Network Working Group C. Huitema Internet-Draft Private Octopus Inc. Intended status: Informational S. Nandakumar Expires: 3 May 2027 C. Jennings Cisco 30 October 2026 Testing of Christian's Congestion Control Code (C4) draft-huitema-ccwg-c4-test-05 Abstract Christian's Congestion Control Code is a new congestion control algorithm designed to support Real-Time applications such as Media over QUIC. It is designed to drive towards low delays, with good support for the "application limited" behavior frequently found when using variable rate encoding, and with fast reaction to congestion to avoid the "priority inversion" happening when congestion control overestimates the available capacity. The design was validated by series of simulations, and also by initial deployments in control networks. We describe here these simulations and tests. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 3 May 2027. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Huitema, et al. Expires 3 May 2027 [Page 1] Internet-Draft C4 Tests October 2026 Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Tests and metrics . . . . . . . . . . . . . . . . . . . . . . 4 3. Description of simulation tests . . . . . . . . . . . . . . . 5 3.1. Reaction to network events . . . . . . . . . . . . . . . 6 3.1.1. Simulation of a simple 20Mbps connection (alone) . . 7 3.1.2. Simulation of a simple 200Mbps connection (alone_200) . . . . . . . . . . . . . . . . . . . . . 7 3.1.3. Simulation of a simple 1.5Mbps connection (alone_1_5M) . . . . . . . . . . . . . . . . . . . . 7 3.1.4. Simulation of a simple 512kbps connection (alone_512k) . . . . . . . . . . . . . . . . . . . . 7 3.1.5. Low and up . . . . . . . . . . . . . . . . . . . . . 7 3.1.6. Drop and back . . . . . . . . . . . . . . . . . . . . 8 3.1.7. Black Hole . . . . . . . . . . . . . . . . . . . . . 8 3.1.8. Short and long . . . . . . . . . . . . . . . . . . . 8 3.1.9. Simulation of a geostationary satellite connection (satellite) . . . . . . . . . . . . . . . . . . . . . 8 3.2. Buffer Bloat . . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. Single connection with Buffer Bloat (bbloat) . . . . 9 3.2.2. Compete with C4 over Buffer Bloat (bbloat_c4) . . . . 9 3.2.3. Compete with BBR over Buffer Bloat (bbloat_bbr) . . . 9 3.2.4. Compete with Cubic over Buffer Bloat (bbloat_cubic) . . . . . . . . . . . . . . . . . . . 9 3.3. Competition . . . . . . . . . . . . . . . . . . . . . . . 10 3.3.1. Short main connection versus C4 (vs_c4) . . . . . . . 10 3.3.2. Short background C4 connection first (after_c4) . . . 10 3.3.3. Short background C4 connection last (before C4) . . . 11 3.3.4. Two long connections . . . . . . . . . . . . . . . . 11 3.3.5. Long background connection last . . . . . . . . . . . 11 3.4. Handling of High Jitter Environments . . . . . . . . . . 11 3.4.1. Bad Wi-Fi test . . . . . . . . . . . . . . . . . . . 12 3.4.2. Wifi fade trial . . . . . . . . . . . . . . . . . . . 12 3.4.3. Wifi suspension trial . . . . . . . . . . . . . . . . 12 3.4.4. Compete over bad Wi-Fi . . . . . . . . . . . . . . . 13 3.5. L4S and ECN . . . . . . . . . . . . . . . . . . . . . . . 13 3.5.1. Basic ECN test (ecn) . . . . . . . . . . . . . . . . 13 3.5.2. Competition with other algorithms . . . . . . . . . . 13 3.6. Handling of Multimedia Applications . . . . . . . . . . . 13 3.6.1. Media on High Speed Connection (media) . . . . . . . 14 3.6.2. Media on 10 Mbps Connection (media10) . . . . . . . . 14 Huitema, et al. Expires 3 May 2027 [Page 2] Internet-Draft C4 Tests October 2026 3.6.3. Media for 20 seconds (media600) . . . . . . . . . . . 14 3.6.4. Media over varying RTT (media_short_long) . . . . . . 15 3.6.5. Media over bad Wi-Fi (media_wb) . . . . . . . . . . . 15 3.6.6. Media over fading Wi-Fi (media_wf) . . . . . . . . . 15 3.6.7. Media with Wi-Fi suspensions (media_ws) . . . . . . . 15 3.6.8. Media over an ECN capable connection (media_ecn) . . 15 3.6.9. Media with a congested feedback path (media_backload) . . . . . . . . . . . . . . . . . . 16 4. Simulation results . . . . . . . . . . . . . . . . . . . . . 16 5. Statistics . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.1. Reaction to network events . . . . . . . . . . . . . . . 16 5.2. Reaction to network events . . . . . . . . . . . . . . . 16 5.2.1. average time for network events tests . . . . . . . . 17 5.2.2. top 90% time for network events tests . . . . . . . . 17 5.2.3. average RTT for network events tests . . . . . . . . 18 5.2.4. top 90% of RTT + standard deviation for network events tests . . . . . . . . . . . . . . . . . . . . . . . . 18 5.3. Competition . . . . . . . . . . . . . . . . . . . . . . . 19 5.3.1. average time for compete tests . . . . . . . . . . . 19 5.3.2. top 90% time for compete tests . . . . . . . . . . . 20 5.3.3. average RTT for compete tests . . . . . . . . . . . . 20 5.3.4. top 90% of RTT + standard deviation for compete tests . . . . . . . . . . . . . . . . . . . . . . . . 21 5.3.5. average load for compete tests . . . . . . . . . . . 22 5.3.6. top 90% load for compete tests . . . . . . . . . . . 22 5.4. Buffer bloat . . . . . . . . . . . . . . . . . . . . . . 23 5.4.1. average time for buffer bloat tests . . . . . . . . . 23 5.4.2. top 90% time for buffer bloat tests . . . . . . . . . 23 5.4.3. average RTT for buffer bloat tests . . . . . . . . . 24 5.4.4. top 90% of RTT + standard deviation for buffer bloat tests . . . . . . . . . . . . . . . . . . . . . . . . 24 5.4.5. average load for buffer bloat tests . . . . . . . . . 24 5.4.6. top 90% load for buffer bloat tests . . . . . . . . . 25 5.5. Wi-Fi . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.5.1. average time for wifi tests . . . . . . . . . . . . . 25 5.5.2. top 90% time for wifi tests . . . . . . . . . . . . . 26 5.5.3. average RTT for wifi tests . . . . . . . . . . . . . 26 5.5.4. top 90% of RTT + standard deviation for wifi tests . 27 5.5.5. average load for wifi tests . . . . . . . . . . . . . 27 5.5.6. top 90% load for wifi tests . . . . . . . . . . . . . 28 5.6. ECN . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 5.6.1. average time for ecn tests . . . . . . . . . . . . . 28 5.6.2. top 90% time for ecn tests . . . . . . . . . . . . . 29 5.6.3. average RTT for ecn tests . . . . . . . . . . . . . . 29 5.6.4. top 90% of RTT + standard deviation for ecn tests . . 29 5.7. Media . . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.7.1. average av_latency for media tests . . . . . . . . . 30 5.7.2. top 90% max_latency for media tests . . . . . . . . . 30 Huitema, et al. Expires 3 May 2027 [Page 3] Internet-Draft C4 Tests October 2026 6. Live Tests . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.1. Loopback tests . . . . . . . . . . . . . . . . . . . . . 31 6.2. Webex prototype deployments . . . . . . . . . . . . . . . 31 7. Security Considerations . . . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 9. Informative References . . . . . . . . . . . . . . . . . . . 31 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction Christian's Congestion Control Code (C4) is a new congestion control algorithm designed to support Real-Time multimedia applications, specifically multimedia applications using QUIC [RFC9000] and the Media over QUIC transport [I-D.ietf-moq-transport]. The design was validated by series of simulations, and also by initial deployments in control networks. We describe here these simulations (see Section 3), the simulation results for each of the test cases (see Section 4), and the live networking tests (see Section 6). 2. Tests and metrics For each simulation scenario, we measure up to 4 different metrics: * The average execution time,defined as the simulated time necessary to execute the scenario, which we express as two numbers: - the average execution time of all the simulations for the scenario, - and, the top 90th percentile of that time. * The RTT observed during the connection, which we express as two numbers: - the average RTT value for all RTT measurements, measured for each simulation and averaged over all simulation. - and, the top 90th percentile over all tests of the sum of the average RTT for a connection and the standard deviation of the RTT for that connection. * The load factor, defined as the share of the bandwidth used by the "main" connection over the period when the two connections compete, or, if there is only one connection, over the duration of the connection. We monitor: Huitema, et al. Expires 3 May 2027 [Page 4] Internet-Draft C4 Tests October 2026 - the average of the load factor over all simulations for the scenario, - and, the top 90th percentile of that load factor. * The frame latency, defined as the average time delay between the moment a media frame is scheduled and its arrival at the receiver. We monitor: - the average value of the average frame latency per connection, - the top 90th percentile of the max frame latency per connection. The 4 different metrics and their variants do not make sense for all scenarios: * we monitor the execution time for all scenarios except the media scenarios, for which the execution time is fixed by the scenario. * we monitor the RTT for all scenarios except the media scenarios, for which the frame latency provides better information. * for the media transmission tests, we only monitor the frame latency; we do not monitor the frame latency for the other test scenarios. * we only monitor the load factor for scenarios that involve multiple competing connections. We do not try to assign fixed target values for the different scenarios. Instead, we run three variants for each test: one in which the "main" connection uses C4, one in which it uses BBR, and one in which it uses Cubic. We want C4 to demonstrate that it is "better" than BBR and Cubic for a majority of the scenarios. Depending on the scenario, we may discuss whether better means a shorter execution time, a shorter RTT, a load factor in the acceptable range, or a shorter frame latency. When C4 does not provde the best results, we want to ensure that it is not worse than both BBR and Cubic, and that the difference to the best scenarios are reasonably small. 3. Description of simulation tests We test the design by running a series of simulations, which cover: * reaction to network events Huitema, et al. Expires 3 May 2027 [Page 5] Internet-Draft C4 Tests October 2026 * competition with other congestion control algorithms * handling of buffer bloat * handling of high jitter environments * handling of multimedia applications * handling of ECN We are running the tests using the picoquic network simulator [Picoquic_ns]. The simulator embeds the picoquic implementation of QUIC [Picoquic]. Picoquic itself comes with support for a variety of congestion control protocols, including Cubic and BBR. We added an implementation of C4. That implementation is designed so that the same code can be used in execution over the network and in simulations, the main difference being a replacement of the socket API by a simulation API. When running in simulation, the code runs in "virtual time", with a virtual clock driven by simulation events such as arrival and departure of packets from simulated queues. With the virtual clock mechanism, we can simulate in a fraction of a second a connection that would last 10 seconds in "real time". 3.1. Reaction to network events The first series of simulation test how C4 behaves in simple scenarios when it is the sole user of a link. The list of test includes: * a 20Mbps connection, * a 200Mbps connection, * a geostationary satellite connection, * a sudden increase in path capacity, i.e. "low and up" * a sudden decrese in path capacity followed by a return to normal, i.e. "drop and back" * a sudden drop to 0 of path capacity for 2 seconds, i.e. a "black hole" * a sudden increase in path latency, from "short" to "long" Huitema, et al. Expires 3 May 2027 [Page 6] Internet-Draft C4 Tests October 2026 3.1.1. Simulation of a simple 20Mbps connection (alone) This scenario simulates a 10MB download over a 20 Mbps link, with an 80ms RTT, and a bottlneck buffer capacity corresponding to 1 BDP. In a typical simulation, we see a initial phase complete in less than 800ms, followed by a recovery phase in which the transmission rate stabilizes to the line rate. After that, the RTT remains very close to the path RTT, except for periodic small bumps during the "push" transitions. 3.1.2. Simulation of a simple 200Mbps connection (alone_200) This scenario simulates a 20MB download over a 200 Mbps link, with a 40ms RTT, and a bottleneck buffer capacity corresponding to 1 BDP. This short test shows that the initial phase correctly discover the path capacity, and that the transmission operates at the expected rate after that. 3.1.3. Simulation of a simple 1.5Mbps connection (alone_1_5M) This scenario simulates a 4MB download over a 1.5 Mbps link, with a 40ms RTT, and a bottleneck buffer capacity corresponding to 1.25 BDP. This short test shows that the initial phase correctly discover the path capacity, and that the transmission operates at the expected rate after that. 3.1.4. Simulation of a simple 512kbps connection (alone_512k) This scenario simulates a 1MB download over a 512 kbps link, with a 34ms RTT, and a bottleneck buffer capacity corresponding to 50ms of transmission. This short test shows that the initial phase correctly discover the path capacity, and that the transmission operates at the expected rate after that. 3.1.5. Low and up The "low and up" scenario simulates a sudden increase in the capacity of the path. At the beginning of the simulation, the simulated bandwidth is set at 5 Mbps. It increases to 10 Mbps after 2.5 seconds. The RTT remains constant at 100ms. The goal of the test is to verify that C4 promptly discovers the increase in bandwidth, and increases the transmission rate. Huitema, et al. Expires 3 May 2027 [Page 7] Internet-Draft C4 Tests October 2026 3.1.6. Drop and back The "drop and back" scenario simulates a sudden decrease in the capacity of the path, followed by return to normal. At the beginning of the simulation, the simulated bandwidth is set at 10 Mbps. It decreases to 5 Mbps after 1.5 second, then returns to 10 Mbps after 2 seconds. The RTT remains constant at 100ms. The goal of the test is to verify that C4 adapts promptly to changes in the available bandwidth on a path. 3.1.7. Black Hole The "black hole" scenario simulates a sudden decrease in the capacity of the path, followed by return to normal. At the beginning of the simulation, the simulated bandwidth is set at . After 2 seconds, the path capacity is set to 0, and is restored to normal 2 seconds later. The RTT remains constant at 70ms. The goal of the test is to verify that C4 recovers promptly after a short suspension of the path. 3.1.8. Short and long The "short and long" scenario simulates a sudden increase in the latency of the path. At the beginning of the simulation, the simulated RTT is set at 30ms. After 1 second, the latency increases to 100ms. The data rate remains constant at 100ms. The goal of the test is to verify that C4 react properly exercises the "slow down" mechanism to discover the new RTT. 3.1.9. Simulation of a geostationary satellite connection (satellite) This scenario simulates a 100MB download over a 250 Mbps link, with a 600ms RTT, and a bottleneck buffer capacity corresponding to 1 BDP, i.e., simulating a geostationary satellite connection. The scenario also tests the support for careful resume [RFC9959] by setting the remembered CWND to 18750000 bytes and the remembered RTT to 600.123ms. 3.2. Buffer Bloat The buffer bloat simulations test the behavior of C4 when the simulated path is configured with very large network buffers. This tests the recommendation in [RFC9743] that algorithms "ought to try to avoid maintaining excessive queues in the network". Huitema, et al. Expires 3 May 2027 [Page 8] Internet-Draft C4 Tests October 2026 All test variants use the same transmission scenario: The RTT of the path is always 80ms. We use 4 variants of this test: a "single connection" variant, and 3 competition scenarios in which the background connection uses C4, BBR or Cubic. 3.2.1. Single connection with Buffer Bloat (bbloat) The single connection with buffer bloat test simulates a single connection trying to download 30 MB of data over a 20Mbit/s path. The path has an 80ms RTT, and the network buffers are configured to hold up to 20 seconds of traffic. The goal is to verify that C4 is about as efficient as Cubic, while maintaining reasonably short RTTs. 3.2.2. Compete with C4 over Buffer Bloat (bbloat_c4) The compete against C4 with buffer bloat test simulates a main connection trying to download 30 MB of data over a 20Mbit/s path, while the background connection using C4 that starts at the same time is trying to download 20 MB. The path has an 80ms RTT, and the network buffers are configured to hold up to 20 seconds of traffic. The goal is to verify that C4 competes reasonably against itself in the presence of buffer bloat. 3.2.3. Compete with BBR over Buffer Bloat (bbloat_bbr) The compete against C4 with buffer bloat test simulates a main connection trying to download 30 MB of data over a 20Mbit/s path, while the background connection using BBR that starts at the same time is trying to download 20 MB. The path has an 80ms RTT, and the network buffers are configured to hold up to 20 seconds of traffic. The goal is to verify that C4 competes reasonably against BBR in the presence of buffer bloat. 3.2.4. Compete with Cubic over Buffer Bloat (bbloat_cubic) The compete against C4 with buffer bloat test simulates a main connection trying to download 30 MB of data over a 20Mbit/s path, while the background connection using Cubic that starts at the same time is trying to download 20 MB. The path has an 80ms RTT, and the network buffers are configured to hold up to 20 seconds of traffic. Huitema, et al. Expires 3 May 2027 [Page 9] Internet-Draft C4 Tests October 2026 We already know that the Cubic algorithm only backs off in response to packet losses, and thus will essentially never back off during our tests. In this test, we want to verify that C4 is not "shut off" when competing with Cubic, even if that means accepting larger RTTs. 3.3. Competition In accordance with [RFC9743], we evaluate competition between C4 connections, or between C4 and Cubic or BBR. We design a series of tests, each correponding to a competition scenario between a "main" connection and a "background" connection. For each test, we run the test using either C4, Cubic or BBR for the "main" connection. The test scenario specifies the algorithm managing the background connection, as well as scenario details. We test that the bandwidth is shared reasonably by monitoring the "load" of the network, defined as the share of the bandwidth used by the "main" connection over the period when the two connections compete. According to [RFC9743], a proposed congestion control algorithm such as C4 shall avoid having a significantly negative impact on flows using a standard congestion control. Impact here encompasses causing packet losses or long queues, or simply consuming too much of the available bandwidth. Using less than 50% of the capacity would be considered good, using more than 70% would be considered bad, and more than 80% really bad. This has a negative side too: using less than 30% of the bandwidth means that algorithm is too during competing period, and using less than 20% would be really bad. 3.3.1. Short main connection versus C4 (vs_c4) Our first test simulates a main connection starting at the same time as a background C4 connection. The path has a 20Mbps data rate and 80ms RTT. The background connection tries to download 10MB, the main connection downloads 5MB. 3.3.2. Short background C4 connection first (after_c4) The "background first" test simulates a main connection competing with the background C4 connection that started 0.5 seconds before the main connection. The path has a 20Mbps data rate and 80ms RTT. The background connection tries to download 10MB, the main connection downloads 5MB. Huitema, et al. Expires 3 May 2027 [Page 10] Internet-Draft C4 Tests October 2026 3.3.3. Short background C4 connection last (before C4) The "background last" simulates a main connections competing with the background connection that starts 0.5 seconds after the main connection. The path has a 50Mbps data rate and 30ms RTT. The background connection tries to download 20MB, the main connection downloads 10MB. 3.3.4. Two long connections The long connection test simulates a main connections starting at the same time as the background. The path has a 20Mbps data rate and 80ms RTT. The background connection tries to download 30MB, the main connection downloads 20MB. There are three variants of that test, depending on the background connection algorithm: C4 (vs_c4_lg), Cubic (vs_cubic_lg) or BBR (vs_bbr_lg). 3.3.5. Long background connection last The long "background last" test simulates a main connections competing with the background connection starting 1 second after it. The path has a 10Mbps data rate and 70ms RTT. The background connection tries to download 15MB, the main connection downloads 10MB. There are three variants of that test, depending on the background connection algorithm: C4 (vs_c4_lg2), Cubic (vs_cubic_lg2) or BBR (vs_bbr_lg2). 3.4. Handling of High Jitter Environments In the design of C4, we have been paying special attention to "bad Wi-Fi" environments, in which the usual delays of a few milliseconds could spike to 50 or even 200ms. We spent a lot of time trying to understand what causes such spikes. Our main hypothesis is that this happens when multiple nearby Wi-Fi networks operate on the same frequency or "channel", which causes collisons due to the hidden node problem. This causes collisions and losses, to which Wi-Fi responses involves two leves of exponential back-off. We built a model to simulate this jitter by combining two generators: * A random value r between 0 and 1 ms to model collision avoidance, Huitema, et al. Expires 3 May 2027 [Page 11] Internet-Draft C4 Tests October 2026 * A Poisson arrival model with lambda=1 providing the number N1 of short scale 1ms intervals to account for collision defferal and retry, * A Poisson arrival arrival model with lambda = 12, and an interval length of 7.5ms to account for Wi-Fi packet restransmission. We combine these generators models by using a coefficient "x" that indicates the general degree of collisions and repetitions: * For a fraction (1-x) of the packets, we set the number N2 to 0. * For a fraction (x) of the packets, we compute N2 from the Poisson arrival model with lambda = 12, and an interval length of 7.5ms. The latency for a single sample will be: ~~~ latency = N1_1ms + N2_7.5ms if N1 >= 1: latency -= r ~~~ The coefficient x is derived from the target average jitter value. If the target is 1ms or less, we set x to zero. If it is higher than 91ms, we set x to 1. If it is in between, we set: ~~~ x = (average_jitter - 1ms)/90ms ~~~ We have been using this simulation of jitter to test our implementation of multiple congestion control algorithms. 3.4.1. Bad Wi-Fi test The "bad Wi-Fi" test simulates a connection experiencing a high level of jitter. The average jitter is set to 7ms, which implies multiple spikes of 100 to 200ms every second. The data rate is set to 10Mbps, and the base RTT before jitter is set to 2ms, i.e., simulating a local server. 3.4.2. Wifi fade trial The "Wi-Fi fade" trial simulates varying conditions. The connection starts with a data rate of 20Mbps, an 80ms latency, and Wi-Fi jitter with average 1ms. After 1 second, the data rate drops to 2Mbps and the jitter average increases to 12ms. After another 2 seconds, data rate and jitter return to the original condition. 3.4.3. Wifi suspension trial The "Wi-Fi suspension" test simulates a connection experiencing multiple "suspensions". For every 1.8 second of a 2 second interval, the data rate is set to 20Mbps, and the base RTT before jitter is set to 10ms. For the last 200ms of these intervals, the data rate is set to 0. This model was developed before we got a better understanding of the Wi-Fi jitter. It is obsolete, but we kept it as a test case anyhow. Huitema, et al. Expires 3 May 2027 [Page 12] Internet-Draft C4 Tests October 2026 3.4.4. Compete over bad Wi-Fi The "compete over bad Wi-Fi" test simulates a main connection using a "bad Wi-Fi" path and competing on the same path with a background connection, with the main connection starting 1 second after the background connection. The path has a 10Mbps data rate and 2ms RTT, plus Wi-Fi jitter set to 7ms average -- the same jitter characteristics as in the "bad Wi-Fi" test (see Section 3.4.1). The background connection tries to download 10MB, the main connection downloads 4MB. There are three variants of that test, depending on the background connection algorithm: C4 (wifi_bad_c4), Cubic (wifi_bad_cubic) or BBR (wifi_bad_bbr). 3.5. L4S and ECN To evaluate the handling of ECN, we run a series of tests in which the bottleneck queue is managed by the "duaQ" adaptie queue management algorithm (AQM) specified for L4S [RFC9743] 3.5.1. Basic ECN test (ecn) The "ECN" test simulates a 20 Mbps link, with an 80ms RTT, and a bottleneck buffer capacity corresponding to 1 BDP. When using C4 we set the ECT1 marking, signaling support of L4S. We do not set these markings when using Cubic or BBR. 3.5.2. Competition with other algorithms The "compete over ECN" tests simulates a main connection competing against a background connection, using the same network path characteristics as the "ECN" test (see Section 3.5.1). There are three variants of this test, with the background connection using either C4 (ecn_c4), Cubic (ecn_cubic) or BBR (ecn_bbr). 3.6. Handling of Multimedia Applications C4 is specifically designed to properly handle multimedia applications. We test that function by running simulations of a call including: * a simulated audio stream sending 80 bytes simulated audio segments every 20 ms. Huitema, et al. Expires 3 May 2027 [Page 13] Internet-Draft C4 Tests October 2026 * a simulated compressed video stream, sending 30 frames per second, organized as groups of 30 frames each starting with a 37500 bytes simulated I-Frame followed by 149 3750 bytes P-frames. * a simulated less compressed video stream, sending 30 frames per second, organized as groups of 30 frames each starting with a 62500 bytes simulated I-Frame followed by 149 6250 bytes P-frames. The simulation sends each simulated audio segment as QUIC datagram, with QUIC priority 2, and each group of frames as a separate QUIC stream with priority 4 for the compressed stream, and a priority 6 for the less compressed stream. If the frames delivered on the less compressed stream fall are delivered more than 250ms later than the expected time, the receiver sends a "STOP SENDING" request on the QUIC stream to cancel it; transmission will restart with the next group of frame, simulating a plausible "simulcast" behavior. The simulator collects statistics on the delivery of media frame, which are summarized as average and maximum frame delivery delay. For each test, the simulation specifies an expected average and an expected maximum delay, as well as a "start measurement" time, typically set long enough to start after the initial "startup" phase. The test passes if the average and max value for the simulated audio and for the simulated compressed video measured after the start time are below the specified values. 3.6.1. Media on High Speed Connection (media) The "media" test verifies simulates the handling of media on a 100 Mbps connection with a 30ms RTT. The test lasts for 5 video groups of frames, i.e. 5 seconds. The measurements start 200ms after the start of the connection. 3.6.2. Media on 10 Mbps Connection (media10) The "media10" test verifies the handling of media on a 10 Mbps connection with a 40ms RTT. The test lasts for 5 video groups of frames, i.e. 5 seconds. The measurements start 200ms after the start of the connection. 3.6.3. Media for 20 seconds (media600) The "media600" media checks that media performance does not degrade over time, simulating a 100Mbps connection with a 30ms RTT. The test lasts for 20 video groups of frames, i.e. 20 seconds. The measurements start 200ms after the start of the connection. Huitema, et al. Expires 3 May 2027 [Page 14] Internet-Draft C4 Tests October 2026 3.6.4. Media over varying RTT (media_short_long) The "media_short_long" media test verifies that media performance does not degrade over time, simulating a 100Mbps connection with a 30ms RTT, that changes to a 100ms RTT after 1 second. The test lasts for 10 video groups of frames, i.e. 10 seconds. The measurements start 5 seconds after the start of the connection. 3.6.5. Media over bad Wi-Fi (media_wb) The "bad Wi-Fi" media test verifies that media performance does not degrade too much on a connection that has the kind of jitter discussed in Section 3.4. The connection has the characteristics similar to the "bad Wi-Fi" scenario described in Section 3.4.1. The average jitter is set to 7ms, which implies multiple spikes of 100 to 200ms every second. The data rate is set to 20Mbps, and the base RTT before jitter is set to 2ms, i.e., simulating a local server. The test lasts for 5 video groups of frames, i.e. 5 seconds. The measurements start 200ms after the start of the connection. 3.6.6. Media over fading Wi-Fi (media_wf) The "fading Wi-Fi" media test verifies that media performance does not degrade too much on a connection that hast characteristics similar to the "fading Wi-Fi" scenario described in Section 3.4.2. The connection starts with a data rate of 20Mbps, 40ms RTT, and Wi-Fi jitter with average 1ms. After 1 second, the data rate drops to 2Mbps and the jitter average increases to 12ms. The test lasts for 5 video groups of frames, i.e. 5 seconds. The measurements start 200ms after the start of the connection. 3.6.7. Media with Wi-Fi suspensions (media_ws) The "varying Wi-Fi" media test verifies that media performance does not degrade too much on a connection experiences suspensions as discussed in Section 3.4.3. For every 1.8 second of a 2 second interval, the data rate is set to 20Mbps, and the base RTT before jitter is set to 10ms. For the last 200ms of these intervals, the data rate is set to 0. The test lasts for 5 video groups of frames, i.e. 5 seconds. The measurements start 200ms after the start of the connection. 3.6.8. Media over an ECN capable connection (media_ecn) The "varying Wi-Fi" media test verifies that media works as expected on a path managed using ECN/L4S. The set up is similar to the "ECN" test discussed in Section 3.5. Huitema, et al. Expires 3 May 2027 [Page 15] Internet-Draft C4 Tests October 2026 3.6.9. Media with a congested feedback path (media_backload) The "media backload" test verifies the performance of media transmission when the feedback path is congested. The test uses the same network characteristics as the "media" test (see Section 3.6.1), but adds traffic on the feedback path, simulating a Cubic connection downloading 10 MB of data, starting 2 seconds into the test. Using Cubic, the congestion window of this connection will grows steadily, building a queue and increasing the RTT values measured by the media connection. 4. Simulation results Simulations include random events, such as network jitter or the precise timing of packet arrivals and departure. Minute changes in starting conditions can have cascading effects. To get reliable results, we run each test 100 times. The simulator produces a log of each test execution (in QLOG format), and a summary of each test results, including the completion time for each test, and for tests checking media the average and max frame delivery time. We present here a summary of the results, including the average and the 90th percentile of the completion time for each test. For media tests, we also report the average frame delivery time and the 90th percentile of the max frame delivery time. We run these tests for C4, Cubic and BBR, and present the results for these 3 congestion control algorithms in a set of tables. All times are expressed in microseconds, and for all results lower time values are considered better. 5. Statistics Here is a collection of statistics on all test cases. 5.1. Reaction to network events Here the statistics for the network events test cases. 5.2. Reaction to network events Here the statistics for the network events test cases. Huitema, et al. Expires 3 May 2027 [Page 16] Internet-Draft C4 Tests October 2026 5.2.1. average time for network events tests +===============+==========+==========+==========+=============+ | average time | c4 | bbr | cubic | c4_draft-04 | | for network | | | | | | events tests | | | | | +===============+==========+==========+==========+=============+ | alone | 4637997 | 4689121 | 4476526 | 4502535 | +---------------+----------+----------+----------+-------------+ | alone_200 | 1145841 | 1218599 | 1115876 | 1120932 | +---------------+----------+----------+----------+-------------+ | alone_1_5M | 21681915 | 21507264 | 21513019 | 21505342 | +---------------+----------+----------+----------+-------------+ | alone_512k | 16283457 | 16176884 | 16224485 | 16173448 | +---------------+----------+----------+----------+-------------+ | low_and_up | 8034286 | 7511805 | 8069761 | 7568928 | +---------------+----------+----------+----------+-------------+ | drop_and_back | 7913757 | 7649319 | 7581882 | 7549810 | +---------------+----------+----------+----------+-------------+ | blackhole | 5672040 | 5803503 | 5650972 | 5591990 | +---------------+----------+----------+----------+-------------+ | short_long | 17796792 | 42080755 | 21453915 | 17536760 | +---------------+----------+----------+----------+-------------+ | satellite | 7154694 | 7170091 | 6704245 | 6807132 | +---------------+----------+----------+----------+-------------+ Table 1 5.2.2. top 90% time for network events tests +===============+==========+==========+==========+=============+ | top 90% time | c4 | bbr | cubic | c4_draft-04 | | for network | | | | | | events tests | | | | | +===============+==========+==========+==========+=============+ | alone | 4906091 | 4724609 | 4502395 | 4561489 | +---------------+----------+----------+----------+-------------+ | alone_200 | 1193595 | 1218673 | 1116173 | 1186748 | +---------------+----------+----------+----------+-------------+ | alone_1_5M | 21682246 | 21510873 | 21537688 | 21511156 | +---------------+----------+----------+----------+-------------+ | alone_512k | 16285709 | 16191787 | 16374860 | 16173943 | +---------------+----------+----------+----------+-------------+ | low_and_up | 8040922 | 7517150 | 8084588 | 7570219 | +---------------+----------+----------+----------+-------------+ | drop_and_back | 7924271 | 7670620 | 7596371 | 7569623 | +---------------+----------+----------+----------+-------------+ | blackhole | 5672078 | 5805059 | 5654402 | 5592062 | Huitema, et al. Expires 3 May 2027 [Page 17] Internet-Draft C4 Tests October 2026 +---------------+----------+----------+----------+-------------+ | short_long | 17798900 | 44361391 | 21547035 | 17538427 | +---------------+----------+----------+----------+-------------+ | satellite | 7157099 | 7170308 | 6704246 | 6807184 | +---------------+----------+----------+----------+-------------+ Table 2 5.2.3. average RTT for network events tests +======================+========+========+========+=============+ | average RTT for | c4 | bbr | cubic | c4_draft-04 | | network events tests | | | | | +======================+========+========+========+=============+ | alone | 94052 | 95441 | 127233 | 113628 | +----------------------+--------+--------+--------+-------------+ | alone_200 | 56947 | 46022 | 54918 | 59296 | +----------------------+--------+--------+--------+-------------+ | alone_1_5M | 50668 | 64430 | 86178 | 92468 | +----------------------+--------+--------+--------+-------------+ | alone_512k | 62632 | 95935 | 95271 | 98346 | +----------------------+--------+--------+--------+-------------+ | low_and_up | 109615 | 116948 | 118071 | 109493 | +----------------------+--------+--------+--------+-------------+ | drop_and_back | 115077 | 120227 | 130108 | 119770 | +----------------------+--------+--------+--------+-------------+ | blackhole | 135412 | 148336 | 149068 | 140658 | +----------------------+--------+--------+--------+-------------+ | short_long | 195044 | 193616 | 300239 | 193251 | +----------------------+--------+--------+--------+-------------+ | satellite | 601388 | 706266 | 610161 | 601057 | +----------------------+--------+--------+--------+-------------+ Table 3 5.2.4. top 90% of RTT + standard deviation for network events tests +========================+========+========+========+=============+ | top 90% of RTT + | c4 | bbr | cubic | c4_draft-04 | | standard deviation for | | | | | | network events tests | | | | | +========================+========+========+========+=============+ | alone | 112001 | 107461 | 168048 | 142636 | +------------------------+--------+--------+--------+-------------+ | alone_200 | 83970 | 57616 | 72160 | 88089 | +------------------------+--------+--------+--------+-------------+ | alone_1_5M | 59744 | 75586 | 90860 | 96658 | +------------------------+--------+--------+--------+-------------+ Huitema, et al. Expires 3 May 2027 [Page 18] Internet-Draft C4 Tests October 2026 | alone_512k | 73775 | 103452 | 106089 | 105400 | +------------------------+--------+--------+--------+-------------+ | low_and_up | 128064 | 134441 | 145844 | 127962 | +------------------------+--------+--------+--------+-------------+ | drop_and_back | 139505 | 150495 | 161227 | 153647 | +------------------------+--------+--------+--------+-------------+ | blackhole | 460294 | 502570 | 451075 | 479784 | +------------------------+--------+--------+--------+-------------+ | short_long | 234671 | 232694 | 410060 | 230002 | +------------------------+--------+--------+--------+-------------+ | satellite | 602614 | 845436 | 621273 | 602375 | +------------------------+--------+--------+--------+-------------+ Table 4 5.3. Competition Here the statistics for the compete test cases. 5.3.1. average time for compete tests +==================+==========+==========+==========+=============+ | average time for | c4 | bbr | cubic | c4_draft-04 | | compete tests | | | | | +==================+==========+==========+==========+=============+ | vs_bbr | 2768730 | 4480386 | 2710457 | 2817345 | +------------------+----------+----------+----------+-------------+ | vs_c4 | 4961834 | 6307900 | 4307723 | 4349648 | +------------------+----------+----------+----------+-------------+ | vs_cubic | 4067022 | 6999001 | 5846835 | 3418203 | +------------------+----------+----------+----------+-------------+ | after_c4 | 6216225 | 6907758 | 6961798 | 6599569 | +------------------+----------+----------+----------+-------------+ | before_c4 | 2699634 | 3063520 | 2488607 | 2633286 | +------------------+----------+----------+----------+-------------+ | vs_c4_lg | 21411570 | 21131629 | 23547764 | 21024837 | +------------------+----------+----------+----------+-------------+ | vs_c4_lg2 | 21184515 | 21153080 | 21638712 | 20961838 | +------------------+----------+----------+----------+-------------+ | vs_bbr_lg | 17050469 | 21348475 | 15267288 | 15608340 | +------------------+----------+----------+----------+-------------+ | vs_bbr_lg2 | 17548233 | 20431875 | 22158986 | 16501414 | +------------------+----------+----------+----------+-------------+ | vs_cubic_lg | 18665679 | 21218334 | 21175277 | 17942252 | +------------------+----------+----------+----------+-------------+ | vs_cubic_lg2 | 16228274 | 15856559 | 20942576 | 17076722 | +------------------+----------+----------+----------+-------------+ Huitema, et al. Expires 3 May 2027 [Page 19] Internet-Draft C4 Tests October 2026 Table 5 5.3.2. top 90% time for compete tests +==================+==========+==========+==========+=============+ | top 90% time for | c4 | bbr | cubic | c4_draft-04 | | compete tests | | | | | +==================+==========+==========+==========+=============+ | vs_bbr | 2777054 | 4561853 | 2715758 | 2821436 | +------------------+----------+----------+----------+-------------+ | vs_c4 | 5636359 | 6905450 | 4554841 | 4521899 | +------------------+----------+----------+----------+-------------+ | vs_cubic | 4494984 | 7028329 | 6129052 | 3787691 | +------------------+----------+----------+----------+-------------+ | after_c4 | 6366914 | 6980237 | 7190470 | 6743285 | +------------------+----------+----------+----------+-------------+ | before_c4 | 2844430 | 3213300 | 2513886 | 2734795 | +------------------+----------+----------+----------+-------------+ | vs_c4_lg | 21584135 | 21354591 | 24412209 | 21132908 | +------------------+----------+----------+----------+-------------+ | vs_c4_lg2 | 21244879 | 21310222 | 21894728 | 21040360 | +------------------+----------+----------+----------+-------------+ | vs_bbr_lg | 20844030 | 21449486 | 14879493 | 15857330 | +------------------+----------+----------+----------+-------------+ | vs_bbr_lg2 | 18244846 | 21336509 | 22520144 | 16599500 | +------------------+----------+----------+----------+-------------+ | vs_cubic_lg | 19640302 | 21412469 | 21953566 | 20324018 | +------------------+----------+----------+----------+-------------+ | vs_cubic_lg2 | 17724897 | 16019731 | 21125242 | 17505908 | +------------------+----------+----------+----------+-------------+ Table 6 5.3.3. average RTT for compete tests +=================+========+========+========+=============+ | average RTT for | c4 | bbr | cubic | c4_draft-04 | | compete tests | | | | | +=================+========+========+========+=============+ | vs_bbr | 124492 | 125857 | 123340 | 104812 | +-----------------+--------+--------+--------+-------------+ | vs_c4 | 113430 | 124494 | 132850 | 114721 | +-----------------+--------+--------+--------+-------------+ | vs_cubic | 129619 | 109457 | 139598 | 136494 | +-----------------+--------+--------+--------+-------------+ | after_c4 | 116592 | 108393 | 112248 | 115545 | +-----------------+--------+--------+--------+-------------+ | before_c4 | 67717 | 71186 | 74193 | 76660 | Huitema, et al. Expires 3 May 2027 [Page 20] Internet-Draft C4 Tests October 2026 +-----------------+--------+--------+--------+-------------+ | vs_c4_lg | 106806 | 110220 | 113787 | 113389 | +-----------------+--------+--------+--------+-------------+ | vs_c4_lg2 | 118146 | 121168 | 108526 | 124713 | +-----------------+--------+--------+--------+-------------+ | vs_bbr_lg | 135313 | 122449 | 141964 | 117425 | +-----------------+--------+--------+--------+-------------+ | vs_bbr_lg2 | 121214 | 128986 | 112559 | 121149 | +-----------------+--------+--------+--------+-------------+ | vs_cubic_lg | 130672 | 91606 | 125410 | 135951 | +-----------------+--------+--------+--------+-------------+ | vs_cubic_lg2 | 124708 | 129258 | 132612 | 126129 | +-----------------+--------+--------+--------+-------------+ Table 7 5.3.4. top 90% of RTT + standard deviation for compete tests +====================+========+========+========+=============+ | top 90% of RTT + | c4 | bbr | cubic | c4_draft-04 | | standard deviation | | | | | | for compete tests | | | | | +====================+========+========+========+=============+ | vs_bbr | 154005 | 156725 | 147826 | 128620 | +--------------------+--------+--------+--------+-------------+ | vs_c4 | 152185 | 159709 | 155513 | 146435 | +--------------------+--------+--------+--------+-------------+ | vs_cubic | 152658 | 137259 | 159758 | 161246 | +--------------------+--------+--------+--------+-------------+ | after_c4 | 148189 | 146770 | 141204 | 146628 | +--------------------+--------+--------+--------+-------------+ | before_c4 | 107023 | 97903 | 99392 | 108898 | +--------------------+--------+--------+--------+-------------+ | vs_c4_lg | 142532 | 149248 | 147244 | 146006 | +--------------------+--------+--------+--------+-------------+ | vs_c4_lg2 | 151239 | 152982 | 137156 | 158239 | +--------------------+--------+--------+--------+-------------+ | vs_bbr_lg | 161934 | 156472 | 160010 | 142672 | +--------------------+--------+--------+--------+-------------+ | vs_bbr_lg2 | 150952 | 155650 | 143578 | 147234 | +--------------------+--------+--------+--------+-------------+ | vs_cubic_lg | 152277 | 113509 | 159776 | 151416 | +--------------------+--------+--------+--------+-------------+ | vs_cubic_lg2 | 150050 | 150889 | 159134 | 146915 | +--------------------+--------+--------+--------+-------------+ Table 8 Huitema, et al. Expires 3 May 2027 [Page 21] Internet-Draft C4 Tests October 2026 5.3.5. average load for compete tests +================================+=====+=====+=======+=============+ | average load for compete tests | c4 | bbr | cubic | c4_draft-04 | +================================+=====+=====+=======+=============+ | vs_bbr | 81% | 47% | 82% | 78% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4 | 46% | 30% | 54% | 51% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic | 52% | 14% | 36% | 65% | +--------------------------------+-----+-----+-------+-------------+ | after_c4 | 38% | 21% | 29% | 35% | +--------------------------------+-----+-----+-------+-------------+ | before_c4 | 60% | 53% | 63% | 61% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4_lg | 48% | 41% | 41% | 52% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4_lg2 | 52% | 55% | 39% | 55% | +--------------------------------+-----+-----+-------+-------------+ | vs_bbr_lg | 75% | 49% | 83% | 80% | +--------------------------------+-----+-----+-------+-------------+ | vs_bbr_lg2 | 71% | 61% | 28% | 75% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic_lg | 66% | 14% | 45% | 70% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic_lg2 | 77% | 79% | 55% | 72% | +--------------------------------+-----+-----+-------+-------------+ Table 9 5.3.6. top 90% load for compete tests +================================+=====+=====+=======+=============+ | top 90% load for compete tests | c4 | bbr | cubic | c4_draft-04 | +================================+=====+=====+=======+=============+ | vs_bbr | 82% | 48% | 82% | 78% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4 | 49% | 36% | 60% | 52% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic | 53% | 15% | 39% | 70% | +--------------------------------+-----+-----+-------+-------------+ | after_c4 | 40% | 23% | 30% | 36% | +--------------------------------+-----+-----+-------+-------------+ | before_c4 | 62% | 56% | 65% | 65% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4_lg | 55% | 54% | 46% | 54% | +--------------------------------+-----+-----+-------+-------------+ | vs_c4_lg2 | 53% | 58% | 41% | 58% | Huitema, et al. Expires 3 May 2027 [Page 22] Internet-Draft C4 Tests October 2026 +--------------------------------+-----+-----+-------+-------------+ | vs_bbr_lg | 83% | 50% | 85% | 81% | +--------------------------------+-----+-----+-------+-------------+ | vs_bbr_lg2 | 74% | 69% | 32% | 76% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic_lg | 69% | 15% | 50% | 78% | +--------------------------------+-----+-----+-------+-------------+ | vs_cubic_lg2 | 81% | 80% | 58% | 74% | +--------------------------------+-----+-----+-------+-------------+ Table 10 5.4. Buffer bloat Here the statistics for the buffer bloat test cases. 5.4.1. average time for buffer bloat tests +====================+==========+==========+==========+=============+ | average time | c4 | bbr | cubic | c4_draft-04 | | for buffer | | | | | | bloat tests | | | | | +====================+==========+==========+==========+=============+ | bbloat | 12794681 | 12995007 | 12622707 | 12642775 | +--------------------+----------+----------+----------+-------------+ | bbloat_c4 | 20994353 | 21363775 | 20716793 | 20935286 | +--------------------+----------+----------+----------+-------------+ | bbloat_bbr | 14881484 | 21328671 | 13942815 | 15320599 | +--------------------+----------+----------+----------+-------------+ | bbloat_cubic | 20660588 | 21588464 | 20716807 | 20736042 | +--------------------+----------+----------+----------+-------------+ Table 11 5.4.2. top 90% time for buffer bloat tests +====================+==========+==========+==========+=============+ | top 90% time | c4 | bbr | cubic | c4_draft-04 | | for buffer | | | | | | bloat tests | | | | | +====================+==========+==========+==========+=============+ | bbloat | 12794853 | 12995526 | 12623909 | 12645052 | +--------------------+----------+----------+----------+-------------+ | bbloat_c4 | 21067518 | 21570439 | 20716848 | 21006655 | +--------------------+----------+----------+----------+-------------+ | bbloat_bbr | 14946487 | 21416699 | 13990176 | 15431313 | +--------------------+----------+----------+----------+-------------+ | bbloat_cubic | 20718563 | 21733982 | 20716830 | 20761314 | Huitema, et al. Expires 3 May 2027 [Page 23] Internet-Draft C4 Tests October 2026 +--------------------+----------+----------+----------+-------------+ Table 12 5.4.3. average RTT for buffer bloat tests +====================+========+========+========+=============+ | average RTT for | c4 | bbr | cubic | c4_draft-04 | | buffer bloat tests | | | | | +====================+========+========+========+=============+ | bbloat | 91531 | 84840 | 182687 | 113442 | +--------------------+--------+--------+--------+-------------+ | bbloat_c4 | 183026 | 99654 | 692469 | 232427 | +--------------------+--------+--------+--------+-------------+ | bbloat_bbr | 168268 | 125759 | 233068 | 132447 | +--------------------+--------+--------+--------+-------------+ | bbloat_cubic | 712963 | 93024 | 635463 | 551412 | +--------------------+--------+--------+--------+-------------+ Table 13 5.4.4. top 90% of RTT + standard deviation for buffer bloat tests +========================+=========+========+========+=============+ | top 90% of RTT + | c4 | bbr | cubic | c4_draft-04 | | standard deviation for | | | | | | buffer bloat tests | | | | | +========================+=========+========+========+=============+ | bbloat | 137063 | 96518 | 266072 | 158066 | +------------------------+---------+--------+--------+-------------+ | bbloat_c4 | 292289 | 146757 | 979722 | 361518 | +------------------------+---------+--------+--------+-------------+ | bbloat_bbr | 220249 | 166261 | 349477 | 160200 | +------------------------+---------+--------+--------+-------------+ | bbloat_cubic | 1068247 | 122959 | 999167 | 860075 | +------------------------+---------+--------+--------+-------------+ Table 14 5.4.5. average load for buffer bloat tests +====================+=====+=====+=======+=============+ | average load for | c4 | bbr | cubic | c4_draft-04 | | buffer bloat tests | | | | | +====================+=====+=====+=======+=============+ | bbloat | 97% | 95% | 98% | 98% | +--------------------+-----+-----+-------+-------------+ | bbloat_c4 | 50% | 15% | 31% | 50% | Huitema, et al. Expires 3 May 2027 [Page 24] Internet-Draft C4 Tests October 2026 +--------------------+-----+-----+-------+-------------+ | bbloat_bbr | 83% | 49% | 89% | 81% | +--------------------+-----+-----+-------+-------------+ | bbloat_cubic | 61% | 12% | 48% | 58% | +--------------------+-----+-----+-------+-------------+ Table 15 5.4.6. top 90% load for buffer bloat tests +====================+=====+=====+=======+=============+ | top 90% load for | c4 | bbr | cubic | c4_draft-04 | | buffer bloat tests | | | | | +====================+=====+=====+=======+=============+ | bbloat | 97% | 95% | 98% | 98% | +--------------------+-----+-----+-------+-------------+ | bbloat_c4 | 52% | 16% | 32% | 53% | +--------------------+-----+-----+-------+-------------+ | bbloat_bbr | 84% | 50% | 89% | 82% | +--------------------+-----+-----+-------+-------------+ | bbloat_cubic | 61% | 12% | 49% | 58% | +--------------------+-----+-----+-------+-------------+ Table 16 5.5. Wi-Fi Here the statistics for the wifi test cases. 5.5.1. average time for wifi tests +=================+==========+==========+==========+=============+ | average time | c4 | bbr | cubic | c4_draft-04 | | for wifi tests | | | | | +=================+==========+==========+==========+=============+ | wifi_bad | 3572565 | 5276858 | 4077668 | 4070606 | +-----------------+----------+----------+----------+-------------+ | wifi_fade | 5064452 | 5416055 | 5336618 | 5073239 | +-----------------+----------+----------+----------+-------------+ | wifi_suspension | 4581278 | 4612549 | 4594461 | 4564955 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_bbr | 7136154 | 8315633 | 6790172 | 7065591 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_c4 | 10813913 | 12025900 | 11507645 | 8664120 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_cubic | 9000711 | 10625081 | 10639380 | 8649554 | +-----------------+----------+----------+----------+-------------+ Huitema, et al. Expires 3 May 2027 [Page 25] Internet-Draft C4 Tests October 2026 Table 17 5.5.2. top 90% time for wifi tests +=================+==========+==========+==========+=============+ | top 90% time | c4 | bbr | cubic | c4_draft-04 | | for wifi tests | | | | | +=================+==========+==========+==========+=============+ | wifi_bad | 3793102 | 6767611 | 4362647 | 4530282 | +-----------------+----------+----------+----------+-------------+ | wifi_fade | 5291851 | 5681330 | 5535374 | 5357776 | +-----------------+----------+----------+----------+-------------+ | wifi_suspension | 4580858 | 4613000 | 4597003 | 4574186 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_bbr | 11125580 | 12430498 | 12815995 | 10736818 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_c4 | 11991545 | 12674921 | 13075119 | 11249655 | +-----------------+----------+----------+----------+-------------+ | wifi_bad_cubic | 11966921 | 12419749 | 13566122 | 11250821 | +-----------------+----------+----------+----------+-------------+ Table 18 5.5.3. average RTT for wifi tests +=================+========+========+========+=============+ | average RTT for | c4 | bbr | cubic | c4_draft-04 | | wifi tests | | | | | +=================+========+========+========+=============+ | wifi_bad | 146549 | 65609 | 92618 | 109023 | +-----------------+--------+--------+--------+-------------+ | wifi_fade | 140240 | 124750 | 136634 | 145297 | +-----------------+--------+--------+--------+-------------+ | wifi_suspension | 13680 | 13150 | 26539 | 13993 | +-----------------+--------+--------+--------+-------------+ | wifi_bad_bbr | 197531 | 194826 | 234190 | 199724 | +-----------------+--------+--------+--------+-------------+ | wifi_bad_c4 | 229368 | 203852 | 220966 | 234733 | +-----------------+--------+--------+--------+-------------+ | wifi_bad_cubic | 238466 | 224264 | 200377 | 256603 | +-----------------+--------+--------+--------+-------------+ Table 19 Huitema, et al. Expires 3 May 2027 [Page 26] Internet-Draft C4 Tests October 2026 5.5.4. top 90% of RTT + standard deviation for wifi tests +====================+========+========+========+=============+ | top 90% of RTT + | c4 | bbr | cubic | c4_draft-04 | | standard deviation | | | | | | for wifi tests | | | | | +====================+========+========+========+=============+ | wifi_bad | 260239 | 145600 | 148298 | 258484 | +--------------------+--------+--------+--------+-------------+ | wifi_fade | 206474 | 174746 | 182279 | 207083 | +--------------------+--------+--------+--------+-------------+ | wifi_suspension | 31952 | 31843 | 45256 | 32878 | +--------------------+--------+--------+--------+-------------+ | wifi_bad_bbr | 324265 | 321729 | 334122 | 330282 | +--------------------+--------+--------+--------+-------------+ | wifi_bad_c4 | 323158 | 318008 | 330354 | 331655 | +--------------------+--------+--------+--------+-------------+ | wifi_bad_cubic | 321710 | 323608 | 320618 | 337028 | +--------------------+--------+--------+--------+-------------+ Table 20 5.5.5. average load for wifi tests +=============================+======+=====+=======+=============+ | average load for wifi tests | c4 | bbr | cubic | c4_draft-04 | +=============================+======+=====+=======+=============+ | wifi_bad | 100% | 68% | 87% | 84% | +-----------------------------+------+-----+-------+-------------+ | wifi_fade | 87% | 78% | 80% | 87% | +-----------------------------+------+-----+-------+-------------+ | wifi_suspension | 90% | 89% | 91% | 91% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_bbr | 64% | 54% | 81% | 64% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_c4 | 39% | 27% | 35% | 51% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_cubic | 46% | 33% | 35% | 50% | +-----------------------------+------+-----+-------+-------------+ Table 21 Huitema, et al. Expires 3 May 2027 [Page 27] Internet-Draft C4 Tests October 2026 5.5.6. top 90% load for wifi tests +=============================+======+=====+=======+=============+ | top 90% load for wifi tests | c4 | bbr | cubic | c4_draft-04 | +=============================+======+=====+=======+=============+ | wifi_bad | 106% | 95% | 96% | 95% | +-----------------------------+------+-----+-------+-------------+ | wifi_fade | 90% | 80% | 84% | 90% | +-----------------------------+------+-----+-------+-------------+ | wifi_suspension | 90% | 89% | 91% | 91% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_bbr | 83% | 79% | 114% | 82% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_c4 | 48% | 37% | 47% | 69% | +-----------------------------+------+-----+-------+-------------+ | wifi_bad_cubic | 64% | 52% | 72% | 67% | +-----------------------------+------+-----+-------+-------------+ Table 22 5.6. ECN Here the statistics for the ecn test cases. 5.6.1. average time for ecn tests +===============+==========+==========+==========+=============+ | average time | c4 | bbr | cubic | c4_draft-04 | | for ecn tests | | | | | +===============+==========+==========+==========+=============+ | ecn | 4651037 | 4657883 | 4406012 | 4465982 | +---------------+----------+----------+----------+-------------+ | ecn_c4 | 11281528 | 13253617 | 15674266 | 12078995 | +---------------+----------+----------+----------+-------------+ | ecn_cubic | 8526561 | 7780693 | 10792917 | 8246796 | +---------------+----------+----------+----------+-------------+ | ecn_bbr | 13254633 | 13605816 | 17087760 | 13089999 | +---------------+----------+----------+----------+-------------+ Table 23 Huitema, et al. Expires 3 May 2027 [Page 28] Internet-Draft C4 Tests October 2026 5.6.2. top 90% time for ecn tests +===============+==========+==========+==========+=============+ | top 90% time | c4 | bbr | cubic | c4_draft-04 | | for ecn tests | | | | | +===============+==========+==========+==========+=============+ | ecn | 4652903 | 4658116 | 4406193 | 4467028 | +---------------+----------+----------+----------+-------------+ | ecn_c4 | 12795636 | 15409855 | 16339295 | 13032878 | +---------------+----------+----------+----------+-------------+ | ecn_cubic | 9324633 | 7685969 | 12007554 | 9023342 | +---------------+----------+----------+----------+-------------+ | ecn_bbr | 13532632 | 13576641 | 17441363 | 13309789 | +---------------+----------+----------+----------+-------------+ Table 24 5.6.3. average RTT for ecn tests +===============+========+========+========+=============+ | average RTT | c4 | bbr | cubic | c4_draft-04 | | for ecn tests | | | | | +===============+========+========+========+=============+ | ecn | 84426 | 89652 | 116924 | 84661 | +---------------+--------+--------+--------+-------------+ | ecn_c4 | 107818 | 100306 | 97318 | 106047 | +---------------+--------+--------+--------+-------------+ | ecn_cubic | 114973 | 124996 | 128516 | 116735 | +---------------+--------+--------+--------+-------------+ | ecn_bbr | 111076 | 102037 | 95512 | 114200 | +---------------+--------+--------+--------+-------------+ Table 25 5.6.4. top 90% of RTT + standard deviation for ecn tests +====================+========+========+========+=============+ | top 90% of RTT + | c4 | bbr | cubic | c4_draft-04 | | standard deviation | | | | | | for ecn tests | | | | | +====================+========+========+========+=============+ | ecn | 94982 | 102213 | 129577 | 96364 | +--------------------+--------+--------+--------+-------------+ | ecn_c4 | 132703 | 119492 | 117583 | 129210 | +--------------------+--------+--------+--------+-------------+ | ecn_cubic | 130867 | 134804 | 135485 | 134465 | +--------------------+--------+--------+--------+-------------+ | ecn_bbr | 135172 | 123960 | 115598 | 136495 | Huitema, et al. Expires 3 May 2027 [Page 29] Internet-Draft C4 Tests October 2026 +--------------------+--------+--------+--------+-------------+ Table 26 5.7. Media Here the statistics for the media test cases. 5.7.1. average av_latency for media tests +====================+========+========+========+=============+ | average av_latency | c4 | bbr | cubic | c4_draft-04 | | for media tests | | | | | +====================+========+========+========+=============+ | media | 30494 | 30480 | 30430 | 33512 | +--------------------+--------+--------+--------+-------------+ | media10 | 44871 | 44874 | 45985 | 45369 | +--------------------+--------+--------+--------+-------------+ | media_600fr | 30789 | 30491 | 30439 | 33625 | +--------------------+--------+--------+--------+-------------+ | media_short_long | 100827 | 129819 | 101359 | 100792 | +--------------------+--------+--------+--------+-------------+ | media_wb | 84656 | 90498 | 78729 | 80315 | +--------------------+--------+--------+--------+-------------+ | media_wf | 82615 | 85021 | 85936 | 82068 | +--------------------+--------+--------+--------+-------------+ | media_ws | 21790 | 21529 | 22198 | 22955 | +--------------------+--------+--------+--------+-------------+ | media_ecn | 32262 | 32365 | 32312 | 34413 | +--------------------+--------+--------+--------+-------------+ | media_backload | 32639 | 42494 | 33786 | | +--------------------+--------+--------+--------+-------------+ Table 27 5.7.2. top 90% max_latency for media tests +=====================+========+========+========+=============+ | top 90% max_latency | c4 | bbr | cubic | c4_draft-04 | | for media tests | | | | | +=====================+========+========+========+=============+ | media | 40926 | 35430 | 33110 | 43453 | +---------------------+--------+--------+--------+-------------+ | media10 | 87527 | 71128 | 92165 | 71128 | +---------------------+--------+--------+--------+-------------+ | media_600fr | 42514 | 35430 | 33148 | 43453 | +---------------------+--------+--------+--------+-------------+ | media_short_long | 112263 | 316395 | 115954 | 111153 | Huitema, et al. Expires 3 May 2027 [Page 30] Internet-Draft C4 Tests October 2026 +---------------------+--------+--------+--------+-------------+ | media_wb | 312122 | 289359 | 264475 | 265337 | +---------------------+--------+--------+--------+-------------+ | media_wf | 290827 | 304982 | 308031 | 290560 | +---------------------+--------+--------+--------+-------------+ | media_ws | 197834 | 195534 | 197259 | 197821 | +---------------------+--------+--------+--------+-------------+ | media_ecn | 50966 | 50996 | 50996 | 47975 | +---------------------+--------+--------+--------+-------------+ | media_backload | 82950 | 293871 | 86944 | | +---------------------+--------+--------+--------+-------------+ Table 28 6. Live Tests We need real life tests as well. 6.1. Loopback tests Loopback tests were performed on Windows, downloading 10GB of data over a loopback connection. They showed picoquic using C4 achieving a data rate of 3Gbps, slightly more than the 2.9Gbps achieved when using Cubic or the 2.6 Gbps achieved when using BBR. 6.2. Webex prototype deployments To do. Write down. 7. Security Considerations This documentation of protocol testing does not have any particular security considerations. We did not include specific security oriented tests in this document. 8. IANA Considerations This document has no IANA actions. 9. Informative References [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . Huitema, et al. Expires 3 May 2027 [Page 31] Internet-Draft C4 Tests October 2026 [I-D.ietf-moq-transport] Nandakumar, S., Vasiliev, V., Swett, I., and A. Frindell, "Media over QUIC Transport", Work in Progress, Internet- Draft, draft-ietf-moq-transport-22, 1 October 2026, . [RFC9959] Kuhn, N., Stephan, E., Fairhurst, G., Secchi, R., and C. Huitema, "Careful Resume: Convergence of Congestion Control from Retained State", RFC 9959, DOI 10.17487/RFC9959, May 2026, . [RFC9743] Duke, M., Ed. and G. Fairhurst, Ed., "Specifying New Congestion Control Algorithms", BCP 133, RFC 9743, DOI 10.17487/RFC9743, March 2025, . [Picoquic] Huitema, C., "Picoquic", GitHub Repository , 2025, . [Picoquic_ns] Huitema, C., "Picoquic Network Simulator", GitHub Repository , 2025, . Acknowledgments TODO acknowledge. Authors' Addresses Christian Huitema Private Octopus Inc. Email: huitema@huitema.net Suhas Nandakumar Cisco Email: snandaku@cisco.com Cullen Jennings Cisco Email: fluffy@iii.ca Huitema, et al. Expires 3 May 2027 [Page 32]