Method and apparatus for searching frame alignment with false alignment protection
AssigneeTellabs Operations, Inc.
InventorShuo Huang
Life of this patent
Estimating the term…
Abstract
A method and apparatus for enhancing frame alignment using cyclic redundancy check (“CRC”) corrections are disclosed. In one embodiment, a process of frame alignment searches a predefined bit pattern within a first multi-frame structure and provides an assumed frame boundary after identifying the predefined bit pattern in the first multi-frame structure. While calculating a CRC value in response to the assumed frame boundary, the process further corrects the CRC value in accordance with a saved residue and F-bits identified by the assumed frame boundary. The assumed frame boundary is subsequently verified by comparing the calculated CRC value with embedded CRC value obtained from a second multi-frame structure.
Claims17
A method for frame alignment, comprising:
- obtaining assumed frames over a data stream with one bit position;
- extracting one frame bit (“F-bit”) from each frame;
- searching a predefined frame alignment signal over the F-bits;
- identifying a first assumed extended super frame (“ESF”) when the predefined frame alignment signal is identified;
- storing cyclic redundancy check (“CRC”) residue generated from a global CRC calculator when the first assumed ESF is identified;
- obtaining a second assumed ESF over the data stream;
- calculating a CRC value in accordance with a global CRC value and the CRC residue and associated F-bits with the second assumed ESF to adjust the global CRC value;
- obtaining a third assumed ESF over the data stream;
- and
- confirming a first ESF alignment when the CRC value matches with embedded CRC value extracted from the third assumed ESF.
A network device comprising:
- a memory capable of being arranged its storage space into multiple storage sections for storing information from a data stream having a data format of multi-frame structure and a section of operation variables;
- a processing device coupled to the memory and configured to identify a frame alignment relating to the data stream, wherein the processing device includes,
- a pattern search module capable of identifying frame alignment signals in accordance with a predefined bit pattern;
- and
- a cyclic redundancy check (“CRC”) module operable to generate a CRC value in response to a portion of residue values generated during previous assumed extended super frame (“ESF”) and a global CRC value generated based on an assumed alignment boundary.
A method for identifying a frame boundary, comprising:
- obtaining assumed frames over a data stream based on a bit position;
- extracting one frame bit (“F-bit”) from each assumed frame;
- saving cyclic redundancy check (“CRC”) residue in accordance with the assumed frames;
- searching a predefined frame alignment signal over the F-bits;
- identifying a first assumed extended super frame (“ESF”) when the predefined frame alignment signal is identified;
- obtaining a second assumed ESF over the data stream based on the first assumed ESF;
- calculating a CRC value in response to a global CRC value, the CRC residue and associated F-bits with the second assumed ESF to adjust the global CRC value;
- and
- confirming an ESF alignment when the CRC value matches with embedded CRC value extracted from the second assumed ESF.
Dependencies are inferred from the claim text.