Cell Relay Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: Throughput of 25Mbps ATM? of 45Mbps ATM?
Rui Pereira Coelho (coelho@ci.ua.pt) wrote: : Hi George, : George Marshall (georgem@nntp.best.com) wrote: : : Line rate 25.6 Mbps : : Line overhead 1 byte every cell: 1/54 : Could you please specify where is stated that there is 1 byte overhead : for each cell in a 25.6 Mbps link? I looked at ATMForum 25.6 Mbps : physical specificaion and I didn't found nothing. Look in section 3.2.2, cell delineation: "Cell delineation shall be accomplished by prepending either of two valid commands to the each ATM cell before transmission. As defined above, the two valid start of cell commands are X_X = Start-of-cell (with scrambler reset), and X_4 = Start-of-cell (with no scrambler reset)" In the earlier parts of section 3.2, it is explained that 'X' is a 4-bit symbol for 'escape', so X_X and X_4 are the two eight-bit commands for Start-of-Cell, with and without scrambler reset, respectively. There's another paragraph a little further down which spells out the 54-byte format. By the way, for anyone just tuning in, most of the ATM Forum specs are available on their web page, at http://www.atmforum.com/atmforum/spec_order.html The 25 Mbps PHY spec is af-phy-0040.000 regards, George Marshall -- George Marshall george@marshalls.org |
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