draft-ietf-httpbis-rand-access-live-00.txt   draft-ietf-httpbis-rand-access-live-latest.txt 
HTTP Working Group C. Pratt HTTP Working Group C. Pratt
Internet-Draft CableLabs Internet-Draft CableLabs
Intended status: Experimental B. Stark Intended status: Experimental B. Stark
Expires: September 8, 2017 AT&T Expires: September 22, 2017 AT&T
D. Thakore D. Thakore
CableLabs CableLabs
March 7, 2017 March 21, 2017
HTTP Random Access and Live Content HTTP Random Access and Live Content
draft-ietf-httpbis-rand-access-live-00 draft-ietf-httpbis-rand-access-live
Abstract Abstract
To accommodate byte range requests for content that has data appended To accommodate byte range requests for content that has data appended
over time, this document defines semantics that allow a HTTP client over time, this document defines semantics that allow a HTTP client
and server to perform byte-range GET and HEAD requests that start at and server to perform byte-range GET and HEAD requests that start at
an arbitrary byte offset within the representation and ends at an an arbitrary byte offset within the representation and ends at an
indeterminate offset. indeterminate offset.
Editorial Note (To be removed by RFC Editor before publication) Editorial Note (To be removed by RFC Editor before publication)
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 8, 2017. This Internet-Draft will expire on September 22, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Performing Range requests on Random-Access Aggregating ("live") 2. Performing Range requests on Random-Access Aggregating ("live")
Content Content
There are two critical operations for accessing randomly accessing There are two critical operations for accessing randomly accessing
live/aggregating representations: live/aggregating representations:
Establishing the randomly accessible range of the representation, o Establishing the randomly accessible range of the representation,
and and
Performing range requests that continue beyond the randomly o Performing range requests that continue beyond the randomly
accessible range. accessible range.
2.1. Establishing the Randomly Accessible Byte Range 2.1. Establishing the Randomly Accessible Byte Range
Establishing if a representation is continuously aggregating ("live") Establishing if a representation is continuously aggregating ("live")
and determining the randomly accessible byte range can both be and determining the randomly accessible byte range can both be
determined using the existing definition for an open-ended byte-range determined using the existing definition for an open-ended byte-range
request. Specifically, [RFC7233] defines a byte-range request of the request. Specifically, [RFC7233] defines a byte-range request of the
form: form:
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For example, for a large video asset, a client may wish to start a For example, for a large video asset, a client may wish to start a
content transfer from the video "key" frame immediately before the content transfer from the video "key" frame immediately before the
point of aggregation and continue the content transfer indefinitely point of aggregation and continue the content transfer indefinitely
as content is aggregated - in order to support low-latency startup of as content is aggregated - in order to support low-latency startup of
a live video stream. a live video stream.
Unlike a byte-range Range request, a byte-range Content-Range Unlike a byte-range Range request, a byte-range Content-Range
response header cannot be "open ended", per [RFC7233]: response header cannot be "open ended", per [RFC7233]:
byte-content-range = bytes-unit SP ( byte-range-resp / byte-content-range = bytes-unit SP
unsatisfied-range ) ( byte-range-resp / unsatisfied-range )
byte-range-resp = byte-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos
unsatisfied-range = "*/" complete-length byte-range-resp = byte-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos
unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT complete-length = 1*DIGIT
last-byte-pos is required in byte-range. So in order to preserve last-byte-pos is required in byte-range. So in order to preserve
interoperability with existing HTTP clients, servers, proxies, and interoperability with existing HTTP clients, servers, proxies, and
caches, this document proposes a mechanism for a Client to indicate caches, this document proposes a mechanism for a Client to indicate
support for handling an indeterminate-length byte-range response, and support for handling an indeterminate-length byte-range response, and
a mechanism for a Server to indicate if/when it's providing a a mechanism for a Server to indicate if/when it's providing a
indeterminate-length response. indeterminate-length response.
A Client can indicate support for indeterminate-length byte-ranges by A Client can indicate support for indeterminate-length byte-ranges by
providing a Very Large Value for the last-byte-pos in the byte-range providing a Very Large Value for the last-byte-pos in the byte-range
 End of changes. 9 change blocks. 
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