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
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0041—Arrangements at the transmitter end
• • 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
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0056—Systems characterized by the type of code used
  • H04L1/0061—Error detection codes
• • 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
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0072—Error control for data other than payload data, e.g. control data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/64—Hybrid switching systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/60—Network streaming of media packets
  • H04L65/65—Network streaming protocols, e.g. real-time transport protocol [RTP] or real-time control protocol [RTCP]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/60—Network streaming of media packets
  • H04L65/70—Media network packetisation
• • 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
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/40—Network security protocols
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/1066—Session management
  • H04L65/1101—Session protocols
• • 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
  • H04L69/22—Parsing or analysis of headers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W28/00—Network traffic management; Network resource management
  • H04W28/02—Traffic management, e.g. flow control or congestion control
  • H04W28/06—Optimizing the usage of the radio link, e.g. header compression, information sizing, discarding information

Definitions

• the invention relates generally to packet communications and, more particularly, to header compression in real-time packet communications.
• header compression refers to the art of minimizing the necessary bandwidth for information carried in packet headers on a per hop basis over
• Header compression is usually realized by sending static information only initially. Semi-static information is then transferred by sending only the change (delta) from the previous header, and completely random information is sent without compression. Hence, header compression is usually realized with a state
• Wireless channels typically have a much higher probability for error, so header compression for use in wireless channels should be designed with a much larger bit error probability in mind (e.g., bit error rates up to 10" 3 ).
• the de-compressor context is often updated by each packet received, and if a packet is lost on the link, the context will
• a request for update is sent from the receiving end when the decompressor realizes that the first packet is discarded (or lost), and then it takes a full round-trip (from receiving end to transmitting end and back) before the update (packet with uncompressed header) arrives. This often results in many lost packets.
• the loss of context state may also occur if the receiving de-compressor fails to successfully decompress a compressed header.
• the quality of real time speech service will degrade substantially with increased packet loss rate due to successive lost speech frames. If the speech frame enors have a bursty characteristic, the speech quality will be worse than for the same speech frame error rate but with a less conelated frame error
• packet loss is to increase the intelligence at the receiver, for example by increasing
• stamp has a more randomized value from the receiver's point of view.
• CRTP CRTP time
• stamp delta value is coded with a varying number of bits depending on the value.
• a large time stamp change since the last packet causes a large delta value, which disadvantageous ⁇ requires more bits in the compressed header to carry the delta value indicative of the time stamp information.
• the time stamp field of the RTP header will have a stochastic behavior difficult to predict in a stream of RTP UPP/IP packets carrying speech.
• the time stamp field is one of the most difficult fields to de-compress
• time stamp delta value is coded
• the present invention advantageously provides techniques for efficiently
• time stamp values A first part of the time stamp value is selected by the header
• the header decompressor based on elapsed time between receipt of consecutive
• the header decompressor combines the second part with the first part received from the header compressor to produce a reconstructed time stamp value.
• FIGURE 1 conceptually illustrates exemplary time stamp compression and decompression techniques according to the invention.
• FIGURE 2 illustrates an exemplary packet data transmitting station according
• FIGURE 3 illustrates exemplary embodiments of the header compressor of
• FIGURE 2 is a diagrammatic representation of FIGURE 1
• FIGURE 3 A illustrates an example of the time stamp field of FIGURE 3.
• FIGURE 4 illustrates exemplary operations which can be performed by the
• FIGURE 5 illustrates an exemplary packet data receiving station according to
• FIGURE 6 illustrates exemplary embodiments of the header decompressor of
• FIGURE 7 illustrates an exemplary embodiment of the time stamp decompressor of FIGURE 6.
• FIGURE 7A illustrates other exemplary embodiments of the time stamp decompressor of FIGURES 6 and 7.
• FIGURE 8 illustrates exemplary operations which can be performed by the time stamp decompressor embodiments of FIGURES 6-7 A.
• FIGURE 9 illustrates exemplary operations which can be performed in FIGURE 8 to calculate the scaled time stamp estimate.
• FIGURE 1 conceptually illustrates exemplary time stamp compression
• the header decompressor at the receiver uses a local clock to estimate the elapsed time between the last speech packet before a period of speech inactivity and the first speech
• the header decompressor can make an estimate of the difference (or the delta) between the time stamp fields of these two speech packets that bound the period of speech inactivity. This estimate of the difference between time stamp values can be used, in
• the channel 13 can be a wireless channel, for example, a UMTS air interface or other cellular radio interface.
• packet n designate the next successive speech packet, namely the first speech packet after the period of speech
• time stamp units by multiplying the elapsed time by an estimate of how much the time stamp value changes per unit time.
• delta_T be the elapsed time represented by the aforementioned time difference T(n) - T(n-l), and let TS_change be the estimate of how much the time
• stamp value changes per unit time.
• the value TS_change can then be multiplied by the value deltaXT to produce an estimate of how many time stamp units are associated with the elapsed time delta_T, in other words, an estimate of the difference between the time stamp values of packet n-1 and packet n.
• time stamp of packet n, TS_estimate is given by adding the estimated difference in
• time stamp values (TS_change multiplied by delta_T) to the known time stamp value of packet n-1.
• the header decompressor attempts to determine whether TS_guess is a correct guess of the original time stamp TS. If not, then another guess
• FIGURE 2 illustrates an exemplary packet data transmission station which can perform the exemplary time stamp compression techniques illustrated in FIGURE 1.
• the transmission station can be, for example, a fixed-site or mobile transmitter
• packet data communications application 24 produces payload information at 25 and header information at 26.
• the payload information can be used in conventional fashion by payload processor 20 to produce a payload 23, and the header information
• a conventional radio transmitter 29 can use well known techniques to transmit the packet 21 over a radio link such as a cellular
• the communications application 24 further provides a resume signal 27 which
• FIGURE 1 The header compressor 28 is responsive to activation of the signal 27 for
• FIGURE 3 illustrates exemplary embodiments of the header compressor 28 of
• FIGURE 2 In the header compressor embodiments of FIGURE 3, a separator 33
• the separator 33 separates the time stamp field information from the other header information received at 26, so that the time stamp information can be compressed
• a divider 35 scales the time stamp
• the time stamp can be expected to increase by a constant incremental amount with each successive packet during a
• the value TS_increment represents an estimate of this constant incremental amount, and can be determined, for example, by empirical observation.
• the divider 35 operates to scale down the time stamp value, thereby reducing the number of bits necessary to represent the time stamp value. In other embodiments, the divider 35 can be omitted or used selectively, as shown in
• a least significant bit extractor 36 receives the scaled time stamp value from divider 35, and extracts the least significant bits (LSBs) from that scaled value.
• an appending apparatus appends to the LSBs a resume code produced by an encoder
• the apparatus 37 can also append a checksum (e.g., CRC checksum), generated from the time stamp
• the selector 30 is controlled by the resume signal 27, so that if the resume
• the other header information (non-time stamp
• separator 33 can be compressed using a conventional header compression techniques at 302, and the resulting compressed header information can
• FIGURE 3A illustrates the time stamp field 31 produced when the resume signal 27 is active in FIGURES 2 and 3.
• the time stamp field 31 includes the resume code, the LSBs of the scaled time stamp value and, as
• checksum generated at 38 optionally includes the checksum generated at 38.
• FIGURE 4 illustrates exemplary time stamp compression operations which can
• the time stamp value (see TS in Figure 1) is used to generate a checksum at 46. Thereafter, the time stamp value
• time stamp field is ready for assembly into the compressed header at 47, after which the next packet is awaited at 48.
• FIGURE 5 illustrates an exemplary embodiment of a packet data receiving
• This receiving station which can perform the exemplary time stamp decompression techniques illustrated in FIGURE 1.
• This receiving station can be, for example, a fixed-site or
• a conventional radio receiver 54 can use well known techniques to receive from a radio communication link, for example a cellular radio link, a received version 21 ' of a transmitted packet such as the packet 21 illustrated in FIGURE 2. As shown in Figure 5, such a received version 21 ' would include a received version 22' of the compressed header 22 of FIGURE 2 and a received version 23 ' of the payload
• the received payload version 23' can be provided to a payload
• processor 58 which can produce, in conventional fashion, received payload information for input at 51 to a packet data communications application 52.
• the received compressed header version 22' is provided to a header decompressor 53 which decompresses the received version 22 ' to produce received header information
• FIGURE 6 illustrates an exemplary embodiment of the header decompressor
• the received version 22' of the compressed header is input to an RTP detector 61 which can use conventional techniques to detect whether or not the received packet is an RTP packet. In response to detecting that the packet is not an RTP packet.
• the detector 61 activates an output signal 66 which controls selectors 68 and 69
• the detector 61 determines that an RTP packet has been
• control signal 66 controls selectors 68 and 69 such that the compressed header is processed through a processing path 600 which implements time stamp field decompression according to the invention.
• the processing path 600 includes a separator 65 which separates the time stamp field from the other fields of the received version 22 ' of the compressed header.
• the received versions of fields other than the time stamp field can then be applied to a conventional header decompressor at 67.
• the received version of the time stamp field at 63 is input to a time stamp decompressor 60.
• stamp decompressor also receives as an input the control signal 66 output from RTP detector 61. In response to the control signal 66 and the time stamp field received at
• the time stamp decompressor 60 outputs a time stamp at 62. This time stamp is appended by appending apparatus 601 to the other decompressed header information
• FIGURE 7 illustrates exemplary embodiments of the time stamp decompressor
• the code detector 70 outputs a control
• the received time stamp field 63 is input via selector 703 to an extractor 72 which extracts received versions of the LSBs and checksum (see FIGURE 3 A) from the time stamp field
• resume code is merely one example of a technique for tnggenng the desired decompression operations
• a time stamp estimator 75 can produce the time stamp estimate, TS_est ⁇ mate, generally as descnbed above relative to Figure 1
• the time stamp estimator has an
• decompressor 73 can be stored at storage unit 77 (which can be a single register),
• stamp estimator 75 when packet n arnves
• the time stamp estimator 75 also receives information indicative of the times T(n) and T(n-l) at which packet n and packet n-1 were received This time
• a storage unit 76 which is coupled to receive local time information from a local clock 74. For each RTP packet detected by the detector 61 in FIGURE 6, the storage unit 76 stores the time of arrival of that packet, as measured
• the storage unit 76 thus need only be a two-deep stack in order
• the time stamp estimator 75 also has access to the time stamp change value
• the time stamp estimator is operable in response to the local time
• TS_estimate is applied to a most significant bit extractor 78 which extracts therefrom the most significant bits (MSBs), which constitute a truncated estimate of the time stamp value.
• MSBs most significant bits
• apparatus 702 appends the least significant bits (LSBs) received from extractor 72 to the most significant bits (MSBs) output from extractor 78, and the result is multiplied by TS_increment at multiplier 71 thereby producing TS_guess as described above.
• LSBs least significant bits
• MSBs most significant bits
• the time stamp estimator 75 uses TS_increment to down scale its time stamp estimate generally in the same manner described above at 35 in FIGURE 3 in order to permit accurate combining of the MSBs and LSBs at 702, so the multiplier 71 is used to
• a verifier 79 receives as input TS_guess and the received version of the
• the verifier 79 is operable to generate a checksum from extractor 72.
• the verifier output signal 704 activates a connection unit 701 which then connects the TS_guess value to selector
• control signal 704 maintains the connection unit 701 in
• time stamp estimator can thus continue to produce time stamp estimates until the checksums match or until satisfaction of a timeout condition implemented, for example, in either the time stamp estimator 75 or the
• the number of bits in TS_estimate can be, for example, equal to the number
• bits in the time stamp value received by LSB extractor 36 of FIGURE 3, and the number of MSBs extracted by extractor 78 in FIGURE 7 can be, for example, equal to the number of most significant bits that remain (and are discarded) after extraction of the LSBs at 36 in FIGURE 3.
• MSBs extracted at 78 can be determined, for example, by empirical observation to determine what combination of LSB/MSB extraction produces desired results under various conditions. For example, different combinations of LSB/MSB extraction can be used, depending on factors such as transmission delay variations, and clock
• the number of MSBs extracted at 78 could depend on the precision of clock 74.
• the compressor and decompressor can be pre-programmed to implement a
• the compressor can dynamically changeable during the course of the packet flow.
• the compressor can
• stamp value can signal this information to the decompressor, for example, as a part of the resume code illustrated in FIGURE 3 A.
• FIGURE 7A illustrates in broken lines alternative embodiments of the Figure 7 decompressor wherein: the connection unit 701 (and verifier 79) of FIGURE 7 are either omitted or used selectively in correspondence to the use or omission of the checksum in Figure 3; and/or the multiplier 71 is either omitted or used selectively in correspondence to the use or omission of the divider 35 in Figure 3.
• the estimator 75 scales TS_estimate or omits scaling thereof in correspondence to the use or omission
• FIGURE 8 illustrates exemplary time stamp decompression operations which can be performed by the time stamp decompressor embodiments of FIGURES 6-7A. It is first determined at 80 whether or not the time stamp field includes the resume
• TS_estimate time stamp estimate
• the least significant bits received in the compressed header are
• time stamp guess (TS_guess). Thereafter at 85, the time stamp guess is used to generate a checksum, and the generated checksum is compared at 86 to the checksum received in the time stamp field. If the generated checksum matches the received checksum, then the time stamp guess is accepted at TS_guess.
• time stamp for example, based on a predetermined elapsed time value, or a predetermined number of guesses. If it is decided not to give up at 88, then another scaled time stamp estimate is calculated at 82, and the operations at 83-86 are repeated. In making another time stamp estimate, the estimator 75 can, for example, change one or more of the least significant bits of the MSBs that will be extracted from the estimate. In one example, if changing a particular bit (or bits) results in successful re-estimation of the time stamp of a given packet, then this same change can be tried first when re-estimating the time stamp of a subsequent packet. If it is
• FIGURE 8 correspond to the embodiments of FIGURE 7A, wherein checksum verification is omitted, or performed selectively.
• FIGURE 9 illustrates exemplary operations which can be performed at 82 in FIGURE 8 to calculate the estimate of the time stamp.
• time stamp units (using TS_change).
• TS_change the number of elapsed time stamp units determined at 92 is added to the time stamp value (TS(n-l)) of the last RTP
• TS increment is applied to the time stamp estimate produced at 93, thereby to produce the desired scaled time stamp estimate.
• the broken lines in Figure 9 correspond to the embodiments of Figure 7 A, wherein scaling is omitted, or performed selectively.
• the resume code of FIGURE 3 A is not
• FIGURE 1 are always used, so the selectors 30, 703 and 700 (see FIGURES 3 and 7) are always controlled to select "Y".
• the operations at 41 and 42 in FIGURE 4, and the operations at 80 and 81 in FIGURE 8, would be omitted in this
• the invention described above provides, among others, the following exemplary advantages: the number of bits needed to code the time stamp value is reduced; the number of bits needed to code the time stamp value can be held constant regardless of the size of the time stamp change; and, because the absolute time stamp value is encoded at the compressor rather than encoding the amount of the time stamp

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Multimedia (AREA)
• Computer Security & Cryptography (AREA)
• Theoretical Computer Science (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
• Time-Division Multiplex Systems (AREA)

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• 1999
  • 1999-06-18 US US09/335,550 patent/US6680921B1/en not_active Expired - Lifetime
• 2000
  • 2000-06-09 DE DE60030117T patent/DE60030117T2/de not_active Expired - Lifetime
  • 2000-06-09 EP EP00946580A patent/EP1190548B1/en not_active Expired - Lifetime
  • 2000-06-09 WO PCT/SE2000/001203 patent/WO2000079762A1/en not_active Ceased
  • 2000-06-09 CN CNB008090432A patent/CN1157034C/zh not_active Expired - Lifetime
  • 2000-06-09 JP JP2001504656A patent/JP4566488B2/ja not_active Expired - Lifetime
  • 2000-06-09 AU AU60315/00A patent/AU6031500A/en not_active Abandoned
  • 2000-06-16 AR ARP000103029A patent/AR025534A1/es active IP Right Grant

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