Apparently, I still don't understand your requirements. You say lossless, yet you aren't willing to deal with retransmissions. This would seem to be problematic when there are link errors.
If what you seek is simply QoS, well, we've solved that problem before. Flow control is not necessary. T On Thu, Jul 24, 2025 at 11:49 AM 韩政鑫(联通集团本部) <hanz...@chinaunicom.cn> wrote: > Hi Tony, > > Thanks for your valuable historical perspective. We’ve reviewed materials > on LAPB and X.25 networks, and it’s true that early approaches like LAPB > had limitations—leading Internet designers to adopt a different > architectural path. > > LAPB in X.25 relies on hop - by - hop retransmission for error correction, > introducing significant latency and throughput bottlenecks. However, modern > flow control mechanisms, such as PFC, detect queue thresholds and rapidly > throttle traffic upstream of congestion points. This actively prevents > congestion without retransmission, using backpressure with extremely low > latency. > > We fully agree that preventing congestion for all traffic across the > entire network is impractical and would incur severe costs. Instead of > targeting all traffic, we prioritize high-priority services to ensure their > performance. Is there value in precisely preventing congestion for high - > priority flows to reduce packet loss and guarantee high throughput for RDMA > transmission over long distance? This is why we propose tenant / flow-level > refined flow control is necessary. > > Additionally, we believe upgrading all network devices is not feasible. > There should be a lightweight, cross - hop technical solution. For example, > only the routers at both ends are upgraded. In special cases, such as when > the distance is quite long, a few intermediate nodes may be further > upgraded to quickly alleviate congestion. > > BR， > ZhengXin > > ------------------------------ > > Zhengxin Han > > > > *发件人：* Tony Li <tony1ath...@gmail.com> > *发送时间：* 2025-07-23 21:29 > *收件人：* > *抄送：* rtgwg <rtgwg@ietf.org>; shavitt <shav...@eng.tau.ac.il>; 庞冉(联通集团本部) > <pang...@chinaunicom.cn>; 阮征(联通集团本部) <rua...@chinaunicom.cn> > *主题：* [rtgwg] Re: Continue discussion on “Use Cases, Requirements, and > Framework for Implementing Lossless Techniques in Wide Area Networks” > presentation in the RTGWG > > 【本邮件为外部邮件，请注意核实发件人身份，并谨慎处理邮件内容中的链接及附件】 > > Hi, > > If your goal is to prevent congestion loss in the network, then you will > find that you effectively need to prevent congestion in the network. > That is possible and has been done before. The approach for doing this is > to ensure that each router has flow-control and retransmission at the link > layer. You also need to extend this back to the originating hosts. > > This has been done before. See the LAPB link layer protocol that > underlies X.25 networks. The performance implications are rather severe. > > You might consider that these approaches are an entirely different > architecture that the Internet designers decided to avoid back around 1969. > > Regards, > Tony > > > On Wed, Jul 23, 2025 at 3:14 PM <"韩政鑫(联通集团本部)"@mf1-de.cloudmails.net> > wrote: > >> Hi all， >> >> >> We gave a presentation in the RTGWG session, focusing on the >> topic “Use Cases, Requirements, and Framework for Implementing Lossless >> Techniques in Wide Area Networks”. During the meeting, we got two >> comments. Since time limited there,we can continue the discussion over th >> is email list. >> >> >> 1、Shouldn’t this be handled at layer four (the transport layer) or the >> application layer using forward error correction（FEC）? That way, it can >> be solved end - to - end, instead of requiring further communication >> between routing devices. (*Comment from Yuval SHAVITT*). >> >> *Response:* >> >> >> - FEC is to detect and correct bit errors in data transmission, which >> ensures data integrity and reduces packet loss caused by bit errors. >> However, our primary focus is on packet loss resulting from network >> congestion due to traffic aggregation and bursts，and such packet loss >> significantly affects RDMA throughput and transmission efficiency. >> - To address this, we propose using fine-grained flow control >> mechanisms (e.g., enhanced PFC) in WAN between the routing devices to >> promptly mitigate congestion, achieving extremely low packet loss >> rate, and guarantee efficient RDMA transmissions over long distance. >> Meanwhile, to avoid large-scale upgrades of network device, we have also >> submitted a draft to the spring working group that supports cross-hop >> flow control notification and processing ( >> >> https://datatracker.ietf.org/doc/draft-ruan-spring-priority-flow-control-sid/ >> ). >> - Admittedly, end-to-end solutions at layer four or the application >> layer, such as fast source rate control notifications (e.g., ECN, >> Fast CNP) are also integrated into our framework to tackle issues >> from the source end. Nevertheless, WAN has long RTTs, these >> mechanisms may suffer from delayed responses, limiting their effectiveness >> in rapidly alleviating congestion. >> - We think network device optimizations and end-side improvements are >> complementary rather than conflicting. Similar to data center networks, >> combining network-layer technologies with transport/application layer >> mechanisms can achieve lossless transmission. Besides, as communication >> operators, we focus more on the network side and hope to further >> reduce the packet loss rate in WANs to provide robust network services for >> upper-layer applications. >> >> 2、Regarding the relationship with DetNet, here are some of our thoughts, >> and we welcome further discussions and insights from the DetNet. >> >> >> - Deterministic networking typically emphasizes bounded low latency >> and jitter, catering to latency critical scenarios like industrial >> control. >> Our current focus, however, is on efficient transmission of massive TB/PB >> level data over long-distance, for example, distributed AI training and >> inference across geographically dispersed data centers. >> - From our view, deterministic networking can achieve lossless >> transmission (with zero packet loss) through pre-resource reservation and >> time-slot-based scheduling. Does the deterministic network eliminate >> network congestion entirely? Additionally, lossless transmission (with >> extremely low packet loss nearly 0) could also be achieved by congestion >> control, path optimization, QoS etc. So does each approach is suited to >> different scenarios, with varying trade-offs between effectiveness and >> implementation costs？ >> >> Draft links: >> >> <https://datatracker.ietf.org/doc/draft-hs-rtgwg-wan-lossless-uc> >> https://datatracker.ietf.org/doc/draft-hs-rtgwg-wan-lossless-uc >> >> https://datatracker.ietf.org/doc/draft-hs-rtgwg-wan-lossless-framework/ >> >> >> *Any feedback and comments are welcome!* >> >> >> Best Regards, >> >> Zhengxin Han >> ------------------------------ >> >> Zhengxin Han >> >> Next Generation Internet Research Department >> >> Research Institute >> CHINA UNITED NETWORK COMMUNICATIONS CORPORATION LIMITED >> >> Mobile: +86-18601275531 >> E-mail: hanz...@chinaunicom.cn <he...@chinaunicom.cn> >> >> >> _______________________________________________ >> rtgwg mailing list -- rtgwg@ietf.org >> To unsubscribe send an email to rtgwg-le...@ietf.org >> >
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