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*To*: stds-802-3-hssg@xxxxxxxx*Subject*: Re: PAM5 and 8B10B and FEC*From*: Jaime Kardontchik <kardontchik.jaime@xxxxxxxxxxx>*Date*: Thu, 02 Mar 2000 15:24:40 -0800*Organization*: microlinear corporation*References*: <85256896.007B0430.00@xxxxxxxxxxxxxxxxxxxx>*Sender*: owner-stds-802-3-hssg@xxxxxxxx

Thank you, Albert Widmer: You wrote the code so you know it best. My two conclusions are unchanged: 1) it is useless to add the 8b/10b coding in a PAM-5 scheme, since the two main advantages of this coding, good DC balance and low running disparity, are not conserved in a 5-level transmission scheme. You still will need to add a scrambler to randomize the transmitted symbols in order to get a reasonable good DC balance. You just waste gates by adding the 8b/10b coder in a PAM-5 transmission scheme. 2) even 442 independent "raw" symbols (instead of my original 524) are too much: 5^4 = 625 < 2 * 442 = 884 so we do not have enough unused points in the 4-dimensional constellation in order to be able to add Trellis coding and get coding gain using FEC. Therefore, if one would still want to have both the 8b/10b coder and FEC in a PAM-n transmission scheme, he would be forced to go to a PAM-6 scheme using the same baud rate or keep PAM-5 but increase the baud rate. Jaime Jaime E. Kardontchik Micro Linear San Jose, CA 95131 email: kardontchik.jaime@xxxxxxxxxxx widmer@xxxxxxxxxx wrote: > Reference: Note by Jaime Kardontchik, same subject, dated 03/02/2000 > 02:15:57 AM > > Jamie, > > I wish to correct a common misconception about Fibre Channel 8B/10B code. > > You wrote: "Now, if you also want to add the 8b/10b coding, your 'raw' data > becomes now something more than 512 symbols: 256 for Current RD(-) and > another 256 symbols for Current RD(+) plus another 12 symbols > corresponding to valid special code groups, like K28.5 and K28.7. In total, > your raw data after adding 8b/10b consists of 524 different symbols." > > The actual number of symbols for 8B/10B code is 440 plus 2 for every > control character used, e.g. 242 for Fibre Channel. > > The code is partitioned into a 6B and a 4B part. The 6B part consists of 18 > disparity independent vectors and 14 (13 for data, 1 for control) disparity > dependent vectors. Similarly, the 4B part consists of 4 disparity > independent and 5 disparity dependent vectors. Therefore, for data, we have > 18x4 = 72 disparity independent 10B vectors and 256-72 = 184 disparity > dependent vectors. So, the total number of 10B data vectors is 72+(2x184) = > 440. Since all control characters are disparity dependent, you have to add > 2 vectors for each control character used. > > Albert Widmer > IBM T.J. Watson Research Center > Yorktown Heights, NY 10598-0218 > email: widmer@xxxxxxxxxx

**References**:**PAM5 and 8B10B and FEC***From:*widmer

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