<?xmlversion="1.0" encoding="UTF-8"?>version='1.0' encoding='utf-8'?> <!DOCTYPE rfc[ <!ENTITY RFC2119 SYSTEM "http://www.rfc-editor.org/refs/bibxml/reference.RFC.2119.xml"> <!ENTITY RFC5234 SYSTEM "http://www.rfc-editor.org/refs/bibxml/reference.RFC.5234.xml"> <!ENTITY RFC7230 SYSTEM "http://www.rfc-editor.org/refs/bibxml/reference.RFC.7230.xml"> <!ENTITY RFC7233SYSTEM"http://www.rfc-editor.org/refs/bibxml/reference.RFC.7233.xml"> <!ENTITY RFC7234 SYSTEM "http://www.rfc-editor.org/refs/bibxml/reference.RFC.7234.xml"> <!ENTITY RFC8216 SYSTEM "http://www.rfc-editor.org/refs/bibxml/reference.RFC.8216.xml"> <!-- Fudge for XMLmind which doesn't have this built in --> <!ENTITY nbsp " "> ]> <!-- Extra statement used by XSLT processors to control the output style. --> <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> <!-- Processing Instructions can be placed here but if you are editing with XMLmind (and maybe other XML editors) they are better placed after the rfc element start tag as shown below. -->"rfc2629-xhtml.ent"> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" number="8673" consensus="true" submissionType="IETF" category="exp" ipr="trust200902" docName="draft-ietf-httpbis-rand-access-live-04"xmlns:x="http://purl.org/net/xml2rfc/ext"> <!-- Processing Instructions- PIs (for a complete list and description, see file http://xml.resource.org/authoring/README.html and below... --> <!-- Some of the more generally applicable PIs that most I-Ds might want to use --> <!-- Try to enforce the ID-nits conventions and DTD validity --> <?rfc strict="yes" ?> <!-- Items used when reviewing the document --> <?rfc comments="no" ?> <!-- Controls display of <cref> elements --> <?rfc inline="no" ?> <!-- When no, put comments at end in comments section, otherwise, put inline --> <?rfc editing="no" ?> <!-- When yes, insert editing marks: editing marks consist of a string such as <29> printed in the blank line at the beginning of each paragraph of text. --> <!-- Create Table of Contents (ToC) and set some options for it. Note the ToC may be omitted for very short documents,but idnits insists on a ToC if the document has more than 15 pages. --> <?rfc toc="yes"?> <?rfc tocompact="yes"?> <!-- If "yes" eliminates blank lines before main section entries. --> <?rfc tocdepth="4"?> <!-- Sets the number of levels of sections/subsections... in ToC --> <!-- Choose the options for the references. Some like symbolic tags in the references (and citations) and others prefer numbers. The RFC Editor always uses symbolic tags. The tags used are the anchor attributes of the references. --> <?rfc symrefs="yes"?> <?rfc sortrefs="yes" ?> <!-- If "yes", causes the references to be sorted in order of tags. This doesn't have any effect unless symrefs is "yes" also. --> <!-- These two save paper: Just setting compact to "yes" makes savings by not starting each main section on a new page but does not omit the blank lines between list items. If subcompact is also "yes" the blank lines between list items are also omitted. --> <?rfc compact="yes" ?> <?rfc subcompact="no" ?> <!-- end of list of popular I-D processing instructionstocInclude="true" symRefs="true" sortRefs="true" version="3" xml:lang="en"> <!-- xml2rfc v2v3 conversion 2.28.0 --> <!-- ***** FRONT MATTER ***** --> <front> <title>HTTP Random Access and Live Content</title> <seriesInfo name="RFC" value="8673" /> <author fullname="Craig Pratt" initials="C." surname="Pratt"> <address> <postal> <street/> <city>Portland</city> <region>OR</region> <code>97229</code><country>US</country><country>United States of America</country> </postal> <email>pratt@acm.org</email> </address> </author> <author fullname="Darshak Thakore" initials="D."surname="Thakore" >surname="Thakore"> <organization abbrev="CableLabs">CableLabs</organization> <address> <postal> <street>858 Coal Creek Circle</street> <city>Louisville</city> <region>CO</region> <code>80027</code><country>US</country><country>United States of America</country> </postal> <email>d.thakore@cablelabs.com</email> </address> </author> <author fullname="Barbara Stark"initials="B.H." surname="Stark" >initials="B." surname="Stark"> <organization>AT&T</organization> <address> <postal> <street/> <city>Atlanta</city> <region>GA</region><country>US</country><country>United States of America</country> </postal> <email>barbara.stark@att.com</email> </address> </author> <date year="2019"month="March"/> <!-- Meta-data Declarations --> <!-- Notice the use of & as an escape for & which would otherwise start an entity declaration, whereas we want a literal &. -->month="November"/> <area>Applications and Real-Time</area><!-- WG name at the upperleft corner of the doc, IETF fine for individual submissions. You can also omit this element in which case in defaults to "Network Working Group" - a hangover from the ancient history of the IETF! --><workgroup>HTTP</workgroup><keyword>http range unit live aggregation</keyword> <!-- The DTD allows multiple area and workgroup elements but only the first one has any effect on output. --> <!-- You can add <keyword/> elements here. They will be incorporated into HTML output files in a meta tag but they have no effect on text or nroff output. --><keyword>http</keyword> <keyword>range</keyword> <keyword>live</keyword> <keyword>aggregation</keyword> <abstract> <t> To accommodatebyte rangebyte-range requests for content that has data appended over time, this document defines semantics that allowaan HTTP client and a server to perform byte-range GET and HEAD requests that start at an arbitrary byte offset within the representation andendsend at an indeterminate offset. </t> </abstract><note title="Editorial Note (To be removed by RFC Editor before publication)"> <t> Discussion of this draft takes place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at <eref target="https://lists.w3.org/Archives/Public/ietf-http-wg/"/>. </t> <t> Working Group information can be found at <eref target="http://httpwg.github.io/"/>; source code and issues list for this draft can be found at <eref target="https://github.com/httpwg/http-extensions/labels/rand-access-live"/>. </t><!-- <t> The changes in this draft are summarized in <xref target="change.log"/>. </t>--> </note></front> <middle> <sectionanchor="introduction" title="Introduction">anchor="introduction"> <name>Introduction</name> <t> Some Hypertext Transfer Protocol (HTTP) clients use byte-range requests(Range(range requests using the "bytes"Range Unit)range unit) to transfer select portions of large representations(<xref target="RFC7233"/>). And in<xref target="RFC7233"/>. In somecasescases, large representations require content to be continuously or periodicallyappended -appended, such as representations consisting of live audio or video sources, blockchain databases, and log files. Clients cannot access the appended/live content using aRangerange request with thebytes"bytes" range unit using the currently defined byte-range semantics without accepting performance or behavior sacrificeswhichthat are not acceptable for many applications. </t> <t> For instance, HTTP clients have the ability to access appended content on an indeterminate-length resource by transferring the entire representation from the beginning and continuing to read the appended content as it's made available. Obviously, this is highly inefficient for cases where the representation is large and only the most recently appended content is needed by the client. </t> <t> Alternatively, clients canalsoaccess appended content by sendingperiodicperiodic, open-endedbytes Rangebyte-range requests using thelast-knownlast known end byte position as the range start. Performing low-frequency periodicbytes Rangebyte-range requests in this fashion (polling) introduces latency since the client will necessarily be somewhat behind in transferring the aggregatedcontent - mimickingcontent, effectively resulting in thebehavior (and latency)same kind of latency issues with the segmented contentrepresentations such astransfer mechanisms in "HTTP Live Streaming"(HLS,(HLS) <xreftarget="RFC8216"/>) ortarget="RFC8216"/> and "Dynamic Adaptive Streaming over HTTP"(MPEG-DASH,<xreftarget="DASH"/>). And whiletarget="MPEG-DASH"/>. While performing theseRangerange requests at higher frequency can reduce this latency, it also incurs more processing overhead and HTTP exchanges as many of the requests will return nocontent -content, since content is usually aggregated in groups of bytes(e.g.(e.g., a video frame, audio sample, block, or log entry). </t> <t> This document describes a usage model for range requestswhichthat enables efficient retrieval of representations that are appended to over time by using large values and associated semantics for communicating range end positions. This model allows representations to be progressively delivered by servers as new content is added. It also ensures compatibility with servers and intermediaries that don't support this technique. </t><section title="Requirements Language"> <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target="RFC2119">RFC 2119</xref>. </t> </section> <section title="Notational Conventions"><section> <name>Notational Conventions</name> <t>This document citesproductions inAugmented Backus-Naur Form (ABNF) productions from <xref target="RFC7233"/>, using the notation defined in <xref target="RFC5234"/>. </t> </section> </section> <sectionanchor="definition" title="Performinganchor="definition"> <name>Performing RangerequestsRequests on Random-Access Aggregating("live") Content">(Live) Content</name> <t> This document recommends a two-step process for accessing resources that haveindeterminate lengthindeterminate-length representations.</t><t></t> <t> Two steps are necessary because of limitations with theRangerange request header fields and the Content-Range response header fields. A server cannot know from a range request that a client wishes to receive a response that does not have a definite end. More critically, the header fields do not allow the server to signal that a resource has indeterminate length without also providing a fixed portion of the resource.</t><t></t> <t> A client first learns that the resource has a representation of indeterminate length by requesting a range of the resource. The server responds with the range that isavailable,available but indicates that the length of the representation is unknown using the existing Content-Range syntax. See <xreftarget="establishing-range" />target="establishing-range"/> for details and examples.</t><t></t> <t> Once the client knows the resource has indeterminate length, it can request a range with a very large end position from the resource. The client chooses an explicit end value larger than can be transferred in the foreseeable term. A serverwhichthat supports range requests of indeterminate length signals its understanding of the client's indeterminate range request by indicating that the range it is providing has a range end that exactly matches the client's requested range end rather than a range that is bounded by what is currently available. See <xreftarget="live-range-requests" />target="live-range-requests"/> for details. </t> <sectionanchor="establishing-range" title="Establishinganchor="establishing-range"> <name>Establishing the Randomly Accessible ByteRange">Range</name> <t>EstablishingDetermining if a representation is continuously aggregating ("live") and determining therandomly-accessiblerandomly accessible byte range can both bedeterminedperformed using the existing definition for an open-ended byte-range request. Specifically, <xrefx:sec="2.1" x:fmt="of" target="RFC7233"/>target="RFC7233" sectionFormat="of" section="2.1"/> defines a byte-range request of the form: </t><figure><artwork type="abnf"><sourcecode type="abnf"><![CDATA[ byte-range-spec = first-byte-pos "-" [ last-byte-pos ]</artwork></figure>]]></sourcecode > <t> which allows a client to send a HEAD request with a first-byte-pos and leave last-byte-pos absent. A server that receives a satisfiable byte-range request (with first-byte-pos smaller than the current representation length) may respond with a 206 status code (Partial Content) with a Content-Range header field indicating the currently satisfiable byte range. For example: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ HEAD /resource HTTP/1.1 Host: example.com Range: bytes=0-</artwork></figure>]]></artwork> <t> returns a response of the form: </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ HTTP/1.1 206 Partial Content Content-Range: bytes 0-1234567/*</artwork></figure>]]></artwork> <t> from the server indicating that (1) the complete representation length is unknown (via the "*" in place of the complete-length field) and (2)thatonly bytes 0-1234567 were accessible at the time the request was processed by the server. The client can infer from this response that bytes 0-1234567 of the representation can be requested andreturned in a timely fashion (the bytes are immediately available).transfer can be performed immediately. </t> </section> <sectionanchor="live-range-requests" title="Byte-Rangeanchor="live-range-requests"> <name>Byte-Range RequestsBeyondbeyond the Randomly Accessible ByteRange">Range</name> <t> Once a client has determined that a representation has an indeterminate length and established the byte range that can be accessed, it may want to perform a request with a start position within therandomly-accessiblerandomly accessible content range and an end position at anindefinite "live"indefinite/live point--- a point where the byte-range GET request is fulfilled on-demand as the content is aggregated. </t> <t> For example, for a large video asset, a client may wish to start a content transfer from the video "key" frame immediately before the point of aggregation and continue the content transfer indefinitely as content isaggregated -aggregated, in order to support low-latency startup of a live video stream. </t> <t> Unlike a byte-rangeRange request,request header field, abyte-range Content-Rangebyte-content-range response header field cannot be"open ended","open-ended", per <xrefx:sec="4.2" x:fmt="of" target="RFC7233"/>:target="RFC7233" sectionFormat="of" section="4.2"/>: </t><figure><artwork type="abnf"><sourcecode type="abnf"><![CDATA[ byte-content-range = bytes-unit SP ( byte-range-resp / unsatisfied-range ) byte-range-resp = byte-range "/" ( complete-length / "*" ) byte-range = first-byte-pos "-" last-byte-pos unsatisfied-range = "*/" complete-length complete-length = 1*DIGIT</artwork></figure>]]></sourcecode> <t> Specifically, last-byte-pos is required in byte-range.SoSo, in order to preserve interoperability with existing HTTP clients, servers, proxies, and caches, this document proposes a mechanism for a client to indicate support for handling an indeterminate-length byte-rangeresponse,response and a mechanism for a server to indicate if/when it's providing an indeterminate-length response. </t> <t> A client can indicate support for handling indeterminate-length byte-range responses by providing a very large value for the last-byte-pos in the byte-range request. For example, a client can perform a byte-range GET request of the form: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=1230000-999999999999</artwork></figure>]]></artwork> <t> where the last-byte-pos in theRequestrequest is much larger than the last-byte-pos returned in response to an open-ended byte-range HEAD request, as described above, and much larger than the expected maximum size of the representation. See <xref target="Security"/> for range value considerations. </t> <t> In response, a server may indicate that it is supplying a continuouslyaggregating ("live")aggregating/live response by supplying the client request's last-byte-pos in the Content-Range response header field. </t> <t> For example: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=1230000-999999999999</artwork></figure>]]></artwork> <t> returns </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ HTTP/1.1 206 Partial Content Content-Range: bytes 1230000-999999999999/*</artwork></figure>]]></artwork> <t> from the server to indicate that the response will start at byte 1230000 andcontinuescontinue indefinitely to include all aggregated content, as it becomes available. </t> <t> A server that doesn't support or supply a continuouslyaggregating ("live")aggregating/live response will supply the currently satisfiable byte range, as it would with an open-ended byte request. </t> <t> For example: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=1230000-999999999999</artwork></figure>]]></artwork> <t>will returnreturns </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ HTTP/1.1 206 Partial Content Content-Range: bytes 1230000-1234567/*</artwork></figure>]]></artwork> <t> from the server to indicate that the response will start at byte1230000 and1230000, end at byte12345671234567, andwillnot include any aggregated content. This is the response expected from a typical HTTP server--- one that doesn't support byte-range requests on aggregating content. </t> <t> A client that doesn't receive a response indicating it is continuously aggregating must use other means to access aggregated content(e.g.(e.g., periodic byte-range polling). </t> <t> A server that does return a continuouslyaggregating ("live")aggregating/live response should return data using chunked transfer coding and not provide a Content-Length header field. A 0-length chunk indicates the end of the transfer, per <xrefx:sec="4.1" x:fmt="of" target="RFC7230"/>.target="RFC7230" sectionFormat="of" section="4.1"/>. </t> </section> </section> <sectionanchor="other-applications" title="Otheranchor="other-applications"> <name>Other Applications of Random-Access AggregatingContent">Content</name> <sectionanchor="starting-at-live" title="Requestsanchor="starting-at-live"> <name>Requests Starting at theAggregation ("Live") Point">Aggregation/Live Point</name> <t> A client that wishes to only receivenewly-aggregatednewly aggregated portions of a resource (i.e., start at the"live" point),live point) can use a HEAD request to learn what range the server has currently available and initiate an indeterminate-length transfer. For example: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ HEAD /resource HTTP/1.1 Host: example.com Range: bytes=0-</artwork></figure>]]></artwork> <t>Withwith the Content-Range response header field indicating the range (or ranges) available. For example: </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ 206 Partial Content Content-Range: bytes 0-1234567/*</artwork></figure>]]></artwork> <t> The client can then issue a request for a range starting at the end value (using a very large value for the end of a range) and receive only new content. </t><figure><artwork<t> For example: </t> <artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=1234567-999999999999</artwork></figure>]]></artwork> <t> with a server returning a Content-Range response indicating that an indeterminate-length response body will beprovidedprovided: </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ 206 Partial Content Content-Range: bytes 1234567-999999999999/*</artwork></figure>]]></artwork> </section> <sectionanchor="shift-buffers" title="Shift Buffer Representations">anchor="shift-buffers"> <name>Shift-Buffer Representations</name> <t> Some representations lend themselves to front-end content removal in addition to aggregation. While still supporting random access, representations of this type have a portion at the beginning (the "0" end) of therandomly-accessiblerandomly accessible region thatbecomebecomes inaccessible over time. Examples of this kind of representation would be an audio-video time-shift buffer or a rolling log file. </t> <t> Forexampleexample, aRangerange request containing: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ HEAD /resource HTTP/1.1 Host: example.com Range: bytes=0-</artwork></figure>]]></artwork> <t> returns </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ 206 Partial Content Content-Range: bytes 1000000-1234567/*</artwork></figure>]]></artwork> <t> indicating that the first 1000000 bytes were not accessible at the time the HEAD request was processed. Subsequent HEAD requests could return: </t><figure><artwork type="example" x:indent-with=" "><artwork type="example"><![CDATA[ Content-Range: bytes 1000000-1234567/*</artwork></figure> <figure><artwork type="example" x:indent-with=" ">]]></artwork> <artwork type="example"><![CDATA[ Content-Range: bytes 1010000-1244567/*</artwork></figure> <figure><artwork type="example" x:indent-with=" ">]]></artwork> <artwork type="example"><![CDATA[ Content-Range: bytes 1020000-1254567/*</artwork></figure>]]></artwork> <t> Note though that the difference between the first-byte-pos and last-byte-pos need not be constant. </t> <t> The client could thenfollow-upfollow up with a GETRangerange requestcontainingcontaining: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=1020000-999999999999</artwork></figure>]]></artwork> <t> with the server returning </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ 206 Partial Content Content-Range: bytes 1020000-999999999999/*</artwork></figure>]]></artwork> <t> with the response body returning bytes 1020000-1254567 immediately andaggregated ("live")aggregated/live data being returned as the content is aggregated. </t> <t> A server that doesn't support or supply a continuouslyaggregating ("live")aggregating/live response will supply the currently satisfiable byte range, as it would with an open-ended byte request.</t> <t>For example: </t><figure><artwork<artwork type="message/http;msgtype="request"" x:indent-with=" ">msgtype="request""><![CDATA[ GET /resource HTTP/1.1 Host: example.com Range: bytes=0-999999999999</artwork></figure>]]></artwork> <t>will returnreturns </t><figure><artwork<artwork type="message/http;msgtype="response"" x:indent-with=" ">msgtype="response""><![CDATA[ HTTP/1.1 206 Partial Content Content-Range: bytes 1020000-1254567/*</artwork></figure>]]></artwork> <t> from the server to indicate that the response will start at byte 1020000, end at byte 1254567, andwillnot include any aggregated content. This is the response expected from a typical HTTP server--- one that doesn't support byte-range requests on aggregating content. </t> <t> Note that responses to GET requestsagainstperformed on shift-buffer representations using Range headers can be cached by intermediaries, since the Content-Range response header indicates which portion of the representation is being returned in the response body.HoweverHowever, GET requests without a Range header cannot be cached since the first byte of the response body can vary from request to request. To ensureRange-lessGET requestsagainstwithout Range headers on shift-buffer representations are not cached, servers hosting a shift-buffer representation should either not return a 200-level response(e.g. sending(e.g., send a 300-level redirect response with a URI that represents the current start of theshift-buffer)shift buffer) or indicate the response is non-cacheable. SeeHTTP Caching (<xref target="RFC7234"/>)<xref target="RFC7234"/> for details on HTTP cache control. </t> </section> </section><!-- Possibly a 'Contributors' section ... --><sectionanchor="RecommendedVLV" title="Recommendationsanchor="RecommendedVLV"> <name>Recommendations forVery Large Values">Byte-Range Request last-byte-pos Values</name> <t> While it would be ideal to define a singlenumerical Very Large Value,large last-byte-pos value for byte-range requests, there's no single value that would work for all applications and platforms.e.g.For example, JavaScript numbers cannot represent all integer values above 2^^53, so a JavaScript application may want to use 2^^53-1 fora Very Large Value.last-byte-pos. This value, however, would not be sufficient for all applications, such ascontinuously-streaminglong-duration high-bitrate streams. Sothe value2^^53-1 (9007199254740991) is recommended as aVery Large Valuelast-byte-pos unless an application has a good justification to use a smaller or larger value.e.g. If it'sFor example, if it is always known that the resource won't exceed a value smaller than the recommendedVery Large Valuelast-byte-pos for an application, a smaller value can be used.And ifIf it's likely that an application will utilize resources larger than the recommendedVery Large Value - suchlast-byte-pos (such as a continuously aggregating high-bitrate mediastream -stream), a larger value should be used. </t> <t> Note that, in accordance with the semantics defined above, servers that support random-access live content will need to return the last-byte-pos provided in theRangebyte-range request in some cases--- even if the last-byte-pos cannot be represented as a numerical value internally by the server. As is the case with anylive/continuously aggregatingcontinuously aggregating/live resource, the server should terminate the content transfer when the end of the resource is reached--- whether the end is due to termination of the content source or the content length exceeds the server's maximum representation length. </t> </section> <sectionanchor="IANA" title="IANA Considerations">anchor="IANA"> <name>IANA Considerations</name> <t>This document has noactions for IANA.</t>IANA actions.</t> </section> <sectionanchor="Security" title="Security Considerations">anchor="Security"> <name>Security Considerations</name> <t> As described above, servers need to be prepared to receive last-byte-pos values inRangerange requests that are numerically larger than the server implementation supports-and return these values in Content-Range response header fields. Servers should check the last-byte-pos value before converting and storing them into numeric form to ensure the value doesn't cause an overflow or index incorrect data. The simplest way to satisfy the live-range semantics defined in this document without potential overflow issues is to store the last-byte-pos as a string value and return it in the byte-range Content-Range response header's last-byte-pos field. </t> </section> </middle> <!-- *****BACK MATTER ***** --> <back><!-- References split to informative and normative --> <references title="Normative References"> &RFC2119; &RFC7230; &RFC7233; &RFC7234;<references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7230.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7233.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7234.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5234.xml"/> </references><references title="Informative References"> &RFC5234; &RFC8216;<references> <name>Informative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8216.xml"/> <referenceanchor="DASH" target="http://standards.iso.org/ittf/PubliclyAvailableStandards/c065274_ISO_IEC_23009-1_2014.zip">anchor="MPEG-DASH" target="https://www.iso.org/standard/75485.html"> <front> <title>Information technology -- Dynamic adaptive streaming over HTTP (DASH) -- Part 1: Media presentation description and segment formats </title><author><organization>ISO</organization></author> <date month="May" year="2014" /> </front><seriesInfo name="ISO/IEC"value="23009-1:2014" />value="23009-1"/> <author> <organization>ISO</organization> </author> <date month="August" year="2019"/> </front> </reference> </references> </references> <section anchor="Acknowledgements"title="Acknowledgements"numbered="false"> <name>Acknowledgements</name> <t> The authors would like to thank Mark Nottingham, Patrick McManus, Julian Reschke, Remy Lebeau, Rodger Combs, Thorsten Lohmar, Martin Thompson, Adrien de Croy,K. Morgan,K. Morgan, RoyT. Fielding,T. Fielding, and Jeremy Poulter. </t> </section> </back> </rfc>