Robust header compression in packet communications

Abstract

A technique for compressing header information to produce a compressed header portion of a data packet to be transmitted across a communication channel includes generating a checksum from the header information, and providing the checksum as the compressed header portion.

What is claimed: 
     
       1. A method of compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said method comprising the steps of:
 determining that the header information of the given data packet includes only static information or information with predictable differences from the header information of a previous data packet; 
 generating a checksum from the header information of the given data packet; and 
 transmitting only the checksum as the compressed header portion of the given data packet in response to determining that the header information of the given data packet includes only static information or information with predictable differences from the header information of the previous data packet. 
 
     
     
       2. The method of  claim 1 , further comprising the steps of:
 determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet; 
 deriving from the header information of the given data packet, additional information for use in reconstructing the header information of the given data packet at a receiving end of the communication channel; and 
 transmitting the additional information in the compressed header portion of the given data packet together with the checksum in response to determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet. 
 
     
     
       3. The method of  claim 1 , wherein said generating step includes generating a Cyclic Redundancy Code (CRC) checksum. 
     
     
       4. The method of  claim 1 , wherein the communication channel includes a wireless communication link. 
     
     
       5. The method of  claim 2 , wherein the information with differences that are not predictable is a time stamp having a value represented by a plurality of bits, and the step of deriving additional information includes:
 selecting at least one least significant bit from the plurality of bits; and 
 transmitting the at least one least significant bit in the compressed header portion of the given data packet together with the checksum. 
 
     
     
       6. An apparatus for compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said apparatus comprising:
 an input for receiving the header information of the given data packet; 
 means for determining that the header information of the given data packet includes only static information or information with predictable differences from the header information of a previous data packet; 
 a checksum generator coupled to said input for generating a checksum from the header information of the given data packet; and 
 an output coupled to said checksum generator for transmitting only the checksum as said compressed header portion of the given data packet. 
 
     
     
       7. The apparatus of  claim 6 , further comprising:
 means for determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet; and 
 a header compressing apparatus coupled to said input for deriving from the header information of the given data packet, additional information for use in reconstructing the header information of the given data packet at a receiving end of the communication channel; 
 wherein responsive to a determination that the header information of the given data packet includes information with differences that are not predictable, the output transmits the additional information in the compressed header portion of the given data packet together with the checksum. 
 
     
     
       8. The apparatus of  claim 6 , wherein said checksum generator is operable to generate a Cyclic Redundancy Code (CRC) checksum. 
     
     
       9. The apparatus of  claim 6 , wherein said communication channel includes a wireless communication link. 
     
     
       10. A method of decompressing a compressed header portion of a given data packet received from a communication channel in order to produce header information, wherein the given data packet is received following a period of inactivity after receiving a previous data packet, said method comprising the steps of:
 obtaining from the compressed header portion of the given data packet, a received version of a checksum that was generated from the header information of the given data packet at a transmitting end of the communication channel; 
 obtaining from the compressed header portion of the given data packet, at least one least significant bit of a time stamp having a value represented by a plurality of bits; 
 determining an absolute time difference between reception of the previous data packet and reception of the given data packet; 
 obtaining an estimate of how much the time stamp typically varies per unit of time; 
 determining a time stamp difference estimate of a difference between a time stamp of the previous data packet and the time stamp of the given data packet, said time stamp difference estimate being determined from the absolute time difference and the estimate of how much the time stamp typically varies per unit of time, wherein the time stamp difference estimate includes most significant bits and least significant bits; 
 combining the most significant bits of the time stamp difference estimate with the at least one least significant bit of the time stamp obtained from the compressed header portion of the given data packet to provide a guess of an uncompressed time stamp value for the given data packet; 
 utilizing the guess of the uncompressed time stamp value for the given data packet to generate a checksum; and 
 comparing the generated checksum with the received version of the checksum to verify the guess of the uncompressed time stamp value. 
 
     
     
       11. A method of compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said method comprising the steps of:
 generating a checksum from the header information of the given data packet;   determining if the header information of the given data packet includes only static information or information with predictable differences from the header information of a previous data packet;
 if the header information contains only static information or information with predictable differences from the header information of the previous data packet, then transmitting only the checksum as the compressed header portion of the given data packet; 
   otherwise, determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet;
 deriving from the header information of the given data packet, additional information for use in reconstructing the header information of the given data packet at a receiving end of the communication channel; and 
   transmitting the additional information in the compressed header portion of the given data packet together with the checksum in response to determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet.   
     
     
       12. A method of compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said method comprising the steps of:
 generating a checksum from the header information of the given data packet;   determining whether the header information of the given data packet includes information with differences that are not predictable from header information of a previous data packet;   if the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet,
 deriving additional information from the header information of the given data packet, based on which the information with differences that are not predictable from the header information of the previous data packet is recoverable at a receiving end of the communication channel; and 
 transmitting the checksum and the additional information in the compressed header portion of the given data packet. 
   
     
     
       13. The method of claim 12, further comprising:
 transmitting only the checksum as the compressed header portion of the given data packet, if the header information of the given data packet does not include information with differences that are not predictable from the header information of the previous data packet.   
     
     
       14. An apparatus for compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said apparatus comprising:
 an input for receiving the header information of the given data packet;   a checksum generator coupled to said input for generating a checksum from the header information of the given data packet; and   means for determining if the header information of the given data packet includes information with unpredictable differences from header information of a previous data packet;   a header compressing apparatus coupled to said input and to said means, and configured to derive additional information from the header information of the given data packet, based on which the information with unpredictable differences from the header information of the previous data packet is recoverable at a receiving end of the communication channel, if said means indicate that the header information of the given data packet includes information with unpredictable differences from the header information of the previous data packet;   an output coupled to said checksum generator, to said means and to said header compressing apparatus, and configured
 to transmit the checksum and the additional information as said compressed header portion of the given data packet, if said means indicate that the header information of the given data packet includes information with unpredictable differences from the header information of the previous data packet, and 
 to transmit the checksum as said compressed header portion of the given data packet, if said means indicate that the header information of the given data packet does not include information with unpredictable differences from the header information of the previous data packet. 
   
     
     
       15. An apparatus for compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said apparatus comprising:
 an input for receiving the header information of the given data packet;   a checksum generator coupled to said input for generating a checksum from the header information of the given data packet; and   means for determining whether the header information of the given data packet includes information with unpredictable differences from header information of a previous data packet;   a header compressing apparatus coupled to said input and to said means, and configured to derive additional information from the header information of the given data packet, based on which the information with unpredictable differences from the header information of the previous data packet is recoverable at a receiving end of the communication channel;   an output coupled to said checksum generator, to said means and to said header compressing apparatus, and configured to transmit the checksum and the additional information as said compressed header portion of the given data packet, if said means indicate that the header information of the given data packet includes information with unpredictable differences from the header information of the previous data packet.   
     
     
       16. The apparatus of claim 15, wherein said output is further configured to transmit the checksum as said compressed header portion of the given data packet, if said means indicate that the header information of the given data packet does not include information with unpredictable differences from the header information of the previous data packet. 
     
     
       17. A method of compressing header information to produce a compressed header portion of a given data packet to be transmitted across a communication channel, said method comprising the steps of:
 determining that the header information of the given data packet includes information with differences that are not predictable from header information of a previous data packet;   deriving from the header information of the given data packet, additional information for use in reconstructing the header information of the given data packet at a receiving end of the communication channel;   generating a checksum from the header information of the given data packet; and   transmitting the additional information in the compressed header portion of the given data packet together with the checksum in response to determining that the header information of the given data packet includes information with differences that are not predictable from the header information of the previous data packet.