U.S. patent application number 11/928042 was filed with the patent office on 2008-02-28 for method and system for fault tolerant media streaming over the internet.
This patent application is currently assigned to Akamai Technologies, Inc.. Invention is credited to F. Thomson Leighton, Daniel M. Lewin, Bruce Maggs, David Shaw.
Application Number | 20080052404 11/928042 |
Document ID | / |
Family ID | 23900461 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080052404 |
Kind Code |
A1 |
Leighton; F. Thomson ; et
al. |
February 28, 2008 |
Method and system for fault tolerant media streaming over the
Internet
Abstract
A replication process provides fault tolerance for a continuous
media stream in a computer network. In one embodiment, the original
or source signal is sent to several splitters which, in turn, each
make copies of the signal and send the copies into a second layer
of devices, which are referred to as "concentrators." A given
concentrator receives as input one or more copies of the source
signal. In a preferred embodiment, a given concentrator receives
two copies of the source signal from at least two different
splitters. The concentrators process the incoming streaming signal
copies, for example, by merging them into a single or composite
copy of the original source signal according to a given processing
algorithm. The output of a given concentrator may then be fed into
a splitter, with the process then being repeated if desired to make
an arbitrary large number of copies of the signal. At the end of
the replication process, the output of a splitter or a concentrator
is fed directly or indirectly to an end user. The replication
process is fault-tolerant, and thus the end user's signal is not
interrupted regardless of signal or equipment problems within the
distribution mechanism.
Inventors: |
Leighton; F. Thomson;
(Newtonville, MA) ; Lewin; Daniel M.; (Cambridge,
MA) ; Shaw; David; (Cambridge, MA) ; Maggs;
Bruce; (Cambridge, MA) |
Correspondence
Address: |
LAW OFFICE OF DAVID H. JUDSON
15950 DALLAS PARKWAY
SUITE 225
DALLAS
TX
75248
US
|
Assignee: |
Akamai Technologies, Inc.
Cambridge
MA
|
Family ID: |
23900461 |
Appl. No.: |
11/928042 |
Filed: |
October 30, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10457266 |
Jun 9, 2003 |
7296082 |
|
|
11928042 |
Oct 30, 2007 |
|
|
|
09478571 |
Jan 6, 2000 |
6665726 |
|
|
10457266 |
Jun 9, 2003 |
|
|
|
Current U.S.
Class: |
709/231 |
Current CPC
Class: |
H04L 65/80 20130101;
H04L 65/607 20130101; H04N 21/26616 20130101; H04L 29/06 20130101;
H04L 65/608 20130101; H04L 29/06027 20130101; H04L 65/4092
20130101; H04L 65/605 20130101 |
Class at
Publication: |
709/231 |
International
Class: |
G06F 15/16 20060101
G06F015/16 |
Claims
1. A method of fault tolerant delivery of live media content, the
content being available in a given media format as a stream of data
packets, comprising: receiving the stream at each of one or more
data centers; from at least one data center, outputting a copy of
each packet in the stream to a set of remote server regions,
wherein a remove server region comprises a set of one or more media
servers associated with the given media format; at a remote server
region, feeding the stream to each of the set of one or more media
servers associated with the given media format so that each of the
set of one or more media servers in the remote server region is
available to provide the stream of data packets; within the remote
server region, at each of the one or more media servers in the set
of media servers, receiving the stream of data packets; and in
response to each end user request that is directed, via a content
delivery network (CDN) domain name server, to one of the set of
media servers in the remote server region that has received the
stream of data packets, outputting the stream of data packets from
a given media server in the remote server region.
2. The method as described in claim 1 wherein data packets are
delivered to each server region via a non-streaming media protocol
and the stream of data packets is output from the given media
server over a streaming protocol.
3. The method as described in claim 2 wherein the streaming
protocol is RTSP.
4. The method as described in claim 2 wherein the non-streaming
media protocol is UDP.
5. The method as described in claim 1 further including the step of
receiving, at a remote server region, two or more copies of the
stream of data packets, with each copy being received from one of
the set of multiple delivery sources.
6. The method as described in claim 1 wherein the stream is
received from an encoder.
Description
[0001] This application is a continuation of prior application Ser.
No. 10.457,266, filed Jun. 9, 2003, which application was a
continuation of Ser. No. 09/478,571, filed Jan. 6, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates generally to digital signal
transmission over a computer network and, in particular, to a
method and system for streaming content over the Internet in a
fault tolerant manner.
[0004] 2. Description of the Related Art
[0005] Most Internet users do not have fast enough access to the
Internet to download large multimedia files quickly. Streaming is a
technique for delivering web-based video, audio and multimedia
files so that these files can be processed as a steady and
continuous stream at the requesting client, typically using a
browser plug-in, such as Microsoft NetPlayer, Apple QuickTime, Real
Networks RealSystem G2, or the like. Streaming video, for example,
is an online video distribution mechanism that provides audio and
video to Internet users, without the users having to wait while
content completely downloads to their hard drives. Through caching,
content is played as it is received, and buffering mechanisms
ensure that content is played smoothly. Theoretically, streaming
video plays to the end user, or viewer, as an immediate and ongoing
broadcast.
[0006] From a network perspective, traditional approaches to
streaming Internet content involve transmitting a streaming signal
from a source to a device known as a splitter (or repeater,
reflector or mirror), which, in turn, replicates the source signal
into multiple signals. Each of the multiple signals is the same,
and each is sent on to a different destination. By cascading
splitters in a tree-like fashion, a single source stream can be
replicated into thousands or more identical copies. In this manner,
a large number of viewers on the Internet can receive the same
streaming signal simultaneously.
[0007] A critical problem with existing streaming methods of this
type is that they are not fault tolerant. FIG. 1 illustrates why
this is the case. In this example, a source signal (A) is sent to a
splitter (B), which then sends copies of the signal to ten
splitters (C1, . . . , C10). Each of the second level splitters
then sends a copy of the signal to five end customers (D1, . . . ,
D50). Thus, for example, splitter C1 sends a copy to end users
D1-D5, splitter C2 sends a copy to end users D6-D10, and so forth.
If communications at a given splitter fail, however, certain users
are unable to receive the original signal. In the network of FIG.
1, this would be the case with respect to users D6-D10 if C2 fails.
To overcome this problem, it is also known in the art to enable end
users to detect they are no longer receiving the streaming signal
and to enable such users to attempt to contact an alternative
splitter (e.g., C3) in an effort to get another copy of the signal.
Such approaches, however, can result in an interruption of the
signal and are expensive to implement.
[0008] Thus, there remains a need in the art to provide improved
streaming techniques that are fault tolerant. The present invention
solves this important problem.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention provides a replication process to
provide fault tolerance for a streaming signal in a computer
network. In one embodiment, the original or source signal is sent
to several splitters which, in turn, each make copies of the signal
and send the copies into a second layer of devices, which are
referred to as "concentrators." A given concentrator receives as
input one or more copies of the source signal. In a preferred
embodiment, a given concentrator receives two copies of the source
signal from at least two different splitters. The concentrators
process the incoming streaming signal copies, for example, by
merging them into a single or composite copy of the original source
signal according to a given processing algorithm. Thus, preferably
a given concentrator receives streams from multiple sources,
removes duplicate packets, and then outputs a single stream. The
output of a given concentrator may then be fed into a splitter,
with the process then being repeated if desired to make an
arbitrary large number of copies of the signal. At the end of the
replication process, the output of a splitter or a concentrator is
fed directly or indirectly to an end user. The replication process
is fault-tolerant, and thus the end user's signal is not
interrupted regardless of signal or equipment problems within the
distribution mechanism.
[0010] One type of processing algorithm that is implemented at a
concentrator simply transmits the first copy of each packet in the
signal stream. Copies of packets that have already been transmitted
are simply discarded. This algorithm may be implemented by
maintaining a data array f(i) that has a first value (e.g., "1") if
packet i in the stream has been forwarded and f(i) that has a
second value (e.g., "0") otherwise. When a copy of packet i is
received from one of the incoming streams, it is forwarded if and
only if f(i) equals the second value. This technique is
advantageous because a complete stream can be reconstructed from
two or more partial streams. Thus, as long as the incoming copies
of the stream collectively contain all the packets of the original
stream, the concentrator produces a copy of the original
stream.
[0011] Another type of processing algorithm that may be implemented
at a concentrator uses a buffering technique. In this approach, a
buffer of a given size is kept for each input stream to create an
n-dimensional array, where n is the number of input streams. At a
given cycle rate, the concentrator transmits a smallest index
packet (namely, a packet that is earliest in the stream sequence)
contained in any of the stream buffers. As each packet is
transmitted, the data in the array is updated so that future copies
of the same packet can be discarded. This protocol enables the
concentrator to reorder the packets in a stream so that they are
output in a correct order.
[0012] One or more concentrators as described above enable fault
tolerant media streaming over a computer network such as the
Internet, an intranet, a virtual private network, or the like.
[0013] The foregoing has outlined some of the more pertinent
objects and features of the present invention. These objects should
be construed to be merely illustrative of some of the more
prominent features and applications of the invention. Many other
beneficial results can be obtained by applying the disclosed
invention in a different manner or modifying the invention as will
be described. Accordingly, other objects and a fuller understanding
of the invention may be had by referring to the following Detailed
Description of the Preferred Embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a more complete understanding of the present invention
and the advantages thereof, reference should be made to the
following Detailed Description taken in connection with the
accompanying drawings in which:
[0015] FIG. 1 is a simplified diagram of a known streaming
architecture in which a plurality of splitters is used to transmit
the source signal to a plurality of end users or viewers;
[0016] FIG. 2 is a simplified diagram illustrative the inventive
use of concentrators according to the teachings of the present
invention;
[0017] FIG. 3 is a flowchart of a first type of processing routine
that may be used in a concentrator;
[0018] FIG. 4 is a flowchart of a second type of processing routine
that may be used in a concentrator;
[0019] FIG. 5 is a block diagram of a concentrator used in the
present invention;
[0020] FIG. 6 is a block diagram of a client-server computing
environment in which the present invention may be implemented;
and
[0021] FIG. 7 is a block diagram illustrating an implementation of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Streaming media is a type of Internet content that has the
important characteristic of being able to play back while still in
the process of being downloaded. A client can play the first packet
of the stream, decompress the second, while receiving the third.
Thus, the user can start enjoying the multimedia without waiting to
the end of transmission. Streaming is very useful for delivering
media because media files tend to be large, particularly as the
duration of the programming increases. To view a media file that is
not streamed, users must first download the file to a local hard
disk--which may take minutes or even hours--and then open the file
with player software that is compatible with the file format. To
view streaming media, the user's browser opens player software,
which buffers the file for a few seconds and then plays the file
while simultaneously downloading it. Unlike software downloads,
streaming media files are not stored locally on users' hard disks.
Once the bits representing content are used, the player discards
them.
[0023] Streaming media quality varies widely according to the type
of media being delivered, the speed of the user's Internet
connection, network conditions, the bit rate at which the content
is encoded, and the format used. These last two concepts are
explained in more detail below. In general, streaming audio can be
FM quality, but streaming video is poor by TV standards, with
smaller screens, lower resolution, and fewer frames per second. The
source for streaming media can be just about any form of media,
including VHS or Beta tapes, audio cassettes, DAT, MPEG video, MP3
audio, AVI, and the like. Prior to streaming the content, the
content must first be encoded, a process which accomplishes four
things: conversion of the content from analog to digital form, if
necessary; creation of a file in the format recognized by the
streaming media server and player; compression of the file to
maximize the richness of the content that can be delivered in
real-time given limited bandwidth; and, establishing the bit rate
at which the media is to be delivered. Streaming media uses lossy
compression, which means that after decompression on the client
end, some portions of the content are not retained. For example,
compression may reduce a VHS video clip with 30 frames per second
to just 15 fps. Typically, media must be encoded at a specific bit
rate, such as 28 kbps, 56 kbps, 100 kbps, or the like. Content
owners typically choose to encode media at multiple rates, so that
users with fast connections get as good an experience as possible,
but users with slow connections can also access the content.
Obviously, the lower the encoding rate, the more original content
must be discarded when compressing.
[0024] Non-streaming content is standards-based in the sense that
the server and client software developed by different
vendors--Apache, Microsoft Internet Explorer, Netscape
Communicator, and the like--generally work well together. Streaming
media, however, usually relies on proprietary server and client
software. The server, client, production and encoding tools
developed by a streaming software vendor are collectively referred
to as a format. Streaming media encoded in a particular format must
be served by that format's media server and replayed by that
format's client. Streaming media clients are often called players,
and typically they exist as plug-ins to Web browsers. Streaming
media clients are also often capable of playing standards-based
non-streaming media files, such as WAV or AVI.
[0025] The three major streaming media formats in use today are:
RealNetworks RealSystem G2, Microsoft Windows Media Technologies
("WMT"), and Apple QuickTime. RealSystem G2 handles all media types
including audio, video, animation, still images and text, but it
does not support HTML. RealSystem G2 supports SMIL, an XML-based
language that allows the content provider to time and position
media within the player window. To deliver the media in real time
Real uses RTSP. To stream in WMT's Advanced Streaming Format,
content providers must have Microsoft NT 4 Server installed. WMT
does not support SMIL or RTSP but has its own protocol that it
calls HTML+Time. Apple QuickTime recently has added the capability
to serve streaming media. QuickTime can support a number of formats
including VR, 3D, Flash, and MP3. QuickTime Streaming uses RTSP to
deliver the movies in realtime, and a dedicated media server is
required.
[0026] By way of further background, RTSP, the Real Time Streaming
Protocol, is a client-server multimedia presentation protocol to
enable controlled delivery of streamed multimedia data over IP
network. It provides "VCR-style" remote control functionality for
audio and video streams, like pause, fast forward, reverse, and
absolute positioning. Sources of data include both live data feeds
and stored clips. RTSP is an application-level protocol designed to
work with lower-level protocols like RTP (Realtime Transport
Protocol) and RSVP (Resource Reservation Protocol) to provide a
complete streaming service over the Internet. It provides means for
choosing delivery channels (such as UDP, multicast UDP and TCP),
and delivery mechanisms based upon RTP. RTSP establishes and
controls streams of continuous audio and video media between the
media servers and the clients. In RTSP, each presentation and media
stream is identified by an RTSP URL. The overall presentation and
the properties of the media are defined in a presentation
description file, which may include the encoding, language, RTSP
URLs, destination address, port, and other parameters. The
presentation description file can be obtained by the client using
HTTP, email or other means. RTSP differs from HTTP for several
reasons. First, while HTTP is a stateless protocol, an RTSP server
has to maintain "session states" in order to correlate RTSP
requests with a stream. Second, HTTP is basically an asymmetric
protocol where the client issues requests and the server responds,
but in RTSP both the media server and the client can issue
requests. For example the server can issue a request to set playing
back parameters of a stream.
[0027] The transport layer of non-streaming content uses the
Transmission Control Protocol, or TCP. This is a
connection-oriented protocol, which means a connection between
server and client is established and maintained until the content
has been completely received. One reason for the connection is that
the client can report if any IP packets are not received, which are
then retransmitted by the server. The result is that a file
successfully transmitted over TCP, a logo for example, is always
identical to its source--although the time required for
transmission may vary widely depending on infrastructure.
[0028] By contrast, the transport layer for streaming media uses
User Datagram Protocol, or UDP. UDP is a connectionless protocol,
under which IP packets are sent from the server to the client
without establishing a connection. This protocol enables streaming
media's real-time nature: no need to wait to resend dropped
packets. But it also means that the content quality may be degraded
markedly between server and client, or that two different users may
have a much different experience.
[0029] The present invention is designed to be used with any
streaming media source, encoding scheme, media format, and
streaming (or other transport) protocol.
[0030] Referring now to FIG. 2, a packet-switched network 200 in
which the present invention is implemented comprises a signal
source A, a set of splitters B1-Bn, and a set of end users D1-Dn.
According to the invention, the network also includes a set of
so-called "concentrators" C1-Cn that facilitate an inventive signal
replication process. This process ensures that each end user will
always receive a copy of the source signal irrespective of
interruptions in the transmission, e.g., due to equipment, device
or communication failures, that occur within other elements of the
distribution system.
[0031] Preferably, concentrators C are positioned within the
network in a physical and/or logical layer located between the
splitters B and the end users D. The physical configuration
illustrated in FIG. 2, of course, is merely exemplary. An end user,
of course, is typically a client computer that includes a browser
or other graphics viewer having a plug-in or native support for
streaming content. In a preferred embodiment, a concentrator C is a
software program, namely, a set of computer instructions that
comprise one or more processes, executable within a processor. As
illustrated in FIG. 2, each concentrator C receives as input one or
more copies of the source signal data stream. In a preferred
embodiment of the invention, each concentrator C receives a copy of
the source signal data stream from at least two (2) different
splitters B. Thus, for example, in this embodiment, the original
signal is sent to several splitters B1, . . . , B5. These splitters
make copies of the signal and send them to the concentrators C1, .
. . , C20. Splitter B1 sends a copy of the signal it received from
source A to each of the concentrators C1, . . . , C8. Splitter B2
sends a copy of the signal it received from source A to each of the
concentrators C9, . . . , C16. Splitter B3 sends a copy to
concentrators C17, . . . , C20 and C1, . . . , C4, whereas B4 sends
copies to C5, . . . , C12, and B5 sends copies to C13, . . . , C20.
Again, these examples are not to be taken to limit the present
invention in any way. In each case, however, it can be seen that
every concentrator C receives a copy of the source signal data
stream from precisely two splitters. Stated another way, each
concentrator receives two streams, UDP1 and UDP2, representing
copies of the original source stream.
[0032] Generally, the function of a concentrator it to process the
incoming streams and to merge them into a single or composite copy
of the source signal data stream that is then output from the
concentrator. A concentrator removes duplicate packets and
preferably outputs a single stream feed. This processing is quite
advantageous. In particular, given several copies of a stream, even
if they are all lossy, a single pristine stream can be generated
from the remnants of the duplicate streams. The technique is very
robust and can take a large number of failures before end user
experience is impaired.
[0033] The processing of the data streams may be accomplished in a
number of different ways. FIG. 3, for example, is a flowchart
illustrating a first embodiment of the processing routine wherein
the concentrator transmits only the first copy of each packet in
the stream. Copies of packets that have already been transmitted
are simply discarded. FIG. 4 illustrates a second embodiment of the
processing routine wherein multiple copies of the streams are
buffered to enable out-of-order packets to be reordered as the
output is generated. Each of the embodiments will now be described
in detail.
[0034] Referring now to FIG. 3, a first embodiment of the
processing routine utilizes an array f(i) for the source signal. An
element in the data array has a given first value, e.g., 1, if
packet i in the stream has been forwarded from the concentrator and
a second value, e.g., 0, otherwise. The routine begins at step 300.
At step 302, an instance of the processing routine is spawned,
typically when the first packet of the stream arrives at the
concentrator. At step 304, the array is initialized. The processing
routine then continues at step 306 to test whether a packet i has
been received from one of the incoming streams. If not, the routine
cycles. If, however, the outcome of the test at step 306 is
positive, which indicates that the packet has been received, a test
is performed at step 308 to determine whether f(i)=0. If so
(because this is the first occurrence of the packet i), the routine
continues at step 310 to forward the packet from the concentrator
without delay. At step 312, the routine updates the array by
setting the value of the packet i in the array equal to 0. Control
then returns to step 306. If, however, the outcome of the test at
step 308 indicates that f(i) is not equal to 0, then the routine
continues at step 314 to discard the packet (since it has already
been forwarded).
[0035] Thus, in effect, the processing routine parses packets as
they arrive at the concentrator. If the parser has already seen the
stream packet, the packet is discarded; otherwise, it is
forwarded.
[0036] The processing routine of FIG. 3 is advantageous in that it
is simple to implement and does not introduce any delay into the
streams (which, for example, might be caused by waiting for a
particular copy of a packet to arrive). This routine also has the
desirable feature that a complete stream can be reconstructed from
two or more partial streams. Thus, as long as the incoming copies
of the stream collectively contain all the packets in the original
stream, then the concentrator will produce a copy of the original
stream.
[0037] As an example, and with reference to FIG. 2 again, if one of
the splitters (e.g., B1) ceases to function, then each of
concentrators C1, . . . C4 will still receive the stream from
splitter B3 and each of concentrators C5, . . . , C8 will still
receive the stream from splitter B4. There is never an interruption
of the signal transmitted by any of the concentrators in this
illustrative example. This property is preserved irrespective of
which splitter is not functioning. Indeed, even if two splitters
(e.g., B1 and B3) suffer packet loss, it is still possible for each
of the concentrators C1, . . . C4 to reconstruct the original
signal using the process described above (provided that the packet
loss is less than 50%).
[0038] Referring now to FIG. 4, an alternate embodiment is shown
wherein each incoming stream at a concentrator has a buffer
associated therewith. By buffering stream packets, the concentrator
may reorder the packets in the stream before output. The routine
begins at step 400. At step 402, the buffers are initialized. The
routine then continues at step 404 to test whether a given cycle
has elapsed. If not, the routine continues at step 406 (for each
stream) to test whether a given incoming packet (for the stream)
has already been forwarded. If the outcome of the test at step 406
is positive, the routine discards the packet at step 408. If the
given incoming packet has not been forwarded, the packet is
buffered at step 410. Control then returns to step 404. Using the
buffering scheme, for example, packets from stream UDP1 are
buffered in a first buffer, packets from stream UDP2 are buffered
in a second buffer, and so on. When the outcome of the test at step
404 indicates that the given cycle has elapsed, control branches to
step 412 to identify the packet that is the earliest in the stream
sequence. At step 414, a test is performed to determine whether
this packet is out of sequence. If so, the routine reorders the
packets as necessary at step 416. The resulting stream is then
output from the concentrator at step 418. At step 420, the array is
updated to reflect the packets that have been forwarded. Step 418
is also reached if there is a negative outcome of the test at step
414.
[0039] Thus, in the routine of FIG. 4, a buffer of a given size is
kept for each input stream copy. At each cycle, the concentrator
transmits the smallest index packet contained in any of the
buffers. As each packet is transmitted, the data in the array is
updated so that future copies of the same packet can be discarded
when they arrive at the concentrator. As can be seen, the protocol
of FIG. 4 is similar to the routine of FIG. 3 except that it has
the additional desired feature that it can reorder the packets in
the stream so that they are output in the correct order. The larger
the buffer size, the more likely it is that out-of-order packets
can be output in order. In this way, packets that are slowed down
in the network have the opportunity to catch up at the buffer.
[0040] Regardless of which technique (FIG. 3 or FIG. 4) is used at
a given concentrator C, the output of a given concentrator can then
be fed back to a splitter or to an end user directly. When the
concentrator is output to a splitter, the process can be repeated
to make an arbitrarily large number of copies of the source signal
data stream. At the end of the replication process, the output of a
splitter or concentrator (or some other device) is fed directly to
a viewer. The resulting replication process is completely
fault-tolerant. In particular, no matter what signal is destroyed,
the end user's signal is not interrupted.
[0041] The number of signals input to each concentrator determines
the number of faulty streams that can be tolerated by the
distribution system. For example, if every concentrator receives
the signal from at least k different splitters, then the system can
tolerate faults in any subset of k-1 signals without compromising
the signal received by any end user. If the faults in signals (or
system components) are random, then the system can tolerate F
faults before any end user's signal is interrupted, where F is
about N{1-1/k} and N is the number of components in the system. If
the packet loss rate being experienced on each stream is p, then
the loss rate, after concentration, is pk.times.the number of
streams.
[0042] In a preferred embodiment, it is desirable to input two (2)
input streams to a given concentrator. The cost of more streams, of
course, is more network bandwidth for the distribution mechanism.
Where multiple input streams are supplied to a concentrator (or
output from a splitter), a variant of the present invention is to
incorporate given coding schemes within the splitters/concentrators
to recover some of the bandwidth used to transmit multiple data
streams. In this variant, as a stream is output from a given device
(e.g., a splitter), it is encoded using an encoding routine. As the
stream enters the concentrator in the underlying layer, it is
decoded and processed in the manner described above. When coding
techniques are used, then the copies of the data stream output from
the splitters need not be identical; rather, the copies may vary as
a result of the encoding algorithm used within a given device.
[0043] In an illustrative embodiment, a useful encoding scheme is
the Rabin Information Dispersal Algorithm. Information dispersal
involves the breaking-up of packets into a collection of subpackets
that are routed in a greedylike fashion to their common destination
along edge-disjoint paths. The advantage of information dispersal
is that the dispersal of large packets into many small subpackets
tends to results in very balanced communication loads on the edges
of a network. As a consequence, the maximum congestion in the
network is likely to be very low, and there is a good chance that
packets will never be delayed at all. In addition, if the contents
of a packet are encoded into a collection of subpackets in a
redundant fashion, an information dispersal algorithm becomes more
fault tolerant as only a fraction of the subpackets have to reach
the destination for the original packet to be reconstructed.
Further information about the Information Dispersal Algorithm may
be found in the following reference, Leighton, Introduction To
Parallel Algorithms and Architectures: Arrays, Trees, Hybercubes,
Morgan Kaufmann (1992), Section 3.4.8, which is incorporated herein
by reference. Thus, in an illustrative embodiment, the Rabin
Information Dispersal Algorithm is implemented within a given
splitter and a given concentrator.
[0044] As noted above, a concentrator for use in the present
invention is a software program executable on a computer. FIG. 5
illustrates a representative concentrator 500 comprising a manager
routine 502, an array manager process 504, and a set of stream
concentration processes 506a-n. One or more coding/decoding
routines 508 may be provided as described in the variant above. In
operation, the manager routine 502 is initialized upon startup of
the concentrator. As an input data stream is received, the manager
routine 502 launches an instance of the stream concentration
process 506, which manages the merging of the individual data
streams into the stream that is then output from the concentrator.
The array manager process is invoked by the manager routine 502 to
establish an array (or other data structure or equivalent work
area) for use by a given stream concentration process 506. By using
multiple stream concentration processes, a given concentrator may
be used to concentrate different content streams under the control
of the manager routine.
[0045] The fault-tolerant distribution mechanism of the present
invention may be implemented within a conventional client-server
distributed computing environment. FIG. 6 illustrates a
conventional client-server environment in which the streaming
framework may be implemented. In this example, a plurality of
Internet client machines 610 are connectable to a computer network
service provider 612 via a network such as a telephone network 614.
The service provider 612 interfaces the client machines 610 to the
remainder of the network 618, which may include a plurality of web
content server machines 620. Network 618 typically includes other
servers (not shown) for control of domain name resolution, routing
and other control functions. A client machine typically includes a
suite of known Internet tools. Various known Internet protocols are
used for these services.
[0046] A given client machine and the server may communicate over
the public Internet, an intranet, or any other computer network. If
desired, given communications may take place over a secure
connection. Thus, for example, a client may communication with the
server using a network security protocol, such as Netscape's Secure
Socket Layer (SSL) protocol or the like.
[0047] A representative client is a personal computer, notebook
computer, Internet appliance or pervasive computing device (e.g., a
PDA or palm computer) that is x86-, Pentium-, PowerPC.RTM.- or
RISC-based. The client includes an operating system such as
Microsoft Windows '98, Microsoft NT, Windows CE or PalmOS. The
client includes a suite of Internet tools including a Web browser,
such as Netscape Navigator or Microsoft Internet Explorer, that has
a Java Virtual Machine (JVM) and support for application plug-ins
or helper applications.
[0048] A representative web server comprises a processor 622, an
operating system 624 (e.g., Linux, Windows NT, Unix, or the like)
and a web server program 626. OS 624 and web server program 626 are
supported in system memory 623 (e.g., RAM). Of course, any
convenient server platform (e.g., Apache, WebSphere, or the like)
may be supported. The server may include an application programming
interface 628 (API) that provides extensions to enable application
developers to extend and/or customize the core functionality
thereof through software programs including plug-ins, CGI programs,
servlets, and the like.
[0049] A representative concentrator is a computer or computer
platform having an operating system and support for network
connectivity. Thus, for example, a representative concentrator
comprises a computer running Windows NT (Intel and DEC Alpha), IBM
AIX, HP-UX, Sun Solaris (SPARC and Intel Edition), Novell NetWare
or Windows '98.
[0050] FIG. 7 illustrates an implementation of the present
invention. The system 700 comprises a pair of relay servers 702 and
704 residing, for example, at a streaming video production facility
706. These servers are equipped, for example, with two (2) network
cards each, one set of which are wired onto a common network with
encoder machines 708, and the other set of which is connected to
the Internet 710. The encoder machines 708 encode the video and
audio data and send the encoded packets to a broadcast address of
the network they share with the relay servers 702 and 704. The
relay servers pick up the packets and re-send them out, for
example, over two dedicated T-1 lines to two different data centers
712 and 714. From these two data centers, content fans out to two
more data centers each 716, 718, 720 and 722, thus making four
duplicates of each data packet. Each of the four data centers sends
a copy of each packet to each of a set of regions 724a-n, with each
server region 724 comprising a set of content hosting servers
726a-n. Each region includes a concentrator 728, which removes the
duplicates and feeds the single remaining stream to each server 726
in that region. Although not meant to be limiting, the server
regions may comprise part of a distributed content hosting system
such as Akamai FreeFlow.TM., which is a high-performance,
fault-tolerant web content delivery service.
[0051] As noted above, the invention may be implemented in software
executable in a processor, namely, as a set of instructions
(program code) in a code module resident in the random access
memory of the computer. Until required by the computer, the set of
instructions may be stored in another computer memory, for example,
in a hard disk drive, or in a removable memory, or downloaded via
the Internet or other computer network.
[0052] In addition, although the various methods described are
conveniently implemented in a general purpose computer selectively
activated or reconfigured by software, one of ordinary skill in the
art would also recognize that such methods may be carried out in
hardware, in firmware, or in more specialized apparatus constructed
to perform the required method steps.
* * * * *