Rapid rate adaptation in nbase-t ethernet

Abstract

A method for fast link recovery for an Ethernet link is disclosed. The method includes detecting a drop in link quality and performing a first fast retrain sequence, including determining and exchanging THP coefficients based on the drop in link quality. If the performed fast retrain fails to recover the link, a data rate associated with the link is reduced, and a second fast retrain sequence performed.

1 . (canceled) 
     
     
         2 . A method for transmitting data over Ethernet link, the method comprising:
 operating the Ethernet link at a first data rate using a first PAM modulation technique for data transfers along the Ethernet link;   detecting a drop in link quality on the Ethernet link from a first signal quality according to a signal quality metric to a second signal quality according to the signal quality metric;   performing a first training sequence in response to the detecting a drop in link quality, the first training sequence for improving the link quality to a quality level that is higher than the second signal quality according to the signal quality metric; and   if the first training sequence fails to improve the link quality to the quality level that is higher than the second signal quality according to the signal quality metric,
 reducing the first data rate to a reduced data rate by using a second-PAM modulation technique having a constellation density that is sparser than the first PAM modulation technique; and 
 performing a second training sequence to determine whether the link quality has reached a quality level that is higher than the second signal quality according to the signal quality metric. 
   
     
     
         3 . The method according to  claim 2 , wherein the performing of the first training sequence comprises:
 performing a fast retrain training sequence without operating the Ethernet link in an offline state.   
     
     
         4 . The method according to  claim 3 , wherein operating the Ethernet link at a first data rate includes employing a first set of filter coefficients corresponding to the first data rate, and performing the fast retrain training sequence further comprises:
 deriving a second set of filter coefficients based on the first set of filter coefficients for reducing the first data rate to the reduced data rate.   
     
     
         5 . The method according to  claim 2 , wherein operating the Ethernet link at the first data rate includes using the first PAM modulation technique at a first baud rate for data transfers along the link, and wherein reducing the data rate further comprises:
 using the second PAM modulation technique that has a constellation density that is sparser than the first multi-PAM modulation while maintaining the first baud rate for data transfers along the link.   
     
     
         6 . The method according to  claim 5 , wherein:
 operating the Ethernet link at the first data rate comprises operating the Ethernet link at 5 Gbps to produce the first data rate;   operating the Ethernet link at the second data rate comprises operating the Ethernet link at 2.5 Gbps to produce the second data rate; and   changing the first PAM modulation technique to the second PAM modulation technique having a constellation density that is sparser while maintaining the baud rate at 200 MHz to generate symbols having fewer data bits to produce the second data rate.   
     
     
         7 . The method according to  claim 6 , wherein:
 operating the Ethernet link at the first data rate comprises operating the Ethernet link using PAM-16 modulation; and   changing the first PAM modulation technique to the second PAM modulation technique comprises changing from PAM-16 modulation to PAM-4 modulation.   
     
     
         8 . The method according to  claim 2 , wherein reducing the first data rate comprises:
 establishing communication between link partners of the Ethernet link via an InfoField Exchange protocol; and   exchanging a signal between the link partners via the Infofield Exchange protocol, the signal representing information to reduce the first data rate to the reduced data rate via the second PAM modulation technique having a constellation density that is sparser than the first PAM modulation technique.   
     
     
         9 . The method according to  claim 2 , wherein detecting the drop in link quality comprises:
 detecting a signal-to-noise ratio (SNR) value that is less than a predefined threshold.   
     
     
         10 . The method according to  claim 2 , wherein detecting the drop in link quality comprises:
 detecting a low density parity check (LDPC) code value that fails to meet a predefined threshold of link quality.   
     
     
         11 . An integrated circuit (IC) Ethernet transceiver chip for communicating with a link partner IC Ethernet transceiver chip, comprising:
 transmitter circuitry including
 modulation circuitry configured to transmit data that is modulated using a first PAM modulation technique into first data symbols for transmission at a first data rate; 
 receiver circuitry including
 circuitry configured to receive from the link partner IC Ethernet transceiver chip a signal indicative of link quality associated with the transmission of the first data symbols; 
 detection circuitry to measure a drop in link quality associated with second data symbols received from the link at the first data rate; and 
 
 training circuitry, in response to the signal indicative of link quality from a first signal quality according to a signal quality metric to a second signal quality according to the signal quality metric,
 to cooperate with the link partner IC Ethernet transceiver chip in performing a first training sequence to improve the link quality to the quality level that is higher than the second signal quality according to the signal quality metric, and 
 if the first training sequence fails to improve the link quality to the quality level that is higher than the second signal quality according to the signal quality metric,
 communicate with the modulation circuitry to reduce the first data rate to a second data rate that is less than the first data rate by using a second PAM modulation technique having a constellation density that is sparser than the first PAM modulation technique, and 
 perform a second training sequence to determine whether the link quality has reached a quality level that is higher than the second signal quality according to the signal quality metric. 
 
 
   
     
     
         12 . The IC Ethernet transceiver chip according to  claim 11 , wherein the training circuitry is configured to perform the first training sequence by training the link consistent with a fast retrain protocol without operating the link in an offline state. 
     
     
         13 . The IC Ethernet transceiver chip according to  claim 12 , wherein the training circuitry is configured to perform the first fast retrain sequence by training the link with second filter coefficients derived from a first set of filter coefficients associated with the first data rate. 
     
     
         14 . The IC Ethernet transceiver chip according to  claim 11 , wherein the transmitter circuitry further comprises:
 timing circuitry configured to generate a transmit clock having a frequency corresponding to a first baud rate for data transfers along the link at the first data rate; and   wherein the timing circuitry is configured to maintain the frequency corresponding to the first baud rate for data transfers along the link at the second data rate.