Re: RE: Parameter Padding Question

Hi Kelly,

the length issue is different from the use 0 for padding issue.

If you pad with more than 3 bytes, a receiver would assume that another
parameter is following. It will most likely then run into problems.

That is why the text says in the bis document says:

A sender MUST NOT pad with more than 3 bytes.

and not SHOULD NOT as you are stating.

Best regards
Michael
On Jan 30, 2006, at 20:46 Uhr, Kelly Mcdonald wrote:

> Barry,
>
> Thanks for your response.
>
> My understanding of the "A sender SHOULD NOT pad with more than 3 
> bytes"
> referred to, that since parameters MUST be a multiple of 4 bytes, you
> could theoretically add additional padding as long as the multiple of 4
> rule was followed
>
> i.e. "0D 00 00 00 00 00 00 00" is technically allowed because it is a
> multiple of 4 bytes, however we SHOULD NOT pad with more than 3 bytes,
> leaving us with "0D 00 00 00"
>
> Comments?
>
>
> Kelly McDonald BSc
> USP GNPS Team Leader
> Nortel Networks
> ESN: 395-1467
> Phone: 613-765-1467
> [email protected]
> [email protected]
>
>
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Barry Nagelberg
> Sent: Monday, January 30, 2006 2:27 PM
> To: [email protected]
> Subject: RE: [Sigtran] RE: Parameter Padding Question
>
>
> Kelly,
>
> Yes, this is still considered a valid message. Please see the 
> definition
> of "SHOULD NOT" from RFC 2119:
>
> <snip>
> 4. SHOULD NOT   This phrase, or the phrase "NOT RECOMMENDED" mean that
>    there may exist valid reasons in particular circumstances when the
>    particular behavior is acceptable or even useful, but the full
>    implications should be understood and the case carefully weighed
>    before implementing any behavior described with this label. <snip>
>
> In this case, the sender may have a "valid reason" to send non-zero
> bytes.
>
> Barry Nagelberg
> Adax, Inc.
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Kelly Mcdonald
> Sent: Monday, January 30, 2006 2:15 PM
> To: Kelly Mcdonald; [email protected]
> Subject: [Sigtran] RE: Parameter Padding Question
>
> SIGTRAN community
> I am hoping you can help me out with a matter of interpreting a section
> that is generating some confusion within my group Specifically a part
> from Section 3.2
>
> Parameter Value: variable length.
> The Parameter Value field contains the actual information to be
> transferred in the parameter. The total length of a parameter 
> (including
> Tag, Parameter Length and Value fields) MUST be a multiple of 4 bytes.
> If the length of the parameter is not a multiple of 4 bytes, the sender
> pads the Parameter at the end (i.e., after the Parameter Value field)
> with all zero bytes. The length of the padding is NOT included in the
> parameter length field. A sender SHOULD NOT pad with more than 3 bytes.
> The receiver MUST ignore the padding bytes.
>
> My question is, if non-zero padding values are used within the 
> parameter
> value, is this still considered a valid message? Based on the parameter
> length value we are able to extract the parameter itself from the
> message irregardless of the padding.
>
> And while the spec calls for zero bytes to be used, it also states that
> the padding bytes MUST be ignored.
>
> Is the receiver expected to extract a parameter even if the padding
> bytes are not zero (i.e. ignore the padding bytes) , or should the
> message be rejected as invalid (as the padding is non-zero)
>
> I hope you can help
>         Thanks
> Kelly McDonald BSc.
> USP GNPS Team Lead
> ESN: 395-1467
> External: 613-765-1467
> [email protected]
> [email protected]
>
>
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