System and method for achieving robust IP/UDP/RTP header compression in the presence of unreliable networks

• US 6,608,841 B1
• Filed: 12/30/1999
• Issued: 08/19/2003
• Est. Priority Date: 12/30/1999
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Networks (Nokia Corporation)
• Inventors: Koodli, Rajeev
• Primary Examiner(s): Olms, Douglas
• Assistant Examiner(s): NGUYEN, VAN KIM T
• Application Number:
  US09/476,205
• Time in Patent Office: 1,328 Days
• Field of Search: 370/252, 370/349, 370/401, 370/402, 370/394, 370/410, 370/474, 370/522-524, 370/477, 370/392, 341/60, 341/51, 709/216, 709/217, 709/246, 709/247
• US Class Current: 370/474
• CPC Class Codes: H04L 69/04 Protocols for data compression, e.g. ROHC
• CPC Class Codes: H04L 69/22 Parsing or analysis of headers
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A robust IP/UDP/RTP header compression mechanism is provided to correctly reconstruct IP/UDP/RTP headers in the presence of packet losses and errors of unreliable networks. The header compression mechanism may include a compressor/de-compressor implemented for operation similarly to RFC 2508 but designed specifically to address robustness when employed in lossy and error-prone networks. The robust header compression scheme requires that, when a second-order difference of a field is non-zero, not only a particular RTP packet whose second-order difference is non-zero is sent with the new first-order difference, but also those following packets are also sent with the new first-order difference as long as: (a) a period pre-determined by factors such as channel characteristics (e.g., link round-trip time RTT/inter-packet separation); or (b) a positive confirmation is received by the compressor that the new first-order difference has been correctly received. In addition, during a period of communicating with the new first-order difference, if the corresponding RTP field changes again with non-zero second-order difference, the “new” first-order difference is combined with the original first-order difference such that the two first-order differences may be appended together as a simple means of communicating the two first-order differences reliably.

Claims

1. A data network, comprising:

a first node comprising a header compressor/de-compressor for compressing/de-compressing headers of data packets for transmission via a bandwidth-limited link; and

a second node comprising a header compressor/de-compressor for compressing/de-compressing headers of data packets for transmission via said bandwidth-limited link,

wherein header compression and reconstruction are obtained by first establishing a context state for non-changing fields as well as first-order differences for changing fields between a compressor of one of said first node and said second node and a de-compressor of another one of said first node and said second node, and then when a second-order difference of any field is non-zero, sending a particular packet whose second-order difference is non-zero with a new first-order difference along with those following packets with the new first-order difference until a positive confirmation is received by the compressor that the new first-order difference has been received or until expiration of a predetermined period.

2. The data network as claimed in claim 1, wherein said predetermined period is set as a quotient of a round-trip time of a data packet and an inter-packet separation time.

3. The data network as claimed in claim 1, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to low-speed lines such as dial-up modems.

4. The data network as claimed in claim 1, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to cellular links.

5. The data network as claimed in claim 1, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to an IP-based network of an Internet Service Provider (ISP), an Internet and different source and destination networks, including, for example, a public switched telephone network (PSTN), an integrated services digital network (ISDN) and other access network infrastructures (ANI) for enabling communications between said first node and said second node.

6. The data network as claimed in claim 1, wherein the compressor combines the new first-order difference with the original first-order difference for transmission to the de-compressor, when the corresponding field changes again with non-zero second-order difference during a period of communicating the first-order difference.

7. The data network as claimed in claim 1, wherein said data packets each includes at least a header field comprising a time stamp and a packet sequence number.

8. The data network as claimed in claim 7, wherein said header compression mechanism is implemented to correctly reconstruct headers of said data packets in the presence of packet losses and errors.

9. The data network as claimed in claim 7, wherein said headers are IP/UDP/RTP headers used for real-time communications on the Internet and for applications such as Voice over IP and Video conferencing.

10. The data network as claimed in claim 8, wherein said header compression mechanism is implemented to terminate sending the first-order difference for changing fields unless the corresponding second-order difference is non-zero, after the context state has been established.

11. A packet network, comprising:

a source terminal providing a plurality of packets each packet including a header field;

a destination terminal;

a bandwidth-limited link providing connection between the source terminal and the destination terminal; and

at least one network interface controller of the source terminal or the destination terminal comprises a header compression mechanism installed therein for header compression and reconstruction, said header compression mechanism establishing a context state for non-changing fields as well as first-order differences for changing fields, and then when a second-order difference of any field is non-zero, sending a particular packet whose second-order difference is non-zero with a new first-order difference along with those following packets with the new first-order difference until a positive confirmation is received indicating that the new first-order difference has been received or until expiration of a predetermined period.

12. The packet network as claimed in claim 11, wherein said predetermined period is set as a quotient of a round-trip time of a data packet and an inter-packet separation time.

13. The packet network as claimed in claim 11, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to low-speed lines such as dial-up modems.

14. The packet network as claimed in claim 11, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to cellular links.

15. The packet network as claimed in claim 11, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to an IP-based network of an Internet Service Provider (ISP), an Internet and different source and destination networks, including, for example, a public switched telephone network (PSTN), an integrated services digital network (ISDN) and other access network infrastructures (ANI) for enabling communications between said first node and said second node.

16. The packet network as claimed in claim 11, wherein the compressor combines the new first-order difference with the original first-order difference for transmission to the de-compressor, when the corresponding field changes again with non-zero second-order difference during a period of communicating the first-order difference.

17. The packet network as claimed in claim 11, wherein said header field comprises a time stamp and a packet sequence number.

18. The packet network as claimed in claim 11, wherein said header compression mechanism is implemented to correctly reconstruct headers of said packets in the presence of packet losses and errors.

19. The packet network as claimed in claim 11, wherein said headers are IP/UDP/RTP headers used for real-time communications on the Internet and for applications such as Voice over IP and Video conferencing.

20. The packet network as claimed in claim 11, wherein said header compression mechanism is implemented to terminate sending the first-order difference for changing fields unless the corresponding second-order difference is non-zero, after the context state has been established.

21. A method for achieving robust header compression between a compressor and a de-compressor in the presence of an unreliable network, comprising:

sending headers of data packets, from said compressor to said de-compressor via a bandwidth-limited link until said de-compressor establishes a context state for non-changing fields of said data packets as well as first-order differences for changing fields;

when the context state has been established between said compressor and said de-compressor, determining whether a second-order difference of any field is non-zero; and

when the second-order difference of any field is non-zero, sending a particular packet whose second-order difference is non-zero with a new first-order difference along with those following packets with the new first-order difference until a positive confirmation is received indicating that the new first-order difference has been received or until expiration of a predetermined period.

22. The method as claimed in claim 21, wherein said predetermined period is set as a product of a round-trip time of a data packet and an inter-packet separation time.

23. The method as claimed in claim 21, wherein said bandwidth-limited link provided to connect said compressor and said de-compressor corresponds to low-speed lines such as dial-up modems.

24. The method as claimed in claim 21, wherein said bandwidth-limited link provided to connect said compressor and said de-compressor corresponds to cellular links.

25. The method as claimed in claim 21, wherein said bandwidth-limited link provided to connect said compressor and said de-compressor corresponds to an IP-based network of an Internet Service Provider (ISP), an Internet and different source and destination networks, including, for example, a public switched telephone network (PSTN), an integrated services digital network (ISDN) and other access network infrastructures (ANI) for enabling communications between said first node and said second node.

26. The method as claimed in claim 21, wherein the new first-order difference is combined with the original first-order difference for transmission to the de-compressor, when the corresponding field changes again with non-zero second-order difference during a period of communicating the first-order difference.

27. The method as claimed in claim 21, wherein said data packets each includes a header field comprising a time stamp and a packet sequence number.

28. The method as claimed in claim 21, wherein said headers are IP/UDP/RTP headers used for real-time communications on the Internet and for applications such as Voice over IP and Video conferencing.

30. The host readable medium as claimed in claim 28, wherein said predetermined period is set as a quotient of a round-trip time of a data packet and an inter-packet separation time.

31. The host readable medium as claimed in claim 28, wherein said bandwidth-limited link provided to connect said first node to said second node corresponds to either low-speed lines or cellular links.

32. The host readable medium as claimed in claim 28, wherein the compressor combines the new first-order difference with the original first-order difference for transmission to the de-compressor, when the corresponding field changes again with non-zero second-order difference during a period of communicating the first-order difference.

33. The host readable medium as claimed in claim 28, wherein said header field comprises a time stamp and a packet sequence number, and said headers are IP/UDP/RTP headers used for real-time communications on the Internet and for applications such as Voice over IP and Video conferencing.

29. A host readable medium comprising instructions that, when executed by a host system including a compressor/de-compressor, cause the host system to obtain robust header compression between a compressor and a de-compressor of a remote system by:

sending headers of data packets, from said compressor to said de-compressor via a bandwidth-limited link until said de-compressor establishes a context state for non-changing fields of said data packets as well as first-order differences for changing fields;

when the context state has been established between said compressor and said de-compressor, determining whether a second-order difference of any field is non-zero; and

when the second-order difference of any field is non-zero, sending a particular packet whose second-order difference is non-zero with a new first-order difference along with those following packets with the new first-order difference until a positive confirmation is received indicating that the new first-order difference has been received or until expiration of a predetermined period.