Ronen, The problem is that in 1000BaseT you need to use the same clock in both directions (earlier copper physical interfaces used a different clock in each directions, but with Gb that would lead to cross talk degrading the performance).
802.3-2005 states that when you use autonegotiation, the master is chosen randomly. In fact, a random or pseudorandom number is generated for this purpose. This would seem to prohibit the use of Gb copper for SyncE, as the direction of the clock flow has a 50% chance of ending up wrong (i.e. "upstream"). However, apparently the 802.3 people in their wisdom foresaw this problem. They defined a control register bit (9.12) which forces a device to be master. If both sides set this bit the autonegotiation fails, so if the link comes up you can be sure the right side is master. Y(J)S From: [email protected] [mailto:[email protected]] On Behalf Of Ronen Solomon Sent: Tuesday, March 24, 2009 04:33 To: [email protected] Cc: Rafi Ram Subject: [TICTOC] bi-directional SyncE - Copper GBE Yaakov In the last meeting you raised the issue of supporting bi-directional SyncE on Copper GBE. Can you please re-emphasis the problem and the proposed solution. Best regards Ronen
_______________________________________________ TICTOC mailing list [email protected] https://www.ietf.org/mailman/listinfo/tictoc
