Indicating end of idle sequence by replacing certain code words with alternative code words

Abstract

Methods and systems for indicating an end of an idle sequence, including: encoding a first frame, encoding a basic idle sequence including code words, producing an idle sequence by replacing certain M code words of the idle sequence with M alternative code words, and encoding a second frame. Each one of the M alternative code words appears in the basic idle sequence. And a second communication node, which is unable to determine a starting point of the second frame based only on a received idle sequence, is able to determine a start of the second frame based on a difference between the received idle sequence and the basic idle sequence.

What is claimed is: 
     
       1. A communication node comprising:
 an encoder configured to encode a first frame, a basic idle sequence, and a second frame, wherein the first frame, the basic idle sequence, and the second frame comprise code words; and 
 an idle sequence modifier configured to produce an idle sequence by replacing certain M code words of the basic idle sequence with M alternative code words; wherein each one of the M alternative code word appears in the basic idle sequence; and a second communication node, which is unable to determine a starting point of the second frame based only on the idle sequence, is able to determine the starting point of the second frame based on a difference between the idle sequence and the basic idle sequence. 
 
     
     
       2. The communication node of  claim 1 , wherein the difference between the idle sequence and the basic idle sequence is measured using Hamming distance. 
     
     
       3. The communication node of  claim 2 , wherein the Hamming distance between the idle sequence and the basic idle sequence is equal to or higher than D_idle, and the second communication node is able to determine the start of the second frame as long as a number of channel errors in a received idle sequence is lower than D_idle/2. 
     
     
       4. The communication node of  claim 3 , wherein D_idle is equal to or higher than 3. 
     
     
       5. The communication node of  claim 3 , wherein the code words have length N_idle, and D_idle is higher than or equal to N_idle−2. 
     
     
       6. The communication node of  claim 1 , wherein the M alternative code words are located at M predetermined locations relative to end of the idle sequence. 
     
     
       7. The communication node of  claim 1 , wherein the encoder is further configured to utilize a line-code having a binary code word length N_idle for encoding the idle sequence. 
     
     
       8. The communication node of  claim 1 , wherein the encoder is configured to maintain over the idle sequence absolute value of running disparity lower than or equal to K, which is lower than N_idle/2. 
     
     
       9. The communication node of  claim 8 , wherein the running disparity at a certain symbol is a difference between number of ones and number of zeroes encoded up to and including the certain symbol. 
     
     
       10. The communication node of  claim 8 , wherein K is lower than N_idle/4. 
     
     
       11. The communication node of  claim 8 , wherein K is lower than 3. 
     
     
       12. A method for indicating an end of an idle sequence, comprising:
 encoding a first frame; 
 encoding a basic idle sequence comprising code words; 
 producing an idle sequence by replacing certain M code words of the idle sequence with M alternative code words, wherein each one of the M alternative code words appears in the basic idle sequence; and 
 encoding a second frame; 
 wherein a second communication node, which is unable to determine a starting point of the second frame based only on a received idle sequence, is able to determine the starting point of the second frame based on a difference between the received idle sequence and the basic idle sequence. 
 
     
     
       13. The method of  claim 12 , wherein the difference between the idle sequence and the basic idle sequence is measured using Hamming distance. 
     
     
       14. The method of  claim 13 , wherein the Hamming distance between the idle sequence and the basic idle sequence is equal to or higher than D_idle, and the second communication node is able to determine the start of the second frame as long as a number of channel errors in the received idle sequence is lower than D_idle/2. 
     
     
       15. The method of  claim 14 , wherein D_idle is equal to or higher than 3. 
     
     
       16. The method of  claim 14 , wherein the code words have length N_idle, and D_idle is higher than or equal to N_idle−2. 
     
     
       17. The method of  claim 12 , wherein the M alternative code words are located at M predetermined locations relative to the end of the idle sequence. 
     
     
       18. The method of  claim 12 , wherein the encoder is further configured to utilize a line-code having a binary code word length N_idle for encoding the idle sequence. 
     
     
       19. The method of  claim 18 , wherein the encoder is configured to maintain over the idle sequence absolute value of running disparity lower than or equal to K, which is lower than N_idle/2. 
     
     
       20. The method of  claim 19 , wherein K is lower than N_idle/4. 
     
     
       21. The method of  claim 19 , wherein K is lower than 3. 
     
     
       22. A communication node comprising:
 an encoder configured to encode a first frame, a basic idle sequence, and a second frame; wherein the first frame, the basic idle sequence, and the second frame comprise symbols; and 
 an idle sequence modifier configured to produce an idle sequence by replacing M certain symbols of the basic idle sequence with M alternative symbols; 
 wherein each one of the M alternative symbols appears in the basic idle sequence; and 
 a second communication node, which is unable to determine a starting point of the second frame based only on a received idle sequence, is able to determine the starting point of the second frame based on a difference between the received idle sequence and the basic idle sequence. 
 
     
     
       23. The communication node of  claim 22 , wherein the symbols are binary symbols. 
     
     
       24. The communication node of  claim 22 , wherein the difference is determined by a detector configured to identify a synchronization sequence.