SORT BY:

LIST ORDER
THREAD
AUTHOR
SUBJECT


SEARCH

IPS HOME


    [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

    Re: frame formats



    Mark:
    
    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
    > 
    
    


Home

Last updated: Tue Sep 04 01:05:12 2001
6315 messages in chronological order