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 this 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: [email protected] <[email protected]> > > > _______________________________________________ > rtgwg mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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