FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“TRANSMISSION APPARATUS, TRANSMISSION
METHOD, AND NETWORK APPARATUS”
SONY CORPORATION, of 1-7-1, Konan, Minato-ku, Tokyo
108-0075, Japan
The following specification particularly describes the invention and the manner in
which it is to be performed.
2
DESCRIPTION
Title of Invention: TRANSMISSION DEVICE, TRANSMISSION METHOD,
AND NETWORK APPARATUS
Technical Field
[0001]
The present invention relates to a transmission device,
a transmission method, and a network apparatus and, in
particular, to a transmission device or the like in which a
delivery server transmits a meta file having information
regarding a predetermined number of video data streams of
given content deliverable via a network to a client terminal
via the network.
Background Art
[0002]
IPTV (Internet Protocol Television) delivery systems
that use a network, such as the Internet, have been proposed
(refer to, for example, PTL 1). In recent years,
standardization of Internet streaming, such as IPTV
(Internet Protocol Television), has been conducted. For
example, standardization of VoD (Video on Demand) streaming
using HTTP (Hypertext Transfer Protocol) streaming and a
technique applied to live streaming has been accomplished.
[0003]
3
In particular, DASH (Dynamic Adaptive Streaming over
HTTP) standardized by ISO/IEC/MPEG has attracted attention.
In DASH, a client terminal acquires streaming data on the
basis of a meta file called MPD (Media Presentation
Description) and the address (url) of chunked media data
written in the meta file and, subsequently, reproduces the
streaming data. In such a case, an example of the media
data is audio/video/subtitle data.
Citation List
Patent Literature
[0004]
PTL 1: Japanese Unexamined Patent Application
Publication No. 2011-193058
Summary of Invention
Technical Problem
[0005]
An object of the present technology is to improve the
efficiency of cache and delivery resource management of
video data streams in a network.
Solution to Problem
[0006]
A concept of the present technology resides in a
transmission device including a meta file generating unit
configured to generate a meta file including information
used by a client terminal to acquire a predetermined number
4
of video data streams of given content deliverable by a
delivery server via a network and a meta file transmitting
unit configured to upon receiving a transmission request
from the client terminal, transmitting the meta file to the
client terminal via the network. The meta file generating
unit sets, in the meta file, an index regarding a cache of
each of the video data streams in the network.
[0007]
In the present technology, the meta file generating
unit generates the meta file. The meta file includes
information used by a client terminal to acquire a
predetermined number of video data streams of given content
deliverable by a delivery server via a network. In addition,
upon receiving a transmission request from the client
terminal, the meta file transmitting unit transmits the meta
file to the client terminal via the network.
[0008]
The meta file generating unit sets, in the meta file,
the index regarding a cache of each of the video data
streams in the network. For example, the index may be the
index of a cache priority of a corresponding video data
stream in the network. Alternatively, the index may be the
index of the cache expiry time of a corresponding video data
stream in the network.
[0009]
5
Note that according to the present technology, for
example, the predetermined number of video data streams may
be multi-view video data streams that constitute a threedimensional
image. In addition, the meta file generating
unit may determine the index regarding a cache of each of
the multi-view video data streams on the basis of viewpoint
groups classified using estimated frequency of a request for
delivery of each of the multi-view video data streams.
[0010]
Furthermore, according to the present technology, for
example, the predetermined number of video data streams may
be MPEG-DASH based video data streams, the meta file may be
an MPD file, and the network may be a CDN. Still
furthermore, for example, the meta file generating unit may
set, in the MPD file, the index regarding a cache of each of
the video data streams in the network using a DescriptorType
element.
[0011]
As described above, according to the present technology,
the index regarding the cache of a video data stream in the
network is set in the meta file. Accordingly, in the
network, cache and delivery resource management of each of
the video data streams can be efficiently performed on the
basis of the index regarding the cache.
[0012]
6
Another concept of the present technology resides in a
network apparatus including a plurality of cache servers and
a predetermined number of cache management servers. Upon
receives a meta file including information used by a client
terminal to acquire a predetermined number of video data
streams of given content deliverable by a delivery server
via a network, the cache server transmits the meta file to
the cache management server. The cache management server
generates a cache control policy on the basis of an index
regarding a cache of each of the video data streams in the
network included in the meta file and distributes the cache
control policy to each of the cache servers.
[0013]
According to the present technology, the network
apparatus includes a plurality of cache servers and a
predetermined number of cache management servers. Upon
receives a meta file including information used by a client
terminal to acquire a predetermined number of video data
streams of given content deliverable by a delivery server
via a network, the cache server transmits the meta file to
the cache management server.
[0014]
The cache management server generates a cache control
policy on the basis of an index regarding a cache of each of
the video data streams in the network included in the meta
7
file and distributes the cache control policy to each of the
cache servers. The cache servers perform a caching process
on the video streams on the basis of the cache control
policy.
[0015]
Note that according to the present technology, for
example, the index regarding a cache may be an index of a
cache priority and/or an index of a cache expiry time. In
addition, according to the present technology, for example,
the predetermined number of video data streams may be MPEGDASH
based video data streams, the meta file may be an MPD
file, and the cache server may be a DASH cache server.
[0016]
As described above, according to the present technology,
a cache control policy is generated on the basis of the
index regarding a cache set in the meta file and is
distributed to each of the cache servers. Thereafter, the
cache server can perform a caching process of each of the
video streams on the basis of the cache control policy.
Accordingly, cache and delivery resource management of each
of the video data streams can be efficiently performed.
Advantageous Effects of Invention
[0017]
According to the present technology, the efficiency in
cache and delivery resource management of video data streams
8
in a network can be improved.
Brief Description of Drawings
[0018]
[Fig. 1] Fig. 1 is a block diagram of an example of the
configuration of a stream delivery system according to an
embodiment.
[Fig. 2] Fig. 2 illustrates a hierarchical structure of
an MPD file.
[Fig. 3] Fig. 3 illustrates an example of the
structures included in the MPD file and arranged on a time
axis.
[Fig. 4] Fig. 4 illustrates an example of a
relationship among the structures hierarchically disposed in
the MPD file.
[Fig. 5] Fig. 5 illustrates an example of a
relationship among Period, Representation, and Segment.
[Fig. 6] Fig. 6 illustrates an example of
classification of multi-view video data streams into
viewpoint groups.
[Fig. 7] Fig. 7 is an example of the flow of a process
performed until after a DASH segment and an MPD file have
been generated from content.
[Fig. 8] Fig. 8 illustrates an example of the
configuration of an IPTV client
[Fig. 9] Fig. 9 illustrates the whole of a widely used
9
DASH-based stream delivery system.
[Fig. 10] Fig. 10 illustrates the definition of the
DescriptorType element.
[Fig. 11] Fig. 11 illustrates the definition of the
ViewPoint element.
[Fig. 12] Fig. 12 illustrates an example of the
definition of a dictionary schema (a name space) as
"urn:aaaa:dash:vp".
[Fig. 13] Fig. 13 illustrates an example of an MPD file
in the case in which a ViewPoint element is defined and
viewpoint information is set in the information regarding
video data streams from the viewpoints.
[Fig. 14] Fig. 14 illustrates the definition of the
CacheParameter element.
[Fig. 15] Fig. 15 illustrates an example of the
definition of a cache parameter dictionary in which the
dictionary schema (the name space) is "urn:aaaa:dash:cp".
[Fig. 16] Fig. 16 illustrates an example of the MPD
file in the case in which a CacheParameter element is
defined and the index of a cache priority is set in the
information regarding a video data stream of each of the
viewpoints.
[Fig. 17] Fig. 17 illustrates the cache parameter
dictionary having an additionally set dictionary schema item
indicating whether the retention period for the cache server
10
in a CDN is long or short.
[Fig. 18] Fig. 18 illustrates an example of the MPD
file in the case in which the CacheParameter element is
defined and the index of a cache expiry time is set in the
information regarding each of the multi-view video data
streams in addition to the index of a cache priority.
[Fig. 19] Fig. 19 illustrates a cache control policy
that is generated on the basis of the index of a cache
priority and the index of a cache expiry time and that
includes lists each including a url regular expression and
corresponding to one of the classes of the index of a cache
priority and one of the classes of the index of a cache
expiry time.
[Fig. 20] Fig. 20 illustrates an example of a cache
control policy.
[Fig. 21] Fig. 21 illustrates an example of assignment
of a url to one of the DASH segments.
[Fig. 22] Fig. 22 illustrates an example of a cache
control process performed by a cache server having a cache
control policy distributed thereto.
[Fig. 23] Fig. 23 illustrates an example of the
operation performed by an IPTV client from the time the IPTV
client requests an MPD file to the time the IPTV client
reproduces the content (the DASH segment).
Description of Embodiments
11
[0019]
Embodiments of the invention are described below. Note
that description is made in the following order:
1. Embodiments
2. Modifications
[0020]
<1. Embodiments>
[Stream Delivery System]
Fig. 1 illustrates an example of the configuration of a
stream delivery system 10 according to an embodiment. The
stream delivery system 10 is an MPEG-DASH based stream
delivery system. The stream delivery system 10 has a
configuration in which a DASH segment streamer 11 and a DASH
MPD server 12 have N IPTV clients 13-1, 13-2, ..., and 13-N
connected thereto via a CDN (Content Delivery Network) 14.
[0021]
The DASH segment streamer 11 generates a stream segment
that complies with DASH (hereinafter referred to as a "DASH
segment") on the basis of media data (e.g., video data,
audio data, and subtitle data) of given content and
transmits the segment in response to an HTTP request from an
IPTV client. The DASH segment streamer 11 is configured as
a Web server.
[0022]
According to the present embodiment, the DASH segment
12
streamer 11 generates the DASH segments of five video data
streams based on video data obtained from, for example, the
following five viewpoints: the leftmost, the left middle,
the middle, the right middle, and the rightmost viewpoints.
In addition, the DASH segment streamer 11 generates the DASH
segments with a plurality of rates as the DASH segments of
the video streams from the plurality of viewpoints. Note
that the term "left middle viewpoint" refers to a viewpoint
from the middle point between the leftmost viewpoint and the
middle viewpoint. In addition, the term "right middle
viewpoint" refers to a viewpoint from the middle point
between the rightmost viewpoint and the middle viewpoint.
[0023]
In addition, in response to a request for the segment
of a given stream transmitted from the IPTV client 13 (13-1,
13-2, ..., 13-N) via the CDN 14, the DASH segment streamer
11 transmits the segment of the stream to the requester (the
IPTV client 13) via the CDN 14. In such a case, the IPTV
client 13 refers to the rate value set in an MPD (Media
Presentation Description) file. Thereafter, the IPTV client
13 selects one of the streams having a rate optimum for the
condition of the network environment in which the client is
located and sends the request.
[0024]
Furthermore, the IPTV client 13 requests the segment of
13
the video data stream observed from a viewpoint in
accordance with the performance of the IPTV client 13. For
example, when the IPTV client 13 has the lowest device grade
and, thus, processes image data observed from only two
viewpoints, that is, the leftmost viewpoint and rightmost
viewpoint, the IPTV client 13 requests the segments of the
video data streams observed from the two viewpoints. Still
furthermore, if, for example, the IPTV client 13 has the
medium device grade and, thus, processes image data observed
from the middle viewpoint in addition to the leftmost and
rightmost viewpoints, the IPTV client 13 requests the
segments of the video data streams observed from the three
viewpoints. Yet still furthermore, if, for example, the
IPTV client 13 has the highest device grade and, thus,
processes image data observed from the five viewpoints, that
is, the left middle viewpoint (the viewpoint observed from
the middle point between the leftmost viewpoint and the
middle viewpoint) and the right middle viewpoint (the
viewpoint observed from the middle point between the
rightmost viewpoint and the middle viewpoint) in addition to
the leftmost, rightmost, and middle viewpoints, the IPTV
client 13 requests the segments of the video data streams
observed from the five viewpoints.
[0025]
The DASH MPD server 12 is a server that generates an
14
MPD file used for acquiring a DASH segment generated by the
DASH segment streamer 11. The DASH MPD server 12 generates
the MPD file on the basis of content meta data received from
a content management server (not illustrated in Fig. 1) and
the address (url) of the segment generated by the DASH
segment streamer 11.
[0026]
In an MPD format, the property is set for each of the
streams, such as the video streams and the audio streams,
using an element called "Representation". For example, for
each of the video data streams having different rates, the
rate is set in the MPD file by changing the representation.
The IPTV client 13 can refer to the rate value and select
the optimum stream in accordance with the conditions of the
network environment in which the IPTV client 13 is located,
as described above.
[0027]
As illustrated in Fig. 2, the MPD file has a
hierarchical structure. The MPD file, which is in XML
format, describes information regarding, for example, the
encoding type, coding rate, image size, and language of a
video stored in the DASH segment streamer 11. The MPD file
hierarchically includes structures, such as Period,
AdaptationSet, Representation, SegmentInfo, Initialization
Segment, and Media Segment.
15
[0028]
The Period structure includes information regarding a
program (a set of, for example, synchronized video and audio
data). In addition, the AdaptationSet structure included in
the Period structure groups the selection ranges
(Representation groups) of the stream. In addition, the
Representation structure included in the AdaptationSet
structure includes information regarding the coding rates of
video and audio and the audio size of the video.
[0029]
In addition, the SegmentInfo structure included in the
Representation structure includes information regarding the
segments of the video and audio. Furthermore, the
Initialization Segment structure included in the SegmentInfo
structure includes initialization information, such as a
data encoding technique. Still furthermore, the Media
Segment structure included in the SegmentInfo structure
includes information, such as the address from which a video
or audio segment is retrieved.
[0030]
Fig. 3 illustrates an example of the structures that
are included in the above-described MPD file and that are
arranged on a time axis. In this example, the MPD file
includes two Periods, and each of the Periods includes two
segments. In addition, in this example, each Period
16
includes two AdaptationSets, and each AdaptationSet includes
two Representations associated with streams having the same
information except for stream properties.
[0031]
Fig. 4 illustrates an example of a relationship among
the structures hierarchically disposed in the abovedescribed
MPD file. As illustrated in Fig. 4(a), Media
Representation, which represents the entire MPD file,
includes a plurality of Periods divided into time intervals.
For example, a first Period starts at 0 second, and the next
Period starts at 100 seconds and so on.
[0032]
As illustrated in Fig. 4(b), Period includes a
plurality of Representations. The plurality of
Representations are grouped by the above-described
AdaptationSet. A Representation group associated with video
data streams having the same information except for
different stream properties (e.g., the rate) is present.
According to the present embodiment, a Representation group
for the video data streams observed from different
viewpoints is present.
[0033]
As illustrated in Fig. 4(c), Representation includes
SegmentInfo. As illustrated in Fig. 4(d), SegmentInfo
includes Initialization Segment and a plurality of Media
17
Segments each describing information regarding Segment
generated by further dividing the Period. Media Segment
includes, for example, information such as the address (url)
used to actually retrieve the segment data of the video and
audio.
[0034]
Note that stream switching is freely performed among a
plurality of Representations grouped in AdaptationSet. In
this manner, a stream having an optimum rate for the
conditions of the network environment in which the IPTV
client is located can be selected and, thus, uninterrupted
video delivery can be provided.
[0035]
Fig. 5 illustrates an example of a relationship among
Period, Representation, and Segment. In this example, an
MPD file includes two Periods. Each of the Periods includes
two Segments. In addition, in this example, each of the
Periods includes a plurality of Representations associated
with the same media content.
[0036]
As described above, an MPD file includes information
regarding, for example, the encoding type, coding rate,
image size, and language of a video stored in the DASH
segment streamer 11. According to the present embodiment,
the DASH MPD server 12 sets, in the information regarding
18
each of the video data streams, an index regarding a cache
of the DASH segment of the video data stream in the CDN 14.
[0037]
The DASH MPD server 12 classifies the above-described
plurality of viewpoints into a predetermined number of
viewpoint groups on the basis of estimation of the frequency
of delivery requests of the video data stream. Thereafter,
the DASH MPD server 12 determines the index regarding a
cache of the video data stream of each of the viewpoints.
For example, as illustrated in Fig. 6, the DASH MPD server
12 classifies the five viewpoints, that is, the leftmost
viewpoint, the left middle viewpoint, the middle viewpoint,
the right middle viewpoint, and the rightmost viewpoint into
three viewpoint groups, that is, a viewpoint group 1, a
viewpoint group 2, and a viewpoint group 3.
[0038]
The viewpoint group 1 includes two viewpoints, that is,
the leftmost viewpoint and the rightmost viewpoint for which
the frequency of a delivery request is estimated to be the
highest. In addition, the viewpoint group 2 includes three
viewpoints, that is, the leftmost viewpoint, the middle
viewpoint, and the rightmost viewpoint for which the
frequency of a delivery request is estimated to be the
second highest. Furthermore, the viewpoint group 3 includes
five viewpoints, that is, the leftmost viewpoint, the left
19
middle viewpoint, the middle viewpoint, the right middle
viewpoint, and the rightmost viewpoint for which the
frequency of a delivery request is estimated to be the
lowest.
[0039]
Note that the index regarding a cache indicates, for
example, a cache priority and/or a cache expiry time of each
of the multi-view video data streams in the CDN 14. For
example, in terms of the cache priority, the priorities of
the video data streams captured from the leftmost viewpoint
and the rightmost viewpoint included in the viewpoint group
1 are set to "high". The priority of the video data stream
captured from the middle viewpoint, which is added to the
viewpoint group 2, is set to "middle". The priorities of
the video data streams captured from the left middle
viewpoint and the right middle viewpoint, which are added to
the viewpoint group 3, are set to "low".
[0040]
In addition, for example, in terms of the cache expiry
time, the time for the video data streams obtained from the
leftmost and the rightmost viewpoints included in the
viewpoint group 1 is set to "long", and the time for the
video data streams obtained from the left middle and the
right middle viewpoints included in only the viewpoint group
3 is set to "short". Note that the MPD file is described in
20
more detail below.
[0041]
Fig. 7 is an example of the flow of a process performed
until after the DASH segment and the DASH MPD file have been
generated from content. Content is transmitted from a
content management server 15 to the DASH segment streamer 11.
The DASH segment streamer 11 generates the DASH segment of
each of the data streams on the basis of, for example, video
data and audio data that constitute the content.
[0042]
In addition, the DASH segment streamer 11 transmits, to
the DASH MPD server 12, the address (url) information of the
generated DASH segment of each of the data streams. The
content management server 15 transmits the meta data of the
content to the DASH MPD server 12. The DASH MPD server 12
generates an MPD file on the basis of the address
information of the DASH segment of each of the data streams
and the meta data of the content.
[0043]
Fig. 8 illustrates an example of the configuration of
the IPTV client 13 (13-1 to 13-N). The IPTV client 13
includes a streaming data control unit 131, an HTTP access
unit 132, and a video reproducing unit 133. The streaming
data control unit 131 acquires an MPD file from the DASH MPD
server 12 and analyzes the information in the MPD file.
21
[0044]
The HTTP access unit 132 requests the segments of the
video and audio used for video reproduction to the DASH
segment streamer 11. At that time, the HTTP access unit 132
additionally takes into account the screen size of the IPTV
client 13 and the conditions of the transmission path and
selects a stream having an image size and a coding rate
optimum for the screen size of the IPTV client 13 and the
conditions of the transmission path. For example, in the
initial stage, the HTTP access unit 132 requests the segment
of a stream having a low coding rate. Thereafter, if the
communication condition is excellent, the HTTP access unit
132 requests the segment of a stream having a high coding
rate.
[0045]
The HTTP access unit 132 transmits the received
segments of the video and audio to the video reproducing
unit 133. The video reproducing unit 133 performs a
decoding process on each of the segments transmitted from
the HTTP access unit 132 and obtains one video content.
Thus, the video reproducing unit 133 reproduces the video
and audio. Note that the processing is performed by each of
the units of the IPTV client 13 through, for example,
software.
[0046]
22
According to the present embodiment, three classes of
the performance of reproduction is provided for the IPTV
client 13. For example, if the device grade is the lowest
and, thus, image data of only two viewpoints, that is, the
leftmost viewpoint and the rightmost viewpoint are processed,
the segments of the video data streams from the two
viewpoints are requested. Thus, a three-dimensional image
based the video data of the two viewpoints is reproduced.
[0047]
In addition, when, for example, image data of three
viewpoints, that is, the leftmost viewpoint, the middle
viewpoint, and the rightmost viewpoint are processed by an
IPTV client 13 having a medium device grade, the segments of
the video data streams of the three viewpoints are requested.
Thus, a three-dimensional image based on the video data of
the three viewpoints is reproduced. Furthermore, when, for
example, image data of five viewpoints, that is, the
leftmost viewpoint, the left middle viewpoint, the middle
viewpoint, the right middle viewpoint, and the rightmost
viewpoint are processed by an IPTV client 13 having the
highest device grade, the segments of the video data streams
of the five viewpoints are requested. Thus, a threedimensional
image based on the video data of the five
viewpoints is reproduced.
[0048]
23
Fig. 9 illustrates the whole of a widely used DASHbased
stream delivery system. All of DASH MPD files and
DASH segments are delivered via the CDN (Content Delivery
Network) 14. The CDN 14 has a configuration in which a
plurality of cache servers (DASH cache servers) are networkarranged.
[0049]
Each of the cache servers receives an HTTP request for
acquiring the MPD file from the IPTV client 13. If the MPD
file is contained in a local MPD cache, the cache server
returns the MPD file to the IPTV client 13 in the form of an
HTTP response. However, if the MPD file is not contained in
the local MPD cache, the cache server forwards the request
to the DASH MPD server 12 or a higher-layer cache server.
Thereafter, upon receiving an HTTP response including the
MPD file, the cache server forwards the HTTP response to the
IPTV client 13. At the same time, the cache server performs
a cache process.
[0050]
In addition, the cache server receives an HTTP request
for acquiring a DASH segment from the IPTV client 13. If
the DASH segment is contained in a local segment cache, the
cache server returns the DASH segment to the IPTV client 13
in the form of an HTTP response. However, if the DASH
segment is not contained in the local segment cache, the
24
cache server forwards the request to the DASH segment
streamer 11 or a higher-layer cache server. Thereafter,
upon receiving an HTTP response including the DASH segment,
the cache server forwards the HTTP response to the IPTV
client 13. At the same time, the cache server performs a
cache process.
[0051]
In the CDN 14, the DASH segment to be delivered to the
IPTV client 13-1 that transmitted an HTTP request first is
temporarily cached by the cache server located in the path.
If an HTTP request is subsequently transmitted from the IPTV
client 13-2, the cached DASH segment is delivered.
Accordingly, the delivery efficiency of HTTP streaming to a
plurality of IPTV clients can be improved.
[0052]
According to the present embodiment, the CDN 14
includes a predetermined number of cache management servers
in addition to the plurality of cache servers. Each of the
cache management servers generates a cache control policy on
the basis of the index regarding a cache of the DASH segment
of each of the video data streams included in the MPD file.
Thereafter, the cache management server distributes the
cache control policy to the cache servers. The cache
servers performs a caching process of the DASH segment of
each of the video data streams.
25
[0053]
[Insertion of Variety of Information into MPD File]
[Insertion of Viewpoint Information]
According to the present embodiment, the MPD file
includes information regarding the multi-view video data
streams that constitute a three-dimensional image, for
example, video data streams from five viewpoints, that is,
the leftmost viewpoint, the left middle viewpoint, the
middle viewpoint, the right middle viewpoint, and the
rightmost viewpoint. The DASH MPD server sets the viewpoint
information in the MPD file using a DescriptorType element.
[0054]
In DASH, by using an element called "DescriptorType", a
new dictionary and a new vocabulary reference can be added.
The dictionary and the vocabulary reference is specified by
a schema URI (or a set of a schema URI and the value defined
in the dictionary schema).
[0055]
Fig. 10 illustrates the definition of the
DescriptorType element. The properties of schema URI
(@schemeIdUri) and a value (@value) can be set under
DescriptorType. The property of the schema URI indicates
URN or URL specifying the dictionary schema (the name space).
The property of the value indicates a value defined in the
dictionary schema specified by the schema URI.
26
[0056]
As described above, according to the present embodiment,
a ViewPoint element serving as an element indicating a
"viewpoint" is defined using the DescriptorType element.
Fig. 11 illustrates the definition of the ViewPoint element.
The property of Schema URI under the viewpoint type
indicates a URN or URL specifying the dictionary schema (the
name space) that defines the viewpoint. The value property
under the viewpoint type indicates the value defined in the
dictionary schema specified by the schema URI.
[0057]
Here, for example, the viewpoint dictionary is defined
using the dictionary schema (the name space)
"urn:aaaa:dash:vp" as illustrated in Fig. 12. In this
viewpoint dictionary, the URN "urn:aaaa:dash:vp:stereoright"
corresponds to the entry of the dictionary
"rightmost". The URN "urn:aaaa:dash:vp:stereo-left"
corresponds to the entry of the dictionary "lefttmost". The
URN "urn:aaaa:dash:vp:center" corresponds to the entry of
the dictionary "middle". The URN "urn:aaaa:dash:vp:stereoright-
center" corresponds to the entry of the dictionary
"right middle". The URN "urn:aaaa:dash:vp:stereo-leftcenter"
corresponds to the entry of the dictionary "left
middle".
[0058]
27
Fig. 13 illustrates an example of an MPD file in the
case in which a ViewPoint element is defined and the
viewpoint information is set in the information regarding
the video data streams of the viewpoints. In such a case,
the ViewPoint element is placed in a ContentComponent
element.
[0059]
As a ViewPoint element, @schemeIdUri =
"urn:aaaa:dash:vp:stereo-left" is set in ContentComponent
inside the AdaptationSet that groups the Representations
including the information corresponding to the video data
stream observed from the leftmost viewpoint. This
description implies that the information in this
AdaptationSet corresponds to the video data stream observed
from the leftmost viewpoint. Note that although the
following description is not intended to be all-inclusive, a
ViewPoint element is similarly placed in ContentComponent
inside the AdaptationSet including the information regarding
another viewpoint so as to indicate the viewpoint.
[0060]
[Insertion of Cache Priority Index]
The case in which the reproduction performance of the
IPTV client 13 is classified into three classes, as
described above, is discussed below. In general, a device
having the lowest processing power (a class-1 device), which
28
is the most widely used, generates an image on the basis of
video data streams from two viewpoints, that is, the
leftmost viewpoint and the rightmost viewpoint.
[0061]
In addition, a device having medium processing power (a
class-2 device) generates an image on the basis of video
data streams from three viewpoints, that is, the leftmost
viewpoint, the middle viewpoint, and the rightmost viewpoint.
Furthermore, a device having the highest processing power (a
class-3 device), which is the least widely used, generates
an image on the basis of video data streams from five
viewpoints, that is, the leftmost viewpoint, the left middle
viewpoint, the middle viewpoint, the right middle viewpoint,
and the rightmost viewpoint. In this manner, the number of
types of stream to be processed increases with increasing
processing power of a device.
[0062]
In general, widely used CDNs have a capability of
actively pre-caching a DASH segment that is likely to be
accessed in advance. In such a case, if it is assumed that
all of the IPTV clients 13 are class-3 devices and, thus,
the DASH segments of five viewpoints are pre-cached for all
of content, the following issue arises. That is, overload
may occur in a replication process into the cache server, or
an insufficient resource problem, that is, insufficient
29
storage capacity may occur. Thus, it may be difficult to
deliver content at a cost appropriate to the service
requirement.
[0063]
To solve such a problem, it is desirable that the CDN
expansion priority of a DASH segment be ranked in accordance
with the type of viewpoint group. For example, the CDN
expansion priorities of video data streams that are observed
from the leftmost viewpoint and the rightmost viewpoint and
that are processed by devices that are likely to be the most
widely used (class-1 devices) are increased to the highest
level. The CDN expansion priorities of video data streams
processed by class-2 devices are increased to the second
highest level. The CDN expansion priorities of video data
streams processed by class-3 devices are increased to the
third highest level.
[0064]
By setting the CDN expansion priorities in the MPD file,
the processing described below is available and, thus, the
cost performance of the resource utilization efficiency of a
CDN can be increased without decreasing the service
provision efficiency of the CDN for the end users (e.g., the
speed until after streaming has started).
[0065]
For example, by setting the CDN expansion priority in
30
the MPD file, a server that manages the CDN cache policy can
analyze the MPD of content to be delivered in advance and
sequentially assign a replication capacity to a stream that
is likely to be accessed by a large number of clients first.
[0066]
In addition, for example, by setting the CDN expansion
priority in the MPD file, the replication process can be
prioritized (e.g., the assignment priority of a CPU resource
can be controlled), and the replication storage area can be
prioritized in accordance with the access performance
(storage staging priority control can be performed for, for
example, an on memory, an SSD (a flash memory drive), and an
HD).
[0067]
According to the present embodiment, as the index
regarding the cache of the DASH segment, the DASH MPD server
12 sets the index of a cache priority (the CDN expansion
priority) in the information regarding each of the multiview
video data streams using the DescriptorType element.
[0068]
According to the present embodiment, by using the
above-described DescriptorType element, the "CDN expansion
priority", that is, CacheParameter element is defined as an
element indicating the cache priority. Fig. 14 illustrates
the definition of the CacheParameter element. The schema
31
URI property under the cache parameter type indicates a URN
or URI specifying the dictionary schema (the name space)
defining the cache parameter. The value property under the
cache parameter type indicates the value defined in the
dictionary schema specified by the schema URI.
[0069]
Herein, for example, a cache parameter dictionary is
defined by setting the dictionary schema (the name space) to
"urn:aaaa:dash:cp", as illustrated in Fig. 15. In this
cache parameter dictionary, the URN "urn:aaaa:dash:cp:high"
corresponds to the entry of the dictionary "high". The URN
"urn:aaaa:dash:cp:middle" corresponds to the entry of the
dictionary "middle". The URN "urn:aaaa:dash:cp:low"
corresponds to the entry of the dictionary "low".
[0070]
Fig. 16 illustrates an example of the MPD file in the
case in which a CacheParameter element is defined and the
index of the cache priority is set in the information
regarding each of the multi-view video data streams. In
such a case, the CacheParameter element is placed in the
Representation element.
[0071]
As a CasheParameter element, @schemeIdUri =
"urn:aaaa:dash:cp:high" is set in each of the
Representations including the information corresponding to
32
the video data stream from the leftmost viewpoint. This
implies that the cache priority (the CDN expansion priority)
of the video data stream from the leftmost viewpoint is
"high".
[0072]
Note that although detailed the following description
is not intended to be all-inclusive, a CasheParameter
element is similarly placed in each of the Representations
including the information regarding the other viewpoints and,
thus, the cache priorities are indicated. That is, it is
indicated that the cache priority of each of the video data
streams from the left middle viewpoint and the right middle
viewpoint is "low". In addition, it is indicated that the
cache priority of the video data stream from the middle
viewpoint is "middle". Furthermore, it is indicated that
the cache priority of the video data stream from the
rightmost viewpoint is "high".
[0073]
[Insertion of Cache Expiry Time Index]
According to the present embodiment, the DASH MPD
server 12 further sets the index of a cache expiry time in
the MPD file using the above-described CacheParameter
element. That is, as illustrated in Fig. 17, the DASH MPD
server 12 additionally defines, as an example of a cache
parameter, the entry of the dictionary schema indicating
33
whether the expiry time of the cache server in the CDN is
long or short. In this cache parameter dictionary
(addition), the entry of URN of "urn:aaaa:dash:cp:long"
corresponds to the entry of the dictionary "long". The
entry of URN of "urn:aaaa:dash:cp:short" corresponds to the
entry of the dictionary "short".
[0074]
Fig. 18 illustrates an example of the MPD file in the
case in which the CacheParameter element is defined and the
index of the cache expiry time is set in the information
regarding each of the multi-view video data streams in
addition to the index of the cache priority. In such a case,
the CacheParameter element is placed in the Representation
element.
[0075]
As a CasheParameter element, @schemeIdUri =
"urn:aaaa:dash:cp:long" is set in each of the
Representations having the information corresponding to the
video data stream from the leftmost viewpoint. This implies
that the cache expiry time of the video data stream from the
leftmost viewpoint is "long".
[0076]
Note that although the following description is not
intended to be all-inclusive, a CasheParameter element is
similarly placed in each of the Representations including
34
the information regarding the other viewpoints and, thus,
the cache expiry times are indicated. That is, it is
indicated that the cache expiry times of each of the video
data streams from the left middle viewpoint and the right
middle viewpoint is "short". In addition, the cache expiry
time of the video data stream from the middle viewpoint is
not specified. In this case, the cache server can select
any cache processing policy.
[0077]
[Cache Control in CDN]
The CDN 14 has a predetermined number of cache
management servers disposed therein in addition to a
plurality of cache servers (refer to Fig. 9). The cache
management server generates a cache control policy on the
basis of the above-described index of a cache set in the MPD
file and distributes the generated cache control policy to
the cache servers in the CDN 14. Each of the cache servers
performs a caching process (an acquisition process and a
replication process) on the DASH segment on the basis of the
distributed cache control policy.
[0078]
For example, if a request for a first MPD file is sent
from an IPTV client (a DASH client) 13, a first cache server
(an edge server) in the CDN 14 that serves as mediator of
the MPD file acquires the requested MPD file from the DASH
35
MPD server 12. At that time, the cache server transmits the
MPD file to the cache management server. The cache
management server analyzes the received MPD file and
generates a cache control policy on the basis of the indices
regarding cache. Thereafter, the cache management server
sends the cache control policy to the cache servers in the
CDN 14.
[0079]
In addition, for example, the cache management server
actively acquires the MPD file by using, for example, a
crawler before the IPTV client 13 sends a first MPD request.
Thereafter, the cache management server analyzes the
acquired MPD file and generates a cache control policy on
the basis of the index regarding cache. Thereafter, the
cache management server sends the cache control policy to
the cache servers in the CDN 14.
[0080]
The cache control policy contains a list of a class
indicated by the index regarding cache with a corresponding
url or a corresponding url regular expression. For example,
if the MPD file includes the above-described index of the
cache priority and the index of the cache expiry time as the
indices regarding cache, the cache control policy contains
each of the classes indicated by the indices with a
corresponding url (or a list including the regular
36
expression), as illustrated in Fig. 19.
[0081]
Fig. 20 illustrates an example of a cache control
policy. In this example, the cache control policy is used
when the MPD file includes the index of the cache priority
and the index of the cache expiry time as illustrated above
in Fig. 18 and if an url is assigned to each of the DASH
segments as illustrated in Fig. 21.
[0082]
In this cache control policy, the urls assigned to the
DASH segments of the video data streams from the leftmost
viewpoint and the rightmost viewpoint are included in a
section in which the priority is "high" and the expiry time
is "long". In addition, in the cache control policy, the
urls assigned to the DASH segments of the video data streams
from the middle viewpoint are included in a section in which
the priority is "middle" and the expiry time is "not
specified (N/A)". Furthermore, in the cache control policy,
the urls assigned to the DASH segments of the video data
streams from the left middle viewpoint and the right middle
viewpoint are included in a section in which the priority is
"low" and the expiry time is "short".
[0083]
An example of a caching process performed by the cache
server that has received a distributed cache control policy
37
is described next with reference to Fig. 22. (a) The cache
management server distributes a cache control policy to the
cache servers. (b) If the IPTV client 13 sends an
acquisition request for the DASH segment at "urlxx", (c) The
cache server that has received the acquisition request
determines whether the local cache contains the DASH segment
at "urlxx".
[0084]
(d) If the local cache contains the DASH segment at
"urlxx", the cache server returns the DASH segment to the
IPTV client 13. (e) However, if the local cache does not
contain the DASH segment at "urlxx", the cache server sends
the acquisition request to the DASH segment streamer 11.
(f) The DASH segment streamer 11 returns the DASH segment to
the IPTV client 13 via the cache server. (g) The IPTV
client that has received the DASH segment at "urlxx" via the
cache server reproduces the video on the basis of the DASH
segment.
[0085]
(h) After returning the DASH segment to the IPTV client
13, the cache server performs a caching process of the DASH
segment on the basis of the caching control policy. That is,
in step ST1, the cache server determines whether the
priority of "urlxx" is "high". If the priority of "urlxx"
is "high", the cache server determines in step ST2 whether
38
the expiry time of "urlxx" is "long". If the expiry time of
"urlxx" is "long", the cache server starts storing the DASH
segment of "urlxx" in a local cache (an on memory) for a
long-term period in step ST3.
[0086]
However, if, in step ST1, the priority of "urlxx" is
not "high" or if, in step ST2, the expiry time of "urlxx" is
not "long", the cache server determines in step ST4 whether
the priority of "urlxx" is "middle". If the priority of
"urlxx" is "middle", the cache server determines in step ST5
whether the expiry time of "urlxx" is "not specified (N/A)".
If the expiry time of "urlxx" is "not specified (N/A)", the
cache server starts storing the DASH segment of "urlxx" in a
local cache (an SSD) for a medium-term period in step ST6.
[0087]
However, if, in step ST4, the priority of "urlxx" is
not "middle" or if, in step ST5, the expiry time of "urlxx"
is not "not specified (N/A)", the cache server determines in
step ST7 whether the priority of "urlxx" is "low". If the
priority of "urlxx" is "low", the cache server determines in
step ST8 whether the expiry time of "urlxx" is "short". If
the expiry time of "urlxx" is "short", the cache server
starts storing the DASH segment of "urlxx" in a local cache
(an HD) for a short-term period in step ST9.
[0088]
39
However, if, in step ST7, the priority of "urlxx" is
not "low" or if, in step ST8, the expiry time of "urlxx" is
not "short", the cache server discards the DASH segment at
"urlxx" in step ST10.
[0089]
[Operation Performed by Stream Delivery System]
An example of the operation performed from the time an
IPTV client 13 request an MPD file to the time the IPTV
client reproduces the content (the DASH segment) is
described next with reference to Fig. 23. Note that in the
illustrated example, for simplicity, the CDN includes only
two cache servers 16 and 17 and a cache management server 18.
[0090]
(1) An IPTV client 13-1 sends an acquisition request
for the MPD file associated with given content to the DASH
MPD server 12 via the cache server 16 in the CDN. (2) The
DASH MPD server 12 transmits the MPD file to the cache
server 16 in the CDN in response to the acquisition request.
As described above, the MPD file includes the index of a
cache priority and the index of a cache expiry time.
[0091]
(3) The cache server 16 transmits the MPD file to the
IPTV client 13-1. (4) In addition, the cache server 16
performs a caching process so as to store the MPD file in an
MPD cache and transmits the MPD file to the cache management
40
server 18. (5) The cache management server 18 analyzes the
MPD file, generates a caching control policy, and sends the
caching control policy to the cache servers 16 and 17.
[0092]
(6) Upon receiving the MPD file, the IPTV client 13-1
transmits the DASH segment (the stream segment) used for
reproducing the given content to the DASH segment streamer
11 via the cache servers 16 and 17 in the CDN on the basis
of the MPD file. In such a case, the IPTV client 13-1 can
select an optimum rate and an optimum viewpoint group in
accordance with the device power of the IPTV client 13-1 and
the conditions of the network environment in which the IPTV
client 13-1 is located.
[0093]
(7) In response to the acquisition request, the DASH
segment streamer 11 transmits the DASH segment to the cache
server 17. (8) The cache server 17 transmits the DASH
segment to the cache server 16. (9) In addition, the cache
server 17 performs a caching process so as to store the DASH
segment in a local cache on the basis of the caching control
policy.
[0094]
(10) Upon receiving the DASH segment from the cache
server 17, the cache server 16 transmits the DASH segment to
the IPTV client 13-1. (11) In addition, the cache server 16
41
performs a caching process so as to store the DASH segment
in a local cache on the basis of the caching control policy.
(12) Upon receiving the DASH segment, the IPTV client 13-1
performs a decoding process on the DASH segment and
reproduces the video and audio of the given content.
[0095]
(13) The cache server 17 transmits a voluntary
acquisition request for a DASH segment that has a high
priority and that differs from the DASH segment stored in
the local cache to the DASH segment streamer 11 on the basis
of the caching control policy. (14) In response to the
acquisition request, the DASH segment streamer 11 transmits
the DASH segment to the cache server 17. (15) The cache
server 17 performs a caching process so as to store the DASH
segment in a local cache.
[0096]
(16) The IPTV client 13-2 sends, to the cache server 16
in the CDN, an acquisition request for the MPD file that is
the same as the acquisition request requested by the IPTV
client 13-1 in the above-described manner. (17) Since the
cache server 16 stores the MPD file in an MPD cache, the
cache server 16 transmits the MPD file to the IPTV client
13-2.
[0097]
(18) Upon receiving the MPD file, the IPTV client 13-2
42
transmits, to the cache server 16 in the CDN, an acquisition
request for the DASH segment (the stream segment) that is
the same as the DASH segment requested by the IPTV client
13-1 in the above-described manner on the basis of the
received MPD file. (19) Since the cache server 16 stores
the DASH segment in the local cache, the cache server 16
transmits the DASH segment to the IPTV client 13-2. (20)
Upon receiving the DASH segment, the IPTV client 13-2
performs a decoding process on the DASH segment and
reproduces the video and audio of the given content.
[0098]
(21) Subsequently, the IPTV client 13-2 sends an
acquisition request for another DASH segment to the cache
server 16. (22) Since the cache server 16 does not store
the DASH segment in the local cache, the cache server 16
forwards the acquisition request for the DASH segment to the
cache server 17.
[0099]
(23) Since the cache server 17 stores the DASH segment
in the local cache, the cache server 17 transmits the DASH
segment to the cache server 16. (24) Subsequently, the
cache server 16 transmits the DASH segment to the IPTV
client 13-2. (25) Upon receiving the DASH segment, the IPTV
client 13-2 performs a decoding process on the DASH segment
and reproduces the video and audio of the given content.
43
[0100]
As described above, in the stream delivery system 10
illustrated in Fig. 1, the MPD file provided from the DASH
MPD server 12 includes the index regarding a cache, such as
the index of the cache priority or the cache expiry time for
each of the DASH segments. The cache management server in
the CDN 14 generates a cache control policy on the basis of
the index regarding cache and distributes the generated
cache control policy to the cache servers.
[0101]
Each of the cache servers in the CDN 14 performs a
caching process of the DASH segment on the basis of the
cache control policy. In this manner, among the cache
servers in the CDN 14, a DASH segment having a higher
priority is stored in the local caches of a larger number of
the cache servers.
[0102]
Accordingly, for the DASH segments of video data
streams included in, for example, the viewpoint group 1, for
which the IPTV client 13 is likely to send the acquisition
request many times, the probability of the DASH segment
being transmitted from the cache server in the CDN 14 rather
than the DASH segment streamer 11 in response to the
acquisition request for the DASH segment from the IPTV
client 13 becomes high. Accordingly, the CDN 14 can
44
efficiently perform a cache and delivery resource management
of the DASH segment of video data streams.
[0103]
<2. Modifications>
Note that according to the above-described embodiment,
examples of the index regarding a cache that is set in the
MPD file include the index of the cache priority and the
index of the cache expiry time. However, the index
regarding a cache is not limited thereto. For example, when
the case in which a cache is requested by sending a request
to a cache server located in the vicinity of the cache is
taken into account, the index of the range of the vicinity
can be used.
[0104]
In addition, in the example according to the abovedescribed
embodiment, the multi-view video data streams that
constitute a three-dimensional image are MPEG-DASH based
video data streams. However, the MPEG-DASH based video data
streams may be replaced with another type of video data
stream that can be grouped. Even in such a case, by setting,
in the MPD file, the index regarding a cache in accordance
with each of the groups, the CDN 14 can efficiently perform
cache and delivery resource management of the DASH segments
of the video data streams.
[0105]
45
In addition, according to the above-described
embodiment, the present technology is applied to a stream
delivery system that delivers MPEG-DASH based video data
streams. It is to be noted that the present technology can
be applied to another similar type of delivery system of a
video data stream in the same manner.
[0106]
Furthermore, the present technology can have the
following configurations.
(1) A transmission device includes a meta file
generating unit configured to generate a meta file including
information used by a client terminal to acquire a
predetermined number of video data streams of given content
deliverable by a delivery server via a network, and a meta
file transmitting unit configured to upon receiving a
transmission request from the client terminal, transmitting
the meta file to the client terminal via the network. The
meta file generating unit sets, in the meta file, an index
regarding a cache of each of the video data streams in the
network.
(2) In the transmission device described in (1), the
index regarding a cache is the index of a cache priority of
a corresponding video data stream in the network.
(3) In the transmission device described in (1), the
index regarding a cache is the index of a cache expiry time
46
of a corresponding video data stream in the network.
(4) In the transmission device described in any one of
(1) to (3), the predetermined number of video data streams
are multi-view video data streams that constitute a threedimensional
image.
(5) In the transmission device described in (4), the
meta file generating unit determines the index regarding a
cache of each of the multi-view video data streams on the
basis of viewpoint groups classified using estimated
frequency of a request for delivery of each of the multiview
video data streams.
(6) In the transmission device described in any one of
(1) to (5), the predetermined number of video data streams
are MPEG-DASH based video data streams, the meta file is an
MPD file, and the network is a CDN.
(7) In the transmission device described in (6), the
meta file generating unit sets, in the MPD file, the index
regarding a cache of each of the video data streams in the
network using a DescriptorType element.
(8) A transmission method includes a meta file
generating step of generating a meta file including
information used by a client terminal to acquire a
predetermined number of video data streams of given content
deliverable by a delivery server via a network, and a meta
file transmitting step of upon receiving a transmission
47
request from the client terminal, transmitting the meta file
to the client terminal via the network. In the meta file
generating step, an index regarding a cache of each of the
video data streams in the network is set in the meta file.
(9) A network apparatus includes a plurality of cache
servers and a predetermined number of cache management
servers. Upon receives a meta file including information
used by a client terminal to acquire a predetermined number
of video data streams of given content deliverable by a
delivery server via a network, the cache server transmits
the meta file to the cache management server. The cache
management server generates a cache control policy on the
basis of an index regarding a cache of each of the video
data streams in the network included in the meta file and
distributes the cache control policy to each of the cache
servers.
(10) In the network apparatus described in (9), the
index regarding a cache is an index of a cache priority
and/or an index of a cache expiry time.
(11) In the network apparatus described in (9) or (10),
the predetermined number of video data streams are MPEG-DASH
based video data streams, the meta file is an MPD file, and
the cache server is a DASH cache server.
[0107]
The present technology is mainly characterized in that
48
by setting, in the MPD file provided by the DASH MPD server
12, the indices regarding a cache, such as the index of the
cache priority and the index of the cache expiry time of
each of the DASH segments, cache and delivery resource
management of the DASH segment of each of the video data
streams in a CDN can be efficiently performed (refer to Figs.
18 and 22).
Reference Signs List
[0108]
10 stream delivery system
11 DASH segment streamer
12 DASH MPD server
13, 13-1 to 13-3 IPTV client
14 CDN
15 content management server
16, 17 cache server
18 cache management server
49
CLAIMS
[Claim 1]
A transmission device comprising:
a meta file generating unit configured to generate a
meta file including information used by a client terminal to
acquire a predetermined number of video data streams of
given content deliverable by a delivery server via a
network; and
a meta file transmitting unit configured to upon
receiving a transmission request from the client terminal,
transmitting the meta file to the client terminal via the
network,
wherein the meta file generating unit sets, in the meta
file, an index regarding a cache of each of the video data
streams in the network.
[Claim 2]
The transmission device according to Claim 1, wherein
the index regarding a cache is the index of a cache priority
of a corresponding video data stream in the network.
[Claim 3]
The transmission device according to Claim 1, wherein
the index regarding a cache is the index of a cache expiry
time of a corresponding video data stream in the network.
[Claim 4]
The transmission device according to Claim 1, wherein
50
the predetermined number of video data streams are multiview
video data streams that constitute a three-dimensional
image.
[Claim 5]
The transmission device according to Claim 4, wherein
the meta file generating unit determines the index regarding
a cache of each of the multi-view video data streams on the
basis of viewpoint groups classified using estimated
frequency of a request for delivery of each of the multiview
video data streams.
[Claim 6]
The transmission device according to Claim 1, wherein
the predetermined number of video data streams are MPEG-DASH
based video data streams, the meta file is an MPD file, and
the network is a CDN.
[Claim 7]
The transmission device according to Claim 6, wherein
the meta file generating unit sets, in the MPD file, the
index regarding a cache of each of the video data streams in
the network using a DescriptorType element.
[Claim 8]
A transmission method comprising:
a meta file generating step of generating a meta file
including information used by a client terminal to acquire a
predetermined number of video data streams of given content
51
deliverable by a delivery server via a network; and
a meta file transmitting step of upon receiving a
transmission request from the client terminal, transmitting
the meta file to the client terminal via the network,
wherein in the meta file generating step, an index
regarding a cache of each of the video data streams in the
network is set in the meta file.
[Claim 9]
A network apparatus comprising:
a plurality of cache servers; and
a predetermined number of cache management servers,
wherein upon receives a meta file including information
used by a client terminal to acquire a predetermined number
of video data streams of given content deliverable by a
delivery server via a network, the cache server transmits
the meta file to the cache management server, and
wherein the cache management server generates a cache
control policy on the basis of an index regarding a cache of
each of the video data streams in the network included in
the meta file and distributes the cache control policy to
each of the cache servers.
[Claim 10]
The network apparatus according to Claim 9, wherein the
index regarding a cache is an index of a cache priority
and/or an index of a cache expiry time.
52
[Claim 11]
The network apparatus according to Claim 9, wherein the
predetermined number of video data streams are MPEG-DASH
based video data streams, the meta file is an MPD file, and
the cache server is a DASH cache server.