RE: iSCSI: Nailing down CRC-32C

[Venkat Rangan <venkat@rhapsodynetworks.com>]

Mark,

Is there any specific advantage to iSCSI Reflection Parameters
to be different from that of Ethernet? Does CRC32-C benefit by
a different set of parameters? If so, what are they, and how do we
get closure on a particular set of parameters?

Purely from the description of the parameters, RefIn=TRUE means that each
byte from the stream is 'reflected' so that bit 0 is fed in first and
then bit 1 etc. RefOut=TRUE means that the 32-bit value of the CRC is also
reflected before the final XOR is done.

Currently, Ethernet has 'RefIn=TRUE' and 'RefOut= TRUE'.

Thanks,

Venkat Rangan
Rhapsody Networks Inc.
http://www.rhapsodynetworks.com

-----Original Message-----
From: Mark Bakke [mailto:mbakke@cisco.com]
Sent: Tuesday, May 15, 2001 5:16 AM
To: Venkat Rangan
Cc: 'julian_satran@il.ibm.com'; ips@ece.cmu.edu
Subject: Re: iSCSI: Nailing down CRC-32C


Venkat-

I assumed the same parameters (iSCSI has not yet specified
the reflection parameters), and obtained the same check you
did with their code.

--
Mark

Venkat Rangan wrote:
> 
> All,
> 
> Based on the finalization of the parameters of CRC-32C per following
> parameters, I obtained a check of 0xE3069283 for the nine-byte string of
> "123456789" (9 bytes) that the Rocksoft CRC document refers to.
> 
> Name   : "CRC-32C"
> Width  : 32
> Poly   : 1EDC6F41   (note that the leading "1" is implied)
> Init   : FFFFFFFF
> RefIn  : True
> RefOut : True
> XorOut : FFFFFFFF
> Check  : E3069283
> 
> It would be nice if other independant checks can validate this.
> 
> Venkat Rangan
> Rhapsody Networks Inc.
> http://www.rhapsodynetworks.com
> 
> The table and code follows:
> 
> /*****************************************************************/
> /*                                                               */
> /* CRC LOOKUP TABLE                                              */
> /* ================                                              */
> /* The following CRC lookup table was generated automagically    */
> /* by the Rocksoft^tm Model CRC Algorithm Table Generation       */
> /* Program V1.0 using the following model parameters:            */
> /*                                                               */
> /*    Width   : 4 bytes.                                         */
> /*    Poly    : 0x1EDC6F41L                                      */
> /*    Reverse : TRUE.                                            */
> /*                                                               */
> /* For more information on the Rocksoft^tm Model CRC Algorithm,  */
> /* see the document titled "A Painless Guide to CRC Error        */
> /* Detection Algorithms" by Ross Williams                        */
> /* (ross@guest.adelaide.edu.au.). This document is likely to be  */
> /* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft".        */
> /*                                                               */
> /*****************************************************************/
> 
> unsigned long  crctable[256] =
> {
>  0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
>  0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
>  0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
>  0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
>  0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
>  0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
>  0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
>  0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
>  0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
>  0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
>  0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
>  0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
>  0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
>  0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
>  0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
>  0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
>  0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
>  0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
>  0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
>  0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
>  0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
>  0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
>  0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
>  0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
>  0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
>  0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
>  0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
>  0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
>  0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
>  0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
>  0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
>  0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
>  0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
>  0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
>  0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
>  0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
>  0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
>  0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
>  0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
>  0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
>  0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
>  0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
>  0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
>  0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
>  0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
>  0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
>  0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
>  0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
>  0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
>  0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
>  0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
>  0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
>  0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
>  0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
>  0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
>  0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
>  0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
>  0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
>  0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
>  0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
>  0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
>  0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
>  0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
>  0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
> };
> 
> /*****************************************************************/
> /*                   End of CRC Lookup Table                     */
> /*****************************************************************/
> 
> /*****************************************************************/
> /*                   ComputeCRC                                  */
> /*****************************************************************/
> #include <stdio.h>
> #include <stdlib.h>
> #include "crctable.h"
> 
> #define TB_INIT 0xFFFFFFFF
> #define TB_INIT_REFLECTED 0xFFFFFFFF
> #define TB_XOROT 0xFFFFFFFF
> 
>    unsigned long crc_reflected ();
>    unsigned long crc_reflected (blk_adr,blk_len)
>    unsigned char *blk_adr;
>    unsigned long  blk_len;
>    {
>     unsigned long crc = TB_INIT_REFLECTED;
>     while (blk_len--)
>        crc = crctable[(crc ^ *blk_adr++) & 0xFFL] ^ (crc >> 8);
>     return crc ^ TB_XOROT;
>    }
> 
> -----Original Message-----
> From: julian_satran@il.ibm.com [mailto:julian_satran@il.ibm.com]
> Sent: Tuesday, May 08, 2001 7:38 AM
> To: ips@ece.cmu.edu
> Subject: Re: iSCSI: Nailing down CRC-32C
> 
> Mark,
> 
> My basic assumption was that everything is (as in all IP related
standards)
> in network order.
> 
> Regards,
> Julo
> 
> Mark Bakke <mbakke@cisco.com> on 07-05-2001 23:00:28
> 
> Please respond to Mark Bakke <mbakke@cisco.com>
> 
> To:   Julian Satran/Haifa/IBM@IBMIL
> cc:   ips@ece.cmu.edu
> Subject:  Re: iSCSI: Nailing down CRC-32C
> 
> Julian-
> 
> That's great; it covers nearly everything.  The only thing left
> is the byte order; are they taken in the same order Ethernet uses?
> 
> If so, I can generate a few test patterns that our implementations
> can all check against.
> 
> Thanks,
> 
> --
> Mark
> 
> julian_satran@il.ibm.com wrote:
> >
> > The CRC part of the appendix (for 07) reads:
> >
> >    The following table lists cyclic integrity checksums that can be
> >    negotiated for the digests and MUST be implemented by every iSCSI
> >    initiator and target. Note that these digest options have only error
> >    detection significance.
> >
> >    +---------------------------------------------+
> >    | Name          | Description                 |
> >    +---------------------------------------------+
> >    | crc-32C       | 32 bit CRC      | 11EDC6F41 |
> >    +---------------------------------------------+
> >    | none          | no digest                   |
> >    +---------------------------------------------+
> >
> >    The generator polynomials for those digests are given in
hex-notation,
> >    for example 3a stands for 0011 1010 - the polynomial
> x**5+X**4+x**3+x+1.
> >
> >    The generator polynomial selected is evaluated in [Castagnioli93].
> >    When using the CRC the CRC register must be initialized to all 1s
> >    (0xFFFFFFFF) and the CRC bits must be complemented before
> transmission.
> >    Padding bytes, when presents in a segment covered by a CRC, have to
be
> >    set to 0 and are included in the CRC.
> >
> >    Regards,
> >    Julo
> >
> > Mark Bakke <mbakke@cisco.com> on 05-05-2001 00:13:09
> >
> > Please respond to Mark Bakke <mbakke@cisco.com>
> >
> > To:   IPS <ips@ece.cmu.edu>
> > cc:
> > Subject:  iSCSI: Nailing down CRC-32C
> >
> > At the interim meeting, it was stated that iSCSI has selected
> > the CRC-32C polynomial as its required iSCSI-level header and
> > data CRC.  Now that we have it, it's time to move on and make
> > sure we can implement it.
> >
> > In the interest of interoperability, we need to not only specify
> > the polynomial, but also the initial values, bit and byte
> > ordering, etc.
> >
> > "A Painless Guide to CRC Error Detection Algorithms"
> > (http://www.ross.net/crc/crcpaper.html) specifies a
> > method to unambiguously characterize these parameters
> > (sections 15 and 16).  Has anyone taken a shot at defining
> > these yet?  Otherwise, here is what it might look like:
> >
> > Name   : "CRC-32C"
> > Width  : 32
> > Poly   : 1EDC6F41   (note that the leading "1" is implied)
> > Init   : FFFFFFFF
> > RefIn  : True
> > RefOut : True
> > XorOut : FFFFFFFF
> > Check  : ?
> >
> > I haven't attempted to create check data based on these yet.  As
> > soon as the other parameters are nailed down, we need to do this.
> >
> > Anyway, I am not a CRC expert, and can't make any statement about
> > the above values being the "best" way to do this, but instead just
> > copied them (except the polynomial itself) from the Ethernet CRC,
> > since that is likely the easiest for everyone implementing hardware
> > to deal with.
> >
> > If someone else is already doing this, let me know; I just wanted
> > to start this thread so we can get closure.
> >
> > Regards,
> >
> > Mark
> >
> > --
> > Mark A. Bakke
> > Cisco Systems
> > mbakke@cisco.com
> > 763.398.1054
> 
> --
> Mark A. Bakke
> Cisco Systems
> mbakke@cisco.com
> 763.398.1054

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054