--- title: Twilight Zone: File Transfer Never Completes «... description: A networking war story from the era of 64kbps WAN links: a customer couldn't transfer one specific file between locations, with the transfer stalling and CRC... canonical: https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Twilight Zone: File Transfer Never Completes « ipSpace.net blog | daily.dev og:description: A networking war story from the era of 64kbps WAN links: a customer couldn't transfer one specific file between locations, with the transfer stalling and CRC... og:url: https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b og:image: https://api.daily.dev/og/posts/xDnQQCk6b.png og:image:alt: Twilight Zone: File Transfer Never Completes « ipSpace.net blog og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Twilight Zone: File Transfer Never Completes « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 3 min read · 0 upvotes · 0 comments ## Summary A networking war story from the era of 64kbps WAN links: a customer couldn't transfer one specific file between locations, with the transfer stalling and CRC errors appearing on the WAN link. The root cause was a clock synchronization issue with baseband modems — a long sequence of zeroes in the file caused the receiving modem to lose sync with the transmitter. Enabling Cisco's software link compression on the PPP/HDLC link replaced those long zero sequences with other bit patterns, resolving the issue. NRZI encoding or encryption would have worked equally well as alternatives. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why would a file transfer stall on a WAN link with CRC errors but only for one specific file? A long sequence of zeroes in the file's binary content can cause a baseband modem to lose clock synchronization with the transmitting modem, producing CRC errors and stalling the transfer. HDLC bit-stuffing prevents long runs of ones (inserting a zero after five consecutive ones) but does nothing to break up long zero sequences. Enabling link compression, NRZI encoding, or encryption all disrupt those zero runs and resolve the issue. _Engineers debugging obscure WAN issues like this find similar field-tested explanations on daily.dev._ ## Similar posts on daily.dev - [Transfer files over an ethernet patch cable](https://daily.dev/posts/transfer-files-over-an-ethernet-patch-cable-d63khzb7h) · Lobsters · 0 upvotes · 0 comments - [The Ethernet cable in your wall can negotiate at 1Gbps and still be bad](https://daily.dev/posts/the-ethernet-cable-in-your-wall-can-negotiate-at-1gbps-and-still-be-bad-ghefhxy6i) · XDA Developers · 0 upvotes · 0 comments - [The OSPF MTU Mismatch Saga « ipSpace.net blog](https://daily.dev/posts/the-ospf-mtu-mismatch-saga-ipspace-net-blog-jmtvuzjm6) · ipSpace.net Blog · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking) [View this post on daily.dev](https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Twilight Zone: File Transfer Never Completes « ipSpace.net blog","url":"https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b"},"datePublished":"2026-08-11T08:52:29.902Z","dateModified":"2026-08-11T09:42:48.546Z","description":"A networking war story from the era of 64kbps WAN links: a customer couldn't transfer one specific file between locations, with the transfer stalling and CRC...","image":"https://media.daily.dev/image/upload/s--ZrL_HSsR--/f_auto/v1722860399/public/Placeholder%2006","thumbnailUrl":"https://media.daily.dev/image/upload/s--ZrL_HSsR--/f_auto/v1722860399/public/Placeholder%2006","isAccessibleForFree":true,"articleSection":"ipSpace.net Blog","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"ipSpace.net Blog","logo":"https://media.daily.dev/image/upload/s--xS7E82MT--/f_auto,q_auto/v1786438303/logos/ipspace?_a=BAMAMicg0","url":"https://daily.dev/sources/ipspace"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"networking","timeRequired":"PT3M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"ipSpace.net Blog","item":"https://daily.dev/sources/ipspace"},{"@type":"ListItem","position":3,"name":"Twilight Zone: File Transfer Never Completes « ipSpace.net blog"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/twilight-zone-file-transfer-never-completes-ipspace-net-blog-xdnqqck6b#faq","mainEntity":[{"@type":"Question","name":"Why would a file transfer stall on a WAN link with CRC errors but only for one specific file?","acceptedAnswer":{"@type":"Answer","text":"A long sequence of zeroes in the file's binary content can cause a baseband modem to lose clock synchronization with the transmitting modem, producing CRC errors and stalling the transfer. HDLC bit-stuffing prevents long runs of ones (inserting a zero after five consecutive ones) but does nothing to break up long zero sequences. Enabling link compression, NRZI encoding, or encryption all disrupt those zero runs and resolve the issue. Engineers debugging obscure WAN issues like this find similar field-tested explanations on daily.dev."}}]} ```