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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: frame formatsMark: There is a potentially important distinction between the 2 choices that is missing from your summary when you indicate that both choices involve a variable length. In option 1, a single header digest after the BHS and AHS, you do not know when you start reading the header how long it will be and therefore you do not know where the digest is. This complicates the reading process, since it will have to either do the read in 2 steps (1st the BHS and then 2nd the AHS (if any) followed by the digest), or 1 read that interprets the data being read "on the fly" to extract the AHS length and extend the length of the read accordingly. In option 2 the first read is always for 48 bytes of header and you always know where the digest is. The second read is needed only if the AHS length field in the BHS is non-zero, and its length is determined by that AHS length field. However, when the 2nd read is started the length IS known and the position of the digest IS known -- you do NOT have the "on the fly" searching needed in option 1. This may (or may not) be a simplification. The other advantage to option 2 is that the input process never has to use unverified data (i.e., the AHS length field) to find the digest (and thus verify the data). Bob Russell InterOperability Lab University of New Hampshire rdr@iol.unh.edu 603-862-3774 On Fri, 30 Mar 2001, Mark Bakke wrote: > > Excellent. Which header digest positioning method will we choose? > > 1. Single header digest, after BHS and AHS > > 2. Two header digests, one for BHS, one for AHS > > 3. Single header digest for BHS; AHS is added to data digest > > Option 3 will not work well with iSCSI proxies and gateways > that may change header information, but keep the data end-to-end. > > To me, that leaves option 1 and 2. So, which is easier, having > a single header digest in a variable location, or having the > potential for two header digests; one in a fixed location, and > an optional one in a variable location? > > I don't believe that we will see AHS on most iSCSI PDUs, so is > it OK to have a "slow path" for these? > > -- > Mark > > julian_satran@il.ibm.com wrote: > > > > Dear colleagues, > > > > It look like Format-2 is selected by popular vote. > > > > Julo > > -- > Mark A. Bakke > Cisco Systems > mbakke@cisco.com > 763.398.1054 >
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