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*To*: "THALER,PAT (A-Roseville,ex1)" <pat_thaler@xxxxxxxxxxx>, "HSSG Reflector (E-mail)" <stds-802-3-hssg@xxxxxxxx>*Subject*: RE: [802.3ae] Questions on section 49.2.5*From*: "Burt Christian" <burt@xxxxxxxxx>*Date*: Tue, 20 Nov 2001 10:08:57 -0500*Sender*: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx

Thanks Pat for the answers, in the first question, I confused data-rate with transfer-rate. Thanks again. Burt S, Christian. Ceyba Inc., Systems Specialist Tel : (613)599-5797 Fax : (613)599-1247 burt@xxxxxxxxx www.ceyba.com > -----Original Message----- > From: THALER,PAT (A-Roseville,ex1) [mailto:pat_thaler@xxxxxxxxxxx] > Sent: Monday, November 19, 2001 7:29 PM > To: Burt Christian; HSSG Reflector (E-mail) > Subject: RE: [802.3ae] Questions on section 49.2.5 > > > > 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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