METHODS AND SYSTEMS FOR ENHANCING LOCAL REPAIR IN ROBUST HEADER COMPRESSION

• US 20070258458A1
• Filed: 05/02/2007
• Published: 11/08/2007
• Est. Priority Date: 05/04/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Kapoor, Rohit
• Granted Patent: US 7,948,989 B2
• Time in Patent Office: Days
• US Class Current: 370/394
• CPC Class Codes: H04L 1/0079 Formats for control data H04L1/16 takes precedence; training sequences H04L25/00 and H04L27/00
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 65/65 Network streaming protocols, e.g. real-time transport protocol [RTP] or real-time control protocol [RTCP]
• CPC Class Codes: H04L 69/04 Protocols for data compression, e.g. ROHC
• CPC Class Codes: H04L 69/161 Implementation details of TCP/IP or UDP/IP stack architecture; Specification of modified or new header fields
• CPC Class Codes: H04L 69/22 Parsing or analysis of headers
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365

Abstract

Methods and systems to enhance local repair in robust header compression (RoHC) decompressors (110, 114), which may improve network transmission efficiency and quality. One method uses lower layer information to enhance local repair at the decompressor (110, 114). Another method uses a user datagram protocol (UDP) checksum to enhance local repair at the decompressor (110, 114).

Claims

1. A method for decompressing a packet header, the method comprising:

determining if decompression of a current packet header failed;

determining a difference between a link layer sequence number (LL SN) of a previous correctly decompressed packet and a link layer sequence number (LL SN) of the current packet to provide repair information used for header decompression, if header decompression failed; and

decompressing the header of the current packet using the repair information.

2. The method of claim 1, further comprising updating context information used for decompression and delivering the current packet to an upper layer.

3. The method of claim 1, further comprising receiving the previous packet and the current packet over a wireless link.

4. The method of claim 1, wherein the header comprises information related to at least one of Internet Protocol (IP), Real-time Transport Protocol (RTP), User Datagram Protocol (UDP), and Transmission Control Protocol (TCP).

5. The method of claim 1, wherein providing repair information used for header decompression further comprises:

determining if the difference between the first link layer sequence number (LL SN) and the second link layer sequence number (LL SN) is greater than or equal to (2̂

k)−

p, where k is a number of link layer sequence number bits in the current packet, and p is a shift in an interpretation interval; and

if the difference is greater than or equal to (2̂

k)−

p, adding the difference to the first link layer sequence number to provide a new reference sequence number.

6. The method of claim 5, further comprising determining whether sequence number wraparound occurred.

7. The method of claim 6, wherein determining whether sequence number wraparound occurred comprises:

determining if the difference is greater than or equal to 2*(L+1), where L is a length of half of an interpretation interval used for decompression;

if the difference is determined to be greater than or equal to 2*(L+1), determining if the difference is greater than or equal to 2̂

(k+1);

if the difference is determined to be greater than or equal to 2̂

(k+1), then decompressing the header of the current packet a plurality of times using a plurality of interpretation intervals; and

if decompressing the header is successful in only one of the interpretation intervals, passing the current packet to an upper layer.

8. The method of claim 7, wherein the interpretation intervals comprise [L+1, 2*(L+1)−

1], [2*(L+1), 3*(L+1)−

2], . . . , [k*(L+1), (k+1)*(L+1)−

(k)], where INTERVAL_LLSN is defined as k*(L+1)≦

INTERVAL_LLSN≦

(k+1)*(L+1)−

(k).

9. The method of claim 7, further comprising:

if the difference is determined to be less than 2̂

(k+1), then determining the wraparound based on information given by a link layer sequence number and least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number in the header.

10. The method of claim 7, further comprising:

if the difference is determined to be less than 2*(L+1), then determining if the difference is less than or equal to L;

if the difference is less than or equal to L, then performing local repair of decompression context information.

11. The method of claim 7, further comprising:

determining if least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number (SN) in a header is in the range of [INTERVAL_LLSN/2, L];

if least significant bits (LSBs) of the radio transport protocol (RTP) sequence number in the header is in the range of [INTERVAL_LLSN/2, L], then performing local repair of decompression context information.

if least significant bits (LSBs) of the real-time transport protocol (RTP) sequence number in the header is not in the range of [INTERVAL_LLSN/2, L], then repairing the wraparound based on information given by a link layer sequence number and least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number in the header.

12. A method for updating information for header decompression, the method comprising:

determining if decompression of a packet header succeeds;

determining if a user datagram protocol (UDP) checksum in the packet header passes; and

if the decompression succeeds and the UDP checksum passes, updating context information used for decompression and delivering the decompressed packet to an upper layer.

13. An apparatus configured to decompress a packet header, the apparatus comprising:

means for determining whether decompression of a current packet header failed;

means for determining a difference between a link layer sequence number (LL SN) of a previous packet and a link layer sequence number (LL SN) of the current packet to provide repair information used for header decompression, if header decompression failed; and

a decompressor configured to decompress the header of the current packet with the repair information.

14. The apparatus of claim 13, wherein the decompressor is further configured to update context information used for decompression and deliver the current packet to an upper layer.

15. The apparatus of claim 13, further comprising a transceiver to receive the previous packet and the current packet over a wireless link.

16. The apparatus of claim 13, wherein the header comprises information related to at least one of internet protocol (IP), real-time transport protocol (RTP), user datagram protocol (UDP), and transmission control protocol (TCP).

17. The apparatus of claim 13, wherein the decompressor further comprises:

means for determining if the difference between the first link layer sequence number (LL SN) and the second link layer sequence number (LL SN) is greater than or equal to (2̂

k)−

p, where k is a number of link layer sequence number (LL SN) bits in the current packet, and p is a shift in an interpretation interval; and

means for adding the difference to the first link layer sequence number to provide a new reference sequence number, if the difference is greater than or equal to (2̂

k)−

p.

18. The apparatus of claim 17, wherein the decompressor further comprises:

means for determining if sequence number wraparound occurred.

19. The apparatus of claim 18, wherein the means for determining if sequence number wraparound occurred further comprises:

means for determining if the difference is greater than or equal to 2*(L+1), where L is a length of half of an interpretation interval used for decompression;

means for determining if the difference is greater than or equal to 2̂

(k+1), if the difference is determined to be greater than or equal to 2*(L+1);

means for decompressing the header of the current packet a plurality of times using a plurality of interpretation intervals, if the difference is determined to be greater than or equal to 2̂

(k+1); and

means for passing the current packet to an upper layer if decompressing the header is successful in only one of the interpretation intervals.

20. The apparatus of claim 19, wherein the interpretation intervals comprise [L+1, 2*(L+1)−

1], [2*(L+1), 3*(L+1)−

2], . . . , [k*(L+1), (k+1)*(L+1)−

(k)], where INTERVAL_LLSN is defined as k*(L+1)≦

INTERVAL_LLSN≦

(k+1)*(L+1)−

(k).

21. The apparatus of claim 19, wherein the decompressor further comprises:

means for repairing the wraparound based on information given by a link layer sequence number (LL SN) and least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number in the header if the difference is determined to be less than 2̂

(k+1).

22. The apparatus of claim 19, wherein the decompressor further comprises:

means for determining if the difference is less than or equal to L, if the difference is determined to be less than 2*(L+1); and

means for performing local repair of decompression context information, if the difference is less than or equal to L.

23. The apparatus of claim 19, wherein the decompressor further comprises:

means for determining if least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number in the header is in the range of [INTERVAL_LLSN/2, L];

means for performing local repair of decompression context information, if least significant bits (LSBs) of the radio transport protocol (RTP) sequence number in the header is in the range of [INTERVAL_LLSN/2, L]; and

means for repairing the wraparound based on information given by a link layer sequence number and least significant bits (LSBs) of a real-time transport protocol (RTP) sequence number in the header, if least significant bits (LSBs) of the real-time transport protocol (RTP) sequence number in the header is not in the range of [INTERVAL_LLSN/2, L].

24. At least one processor for header decompression comprising:

a first module configured to determine if decompression of a packet header succeeds;

a second module configured to determine if a user datagram protocol (UDP) checksum in the packet header passes; and

a third module configured to update context information used for decompression and delivering the decompressed packet to an upper layer if the decompression succeeds and the UDP checksum passes.

25. An apparatus configured to decompress a packet header, the apparatus comprising:

means for determining whether decompression of a current packet header failed;

means for determining a difference between a link layer sequence number (LL SN) of a previous packet and a link layer sequence number (LL SN) of the current packet to provide repair information used for header decompression if header decompression failed; and

means for decompressing the header of the current packet with the repair information.

26. A method for determining an interpretation interval comprising:

determining a difference between a link layer sequence number (LL SN) of a current received packet and a link layer sequence number (LL SN) of a last correctly decompressed packet; and

determining a ratio of the difference in link layer sequence number (LL SN) and a number of bits representing the interpretation interval, wherein the ratio represents an interpretation interval the current packet lies in.

27. A method for determining an interpretation interval comprising:

determining a first difference between a real-time transport protocol sequence number (RTP SN) of a first decompressed packet and a real-time transport protocol sequence number (RTP SN) for a second decompressed packet;

determining a second difference between a link layer sequence number (LL SN) for the first decompressed packet and a link layer sequence number (LL SN) for the second decompressed packet;

determining if a third difference between the first and second differences is greater than a threshold;

storing the third difference if the third difference is greater than the threshold;

determining if a next decompressed packet fails a cyclic redundancy check (CRC); and

calculating an interpretation interval for decompression of the next packet based on the third difference if a local repair mode is invoked.

28. The method of claim 27, further comprising:

determining if N packets are correctly decompressed subsequent to decompression of the next packet; and

if the N packets are correctly decompressed, resetting to zero, the value of the stored third difference.

29. An apparatus for determining an interpretation interval comprising:

means for determining a first difference between a real-time transport protocol sequence number (RTP SN) of a first decompressed packet and a real-time transport protocol sequence number (RTP SN) for a second decompressed packet;

means for determining a second difference between a link layer sequence number (LL SN) for the first decompressed packet and a link layer sequence number (LL SN) for the second decompressed packet;

means for determining if a third difference between the first and second differences is greater than a threshold;

means for storing the third difference if the third difference is greater than the threshold;

means for determining if a next decompressed packet fails a cyclic redundancy check (CRC); and

means for calculating an interpretation interval for decompression of the next packet based on the third difference if a local repair mode is invoked.

30. A computer program product comprising:

computer readable medium comprising;

code for causing a computer to determine if decompression of a current packet header failed;

code for causing a computer to determine a difference between a link layer sequence number (LL SN) of a previous correctly decompressed packet and a link layer sequence number (LL SN) of the current packet to provide repair information used for header decompression, if header decompression failed; and

code for causing a computer to decompress the header of the current packet using the repair information.

31. A computer program product comprising:

computer readable medium comprising;

code for causing a computer to determine a first difference between a real-time transport protocol sequence number (RTP SN) of a first decompressed packet and a real-time transport protocol sequence number (RTP SN) for a second decompressed packet;

code for causing a computer to determine a second difference between a link layer sequence number (LL SN) for the first decompressed packet and a link layer sequence number (LL SN) for the second decompressed packet;

code for causing a computer to determine if a third difference between the first and second differences is greater than a threshold;

code for causing a computer to store the third difference if the third difference is greater than the threshold;

code for causing a computer to determine if a next decompressed packet fails a cyclic redundancy check (CRC); and

code for causing a computer to calculate an interpretation interval for decompression of the next packet based on the third difference if a local repair mode is invoked.