tid-to-link-mapping-element.cc

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/*
 * Copyright (c) 2022
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Sharan Naribole <sharan.naribole@gmail.com>
 */
 
#include "tid-to-link-mapping-element.h"
 
#include "ns3/assert.h"
#include "ns3/simulator.h"
 
namespace ns3
{
 
/// Bitmask with all bits from 63 to 26 set to 1, all the others set to 0
static constexpr uint64_t BIT_63_TO_26_MASK = 0xfffffffffc000000;
 
uint16_t
TidToLinkMapping::Control::GetSubfieldSize() const
{
    // IEEE 802.11be D3.1 Figure 9-1002ap
    NS_ASSERT_MSG(!defaultMapping || !presenceBitmap.has_value(),
                  "Presence bitmap not expected if default mapping is set");
    auto size = WIFI_TID_TO_LINK_MAPPING_CONTROL_BASIC_SIZE_B;
    if (!presenceBitmap.has_value())
    {
        return size;
    }
    return size + WIFI_LINK_MAPPING_PRESENCE_IND_SIZE_B;
}
 
void
TidToLinkMapping::Control::Serialize(Buffer::Iterator& start) const
{
    auto val = static_cast<uint8_t>(direction) | ((defaultMapping ? 1 : 0) << 2) |
               ((mappingSwitchTimePresent ? 1 : 0) << 3) |
               ((expectedDurationPresent ? 1 : 0) << 4) | ((linkMappingSize == 1 ? 1 : 0) << 5);
 
    start.WriteU8(val);
    NS_ASSERT_MSG(!defaultMapping || !presenceBitmap.has_value(),
                  "Presence bitmap not expected if default mapping is set");
    if (presenceBitmap.has_value())
    {
        start.WriteU8(presenceBitmap.value());
    }
}
 
uint16_t
TidToLinkMapping::Control::Deserialize(Buffer::Iterator start)
{
    auto i = start;
    uint8_t count = 0;
    auto val = i.ReadU8();
    count++;
 
    direction = static_cast<WifiDirection>(val & 0x03);
    defaultMapping = (((val >> 2) & 0x01) == 1);
    mappingSwitchTimePresent = (((val >> 3) & 0x01) == 1);
    expectedDurationPresent = (((val >> 4) & 0x01) == 1);
    linkMappingSize = (((val >> 5) & 0x01) == 1 ? 1 : 2);
    if (defaultMapping)
    {
        presenceBitmap.reset();
        return count;
    }
    presenceBitmap = i.ReadU8();
    return ++count;
}
 
WifiInformationElementId
TidToLinkMapping::ElementId() const
{
    return IE_EXTENSION;
}
 
WifiInformationElementId
TidToLinkMapping::ElementIdExt() const
{
    return IE_EXT_TID_TO_LINK_MAPPING_ELEMENT;
}
 
void
TidToLinkMapping::SetMappingSwitchTime(Time mappingSwitchTime)
{
    // The 2 octet Mapping Switch Time field has units of TUs and is set to the time at which
    // the new mapping is established using as a time-base the value of the TSF corresponding
    // to the BSS identified by the BSSID of the frame containing the TID-To-Link Mapping
    // element: i.e., bits 10 to 25 of the TSF. (Sec. 9.4.2.314 of 802.11be D3.1)
    NS_ABORT_IF(mappingSwitchTime < Simulator::Now());
    auto switchTimeUsec = static_cast<uint64_t>(mappingSwitchTime.GetMicroSeconds());
    // set the Mapping Switch Time field to bits 10 to 25 of the given time
    m_mappingSwitchTime = (switchTimeUsec & ~BIT_63_TO_26_MASK) >> 10;
    m_control.mappingSwitchTimePresent = true;
}
 
std::optional<Time>
TidToLinkMapping::GetMappingSwitchTime() const
{
    if (!m_control.mappingSwitchTimePresent)
    {
        return std::nullopt;
    }
 
    auto nowUsec = static_cast<uint64_t>(Simulator::Now().GetMicroSeconds());
    uint64_t switchTimeUsec = (*m_mappingSwitchTime << 10) + (nowUsec & BIT_63_TO_26_MASK);
    if (switchTimeUsec < nowUsec)
    {
        // The switch time derived from the value in the corresponding field may be less than the
        // current time in case the bits 10 to 25 of TSF have been reset since the transmission
        // of the frame carrying this field. In such a case we have to increase bits 63 to 26 by 1
        switchTimeUsec += (1 << 26);
    }
    return MicroSeconds(switchTimeUsec);
}
 
void
TidToLinkMapping::SetExpectedDuration(Time expectedDuration)
{
    auto durationTu = static_cast<uint64_t>(expectedDuration.GetMicroSeconds()) >> 10;
    m_expectedDuration = (durationTu & 0x0000000000ffffff); // Expected Duration size is 3 bytes
    m_control.expectedDurationPresent = true;
}
 
std::optional<Time>
TidToLinkMapping::GetExpectedDuration() const
{
    if (!m_control.expectedDurationPresent)
    {
        return std::nullopt;
    }
 
    return MicroSeconds(*m_expectedDuration << 10);
}
 
void
TidToLinkMapping::SetLinkMappingOfTid(uint8_t tid, std::set<uint8_t> linkIds)
{
    NS_ABORT_MSG_IF(tid > 7, "Invalid tid: " << +tid);
    NS_ABORT_MSG_IF(m_control.defaultMapping,
                    "Per-TID link mapping not expected if default mapping is set");
 
    // derive link mapping for the given TID
    uint16_t linkMapping = 0;
 
    for (const auto& linkId : linkIds)
    {
        linkMapping |= (1 << linkId);
        if (linkId > 7)
        {
            m_control.linkMappingSize = 2;
        }
    }
 
    m_linkMapping[tid] = linkMapping;
    m_control.presenceBitmap = m_control.presenceBitmap.value_or(0) | (1 << tid);
}
 
std::set<uint8_t>
TidToLinkMapping::GetLinkMappingOfTid(uint8_t tid) const
{
    auto it = m_linkMapping.find(tid);
 
    if (it == m_linkMapping.cend())
    {
        return {};
    }
 
    std::set<uint8_t> linkIds;
    for (uint8_t linkId = 0; linkId < 15; linkId++)
    {
        if (((it->second >> linkId) & 0x0001) == 1)
        {
            linkIds.insert(linkId);
        }
    }
    NS_ABORT_MSG_IF(linkIds.empty(), "TID " << +tid << " cannot be mapped to an empty link set");
 
    return linkIds;
}
 
uint16_t
TidToLinkMapping::GetInformationFieldSize() const
{
    // IEEE 802.11be D3.1 9.4.2.314 TID-To-Link Mapping element
    uint16_t ret = WIFI_IE_ELEMENT_ID_EXT_SIZE; // Element ID Extension
    ret += m_control.GetSubfieldSize();
    if (m_control.mappingSwitchTimePresent)
    {
        ret += 2; // Mapping Switch Time
    }
    if (m_control.expectedDurationPresent)
    {
        ret += 3; // Expected Duration
    }
 
    NS_ASSERT_MSG(!m_control.defaultMapping || m_linkMapping.empty(),
                  "Per-TID link mapping not expected if default mapping is set");
    ret += m_control.linkMappingSize * (m_linkMapping.size());
    return ret;
}
 
void
TidToLinkMapping::SerializeInformationField(Buffer::Iterator start) const
{
    // IEEE 802.11be D3.1 9.4.2.314 TID-To-Link Mapping element
    m_control.Serialize(start);
    if (m_control.mappingSwitchTimePresent)
    {
        start.WriteHtolsbU16(*m_mappingSwitchTime);
    }
    if (m_control.expectedDurationPresent)
    {
        start.WriteU8((*m_expectedDuration >> 0) & 0xff);
        start.WriteU8((*m_expectedDuration >> 8) & 0xff);
        start.WriteU8((*m_expectedDuration >> 16) & 0xff);
    }
 
    NS_ASSERT_MSG(!m_control.defaultMapping || m_linkMapping.empty(),
                  "Per-TID link mapping not expected if default mapping is set");
 
    for (const auto& [tid, linkMapping] : m_linkMapping)
    {
        if (m_control.linkMappingSize == 1)
        {
            start.WriteU8(linkMapping);
        }
        else
        {
            start.WriteHtolsbU16(linkMapping);
        }
    }
}
 
uint16_t
TidToLinkMapping::DeserializeInformationField(Buffer::Iterator start, uint16_t length)
{
    auto i = start;
    uint16_t count = 0;
    auto nCtrlOctets = m_control.Deserialize(i);
    NS_ASSERT_MSG(nCtrlOctets <= length, "Tid-to-Link Mapping deserialize error");
    i.Next(nCtrlOctets);
    count += nCtrlOctets;
    if (m_control.mappingSwitchTimePresent)
    {
        m_mappingSwitchTime = i.ReadLsbtohU16();
        count += 2;
    }
    if (m_control.expectedDurationPresent)
    {
        uint8_t byte0 = i.ReadU8();
        uint8_t byte1 = i.ReadU8();
        uint8_t byte2 = i.ReadU8();
        m_expectedDuration = byte2;
        m_expectedDuration.value() <<= 8;
        m_expectedDuration.value() |= byte1;
        m_expectedDuration.value() <<= 8;
        m_expectedDuration.value() |= byte0;
        count += 3;
    }
    m_linkMapping.clear();
    if (m_control.presenceBitmap.has_value())
    {
        NS_ABORT_MSG_IF(m_control.defaultMapping,
                        "Default mapping should not be set when presence bitmap is present");
        const auto presenceBitmap = m_control.presenceBitmap.value();
        for (uint8_t tid = 0; tid < 8; tid++)
        {
            if (((presenceBitmap >> tid) & 0x01) == 1)
            {
                if (m_control.linkMappingSize == 1)
                {
                    m_linkMapping[tid] = i.ReadU8();
                    count++;
                }
                else
                {
                    m_linkMapping[tid] = i.ReadLsbtohU16();
                    count += 2;
                }
            }
        }
    }
 
    NS_ABORT_MSG_IF(count != length,
                    "TID-to-Link Mapping Length (" << +length
                                                   << ") differs "
                                                      "from actual number of bytes read ("
                                                   << +count << ")");
    return count;
}
 
} // namespace ns3