U.S. patent application number 09/817953 was filed with the patent office on 2001-10-04 for distributed client-based data caching system.
This patent application is currently assigned to BackWeb Technologies, Ltd.. Invention is credited to Delaney, Hubert, Faigon, Ofer, Hass, Lior, Ruppin, Adi.
Application Number | 20010027479 09/817953 |
Document ID | / |
Family ID | 22604301 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010027479 |
Kind Code |
A1 |
Delaney, Hubert ; et
al. |
October 4, 2001 |
Distributed client-based data caching system
Abstract
A system and method for enabling data package distribution to be
performed by a plurality of peer clients connected to each other
through a network, such as a LAN (local area network). Each peer
client can obtain data packages from each other or from an external
server. However, each peer client preferably obtains data packages
from other peer clients, rather than obtaining data packages from
the external server.
Inventors: |
Delaney, Hubert; (Wilton,
CT) ; Ruppin, Adi; (Ramat Gan, IL) ; Hass,
Lior; (Tel Aviv, IL) ; Faigon, Ofer;
(Jerusalem, IL) |
Correspondence
Address: |
Martin C. Fliesler, Esq.
FLIESLER, DUBB, MEYER & LOVEJOY LLP
Suite 400
Four Embarcadero Center
San Francisco
CA
94111-4156
US
|
Assignee: |
BackWeb Technologies, Ltd.
|
Family ID: |
22604301 |
Appl. No.: |
09/817953 |
Filed: |
March 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09817953 |
Mar 26, 2001 |
|
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09166686 |
Oct 5, 1998 |
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Current U.S.
Class: |
709/216 ;
707/E17.12; 709/218; 709/219 |
Current CPC
Class: |
H04L 67/1091 20130101;
G06F 16/9574 20190101; G06F 16/9537 20190101; H04L 67/104 20130101;
H04L 67/288 20130101; H04L 67/51 20220501; H04L 69/329 20130101;
H04N 21/4788 20130101; H04L 67/1068 20130101; H04N 21/632 20130101;
H04L 67/56 20220501; H04L 67/568 20220501 |
Class at
Publication: |
709/216 ;
709/218; 709/219 |
International
Class: |
G06F 015/167 |
Claims
What is claimed is:
1. A method for distributing data packages across a network, the
network featuring an external server for serving at least one data
package, the external server being a dedicated server, the steps of
the method being performed by a data processor, the method
comprising the steps of: (a) providing a plurality of peer clients
attached to the network and providing a list of data packages, said
data packages being stored by each of said plurality of peer
clients, each data package of said data packages having an entry in
said list, said entry indicating a unique identifier for said data
package and a location of said data package in at least one of said
plurality of peer clients; (b) examining said list of data packages
by a first peer client to find an entry for a required data
package; and (c) if said entry for said data package is present on
said list of data packages of said first peer client, retrieving
said data package from said location at another of said plurality
of peer clients according to said entry for said data package.
2. The method of claim 1, wherein said list of data packages is
stored on the external server.
3. The method of claim 1, wherein said list of data packages is
stored on at least said first peer client.
4. The method of claim 3, wherein alternatively said entry for said
data package is absent from said list of data packages of said
first peer client, the method further comprising the steps of: (d)
sending a request message for said data package by said first peer
client to at least one other peer client; and (e) if a response
message is received by said first peer client from said at least
one other peer client, retrieving said data package from said at
least one other peer client by said first peer client.
5. The method of claim 4, the method further comprising the step
of: (f) altering said list of data packages being stored by at
least said first peer client for indicating said location of said
data package according to said response message.
6. The method of claim 5, wherein said request message and said
response message are transmitted to said plurality of peer clients
by broadcasting.
7. The method of claim 5, wherein said request message and said
response message are transmitted to said plurality of peer clients
by multicasting.
8. The method of claim 5, wherein said request message and said
response message are transmitted to said plurality of peer clients
by polling each peer client individually.
9. The method of claim 5, wherein if said response message is not
received from said at least one other peer client by said first
peer client, the method further comprises the step of: (g)
obtaining said data package by said first peer client from the
external server.
10. The method of claim 9, further comprising the step of sending a
response message by said first peer client to said at least one
other peer client substantially before said first peer client
obtains said data package from the external server.
11. The method of claim 10, wherein said list of data packages is
stored on each of said plurality of peer clients, the method
further comprising the steps of: (h) receiving said response
message from said first peer client by said at least one other peer
client; and (i) altering said list of data packages being stored by
said at least one other peer client for indicating said location of
said data package according to said response message.
12. The method of claim 10, wherein said list of data packages is
stored on each of said plurality of peer clients, the method
further comprising the steps of: (h) receiving said response
message from said first peer client by said at least one other peer
client; and (i) altering said list of data packages being stored by
said at least one other peer client for indicating said location of
said data package according to a probabilistic function.
13. The method of claim 1, wherein said probabilistic function is
performed according to a set of equations: 3 New location = { Old
location Po ( x ) = 1 / ( generation + 1 ) New location Pn ( x ) =
1 - 1 / ( generation + 1 ) wherein Pn(x) is a probability that said
new location is substituted for said old location, Po(x) is a
probability that said old location is retained, and "generation"
indicates how many times said location had been previously
changed.
14. The method of claim 10, further comprising the steps of: (h)
receiving said response message from said first peer client by said
at least one other peer client; and (i) retrieving said data
package from said first peer client by said at least one other peer
client substantially after said first peer client has obtained said
data package.
15. The method of claim 1, wherein an upper limit is predetermined
for a number of said plurality of peer clients served substantially
simultaneously by said at least one other peer client, such that if
a number of said plurality of peer clients served substantially
simultaneously by said at least one other peer client is greater
than said upper limit, the method further comprises the step of:
(d) sending a busy message from said at least one other peer client
to said first peer client.
16. The method of claim 1, wherein the external server is a Web
server, and said plurality of peer clients is a plurality of Web
browsers.
17. The method of claim 1, wherein the external server is a
BackWeb.TM. server, and said plurality of peer clients is a
plurality of BackWeb.TM. clients.
18. The method of claim 1, wherein said unique identifier for said
data package is an MD5 digest of said data package.
19. The method of claim 1, wherein the step of retrieving said data
package is performed according to a protocol based on TCP/IP.
20. The method of claim 19, wherein said protocol is HTTP.
21. The method of claim 19, wherein said protocol is FTP.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to a distributed client-based
data caching system Specifically, the system of the present
invention enables data packages to be served to a client through a
flexible, non-deterministic distributed system of peer clients
which cache the data packages, in order to maximize efficiency and
speed for serving the data package to the client.
[0002] Networks which connect two or more computers, such as the
Internet or intranets, enable client computers to obtain data
packages, such as documents, images, messages, data packages or
other types of data, from remote storage media which are not
installed on the client computer itself. Instead, these remote
storage media are managed and operated through a remote computer,
known as a server computer or simply as a "server" (in the same
vein, the client computer is also often termed only a "client").
The advantage of such a system is that the client computer can
potentially obtain data from any server on the network. The
disadvantage of the system is the requirement for sufficient
bandwidth on the network to enable data to be transmitted from the
server to the client. Furthermore, if the load is not evenly
distributed between servers on the network, one server may become
overwhelmed with requests, thereby decreasing the speed and
efficiency of retrieval. Thus, currently many networks cannot
provide rapid and efficient data retrieval due to the heavy demands
placed upon the available bandwidth.
[0003] Proxy servers are often installed to conserve bandwidth on
an Internet connection or on connections to other LANs (local area
networks). These proxy servers cache frequently accessed data,
thereby reducing the load on the main server, and distributing
demand for bandwidth more evenly across the network. Unfortunately,
such proxy servers are typically expensive to maintain.
Furthermore, proxy servers require dedicated computers to be
installed and configured. Each computer on the LAN has to be
separately configured in order to communicate with the proxy
server. Such configuration is deterministic, such that each client
must be configured to communicate with each proxy server
separately. Thus, proxy servers have many drawbacks.
[0004] A more useful solution would enable Intranets to reap the
benefits of the proxy server, without requiring dedicated machines
and without requiring any special installation or configuration.
Furthermore, such a solution would not be deterministic, such that
each client could communicate with more than one server according
to the load on each server, rather than according to the
configuration of the client itself. Unfortunately, such a solution
is not currently available.
[0005] Therefore, there is an unmet need for, and it would be
highly useful to have, a distributed client-based data caching
system which enables data to be stored and retrieved from a
plurality of peer clients, or "caching entities", yet which does
not require any special configuration or installation of separate
servers.
SUMMARY OF THE INVENTION
[0006] The present invention is of a distributed client-based data
caching system, which enables data to be served to a client through
a flexible, non-deterministic distributed system of caching
entities, in order to maximize efficiency and speed for serving the
document to the client. The caching entities are peer clients which
serve the data to each other, thereby reducing the amount of
bandwidth required to obtain data from an external server.
[0007] According to the present invention, there is provided a
method for distributing data packages across a network, the network
featuring an external server for serving at least one data package,
the external server being a dedicated server, the steps of the
method being performed by a data processor, the method comprising
the steps of: (a) providing a plurality of peer clients attached to
the network and a list of data packages being stored by each of the
plurality of peer clients, each data package on the list of data
packages having an entry, the entry indicating a unique identifier
for the data package and a location of the data package in at least
one of the plurality of peer clients; (b) examining the list of
data packages by a first peer client to find an entry for a data
package; and (c) if the entry for the data package is present on
the list of data packages of the first peer client, retrieving the
data package from the location at another of the plurality of peer
clients according to the entry for the data package.
[0008] Alternatively, the list of data packages is stored on the
external server.
[0009] According to preferred embodiments of the present invention,
the list of data packages is stored on at least the first peer
client. Preferably, if alternatively the entry for the data package
is absent from the list of data packages of the first peer client,
the method further comprises the steps of: (d) sending a request
message for the data package by the first peer client to at least
one other peer client; and (e) if a response message is received by
the first peer client from the at least one other peer client,
retrieving the data package from the at least one other peer client
by the first peer client.
[0010] Preferably, the request message and the response message are
transmitted to the plurality of peer clients by broadcasting.
Alternatively, the request message and the response message are
transmitted to the plurality of peer clients by multicasting. Also
alternatively, the request message and the response message are
transmitted to the plurality of peer clients by polling each peer
client individually.
[0011] Also alternatively and preferably, if the response message
is not received from the at least one other peer client by the
first peer client, the method further comprises the step of: (f)
obtaining the data package by the first peer client from the
external server. Preferably, the method further comprises the step
of sending a response message by the first peer client to the at
least one other peer client substantially before the first peer
client obtains the data package from the external server. More
preferably, the list of data packages is stored on each of the
plurality of peer clients, and the method further comprises the
steps of: (g) receiving the response message from the first peer
client by the at least one other peer client; and (h) altering the
list of data packages being stored by the at least one other peer
client for indicating the location of the data package according to
the response message.
[0012] Alternatively, the list of data packages is stored on each
of the plurality of peer clients, and the method further comprises
the steps of: (g) receiving the response message from the first
peer client by the at least one other peer client; and (h) altering
the list of data packages being stored by the at least one other
peer client for indicating the location of the data package
according to a probabilistic function.
[0013] Preferably, the probabilistic function is performed
according to a set of equations: 1 New location = { Old location Po
( x ) = 1 / ( generation + 1 ) New location Pn ( x ) = 1 - 1 / (
generation + 1 )
[0014] wherein Pn(x) is a probability that the new location is
substituted for the old location, Po(x) is a probability that the
old location is retained, and "generation" indicates how many times
the location had been previously changed.
[0015] Also preferably, an upper limit is predetermined for a
number of the plurality of peer clients served substantially
simultaneously by the at least one other peer client, such that if
a number of the plurality of peer clients served substantially
simultaneously by the at least one other peer client is greater
than the upper limit, the method further comprises the step of: (d)
sending a busy message from the at least one other peer client to
the first peer client.
[0016] Preferably, the external server is a Web server, and the
plurality of peer clients is a plurality of Web browsers.
[0017] Also preferably, the external servis a BackWeb.TM. server,
and the plurality of peer clients is a plurality of BackWeb.TM.
clients.
[0018] Preferably, the unique identifier for the data package is an
MD5 digest of the data package.
[0019] According to still other preferred embodiments of the
present invention, the step of retrieving the data package is
performed according to a protocol based on TCP/IP. Preferably, the
protocol is HTTP. Alternatively and preferably, the protocol is
FTP.
[0020] Hereinafter, the term "protocol based on TCP/IP" includes
any such protocol, including but not limited to the HTTP (hypertext
transfer protocol) and FTP (file transfer protocol) protocols.
[0021] Hereinafter, the term "data package" refers to any discrete,
identifiable unit of data, including but not limited to documents,
images, messages, data packages or any other type of data.
[0022] Hereinafter, the term "computing platform" refers to a
particular computer hardware system or to a particular software
operating system. Examples of such hardware systems include, but
are not limited to, personal computers (PC), Apple Macintosh.TM.
computers, mainframes, minicomputers and workstations, which are
also non-limiting examples of data processors for operating a
software application under an operating system. Examples of such
software operating systems include, but are not limited to, UNIX,
VMS, Linux, MacOS.TM., DOS, one of the Windows.TM. operating
systems by Microsoft Inc. (Seattle, Wash., USA), including Windows
NT.TM., Windows 3.x.TM. (in which "x" is a version number, such as
"Windows 3.1.TM..lambda.), Windows95.TM. and Windows98.TM..
[0023] For the present invention, a software application could be
written in a substantially suitable programming language, which
could easily be selected by one of ordinary skill in the art. The
programming language chosen should be compatible with the operating
system according to which the software application is executed.
Examples of suitable programming languages include, but are not
limited to, C, C++ and Java.
[0024] Hereinafter, the term "broadcast" may also include
"multicast" as well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0026] FIGS. 1A and 1B are schematic block diagrams of an exemplary
basic system and method according to the present invention;
[0027] FIGS. 2A-2E are schematic block diagrams of an exemplary
request/response protocol and method according to the present
invention;
[0028] FIG. 3 is a schematic block diagram of an exemplary
preferred data-flow diagram according to the present invention;
[0029] FIG. 4 is a flowchart of a method for operating the system
of the present invention with Web browsers; and
[0030] FIGS. 5A and 5B are exemplary request and response messages
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The present invention is of a distributed client-based data
caching system, which enables data to be served to a client through
a flexible, non-deterministic distributed system of caching
entities, in order to maximize efficiency and speed for serving the
data to the client. The caching entities are peer clients which
serve the data to each other, thereby reducing the amount of
bandwidth required to obtain data from an external server.
[0032] The system of the present invention enables clients to share
data packages among themselves across their local network
neighborhood, for example within a LAN, thereby eliminating the
need for a specialized proxy server. Furthermore, the network
traffic is not significantly affected, since modern network
architectures are well suited for peer-to-peer communications. Most
currently operating networks have a star topology, using switching
hubs, in which communication between two peers does not affect
simultaneous communication among other nodes on the network. Thus,
the system of the present invention overcomes the drawbacks of a
proxy server, yet does not add significant loads to the traffic on
the network itself.
[0033] For currently available client-server software applications
known in the art, whenever a client requires a data package, the
following algorithm is performed. First, the software application
attempts to locate the data package locally on the memory or on the
disk or disks of the client. Then, if the data package is not found
locally, the software application retrieves the data package from
the appropriate server.
[0034] By contrast, the operation of the system of the present
invention adds an intermediate step. For the present invention, if
the data package is not found locally, an attempt is made to
retrieve the data package from a peer client on the local network
"neighborhood" before resorting to retrieving the data package from
the server.
[0035] Thus, for the system of the present invention, every client
actually functions as a caching proxy. Once a client requires a
data package, it queries all the hosts, which are actually peer
clients, on the local network for that data package. If no
neighboring peer client has the data package, the client retrieves
the data package from the external server as usual. However, if a
neighboring client already has the required data package, the
requesting client will download this data package from the peer
client rather than from the external server.
[0036] The principles and operation of the distributed client-based
data caching system according to the present invention may be
better understood with reference to the drawings and the
accompanying description.
[0037] FIG. 1A is a schematic block diagram of an exemplary system
according to the present invention, while FIG. 1B is a flowchart of
the operation of the system of FIG. 1A. FIG. 1A shows a system 10
which includes a plurality of peer clients 12 connected by a local
network 14 of some type, for example a LAN, indicated by the
heavier line in FIG. 1A. Two peer clients 12, labeled as "peer
client 1" 20 and "peer client 2" 22, are shown for the purposes of
illustration only and without intending to be limiting in any way.
Each peer client 12 is also connected to an external server 16 of
some type by an external connection 18. Although only one external
server 16 is shown, a plurality of external servers could also be
implemented. External server 16 is a dedicated server, in the sense
that this server has a primary or at least a substantially
significant role as a server for data packages. As shown for the
purposes of illustration, external connection 18 only connects to
local network 14 at one point, although multiple such external
connections could also be implemented (not shown). In addition,
external connection 18 could also optionally connect each peer
client 12 directly to server 16 (not shown).
[0038] The operation of system 10 according to the present
invention is illustrated with reference also to FIG. 1B. In step 1,
peer client 12, such as peer client 12 looks for a data package in
the local memory or disk cache of that particular peer client 12.
If the desired data package is not found on the local disk cache,
then in step 2, peer client 12 queries any other peer client(s) 12
on local network 14 to determine whether any other peer client 12
has a particular data package. For example, peer client 20 could
query peer client 22, to determine whether peer client 22 has the
desired data package. In step 3a, if peer client 22 has the desired
data package, then peer client 20 obtains the data package from
peer client 22. Alternatively, as shown in step 3b, if peer client
22 does not have the desired data package, then peer client 20
obtains the data package from server 16 through external connection
18. Thus, every peer client 12 is also potentially a server which
is internal to local network 14, and hence could be described as an
"internal server" to distinguish peer client 12 from external
server 16.
[0039] Each peer client 12 could also be described as a "caching
entity" and the data stored by each client for serving to other
peer clients 12 as "cached data" or "cached data packages".
[0040] A number of different possible embodiments of the system of
the present invention can be implemented, of which two illustrative
embodiments are shown with reference to theFigures below. Briefly,
FIGS. 2A-2D illustrate an exemplary embodiment of the system of the
present invention for implementation with the software application
of BackWeb.TM. (BackWeb Technologies Ltd., Ramat Gan, Israel) on a
local area network (LAN). FIGS. 4 and 5A-5B illustrate an exemplary
embodiment of the system of the present invention for
implementation with a Web browser software application on the
Internet.
[0041] FIG. 2A shows an exemplary local network 24 which features a
plurality of peer clients 12 of which three are shown for the
purposes of discussion only and without intending to be limiting in
any way. For the purposes of discussion only, suppose a peer client
26, labeled "A", wishes to obtain four data packages "W", "X", "Y"
and "Z". None of these data packages are local to peer client 26,
which must therefore obtain these data packages from either another
peer client 12 as an internal server, or from an external server
(not shown). Local area network 24 features two other peer clients
12: peer client 28, labeled "B", and peer client 30, labeled "C".
Peer client 26 must therefore first communicate a request to peer
client 28 and peer client 30 to see if the desired data packages
are available at either location, and then peer client 26 must
obtain these data packages from peer client 28 or peer client 30 if
the desired data packages are available.
[0042] Preferably, two protocols are used for communication between
peer clients on a local area network (LAN), a data package-exchange
protocol and a control protocol. Specifically, the data package
exchange protocol is used to transfer data packages between peer
clients, once the desired data package has been located, and is
described in greater detail with respect to FIG. 2B below. The
control protocol enables each peer client to efficiently build and
maintain tables which describe the location of available data
packages across the local area network, by exchanging messages.
[0043] Each peer client maintains two hash-tables which contain
information about data package location: a local-data packages
table and a network-data packages table. The local-data packages
table is a hash-table of data packages which reside on the storage
medium or media of the peer client itself. The network-data
packages table is a hash-table of data packages which reside on the
storage medium or media of other clients on the local network. This
table contains the local area network address of the peer client on
which each data package is being stored. The size of this
hash-table is preferably limited in order to reduce memory
consumption. More preferably, each entry in the table has a
time-stamp, such that older entries are purged when the size of the
table exceeds the upper permissible limit.
[0044] In order to effectively identify the desired data package,
preferably each data package has a unique identifier or
"fingerprint" associated with it. More preferably, this unique
identifier is an MD5 digest of the content of the data package (for
a description of the MD5 specification, which is an industry
standard and would therefore be obvious to one of ordinary skill in
the art, see "RFC 1321" at http://ds.internic.
net/rfc/rfc1321.txt).
[0045] Once any peer client knows both the unique identifier and
the location of the data package on the local network, that client
can then proceed to download the data package. However, the peer
client may not know the location of the desired data package, in
which case the client must follow a control protocol according to
the present invention in order to determine the location of the
desired data package and to enable the client to build these hash
tables with respect to future attempts to locate a data
package.
[0046] The control protocol is used to provide each client with
knowledge about the locations of data packages across the local
network. In the preferred implementation illustrated with respect
to FIGS. 2A-2D, control messages are preferably sent and received
as broadcast or multicast packets. Local area networks such as
Ethernet networks support broadcast or multicast packets such that
all peer clients on a local area network receive the broadcast or
multicast packets. Effectively, a single packet can be sent to all
peer clients by using broadcast or multicast, thereby reducing the
amount of traffic on the network required as a result of
transmitting the request message (see for example Chapter 12,
"Broadcasting and Multicasting", of TCP/IP Illustrated Volume, by
W. Richard Stevens, Addison-Wesley, 1994). However, optionally the
system of the present invention could poll each peer client
individually with a control message for that peer client, although
this is not preferred since such individually addressed messages
would consume excessive amounts of available bandwidth. In such a
situation, preferably polling would be restricted to a certain
group of peer clients as internal servers, in order to reduce the
amount of traffic on the local area network.
[0047] For the preferred implementation in which broadcast or
multicast is used, more preferably, the decision to select either
IP multicast or broadcast is made according to the configuration
set by the network administrator for the local area network. IP
multicast is preferable in terms of load on the clients of the
local network, but may not be supported on all platforms (operating
systems). More preferably, the TTL or Time to Live may be
configured. The TTL specifies the number of routers a packet can
cross before being dropped. Configuring the TTL enables data
package sharing to be expanded across subnet boundaries.
[0048] As shown with respect to FIG. 2B, the control protocol of
the present invention preferably operates as follows. In step 1,
peer client "A" from FIG. 2A looks for a data package on the local
storage medium or media. In step 2, since the data package was not
found locally on the medium or media of peer client "A", peer
client "A" must download the data package and therefore preferably
multicasts (or alternatively broadcasts) a request message. A
request message preferably contains a protocol identifying version
number (PVN) for the control protocol of the present invention and
a list of MD5 digests of the needed data packages, as shown in FIG.
2C.
[0049] Optionally and preferably, if more than one data package is
desired, a list of requested data packages is included in the
request message rather than a single MD5 digest, in order to reduce
the total number of request messages on the network.
[0050] In step 3, the neighboring clients, shown as peer clients
"B" and "C" in FIG. 2A, receive this request message and search for
the requested data package in their local-data packages hash-table.
A peer client which does not find the data package locally does not
reply, as shown in step 4a. Otherwise, in step 4b the peer client
sends a response message, preferably after waiting a short random
time interval to determine whether another peer client will respond
first. More preferably, the peer client does not distribute the
response message if another client responded previously, in order
to reduce unnecessary traffic on the local area network. Also more
preferably, the peer client distributes the response message by
broadcast or multicast.
[0051] For example, as shown in FIG. 2A, if peer client "A"
requests a data package "W", peer client "B" would reply with the
response message, since peer client "B" has the data package stored
locally. By contrast, peer client "C" would not reply with a
response message, since peer client "C" does not have data package
"W" stored locally. On the other hand, if peer client "A" requests
a data package "X", both peer client "B" and peer client "C" could
respond. In this situation, preferably only peer client "B" or peer
client "C" would respond, depending on which peer client had the
shorter random interval for waiting before sending the response
message.
[0052] More preferably, responses are sent only for data packages
with yet unknown locations. For example, suppose client "A"
requests data packages "W", "X", "Y" and "Z". Client "B" has data
packages "W", "X" and "Y", and is the first to r, with a reply
message indicating possession of data packages "W", "X" and "Y".
Suppose another client, "C" has data packages "X", "Y" and "Z".
Since it replied after client "B", the response message from client
"C" will only indicate possession of data package "Z" because this
is the only data package with an as yet unknown location.
[0053] A response message optionally contains the identifying PVN,
the list of MD5 digests of data packages that were found and a TCP
port number, as shown in FIG. 2D. The port number identifies on
which TCP port the responding peer client is waiting for data
package requests. Alternatively, the response message optionally
contains other indicators which enable the requesting client to
retrieve one or more data packages from the responding peer.
Preferably, response messages are also be broadcast for data
packages which are currently being downloaded from an external
server, for reasons described in greater detail below.
[0054] In step 5, the peer client downloads the data package or
data packages. In principle, according to a relatively simple
embodiment of the present invention, at this stage the requesting
client either receives a reply and downloads the data packages from
the client that replied; or, if a reply is not received within a
certain period of time, proceeds to download these data packages
from an external server. If the peer client is downloading a data
package from another peer client as an internal server, the data
package-exchange protocol is used to obtain the data package. The
data package-exchange protocol is based on some appropriate
peer-to-peer communication protocol, including but not limited to
the HTTP protocol (see RFC-2068, "Hypertext Transfer
Protocol-HTTP/1.1", available from
http://ds.internic.net/rfc/rfc2068.txt as of Sep. 23, 1998).
[0055] Preferably, a more complex implementation is employed, since
such a simple implementation may cause multiple clients to fetch
the same data packages from the external server simultaneously.
This situation would arise if several peer clients need to download
the same data packages at approximately the same time, which is a
very probable scenario for push clients for which content delivery
is triggered by an external server, since none of these clients
would receive a response to its request. Instead, the other clients
would still be downloading the data package when the new client
request is broadcast, such that none of them would be ready to
serve these data packages. Thus, many or even all of the clients
would attempt to retrieve the data package from the external server
and not from another peer client, thereby increasing the amount of
traffic on the network and reducing the efficiency of operation of
the system of the present invention.
[0056] Preferably, the problem is solved by notifying other clients
when a first client is downloading the data package from the
external server, even if the process of retrieving the data package
is not yet complete. In this preferred embodiment, the first client
which requires the data package obtains the data package from the
external server. Other clients which require the data package will
then download it from the first client, even if the first client is
still in the process of retrieving the data package from the
external server. The preferred embodiment of the method of the
present invention is described in greater detail with regard to
FIG. 2E.
[0057] In step 1, the requesting client again transmits the
request, again preferably by broadcasting or multicasting, and then
waits for a response. If no response is received within a certain
period of time, in step 2 the client transmits a response message
as if replying to its own request, indicating that this client
either has the data package, or in this case, that the client is
retrieving the data package. In step 3, the client retrieves the
data package from the external server.
[0058] In step 4, other clients create an entry in their network
data packages hash table, indicating the location of the client
which will be serving the data package. Thus, preferably only a
single client accesses the external server for any given data
package.
[0059] If a request is sent for multiple data packages, but a
response is received indicating the location of only some of the
data packages at a neighboring peer client or clients, the client
first obtains these data packages from the neighboring peer client
or clients. Next, the client then transmits the response message
for the rest of the data packages, and proceeds to obtain the
remaining data package or data packages from the external server.
Thus, the client only obtains the data package or data packages
from the external server which are not available locally, rather
than obtaining all of the data packages from the external server,
thereby reducing network traffic.
[0060] According to preferred embodiments of the present invention,
preferably the process of downloading data package from peer
clients is optimized to reduce the amount of time required for
downloading, the load on each individual client and the overall
network traffic. Such optimization is performed as follows.
[0061] First, preferably the exit degree of each client is bound,
such that each client is only able to serve a fixed, limited number
of other clients simultaneously. More preferably, the default limit
is three other clients, for example, or some another appropriate
number which is preferably configured by the user or by the network
administrator. If an additional client attempts to download a data
package from a client which is already serving the maximum number
of other clients will receive a "busy" message. This feature limits
the load on each individual client.
[0062] Also preferably, the present invention is able to optimize
the selection of the best client from which the data package should
be obtained. For example, if client "A" had already downloaded a
larger portion of the required data package than client "B",
transferring the data package from client "A" is more optimal. Such
clients are preferentially selected to serve data packages, since
these clients will be able to serve the data package after a
shorter time period has elapsed. Such preferential selection occurs
by shortening the time period for waiting before these clients
respond, thereby increasing the likelihood that they will serve the
data packages. For this reason, the client preferably calculates
the random delay before responding such that the delay is inversely
proportional to the percentage of the data package which has been
already downloaded. In addition, the random delay is preferably
proportional to the number of clients being served at the moment,
in order to decrease the likelihood of overloading already busy
clients.
[0063] In addition, according to other preferred embodiments of the
present invention, preferably the entries of the locations of data
packages in the network data packages table are updated according
to a probabilistic function. Such a function is preferred in order
to prevent all of the clients from registering a single client as
the server for any particular data package, for example. When
different clients respond, usually at different times, indicating
they have a specific data package, the remaining clients listening
across the network update the entry for this data package in their
network data packages table, by adding the IP address, or some
other type of address according to the addressing system employed
by the network, of the client which can serve the data package to
this table. In a simple implementation, the clients would store
only the last advertised location of each data package, and
therefore many or all clients might attempt to obtain the data
package from a single client as the internal server, thereby
overloading that client.
[0064] To avoid this situation, preferably the following
probabilistic algorithm is used to determine the particular client
address which is stored in the network data packages table. Each
time a new client transmits a response message, indicating that
this client is able to serve particular data package, the
probability that the new IP address of the new client is
substituted for the old IP address is calculated according to the
following equations: 2 New IP address = { Old IP address Po ( x ) =
1 / ( generation + 1 ) New IP address Pn ( x ) = 1 - 1 / (
generation + 1 )
[0065] wherein Pn(x) is the probability that a new IP address is
substituted for the old IP address, Po(x) is the probability that
the old IP address is retained, and "generation" is a number
indicating how many times this address had been previously
changed.
[0066] For example, if client "A" responds indicating it has data
package "X", then initially all other peer clients store the IP
address of client "A" as the location of data package "X". If
client "B" then broadcasts a response also indicating that client
"B" has data package "X", then the probability that any one client
now changes the IP address for the location of data package "X" is
50%. In other words, about half of the clients should now point to
client "A" and about half should point to client "B".
[0067] Such a substantially even distribution of load across
multiple clients should produce data-flow with a tree-shaped
topology, as shown in FIG. 3, rather than a random topology, thus
optimizing the average download time and the load on the serving
clients.
[0068] Furthermore, if any client requests a particular data
package during the period required by client "A" for downloading
that package, preferably client "A" sends a broadcast or multicast
message indicating that the package is in the process of being
downloaded. Therefore, preferably only a single client "B" polls
client "A" for each data package, for example. Other clients
preferably automatically receive any responses from that polling
action through the broadcast or multicast transmission, and thus
will not be forced to poll for themselves.
[0069] The polling (request/response) traffic is optimized since
there is usually no need to transmit both a request and a response
for each data package needed by each client. Such optimization is
possible since each client preferably receives substantially all of
the request/response communication of all the other clients and
"remembers" the location of the data packages in the network-data
packages table.
[0070] As previously described, the actual process for receiving a
data package from an internal server is performed according to the
data package exchange protocol, by using the HTTP protocol or some
other suitable peer-to-peer communication protocol. The data
package transfer software application of the present invention
preferably features a timer, for detection of an aborted transfer
or a very slow data package transfer, for example. The timer
determines when such a transfer has timed out. If a time-out
occurs, the requesting client preferably repeats the whole process.
If the transfer remains unsuccessful after a plurality of attempts,
the client preferably ceases to attempt to transfer the data
package from the peer client as the internal server, and instead
transfers the data package or data packages directly from the
external server.
[0071] Again, as described previously, if a requested data package
has not yet finished being downloaded by a peer client, the
requesting client receives a message indicating that the data
package is not ready, as well as an indication of the fraction of
the data package already downloaded. The requesting client
continues polling the serving client until the data package
download is complete. If the download becomes substantially slower
or is otherwise interrupted or terminated for a long period of
time, the requesting client behaves as if a time-out occurred.
[0072] According to additional preferred features of the present
invention, substantially automatic detection of peer clients is
supported. Such automatic detection enables each peer client to
detect the presence of other peer clients on the network. If such
peer clients are not found, preferably the system of the present
invention is disabled, since the operation of the system as
described above would only prolong the time period required to
download a data package if no other peer clients are available.
[0073] Preferably, the amount of bandwidth on the local area
network which is consumed by each peer client serving data packages
to other clients is limited, to avoid over-burdening any specific
host. This limit is preferably configurable by the user or by the
network administrator.
[0074] Furthermore, in order to protect peer clients from
unauthorized access of local storage media through the system of
the present invention, certain security features are preferably
included. For example, preferably only data packages identified in
the hash tables are able to be transferred from the client. Thus,
transmitted data packages are preferably only data packages which
were intended to be served to the peer clients, such that malicious
users preferably cannot use the system of the present invention to
obtain "random" data packages from the storage media of a peer
client. Data packages are more preferably only referenced by their
unique identifier, such as their 128-bit MD5 digest, such that a
data package is only able to be downloaded from a client if the
intended recipient knows this digest. Thus, the name of a data
package alone is preferably not sufficient information to permit
retrieval of the data package from a peer client.
[0075] According to another embodiment of the present invention,
the system of the present invention is also applicable to Web
browsers, FTP clients, and other software applications involving
client-server data-transfer. As described with reference to FIGS. 4
and 5A-5B, another exemplary embodiment of the present invention is
used for caching Web content.
[0076] In step 1 of FIG. 4, a Web browser being operated by a
client computer requests a specific data package. First the Web
browser looks at the local cache, as is known to one of ordinary
skill in the art. If the data package is found in the local cache,
then that data package is retrieved from the local cache.
Otherwise, the Web browser issues a message requesting this data
package, preferably by using broadcast or multicast message
transmission. The data package is preferably uniquely defined by a
unique identifier. More preferably, the unique identifier is the
URL of the data package, or alternatively and preferably a
combination of the URL of the data package and timestamp, or by any
other suitable unique identifier.
[0077] For optimization, if more than one data package is required,
the Web browser preferably transmits one request message containing
the list of needed data packages, thereby reducing the total
network traffic across the network. Such a situation may arise if,
for example, the Web browser had just parsed an HTML (hypertext
mark-up language) document, or Web page, which contains many links
to follow. Preferably and optionally, each request message contains
an identifying "magic number", which may contain the protocol
version (PVN). For instance: "V1.0". As shown in FIG. 5A, the
request message includes the list of URL's or other unique
identifiers to identify the data package or data packages being
requested, which is similar in function to the list of MD5 digests
described previously for request messages, and a unique identifier
identifying the request message, shown as "REQ".
[0078] In step 2, other Web browsers across the network listen to
detect request messages of this type. These Web browsers, which are
peer clients for this embodiment of the present invention, receive
this request message and check their own cache for the requested
URL. If the requested URL is found in the local cache of a Web
browser, that Web browser preferably waits a random interval and
then preferably transmits a response message indicating it has the
required data package (or data packages). Preferably, the message
is broadcast or multicast. More preferably, that Web browser does
not reply if another Web browser had replied first. A reply message
is preferably sent by a particular Web browser even if the
requested URL is still being downloaded by that Web browser.
[0079] In step 3, if no response to an issued requmessage is
received within a certain amount of time, for example 5 seconds,
then the process is preferably timed out. In this case, the Web
browser preferably no longer attempts to obtain the URL from
another Web browser, and the URL is obtained from the regular Web
server using regular HTTP protocol. Before starting to download the
data package from the regular Web server, the Web browser
preferably transmits a response message indicating that this
particular Web browser is downloading the data package.
[0080] On the other hand, if a response message is received, the
Web browser obtains the URL from the other Web browser which
indicated that it had the URL in the local cache. Preferably, Web
browsers across the network record the URLs and the address from
which the response message originated for future use, such that
these Web browsers would be able to download the URL at a future
time without first transmitting the request message.
[0081] Once the Web browser is able to locate a data package on a
neighboring Web browser, the Web browser attempts to download the
data package. The downloading process is performed with a suitable
data-transfer protocol, such as HTTP or FTP. If a time-out or other
failure occurs during the processing of data package transfer, the
receiving Web browser preferably performs substantially the entire
procedure more than once. More preferably, the number of permitted
attempts to retry the transfer is configurable. If the process
fails after these attempts have been performed, preferably the Web
browser transfers the required data package or data packages from
the regular Web server.
[0082] According to preferred features of this embodiment of the
present invention, data package downloading is well distributed,
such that the Web browsers do not obtain a data package from only a
single Web browser, but rather obtain the data package from a
plurality of Web browsers. Such distribution is maintained as
follows.
[0083] First, preferably the number of simultaneous data package
transfers from a single Web browser is limited. If this number is
exceeded, the Web browser transmits a "busy" message to other Web
browsers attempting to transfer the data package. Next, preferably
once a Web browser receives a message giving the location of a
particular data package, the corresponding entry in the hash table
for that data package is not altered every time another response
message is received pertaining to this data package. The hash table
is preferably altered by subsequent messages in a probabilistic
manner, such that the probability that any particular entry is
updated to indicate a new location of a data package is equal to
1/(generation+1), where `generation` counts the number of times a
response message was received for that data package.
[0084] For example, if Web browser "A" transmits a response message
indicating that data package "X" is on the local cache, then
initially all of the neighboring Web browsers have an entry in the
hash table indicating that Web browser "A" is the location of data
package "X". If Web browser "B" then transmits a response message
for data package "X", then each Web browser preferably now alters
the entry in the hash table to indicate a new location of data
package "X" with a probability of about fifty percent, such that
about fifty percent of the Web browsers now have an entry
indicating that the data package is available from Web browser "A"
and such that about fifty percent of the Web browsers now have an
entry indicating that the data package is available from Web
browser "B". Thus, a good load distribution can be achieved.
[0085] The random delay (mentioned in step 2 above) chosen by a
browser is proportional to the number of currently served browsers,
or the number of browsers currently downloading data packages from
that browser, and inversely proportional to the amount of the data
package already downloaded by it. This way the browsers more
eligible to download from are more likely to be chosen by other
browsers to serve these data packages.
[0086] While the invention has been described with respect to a
limited number of embodiments, it will be appreciated that many
variations, modifications and other applications of the invention
may be made.
* * * * *
References