Patent Application
20140189488
The present disclosure relates generally to the compression of presence information for transmission in a wireless communications network.
Wireless communication devices may provide information about their location, status and/or availability to other wireless communication devices, as ‘presence information’. Presence may be defined as the ability of a person or device to communicate with others and to display levels of availability.
A ‘presentity’ is an entity that provides presence information to other entities, such as persons, devices or services. A ‘watcher’ is an entity that requests presence information about a presentity, from a presence service. A ‘presence server’ is a software platform that gathers presence information from multiple providers (presentities). The presence server shares the presence information between the providers and any other applications that are interested in the presence information, i.e. watchers.
A watcher creates a ‘subscription’ with the presence server when it wishes to view the presence of a presentity. A watcher can create a subscription for individual presentities, or for a group of presentities. A subscription for a group of presentities may also be called a ‘resource list’. In many presence systems, a watcher creates resource lists and adds onto these lists all the presentities that it intends to watch. Subscriptions are made to these lists, instead of making individual subscriptions.
When the server receives a presence update (as a ‘PUBLISH’ message) from a presentity, it forwards that update (as a ‘NOTIFY’ message) to various watchers. Those watchers are the watchers who have subscribed (with a ‘SUBSCRIBE’ message) to the presence of that presentity. A watcher usually has a combination of individual and group subscriptions, depending on the type of presentities it is watching.
The presence documents that contain the presence info are usually in an XML format, called ‘Presence Information Data Format’ or simply PIDF. Since the presence documents are in Extensible Mark-up Language (XML) format, they tend to be large in size. The size of these presence documents may make them too large to send using the most efficient transmission protocols. Due to their size, the presence documents may need to be sent over Transmission Control Protocol (TCP), which is undesirable due to the nature of the TCP protocol.
Known communications systems use dictionary-based compression schemes like the ‘Presence-Specific Static Dictionary for Signalling Compression’ (SIGCOMP) standard to compress some documents. However, known dictionary-based compression schemes are computationally intensive, due to their high complexity. They therefore lead to high Central Processing Unit (CPU) utilization. For these reasons, dictionary-based compression schemes are unsuitable in a server which handles a very large number of presentity events per second.
Communication system 100 comprises a first presentity 110. First presentity 110 produces a first dictionary P1, when compressing a presence document that presentity 110 creates. First presentity 110 forwards first dictionary P1 to presence server 120 as a PUBLISH event. Presence server 120 serves both to decompress and compress the first dictionary P1. A second presentity 170 produces a second dictionary P2, when compressing a presence document that presentity 170 creates. Second presentity 170 forwards second dictionary P2 to presence server 120 as a PUBLISH event. Presence server 120 decompresses the first dictionary P1 and the second dictionary P2.
Presence server 120 combines first dictionary P1 and second dictionary P2 to create a dictionary W1 for a first watcher 130, and a dictionary W2 for a second watcher 140. Dictionary W1 also contains dictionaries provided by other presentities on the watch list of first watcher 130. Dictionary W2 also contains dictionaries provided by other presentities on the watch list of second watcher 140. Presence server 120 forwards dictionary W1 to first watcher 130 and dictionary W2 to second watcher 140. First watcher 130 stores the dictionary W1, as shown at 150. Second watcher 140 stores the dictionary W2, as shown at 160.
Whenever a new presence document is provided to presence server 120 from another presentity, the dictionaries W1 and/or W2 need to be updated, if either first watcher 130 or second watcher 140 is a subscriber to the presentity providing the new presence document. Presence server 120 therefore carries out significant amounts of compression and decompression. There is also a significant transmission load in re-forwarding dictionaries W1 and W2 to first watcher 130 and second watcher 140. Presence server 120 will store one dictionary, such as W1 or W2, which is a ‘bespoke’ dictionary for each watcher. Each of dictionaries W1 and W2 is a ‘bespoke’ dictionary for an individual watcher.
When dictionaries P1 and P2 in
There have been proposals in academic literature about using Abstract Syntax Notation (ASN) ‘ASN-1’ encoding for compressing XML. However, the compression performance of ASN-1 degrades significantly when it encounters large dynamic strings in an XML document. Dynamic strings are the strings that are not defined (or ‘enumerated’) as part of the XML schema. The presentities of many systems tend to have large names and Uniform Resource Locators (URLs), which are uncompressible through ASN-1. An example of such presentities is the users, devices and sub-devices of a wireless video communications system. The compressed presence documents generated in such a system remain large enough that it is necessary to use TCP for transmission. This situation is due to the presence of a large number of uncompressible strings (e.g., camera name) in such presence documents, even after ASN-1 compression.
Accordingly, there is a need for a method and apparatus for compressing information in a wireless network.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
A method of compressing presence information in a presence document for wireless transmission is provided. A presentity in a wireless communications system creates a presence document in XML format, and applies a dictionary-based compression to a first portion of the presence document, the first portion of the presence document comprising at least one item of uncompressible information. The presentity applies a non-dictionary-based, structured information representation to a second portion of the presence document. The at least one item of uncompressible information may comprise an unenumerated character string, and may be a dynamic entity. The at least one item of uncompressible information may comprise one or more of: user names; URLs; device names; dates and IP addresses. The non-dictionary-based, structured information representation may be ASN-1 encoding. The second portion of the presence document may comprise one or more of tags, enumerated strings, and XML fields.
At 210, a presentity creates an XML format presence document, which is to be transmitted to a presence server with a PUBLISH message. At 220, the presentity applies dictionary-based compression to uncompressible information in the presence document. The uncompressible information can be considered to constitute a first portion of presence document. However, the uncompressible information will often be distributed throughout the presence document. So the ‘first portion’ of the document may be considered to be some or all of the various parts of the presence document that contain uncompressible information. If, in a non-limiting numerical example, 30% of the presence document comprises uncompressible information, then the first portion is some or all of this 30% of the presence document. The dictionary-based compression leads to the creation of a dictionary.
At 230, the presentity applies a non-dictionary-based, structured information representation method to a second portion of the presence document. The second portion of the presence document is some or all of the part of the presence document that does not contain dynamic strings. So the ‘second portion’ of the document may be considered to be some or all of the various parts of the presence document that contain compressible information. If, in the non-limiting numerical example given above, 70% of the presence document comprises compressible information, then the second portion is some or all of this 70% of the presence document.
In one embodiment, the presentity applies the dictionary-based compression to all the uncompressible information in the presence document, and applies the non-dictionary based, structured information representation to all the compressible information.
At 240, the presentity forwards both the dictionary and the compressed presence document to the presence server. The dictionary and the compressed presence document may be forwarded to the presence server as part of a PUBLISH message sent to the presence server. In a non-limiting numerical example, a typical presence document may be compressed to a size of 1500 bytes or less using the method of
In step 220 of
The method of
The method of
In some embodiments, the presentity may wait for an acknowledgment from a receiving party that the dictionary of indices has been received, before replacing the item of uncompressible information in the first portion of the presence document by the corresponding index from the dictionary of indices. Here the receiving party may be a watcher. The watcher may transmit the acknowledgement of receipt of the dictionary of indices back to the presentity via the presence server.
When the presentity creates a new presence document, it may contain one or more dynamic strings for which there is no entry in an existing dictionary, which was created by the presentity for an earlier document. The presentity may then just create an updated entry for the dictionary of indices. The updated entry may comprise a new index, corresponding to the new item of uncompressible information in the new presence document. However, the updated entry may instead just comprise an update of an existing index in the dictionary of indices, rather than an entirely new entry. The presence server may then transmit the updated entry to the receiving party. After transmitting the updated entry for the dictionary of indices to the receiving party, the presentity may wait for an acknowledgment from the receiving party that the updated entry has been received, before using the new index or the updated index, to replace an item of uncompressible information in the first portion of the presence document.
The updated entries, i.e. new entries and/or updates to existing entries, may be incorporated into the XML presence document, and communicated as part of XML presence document itself. However, these dictionary updates may not be used in compression until after the remote party confirms the receipt of these updates with an acknowledgement.
The presence document may be in the Presence Information Data Format of XML. The presentity may use the entity reference mechanism of the XML standard to indicate the dictionary indices in the presence document. The entity reference mechanisms allows an element of an XML document to refer to another element of the same XML document (i.e., internal reference), or another element of a different XML document (i.e., external reference). Both the internal and external entity reference mechanisms of the XML standard may be used, and in each case the dictionary indices will be transmitted within the presence document.
Step 220 of
At 310, the presentity creates a presence document in XML format. At 320, the presentity considers a first string within the presence document.
If the first string is uncompressible, then the method 300 proceeds to 330. At 330, the presentity creates a dictionary entry for the string. An index is also created, to accompany the dictionary entry. Then, at 340, the presentity replaces the string in the presence document, by substituting the index. At 360, method 300 will decide that all strings have not yet been checked, and return to decision box 320 for the next string in the presence document.
If, instead, at 320, the method finds that the first string is compressible, then method 300 proceeds to 350. At 350, a non-dictionary-based, structured information representation method is applied to the string. Then method 300 passes to decision 360.
When all the strings in the presence document have been checked and processed either as shown at 330 and 340, or as shown at 350, then decision 360 will result in the method passing to 370. At 370, the presentity transmits the presence document and the dictionary to the presence server, with the presence document having been compressed.
The method 300 of
In a wireless communication system with multiple presentities, each presentity may create a dictionary containing the indices and the corresponding strings for presence documents that it creates. The presentity then sends the initial PIDF presence document along with the dictionary to the presence server. We can refer to this first presentity as P1. The presence server stores P1's dictionary. A NOTIFY message from the presence server to a watcher contains P1's dictionary and P1's presence document. The watcher stores P1's dictionary locally. Similarly, a second presentity P2 sends an initial PIDF presence document along with its dictionary to the presence server. The server stores P2's dictionary. A NOTIFY message to the watcher provides P2's dictionary and P2's presence document. The watcher also stores P2's dictionary locally.
At this point, both the server and the watcher have the same set of dictionaries. Both the server and the watcher have P1 and P2's dictionaries. However, the presentities P1 and P2 have only one dictionary each—their own. This process continues for all presentities P1, P2, . . . Pi, where the watcher has subscribed to each of presentities P1, P2, . . . Pi.
A first presentity 410 provides a first dictionary P1 together with a first presence document, with the first dictionary P1 illustrated as ‘P1 DICT’ on
Presence server 420 does not need to decompress first dictionary P1. Instead, presence server 420 forwards the first dictionary P1 and the first presence document to each watcher that has subscribed to first presentity 410, as a NOTIFY message. In the case of
A second presentity 470 provides a second dictionary P2 together with a second presence document, with the second dictionary P2 illustrated as ‘P2 DICT’ on
Presence server 420 does not need to decompress second dictionary P2. Instead, presence server 420 forwards the second dictionary P2 and the second presence document to each watcher that has subscribed to second presentity 470, as a NOTIFY message. In the case of
A comparison of
More particularly,
A storage area 622 of presence server 620 may comprise a database. Storage area 622 is illustrated as holding a first compressed PIDF document 624 from first presentity 610, and a second compressed PIDF document 628 from second presentity 670. Storage area 622 is also illustrated as storing a third document 626, which comprises the first compressed PIDF document from first presentity 610 and the first dynamic dictionary 614, held as a full dictionary for first presentity 610. Storage area 622 is also illustrated as storing a fourth document 630, which comprises the second compressed PIDF document 628 from second presentity 670 and the second dynamic dictionary 674, which is held as a full dictionary for second presentity 670.
A first watcher 640 holds static dictionary 612, first dynamic dictionary 614 and second dynamic dictionary 674. A second watcher 650 also holds static dictionary 612, first dynamic dictionary 614 and second dynamic dictionary 674. First watcher 640 and second watcher 650 are watchers who have each already received first dynamic dictionary 614 and second dynamic dictionary 674, so can be considered to be ‘pre-existing’ subscribers. From the time point illustrated in
A third watcher 650 is a new subscriber, i.e. not a pre-existing subscriber. Third watcher 660 subscribed to first presentity 610 and second presentity 670, sometime after first watcher 640 and second watcher 640 have already received their dictionaries, and after first presentity 610 and second presentity 670 have each issued at least one dictionary update. Third watcher 660 does finally hold each of static dictionary 612, first dynamic dictionary 614 and second dynamic dictionary 674, in the situation shown in
In
Summarizing the various embodiments of
When any or all of dictionary indices ‘&B’, ‘&C’ and ‘&D’ have already been defined in a static dictionary that is available to the presentity that produced document 710, then those indices, as defined in the static dictionary, can be used straight away. There is then no need to define them as shown in lines 2-6 of document 720.
A presentity P1 shown as reference 902 provides a first dictionary 910 with a PUBLISH message 915. Once published, first dictionary 910 is stored by a presence server 908, shown as reference 920. A watcher 1 shown as reference 906 subscribes 925 to first dictionary 910, and also to a second dictionary 940 from a second presentity P2 shown with reference 904.
Presence server 908 can forward first dictionary 910 and the compressed presence document from Presentity P1 to Watcher 1, with a NOTIFY message 935. Watcher 1 stores first dictionary 910 as shown at 930.
Presentity P2, shown with reference 904, then provides a second dictionary 940 with a PUBLISH message 945. Once published, second dictionary 940 is stored by presence server 908, shown as reference 950.
Presence server 908 can forward second dictionary 940 and the compressed presence document from Presentity P2 to Watcher 1, with the NOTIFY message 955. Watcher 1 stores second dictionary 940 as shown at 960.
Subsequently, presence server 908 needs only to send to Watcher 1 a compressed PIDF presence document from either Presentity P1 or Presentity P2, when either Presentity P1 or Presentity P2 provides a new presence document that does not have dictionary updates. The compressed PIDF presence document is sent as a NOTIFY message, as shown for example at 965. If dictionary updates are needed, then these would also be sent with the compressed PIDF presence document shown at 965.
Presence server 1008 rejects the PUBLISH message 1015 with a ‘4xx’ response at 1075. The response carries the correct range of indices to use. Presentity P1 then sends a PUBLISH message 1085 with the correct indices.
The situation illustrated in
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
