Re: (virtual) hum on CARD open issues

Hi Vijay,

please see below for comments.
marco

Vijay Devarapalli wrote:

>Singh Ajoy-ASINGH1 wrote:
>  
>
>>>1. Issue #2: R-flag for CARD Request rate limiting. What to do about potential Dos issues? WG consensus is to Keep the R-flag approach. Meeting consensus is to add clarifying text to section 4.2 (4.3?)
>>>      
>>>
>>this is wrong, IMHO. rate limiting is a well known mechanism.
>>introducing a new flag is not a bright idea.
>>
>>ajoy-> Why it is a bad idea?  Well, I am neutral in this
>>issue but I am not convinced why using R bit is worse than
>>your proposed solution.
>>    
>>
>
>simple. rate-limiting is implemented in a wide variety of
>protocols (infact for any message that creates state at
>the receiving node). nothing new here. you dont need a new
>mechanism for this.
>  
>
I see your point. However, I don't see a reason why the flag as 
flow-control indicator
should not work. Maybe there is also a benefit from implementation point 
of view on
the MN. In case of having a flag, MN is notified when exceeding the 
request rate. Of course,
AR has to maintain a per-MN state. Furthermore, rules have to be 
specified for MNs
on how to behave when CARD Reply indicates exceeding rate. But from 
implementation point
of view, this does not look very complicated on the MN side. However, 
having a
"n-requests allowed per second"-rule on the MN, this needs to be 
controlled and
implemented on the MN side, which looks like requiring a bit more effort

Alternative proposal was to indicate a maximum rate for a particular AR 
in the
first CARD Reply. This keeps individual request rates flexible and avoids
defining static numbers.

>  
>
>>>3. Issue #33: Inter-AR CARD protocol transport from UDP to ICMP. The editor recommends the use of ICMP to make it consistent with the mobile interface. Potential downsides: ICMP has potential security implications. ICMP message types on binding is also very implementation specific. Also, securing ICMP would require that all ICMP packets be secured. Meeting consensus is to keep UDP.
>>>      
>>>
>>2 and 3 dont go togetheer. defining CARD messages as ICMP
>>options lets you piggyback these options on FMIPv6 messages.
>>I am not sure how you can achieve piggybacking if the MN-AR
>>signaling becomes UDP. ICMP was the right choice between
>>the MN and the AR.
>>
>>AJOY-> Well I did not attend IETF meeting, but I guess this means ICMP for
>>MN-AR and UDP for AR-AR interface. Others' please correct me.
>>    
>>
>
>oops... I misunderstood. I thought the concensus at the 
>meeting was to use UDP for both.
>
>  
>
>>BTW, why are you in favor of
>>using ICMP for AR-AR interface?
>>    
>>
>
>otherwise you need seperate code for processing an ICMP
>CARD Request (from the MN) and UDP CARD Request (from 
>the PAR). also, if it is an ICMP message, I can piggyback
>CARD messages on HI/HACK messages of FMIPv6.
>
>
>  
>
>>unbelievable. the CARD protocol is already complicated (IMO).
>>the emphasis should be on reducing the complexity. just use
>>a value of infinity for the lifetime field to indicate a
>>static capability. any other value for the lifetime indicates
>>dynamic capability. I think for the CARD protocol, emphasis
>>should be on making it a simpler protocol than saving 4 bytes
>>over the air. :)
>>
>>if you are concerned about an overhead of 4 bytes, make the
>>lifetime field 2 bytes. a 2 byte lifetime field gives you
>>65536 seconds which should be enough. do you need a 4 byte
>>lifetime field?
>>
>>AJOY-> I disagree here. Saving even 2 bytes per capability is
>>huge saving for bandwidth constraint network. I am not sure
>>processing one flag will make CARD protocol any more complicated.
>>Btw, in cellular standard I have seen even more complicated
>>procedure for saving 4 bits per frame. Please note that
>>the CARD protocol is being proposed as an experimental
>>protocol so we will have opportunity to make such
>>changes in future if required.
>>    
>>
>
>but in the current form not many people are going to use 
>it. it might remain forever as an experimental, untouched,
>ignored, just another RFC.... that is something we should 
>avoid. I want a protocol that I can use. :)
>  
>
 From complexity and implementation point of view, I don't really 
understand why
the proposed mechanism makes the protocol complex? I don't see
any difference between having a check on the lifetime (==0x00000000?) 
and in case it's
zero assume the capability to be static, and having a check on a 
specific flag (flag == 1?),
indicating a static capability, hence, no lifetime field is present but 
"value" descriptor
follows immediately.
But if there are any further argumements and concerns, we can again 
think about it.

Any other comments?

marco

>Vijay
>
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