1、Information technology Dynamic adaptive streaming over HTTP (DASH) Part 5: Server and network assisted DASH (SAND) Technologies de linformation Diffusion en flux adaptatif dynamique sur HTTP (DASH) Partie 5: DASH assist par serveur et rseau (SAND) INTERNATIONAL STANDARD ISO/IEC 23009-5 Reference num
2、ber ISO/IEC 23009-5:2017(E) First edition 2017-02 ISO/IEC 2017 ii ISO/IEC 2017 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO/IEC 2017, Published in Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or b
3、y any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 C
4、P 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.org ISO/IEC 23009-5:2017(E) ISO/IEC 23009-5:2017(E)Foreword v Introduction vi 1 Scope . 1 2 Normative references 1 3 T erms, definitions, s ymbols and abbr e viat ed t erms . 1 3.1 Terms an
5、d definitions . 1 3.2 Abbreviated terms . 2 3.3 Conventions . 2 4 Overview . 3 5 SAND reference architecture and interfaces . 3 6 SAND messages . 7 6.1 General . 7 6.2 Common Envelope for SAND messages . 7 6.3 Metrics messages 9 6.3.1 General 9 6.3.2 TCPConnections 9 6.3.3 HTTPRequestResponseTransac
6、tions . 9 6.3.4 RepresentationSwitchEvents 9 6.3.5 BufferLevel .10 6.3.6 PlayList 10 6.4 Status Messages 11 6.4.1 AnticipatedRequests 11 6.4.2 SharedResourceAllocation .11 6.4.3 AcceptedAlternatives 12 6.4.4 AbsoluteDeadline .13 6.4.5 MaxRTT .14 6.4.6 NextAlternatives 14 6.4.7 ClientCapabilities .15
7、 6.5 PER Messages 16 6.5.1 ResourceStatus .16 6.5.2 DaneResourceStatus 17 6.5.3 SharedResourceAssignment .19 6.5.4 MPDValidityEndTime . .19 6.5.5 Throughput 20 6.5.6 AvailabilityTimeOffset21 6.5.7 QoSInformation22 6.5.8 DeliveredAlternative23 6.5.9 DaneCapabilities .24 6.6 PED Messages .25 7 SAND me
8、ssage representation format 25 8 Transport Protocol to carry SAND messages .25 8.1 General 25 8.2 Protocol to carry metrics and status messages .25 8.2.1 General.25 8.2.2 Sending a message directly to Metrics server or DANE 26 8.2.3 Attaching a message to requests for media .26 8.3 Protocol to carry
9、 PER messages . .27 8.3.1 General.27 8.3.2 Assistance .28 8.3.3 Enforcement .28 8.3.4 Error case 28 ISO/IEC 2017 All rights reserved iii Contents Page ISO/IEC 23009-5:2017(E)9 Signalling of SAND communication channel .28 9.1 General 28 9.2 XML schema for sand: Channel element .29 10 Optional transpo
10、rt protocols to carry SAND messages .30 10.1 General 30 10.2 WebSocket protocol .30 10.2.1 General.30 10.2.2 Signalling via the MPD .31 10.2.3 WebSocket messages . 32 11 Reporting of metrics via SAND protocols .32 Annex A (normative) XML Schema for SAND messages .33 Annex B (normative) SharedResourc
11、eAllocation allocation strategies.41 Annex C (normative) MIME type registration for SAND message 45 Bibliogr aph y .47 iv ISO/IEC 2017 All rights reserved ISO/IEC 23009-5:2017(E) Foreword ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission)
12、 form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO and I
13、EC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC J
14、TC 1. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of document should be noted. This document was drafted in accordance with th
15、e editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives). Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details
16、of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents). Any trade name used in this document is information given for the convenience of users and does not constitute an en
17、dorsement. For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the follow
18、ing URL: w w w . i s o .org/ iso/ foreword .html. The committee responsible for this document is ISO/IEC JTC 1, Information technology, Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information. A list of all parts in the ISO/IEC 23009 series can be found on the ISO website
19、. ISO/IEC 2017 All rights reserved v ISO/IEC 23009-5:2017(E) Introduction In order to enhance the delivery of DASH content, this document introduces messages between DASH clients and network elements or between various network elements for the purpose of improving the efficiency of streaming session
20、s by providing information about real-time operational characteristics of networks, servers, proxies, caches, CDNs, as well as DASH clients performance and status.vi ISO/IEC 2017 All rights reserved Information technology Dynamic adaptive streaming over HTTP (DASH) Part 5: Server and network assiste
21、d DASH (SAND) 1 Scope This document defines the following: the functional SAND architecture which identifies the SAND network elements and the nature of SAND messages exchanged among them; the semantics of SAND messages exchanged between the network elements present in the SAND architecture; an enco
22、ding scheme for the SAND messages; the SAND message delivery protocol. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undat
23、ed references, the latest edition of the referenced document (including any amendments) applies. ISO 8601, Data elements and interchange formats Information interchange Representation of dates and times ISO/IEC 23009-1:2014, Information technology Dynamic adaptive streaming over HTTP (DASH) Part 1:
24、Media presentation description and segment formats IETF RFC 3986, Uniform Resource Identifier (URI): Generic Syntax IETF RFC 6455, The WebSocket Protocol IETF RFC 7233:2014, Hypertext Transfer Protocol (HTTP/1.1): Range Requests 3 Terms, definitions, abbreviated terms and conventions 3.1 Terms and d
25、efiniti ons For the purposes of this document, the terms and definitions given in ISO/IEC 23009-1 and the following apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at http:/ www .electropedia. org/ ISO Online bro
26、wsing platform: available at http:/ www. iso. org/ obp INTERNATIONAL ST ANDARD ISO/IEC 23009-5:2017(E) ISO/IEC 2017 All rights reserved 1 ISO/IEC 23009-5:2017(E) 3.1.1 DASH Aware Network Element DANE network element which has at least minimum intelligence about DASH; for instance, it may be aware th
27、at the delivered objects are DASH-formatted objects such as the MPD or DASH segments, and may prioritize, parse or even modify such objects 3.1.2 SAND messages messages exchanged between DASH clients, DASH aware Network Elements or Metrics Server in order to either enhance reception (PER) or deliver
28、y (PED) of DASH service, or to report status or metrics from the DASH client to DASH aware Network Elements or Metrics Server 3.2 A bbr e viat ed t erms DANE DASH aware network element DASH Dynamic Adaptive Streaming over HTTP DM DASH Metrics HTTP Hypertext Transfer Protocol MPD Media Presentation D
29、escription PED parameters enhancing delivery PER parameters enhancing reception RNE regular network element SAND server and network assisted DASH TLS transport layer security URI Uniform Resource Identifier URL Uniform Resource Locator URN Uniform Resource Name UTC Coordinated Universal Time UTF uni
30、code transformation format UUID universally unique identifier XML Extensible Mark-Up Language 3.3 Conventions The following naming conventions apply in this document. Elements in an XML document are identified by an upper-case first letter and in bold face as Element. To express that an element Elem
31、ent1 is contained in another element Element2, we may write Element2.Element1. If an elements name consists of two or more combined words, camel-casing is typically used, e.g. ImportantElement. Elements may be present either exactly once, or the minimum and maximum occurrence is defined by . . Attri
32、butes in an XML document are identified by a lower-case first letter, as well as they are preceded by a -sign, e.g. attribute. To point to a specific attribute attribute contained 2 ISO/IEC 2017 All rights reserved ISO/IEC 23009-5:2017(E) in an element Element, one may write Element attribute. If an
33、 attributes name consists of two or more combined words, camel-casing is typically used after the first word, e.g. veryImportantAttribute. Attributes may have assigned a status in the XML as mandatory (M), optional (O), optional with default value (OD) and conditionally mandatory (CM). Namespace qua
34、lification of elements and attributes is used as per XML standards, in the form of namespace: Element or namespace: attribut e. The fully qualified namespace will be provided in the schema fragment associated with the declaration. External specifications extending the namespace of DASH are expected
35、to document the element name in the semantic table with an extension namespace prefix. Variables defined in the context of this document are specifically highlighted with italics, e.g. InternalVariable. Structures that are defined as part of the hierarchical data model are identified by an upper-cas
36、e first letter, e.g. Period, Adaptation Set, Representation, Segment, etc. The term “this clause” refers to the entire clause included within the same first heading number. The term “this subclause” refers to all text contained in the subclause with the lowest hierarchy heading. 4 Overview In recent
37、 years, the Internet has become an important channel for the delivery of multimedia using HTTP as its primary protocol. In 2014, ISO/IEC published the second edition of MPEG Dynamic Adaptive Streaming over HTTP (DASH) as an International Standard that specified formats for the media presentation des
38、cription (MPD), as well as ISO-BMFF and MPEG-2 TS based segments. DASH does not define a system or protocol, but is considered as an enabler for efficient and high-quality delivery of multimedia content over the Internet. In order to enhance the delivery of DASH content, this document introduces mes
39、sages between DASH clients and network elements or between various network elements for the purpose of improving efficiency of streaming sessions by providing information about real-time operational characteristics of networks, servers, proxies, caches, CDNs as well as DASH clients performance and s
40、tatus. The Server and network assisted DASH (SAND) addresses the following: unidirectional/bidirectional, point-to-point/multipoint communication with and without session (management) between servers/CDNs and DASH clients; mechanisms for providing content-awareness and service-awareness towards the
41、underlying protocol stack including server and/or network assistance; various impacts on elements of the existing Internet infrastructure such as servers, proxies, caches and CDNs; QoS and QoE support for DASH-based services; scalability in general and specifically for logging interfaces; analytics
42、and monitoring of DASH-based services. 5 SAND reference architecture and interfaces The SAND reference architecture is based on the following four broad categories of elements. a) DASH clients. ISO/IEC 2017 All rights reserved 3 ISO/IEC 23009-5:2017(E) b) Regular network elements (RNE), which are DA
43、SH unaware and treat DASH delivery objects as any other object, but are present on the path between origin server and DASH clients, e.g. transparent caches. Note that such regular network elements are not in the scope of this document. c) DASH aware network elements (DANE), which have at least minim
44、um intelligence about DASH; for instance, they may be aware that the delivered objects are DASH-formatted objects such as the MPD or DASH segments, and may prioritize, parse or even modify such objects. More details on typical DANE functionalities are provided. d) Metrics server, which are DASH awar
45、e and are in charge of gathering metrics from DASH clients. Based on these elements, the SAND reference architecture is defined as shown in Figure 2. Within this architecture, the following four categories of messages, called SAND messages as shown in Figure 1, are exchanged: Parameters Enhancing De
46、livery (PED) messages that are exchanged between DANEs; Parameters Enhancing Reception (PER) messages that are sent from DANEs to DASH clients; status messages that are sent from DASH clients to DANEs; metrics messages that are sent from DASH clients to Metrics servers. PER messages -DANE PER messag
47、es -Figure 1 SAND messages4 ISO/IEC 2017 All rights reserved ISO/IEC 23009-5:2017(E) Figure 2 SAND reference architecture In this context, a media origin that serves DASH content may also receive status messages from the clients, send PED parameters to other DANEs, and is therefore also considered a
48、s a DANE element. Similarly, a third-party server that may receive SAND status messages from DASH clients or send SAND PER messages to the clients is considered as a DANE element. Note that the third-party server may not necessarily be on the media delivery path and it may not see the DASH segments.
49、 However, as it may understand the SAND status messages or produce SAND PER messages to DASH clients, e.g to improve delivery efficiency, it is nevertheless considered as a DANE element. A DASH client may send two types of messages: metric messages carrying metric information and status messages carrying operational information. The metrics and status messages have a similar structure; however, it is important to distinguish t
