Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
  • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/04—Protocols for data compression, e.g. ROHC
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/18—Multiprotocol handlers, e.g. single devices capable of handling multiple protocols

Definitions

• the present invention relates to the compression of messages in communication using data protocols, e.g. Internet protocols.
• data protocols e.g. Internet protocols.
• IPs Internet Protocols
• SIP Session Initiation Protocol
• SIP is an application layer protocol for establishing, modifying, and terminating multimedia sessions or calls. These sessions may include Internet multimedia conferences, Internet telephony, and similar applications. As is understood in this art, SIP can be used over either the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP).
• TCP Transmission Control Protocol
• UDP User Datagram Protocol
• RTSP Real Time Streaming Protocol
• RTSP may also be used with UDP, TCP, or other protocols as a transport protocol.
• SDP Session Description Protocol
• SDP is used to advertise multimedia conferences and communicate conference addresses and conference tool- specific information. SDP is also used for general real-time multimedia session description purposes. SDP is carried in the message body of SIP and RTSP messages. SIP, RTSP, and SDP are all ASCII text based using the ISO 10646 character set in UTF-8 encoding.
• IP Internet Protocol
• SIP Session Initiation Protocol
• SIP, RTSP, and SDP protocols share similar characteristics which have implications in their use with cellular radio access.
• One of these similarities is the general request and reply nature of the protocols. Typically, when a sender sends a request, the sender stays idle until a response is received.
• SIP, RTSP, and SDP are all ASCII text based using the ISO 10646 character set with UTF-8 encoding. As a result, information is usually represented using a greater number of bits than would be required in a binary representation of the same information.
• Still another characteristic that is shared by the protocols is that they are generally large in size in order to provide the necessary information to session participants.
• IP protocol suite introduces due to large headers and text-based signaling protocols. It is very important in cellular systems to use the scarce radio resources in an efficient manner. In cellular systems it is important to support a sufficient number of users per cell, otherwise implementation and operation costs will be prohibitive. Frequency spectrum, and thus bandwidth, is a costly resource in cellular links and should be used efficiently to maximize system resources.
• a dictionary compression scheme uses a data structure known as a dictionary to store strings of symbols which are found in the input data. The scheme reads in input data and looks for strings of symbols which match those in the dictionary. If a string match is found, a pointer or index to the location of that string in the dictionary is output and transmitted instead of the string itself. If the index is smaller than the string it replaces, compression will occur.
• a decompressor contains a representation of the compressor dictionary so that the original string may be reproduced from the received index.
• An example of a dictionary compression method is the Lempel-Ziv (LZ77) algorithm. This algorithm operates by replacing character strings which have previously occurred in the file by references to the previous occurrence. This method is, of course, particularly successful in files where repeated strings are common.
• Dictionary compression schemes may be generally categorized as either static or dynamic.
• a static dictionary is a predefined dictionary, which is constructed before compression occurs, and which does not change during the compression process.
• Static dictionaries are typically either stored in the compressor and decompressor prior to use, or transmitted and stored in memory prior to the start of compression operations.
• a dynamic or adaptive dictionary scheme allows the contents of the dictionary to change as compression occurs.
• a dynamic dictionary scheme starts out with either no dictionary or a default, predefined dictionary and adds new strings to the dictionary during the compression process. If a string of input data is not found in the dictionary, the string is added to the dictionary in a new position and assigned a new index value. The new string is transmitted to the decompressor so that it can be added to the dictionary of the decompressor. The position of the new string does not have to be transmitted, as the decompressor will recognize that a new string has been received, and will add the string to the decompressor dictionary in the same position in which it was added in the compressor dictionary. In this way, a future occurrence of the string in the input data can be compressed using the updated dictionary.
• the dictionaries at the compressor and decompressor are constructed and updated dynamically as compression occurs.
• One method of dictionary compression is of the type known as sliding window compression.
• the compressor moves a fixed-size sliding window from left to right through the file during compression.
• the compression algorithm searches the file to the left of the window for matches to strings currently in the window. If a match is found the string is replaced by a reference to the location of the match within the file along with a reference to the length of the match.
• the window may consist of a text window consisting of a large block of recently decoded text and a look- ahead buffer. In this version, the look-ahead buffer is used to search for matches within the text window. If a match is found the string is replaced by a reference to the location of the match within the text window and reference to the length of the match. This information is used by the decompressor which maintains the same dictionary to reproduce the original information.
• Another method for the compression of data is the use of a binary code tree.
• symbols or strings which are to be compressed are represented in a tree structure by a variable number of bits such that each symbol is uniquely decodable.
• symbols with higher probabilities of occurrence in the input data are represented by a shorter number of bits than those which have lower probabilities of occurrence.
• individual symbols are laid out as a string of leaf nodes connected to a binary tree. Symbols with higher probabilities of occurrence are represented as shorter branches of the tree resulting in a fewer number of bits being required to represent them. Conversely, symbols with lower probabilities of occurrence are represented as longer branches of the tree requiring a greater number of representation bits.
• binary code trees may be static or dynamic.
• static binary code tree scheme a predefined binary code tree is constructed prior to compression and does not change during the compression process.
• static binary code trees may be stored in the compressor and decompressor in advance, or transmitted and stored prior to the start of compression.
• a dynamic or adaptive binary code tree allows for the addition of new symbols or strings to the code tree during the compression process.
• Various methods may be used to update the nodes of the tree according to the type of binary code tree compression used to allow for the addition of new symbols and the rearrangement of the code tree.
• the binary code tree in the decompressor must also be updated according to the same rules as the binary code tree in the compressor.
• One example of a binary code tree compression scheme is that of a Huffman coding compression scheme.
• Huffman compression is a general compression method intended primarily for compression of ASCII files. Characters occurring frequently in the files are replaced by shorter codes, i.e. codes with less than the 8 bits used by the ASCII code. Huffman compression can be successful in files where relatively few characters are used.
• a general criteria for successful compression using the aforementioned binary compression algorithms is that the file to be compressed is reasonably large.
• the codes for Huffman compression must not be too large compared to the file which is being compressed.
• the file to be compressed must be large enough to have many repeated strings to achieve efficient compression.
• the messages produced by the aforementioned protocols are mostly a few hundred bytes and not large enough to allow efficient compression with the aforementioned algorithms on a message by message basis.
• the present invention is directed to a method, system, and apparatus for increasing the efficiency of the compression of a communication protocol for use over bandwidth limited communication links.
• One aspect of the present invention uses the knowledge of the structure and content of communication protocols to form a static dictionary or static binary code tree. As a result, the compression efficiency can be greatly increased.
• Another aspect of the present invention provides a combined static and dynamic dictionary or binary code tree to perform communication protocol compression.
• the static binary code tree or static dictionary is constructed by studying flows of data protocols in the conditions of their intended usage.
• FIGURE 1 illustrates an exemplary system for communication in accordance with the present invention
• FIGURE 2 illustrates an exemplary embodiment in accordance with the present invention
• FIGURE 3 illustrates an exemplary data packet for compression and decompression in accordance with the present invention
• FIGURE 4 illustrates another exemplary embodiment in accordance with the present invention.
• FIGURE 5 illustrates another exemplary embodiment in accordance with the present invention.
• FIGURE 1 illustrates an exemplary system for communication in accordance with the present invention.
• a mobile terminal 110 is in communication with a base station 120 using communication protocols over a communication link 115, e.g. a wireless link.
• the base station 120 is in communication with a fixed network 130,such as a PSTN, via a link 125.
• Fixed network 130 is in communication with a base station 140 via a link 135.
• Base station 140 is in communication with a terminal 150, which may be a mobile terminal or a fixed terminal, using communication link 145.
• the mobile terminal 110 communicates with the base station 120 using compressed data over the communication link 115.
• base station 140 may communicate with terminal 150 using compressed data.
• components in the system of FIGURE 1, such as mobile terminal 110 and base station 140 may include a memory 160 and processor 155 used for storing and executing software instructions which implement compression and decompression algorithms.
• the present invention may be used in other communication systems, such as a cellular network, that use communication protocols over links in which compression is desired.
• FIGURE 2 illustrates an exemplary embodiment of the present invention.
• an entity A (210) communicates with an entity B (230) using communication links (250, 255) in which data compression is used.
• Each entity includes a data compressor (215, 245) and a data decompressor (225, 235).
• a dictionary compression methodology is used.
• a static dictionary 220 in each entity is used to compress and decompress data to be communicated over the communication links using a data protocol.
• the compressor and/or decompressor may be implemented using a processor and associated memory having stored therein instructions for a compression/decompression algorithm(s).
• the communication entities may comprise a number of communication devices.
• entity A may comprise mobile terminal 110
• entity B may comprise base station 140.
• entity A (210) and entity B (230) use identical static dictionaries 220.
• the static dictionary 220 may be built from protocol field-names and common symbol strings used by the communication protocol, e.g. , an Internet protocol, which is being used to communicate over the communication links (250, 255).
• the communication entities may comprise a number of communication devices.
• entity A may comprise a mobile terminal
• entity B may comprise a base station.
• entries that may be used to form the dictionary include media- type information such as audio, video, and image information.
• Other examples of dictionary entries which may used to form the dictionary include the protocol token JO-
• FIGURE 3 illustrates an exemplary data packet 310 for compression and decompression in accordance with the present invention.
• data packet 310 represents information which will be transmitted according to a given data protocol.
• String A (320) and string C (340) represent portions of the data packet 310 which are not found in the static dictionary.
• String B (330) and string D (350) represents portions of the data packet 310 which are found in the static dictionary.
• an index 370 to a location of string B in the static dictionary and an index 380 to a location of string D in the static dictionary need to be transmitted for those portions of the data packet 310.
• String A (330) and string C (340) may then be added as uncompressed data to index 370 and index 380 to form the compressed data packet 360.
• strings A (320) and string C (340) may be compressed using any of a number of compression methods known to one skilled in the art.
• the compressed data packet 360 is then transmitted to a receiving entity.
• the index 370 and index 380 are matched to the corresponding entries in the identical static dictionary of the receiving entity to form a reconstruction of string B (330') and string D (350').
• the received string A (320') and string C (340') is combined with the reconstruction of string B (330') and string D (350') to form a reconstruction of the original data packet (310').
• FIGURE 4 illustrates another exemplary embodiment of the present invention. Since the nature and format of data which is transmitted using bidirectional communication is often different for each direction of communication, a compression scheme which can be tailored individually to each communication direction is beneficial.
• an entity A (410) includes a data compressor 415 with associated static dictionary A (420), and a data decompressor 425 with associated static dictionary B (430) .
• An entity B (440) includes a data decompressor 445 with associated static dictionary A (420), and data compressor 455 with associated static dictionary B (430).
• entity A (410) sends a message or data compressed using data compressor 415 to entity B (440) over communication link 460 to be decompressed with decompressor 445 using static dictionary A (420).
• compressor 415 of entity A (410) and decompressor 445 of entity B (440) use identical static dictionary A (420) for compression and decompression.
• entity B (440) sends a message or data compressed using data compressor 455 to entity A (410) over communication link 465 to be decompressed using decompressor 425.
• decompressor 425 of entity A (410) use identical static dictionary B (430) for compression and decompression.
• This exemplary embodiment of the present invention allows for the design of static dictionaries which are optimized for each direction of communication.
• FIGURE 5 illustrates another exemplary embodiment in accordance with the present invention in which a combined static and dynamic dictionary is used.
• an initial static dictionary is used as a starting dictionary for the compressor and decompressor at each communication entity.
• the dictionary operates as a dynamic dictionary.
• an entity A (510) including a compressor 515 with an associated static/dynamic dictionary 520, communicates with an entity B (530), including a decompressor 535 with an associated static/dynamic dictionary 540, using a first communication link 550.
• a message to be compressed and transmitted to entity B (530) is tested against the dictionary 520. If a portion of the message matches a dictionary entry, that portion is replaced by its corresponding index. The message portion which is not matched to an entry in the dictionary 520, or alternatively selected fields of this message portion, are then added to the dictionary 520 for use in future compression.
• entity B (530) The index and the uncompressed portion are then transmitted to entity B (530) over the first communication link 550.
• Entity B (530) then decodes and separates the received message into the index information and the uncompressed portion.
• the decompressor 535 in entity B (530) reproduces the compressed information by matching the index to an entry in its dictionary 540, which is then added to the uncompressed data to form the original message.
• the message portion which was added to the dictionary 520 in entity A (510) is then added to the dictionary 540 of entity B (530) so that each entity maintains matching dictionaries.
• Subsequent messages transmitted from entity A (510) to entity B (530) are compressed by using the updated dictionary 520 and decompressed by entity B (530) using updated dictionary 540.
• dictionary 520 of entity A (520) and dictionary 540 of entity B are dynamically updated to allow the compression methodology to adapt to the data that is being transmitted, which provides for continual improvement in compression efficiency.
• entity A (510) may include a decompressor 525 and entity B (530) may include a compressor 545, respectively, thus allowing for entity B (530) to send compressed messages to entity A (510) using a second communication link 555.
• entity A may include a decompressor 525
• entity B may include a compressor 545, respectively, thus allowing for entity B (530) to send compressed messages to entity A (510) using a second communication link 555.
• Decompressor 525 of entity A may use the same static/dynamic dictionary 520 as compressor 515.
• compressor 545 of entity B may use the same static/dynamic dictionary 540 as decompressor 535.
• a separate static/dynamic dictionary may be used for each compressor/decompressor pair, allowing for the use of static/dynamic dictionaries which can be optimized for each direction of communication.
• a sliding window dictionary compression method may be used. As in the previous embodiment, an initial static dictionary is used as a starting dictionary for the compressor and decompressor, which then operates as a dynamic dictionary as soon as communication begins.
• a message to be compressed is appended to the dictionary in a first entity containing a compressor.
• the dictionary with the appended message is then processed according to a sliding window compression method, e.g. Lempel-Ziv, to produce the compressed message.
• the dictionary may also be compressed along with the attached message.
• the part of the compressed message corresponding to the static/dynamic dictionary is removed and replaced with a reference or an index to a corresponding location in the dictionary.
• the rest of the compressed message along with the reference information is transmitted to the decompressor in a second entity.
• the received compressed message is appended to a compressed version of the static/dynamic dictionary in the second entity so that the decompressor has the same dictionary as the compressor.
• the result is then processed by the corresponding decompression method, e.g. Lempel-Ziv, to produce the original message.
• the dictionary is not compressed by the compression method.
• the dictionary may be preloaded into the buffers and search trees used in the implementation of the compression algorithm prior to operation. When a message to be compressed arrives, the actual compression will start at the position in the buffer in which the message has been loaded. Thus the dictionary will not be compressed, only the message itself.
• the corresponding dictionary of the decompressor will also be in an uncompressed form.
• An important aspect of the present invention is the construction of the static dictionary.
• One exemplary methodology of constructing a static dictionary in accordance with the present invention includes studying flows of data packets to collect statistical data for the desired communication protocols over the communication links in which compression is desired. Through the use of this statistical data the static dictionary may be constructed using the most frequently used protocol field names and other common strings of a given communication protocol to provide optimal compression of the data or messages which are to be sent. The static dictionary may then be constructed and stored at both a first communication entity and a second communication entity prior to use. Such storage prior to use would be particularly beneficial for use in short communication sessions so that overhead which may occur at the beginning of a communication session is reduced. Alternately the static dictionary may be sent from the compressor to the decompressor at the beginning of a communication session before compression occurs.
• a static binary code tree scheme may be used.
• a static binary code tree may be constructed using statistical methods such as studying flows of packets for the desired data protocol over the communication link. Using this statistical information, the static binary code tree may be constructed such that protocol field names and other common strings of the data protocol which have a higher probability of occurrence are represented with a smaller number of bits than those that have a lower probability of occurrence. As a result, compression efficiency is increased.
• One such example of a binary code tree compression scheme which may be used in the practice of the present invention is that of a Huffman coding method.
• a static binary code tree may be used in combination with a static dictionary.
• a static dictionary is first constructed using a desired methodology such as one of the aforedescribed methodologies in accordance with the present invention.
• a static binary code tree may then be constructed by studying flows of packets for the desired data protocol with the static dictionary in use and constructing the static binary code tree accordingly.
• the combined use of static dictionary compression and static binary code tree compression, such as that of Huffman coding, may be used to increase compression efficiency of the transmitted data.

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• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Theoretical Computer Science (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)
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• Computer And Data Communications (AREA)

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• 2001
  • 2001-10-30 TW TW90126862A patent/TW543311B/zh not_active IP Right Cessation
  • 2001-11-15 AU AU2002215287A patent/AU2002215287A1/en not_active Abandoned
  • 2001-11-15 JP JP2002543788A patent/JP3958211B2/ja not_active Expired - Lifetime
  • 2001-11-15 CA CA2428788A patent/CA2428788C/en not_active Expired - Lifetime
  • 2001-11-15 CN CNB01822069XA patent/CN1316749C/zh not_active Expired - Lifetime
  • 2001-11-15 WO PCT/SE2001/002549 patent/WO2002041497A2/en active Application Filing
  • 2001-11-15 EP EP01983894A patent/EP1334557A2/en not_active Withdrawn

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