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wifi: Fix the time the NSlotsLeftAlert CAM trace is fired

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It cannot be earlier than the access grant start time.
This commit is contained in:
Stefano Avallone
2025-01-19 22:54:48 +01:00
parent 96fa2a6753
commit df7f3ef27b
4 changed files with 67 additions and 25 deletions
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1
RELEASE_NOTES.md
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@@ -41,6 +41,7 @@ The required Doxygen version for documentation generation is now version 1.13.
- (mobility) !2397 - Fix Rectangle::GetClosestSideOrCorner. It could assign the incorrect side when the checked position was outside the rectangle.
- (wifi) #2368 - Fix various issues related to Content Channels and RU allocation. Fixes mostly covers cases where OFDMA is used with central 26 tones, where a single user is being assigned the whole PPDU bandwidth or where a RU is larger than 20 MHz.
- (zigbee) !2383 - Fix malformed RREP command with missing command options field.
- (wifi) Fix the time the `NSlotsLeftAlert` trace source of `ChannelAccessManager` is fired (it cannot be earlier than the access grant start time)
## Release 3.44

55
src/wifi/doc/source/wifi-design.rst
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@@ -1408,22 +1408,45 @@ A similar check is applied to possibly postpone the switch back to the preferred
SwitchMainPhyBack timer expires.
The Advanced EMLSR Manager also connects a callback to the ``NSlotsLeftAlert`` trace source of the
Channel Access Manager, which sends notifications when at most a configurable number of slots
remain until the backoff of an AC expires. When the Advanced EMLSR Manager receives such a
notification, it evaluates the opportunity of switching the main PHY to the auxiliary link on which
the notification has been received. Specifically, the Advanced EMLSR Manager performs the check
described above to determine whether the potential UL transmit opportunity shall be dropped (it is
dropped if a PPDU being received on another EMLSR link might be an ICF and the ``AllowUlTxopInRx``
attribute is set to false) and then it checks whether it is convenient for the main PHY to switch
to the auxiliary link as described above (with the exception that the expected delay until backoff
end is also taken into account). If the main PHY is requested to switch to the auxiliary link and
the backoff on the auxiliary link counts down to zero while the main PHY is switching, a NAV and
CCA check is performed as described above (by the aux PHY in the PIFS period preceding the main PHY
channel switch end or by the main PHY in the PIFS period following the main PHY channel switch end).
Similarly, a NAV and CCA check is performed (by the main PHY) if the remaining backoff time when
the main PHY switch is completed is less than a PIFS. Otherwise, SwitchMainPhyBack timer is started
having a duration of SwitchMainPhyBackDelay plus the remaining time until the backoff of the AC
involved in the Channel Access Manager notification is expected to expire.
Channel Access Manager, which sends notifications when at most a configurable number of slots remain
until the backoff of an AC expires. It must be noted that this notification is only sent if channel
access has been requested by the AC for which the number of remaining backoff slots has reached
the given threshold. Thus, if an AC terminates a TXOP and generates a new backoff value, but it
has no packets in the queue, then channel access is not requested and the notification is not
scheduled; if a new packet arrives after that the backoff counter has reached zero, channel access
is requested and notification is sent immediately (while channel access is gained at the next slot
boundary, which may be a few microseconds later). If channel access is requested while the backoff
counter is non-zero, the notification is sent when the number of slots remaining until the backoff
of an AC expires reaches the configured value, if the backoff counter starts at a value greater than
or equal to the configured value, or as soon as the notification can be sent based on the value of
the ``NSlotsLeftMinDelay`` attribute of the Channel Access Manager. This attribute indicates the
minimum amount of time that must elapse since the start of the AIFS to enable the dispatching of
the notification. Example:
::
BE AC (thus AIFS = SIFS + 3 * slots), Backoff = 3, NSlotsLeft >= 5, NSlotsLeftMinDelay = PIFS
|------AIFS--------|
| SIFS | s | s | s | s | s | s |
^
|
send notification
When the Advanced EMLSR Manager receives such a notification, it evaluates the opportunity of
switching the main PHY to the auxiliary link on which the notification has been received. Specifically,
the Advanced EMLSR Manager performs the check described above to determine whether the potential UL
transmit opportunity shall be dropped (it is dropped if a PPDU being received on another EMLSR link
might be an ICF and the ``AllowUlTxopInRx`` attribute is set to false) and then it checks whether it is
convenient for the main PHY to switch to the auxiliary link as described above (with the exception that
the expected delay until backoff end is also taken into account). If the main PHY is requested to switch
to the auxiliary link and the backoff on the auxiliary link counts down to zero while the main PHY is
switching, a NAV and CCA check is performed as described above (by the aux PHY in the PIFS period
preceding the main PHY channel switch end or by the main PHY in the PIFS period following the main PHY
channel switch end). Similarly, a NAV and CCA check is performed (by the main PHY) if the remaining
backoff time when the main PHY switch is completed is less than a PIFS. Otherwise, SwitchMainPhyBack
timer is started having a duration of SwitchMainPhyBackDelay plus the remaining time until the backoff
of the AC involved in the Channel Access Manager notification is expected to expire.
The Advanced EMLSR Manager has the ``InterruptSwitch`` attribute that can be set to true to
interrupt a main PHY switch when it is determined that the main PHY shall switch to a different

31
src/wifi/model/channel-access-manager.cc
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@@ -29,6 +29,8 @@ NS_LOG_COMPONENT_DEFINE("ChannelAccessManager");
NS_OBJECT_ENSURE_REGISTERED(ChannelAccessManager);
const Time ChannelAccessManager::DEFAULT_N_SLOTS_LEFT_MIN_DELAY = MicroSeconds(25);
/**
* Listener for PHY events. Forwards to ChannelAccessManager.
* The ChannelAccessManager may handle multiple PHY listeners connected to distinct PHYs,
@@ -187,16 +189,23 @@ ChannelAccessManager::GetTypeId()
MakeBooleanAccessor(&ChannelAccessManager::m_proactiveBackoff),
MakeBooleanChecker())
.AddAttribute("NSlotsLeft",
"Fire the NSlotsLeftAlert trace source when the backoff counter with "
"the minimum value among all ACs reaches this value or it is started "
"with a value less than this attribute. If this value is zero, the "
"trace source is never fired.",
"The NSlotsLeftAlert trace source is fired when the number of remaining "
"backoff slots for any AC is equal to or less than the value of this "
"attribute. Note that the trace source is fired only if the AC for which "
"the previous condition is met has requested channel access. Also, if "
"the value of this attribute is zero, the trace source is never fired.",
UintegerValue(0),
MakeUintegerAccessor(&ChannelAccessManager::m_nSlotsLeft),
MakeUintegerChecker<uint8_t>())
.AddAttribute("NSlotsLeftMinDelay",
"The minimum gap between the end of a medium busy event and the time "
"the NSlotsLeftAlert trace source can be fired.",
TimeValue(ChannelAccessManager::DEFAULT_N_SLOTS_LEFT_MIN_DELAY),
MakeTimeAccessor(&ChannelAccessManager::m_nSlotsLeftMinDelay),
MakeTimeChecker())
.AddTraceSource("NSlotsLeftAlert",
"The backoff counter of the AC with the given index reached the "
"threshold set through the NSlotsLeft attribute.",
"The number of remaining backoff slots for the AC with the given index "
"reached the threshold set through the NSlotsLeft attribute.",
MakeTraceSourceAccessor(&ChannelAccessManager::m_nSlotsLeftCallback),
"ns3::ChannelAccessManager::NSlotsLeftCallback");
return tid;
@@ -799,10 +808,14 @@ ChannelAccessManager::DoRestartAccessTimeoutIfNeeded()
if (m_nSlotsLeft > 0)
{
if (const auto slots = m_nSlotsLeft * GetSlot(); expectedBackoffDelay > slots)
const auto expectedNotifyTime =
Max(expectedBackoffEnd - m_nSlotsLeft * GetSlot(),
accessGrantStart - GetSifs() + m_nSlotsLeftMinDelay);
if (expectedNotifyTime > now)
{
// make the timer expire when the specified number of slots are left
expectedBackoffDelay -= slots;
// make the timer expire when it's time to notify that the given slots are left
expectedBackoffDelay = expectedNotifyTime - now;
}
else
{

5
src/wifi/model/channel-access-manager.h
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@@ -511,6 +511,11 @@ class ChannelAccessManager : public Object
uint8_t m_nSlotsLeft; //!< fire the NSlotsLeftAlert trace source when the
//!< backoff counter with the minimum value among all
//!< ACs reaches this value
Time m_nSlotsLeftMinDelay; //!< the minimum gap between the end of a medium busy event and
//!< the time the NSlotsLeftAlert trace source can be fired
/// default value for the NSlotsLeftMinDelay attribute, corresponds to a PIFS in 5GHz/6GHz bands
static const Time DEFAULT_N_SLOTS_LEFT_MIN_DELAY;
/**
* TracedCallback signature for NSlotsLeft alerts.