Generation and use of CRC in communications network
AssigneeInternational Business Machines Corporation
InventorsJames J. Allen, Jr., Jean L. Calvignac, Natarajan Vaidhyanathan, Fabrice J. Verplanken
Life of this patent
Estimating the term…
Abstract
The CRC for the CPS Header of an ATM AAL2 cell is generated by a CRC generator which uses the 8 bits of the CID field to generate partial 5 bits CRCs which are loaded in a first table. The 6 bits LI field and 5 bits UUI field are added to the partial 5 bits CRC to form 16 bits. The CRC generator uses the 2.sup.16 bits to generate a second CRC table. The CRC for a particular CPS header is generated by correlating bits in the CID field, LI field and UUI field with the two tables.
Claims14
A method for generating a cyclical redundancy check (CRC), comprising:
- partitioning via a processor a group of bits into a first group of bits and a second group of bits;
- generating via the processor a first table that comprises 2n partial CRC's, wherein n is a positive integer that represents a number of bits in a channel identifier (CID) field of a header of a common part sublayer (CPS) packet;
- concatenating via the processor each of the partial CRC's with the bits in the first group of bits to form a third group of bits;
- and
- generating via the processor a second table that comprises 2m+L+U CRC's, wherein L is a positive integer that represents a number of bits in a length code (LI) field of the header, and U is a positive integer that represents a number of bits in a user-to-user information (UUI) field of the header;
- and
- wherein the generated CRCs are for an asynchronous transfer mode (ATM) adaptation layer (AAL2) cell.
A tangible computer-readable storage device encoded with instructions that, when executed by a computer, cause the computer to perform the steps of:
- using a portion of bits in a predefined field as an address to access a first table of partial cyclical redundancy checks (CRCs);
- concatenating the partial CRC at the accessed address in the first table with remaining bits in the predefined field to form an address to access a second table;
- and
- using bits in a portion of a CPS header received in an asynchronous transfer mode (ATM) adaptation layer (AAL2) cell and values in the first and second tables to calculate a CRC for a received cell, by:
- flagging a CRC retrieved from the second table as a CRC for a predefined field;
- placing the flagged CRC in the CRC field of a CPS packet;
- and
- transmitting, as part of an ATM AAL2 cell, the CPS header with a channel identifier (CID) field, a length code (LI) field, a user to user information (UUI) field and the CRC field populated with defined values.
An apparatus, comprising:
- a central processing unit (CPU) operatively connected to at least one storage device through a system bus, and wherein the CPU:
- stores a first table and a second table in the at least one storage device;
- generates partial cyclical redundancy checks (CRCs) based upon a number of bits in a portion of a predefined field;
- accesses the at least one storage device to load the first table with the partial CRCs;
- generates CRCs based upon a number of bits in a partial CRC concatenated to the remaining portion of bits in selected subfields of the predefined field, and accesses the at least one storage device to load the CRCs in the second table;
- and
- generates an asynchronous transfer mode (ATM) adaptation layer (AAL2) cell and uses bits in a channel identifier (CID) field, a length code (LI) field and a user to user information (UUI) field to access the first and second tables, and uses a value from the second table as a CRC for a CRC field of the ATM AAL2 cell.
Dependencies are inferred from the claim text.