[Sis-csi] IP Header Compression

[Howard Weiss]

The PTD authentication appears to be the old ESA authentication standard 
which I looked at a while back and concluded that it was very weak - the 
authentication word was too short and it was based on a flawed 
cryptographic concept (hard knap-sack problem).  From what I understand, 
ESA has since deprecated this and it is no longer a standard.  And I 
also understand that while it has been implemented in the PTD, none of 
the ground systems use it.

Howie

Adrian J. Hooke wrote:

>> At 12:17 PM 9/7/2005, Krupiarz, Christopher wrote:
>> ... Could you elaborate a bit on how you would see commanding done in 
>> an emergency situation without using an IP packet?  I probably got 
>> lost along the way, but I made the assumption that in this 
>> architecture all packets that a spacecraft received would be an IP 
>> packet.  The hardware decode command (I think equivalent to our 
>> critical commands here) would just be a bit string, but it would 
>> still be in an IP packet.
>
> ===================
> At 08:32 AM 9/7/2005, Matthew Cosby wrote:
>
>> In Europe we get around this problem with a Command Pulse 
>> Distribution Unit (CPDU) installed in the Packet Telecommand Decoder 
>> (PTD -  "hunk of hardware that doesn't rely on the correct operation 
>> of the flight computer" ). This hardware commanding utilises the 
>> Multiplexed Access Point (MAP) identifiers in the segmentation layer 
>> of the Telecommand Stack.
>>
>> I have attached a data sheet of PTD for you read - Section 4.5. The 
>> upshot of it is you can send a command to the PTD (within the 
>> communications system) that can toggle up to 256 lines, for resetting 
>> the flight computer, switching antenna, etc without needing to worry 
>> about the high level stuff on top.
>
> ===================
>
> As Matt notes, there is extensive and well-tested standard 
> infrastructure built around the concept of direct Link-layer 
> "hardware" commanding. If you read section 4.3 of the PTD data sheet 
> you will also see that command authentication is covered and if I 
> remember correctly, bog standard CCSDS Link layer data protection has 
> already been quite widely implemented in Europe for "asset"-class 
> missions:
>
>   -- Perhaps we can hear more about these capabilities from Matt and Dai?
>   -- Howie; what's your take on the strength of the security that is 
> provided by the PTD?
>
> I'm not sure that the CSI architecture should assume (as Chris 
> suggests) that *all* traffic is IP-based. Given where we are today, 
> wouldn't it be reasonable to expect an evolutionary progression, with 
> a mix of some services that are built directly on the Link layer and 
> other services that are Network based?
>
> Perhaps the CSI group should revisit the AOS architecture that is 
> expressed in Figure 2-2 (page 2-5) of 
> http://public.ccsds.org/publications/archive/701x0b3.pdf to see what 
> possibilities exist? It should be noted that the AOS architecture is 
> now ~15 years old and that we are still waiting for any significant 
> customers of space networking to emerge. Rather than starting over, 
> one would hope that the CSI group would build on the 
> internationally-agreed AOS framework and at the end of the day the 
> group would be able to recommend a comprehensive update to the AOS 
> service model (as defined in section 2 of the specification) and to 
> the corresponding protocol specs. In particular, someone might want to 
> at least propose a Pink Sheet to change the selection of the protocol 
> that is currently recommended to implement the Internet service... :-\
>
> ///adrian
>
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-- 

Howard Weiss
SPARTA, Inc.
7075 Samuel Morse Drive
Columbia, MD 21046
410.872.1515 x201 || 410.872.8079 (fax)

Mike Nichols: "Cheer up, life isn't everything!"

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