Here is something everyone should read and become familiar with taken from Section 5 of the latest version of "IP Parcels and Advanced Jumbos":
https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/ A new link service model is offered that will be essential for supporting air/land/sea/space mobile Internetworking. IP Parcels and Advanced Jumbos are the vehicles that support end-to-end as opposed to hop-by-hop link error detection in the new model. This is a truly transformational concept for the Internet - many may already know about it, but everyone should become aware of it. Fred --- 5. IP Parcel and Advanced Jumbo Link Service Model The classical Internetworking link service model requires each link in the path to apply a link-layer packet integrity check often termed a "Cyclic Redundancy Check (CRC)". The link near-end calculates and appends a CRC code value (often 4 octets) to each packet pending transmission, and the link far-end verifies the CRC upon packet receipt. If the CRC is incorrect, the link far-end unconditionally discards the packet. This process is repeated for each link in the path so that only packets that pass all link-layer CRC checks are delivered to the final destination. While this link service model has contributed to the unparalleled success of terrestrial Internetworks (including the global public Internet), new uses in which significant delays or disruptions can occur are not as well supported. For example, a path that contains links with significant bit errors may be challenged to pass a majority percentage of packets since loss due to CRC failures can occur at any hop while each packet lost must be retransmitted. With the advent of space-domain Internetworking, the long delays associated with interplanetary signal propagation can also often render any retransmissions useless especially when communications latency is critical. IP parcels and advanced jumbos now offer a new link service model; instead of requiring an independent CRC at each intermediate link hop, IP parcels and advanced jumbos include a CRC code with each segment that is calculated and inserted by the original source and verified by the final destination. Each intermediate hop must therefore pass IP parcels and advanced jumbos without applying traditional link layer CRC checks and/or discarding packets that contain errors. This relaxes the burden on intermediate systems and delivers all data that transits the path to the destination end system which is uniquely positioned to coordinate recovery of any data that was either lost or corrupted in transit. Each IP parcel and/or advanced jumbo-capable hop along the path from the original source to the final destination must therefore provide an API primitive to inform the link ingress to disable link-layer integrity checks for the current IP parcel or advanced jumbo payload. The parcel/advanced jumbo may therefore collect cumulative link errors along the path, but these will be detected by the per segment CRC checks performed by the final destination. The final destination in turn delivers each segment to the local transport layer along with a "CRC error" flag that is set if a CRC error was detected or clear otherwise. The CRC indication is then taken under advisement by the transport layer, which should consult any transport or higher-layer integrity checks to pursue corrective actions. IP parcels and advanced jumbos therefore provide a revolutionary advancement for delay/disruption tolerance in air/land/sea/space mobile Internetworking applications. As the Internet continues to evolve from its more stable fixed terrestrial network origins to one where more and more nodes operate in the mobile edge, this new link service model relocates error detection and correction responsibilities from intermediate systems to the end systems that are best positioned to take corrective actions. Note: To be verified, IP parcels and advanced jumbos may be realized through simple software updates for widely-deployed link types such as 1/10/100-Gbps Ethernet. If the network driver API provides a primitive allowing the IP layer to disable link layer integrity checks on a per-"packet" basis, even very large IP parcels and advanced jumbos should be capable of transiting the link since Ethernet link transmission unit sizes are bounded by software and not hardware constraints. _______________________________________________ Int-area mailing list Int-area@ietf.org https://www.ietf.org/mailman/listinfo/int-area
