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*To*: Burt Christian <burt@xxxxxxxxx>, "HSSG Reflector (E-mail)" <stds-802-3-hssg@xxxxxxxx>*Subject*: RE: [802.3ae] Questions on section 49.2.5*From*: "THALER,PAT (A-Roseville,ex1)" <pat_thaler@xxxxxxxxxxx>*Date*: Mon, 19 Nov 2001 17:29:27 -0700*Sender*: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx

My responses are bracketed by my initials. Pat -----Original Message----- From: Burt Christian [mailto:burt@xxxxxxxxx] Sent: Monday, November 19, 2001 1:53 PM To: HSSG Reflector (E-mail) Subject: [802.3ae] Questions on section 49.2.5 Hi, I have the following questions about section 49.2.5 1. In the first paragraph, the ratio between the data-rates of XGMII and the PMA service interface is mentioned to be 16:33. Is this correct or is 32:33, the correct ratio ? <PAT begin> 16:33 is the correct ratio. Here is the calculation: The XGMII sends 32 unencoded bits each cycle. The PMA sends 16 encoded bits each cycle. Let Ud be the unencoded data rate; Cxgmii be the tranfer rate of the XGMII; and Cpma be the PMA service interface transfer rate. Cxgmii = Ud/32 transfers/second Cpma = Ud unencoded bits * 66 encoded bits * 1 transfer ----------------- ------------------ ---------- s 64 unencode bits 16 bits = Ud *33/512 transfers/second Therefore Cxgmii Ud/32 16 ------ = ----------- = ------ Cpma Ud *33/512 32 <PAT end> 2. With respect to the following sentence in the same paragraph: "Where the XGMII and PMA sublayer data rates are not synchronized to that ratio, the transmit process will need to insert idles, delete idles, or delete sequence ordered sets to adapt between the rates." The above rate adaptation is intended for adapting for the minute frequency offset that can be present if the XGMII transmit clock (TX_CLK) and the PMA_TXCLK are not frequency locked - correct ? What I am trying to clarify is that this rate-adaptation is completely independent of the rate adaptation required for interfacing to WIS. <PAT begin> The ability to avoid rate adaptation by synchronizing PMA clock to the XGMII clock on transmit and vice versa on receive applies only to the LAN PHY. Such synchronization only works for the LAN PHY where the XGMII and PMA are running at the same nominal data rate. With the WAN PHY, they are running at different nominal data rates and rate adaptation must be performed. When the clocks have not been synchronized, the same rate adaptation mechanism (inserting idles and deleting idles or ordered sets) applies to adjusting for the small difference when due a PMA and XGMII running at nominal the same data rate as they do for the LAN PHY and to rate adaptation for the somewhat larger rate mismatch of the WAN PHY. In the case of the WAN Phy, one knows that one will be deleting idles at the transmitter and adding them at the receiver (and that the MAC will be inserting extra idles as necessary). This contrasts with the LAN PHY case where one doesn't know the direction of the mismatch. One will also need a bit bigger elastic buffer for the WAN PHY case. Therefore, the constraints on implementation differ slightly for the two cases but the general mechanism is the same. <PAT end> Thanks. Burt S, Christian. Ceyba Inc., Systems Specialist Tel : (613)599-5797 Fax : (613)599-1247 burt@xxxxxxxxx www.ceyba.com

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