple. • Proposal: for VHT, the global operating classes suffice for US, Europe and Japan since there is no time/location/AP-state dependence in the client permissions that cannot be expressed by one or more of the country string, a nearby AP actually operating on this channel (or not), and the separate TPC protocol. • That is, delete new US operating classes 35, 36; Europe operating classes 19, 20; Japan operating classes 60, 61. Just use the global numbers instead (128, 129) Brian Hart, Cisco Systems

Operating Class Tables (2/4) Is a standalone Global Operating Table better? Usually not. • How would an AP use only the Global Operating Table? • Consider an AP that supports multiple bandwidths (and so multiple Operating Classes) and wishes to support legacy clients that only understand older country-table-specific operating classes • Country-table-specific operating classes are the default expectation for 11k/s/v devices • Practically the AP would be stuck with its local Country Operating Class Table, and the 802.11 would have to continue to maintain this table, even for regulations that did not deviate from international norms • It doesn’t get better elsewhere - domains other than US/Europe/Japan with just one highly specific regulation would have their own table created • Then, to get most use out of the ECSA and Supported Operating Classes elements etc, all global classes would have to be replicated in that country’s table too • Thus a separate Global operating table is only useful for 100% vanilla countries. • (Or, two Country elements could be sent: country-specific first, global second • High risk that clients of erratic behavior – not advised) Brian Hart, Cisco Systems

Operating Class Tables (3/4) Solution Details • Differentiate Operating Classes purely by 2-octet Country code and Operating Class: 1-80 is country-dependent, 81-191 is Global (and country-independent), 192-254 is Vendor Specific (e.g. 254 is used by the Bluetooth SIG), 0,255 are reserved • Aggressively deprecate Operating Classes made redundant by 11mb changes to maximize room for future growth. Start this at VHT APs: disallow them from using operating classes identified as redundant Aggressively deprecate redundant Country Operating Classes to create room for future growth (Japan can be lowered to ~22/80 i.e. The same values are used worldwide Brian Hart, Cisco Systems

Operating Class Tables (4/4) Supported Operating Classes Element • The Supported Operating Classes element advertises the operating classes that a STA is capable of operating “within this country” • No Table is specified, so must be wrt the Table indicated in the Country element by the AP • i.e. no ability to report the support of Operating Classes in a different table • E.g. consider a client associated to Japan 4.94-4.99 and 5.03-5.091 GHz. Due to the specific regulatory features in this band and country, the AP needs to advertise an operating class from the Japan table. • Therefore client’s supported operating classes must be reported using the values from the Japan table • Note that a legacy 11j STA knows about 3x the number of operating classes as are now defined in the Global Operating Table. (It is believe that there is limited field support for these Operating Classes, and so most can be aggressively deprecated then reclaimed at a later time, with little impact) • But, if we adopt the thinking of the earlier slide, no change is needed to the Supported Operating Classes element – in a given country, the operating classes that can be reported are the union of the country table and the global table Brian Hart, Cisco Systems

Shared Spectrum (1/3) Background • BTW, 5.725 to 5.825 GHz is shared spectrum (15.247, UNII): your device can be homologated under one or both of two sets of regulations – “shared spectrum” • But this is mostly OK: a UNII client can be associated to a 15.247 AP or vice versa, as long as each individually meets its regulatory requirements Brian Hart, Cisco Systems

Shared Spectrum (2/3) AP declaration of its rules • Currently the Operating Class is overloaded with two sets of semantics: a) the permissions of the BSS: i.e. AP indicates permissions to clients so that they can follow them, and b) the regulations under which the AP is presently operating (e.g. UNII or 15.247) • If clients can join an AP under one of multiple regulations, and if the AP is homologated under several regulations then the AP should be able to advertise multiple operating classes per BSS (= for clients) for the same bandwidth • But which one is the AP adopting for its own transmissions? • The simplest idea is “the first transmitted regulations”. But, if the advertising order is first-promulgated-regulation-transmitted-first (to avoid disconcerting legacy STAs) then the AP cannot take advantage of newer regulations • Solution: Redefine First Channel according to the following table • (First Channel is now defined as 1-200, 201 or 224-227) Brian Hart, Cisco Systems

Shared Spectrum (3/3)Client Association to AP • If an AP is homologated under one set of regulations and the client is homologated under a different set, and the client’s set of regulations is time/location*/AP-state dependent, then the AP cannot help the client be compliant, so there are several possibilities for manufacturers in order that their products can get homologated: • Client must not associate to the AP, or • Client must configure itself to be compliant regardless of the time/location/AP-state dependence of the regulations (if such a configuration even exists) • *Where the location dependence is finer grained than the Country, since an AP can help to this extent • Solution: Add a Note that client homologated for one regulatory class may associate to an AP not homologated for that regulatory class only if the client is able to ensure compliance without help from the AP Brian Hart, Cisco Systems

Open Discussion Brian Hart, Cisco Systems

Backup Slides Brian Hart, Cisco Systems

Some non-Wi-Fi product vendors have not maintained our level of care – and we want to continue avoiding their path It is generally regarded as a career-limiting maneuver to depend on a senior exec to clean up your mess • E.g. FCC enforcement: 15 companies named, shamed and/or fined at: http://www.fcc.gov/encyclopedia/weather-radar-interference-enforcement • For one large corporation, the Consent Decree included: • a. Compliance Officer. LargeCorp will designate a senior corporate manager ("Compliance Officer") who is responsible for administering the Compliance Plan. • c. Compliance Reports. LargeCorp will file compliance reports with the Commission 90 days after the Effective Date, 12 months after the Effective Date, and 24 months after the Effective Date. Each report shall include a compliance certificate from the Compliance Officer stating that the Compliance Officer has personal knowledge that LargeCorp has established operating procedures intended to ensure compliance with this Consent Decree, together with an accompanying statement explaining the basis for the Compliance Officer's compliance certification. • b. Training. LargeCorp will train and provide materials concerning Section 302(b) of the Act and Parts 2 and 15 of the Rules pertaining to U-NII devices and the requirements of the Consent Decree to those of its employees who are involved directly in the development and marketing of U-NII devices imported, marketed and sold by LargeCorp in the United States. i.e. the exec can now be subject to jail time if the mess doesn’t get cleaned up - and promptly: actions have consequences Re-engineering; and/or restricted orderability of products (fewer sales channels) Expensive personnel down-time Brian Hart, Cisco Systems

More regulatory background • Each client’s manufacturer is responsible for ensuring that the client meets the regulations for which it was homologated • Obvious … but also incomplete • More importantly, the default unlicensed radio frequency device regulatory approval is as a master device; to be approved as a client device the manufacturer must show that the frequencies and transmit powers the client device uses conform to regulations: • client devices have the obligation to emit equal or less than what masters permit them to • using exactly the same mechanisms that masters and clients were documented to use when working together when masters and clients were presented by manufacturer for homologation (see next slide) • Especially if the local regulations could be location/time/AP-state dependent, but – by the previous bullet – actually anyhow, then the client also needs to hear the client permissions from its AP • The client needs to get enough current-channel permissions from the Beacon that it can transmit to the AP (bootstrap) and preferably select one AP over another • The client needs to get all current-channel permissions from the Probe/(Re)Assoc Response that it can participate fully in the BSS • The client needs to get the next-channel permissions before/inside the channel switch Brian Hart, Cisco Systems

WISPA Links • Are you near TDWR? • http://wispa.cms.memberfuse.com/tdwr-locations-and-frequencies • // starting to list two frequencies per TDWR • If so, register here • http://www.spectrumbridge.com/udia/home.aspx • “This tool allows a user (network operator or installer) to: • Search and confirm if their device is operating within 35 km proximity of TDWR site(s) • Voluntarily register certain technical information into the online database” Brian Hart, Cisco Systems

5 GHz reality • 11a/11h: CSA frame contains CSA element/CSA element in Bea/PrResp; takes you to anywhere within 5 GHz • 11n: • CSA element + Secondary Channel Offset element in Bea/PrResp • 11a/11h clients only had to understand the CSA element to get switched • CSA element is marked as not extensible by 11mb • CSA frame contains CSA element + Secondary Channel Offset element • 11a/11h clients only had to understand the CSA element in the frame to get switched • ECSA element contains Operating Class and Ch# • Have to also send the CSA element for 11a/11h clients to get switched • ECSA element is marked as not extensible by 11mb • ECSA frame contains Operating Class and Ch# • Operating class encodes location of primary channel within 40 MHz • Neither ECSA nor Operating Class understood by 11a/11h clients • Have to also send CSA frame for 11a/11h clients to get switched • Shall send CSA+optionally-ECSA or ECSA+optionally-CSA if dot11ExtendedChannelSwitchActivated is false or true respectively • CSA – freq only; no AP-state; ECSA – includes operating class to report AP state • dot11ExtendedChannelSwitchActivated must be true for 3.65 GHz, 11v, or mesh (but not for 11n nor 11ac) • So we must allow for a mix of dot11ExtendedChannelSwitchActivated true and false • No CSA<2004, rules came in 2005 for ChAvCheck; and then CSA start to be required practically; so 2004-2005 was like <2004 • Operating triplets are little used Brian Hart, Cisco Systems

TPC, Operating Classes, and Channel Switching