EP0552861A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Modifying check codes in data packet transmission
Assignee: AT&T Inc
•
Filing: 1993-01-05
•
Granted: —
•
Expires: 2013-01-05
Abstract
Abstract Disclosed is a method and circuit for modifying the check code (CRC₁) of a data packet based on a first seed (14) to accommodate the addition or subtraction of a header (H 2a ,H 2b ). A number of bits, which include a second seed (17), an exclusive OR function of the first seed (14) and a portion (H 2a ) of a header (H 2a , H 2b ) , and a string of zeros (21) dependent upon the length of an incoming data packet (16), is sent through a CRC generator. The resulting CRC calculation and the incoming packet check code (CRC₁) are exclusive ORed to produce a modified check code (CRC₂) taking into account the addition or subtraction of the header.
Inventors
- 👤 Subrahmanyam Dravida
- 👤 Daniel Scott Greenberg
- 👤 David Joseph Hodgdon
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 06:43
CPC Classifications
H; H03; H03M; H03M13/00; H03M13/03; H03M13/05; H03M13/09; H03M13/093; H04; H04L; H04L1/00; H04L1/0078; H04L1/0083; H04L12/00; H04L12/54; H04L12/56
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
156 words
A method of re-transmitting an incoming data packet which includes a data field (16, 15) and a cyclic redundancy check code (CRC₁) based on a first seed field (14) having a first bit length comprising the steps of: receiving said data packet; generating a bit stream; loading said bit stream into a CRC generator (38) to produce an updated CRC code; and exclusive ORing the updated code with the CRC code (CRC₁) of the incoming packet to produce a modified CRC code (CRC₂) for the data packet CHARACTERIZED IN THAT the bit stream comprises: a second seed field (17); a first field (20) comprising the exclusive OR function of at least a portion of the first seed field (14) and at least a portion (H 2a ) of a header (H 2a , H 2b ); and a number of zeros (21) equal to the bit length of the data field (16, 15) of the packet.
Claim 2
Dependent Claim
18 words
The method according to claim 1 wherein the first seed field is equal to the second seed field.
Claim 3
Dependent Claim
39 words
The method according to claim 1 wherein the bit stream further comprises a second field (18) consisting of a remaining portion (H 2b ) of the header in excess of the bit length of the first seed field (14).
Claim 4
Dependent Claim
54 words
The method according to claim 1 wherein the bit stream (FIG. 8) further comprises a second field (49) consisting of a remaining portion of the first seed field (14) in excess of the bit length of the header (H 2c ) exclusive ORed with at least a portion of the second seed field (17).
Claim 5
Dependent Claim
22 words
The method according to claim 1 wherein the header (H 2a , H 2b ) is added to the re-transmitted data packet.
Claim 6
Dependent Claim
22 words
The method according to claim 1 wherein the header (H 2a , H 2b ) is subtracted from the incoming data packet.
Claim 7
Dependent Claim
74 words
The method according to claim 3 wherein the first field (20) consists of the exclusive OR function of the first seed field (14) and the number of least significant bits of the header (H 2a , H 2b ) equal to the bit length of the seed, and the second field (18) consists of the most significant bits (H 2b ) of the header in excess of the bit length of the seed field.
Claim 8
Dependent Claim
189 words
A circuit for re-transmitting an incoming data packet which includes a data field (16, 15) and a cyclic redundancy check code (CRC₁) based on a first seed field (14) having a first bit length comprising: means (30) for receiving the incoming data packet; means (33, 34, 35, 36, 37) for generating a bit stream; a CRC generator (38); means (50) for loading the bit stream into the generator; means (32) for exclusive ORing the updated CRC code generated at the output of the generator with the CRC code (CRC₁) of the incoming packet to produce a modified CRC code (CRC₂); and means (31) for re-transmitting the data packet with the modified CRC code; CHARACTERIZED IN THAT the means for generating the bit stream includes means for generating a second seed field (17), a field (20) comprising the exclusive OR function of at least a portion (H 2a ) of a header (H 2a , H 2b ) and at least a portion of the first seed field (14), and a string of zeros (21) equal to the bit length of the data field (16, 15) of the incoming packet.
Claim 9
Dependent Claim
22 words
The circuit according to claim 8 wherein the means for generating the bit stream comprises a parallel-in, serial out shift register (33).
Claim 10
Dependent Claim
27 words
The circuit according to claim 9 wherein the means for generating the bit stream further comprises a bit-wise exclusive OR gate (36) coupled to the shift register.
Claim 11
Dependent Claim
20 words
The circuit according to claim 8 wherein the means for receiving the incoming packet comprises a serial shift register (30).
Claim 12
Dependent Claim
18 words
The circuit according to claim 8 wherein the means for re-transmitting the data packet comprises a multiplexer (31).
Claim 13
Dependent Claim
63 words
The circuit according to claim 8 wherein the means for exclusive ORing the updated CRC code and the CRC code of the incoming packet comprises an exclusive OR gate (32) with an input coupled to the CRC generator (38), an input coupled to the means for receiving the packet (30), and an output coupled to the means for re-transmitting the data packet (31).
Claim 14
Dependent Claim
25 words
The circuit according to claim 8 further comprising means (52) for calculating the header based on the position of the circuit in a data bank.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.