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-DUT state considerations
-^^^^^^^^^^^^^^^^^^^^^^^^
-
-This page discusses considerations for Device Under Test (DUT) state.
-DUTs such as VPP require configuration, to be provided before the aplication
-starts (via config files) or just after it starts (via API or CLI access).
-
-During operation DUTs gather various telemetry data, depending on configuration.
-This internal state handling is part of normal operation,
-so any performance impact is included in the test results.
-Accessing telemetry data is additional load on DUT,
-so we are not doing that in main trial measurements that affect results,
-but we include separate trials specifically for gathering runtime telemetry.
-
-But there is one kind of state that needs specific handling.
-This kind of DUT state is dynamically created based on incoming traffic,
-it affects how DUT handles the traffic, and (unlike telemetry counters)
-it has uneven impact on CPU load.
-Typical example is NAT, where detecting new sessions takes more CPU than
-forwarding packet on existing (open or recently closed) sessions.
-We call DUT configurations with this kind of state "stateful",
-and configurations without them "stateless".
-(Even though stateless configurations contain state described in previous
-paragraphs, and some configuration items may have "stateful" in their name,
-such as stateful ACLs.)
-
-Stateful DUT configurations
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Typically, the level of CPU impact of traffic depends on DUT state.
-The first packets causing DUT state to change have higher impact,
-subsequent packets matching that state have lower impact.
-
-From performance point of view, this is similar to traffic phases
-for stateful protocols, see
-`NGFW draft <https://tools.ietf.org/html/draft-ietf-bmwg-ngfw-performance-05#section-4.3.4>`.
-In CSIT we borrow the terminology (even if it does not fit perfectly,
-see discussion below). Ramp-up traffic causes the state change,
-sustain traffic does not change the state.
-
-As the performance is different, each test has to choose which traffic
-it wants to test, and manipulate the DUT state to achieve the intended impact.
-
-Ramp-up trial
-`````````````
-
-Tests aiming at sustain performance need to make sure DUT state is created.
-We achieve this via a ramp-up trial, specific purpose of which
-is to create the state.
-
-Subsequent trials need no specific handling, as long as the state
-remains the same. But some state can time-out, so additional ramp-up
-trials are inserted whenever the code detects the state can time-out.
-Note that a trial with zero loss refreshes the state,
-so only the time since the last non-zero loss trial is tracked.
-
-For the state to be set completely, it is important both DUT and TG
-do not lose any packets. We achieve this by setting the profile multiplier
-(TPS from now on) to low enough value.
-
-It is also important each state-affecting packet is sent.
-For size-limited traffic profile it is guaranteed by the size limit.
-For continuous traffic, we set a long enough duration (based on TPS).
-
-At the end of the ramp-up trial, we check DUT state to confirm
-it has been created as expected.
-Test fails if the state is not (completely) created.
-
-State Reset
-```````````
-
-Tests aiming at ramp-up performance do not use ramp-up trial,
-and they need to reset the DUT state before each trial measurement.
-The way of resetting the state depends on test,
-usually an API call is used to partially de-configure
-the part that holds the state, and then re-configure it back.
-
-In CSIT we control the DUT state behavior via a test variable "resetter".
-If it is not set, DUT state is not reset.
-If it is set, each search algorithm (including MRR) will invoke it
-before all trial measurements (both main and telemetry ones).
-Any configuration keyword enabling a feature with DUT state
-will check whether a test variable for ramp-up rate is present.
-If it is present, resetter is not set.
-If it is not present, the keyword sets the apropriate resetter value.
-This logic makes sure either ramp-up or state reset are used.
-
-..
-    TODO: Classify trials into main and telemetry, in a separate place.
-
-Notes: If both ramp-up and state reset were used, the DUT behavior
-would be identical to just reset, while test would take longer to execute.
-If neither were used, DUT will show different performance in subsequent trials,
-violating assumptions of search algorithms.
-
-DUT versus protocol ramp-up
-```````````````````````````
-
-There are at least three different causes for bandwidth possibly increasing
-within a single measurement trial.
-
-The first is DUT switching from state modification phase to constant phase,
-it is the primary focus of this document.
-Using ramp-up traffic before main trials eliminates this cause
-for tests wishing to measure the performance of the next phase.
-Using size-limited profiles eliminates the next phase
-for tests wishing to measure performance of this phase.
-
-The second is protocol such as TCP ramping up their throughput to utilize
-the bandwidth available. This is the original meaning of "ramp up"
-in the NGFW draft (see above).
-In existing tests we are not using this meaning of TCP ramp-up.
-Instead we use only small transactions, and large enough initial window
-so TCP acts as ramped-up already.
-
-The third is TCP increasing offered load due to retransmissions triggered by
-packet loss. In CSIT we again try to avoid this behavior
-by using small enough data to transfer, so overlap of multiple transactions
-(primary cause of packet loss) is unlikely.
-But in MRR tests, packet loss and non-constant offered load are still expected.
-
-Stateless DUT configuratons
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-These are simple configurations, which do not set any resetter value
-(even if ramp-up duration is not configured).
-Majority of existing tests are of this type, using continuous traffic profiles.
-
-In order to identify limits of Trex performance,
-we have added suites with stateless DUT configuration (VPP ip4base)
-subjected to size-limited ASTF traffic.
-The discovered rates serve as a basis of comparison
-for evaluating the results for stateful DUT configurations (VPP NAT44ed)
-subjected to the same traffic profiles.
-
-DUT versus TG state
-~~~~~~~~~~~~~~~~~~~
-
-Traffic Generator profiles can be stateful (ASTF) or stateless (STL).
-DUT configuration can be stateful or stateless (with respect to packet traffic).
-
-In CSIT we currently use all four possible configurations:
-
-- Regular stateless VPP tests use stateless traffic profiles.
-
-- Stateless VPP configuration with stateful profile is used as a base for
-  comparison.
-
-- Some stateful DUT configurations (NAT44DET, NAT44ED unidirectional)
-  are tested using stateless traffic profiles and continuous traffic.
-
-- The rest of stateful DUT configurations (NAT44ED bidirectional)
-  are tested using stateful traffic profiles and size limited traffic.