Hi Sebastian,Actually, "passing information on to endpoints" is an idea much older than 2019. It was in the original TCP V4 specification in 1981. See RFC792 ( https://www.rfc-editor.org/rfc/rfc792 ) pages 10-11.
I remember the discussions when the "Source Quench" (SQ) mechanism was being defined in the Internet Meetings around 1980. Personally I never thought SQ was a viable feedback technique, but it was OK as a placeholder for some future protocol that switches could use to exert back-pressure on the users' traffic, once a more effective mechanism was invented.
Instead of "slowing down", some implementors of TCP circa 1981 designed their systems to immediately retransmit a datagram that had caused a SQ to come back, figuring that the SQ meant that their original datagram had been discarded.
Jack On 2/27/24 12:45, Sebastian Moeller wrote:
Hi Jack,On 27. Feb 2024, at 21:11, Jack Haverty via Nnagain<[email protected]> wrote: Hi Bob, Measuring and monitoring Wifi behavior isn't necessary or sufficient. Same with Starlink or whatever else comes along in the future. The architecture of the Internet places different mechanisms, that in past times were contained in the switching equipment, now at many different places along a data path. Much of the mechanism is even in the users' devices themselves, which make all sorts of decisions about datagram size, acknowledgements, retransmission, discarding duplicates, et al. Those mechanisms interact with the decisions being made in network equipment such as switches. The overall behavior dictates what the end users see as behavior and reliability of "the net" as they experience it. The performance of the overall system is influenced by the interaction of its many pieces. My point was that to manage network service ("network" being defined by the users), you have to monitor and measure performance as seen by the users, as close to the keyboard/mouse/screen/whatever as you can get. That's why we decided to require a computer of some kind on each users' LAN environment, so we could experience and measure what they were likely experiencing, and use our measurements of switches, circuits, etc. to analyze and fix problems. It was also helpful to have a database of the metrics captured during previous "normal" network activity, to use as comparisons. As one example, I remember one event when a momentary glitch on a transpacific circuit would cause a flurry of activity as TCPs in the users' computers compensated, and would settle back to a steady state after a few minutes. But users complained that their file transfers were now taking much longer than usual. After our poking and prodding, using those remote computers as tools to see what the users were experiencing, we discovered that everything was operating as expected, except that every datagram was being transmitted twice and the duplicates discarded at the destination. The TCP retransmission mechanisms had settled into a new stable state. To the network switches, the datagrams all seeemed OK, but there was significantly more traffic than usual. No one was monitoring all those user devices out on the LANs so no one except the users noticed anything wrong. Eventually another glitch on the circuit would cause another flurry of activity and perhaps settle back into the desired state where datagrams only got sent once. We monitored whatever we could using SNMP to the routers and computers that had implemented such things, and we used our remote computers to also collect data from the users' perspective. Often we could tell a LAN manager that some particular deviceat his/her site was having problems, by looking for behavior that differed from the "normal" historical behavior from a week or so earlier. It would be interesting for example to collect metrics from switches about "buffer occupancy" and "transit time" (I don't recall if any MIB in SNMP had such metrics), and correlate that with TCP metrics such as retransmission behavior and duplicate detection.[SM] We could do even better, pas this information on to endpoints to actually allow them to not only react to overload but also to imminent overload... say by not collecting the absolute buffer occupancy, but say the max(current hop buffer occupancy, buffer occupancy already recorded in packet) (As much as would wish, this is not my idea, but Arslan,, and McKeow's. in “Switches Know the Exact Amount of Congestion.” In Proceedings of the 2019 Workshop on Buffer Sizing, 1–6, 2019.) Regards SebastianJack On 2/27/24 09:48, rjmcmahon wrote:Hi Jack, On LAN probes & monitors; I've been told that 90% of users devices are now wirelessly connected so the concept of connecting to a common wave guide to measure or observe user information & flow state isn't viable. A WiFi AP could provide its end state but wireless channels' states are non-trivial and the APs prioritize packet forwarding at L2 over state collection. I suspect a fully capable AP that could record per quintuple and RF channels' states would be too expensive. This is part of the reason why our industry and policy makers need to define the key performance metrics well. BobYes, latency is complicated.... Back when I was involved in the early Internet (early 1980s), we knew that latency was an issue requiring much further research, but we figured that meanwhile problems could be avoided by keeping traffic loads well below capacity while the appropriate algorithms could be discovered by the engineers (I was one...). Forty years later, it seems like it's still a research topic. Years later in the 90s I was involved in operating an international corporate intranet. We quickly learned that keeping the human users happy required looking at more than the routers and circuits between them. With much of the "reliability mechanisms" of TCP et al now located in the users' computers rather than the network switches, evaluating users' experience with "the net" required measurements from the users' perspective. To do that, we created a policy whereby every LAN attached to the long-haul backbone had to have a computer on that LAN to which we had remote access. That enabled us to perform "ping" tests and also collect data about TCP behavior (duplicates, retransmissions, etc.) using SNMP, etherwatch, et al. It was not unusual for the users' data to indicate that "the net", as they saw it, was misbehaving while the network data, as seen by the operators, indicated that all the routers and circuits were working just fine. If the government regulators want to keep the users happy, IMHO they need to understand this. Jack Haverty On 2/26/24 16:25, rjmcmahon wrote:https://docs.google.com/document/d/19ADByjakzQXCj9Re_pUvrb5Qe5OK-QmhlYRLMBY4vH4/editOn top of all that, the latency responses tend to be non parametric and may need full pdfs/cdfs along with non-parametric statistical process controls. Attached is an example from many years ago which was a firmware bug that sometimes delayed packet processing, creating a second node in the pdf. Engineers and their algorithms can be this way it seems. Bob I didn't study the whole report, but I didn't notice any metrics associated with *variance* of latency or bandwidth. It's common for vendors to play games ("Lies, damn lies, and statistics!") to make their metrics look good. A metric of latency that says something like "99% less than N milliseconds" doesn't necessarily translate into an acceptable user performance. It's also important to look at the specific techniques used for taking measurements. For example, if a measurement is performed every fifteen minutes, extrapolating the metric as representative of all the time between measurements can also lead to a metric judgement which doesn't reflect the reality of what the user actually experiences. In addition, there's a lot of mechanism between the ISPs' handling of datagrams and the end-user. The users' experience is affected by how all of that mechanism interacts as underlying network behavior changes. When a TCP running in some host decides it needs to retransmit, or an interactive audio/video session discards datagrams because they arrive too late to be useful, the user sees unacceptable performance even though the network operators may think everything is running fine. Measurements from the end-users' perspective might indicate performance is quite different from what measurements at the ISP level suggest. Gamers are especially sensitive to variance, but it will also apply to interactive uses such as might occur in telemedicine or remote operations. A few years ago I helped a friend do some tests for a gaming situation and we discovered that the average latency was reasonably low, but occasionally, perhaps a few times per hour, latency would increase to 10s of seconds. In a game, that often means the player loses. In a remote surgery it may mean horrendous outcomes. As more functionality is performed "in the cloud" such situations will become increasingly common. Jack Haverty On 2/26/24 12:02, rjmcmahon via Nnagain wrote: Thanks for sharing this. I'm trying to find out what are the key metrics that will be used for this monitoring. I want to make sure iperf 2 can cover the technical, traffic related ones that make sense to a skilled network operator, including a WiFi BSS manager. I didn't read all 327 pages though, from what I did read, I didn't see anything obvious. I assume these types of KPIs may be in reference docs or something. Thanks in advance for any help on this. Bob And... Our bufferbloat.net submittal was cited multiple times! Thank you all for participating in that process!https://docs.fcc.gov/public/attachments/DOC-400675A1.pdfIt is a long read, and does still start off on the wrong feet (IMHO), in particular not understanding the difference between idle and working latency. It is my hope that by widening awareness of more of the real problems with latency under load to policymakers and other submitters downstream from this new FCC document, and more reading what we had to say, that we will begin to make serious progress towards finally fixing bufferbloat in the USA. I do keep hoping that somewhere along the way in the future, the costs of IPv4 address exhaustion and the IPv6 transition, will also get raised to the national level. [1] We are still collecting signatures for what the bufferbloat project members wrote, and have 1200 bucks in the kitty for further articles and/or publicity. Thoughts appreciated as to where we can go next with shifting the national debate about bandwidth in a better direction! Next up would be trying to get a meeting, and to do an ex-parte filing, I think, and I wish we could do a live demonstration on television about it as good as feynman did here:https://www.youtube.com/watch?v=raMmRKGkGD4Our original posting is here:https://hackaday.com/2024/02/14/floss-weekly-episode-769-10-more-internet/Larry's wonderful post is here:https://circleid.com/posts/20231211-its-the-latency-fcc[1] How can we get more talking about IPv4 and IPv6, too? Will we have to wait another year?--https://blog.cerowrt.org/post/2024_predictions/ Dave Täht CSO, LibreQos_______________________________________________ Nnagain mailing list[email protected] https://lists.bufferbloat.net/listinfo/nnagain_______________________________________________ Nnagain mailing list[email protected] https://lists.bufferbloat.net/listinfo/nnagain<OpenPGP_0x746CC322403B8E50.asc>_______________________________________________ Nnagain mailing list [email protected] https://lists.bufferbloat.net/listinfo/nnagain
OpenPGP_0x746CC322403B8E50.asc
Description: OpenPGP public key
OpenPGP_signature.asc
Description: OpenPGP digital signature
_______________________________________________ Nnagain mailing list [email protected] https://lists.bufferbloat.net/listinfo/nnagain
