Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/18—Service support devices; Network management devices
  • H04W88/181—Transcoding devices; Rate adaptation devices
• • 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
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/1607—Details of the supervisory signal
  • H04L1/1671—Details of the supervisory signal the supervisory signal being transmitted together with control information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/1607—Details of the supervisory signal
  • H04L1/1657—Implicit acknowledgement of correct or incorrect reception, e.g. with a moving window

Definitions

• the present invention relates to improved compression for 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. 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 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
• RTSP Real-Time Transport Protocol
• SDP Session Initiation Protocol
• 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 way. It must be possible to support a sufficient number of users per cell, otherwise costs will be prohibitive. Frequency spectrum, and thus bandwidth, is a costly resource in cellular links and must be used carefully.
• UMTS and EDGE mobile communication systems and in future releases of second generation systems, such as GSM and IS-95 much of the signaling traffic will be performed by using Internet protocols.
• most of the Internet protocols have been developed for fixed, relatively broadband connections. When access occurs over narrow band cellular links, compression of the protocol messages is needed to meet quality of service requirements, such as set-up time and delay. Typically, compression over the entire communication path is not needed. However, compression of traffic over the radio link, such as from a wireless user terminal to a core network, is greatly desirable.
• Standard binary compression methods such as Lempel-Ziv and Huffman coding
• Lempel-Ziv and Huffman coding are very general in the sense that they do not utilize any explicit knowledge of the structure of the data to be compressed.
• the use of such methods on Internet data protocols, e.g., SIP and RTSP present difficulties for the efficient compression of communication methods.
• Standard binary compression methods available today are typically designed for large data files. As a consequence, use of such methods for small messages or messages with few repeated strings results in compression performance which is generally very poor. In fact, if the message to be compressed is small and/or contains few repeated strings, the use of some standard compression methods may result in a compressed packet which is actually larger than the original uncompressed packet, thereby achieving a counterproductive result.
• 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 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 dictionaiy 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 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 that 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 im 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.
• a general criteria for successful compression using the aforementioned binary compression algorithms is that the file to be compressed is reasonably large. This is a consequence of the compression algorithms.
• 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 and robustness of the compression of a communication protocol for communication between entities over bandwidth limited communication links.
• the present invention uses the request-reply nature of communication protocols to update compression and decompression dictionaries.
• Each communication entity will update its dictionary with a new message as soon as it is known that the other communication entity has access to the message.
• an entity updates a compression/decompression dictionary by updating the dictionary with sent messages as soon as a reply arrives from the other entity, and by updating the dictionary with received messages immediately.
• received messages are used to update an entity's decompression dictionary and sent messages are used to update an entity's compression dictionary.
• 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 method of data compression in accordance with the invention of FIGURE 2;
• FIGURE 4 illustrates another exemplary embodiment in accordance with the present invention.
• FIGURE 5 illustrates an exemplary method of data compression in accordance with the invention of FIGURE 4.
• 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. It should also be understood that 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.
• entity A (210) communicates with an entity B (230) using communication links (250, 255) with a communication protocol in which a dictionary data compression method is used.
• Entity A (210) includes a compressor 215 for compressing data to be transmitted to entity B (230) over communication link 250, and a decompressor 225 for decompressing data received from entity B (230) over communication link 255.
• Entity A (210) contains a dictionary 220 which is associated with compressor 215 and decompressor 225.
• 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 a mobile terminal
• entity B may comprise a base station.
• Entity B contains a decompressor 235 for decompressing data received from communication link 250 and a compressor 245 for compressing data to be transmitted over communication link 255.
• Entity B (230) contains a dictionary 240 associated with decompressor 235 and compressor 245.
• the decompressor 235 and compressor 245 use the shared dictionary 240 for the compression and decompression of messages.
• FIGURE 3 illustrates an exemplary method of data compression in accordance with the invention of FIGURE 2. In this exemplary method, the reply-request nature of communication protocols is used to update compression dictionaries at each communication entity.
• entity A (210) and entity B (230) communicate using compressed messages over communication links (250,255) through the use of a communication protocol.
• each entity may begin with an empty dictionary which is updated during the communication session.
• the entities may begin with the same default dictionaries which are then updated during the communication session.
• the general method of updating compression/decompression dictionaries according to the present method is for each entity to update its dictionary with a particular message as soon as it is known that the other entity has access to that particular message.
• an entity will update its dictionary with a message which it has sent as soon as a reply arrives from the other entity indicating that it has received the message. Consequently, an entity will update its dictionary with a received message immediately upon arrival.
• a dictionary need not be updated with an entire message of the communication protocol. Alternately, only portions of a message in which it would be beneficial to be added to the compression dictionary may be compressed using the current method. This portion of the message may be compressed using the method of the present invention while the remainder of the message may be sent in an uncompressed format or be compressed using an alternate method known to one skilled in the art.
• flow arrows indicate the message flow (M1-M4) between entity A (210) and entity B (230) during an exemplary communication session.
• the dictionary columns indicate the contents of entity A's dictionary (220) and entity B's dictionary (240) at given instances during the communication session.
• the notation of E represents an empty dictionary, while the notation Mn-Mm represents messages n through m as being in the dictionary at that current instant.
• the notations of C(M) and DC(M) represent the respective compression and decompression of message M using the current dictionary as indicated in the dictionary column.
• entity A (210) and entity B (230) both begin with empty dictionaries (E) prior to the start of the communication session.
• Entity A prepares to send a first request message, Ml, to entity B.
• Ml is compressed using entity A's empty dictionary (step 305).
• Entity A temporarily stores Ml in memory and sends the compressed version of Ml to entity B (step 310).
• entity B receives the compressed message Ml, it decompresses the compressed message Ml using its current empty dictionary (E) to reproduce the original message Ml (step 315).
• entity B adds Ml to its dictionary (step 320).
• entity B When entity B prepares to send a response or reply message, M2, to entity A, entity B compresses M2 by using the dictionary containing Ml (step 325), i.e. by replacing strings in M2 that were also in Ml with a reference to their location in the dictionary. Entity B then temporarily stores M2 in memory and sends the compressed version of M2 to entity A (step 330).
• entity A receives the compressed M2 reply message, entity A adds Ml to its dictionary (step 335) and decompresses M2 using the updated dictionary now containing Ml (step 340). Entity A then appends M2 to its dictionary so that the dictionary now contains both Ml and M2 (step 345).
• entity A prepares to send another request M3 to entity B by first compressing
• Entity A temporarily stores M3 in memory. Entity A then sends the compressed M3 message to entity B (step 355). When entity B receives the compressed message M3, it adds
• M2 to its dictionary (step 360) and decompresses M3 using its current dictionary containing Ml and M2 (step 365). Entity B then adds M3 to its dictionary (step 370).
• entity B When entity B sends a response, M4, to entity A, entity B compresses M4 using the dictionary containing M1-M3 (step 375). Entity B temporarily stores M4 and sends the compresses message M4 to entity A (step 380).
• entity A receives the response message M4, entity A adds M3 to its dictionary (step 385) and decompresses M4 using the dictionary containing M1-M3 (step 390). Entity A then adds M4 to its dictionary (step 395) to be used in the compression and decompression of further messages.
• both communication entities maintain identically updated dictionaries for compression and decompression of communication protocol messages.
• FIGURE 4 illustrates another exemplary embodiment in accordance with the present invention.
• entity A (410) communicates with entity B (440) using communication links (470, 475) in which a dictionary compression method is used.
• Entity A (410) includes a compressor 415 for compressing data to be transmitted to entity B (440) over communication link 470, and a decompressor 425 for decompressing data received from entity B (440) using communication link 475.
• Entity B (440) contains a decompressor 445 for decompressing data received from communication link 470, and a compressor 455 for compressing data to be transmitted over communication link 475 to entity A (410).
• each entity is not configured to communicate with one another in regards to compression and decompression operations.
• each entity must maintain separate dictionaries for compression and decompression.
• the compressor 415 of entity A (410) includes an associated compression dictionary 415 and decompressor 425 of entity A (410) includes an associated decompression dictionary 430.
• the decompressor 425 of entity A (410) includes an associated decompression dictionary 430.
• entity B includes an associated decompression dictionary 450 and compressor 455 of the entity B (440) includes an associated decompression dictionary 460.
• the previous method is modified such that received messages are used to update the decompression dictionaries in each entity, while sent messages are used to update the compression dictionaries of each entity as soon as the entity is aware that the sent message was received.
• an entity will not have the same dictionary for compression and decompression.
• the contents of entity A's compression dictionary 420 will correspond to the contents of entity B's decompression dictionary 450
• entity B's compression dictionary 460 will correspond to the contents of entity A's decompression dictionary
• flow arrows indicate the message flow (M1-M4) between entity A (410) and entity B (440) during an exemplary communication session.
• the dictionary columns indicate the contents of entity A's compressor dictionary (420) and decompressor dictionary (430), and entity B's decompressor dictionary (450) and compressor dictionary (460) at given instances during the communication session.
• the notation of E represents an empty dictionary, while the notation Mn-Mm represents messages n through m as being in the dictionary at that current instant.
• the notations of C(M) and DC(M) represent the respective compression and decompression of message M using the current compressor or decompression dictionary of each entity, as indicated in the dictionary columns.
• compressor dictionary (420) and decompressor dictionary (430) of entity A (410), and decompressor dictionary (450) and compressor dictionary (460) of entity B (440) begin with empty dictionaries (E) prior to the start of the communication session.
• Entity A prepares to send a first request message, Ml , to entity B.
• Ml is compressed using entity A's empty compressor dictionary (420)
• Entity A (410) temporarily stores Ml in memory and sends the compressed version of Ml to entity B (step 510).
• entity B receives the compressed message Ml, it decompresses the compressed message Ml using its current empty decompressor dictionary (450) to reproduce the original message Ml (step 515).
• entity B adds Ml to its decompressor dictionary (450) (step 520).
• entity B When entity B prepares to send a response or reply message, M2, to entity A, entity B compresses M2 by using currently empty compressor dictionary (460) (step 525). Entity B then temporarily stores M2 in memory and sends the compressed version of M2 to entity A (step 530). When entity A receives the compressed M2 reply message, entity A decompresses M2 using the currently empty decompressor dictionary (430) (step 535). The received message M2 serves as an implicit acknowledgment to entity A that message Ml was received by entity B. As a result, entity A adds Ml to its compressor dictionary (420) (step 540). Entity A also adds M2 to its decompressor dictionary (430) (step 545). Further requests and responses are performed in the same manner.
• M2 When entity B prepares to send a response or reply message, M2, to entity A, entity B compresses M2 by using currently empty compressor dictionary (460) (step 525). Entity B then temporarily stores M2 in memory and sends the compressed version of M2 to
• entity A prepares to send another request M3 to entity B by first compressing M3 using entity A's current compressor dictionary (420) containing Ml (step 550). In addition, entity A temporarily stores M3 in memory. Entity A then sends the compressed M3 message to entity B (step 555). When entity B receives the compressed message M3, it decompresses M3 using its current decompressor dictionary (450) containing Ml (step 560). In addition, entity B adds M2 to its compressor dictionary (460) (step 565). Entity B then adds M3 to its decompressor dictionary (step 570). When entity B sends a response, M4, to entity A, entity B compresses M4 using the compressor dictionary (450) containing M2 (step 575).
• Entity B temporarily stores M4 and sends the compresses message M4 to entity A (step 580).
• entity A receives the response message M4, entity A decompresses M4 using the decompressor dictionary (430) containing M2 (step 585), and adds M3 to its compressor dictionary (420) (step 590). Entity A then adds M4 to its decompressor dictionary (430) (step 595).
• the system and method of the present invention for updating compression and decompression dictionaries provide for the benefit of a greatly increased compression efficiency by using the request-reply nature of communication protocols to provide for fast dictionary updates.
• the present invention provides for robustness since updates to a dictionary are not performed until the communication entity is aware that the other communication entity has access to the new part of the dictionary. Hence, if a message is lost, the dictionaries will not be updated, and the next request will be compressed with the dictionary that was used to compress the lost message.
• the present method allows for robustness in instances when a strict request- reply sequence is not followed. In this way, communication entities may retain matching dictionaries regardless of whether a communication message was not sent or was lost during transmission.

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• Signal Processing (AREA)
• Theoretical Computer Science (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)
• Information Transfer Between Computers (AREA)
• Communication Control (AREA)

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• 2001
  • 2001-11-15 AR ARP010105351 patent/AR042582A1/es not_active Application Discontinuation
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  • 2001-11-16 AU AU2002214521A patent/AU2002214521A1/en not_active Abandoned
  • 2001-11-16 EP EP01983066A patent/EP1334559A2/de not_active Ceased
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