Error detection/correction and fault detection/recovery – Pulse or data error handling – Error/fault detection technique
Reexamination Certificate
2001-01-02
2004-11-16
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error/fault detection technique
C370S913000
Reexamination Certificate
active
06820233
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to header compression/decompression in packet flows and, more particularly, to the calculation of checksums for use by a header compressor or decompressor.
BACKGROUND OF THE INVENTION
The wide popularity of personal wireless communication devices such as cellular telephones and others, combined with the increasing use of the Internet, has driven a desire to provide Internet Protocol (IP) traffic over wireless communication links. Due to the relatively scarce communication resources available in conventional wireless communication links, various techniques have been developed to compress the information included in the headers of data packets, for example the IP headers used in packets that carry IP traffic. In the transmitting station, the full header information is compressed by a header compressor, and the compressed header information is transmitted over the wireless communication link. At the receiving station, a header decompressor reconstructs the full header from the compressed header information that was transmitted. This reduces the amount of wireless communication link resources necessary for transmission of the header information.
FIG. 1
diagrammatically illustrates an example of a conventional wireless communication station (e.g., a cellular telephone) that provides for wireless packet communications (for example IP traffic) with header compression/decompression. In the example of
FIG. 1
, a packet processor
14
is coupled for bidirectional communication with a communications application
11
and a wireless communications interface
13
. The packet processor
14
receives communications information from the communications application
11
, and assembles this information into appropriate packets, which are then forwarded to the wireless communications interface
13
for transmission across a wireless communication link
15
. The packets
10
produced by the packet processor
14
include a header portion
18
and a payload portion
16
. Payload portion
16
includes payload information, and the header portion
18
includes compressed header information
17
and a checksum
19
. As shown in
FIGS. 1 and 2
, the packet processor
14
uses a header compressor
21
to compress full header information received from the communications application
11
in order to produce the compressed header information
17
. Also, the packet processor
14
uses a checksum generator
12
to produce the checksum
19
, which checksum covers the full header information.
When the communication station of
FIG. 1
receives a packet
10
via the wireless communication link
15
, the packet processor
14
uses a header decompressor and the checksum generator
12
to reconstruct the full header information from the compressed header information
17
and the checksum
19
. The header from which the compressed header information was produced is the target header that the reconstructed header attempts to match. The reconstructed full header information is then provided to the communications application
11
along with the payload information. When a context update occurs, additional information to update the context is added to the header by the transmitting end, and checksum generation is needed at the receiving end (see broken line in FIG.
3
).
In some known header compression/decompression schemes, the decompressor attempts to guess (or estimate) the full header from the received compressed header information. Such techniques can be effective because some portions of a packet header can usually be expected to change in a relatively easily predictable fashion. For example, some conventional real time voice applications utilize in their headers time stamp fields that are relatively easily predictable. Other examples include real time video applications, and headers for regular best effort services such as, for example, FTP. When the decompressor makes a guess of (or estimates) the full header, a checksum is generated based on this guess/estimate, and is then compared to the checksum that was received with the compressed header. This is illustrated in FIG.
3
. The guess generator
31
of the header decompressor of packet processor
14
receives the compressed header information
17
from the wireless communications interface
13
. The full header guess produced by the guess generator is then applied to a checksum generator
12
, which produces therefrom a checksum
19
′. This checksum
19
′ is then compared at
33
to the checksum
19
received with the compressed header information. If the checksums match, then the guess/estimate is considered to be a correct reconstruction of the target header. However, if the checksums do not match at
33
, then the guess generator
31
is instructed to guess again, whereupon the above-described checksum generation and comparison process is repeated.
Disadvantageously, the checksum generation process described above with respect to both header compression and header decompression is computationally complex, and the computational requirements at the decompressor increase as the number of guesses increases.
It is therefore desirable to reduce the computational complexity associated with checksum generation in header compressors and decompressors.
The present invention reduces the computational complexity of checksum generation by utilizing static checksum information associated with header bits that do not change from header to header. This static checksum information can be used together with information about header bits that have changed, in order to generate the desired checksum. According to some embodiments, a static checksum coding state associated with the unchanging header bits can be used in combination with the changing header bits themselves to produce the desired checksum. In other embodiments, a checksum component associated with the unchanging header bits can be used in combination with checksum components associated with the changing header bits to produce the checksum. The use of static checksum information advantageously reduces the computational complexity of checksum generation. The reduced-complexity checksum generation of the present invention can be used to calculate checksums associated with reconstructed headers at a header decompressor, and can also be used at the compressor end to calculate the checksums that are transmitted along with the compressed header information.
REFERENCES:
patent: 5935268 (1999-08-01), Weaver
patent: 5987022 (1999-11-01), Geiger et al.
patent: WO 00 79763 (2000-12-01), None
Degermark, M. et al.: “low-Loss TCP/IP Headrer Compression for Wireless Networks”, Wireless Networks, ACM, US vol. 3, No. 5, Oct. 1, 1997, pp 375-387, XP000728935, ISSN: 1022-0038.*
Larzon, L.-A.; Degermark, M.; Pink, S.; “Efficient use of wireless bandwidth for multimedia applications”,Mobile Multimedia Communications, 1999. (MoMuC '99) 1999 IEEE International Workshop on , Nov. 15-17, 1999, pp187-193.*
Degermark et al., “Robust Checksum-Based Header Compression (ROCCO)”, Jun. 15, 2000, Network Working Group Internet Draft, http://www.ludd.luth.se/users/larsman/rocco/drafts/draft-ietf-rohc-rtp-rocco-01.txt, pp 1-67.*
Network Working Group, RFC 1144: “Compressing TCP/IP Headers for Low-Speed Serial Links”, V. Jacobson, Author, Feb., 1990.*
Degermark M et al.: “Low-Loss TCP/IP Header Compression For Wireless Networks”, Wireless Networks, ACM, US, vol. 3, No. 5, Oct. 1, 1997, pp. 375-387, XP000728935, ISSN: 1022-0038 *the whole document*.
Degermark Mikael
Hakansson Stefan
Hannu Hans
Johansson Ingemar
Jonsson Lars-Erik
De'cady Albert
Jackson Walker L.L.P.
Trimmings John P
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