Note: Descriptions are shown in the official language in which they were submitted.
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A Method for Detecting State Changes Between Data Stored in a First Computing
Device
and Data Received from a Second Computing Device
Field
[0001] This specification relates generally to mobile data communication
systems, and more
particularly to a method for detecting state changes between data stored in a
first computing
device and data retrieved from a second computing device.
Background
[0002] Mobile communication devices are becoming increasingly popular for
business and
personal use due to a relatively recent increase in number of services and
features that the
devices and mobile infrastructures support. Handheld mobile communication
devices,
sometimes referred to as mobile stations, are essentially portable computers
having wireless
capability, and come in various forms. These include Personal Digital
Assistants (PDAs), cellular
phones and smart phones.
[0003] It is known in the art to provide Internet browser functionality in
such mobile
communication devices. In operation, a browser user-agent in the handheld
mobile
communication device issues commands to an enterprise or proxy server
implementing a
Mobile Data Service (MDS), which functions as an acceleration server for
browsing the Internet
and transmitting text and images to the mobile device for display. Such
enterprise or proxy
servers generally do not store the state of their clients (i.e. the browser
user-agent), or if they
do, the state that is stored is minimal and limited to HTTP state (i.e.
cookies). Typically, such
enterprise or proxy servers fetch and transmit data to the browser user-agent
when the browser
makes a data request. In order to improve the performance of the browser on
the mobile
device, some enterprise or proxy servers fetch all the data required in order
to fulfill the data
request from the browser, aggregate the fetched data, and transmit the data to
the device
browser. For instance, if a HyperText Markup Language (HTML) page is
requested, the
enterprise or proxy server fetches any additional files referenced within the
HTML page (e.g.
Images, inline CSS code, JavaScript, etc.). Since the proxy server fetches all
the additional files
within the HTML file, the device does not have to make additional data
requests to retrieve
these additional files. Although this methodology is faster than having the
device make multiple
requests, the proxy server nonetheless has to send all of the data again if
the site is later
revisited. This is because the proxy server has no knowledge of the device
caches (e.g. caches
that are saved in persistent memory, for different types of data such as a
content cache to store
raw data that is cached as a result of normal browser activity, a channel
cache containing data
CA 02615714 2008-06-12
that is sent to the device by a channel or cache push, and a cookie cache
containing cookies
that are assigned to the browser by visited Web pages). For example, if a user
browses to
CNN.comTM, closes the browser to perform some other function (e.g. place a
telephone call or
access e-mail messages, etc.) and then later accesses the CNN.conem Web site
(or follows a
link from CNN.comTM to a news story), the banner "CNN.com" will be transmitted
from the MDS
to the device browser each time the site is accessed, thereby consuming
significant bandwidth,
introducing delay, etc.
[0004] It is known in the art to provide local file caching. One approach is
set forth in GloMop:
Global Mobile Computing By Proxy, published September 13, 1995, by the GloMop
Group,
wherein PC Card hard drives are used as portable file caches for storing, as
an example, all of
the users' email and Web caches. The user synchronizes the file caches and the
proxy server
keeps track of the contents. Mobile applications (clients) are able to check
the file caches before
asking for information from the proxy server by having the server verify that
the local version of
a given file is current.
Summary
[0005] In general, there is provided a method for detecting state changes
between data stored
in a first computing device and data retrieved from a second computing device.
The method
includes: generating a first hash value of the data stored in the first
computing device;
generating a second hash value of corresponding data retrieved from the second
computing
device; and comparing the first hash value to the second hash value and
detecting a state
change in the event of a difference there between.
[0006] A specific application of this method provides for communicating
information between
the second computing device, such as an enterprise or proxy server and the
first computing
device, such as a mobile Internet browser. An HTTP-like protocol is set forth,
referred to herein
as the Browser Session Management (BSM) protocol, for providing a control
channel between
the second computing device, and the first computing device, so that the first
computing device
can communicate to the second computing device what data the first computing
device has
stored in memory (from previous browsing). The BSM protocol is an "out of
band" protocol in
that BSM communications are in addition to the usual stream of HTTP requests
from the first
computing device to the second computing device, and provide "metadata"
relating to cache
contents. This metadata is used by the second computing device when handling
subsequent
requests from the first computing device, to determine what data to send to
the first computing
device, thereby significantly reducing data transfer on subsequent requests
relative to the prior
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art methodology discussed above.
[0007] Because the second computing device is aware of what the first
computing device has
stored in its cache, the amount of data sent to the first computing device may
be reduced,
thereby increasing the performance of the first computing device and reducing
operational cost.
For the application given above wherein the first computing device is a mobile
device browser
and the second computing device is a proxy server, if after the first request
the CNN.comTM
banner is cached and if the proxy server "knows" that the information has been
cached then
there will be no need to send the CNN.comTM banner to the mobile device
browser upon
subsequent visits to the CNN Web site.
[0008] According to another aspect, messages from the device to the proxy
server contain hash
values of different portions of documents (rather than the actual URLs) which
are used by the
proxy server to detect state changes in the device and utilize the information
in preparing
documents for transmission to the device. In another embodiment, the device
sends hashes of
the actual data of the portions (i.e. the actual image data, JavaScripts,
StyleSheets, etc.) and
the proxy server compares the received and stored data hashes for the portions
to determine if
the device already has the data for a particular portion (e.g. previously
retrieved with a different
URL), in which case the proxy server sends a response to the device with a
header that
indicates the device already has the data that is to be used for that portion.
A person of skill in
the art will appreciate that a one-way hash function transforms data into a
value of fixed length
(hash value) that represents the original data. Ideally, the hash function is
constructed so that
two sets of data will rarely generate the same hash value. Examples of known
hash functions
include MD2, MD5 and SHA-1.
In contrast to the prior art GloMop caching methodology discussed above, the
exemplary
method set forth herein synchronizes the cache contents when the mobile device
browser
connects to the proxy server in order to initiate a session and keeps track of
changes to the
cache via knowledge of what data has been sent to the mobile device browser in
combination
with state information periodically received from the mobile device browser
identifying what has
actually been cached. Also, as set forth in greater detail below, the proxy
server uses this cache
knowledge to determine what to send back to the mobile device browser. In
contrast, the prior
art GloMop methodology does not contemplate sending any state information to
the proxy
server for identifying what has actually been cached in the device. Moreover,
the prior art
GloMop approach first checks the local cache, and then queries the proxy
server to determine
whether a particular data item in the cache is current or not.
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According to the GloMop prior art, the proxy server does not use its own
knowledge of the
mobile device browser cache to determine what to send back to the mobile
device browser.
[0010] Additional aspects and advantages will be apparent to a person of
ordinary skill in
the art, residing in the details of construction and operation as more fully
hereinafter described
and claimed, reference being had to the accompanying drawings.
Brief Description of the Drawings
[0011] A detailed description of the preferred embodiment is set forth in
detail below, with
reference to the following drawings, in which:
[0012] Figure 1 is a block diagram of a communication system for implementing
Internet
browsing functionality in a mobile communication device;
[0013] Figure 2A shows communication protocol stacks for the communication
system of
Figure 1;
[0014] Figure 2B shows communication protocol stacks for a Browser Session
Management
(BSM) protocol according to an exemplary embodiment;
[0015] Figure 3 is a flowchart showing the method for communicating
information between a
proxy server and a mobile Internet browser, according to the preferred
embodiment; and
[0016] Figure 4 is a flowchart of an exemplary method according to the present
specification.
Detailed Description
[0017] Figure 1 depicts the architecture of a system for providing wireless
e-mail and data
communication between a mobile device 1 and an enterprise or proxy server 9.
Communication
with the device 1 is effected over a wireless network 3, which in turn is
connected to the Internet
and proxy server 9 through corporate firewall 7 and relay 8. Alternatively,
the device 1 can
connect directly (via the Internet) through the corporate firewall 7 to the
proxy server 9. When a
new message is received in a user's mailbox within email server 11, enterprise
or proxy server 9
is notified of the new message and email application 10 (e.g. Messaging
Application
Programming Interface (MAPI), MS Exchange, etc.) copies the message out to the
device 1
using a push-based operation. Alternatively, an exemplary architecture for
proxy server 9 may
provide a browsing proxy but no email application 10. Indeed, the exemplary
embodiment set
forth herein relates to mobile browser device functionality and is not related
to email
functionality. Proxy server 9 also provides access to data on an application
server 13 and the
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Web server 15 via a Mobile Data Service (MDS) 12. Additional details regarding
e-mail
messaging, MAPI sessions, attachment service, etc., are omitted from this
description as they
are not germane. Nonetheless, such details would be known to persons of
ordinary skill in the
art.
[0018] In terms of Web browsing functionality, the device 1 communicates
with enterprise or
proxy server 9 using HTTP over an IP protocol optimized for mobile
environments. In some
embodiments, the device 1 communicates with the proxy server 9 using HTTP over
TCP/IP,
over a variant of TCP/IP optimized for mobile use (e.g. Wireless Profiled
TCP), or over other,
proprietary protocols. For example, according to the communications protocol
of Fgure 2A,
HTTP is run over Internet Point-to-Point Protocol (IPPP) and an encrypted
Global Messaging
Exchange (GME) channel over which datagrams are exchanged to transport data
between the
device 1 and proxy server 9. The GME datagrams are 64Kbit in size whereas the
wireless
network 3 can only transport UDP datagrams with payloads up to 1500 bytes.
Therefore, a
Message Delivery Protocol (MDP) is used to separate the GME datagrams into one
or more
MDP packets, each of which is less than 1500 bytes (default size 1300 bytes),
which are
transported over UDP/IP to and from the relay 8 which, in turn communicates
with the proxy
server 9 via Server Relay Protocol (SRP)/TCP/IP. The MDP protocol includes
acknowledgements, timeouts and re-sends to ensure that all packets of the GME
datagram are
received.
[0019] The communication between the device 1 and proxy server 9 is
optionally encrypted
with an encryption scheme, such as Triple Data Encryption Algorithm (IDEA,
formerly referred
to as Triple Data Encryption Standard (Triple DES)), as is known in the art.
The proxy server 9
enables Internet access, preprocesses and compresses HTML and XML content from
the Web
server 15 before sending it to the device 1, transcodes content type, stores
HTTP cookies on
behalf of the device 1, and supports certificate authority authentications,
etc.
[0020] In response to a request from the device browser, the proxy server 9
retrieves
content from Web server 15 and creates a custom document containing both
images to be
displayed on the device and data in the form of compressed versions of
requested portions of
the document. The document is preferably of "multi-part" format to improve
transmission to and
processing efficiency within the device 1. Specifically, in order to display
composite Web pages
(i.e. pages composed of a main WML or HTML page and one or more related
auxiliary files,
such as style sheets, JavaScript files, or image files) the device browser is
normally required to
send multiple HTTP requests to the proxy server 9. However, according to the
multi-part
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generation feature, the proxy server 9 posts all necessary parts of a
composite Web page in a
single bundle, enabling the browser to download all the required content with
a single request.
The header in the server response identifies the content as a multi-part
bundle (e.g. Multi-
Purpose Mail Extensions (MIME)/multipart,as defined by RFC 2112, E. Levinson,
March 1997).
[0021] In order to indicate device browser state information to the proxy
server 9, three
transitional state messages are defined herein, as follows: CONNECT, UPDATE
and
DISCONNECT, each of which conforms to the exemplary BSM protocol. As shown in
Figure 2B,
the BSM communications protocol is identical to the protocol of Figure 2A
except that the
conventional HTTP layer of the protocol stack is replaced by an HTTP-like BSM
layer.
[0022] The CONNECT transitional message creates a new session with a
connection
identifier carried in the payload, device information and state data (e.g.
current cache and
device information) in the form of a set of hash functions for use by the
proxy server 9 in
preparing a response. Specific care is taken not to identify to the proxy
server 9 what cookies or
cache entries are contained on the device 1. Only hash values of the state
data are sent to the
proxy server 9 in order to protect the identity of state data on the device 1.
[0023] The CONNECT message also contains a unique authentication key for
generating a
MAC (Message Authentication Code) using a Hash Message Authentication Code
(HMAC)
algorithm that incorporates a cryptographic hash function in combination with
the authentication
key. Each portion of a multi-part document from the proxy server 9 also
contains an HMAC,
generated using the authentication key, that is used for authenticating the
proxy server 9 before
adding that portion to the device cache. This prevents a third party from
creating its own multi-
part document and sending it to the device 1 for injecting cache entries that
could be used to
extract personal information from the user.
[0024] Upon receipt of the CONNECT message, the proxy server 9 uses the
state
information to regulate or control the transmission of content retrieved from
Web server 15 (step
23) to the device 1. One example of an application where this information can
be used is when
the proxy server 9 is pre-fetching images, inline Cascading Style Sheets
(CSS), JavaScript, and
the like for an HTML document. If the proxy server 9 already knows that the
device 1 has the
image, inline CSS, or JavaScript document, there is no need for resending the
documents.
[0025] The UPDATE transition message notifies the proxy server 9 of changes
that have
occurred on the device 1 since the last CONNECT message or the last UPDATE
message,
between the device 1 and proxy server 9 (e.g. new cache entries added because
of a push, or
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invoking the "Low Memory Manager" (LMM) or other memory-space preservation
policies on the
device and purging items from the cache).
[0026] The DISCONNECT transition message notifies the proxy server 9 that
the device 1
will no longer send any more messages using the connection identifier
specified in the payload.
The proxy server 9 can then de-allocate any memory reserved for the connect
session between
the device 1 and proxy server 9. Upon receiving the disconnect message, the
proxy server 9
deletes any session cookies for the device 1 (if it is processing cookies)
along with state
information. Receiving a request on the identified connection after the
DISCONNECT has been
received, and before any subsequent CONNECT message has been received, is
defined as an
error.
[0027] Since state is indicated from the device 1 to the proxy server 9,
and state may be
stored in transient memory within proxy server 9, a mechanism is provided for
the proxy server
9 to return to the device 1 a message indicating that the session the device
is trying to use is not
valid. Once this occurs, the device 1 issues a new CONNECT message and
establishes a new
session with the proxy server 9, and re-issues the original request.
[0028] The data protocol set forth herein is similar to HTTP in order to
reduce complexity
and to reuse code that already exists for the HTTP protocol. Thus, data
transmission according
to this protocol begins with a STATE keyword; followed by a BSM (Browser
Session
Management) protocol identifier and a "Content-Length" header. The end of the
"headers" is
indicated by a double CRLF (a sequence of control characters consisting of a
carriage return
(CR) and a line feed (LF)), much like HTTP. After the double CRLF pair (i.e.
1r1n) a WBXML
(WAP Binary Extensible Markup Language) encoded document is inserted as the
message
payload. The WBXML document is later decoded using a DTD (Document Type
Definition) and
codebook, as discussed in greater detail below. The indication of the protocol
version refers to
what version of the DTD to validate the request against (ie. BSM/1.1
stipulates using version 1.1
of the DTD). It should be noted that WBXML encoding of the contents of BSM
messages is set
forth to allow for more efficient processing of the BSM message at the device
1, but that in
alternate embodiments, the BSM message may be formatted as normal (textual)
XML.
[0029] The following is an example communication using the protocol
according to the
preferred embodiment:
CONNECT BSM/1.01r1n
Content-Length: 40\r\n
1r1n
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<WBXML Encoded document of length 40 bytes>
BSM/1.0 2001r1n
r\n
[0030] In the foregoing, the first four lines form the CONNECT message from
the device 1
to the proxy server 9, and the last two lines are the response from the proxy
server 9.
[0031] An exemplary XML document, is as follows:
<?xml version="1.0"?>
<!DOCTYPE bsm PUBLIC "-// DTD BSM 1.0//EN"
"http://www.something.com/go/mobi1e/BSM/bsm_1Øxm1"
<bsm id="2" hmac="12345678901234567890"
<cache>
<size>123012</size>
<entry urlHash="FEEDDEED01" dataHash="FDDEDEED11" etag="SomeEtag"
expiry="256712323"/>
</cache>
<device>
<version>4Ø1.123</version>
<memfree>12342342</memfree>
</device>
</bsm>
[0032] In the example, the state data includes the URL of an HTML page
within the device
cache. It will be noted that the XML document payload includes a connection
identifier (i.e. bsm
id="2"), a value indicating when the document was last modified (i.e.
etag="SomeEtag"), a page
expiry (i.e. expiry="256712323"), and hash values for a URL (i.e. entry
urlHash="FEEDDEED01") and a data attribute (i.e. entry dataHash="FDDEDEED11")
rather
than transmitting the actual URL and data attribute themselves. Thus, as shown
in Figure 3, the
hashes of the URL and data attribute of the cached page are sent to the proxy
server 9 in the
CONNECT string (step 21). The proxy server 9 then fetches the requested page
from Web
server 13 (step 23), computes hashes of device browser state data (step 25)
and data from the
Web server 13 (step 27), and compares the hashes of the URL and data attribute
of the
requested page with the hashed URL and data attribute of the cached page, and
also compares
the time stamps/expiration information (step 29) in order to determine whether
the cached page
is current. Specifically, in response to the proxy server 9 retrieving a
portion from the Web server
13, it computes the dataHash and urlHash of that portion and performs a
comparison to the
dataHashes and urlHashes of the entries it has saved. There are three cases.
[0033] In the first case, if both the dataHash and the urlHash of the
retrieved portion match
the dataHash and urlHash of a cache entry that the proxy server 9 knows the
device 1 has, then
the server 13 simply omits this portion from the response, as the device 1
still has a valid entry
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in its cache.
[0034] In the second case, if the dataHash of the retrieved portion matches
the dataHash of
a cache entry that the proxy server 9 knows the device 1 has, but the urlHash
of the retrieved
portion does not match the urlHash of that cache entry, the server 13 inlines
this updated
portion in the combined response to the device 1. However, because the
dataHash matches a
dataHash of an entry that already exists on the device 1, the inlined response
does not include
the actual data, but instead only includes a new HTTP header whose value is
the new
dataHash. When the device 1 receives this inlined portion, it detects the
special header, looks
for the cache entry with that dataHash, and either creates or updates its
cache entry for that
URL with the data corresponding to the dataHash by copying that data from the
other cache
entry (the cache for device 1 is modified to have two indexes, one to retrieve
cache entries by
URL, the other to retrieve cache entries by dataHash). Finally, if the proxy
server 9 already has
a cache entry for the urlHash, it updates that entry with the new dataHash;
otherwise it creates
a new entry for this portion.
[0035] In the third case, if the dataHash of the retrieved portion does not
match the
dataHash of any of the cache entries that the proxy server 9 has received from
the device 1 in
the BSM messages, then the server inlines the entire portion (headers and new
data), since this
portion has been updated and the device 1 does not contain the updated value
anywhere in its
cache.
[0036] Although not indicated in Figure 3, it will be appreciated that each
inline part to be
added to a document to be displayed at the device 1 is fetched. If the
response code from the
proxy server indicates a "304" (step 31), then the part (i.e., the "304"
response) is written as a
block in the multipart document. On the other hand, if the proxy server 9
returns a "200" (step
33), then the hash compare operation is performed, and the portion is only
included in the
multipart document if the hash compare function indicates it is not already on
the device 1.
[0037] An exemplary DTD, according to the preferred embodiment, is as
follows:
<!ELEMENT barn (cache?, device)>
<!ATTLIST barn
id NMTOKEN 4REQUIRED
<!ELEMENT cache (size, (entry)+)>
<!ATTLIST cache
action (addiremovelremove_allIquick_add) "add"
<!ELEMENT entry EMPTY>
<!ATTLIST entry
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ur1Hash CDATA #REQUIRED
dataHash CDATA #REQUIRED
etag CDATA #IMPLIED
expiry NMTOKEN #IMPLIED
size NMTOKEN #IMPLIED
last-modified NMTOKEN #IMPLIED
<!ELEMENT size (#PCDATA)>
<!ELEMENT device (version, memfree)>
<!ELEMENT version (#PCDATA)>
<!ELEMENT memfree (#PCDATA)>
<!ELEMENT hmac (#PCDATA)>
Element/Code
MAC 12
Attribute/Code
size 9 (instead of action)
lastModified 10
actionAdd 11
actionRemove 12
actionRemoveAll 13
actionQuickAdd 14
[0038] Finally, an exemplary codebook, is as follows:
Element Code
Session 5
Cache 6
Size 7
Entry 8
Device 9
Version 10
MemFree 11
HMAC 12
Attribute Code
Id 5
UrlHash 6
dataHash 7
ETag 8
Expiry 9
Action 10
[0039] As is well known in the art, the codebook is used as a
transformation for
compressing the XML document to WBXML, wherein each text token is represented
by a single
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byte from the codebook.
[0014] As discussed above, the proxy server 9 transmits multi-part
documents in a
proprietary format of compressed HTML, interspersed with data for images and
other auxiliary
files (which may or may not be related to the main HTML Web page). However, in
a departure
from conventional HTML, each document part may also include a response code
(e.g. "200" for
OK, or "304" for "not modified" to indicate that the specified document part
has already been
cached in the device 1). This may be used for selective downloading of
document parts rather
than entire documents and for indicating when a part (e.g. image) is about to
expire. This is
useful, for example, when one Web page links to another page containing one or
more common
elements.
[0015] Of course, certain device requests (e.g. page refresh) will always
result in a full
document download, irrespective of device state information stored in the
proxy server 9.
[0016] It is contemplated that the inclusion of response codes may be used
by heuristic
processes within the proxy server 9 to learn user behaviour and modify
downloading of
documents based on tracking the history of certain changes reflected in the
hash value (e.g. the
server 9 may learn to download a certain page (e.g. CNN news) at a particular
time each day
based the user's history of issuing requests for that page at regular times.
As discussed above,
because the downloaded documents are multi-part and contain embedded response
codes,
only those portions of the document that have changed are actually downloaded.
[0017] Figure 4 illustrates a broad aspect of the exemplary method, wherein
a first hash
value is generated in a first computing device, such as mobile device 1 (step
41), and a second
hash value is generated in a second computing device, such as proxy server 9
(step 43). The
first and second hash values are then compared (step 45). If the hash values
are identical (step
47), no change of state is detected between the data stored in the first and
second computing
devices. On the other hand, if the hash values are identical (step 49), state
change is detected
between the data stored in the first and second computing devices. The method
then ends (step
51).
[0018] As indicated above, the protocol of the preferred embodiment is
preferably carried
over a proprietary IPPP transport layer, but can also be easily adapted to run
over TCP/IP on a
specific port. The protocol is preferably implemented as a handler in the
proxy server 9, thereby
simplifying any currently existing protocol. (e.g. to avoid overloading a
current HTTP protocol).
[0019] A person skilled in the art, having read this description of the
preferred embodiment,
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may conceive of variations and alternative embodiments. For example, the
conditional transfer
of data based on communication of state information, as set forth above, may
also be applied to
separately transmitting individual portions of the multipart document as
opposed to transmitting
the entire document at once.
[0020] In some embodiments, the proxy server 9 uses heuristic algorithms to
learn what
additional data requests the device may make based on knowledge of the current
request, and
knowledge of past activity. In some instances, the device may follow a pattern
of requesting a
first Web page, and then a second Web page. For example, the device may first
request the
cnn.com-rm Web page, and then request the "cnn.cominews" Web page. The proxy
server 9
learns this pattern, and whenever the device requests the first Web page, the
proxy server 9
determines that the device is likely to then request the second Web page. The
proxy server 9
then fetches the second Web page, and uses its knowledge of the data cached on
the device 1
(i.e. from the state information transferred to the proxy server 9 during
initiation of the present
connection) to determine whether the second Web page already exists within the
data cached
on the device. If so, the proxy server 9 includes information about the second
Web page via
response codes embedded within the response provided for the first Web page.
If the device 1
requires the second Web page, then the device 1 can reference its cache and
can avoid having
to make a request to the proxy server 9 for the second Web page.
[0021] In other embodiments, heuristic processes within the proxy server 9
learn user
behaviour and modify downloading of documents based on tracking the history of
certain
changes reflected in the hash value (e.g. the proxy server 9 may learn to
download a certain
page (e.g. CNN news) at a particular time each day based the user's history
of issuing
requests for that page at regular times). As discussed, because the downloaded
documents are
multi-part and contain embedded response codes, only those portions of the
document that
have changed are actually downloaded.
[0022] All such variations and alternative embodiments are believed to be
within the ambit
of the claims appended hereto.
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