U.S. patent application number 14/436220 was filed with the patent office on 2015-10-08 for method and apparatus for distributing media content services.
The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Michael Huber, Anthony Richard Jones, Thomas Lundqvist.
Application Number | 20150289003 14/436220 |
Document ID | / |
Family ID | 47216204 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150289003 |
Kind Code |
A1 |
Huber; Michael ; et
al. |
October 8, 2015 |
Method and Apparatus for Distributing Media Content Services
Abstract
A method of distributing a plurality of media content services
(S1-S5) across a distribution network comprising dividing each of
the plurality of media content services (S1-S5) into segments and
transmitting the segments of each of the plurality of media content
services as a sequence of bursts (305), wherein there is a window
period (303) between successive bursts (305) during which media
content is not transmitted. Each of the media content services
(S1-S5) has a respective bit rate and the transmitting comprises
transmitting each of the segments at a higher bit rate to create
the window periods (303) between successive bursts (305). Starts of
bursts (305) of the plurality of media content services (S1-S5) are
staggered in time with respect to one another. At least one of the
media content services (S1-S5) can comprise a plurality of media
content service representations of different bit rate. The media
content services and media content service representations can be
transmitted as multicasts.
Inventors: |
Huber; Michael; (Taby,
SE) ; Jones; Anthony Richard; (Southampton, GB)
; Lundqvist; Thomas; (Stockholm, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Family ID: |
47216204 |
Appl. No.: |
14/436220 |
Filed: |
February 14, 2013 |
PCT Filed: |
February 14, 2013 |
PCT NO: |
PCT/EP2013/052978 |
371 Date: |
April 16, 2015 |
Current U.S.
Class: |
725/116 |
Current CPC
Class: |
H04N 21/8456 20130101;
H04N 21/2181 20130101; H04N 21/4621 20130101; H04N 21/64792
20130101; H04L 65/80 20130101; H04N 21/64322 20130101; H04N
21/26216 20130101; H04N 21/6405 20130101; H04L 65/4076 20130101;
H04N 21/44209 20130101; H04L 65/1083 20130101; H04N 21/23439
20130101; H04N 21/6332 20130101; H04N 21/6125 20130101; H04N
21/23805 20130101 |
International
Class: |
H04N 21/262 20060101
H04N021/262; H04N 21/647 20060101 H04N021/647; H04N 21/218 20060101
H04N021/218; H04N 21/61 20060101 H04N021/61; H04N 21/6405 20060101
H04N021/6405 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2012 |
EP |
PCT/EP2012/070960 |
Claims
1. A method of distributing a plurality of media content services
across a distribution network comprising: dividing each of the
plurality of media content services into segments; and transmitting
the segments of each of the plurality of media content services as
a sequence of bursts, wherein there is a window period between
successive bursts during which media content is not transmitted,
wherein each of the media content services has a respective bit
rate and the transmitting comprises transmitting each of the
segments at a higher bit rate to create the window periods between
successive bursts, and wherein starts of bursts of the plurality of
media content services are staggered in time with respect to one
another.
2. A method according to claim 1 wherein the starts of bursts of
the plurality of media content services are staggered in time with
respect to one another such that, for any pair of the plurality of
media content services, the window periods of the media content
services do not overlap.
3. A method according to claim 1 wherein the bursts of the
plurality of media content services are of equal burst duration and
the starts of bursts of any pair of the plurality of media content
services are staggered in time by a time period which is less than,
or equal to, the burst duration.
4. A method according to claim 1 wherein each of the media content
services is transmitted as a multicast.
5. A method according to claim 1 further comprising receiving or
generating a plurality of media content service representations for
at least one of the media content services, each of the media
content representations having a different bit rate, and wherein
the step of dividing each of the media content services into
segments divides each of the media content service representations
into segments, wherein the segments of the plurality of media
content service representations of a respective media content
service are aligned in time; and wherein the step of transmitting
the segments comprises transmitting the segments of each of the
plurality of media content service representations as a sequence of
bursts, wherein the bursts of the plurality of media content
service representations of a respective media content service are
aligned in time.
6. A method according to claim 5 wherein each of the media content
service representations is transmitted as a multicast.
7. A method according to claim 1 wherein each burst comprises a
plurality of Internet Protocol packets.
8. A method according to claim 1 wherein the media content services
are video services.
9. Apparatus for distributing a plurality of media content service
across a distribution network comprising: an interface for
receiving the plurality of media content services; segmenting
apparatus arranged to divide each of the plurality of media content
services into segments; an output unit arranged to transmit the
segments of each of the plurality of media content services as a
sequence of bursts, wherein there is a window period between
successive bursts during which media content is not transmitted,
wherein each of the received or generated media content services
has a respective bit rate and the transmitting comprises
transmitting each of the segments at a higher bit rate to create
the window periods between successive bursts, and wherein starts of
bursts of different media content services are staggered in time
with respect to one another.
10. Apparatus according to claim 9 wherein the starts of bursts of
the plurality of media content services are staggered in time with
respect to one another such that, for any pair of the plurality of
media content services, the window periods of the media content
services do not overlap.
11. Apparatus according to claim 9 wherein the bursts of the
plurality of media content services are of equal burst duration and
the starts of bursts of any pair of the plurality of media content
services are staggered in time by a time period which is less than,
or equal to, the burst duration.
12. Apparatus according to claim 9 which is arranged to transmit
each of the media content service representations as a
multicast.
13. Apparatus according to claims 9 wherein the segmenting
apparatus is arranged to divide at least one of the media content
services into a plurality of segmented media content service
representations, each of the media content representations having a
different bit rate, wherein the segments of the plurality of media
content service representations of a respective media content
service are aligned in time; and wherein the output unit is
arranged to transmit the segments of each of the plurality of media
content service representations as a sequence of bursts, wherein
the bursts of the plurality of media content service
representations of a respective media content service are aligned
in time.
14. Apparatus according to claim 13 which is arranged to transmit
each of the media content service representations as a multicast.
Description
TECHNICAL FIELD
[0001] This invention relates to a method and apparatus for
distributing a media content service.
BACKGROUND
[0002] Traditional telecommunications systems have evolved rapidly
in recent years to encompass considerably more capability than
simply delivering a telephony service. Internet technology based on
data packets and associated transmission protocols, for example the
Internet Protocol (IP), has now superseded the old space switching
techniques and dedicated transmission resources during a telephone
call or data transmission session.
[0003] The convergence of flexible delivery technologies has
enabled services to be mixed in the same physical resource so that
for example, in telephony networks, subscribers are now able to
receive audio-visual content, including relayed broadcast
television and radio services, as well as access internet
resources, all via their telephone lines. Similarly, the expansion
of wireless networks have enabled a user to receive a range of
communications services over a wireless delivery channel.
[0004] A Digital Subscriber Loop (xDSL) modem/router, which is
widespread in homes, acts as a common assembly point for all
domestic communications traffic, such as telephony, computer-based
web browsing, email, home shopping or streaming of video material.
As will be appreciated by a skilled person, the capacity of the
digital subscriber loop has to be shared among the services being
provided to the subscriber at any particular time.
[0005] There is considerable interest in receiving "streamed"
services which deliver a stream of video and/or audio material to
users. The content can be live content or it can be recorded
content which is requested on demand. In an Internet Protocol
Television (IPTV) system, video and audio content is delivered to
users via Internet Protocol (IP) delivery mechanisms. These types
of services require a continuous and uninterrupted flow of data. A
premises may have multiple terminals which are capable of receiving
media content. The demands placed on the delivery channel can vary
according to how many terminals require content at a particular
time.
[0006] Streamed media content services can be provided by one of
two methods: Unicast or Multicast. Unicast provides the subscribing
receiver with a direct and unique two-way path through the delivery
network all the way back to the media server supplying the required
data stream. The main streaming activity is managed on a one-to-one
basis between the receiver and the source server. The network
between the source server and receiver typically comprises a series
of intermediate servers installed at network nodes which are not
directly involved in the service but only support the transfer of a
packet stream. Typically the protocols used to support the
transmissions are simple forms of Internet Protocol (IP) itself
augmented by one or more higher layer protocols to provide flow
control. These protocols extend across the span of the link between
the source server and a given receiver. This method of distribution
is wasteful of network capacity because, at busy times and for
popular media streams, many copies exist in the network
simultaneously and this contributes to network congestion.
[0007] A Unicast system can support Adaptive Bit Rate Streaming
(ABR). This allows some form of rate adaptation. A given service is
encoded at a selection of different bit rates (known as
representations), with synchronised boundary points at defined
locations (e.g. every 50 frames). For each representation, content
between successive boundary points is converted into a discrete
file. Clients fetch a segment of one of the representations in
turn. If a higher or a lower bit rate is required, the next segment
is fetched from one of the other representations. The segments are
constructed such that there is no discontinuity in decoded
pictures/audio if the client switches between representations at
the boundary points. This system requires the unicast two-way path
between source and receiver to request files and deliver the
requested files.
[0008] Multicast makes more efficient use of bandwidth by sharing
content streams among several receivers. Intermediate network
routers are now more closely involved in the service delivery such
that some control and management functions are delegated from the
source server. This control is supported by more extensive
protocols devised for this type of application such as Protocol
Independent Multicast (PIM) and Internet Group Multicast Protocol
(IGMP). When a new receiver requests a given media item, the
network router system finds an existing stream of that content
already in the network and directs a copy of it to that new
receiver from an appropriately near network node. A new receiver
has to be able to join this existing stream under controlled
conditions that do not adversely affect existing receivers. Any
receiver in this group also has to be able leave the stream, or
pause its consumption, without affecting the others. There is now a
clear separation of control and management from the content. This
complicates the control function because several receivers will
have different instantaneous bit rate and control needs and so the
segmentation of the stream as it passes through a given network has
to deal with the conflicting demands. These are managed directly
between the receiving device itself and the nearest upstream
router/server that will mediate control functions including any
need to refer back to earlier network servers or even the original
source server.
[0009] Currently, each TV service has to be set up with a
conservative configuration. This can be a capped Variable Bit Rate
(VBR) with a safe cap value. This is because it is not possible to
change bit rate of a service on the fly without interrupting the TV
service.
[0010] In summary, while unicast systems can support an adaptive
bit rate of a streamed service over time, this comes at a
significant cost in terms of resources of the delivery network to
support a large number of unicast paths, and may require additional
servers located near to clients of the network to maintain
acceptable response times. Multicast systems can more efficiently
use bandwidth resources of the network, but do not support adaptive
bit rate needs of client devices.
[0011] The present invention seeks to provide an alternative way of
distributing media content services, such as video services.
SUMMARY
[0012] An aspect of the present invention provides a method of
distributing a plurality of media content services across a
distribution network. The method comprises dividing each of the
plurality of media content services into segments. The method
further comprises transmitting the segments of each of the
plurality of media content services as a sequence of bursts,
wherein there is a window period between successive bursts during
which media content is not transmitted. Each of the media content
services has a respective bit rate and the transmitting comprises
transmitting each of the segments at a higher bit rate to create
the window periods between successive bursts. Starts of bursts of
the plurality of media content services are staggered in time with
respect to one another.
[0013] Advantageously, the starts of bursts of the plurality of
media content services are staggered in time with respect to one
another such that window periods of any pair of the plurality of
media content services do not overlap.
[0014] Advantageously, the bursts of the plurality of media content
services are of equal burst duration and the starts of bursts of
any pair of the plurality of media content services are staggered
in time by a time period which is less than, or equal to, the burst
duration.
[0015] Advantageously, the method further comprises receiving or
generating a plurality of media content service representations for
at least one of the media content services, each of the media
content representations having a different bit rate. The step of
dividing each of the media content services into segments divides
each of the media content service representations into segments,
wherein the segments of the plurality of media content service
representations of a respective media content service are aligned
in time. The step of transmitting the segments comprises
transmitting the segments of each of the plurality of media content
service representations as a sequence of bursts, wherein the bursts
of the plurality of media content service representations of a
respective media content service are aligned in time.
[0016] Advantageously, each of the media content services is
transmitted as a multicast.
[0017] Advantageously, each of the media content service
representations is transmitted as a multicast.
[0018] Advantageously, each burst comprises a plurality of Internet
Protocol packets.
[0019] Advantageously, the media content services are video
services. Each media content service can be an IPTV service.
[0020] Advantageously, the dividing comprises inserting data which
indicates a boundary of a segment and the step of transmitting each
of the segments uses the inserted data to determine a boundary of a
segment.
[0021] Advantageously, the method further comprises transmitting an
information element which indicates at least one of: an end of a
burst; an advance notice of an end of a burst. The information
element can be carried within each of the bursts.
[0022] Advantageously, each of the media content service
representations is transmitted as a first multicast with a
multicast destination IP address, and the method comprises
transmitting a second multicast which carries the information
element, wherein the second multicast has the same destination IP
address as the first multicast.
[0023] Advantageously, the method further comprises adapting the
media content data into packets for transport over the distribution
network, and the step of transmitting each of the segments as a
burst operates on the packets.
[0024] Advantageously, the method further comprises transmitting
information about which media content service representations are
available for selection.
[0025] The method can be performed by a node of the distribution
network such as a head end node, or by any other node or
combination of nodes.
[0026] Advantageously, at least two of the plurality of media
content service representations for the video service have a
different video resolution.
[0027] Another aspect of the invention provides apparatus for
distributing a plurality of media content service across a
distribution network. The apparatus comprises an interface for
receiving the plurality of media content services. The apparatus
further comprises segmenting apparatus arranged to divide each of
the plurality of media content services into segments. The
apparatus further comprises an output unit arranged to transmit the
segments of each of the plurality of media content services as a
sequence of bursts, wherein there is a window period between
successive bursts during which media content is not transmitted.
Each of the received or generated media content services has a
respective bit rate and the transmitting comprises transmitting
each of the segments at a higher bit rate to create the window
periods between successive bursts. Starts of bursts of different
media content services are staggered in time with respect to one
another.
[0028] Advantageously, at least one embodiment provides a way of
delivering media content services (e.g. video services) in a manner
which makes efficient use of resources of the distribution
network.
[0029] Advantageously, at least one embodiment allows a client
device to dynamically alter the bit rate of the media content
service. The client device may need to adapt the bit rate due to
varying bandwidth demands required of the delivery channel, such as
a change to the number of media content services used at any
particular time, or a change to the bandwidth of the delivery
channel (e.g. with a wireless delivery channel).
[0030] Advantageously, at least one embodiment provides a way of
allowing a client device to dynamically alter the bit rate of the
media content service without significant disruption to the media
content service.
[0031] The functionality described here can be implemented in
hardware, software executed by a processing apparatus, or by a
combination of hardware and software. The processing apparatus can
comprise a computer, a processor, a state machine, a logic array or
any other suitable processing apparatus. The processing apparatus
can be a general-purpose processor which executes software to cause
the general-purpose processor to perform the required tasks, or the
processing apparatus can be dedicated to perform the required
functions. Another aspect of the invention provides
machine-readable instructions (software) which, when executed by a
processor, perform any of the described methods. The
machine-readable instructions may be stored on an electronic memory
device, hard disk, optical disk or other machine-readable storage
medium. The machine-readable medium can be a non-transitory medium.
The machine-readable instructions can be downloaded to the storage
medium via a network connection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Embodiments of the invention will be described, by way of
example only, with reference to the accompanying drawings in
which:
[0033] FIG. 1 shows a typical system for delivering services to
subscriber premises over a delivery channel;
[0034] FIG. 2 shows a modified system corresponding with FIG. 1 in
accordance with an embodiment of the invention;
[0035] FIG. 3 shows processing performed on a media content stream
to create a set of segmented representations in accordance with an
embodiment of the invention;
[0036] FIG. 4 shows processing performed on representations of a
media content stream of different bit rates to form bursts in
accordance with an embodiment of the invention;
[0037] FIG. 5 shows a method of processing media content which can
be performed at one or more nodes of a distribution network;
[0038] FIGS. 6 and 7 show time lines of an operation to change the
bit rate of a media content stream received at a subscriber
apparatus;
[0039] FIG. 8 shows apparatus in accordance with an embodiment of
the invention;
[0040] FIG. 9 shows part of the apparatus of FIG. 8 in more
detail;
[0041] FIG. 10 shows packets used to carry media content data;
[0042] FIG. 11 shows a media content distribution network in more
detail;
[0043] FIG. 12 shows transmission of multicasts to a subscriber
apparatus;
[0044] FIGS. 13 and 14 show possible timing schemes for the
transmission of a plurality of media content services;
[0045] FIG. 15 shows another possible timing scheme for the
transmission of a plurality of media content services in which
window periods are offset from one another;
[0046] FIG. 16 shows the scheme of FIG. 15 in more detail, showing
the timing relationship of representations of each of the media
content services;
[0047] FIG. 17 shows another possible timing scheme for the
transmission of a plurality of media content services in which
bursts are of different durations;
[0048] FIGS. 18 and 19 show methods of processing media content
which can be performed at one or more nodes of a distribution
network;
[0049] FIG. 20 shows processing apparatus for a computer-based
implementation.
DETAILED DESCRIPTION
[0050] FIG. 1 is a schematic diagram of a typical system for
providing communication services to subscriber premises 5. The
various resources shown contribute to the delivery of a group of
services to a subscriber over the digital subscriber loop 32
between a premises 5 and the network.
[0051] At the subscriber side shown on the right-hand side of FIG.
1, a number of different devices are present that may require
services to be provided over a digital subscriber loop. Typically,
such devices may include: a telephone 2; computers 4, 6; video
decoders 8 and 10; together with other terminals denoted
generically by terminal 12. These devices 2-12 are coupled to a
digital subscriber loop (xDSL) router 40 over a local subscriber
network 16, which is typically provided by an Ethernet or a
wireless network.
[0052] On the network side shown on the left-hand side of FIG. 1, a
digital subscriber loop (xDSL) access multiplexer (DSLAM) 20 is
coupled via a distribution network 60 to a plurality of service
sources 24-30. The distribution network 60 can be an Internet
Protocol (IP) based distribution network in which all of the
services 24-30 are transported using IP. The term xDSL includes
Asymmetric Digital Subscriber Line (ADSL) and variants (ADSL2,
ADSL2+), Very high bit-rate Digital Subscriber Line (VDSL) and
other variants.
[0053] The services 24-30 shown at the left are examples of various
types of service, all of which may be combined using Internet
Protocol (IP) for delivery across the digital subscriber loop to
the consumer, where they are separated again for the individual
destination devices in the home, as will be understood by a skilled
person. The Internet Protocol (IP) infrastructure at the Service
Provider end is configured differently on demand for each
subscriber, as will be understood by a skilled person, and
additional DSLAMs 21, 22 are shown for completeness.
[0054] A video source 30 is shown supplying an input to the
distribution network 60. There are various types of video service.
A first type of video service is live video that is delivered in
real time. A second type of video service uses video data which is
stored as video files in servers. These video files may be watched
in real time as if they were live video or may be transferred in
non-real time for later playback at the subscriber's premises.
Typically, this video service type might be used for a film library
that enables a film to be downloaded by a subscriber for immediate
viewing or stored for later use. The stored video files may be for
video service recording content accessed in accordance with the
requirements of an individual subscriber, for example in accordance
with a digital video recorder (DVR) schedule of a subscriber. In
some embodiments this non real-time video service content may be
deferred by being temporarily buffered in the network when the
digital subscriber loop is being heavily utilised, and being moved
to the local storage when capacity across the digital subscriber
loop becomes available.
[0055] FIG. 2 is a schematic diagram corresponding with FIG. 1 and
showing additional elements in accordance with embodiments of the
invention. Elements in FIG. 2 having the same or similar function
to corresponding elements in FIG. 1 have been given the same
reference numerals.
[0056] In FIG. 2, apparatus 41 provided at a subscriber end 5
includes a control function which is able to select a
representation of a media content stream, at a particular bit rate,
and can join a multicast which provides that representation. The
control function is able to dynamically select between
representations over a period of time, and can leave a multicast of
one representation and can join a multicast of another
representation. In some embodiments, apparatus 42 provided at a
subscriber end 5 can arbitrate between multiple demands of devices
2-12. Apparatus 42 can conveniently form part of xDSL router 40 or
it can be a separate device which is connected to the xDSL router
40. Alternatively, the functionality of apparatus 42 can form part
of a device 2-12 connected to the xDSL router 40. Policy, which can
be used by the apparatus 42 to arbitrate between demands, can be
located 44 at the subscriber apparatus and/or in the network 62.
Distribution network 60 includes additional processing functions 69
to form multicast streams which provide a set of representations of
a service at different bit rates. As described below, these
representations are transmitted as a sequence of bursts with window
periods between successive bursts which allow a subscriber
apparatus to join and/or leave a multicast of a required
representation. The processing functions 69 can be performed by a
distribution head end 61 or by any other node or combination of
nodes.
[0057] In embodiments of the invention, each media content service
is made available in a plurality of media content service
representations, each having a different bit rate. For example, a
video service 1 can be made available in three video service
representations 1a, 1b, 1c and video service 2 can be made
available in three video service representations 2a, 2b, 2c. In
different embodiments, and for different video services, the number
of video services representations available for selection may be
greater or less than 3, as decided by a skilled person. One or more
other properties of the video service can vary among the
representations, such as video resolution, frame rate. Audio rates
(or number of audio channels) can also vary between
representations. For example, consider representations 1a, 1b, 1c
have progressively higher bit rates. At least one of the higher bit
rate representations (e.g. 1c) can have a higher resolution than
one of the lower bit rate representations (e.g. 1a, 1b).
[0058] FIG. 3 shows processing performed on a media content stream
85 to form a set of representations 80A, 80B at different bit
rates. In this example embodiment the media content is video. Each
video service 85 is coded as a set of representations 80A, 80B. For
simplicity, FIG. 3 shows Constant Bit Rate (CBR) rate streams but
the coding does not have to be constant bit rate. For example, it
could be variable bit rate (VBR) or variable bit rate with a
particular peak or mean bit rate value, such as capped Variable Bit
Rate (VBR). The values of 5 Mbit/s and 7 Mbit/s are example values,
and it will be appreciated that a representation can be generated
at any other desired value and that any number of representations
may be generated. Each representation is divided into a sequence of
segments 81A, 81B. Segment boundaries 82 are aligned, such that the
segment boundaries of one representation 80A are aligned in time
with the segment boundaries of another representation 80B. A
corresponding segment in each of the representations correspond to
the same frames of video content. As will be explained, this allows
a receiver to switch between representations at one of the segment
boundaries 88 and perform a smooth transition between
representations. Advantageously, a segment boundary 88 occurs at
the end of a Group of Pictures (GOP) 83.
[0059] A feature of compressed video data stream syntax is the
Group of Pictures (GOP) which comprises a sequence of complete and
contiguous video pictures or frames. The Group of Pictures (GOP)
begins with a frame selected to be a master frame, denoted as an
"I" or Intra Frame for that sequence. This I Frame is coded without
reference to any other frame in the sequence and exploits only
spatial redundancy within the I frame. Since I frames may be
decoded without reference to picture information in any other
frame, I frames can be relied upon as a starting point for a
decoder.
[0060] The other frames or pictures in a Group of Pictures (GOP)
can be coded very efficiently by exploiting temporal redundancy in
the image sequence. These frames are coded so that information is
transmitted describing differences between the current frame and
already coded reference frames temporally adjacent to it. Such
frames are of two types: one type is a Predicted or P frame type,
which is predicted and coded only from one direction of the image
sequence, for example from earlier frames in the image sequence.
The other type is a Bidirectional frame or B frame type, which are
predicted from both forward and backward directions of the
sequence, for example by interpolation from earlier and later
frames in the video sequence.
[0061] As will be appreciated, the success of compression
algorithms in achieving low bit rates is because the P and B Frames
use smaller amounts of data to encode the picture than an I Frame
and are more numerous in a Group of Pictures (GOP). An I Frame uses
more data to encode the picture and so these are relatively sparse
in a Group of Pictures (GOP). The I frame is very useful when
streams are interrupted or suffer occasional errors because it
resets the decoder with an independent Frame.
[0062] Thus a Group of Pictures (GOP) can be structured as a
sequence of I, P and B Frames in an arbitrary pattern e.g. IBBPBBP
. . . until the next I Frame is inserted. The length of the Group
of Pictures (GOP) will affect coding efficiency because it uses
predominantly small coded frame sizes. Such a Group of Pictures
(GOP) is known as a Closed Group of Pictures (GOP) because it is
self-contained and has defined entry points at the I Frame for
decoders such that coded pictures following the I frame do not
reference any pictures before the I frame. This is useful for this
application because the I Frames allow points in a stream at which
a bit rate change can be made without necessarily disrupting the
decoder.
[0063] Advantageously, the video service representations of a video
service have aligned segment boundaries 88 so that their GOP
patterns are aligned. Data for the different bit rate
representations 80A, 80B is packetised. FIG. 3 shows a sequence of
Transport Stream (TS) packets 84A, 84B for each representation. The
number of packets per segment varies according to the bit rate of
the representation. The higher bit rate stream 80B has more packets
than the lower bit rate stream 80A.
[0064] Advantageously, segment boundaries are marked by introducing
Boundary Points (BP) that mark the location of the segment
boundaries in the segmented streams 80A, 80B where it is possible
to switch cleanly between the representations and deliver the
segments using multicast. These BPs can also act as reference
points in the stream for any other purpose. The BP can be inserted
in a continuous stream, for example as a short gap, or the
segmented media data stream can be momentarily paused so that the
absence of data allows time for receivers to adjust themselves to
any changing circumstances including new receivers joining the
stream or existing ones pausing or leaving it.
[0065] Conveniently, media data can be encoded according to Motion
Pictures Experts Group MPEG-2 format and encapsulated into MPEG
Transport Streams, but it will be appreciated that segments 81A,
81B can also be coded and encapsulated in any other suitable
format, such as the MPEG-4 File Format.
[0066] FIG. 4 shows processing performed on segmented media content
streams 80A, 80B, to form a set of bursts at different bit rates.
As will be explained below, the segmented streams 80A, 80B are fed
into a multicast playout block that makes each segment play out in
less time than the interval between the boundary points. The
purpose of this is to deliberately introduce a window period
between transmitted bursts 82A, 82B. The duration of the window
period 83 is sufficient for a multicast receiver to leave one
representation of the stream and join a different representation at
a different bit rate. The switching between multicasts can be
achieved using multicast Leave and Join messages. The duration of
the window period 83 is sufficient for a receiver to send requests
to join and leave respective multicasts and for switches and
routers in the distribution network 60 to action the requests. The
multicasts bursts 82A, 82B have a higher bit rate compared to the
respective segmented representations 80A, 80B. The bit rate of the
bursts is increased by a factor of a, where:
a = segment duration ( segment duration - window duration ) ( 1 )
##EQU00001##
For clarity, FIG. 4 shows the start point of the bursts 82A, 82B
aligned in time with the start point of the segments 81A, 81B of
representations 80A, 80B, to illustrate the comparison in length of
the segments 81A, 81B compared to the bursts 82A, 82B. It will be
appreciated that a short buffer period (of at least the length of
the window period) is required before the burst can be played out,
which would be represented in FIG. 4 as an offset along the time
axis between the start of segments 81A, 81B and the start of bursts
82A, 82B.
[0067] The start of bursts of different content services can be
aligned in time (i.e. all bursts of all services start at the same
time) or the start times can be staggered with respect to one
another. Aligning the start times of bursts of different services
in time can have an advantage of allowing a quicker channel change
between services.
[0068] One consequence of adding window periods 83 to the
transmitted streams is that the flow of content becomes jittered
beyond the level that normal packet transmission produces. This can
be accommodated by buffering provided within the reception
apparatus. The window period duration will influence the amount of
jitter produced and so there is an optimum size that is related to
the worst case response times of the chain of routers/servers
delivering the content. This time is taken for switches to
recognise and implement all those steps that are required to keep
the stream flowing including the potential need for the multicast
content to be found at or near the source server. For segment
durations of the order of about 2 seconds, a possible value of the
window period is around 330 milliseconds. The window size is a
function of the responsiveness of the network to support multicast
leave and join functions and it will be appreciated that the window
period can be modified to a higher or lower value. More generally,
the window period could have a value selected from the range of 0.1
ms and 10 seconds and, more advantageously, the range 10 ms-350 ms.
As switches and routers increase in performance, it is possible
that the window duration can be reduced to the lower en d of the
ranges stated above.
[0069] Internet Group Management Protocol (IGMP)v3 provides an
explicit LEAVE message, allowing multicast clients to signal they
no longer require the multicast to be forwarded to them. This can
be implemented in IP switches as "Fast Leave", where the multicast
forwarding is stopped immediately when the LEAVE message is
received. There is also an IGMP Join message to join a
multicast.
[0070] FIG. 5 shows a method of processing media content service
data which can be performed by a node in the distribution network
60. Step 101 comprises generating a plurality of media content
service representations for the media content service, each of the
media content representations having a different bit rate. Step 102
comprises dividing each of the media content service
representations into segments. Segments of the plurality of media
content service representations are aligned in time. The dividing
can comprise marking boundary points between segments by inserting
signalling data into the data stream for each representation. Step
103 comprises transmitting the segments of each of the plurality of
media content service representations as a sequence of bursts. So,
the segments of a first representation are transmitted as a first
sequence of bursts, the segments of a second representation are
transmitted as a second sequence of bursts, and so on. Bursts of
the plurality of media content service representations are aligned
in time and there is a window period between adjacent bursts during
which media content is not transmitted. So, the bursts of the first
representation are time-aligned with the bursts (representing the
same part of the content) of the second representation, and with
the bursts of any other representations, where the time-aligned
bursts represent the same part of the content (e.g. the same video
frame). Each of the media content service representations is
transmitted as a multicast. Each of the generated media content
service representations 80A, 80B has a respective bit rate and the
transmitting comprises transmitting each of the segments 81A, 81B
at a higher bit rate to create the window periods 83 between
successive bursts 82A, 82B.
[0071] FIGS. 6 and 7 show time lines of an operation to change the
bit rate of a media content stream received at a subscriber
apparatus. FIG. 6 shows two multicast representations 87A, 87B of
different bit rates which are transmitted across distribution
network 60. A subscriber apparatus can select one of these
representations by joining the multicast. The subscriber apparatus
receives bursts 82B of representation 87B (high bit rate) during
periods t1-t2 and t3-t4. At time t4 the subscriber apparatus sends
signalling to leave the multicast of representation 87B (high bit
rate) and to join the multicast of representation 87A (low bit
rate). At time t6 the subscriber apparatus receives a burst 82A of
representation 87A (low bit rate). The switch between leaving
multicast of representation 87B and joining the representation of
multicast 87A occurs during the window period t4-t6. Thus, the
subscriber apparatus receives a seamless flow of data for the media
content service, even though a change in the delivery bit rate has
occurred. The order of signalling can be reversed, such that the
request to join the new multicast 87A is sent before sending the
request to leave the existing multicast 87B. A worst case time for
joining a multicast is longer than a worst case time for leaving a
multicast, and so it is advantageous to issue the command to join
first.
[0072] FIG. 7 shows further detail of the process to change the bit
rate of a media content stream received at a subscriber apparatus.
There are various ways in which a subscriber apparatus can detect
the end of a burst and the start of the period when the apparatus
can safely switch between representations. It is possible to
configure a terminal to measure a "time out" period at the
beginning of a window period, but this introduces an undesirable
latency. It is more advantageous to send signalling which
explicitly indicates an end of a burst, or which gives advance
notice of when an end of burst will occur. This signals to the
subscriber apparatus when it is possible to safely switch between
representations, with minimal delay. Advantageously the locations
in the data stream where the switching between streams can safely
occur are explicitly signalled within, or alongside, the
multicasts, thus allowing a receive device to immediately be aware
that a switching opportunity exists. Signalling can be provided,
for example, in IP packets that share the same multicast
destination address as the IP packets carrying the media content
service, but different UDP destination port numbers, allowing
simple detection and discrimination at the receive device. This has
the advantage that whenever the multicast that carries the media
content is routed (in response to IGMP joins) the signalling would
also automatically follow. Alternatively, the signalling could be
delivered in a separate multicast having a separate multicast
destination address, with the subscriber apparatus joining/leaving
both the multicast carrying the media content and the multicast
carrying the end of burst signalling. Another possibility is to
include a trailer indicating an end of burst in the media
multicast. Examples include: adding trailer data at the end of the
last UDP datagram, sending an empty datagram, or changing a
parameter such as the sync byte (normally hexadecimal 47) to a
different value. Other possibilities are to send an information
element which gives advance notice of an end of a segment, such as
a number of TS packets remaining in the current segment, an RTP
sequence number of the last IP packet in the current segment, or
some other suitable advance notice.
[0073] The scheme described above can be used when representations
at different bit rates to minimise disruption to the delivery and
presentation of media content. When a terminal first joins a
service the joining could occur during the window or it may occur
at any time.
[0074] FIG. 8 shows apparatus for creating a set of segmented
representations and forming bursts in accordance with an embodiment
of the invention. The apparatus 69 shown in FIG. 8 can be provided
at a distribution head end node 61. The apparatus receives an input
feed 85 of content (e.g. video) per service. A set of
encoders/transcoders 65 generate, in parallel, a set of
representations of the content at a set of different bit rates. The
representations can differ in another quantity, such as video
resolution. A timing generator 64 outputs a signal that determines
the boundary point of the segments. For example, this can output a
signal once per 50 frames (2 seconds), or at any other suitable
time interval. The signal output by generator 64 is applied to all
of the parallel encoders 65 for that service. Advantageously, the
set of coders 65 can close the GOP (see FIG. 3) and a unit 76 can
insert in-band signalling such as a Random Access Point (RAP) and a
Boundary Point (BP). The outputs of the set of coders 65 are the
set of representations 80A, 80B which have time-aligned segments.
The representations 80A, 80B are applied to a burst generator unit
67 which creates the bursts (82A, 82B, FIG. 4) separated by window
periods (83, FIG. 4). Unit 67 plays out data at a higher bit rate
than the bit rate at which data was received to create the bursts.
Unit 67 recognises the start and end of segments 81A, 81B in the
representations 80A, 80B by detecting signalling (e.g. the in-band
BP signalling inserted by the encoders 65).
[0075] GOPs do not necessarily have to be closed at the boundary
point. By default they are closed. However closed GOPs are slightly
more inefficient than open GOPs, so it is possible that open GOPs
could also be used. The use of open GOPs has a disadvantage that,
when changing representations, there may be some visible impairment
to the pictures for the first GOP of the new representation. If
representation switches occur infrequently, then open GOPs may be
acceptable.
[0076] Advantageously, multicast address information is added at
the IP adaptation stage, which can occur at the head end 61, or at
a node downstream of the head end. Multicast IP datagrams have a
destination IP address is set to be in a range reserved for
multicast.
[0077] The apparatus shown in FIG. 8 can operate on data at one of
various possible levels. In one advantageous scheme, data is
encoded into Transport Stream (TS) packets at a normal rate and the
burst generator unit 67 operates on TS packets. Transport Stream
packets can be adapted into IP packets 66 before burst generator
unit 67, or after unit 67. An alternative is to form bursts before
any packetisation (at TS or IP level), but this is less
desirable.
[0078] FIG. 8 shows several possible places where end of burst
signalling can be added. Each encoder 65 can include an end of
burst signal insertion unit 77 which adds an information element
indicating the end of a burst into the encoded data, which includes
a header of the TS packets. Alternatively, the burst generator unit
67 can include an end of burst signal insertion unit 78 which is
arranged to insert an information element indicating the end of a
burst into each of the bursts. Where end of burst signalling is
provided as a multicast (with same or different address), the
multicast can be generated at apparatus 61.
[0079] Typically, a network operator will receive a media content
service feed from a service provider and will then convert the feed
to the right characteristics for the distribution network and end
users of the network. FIG. 8 shows a set of encoders/transcoders 65
which operate upon an input data stream 85 to form the multiple
representations at different bit rates. However, for situations
where a set of representations at different bit rates already
exist, it is possible for the input 85 to be a set of
representations at different bit rates. The multiple
representations can be generated at a point of origin into the
distribution network 60 or could be supplied by a service
provider.
[0080] The multiple representations of a video service can include
Standard Definition (SD) and High Definition (HD) representations
of the same content. The distribution network may receive an SD
feed and an HD feed of the content as inputs 85 or just one (SD or
HD) feed with transcoding 65 to generate the other of the SD and HD
representations. So, input 85 may be a high quality HD feed and
encoders 65 transcode the HD feed to generate lower bit rate, lower
resolution, versions of the content.
[0081] FIG. 9 shows further detail of the playout unit 67 of the
apparatus of FIG. 8. The burst generator unit 67 comprises a
parallel set of units 70. Each unit 70 has an input 71 for
receiving a segmented stream 80A, 80B of one of the
representations. Data is applied to a buffer 72. The buffer
operates according to a First In First Out (FIFO) principle. Data
is also applied to a detector 73 which detects signalling (e.g. BP
signalling) within the data stream indicating the start and end of
a segment. Detector 73 applies an output to a unit 74 which
controls playout of data from the buffer 72. A segment of data is
played out in one continuous block, which can be in the form of a
sequence of TS or IP packets carrying TS packets. Unit 74 controls
the playout rate, which is greater than the rate at which data was
originally received. Data is output 75 in burst form, as explained
above.
[0082] FIG. 10 shows an example format of packets used to carry
media content data. Video data comprises data representing GOPs. A
GOP comprises one or more of I frames, B frames and P frames. GOPs
are carried in Transport Stream (TS) packets. Other possible
formats include MPEG Dynamic Adaptive Streaming over HTTP
(MPEG-DASH). A TS packet has a length of 188 bytes, of which 4 (or
more) bytes are header bytes. A header of a TS packet can include
signalling which indicates a Boundary Point. The BP can be
signalled within the adaptation header (AH) of a TS packet. For an
IP-based distribution network, TS packets are carried within the
payloads of IP packets. Typically, 7 TS packets are aggregated into
one IP packet. Typically, a segment will comprise multiple IP
packets. IP packets may be spaced by a short inter-packet gap,
which is considerably shorter than the window period. Segments may
start with one or more TS packets before the first TS packet
carrying (video) content data. One example of this is where
encryption is used. The TS packet immediately before the first
packet carrying video content contains data needed for provisioning
the correct decryption key.
[0083] FIG. 11 shows distribution networks 60 that may be used to
multicast media content data, and protocols used to carry the data
and control data flows. The upper part of FIG. 11 represents a
distribution network for IPTV services using xDSL to subscriber
premises. A distribution head end 91 receives inputs 30 from
content (e.g. video) sources, which can be live or recorded
sources. The distribution network between the head end 91 and a DSL
access module comprises distribution nodes 92, which include IP
routers. The subscriber loop 32 to a subscriber premises is
terminated, at the subscriber side, by a customer premises router,
which can also be called a Residential Gateway (RG). Data is
carried over the distribution network using IP. The Internet Group
Management Protocol (IGMP) is a communications protocol used on the
IP distribution network to establish multicast group memberships.
Protocols such as IGMP are used to support the communication
between upstream routers/servers and support the Leave and Join
actions described above. Protocol-Independent Multicast (PIM) is
another protocol used within the distribution network. Within the
customer premises, content can be distributed by wired network
protocols (e.g. Ethernet) or wireless network protocols (e.g. IEEE
802.x). PIM is used between routers, whereas IGMP is layer 2 and is
used by switches. The protocols register a destination's interest
in receiving a multicast, either for itself, or to be forwarded to
one or more next destinations. When there is a leave, the traffic
stops if there is nothing else at that destination that is joined.
The fast leave operation terminates that flow immediately, whereas
without fast leave, a switch will respond to a leave command
sending out a request to see if any destination is still
interested, keeping the traffic flowing until a timeout occurs. The
fast leave operation is used in embodiments of the invention to
switch between multicast representations.
[0084] The lower part of FIG. 11 represents a wireless distribution
network, and comprises a Mobile Network Access Portal 93,
Distribution Network Nodes 94 and wireless Base Stations 95. There
is a wireless delivery channel between a base station 95 and a
receiving device 96, which can use a 3G or 4G wireless protocol. As
before, the IGMP can be used to establish multicast group
memberships, and Protocol-Independent Multicast (PIM) can be used
within the distribution network. The mobile receiving device 96 can
share content with other devices using a wired or wireless
connection. In the wireless system, base station 95 can perform the
join multicast/leave multicast functionality (equivalent to that
performed at the customer premises router 40) to share the limited
resource of the overall wireless network capacity of the cell
between multiple mobile receiving devices 96. Alternatively, a
mobile receiving device 96 can perform the join multicast/leave
multicast functionality, to share the limited resource of the
wireless connection between device 96 and the base station 95
between multiple services required by the device 96.
[0085] FIG. 12 shows transmission of multicasts to a subscriber
apparatus 41. Nodes within the distribution network can comprise a
headend, a network node (such as a Central Office, and a multi-cast
capable DSLAM. The (S,G) notation denotes S=Source Address,
G=Multicast Destination Address. G1a, G1b are multicasts carrying
different representations of one particular media content service.
The multicasts are shown being sent in parallel from the headend 91
to node 92, because the multicasts are received by subscriber
apparatus 41 at multiple premises within the network, but the
multicasts are sent one at a time from the node 92 to the
subscriber apparatus (RG) 41 based on the RG first requesting one
of the representations (S, G1a) and then changing to the other of
the representations (S, G1b) for a bit rate adjustment on that
service. The RG 41 can concatenate the incoming multicasts, which
may switch between representations, and form a single continuous
multicast output to a conventional receiver 4, 6, 8, 10, 12. As
explained above, the functionality of switching between multicast
streams may be performed by a device 4, 6, 8, 10, 12 connected
downstream of the RG, and that device would perform the
concatenation.
Changing Between Media Content Services
[0086] It has been described how HTTP adaptive streaming technology
can be combined with IP multicast. The basic principles are: [0087]
the individual representations (e.g. different bitrates) of a media
content stream (e.g. linear TV channel) are sent on separate
multicast streams; [0088] the distribution of segments are
separated by a gap in time during which no data is sent; [0089]
each segment is distributed as an overspeed burst--i.e. faster than
real-time. The burst factor is calculated based on the gap in time
that separates the segments; [0090] a client can change
representation during designated gaps, called window periods.
[0091] An effect of distributing media content services in this
manner is that more network bandwidth is consumed compared to
sending segments at their original (real time) speed. The total
bandwidth consumed by all of the media content streams may, in a
worst case, be equivalent to the combined extra bandwidth needed
for sending segments in overspeed mode.
[0092] Another effect of distributing media content services in
this manner is that clients must change between representations
during a window period. This means that all network signalling
associated with changing representations may, in a worst case,
occur during specific points in time followed by periods with no or
little network signalling.
[0093] The two effects described above can be reduced, or avoided,
by the relative timing of the starts of bursts of the media content
services. Advantageously, by evenly distributing the gaps across
media content services it is ensured that the total bandwidth
consumed by the media content services is efficiently utilised.
Even distribution of gaps also ensures that the combined signalling
in the network associated with changing bitrate is evenly
distributed in time.
[0094] FIG. 13 shows five different media content services S1-S5
with synchronised distribution of window periods 303, i.e. bursts
305 of each of the media content services S1-S5 start at the same
time, and window periods 303 between bursts 305 are synchronised.
The shaded areas indicate periods when all of the media content
services occupy bandwidth in overspeed mode. With synchronised
window periods 303 the media content services occupy maximum
bandwidth during the period when the bursts are transmitted. This
is the most inefficient scenario in terms of bandwidth
utilisation.
[0095] FIG. 14 shows five different media content services S1-S5
that are sent with unevenly and randomly distributed window periods
303. The periods 304 bounded by dashed lines indicate periods in
time when all of the media content services S1-S5 consume network
bandwidth in over-speed mode. It can also be seen that window
periods 303 of several of the media content services overlap in
time, such as services S2, S4 and S5. Accordingly, signalling to
switch between representations (and therefore multicasts of those
services) will occur during the same time period for services S2,
S4 and S5.
[0096] FIG. 15 shows five media content services S1-S5 with the
starts of bursts 305 staggered in time with respect to one another.
FIG. 15 shows an advantageous embodiment where, for any pair of the
plurality of media content services S1-S5, window periods 303 of
the services do not overlap in time. Starts of bursts 305 of media
content service S2 are offset by a period 301 from starts of bursts
of media content service S1 by a period 301. By setting period 301
to be greater than, or equal to, the window period 303, this
results in no overlap between the window periods 303 of media
content services S1 and S2. This relationship applies to all of the
media content services S1-S5, such that, for any pair of the
plurality of media content services S1-S5, the window periods 303
of the services do not overlap. This is the most efficient scenario
in terms of bandwidth utilisation.
[0097] FIG. 15 shows an advantageous embodiment where the plurality
of media content services S1-S5 are of equal burst duration 302 and
the starts of bursts 305 of any pair of the plurality of media
content services S1-S5 are staggered in time by a time period which
is less than, or equal to, the burst duration 302. For illustrative
purposes the media content services S1-S5 in this example all have
the same window period 303, but there can be different values of
window period 303 for services S1-S5. Although bursts of media
content services S1-S5 are shown of equal duration, there can be
different values of burst duration for services S1-55.
[0098] Even though individual media content services may have
different characteristics in practice the principles and advantages
of the embodiments still apply in that starts of bursts and window
periods are distributed as evenly as possible to ensure optimal
network bandwidth utilisation.
[0099] The process of a client device changing between receiving a
first media content service and receiving a second media content
service will be called a channel change. In FIG. 15, the starts of
bursts of any pair of the plurality of media content services S1-S5
are staggered in time by a period of time which is less than the
burst duration 302. A client device can send signalling to switch
between different media services at any time.
[0100] FIG. 16 shows a similar plurality of media content services
S1-S5 as FIG. 15. FIG. 16 shows each of the plurality of media
content services in more detail. Each of the plurality of media
content services S1-S5 comprises multiple representations. The
representations of a media content service differ in bit rate from
one another. FIG. 16 shows two representations per service S1-S5,
but the number of representations per service can be any value
>1. The number of representations per service can differ between
services, e.g. service S1 can have two representations, service S2
can have four representations, and so on. The bursts 305 of the
plurality of media content service representations of a respective
media content service are aligned in time. So, the representations
of service S1 are aligned in time, with starts of bursts aligned in
time. Similarly, the representations of service S2 are aligned in
time, and so on. This allows client devices to switch between
representations of a service in a seamless manner, as previously
described. However, the bursts of different services S1-S5 are
offset in time from one another. This reduces the overall bandwidth
required of network resources, and reduces the number of
simultaneous multicast joining/leaving operations at any point in
time. FIG. 16 shows a window period 303 between bursts 305. Starts
of bursts 305 of services Si and S2 are offset by a period of time
301. Advantageously, period 301 is greater than, or equal to, the
window period 303. Any of the features described above in respect
of media content representations can apply.
[0101] The transmission relationship shown in FIGS. 15 and 16 can
be determined by a distribution node (e.g. an encoder or
transcoder) or by a content source. The distribution node can be
implemented as shown in FIGS. 8 and 9. The distribution node may
receive a single feed of a media content service and generate the
plurality of representations per media content service.
Alternatively, the distribution node may receive a plurality of
representations per media content service which have been generated
by another node, such as a source encoder.
[0102] The relationship between media content services (and
representations) described above, and shown in FIG. 16, has an
advantage that the bandwidth and network resources needed to handle
signalling are reduced because, at any point in time, signalling to
switch between representations of a media content service is
occurring for a reduced number of the media content services. In
FIG. 16, at any point in time, signalling to switch between
representations of a media content service is occurring for only
one of the media content services. This allows the routers and
switches of the distribution network to be dimensioned to handle a
reduced amount of signalling compared to a transmission
relationship with synchronised window periods.
[0103] FIG. 17 shows another possible timing scheme for the
transmission of a plurality of media content services. The bursts
305 of services S1 and S2 are of different duration to the bursts
305 of services S3 and S4. Advantageously the services S1-S4 are
transmitted such that starts of bursts 305 are offset for the
plurality of services S1-S4. At any point in time, only two of the
media content services S1-S4 simultaneously have a window period,
thereby reducing the periods of time during which clients devices
will be signalling to join and leave multicasts. In FIG. 17, bursts
305 and window periods 303 are of equal duration. Alternatively,
the bursts 305 can be of longer duration than window periods, as
shown in FIGS. 15 and 16.
[0104] FIG. 18 shows a method of processing media content service
data which can be performed by a node in the distribution network
60. Step 341 comprises dividing each of the plurality of media
content services into segments. Step 342 comprises transmitting the
segments of each of the plurality of media content services as a
sequence of bursts. There is a window period between successive
bursts during which media content is not transmitted. Each of the
media content services has a respective bit rate and the
transmitting comprises transmitting each of the segments at a
higher bit rate to create the window periods between successive
bursts. Starts of bursts of the plurality of media content services
are staggered in time with respect to one another.
[0105] FIG. 19 shows a method of processing media content service
data which can be performed by a node in the distribution network
60. The method is similar to FIG. 17, but each of the media content
services comprises a set of representations, such as those shown in
FIG. 16. Step 351 comprises receiving or generating a plurality of
media content service representations for at least one of the media
content services, each of the media content representations having
a different bit rate. Step 352 comprises dividing each of the media
content service representations into segments. The segments of the
plurality of media content service representations of a respective
media content service are aligned in time. Step 353 comprises
transmitting the segments of each of the plurality of media content
service representations as a sequence of bursts. Bursts of the
plurality of media content service representations of a respective
media content service are aligned in time. There is a window period
between successive bursts during which media content is not
transmitted. Each of the media content services has a respective
bit rate and the transmitting comprises transmitting each of the
segments at a higher bit rate to create the window periods between
successive bursts. Starts of bursts of the plurality of media
content services are staggered in time with respect to one another.
Advantageously, each of the media content service representations
is transmitted as a multicast.
[0106] FIG. 20 shows an exemplary processing apparatus 200 which
may be implemented as any form of a computing and/or electronic
device, and in which embodiments of the system and methods
described above may be implemented. Processing apparatus 200 can be
provided at one of the distribution network nodes, or at a
subscriber apparatus 41. Processing apparatus may implement the
method shown in any of FIGS. 5, 18 and 19. Processing apparatus 200
comprises one or more processors 201 which may be microprocessors,
controllers or any other suitable type of processors for executing
instructions to control the operation of the device. The processor
201 is connected to other components of the device via one or more
buses 206. Processor-executable instructions 203 may be provided
using any computer-readable media, such as memory 202. The
processor-executable instructions 203 can comprise instructions for
implementing the functionality of the described methods. The memory
202 is of any suitable type such as read-only memory (ROM), random
access memory (RAM), a storage device of any type such as a
magnetic or optical storage device. Additional memory 204 can be
provided to store data 205 used by the processor 201. The
processing apparatus 200 comprises one or more network interfaces
208 for interfacing with other network entities.
[0107] Modifications and other embodiments of the disclosed
invention will come to mind to one skilled in the art having the
benefit of the teachings presented in the foregoing descriptions
and the associated drawings. Therefore, it is to be understood that
the invention is not to be limited to the specific embodiments
disclosed and that modifications and other embodiments are intended
to be included within the scope of this disclosure. Although
specific terms may be employed herein, they are used in a generic
and descriptive sense only and not for purposes of limitation.
* * * * *