CSIT-992: Add libraries for optimized search

+ Place the libraries into resources/libraries/python/search/.
 + Except OptimizedTrexSearch in TrafficGenerator.py
+ Change traffic generator to support floats for duration and warmup.
+ Remove explicit type conversions where not needed.
+ Add robot keywords to performance_utils.robot
 + for calling the optimized search.
 + for reporting the resulting values.
 + for checking the minimal performance has been reached.
 + for running five second "Traffic should pass with no loss" after the search.
- Add methodology documentation in subsequent Change.
- Add simulator for testing algorithm correctness in a subsequent Change.
- Add tests using the libraries in subsequent Change.

Change-Id: Ia041008382ee4c9a562172099aea794c854d5f2f
Signed-off-by: Vratko Polak <vrpolak@cisco.com>

7 files changed, 783 insertions, 0 deletions

diff --git a/resources/libraries/python/search/AbstractRateProvider.py b/resources/libraries/python/search/AbstractRateProvider.py
new file mode 100644
index 0000000000..125c2af8cc
--- /dev/null
+++ b/resources/libraries/python/search/AbstractRateProvider.py
@@ -0,0 +1,35 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining AbstractRateProvider class."""
+
+from abc import ABCMeta, abstractmethod
+
+
+class AbstractRateProvider(object):
+    """Abstract class defining common API for rate providers."""
+
+    __metaclass__ = ABCMeta
+
+    @abstractmethod
+    def measure(self, duration, transmit_rate):
+        """Perform trial measurement and return the result.
+
+        :param duration: Trial duration [s].
+        :param transmit_rate: Target transmit rate [pps].
+        :type duration: float
+        :type transmit_rate: float
+        :returns: Structure containing the result of the measurement.
+        :rtype: ReceiveRateMeasurement
+        """
+        pass
diff --git a/resources/libraries/python/search/AbstractSearchAlgorithm.py b/resources/libraries/python/search/AbstractSearchAlgorithm.py
new file mode 100644
index 0000000000..ae326bd4ca
--- /dev/null
+++ b/resources/libraries/python/search/AbstractSearchAlgorithm.py
@@ -0,0 +1,49 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining AbstractSearchAlgorithm class."""
+
+from abc import ABCMeta, abstractmethod
+
+
+class AbstractSearchAlgorithm(object):
+    """Abstract class defining common API for search algorithms."""
+
+    __metaclass__ = ABCMeta
+
+    def __init__(self, rate_provider):
+        """Store the rate provider.
+
+        :param rate_provider: Object able to perform trial measurements.
+        :type rate_provider: AbstractRateProvider
+        """
+        # TODO: Type check for AbstractRateProvider?
+        self.rate_provider = rate_provider
+
+    @abstractmethod
+    def narrow_down_ndr_and_pdr(
+            self, fail_rate, line_rate, allowed_drop_fraction):
+        """Perform measurements to narrow down intervals, return them.
+
+        :param fail_rate: Minimal target transmit rate [pps].
+        :param line_rate: Maximal target transmit rate [pps].
+        :param allowed_drop_fraction: Fraction of dropped packets for PDR [1].
+        :type fail_rate: float
+        :type line_rate: float
+        :type allowed_drop_fraction: float
+        :returns: Structure containing narrowed down intervals
+            and their measurements.
+        :rtype: NdrPdrResult
+        """
+        # TODO: Do we agree on arguments related to precision or trial duration?
+        pass
diff --git a/resources/libraries/python/search/NdrPdrResult.py b/resources/libraries/python/search/NdrPdrResult.py
new file mode 100644
index 0000000000..47fb757c07
--- /dev/null
+++ b/resources/libraries/python/search/NdrPdrResult.py
@@ -0,0 +1,65 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining NdrPdrResult class."""
+
+from .ReceiveRateInterval import ReceiveRateInterval
+
+
+class NdrPdrResult(object):
+    """Two measurement intervals, return value of search algorithms.
+
+    Partial fraction is NOT part of the result. Pdr interval should be valid
+    for all partial fractions implied by the interval."""
+
+    def __init__(self, ndr_interval, pdr_interval):
+        """Store the measured intervals after checking argument types.
+
+        :param ndr_interval: Object containing data for NDR part of the result.
+        :param pdr_interval: Object containing data for PDR part of the result.
+        :type ndr_interval: ReceiveRateInterval
+        :type pdr_interval: ReceiveRateInterval
+        """
+        # TODO: Type checking is not very pythonic,
+        # perhaps users can fix wrong usage without it?
+        if not isinstance(ndr_interval, ReceiveRateInterval):
+            raise TypeError("ndr_interval, is not a ReceiveRateInterval: "
+                            "{ndr!r}".format(ndr=ndr_interval))
+        if not isinstance(pdr_interval, ReceiveRateInterval):
+            raise TypeError("pdr_interval, is not a ReceiveRateInterval: "
+                            "{pdr!r}".format(pdr=pdr_interval))
+        self.ndr_interval = ndr_interval
+        self.pdr_interval = pdr_interval
+
+    def width_in_goals(self, relative_width_goal):
+        """Return a debug string related to current widths in logarithmic scale.
+
+        :param relative_width_goal: Upper bound times this is the goal
+            difference between upper bound and lower bound.
+        :type relative_width_goal: float
+        :returns: Message containing NDR and PDR widths in goals.
+        :rtype: str
+        """
+        return "ndr {ndr_in_goals}; pdr {pdr_in_goals}".format(
+            ndr_in_goals=self.ndr_interval.width_in_goals(relative_width_goal),
+            pdr_in_goals=self.pdr_interval.width_in_goals(relative_width_goal))
+
+    def __str__(self):
+        """Return string as tuple of named values."""
+        return "NDR={ndr!s};PDR={pdr!s}".format(
+            ndr=self.ndr_interval, pdr=self.pdr_interval)
+
+    def __repr__(self):
+        """Return string evaluable as a constructor call."""
+        return "NdrPdrResult(ndr_interval={ndr!r},pdr_interval={pdr!r})".format(
+            ndr=self.ndr_interval, pdr=self.pdr_interval)
diff --git a/resources/libraries/python/search/OptimizedSearchAlgorithm.py b/resources/libraries/python/search/OptimizedSearchAlgorithm.py
new file mode 100644
index 0000000000..43559e049b
--- /dev/null
+++ b/resources/libraries/python/search/OptimizedSearchAlgorithm.py
@@ -0,0 +1,480 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining OptimizedSearchAlgorithm class."""
+
+import logging
+import math
+import time
+
+from .AbstractSearchAlgorithm import AbstractSearchAlgorithm
+from .NdrPdrResult import NdrPdrResult
+from .ReceiveRateInterval import ReceiveRateInterval
+
+
+class OptimizedSearchAlgorithm(AbstractSearchAlgorithm):
+    """Optimized binary search algorithm for finding NDR and PDR bounds.
+
+    Traditional binary search algorithm needs initial interval
+    (lower and upper bound), and returns final interval after bisecting
+    (until some exit condition is met).
+    The exit condition is usually related to the interval width,
+    (upper bound value minus lower bound value).
+
+    The optimized algorithm contains several improvements
+    aimed to reduce overall search time.
+
+    One improvement is searching for two intervals at once.
+    The intervals are for NDR (No Drop Rate) and PDR (Partial Drop Rate).
+
+    Next improvement is that the initial interval does need to be valid.
+    Imagine initial interval (10, 11) where 11 is smaller
+    than the searched value.
+    The algorithm will try (11, 13) interval next, and if 13 is still smaller,
+    (13, 17) and so on, doubling width until the upper bound is valid.
+    The part when interval expands is called external search,
+    the part when interval is bisected is called internal search.
+
+    Next improvement is that trial measurements at small trial duration
+    can be used to find a reasonable interval for full trial duration search.
+    This results in more trials performed, but smaller overall duration
+    in general.
+
+    Next improvement is bisecting in logarithmic quantities,
+    so that exit criteria can be independent of measurement units.
+
+    Next improvement is basing the initial interval on receive rates.
+
+    Final improvement is exiting early if the minimal value
+    is not a valid lower bound.
+
+    The complete search consist of several phases,
+    each phase performing several trial measurements.
+    Initial phase creates initial interval based on receive rates
+    at maximum rate and at maximum receive rate (MRR).
+    Final phase and preceding intermediate phases are performing
+    external and internal search steps,
+    each resulting interval is the starting point for the next phase.
+    The resulting interval of final phase is the result of the whole algorithm.
+
+    Each non-initial phase uses its own trial duration and width goal.
+    Any non-initial phase stops searching (for NDR or PDR independently)
+    when minimum is not a valid lower bound (at current duration),
+    or all of the following is true:
+    Both bounds are valid, bound bounds are measured at the current phase
+    trial duration, interval width is less than the width goal
+    for current phase."""
+
+    class ProgressState(object):
+        """Structure containing data to be passed around in recursion."""
+
+        def __init__(self, result, phases, duration, width_goal,
+                     allowed_drop_fraction, fail_rate, line_rate):
+            """Convert and store the argument values.
+
+            :param result: Current measured NDR and PDR intervals.
+            :param phases: How many intermediate phases to perform
+                before the current one.
+            :param duration: Trial duration to use in the current phase [s].
+            :param width_goal: The goal relative width for the curreent phase.
+            :param allowed_drop_fraction: PDR fraction for the current search.
+            :param fail_rate: Minimum target transmit rate
+                for the current search [pps].
+            :param line_rate: Maximum target transmit rate
+                for the current search [pps].
+            :type result: NdrPdrResult
+            :type phases: int
+            :type duration: float
+            :type width_goal: float
+            :type allowed_drop_fraction: float
+            :type fail_rate: float
+            :type line_rate: float
+            """
+            self.result = result
+            self.phases = int(phases)
+            self.duration = float(duration)
+            self.width_goal = float(width_goal)
+            self.allowed_drop_fraction = float(allowed_drop_fraction)
+            self.fail_rate = float(fail_rate)
+            self.line_rate = float(line_rate)
+
+    def __init__(self, rate_provider, final_relative_width=0.005,
+                 final_trial_duration=30.0, initial_trial_duration=1.0,
+                 intermediate_phases=2, timeout=600.0):
+        """Store rate provider and additional arguments.
+
+        :param rate_provider: Rate provider to use by this search object.
+        :param final_relative_width: Final lower bound transmit rate
+            cannot be more distant that this multiple of upper bound [1].
+        :param final_trial_duration: Trial duration for the final phase [s].
+        :param initial_trial_duration: Trial duration for the initial phase
+            and also for the first intermediate phase [s].
+        :param intermediate_phases: Number of intermediate phases to perform
+            before the final phase [1].
+        :param timeout: The search will fail itself when not finished
+            before this overall time [s].
+        :type rate_provider: AbstractRateProvider
+        :type final_relative_width: float
+        :type final_trial_duration: float
+        :type initial_trial_duration: int
+        :type intermediate_phases: int
+        :type timeout: float
+        """
+        super(OptimizedSearchAlgorithm, self).__init__(rate_provider)
+        self.final_trial_duration = float(final_trial_duration)
+        self.final_relative_width = float(final_relative_width)
+        self.intermediate_phases = int(intermediate_phases)
+        self.initial_trial_duration = float(initial_trial_duration)
+        self.timeout = float(timeout)
+
+    def narrow_down_ndr_and_pdr(
+            self, fail_rate, line_rate, allowed_drop_fraction):
+        """Perform initial phase, create state object, proceed with next phases.
+
+        :param fail_rate: Minimal target transmit rate [pps].
+        :param line_rate: Maximal target transmit rate [pps].
+        :param allowed_drop_fraction: Fraction of dropped packets for PDR [1].
+        :type fail_rate: float
+        :type line_rate: float
+        :type allowed_drop_fraction: float
+        :returns: Structure containing narrowed down intervals
+            and their measurements.
+        :rtype: NdrPdrResult
+        :raises RuntimeError: If total duration is larger than timeout.
+        """
+        fail_rate = float(fail_rate)
+        line_rate = float(line_rate)
+        allowed_drop_fraction = float(allowed_drop_fraction)
+        line_measurement = self.rate_provider.measure(
+            self.initial_trial_duration, line_rate)
+        # 0.999 is to avoid rounding errors which make
+        # the subsequent logic think the width is too broad.
+        max_lo = max(
+            fail_rate, line_rate * (1.0 - 0.999 * self.final_relative_width))
+        mrr = min(max_lo, max(fail_rate, line_measurement.receive_rate))
+        mrr_measurement = self.rate_provider.measure(
+            self.initial_trial_duration, mrr)
+        # Attempt to get narrower width.
+        max2_lo = max(
+            fail_rate, mrr * (1.0 - 0.999 * self.final_relative_width))
+        mrr2 = min(max2_lo, mrr_measurement.receive_rate)
+        if mrr2 > fail_rate:
+            line_measurement = mrr_measurement
+            mrr_measurement = self.rate_provider.measure(
+                self.initial_trial_duration, mrr2)
+        starting_interval = ReceiveRateInterval(
+            mrr_measurement, line_measurement)
+        starting_result = NdrPdrResult(starting_interval, starting_interval)
+        state = self.ProgressState(
+            starting_result, self.intermediate_phases,
+            self.final_trial_duration, self.final_relative_width,
+            allowed_drop_fraction, fail_rate, line_rate)
+        state = self.ndrpdr(state)
+        return state.result
+
+    def _measure_and_update_state(self, state, transmit_rate):
+        """Perform trial measurement, update bounds, return new state.
+
+        :param state: State before this measurement.
+        :param transmit_rate: Target transmit rate for this measurement [pps].
+        :type state: ProgressState
+        :type transmit_rate: float
+        :returns: State after the measurement.
+        :rtype: ProgressState
+        """
+        # TODO: Implement https://stackoverflow.com/a/24683360
+        # to avoid the string manipulation if log verbosity is too low.
+        logging.info("result before update: %s", state.result)
+        logging.debug(
+            "relative widths in goals: %s", state.result.width_in_goals(
+                self.final_relative_width))
+        measurement = self.rate_provider.measure(state.duration, transmit_rate)
+        ndr_interval = self._new_interval(
+            state.result.ndr_interval, measurement, 0.0)
+        pdr_interval = self._new_interval(
+            state.result.pdr_interval, measurement, state.allowed_drop_fraction)
+        state.result = NdrPdrResult(ndr_interval, pdr_interval)
+        return state
+
+    @staticmethod
+    def _new_interval(old_interval, measurement, allowed_drop_fraction):
+        """Return new interval with bounds updated according to the measurement.
+
+        :param old_interval: The current interval before the measurement.
+        :param measurement: The new meaqsurement to take into account.
+        :param allowed_drop_fraction: Fraction for PDR (or zero for NDR).
+        :type old_interval: ReceiveRateInterval
+        :type measurement: ReceiveRateMeasurement
+        :type allowed_drop_fraction: float
+        :returns: The updated interval.
+        :rtype: ReceiveRateInterval
+        """
+        old_lo, old_hi = old_interval.measured_low, old_interval.measured_high
+        # Priority zero: direct replace if the target Tr is the same.
+        if measurement.target_tr in (old_lo.target_tr, old_hi.target_tr):
+            if measurement.target_tr == old_lo.target_tr:
+                return ReceiveRateInterval(measurement, old_hi)
+            else:
+                return ReceiveRateInterval(old_lo, measurement)
+        # Priority one: invalid lower bound allows only one type of update.
+        if old_lo.drop_fraction > allowed_drop_fraction:
+            # We can only expand down, old bound becomes valid upper one.
+            if measurement.target_tr < old_lo.target_tr:
+                return ReceiveRateInterval(measurement, old_lo)
+            else:
+                return old_interval
+        # Lower bound is now valid.
+        # Next priorities depend on target Tr.
+        if measurement.target_tr < old_lo.target_tr:
+            # Lower external measurement, relevant only
+            # if the new measurement has high drop rate.
+            if measurement.drop_fraction > allowed_drop_fraction:
+                # Returning the broader interval as old_lo
+                # would be invalid upper bound.
+                return ReceiveRateInterval(measurement, old_hi)
+        elif measurement.target_tr > old_hi.target_tr:
+            # Upper external measurement, only relevant for invalid upper bound.
+            if old_hi.drop_fraction <= allowed_drop_fraction:
+                # Old upper bound becomes valid new lower bound.
+                return ReceiveRateInterval(old_hi, measurement)
+        else:
+            # Internal measurement, replaced boundary
+            # depends on measured drop fraction.
+            if measurement.drop_fraction > allowed_drop_fraction:
+                # We have found a narrow valid interval,
+                # regardless of whether old upper bound was valid.
+                return ReceiveRateInterval(old_lo, measurement)
+            else:
+                # In ideal world, we would not want to shrink interval
+                # if upper bound is not valid.
+                # In the real world, we want to shrink it for
+                # "invalid upper bound at line rate" case.
+                return ReceiveRateInterval(measurement, old_hi)
+        # Fallback, the interval is unchanged by the measurement.
+        return old_interval
+
+    @staticmethod
+    def double_relative_width(relative_width):
+        """Return relative width corresponding to double logarithmic width.
+
+        :param relative_width: The base relative width to double.
+        :type relative_width: float
+        :returns: The relative width of double logarithmic size.
+        :rtype: float
+        """
+        return 1.999 * relative_width - relative_width * relative_width
+        # The number should be 2.0, but we want to avoid rounding errors,
+        # and ensure half of double is not larger than the original value.
+
+    @staticmethod
+    def double_step_down(relative_width, current_bound):
+        """Return rate of double logarithmic width below.
+
+        :param relative_width: The base relative width to double.
+        :param current_bound: The current target transmit rate to move [pps].
+        :type relative_width: float
+        :type current_bound: float
+        :returns: Transmit rate smaller by logarithmically double width [pps].
+        :rtype: float
+        """
+        return current_bound * (
+            1.0 - OptimizedSearchAlgorithm.double_relative_width(
+                relative_width))
+
+    @staticmethod
+    def double_step_up(relative_width, current_bound):
+        """Return rate of double logarithmic width above.
+
+        :param relative_width: The base relative width to double.
+        :param current_bound: The current target transmit rate to move [pps].
+        :type relative_width: float
+        :type current_bound: float
+        :returns: Transmit rate larger by logarithmically double width [pps].
+        :rtype: float
+        """
+        return current_bound / (
+            1.0 - OptimizedSearchAlgorithm.double_relative_width(
+                relative_width))
+
+    @staticmethod
+    def half_relative_width(relative_width):
+        """Return relative width corresponding to half logarithmic width.
+
+        :param relative_width: The base relative width to halve.
+        :type relative_width: float
+        :returns: The relative width of half logarithmic size.
+        :rtype: float
+        """
+        return 1.0 - math.sqrt(1.0 - relative_width)
+
+    @staticmethod
+    def half_step_up(relative_width, current_bound):
+        """Return rate of half logarithmic width above.
+
+        :param relative_width: The base relative width to halve.
+        :param current_bound: The current target transmit rate to move [pps].
+        :type relative_width: float
+        :type current_bound: float
+        :returns: Transmit rate larger by logarithmically half width [pps].
+        :rtype: float
+        """
+        return current_bound / (
+            1.0 - OptimizedSearchAlgorithm.half_relative_width(relative_width))
+
+    def ndrpdr(self, state):
+        """Pefrom trials for this phase. Return the new state when done.
+
+        :param state: State before this phase.
+        :type state: ProgressState
+        :returns: The updates state.
+        :rtype: ProgressState
+        :raises RuntimeError: If total duration is larger than timeout.
+        """
+        if state.phases > 0:
+            # We need to finish preceding intermediate phases first.
+            saved_phases = state.phases
+            state.phases -= 1
+            # Preceding phases have shorter duration.
+            saved_duration = state.duration
+            duration_multiplier = state.duration / self.initial_trial_duration
+            phase_exponent = float(state.phases) / saved_phases
+            state.duration = self.initial_trial_duration * math.pow(
+                duration_multiplier, phase_exponent)
+            # Shorter durations do not need that narrow widths.
+            saved_width = state.width_goal
+            state.width_goal = self.double_relative_width(state.width_goal)
+            # Recurse.
+            state = self.ndrpdr(state)
+            # Restore the state for current phase.
+            state.duration = saved_duration
+            state.width_goal = saved_width
+            state.phases = saved_phases  # Not needed, but just in case.
+        logging.info(
+            "starting iterations with duration %s and relative width goal %s",
+            state.duration, state.width_goal)
+        start_time = time.time()
+        while 1:
+            if time.time() > start_time + self.timeout:
+                raise RuntimeError("Optimized search takes too long.")
+            # Order of priorities: improper bounds (nl, pl, nh, ph),
+            # then narrowing relative Tr widths.
+            # Durations are not priorities yet,
+            # they will settle on their own hopefully.
+            ndr_lo = state.result.ndr_interval.measured_low
+            ndr_hi = state.result.ndr_interval.measured_high
+            pdr_lo = state.result.pdr_interval.measured_low
+            pdr_hi = state.result.pdr_interval.measured_high
+            ndr_rel_width = max(
+                state.width_goal, state.result.ndr_interval.rel_tr_width)
+            pdr_rel_width = max(
+                state.width_goal, state.result.pdr_interval.rel_tr_width)
+            # If we are hitting line or fail rate, we cannot shift,
+            # but we can re-measure.
+            if ndr_lo.drop_fraction > 0.0:
+                if ndr_lo.target_tr > state.fail_rate:
+                    new_tr = max(state.fail_rate, self.double_step_down(
+                        ndr_rel_width, ndr_lo.target_tr))
+                    logging.info("ndr lo external %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+                elif ndr_lo.duration < state.duration:
+                    logging.info("ndr lo fail re-measure")
+                    state = self._measure_and_update_state(
+                        state, state.fail_rate)
+                    continue
+            if pdr_lo.drop_fraction > state.allowed_drop_fraction:
+                if pdr_lo.target_tr > state.fail_rate:
+                    new_tr = max(state.fail_rate, self.double_step_down(
+                        pdr_rel_width, pdr_lo.target_tr))
+                    logging.info("pdr lo external %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+                elif pdr_lo.duration < state.duration:
+                    logging.info("pdr lo fail re-measure")
+                    state = self._measure_and_update_state(
+                        state, state.fail_rate)
+                    continue
+            if ndr_hi.drop_fraction <= 0.0:
+                if ndr_hi.target_tr < state.line_rate:
+                    new_tr = min(state.line_rate, self.double_step_up(
+                        ndr_rel_width, ndr_hi.target_tr))
+                    logging.info("ndr hi external %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+                elif ndr_hi.duration < state.duration:
+                    logging.info("ndr hi line re-measure")
+                    state = self._measure_and_update_state(
+                        state, state.line_rate)
+                    continue
+            if pdr_hi.drop_fraction <= state.allowed_drop_fraction:
+                if pdr_hi.target_tr < state.line_rate:
+                    new_tr = min(state.line_rate, self.double_step_up(
+                        pdr_rel_width, pdr_hi.target_tr))
+                    logging.info("pdr hi external %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+                elif pdr_hi.duration < state.duration:
+                    logging.info("ndr hi line re-measure")
+                    state = self._measure_and_update_state(
+                        state, state.line_rate)
+                    continue
+            # If we are hitting line_rate, it is still worth narrowing width,
+            # hoping large enough Df will happen.
+            # But if we are hitting fail rate (at current duration),
+            # no additional measurement will help with that,
+            # so we can stop narrowing in this phase.
+            if (ndr_lo.target_tr <= state.fail_rate
+                    and ndr_lo.drop_fraction > 0.0):
+                ndr_rel_width = 0.0
+            if (pdr_lo.target_tr <= state.fail_rate
+                    and pdr_lo.drop_fraction > state.allowed_drop_fraction):
+                pdr_rel_width = 0.0
+            if max(ndr_rel_width, pdr_rel_width) > state.width_goal:
+                # We have to narrow some width.
+                if ndr_rel_width >= pdr_rel_width:
+                    new_tr = self.half_step_up(ndr_rel_width, ndr_lo.target_tr)
+                    logging.info("Bisecting for NDR at %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+                else:
+                    new_tr = self.half_step_up(pdr_rel_width, pdr_lo.target_tr)
+                    logging.info("Bisecting for PDR at %s", new_tr)
+                    state = self._measure_and_update_state(state, new_tr)
+                    continue
+            # We do not need to improve width, but there still might be
+            # some measurements with smaller duration.
+            # We need to re-measure with full duration, possibly
+            # creating invalid bounds to resolve (thus broadening width).
+            if ndr_lo.duration < state.duration:
+                logging.info("re-measuring NDR lower bound")
+                self._measure_and_update_state(state, ndr_lo.target_tr)
+                continue
+            if pdr_lo.duration < state.duration:
+                logging.info("re-measuring PDR lower bound")
+                self._measure_and_update_state(state, pdr_lo.target_tr)
+                continue
+            # Except when lower bounds have high Df, in that case
+            # we do not need to re-measure _upper_ bounds.
+            if ndr_hi.duration < state.duration and ndr_rel_width > 0.0:
+                logging.info("re-measuring NDR upper bound")
+                self._measure_and_update_state(state, ndr_hi.target_tr)
+                continue
+            if pdr_hi.duration < state.duration and pdr_rel_width > 0.0:
+                logging.info("re-measuring PDR upper bound")
+                self._measure_and_update_state(state, pdr_hi.target_tr)
+                continue
+            # Widths are narrow (or failing), bound measurements
+            # are long enough, we can return.
+            logging.info("phase done")
+            break
+        return state
diff --git a/resources/libraries/python/search/ReceiveRateInterval.py b/resources/libraries/python/search/ReceiveRateInterval.py
new file mode 100644
index 0000000000..11f812d886
--- /dev/null
+++ b/resources/libraries/python/search/ReceiveRateInterval.py
@@ -0,0 +1,84 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining ReceiveRateInterval class."""
+
+import math
+
+from .ReceiveRateMeasurement import ReceiveRateMeasurement
+
+
+class ReceiveRateInterval(object):
+    """Structure defining two Rr measurements, and their relation."""
+
+    def __init__(self, measured_low, measured_high):
+        """Store the bound measurements after checking argument types.
+
+        :param measured_low: Measurement for the lower bound.
+        :param measured_high: Measurement for the upper bound.
+        :type measured_low: ReceiveRateMeasurement
+        :type measured_high: ReceiveRateMeasurement
+        """
+        # TODO: Type checking is not very pythonic,
+        # perhaps users can fix wrong usage without it?
+        if not isinstance(measured_low, ReceiveRateMeasurement):
+            raise TypeError("measured_low is not a ReceiveRateMeasurement: "
+                            "{low!r}".format(low=measured_low))
+        if not isinstance(measured_high, ReceiveRateMeasurement):
+            raise TypeError("measured_high is not a ReceiveRateMeasurement: "
+                            "{high!r}".format(high=measured_high))
+        self.measured_low = measured_low
+        self.measured_high = measured_high
+        # Declare secondary quantities to appease pylint.
+        self.abs_tr_width = None
+        """Absolute width of target transmit rate. Upper minus lower."""
+        self.rel_tr_width = None
+        """Relative width of target transmit rate. Ansolute divided by upper."""
+        self.sort()
+
+    def sort(self):
+        """Sort bounds by target Tr, compute secondary quantities."""
+        if self.measured_low.target_tr > self.measured_high.target_tr:
+            self.measured_low, self.measured_high = (
+                self.measured_high, self.measured_low)
+        self.abs_tr_width = (
+            self.measured_high.target_tr - self.measured_low.target_tr)
+        self.rel_tr_width = self.abs_tr_width / self.measured_high.target_tr
+
+    def width_in_goals(self, relative_width_goal):
+        """Return float value.
+
+        Relative width goal is some (negative) value on logarithmic scale.
+        Current relative width is another logarithmic value.
+        Return the latter divided by the former.
+        This is useful when investigating how did surprising widths come to be.
+
+        :param relative_width_goal: Upper bound times this is the goal
+            difference between upper bound and lower bound.
+        :type relative_width_goal: float
+        :returns: Current width as logarithmic multiple of goal width [1].
+        :rtype: float
+        """
+        return math.log(1.0 - self.rel_tr_width) / math.log(
+            1.0 - relative_width_goal)
+
+    def __str__(self):
+        """Return string as half-open interval."""
+        return "[{low!s};{high!s})".format(
+            low=self.measured_low, high=self.measured_high)
+
+    def __repr__(self):
+        """Return string evaluable as a constructor call."""
+        return ("ReceiveRateInterval(measured_low={low!r}"
+                ",measured_high={high!r})".format(
+                    low=self.measured_low, high=self.measured_high))
diff --git a/resources/libraries/python/search/ReceiveRateMeasurement.py b/resources/libraries/python/search/ReceiveRateMeasurement.py
new file mode 100644
index 0000000000..58aa819017
--- /dev/null
+++ b/resources/libraries/python/search/ReceiveRateMeasurement.py
@@ -0,0 +1,54 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining ReceiveRateMeasurement class."""
+
+
+class ReceiveRateMeasurement(object):
+    """Structure defining the result of single Rr measurement."""
+
+    def __init__(self, duration, target_tr, transmit_count, drop_count):
+        """Constructor, normalize primary and compute secondary quantities.
+
+        :param duration: Measurement duration [s].
+        :param target_tr: Target transmit rate [pps].
+            If bidirectional traffic is measured, this is bidirectional rate.
+        :param transmit_count: Number of packets transmitted [1].
+        :param drop_count: Number of packets transmitted but not received [1].
+        :type duration: float
+        :type target_tr: float
+        :type transmit_count: int
+        :type drop_count: int
+        """
+        self.duration = float(duration)
+        self.target_tr = float(target_tr)
+        self.transmit_count = int(transmit_count)
+        self.drop_count = int(drop_count)
+        self.receive_count = transmit_count - drop_count
+        self.transmit_rate = transmit_count / self.duration
+        self.drop_rate = drop_count / self.duration
+        self.receive_rate = self.receive_count / self.duration
+        self.drop_fraction = float(self.drop_count) / self.transmit_count
+        # TODO: Do we want to store also the real time (duration + overhead)?
+
+    def __str__(self):
+        """Return string reporting input and drop fraction."""
+        return "d={dur!s},Tr={rate!s},Df={frac!s}".format(
+            dur=self.duration, rate=self.target_tr, frac=self.drop_fraction)
+
+    def __repr__(self):
+        """Return string evaluable as a constructor call."""
+        return ("ReceiveRateMeasurement(duration={dur!r},target_tr={rate!r}"
+                ",transmit_count={trans!r},drop_count={drop!r})".format(
+                    dur=self.duration, rate=self.target_tr,
+                    trans=self.transmit_count, drop=self.drop_count))
diff --git a/resources/libraries/python/search/__init__.py b/resources/libraries/python/search/__init__.py
new file mode 100644
index 0000000000..619c4c09c5
--- /dev/null
+++ b/resources/libraries/python/search/__init__.py
@@ -0,0 +1,16 @@
+# Copyright (c) 2018 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+__init__ file for directory resources/libraries/python/search
+"""