[Sis-csi] 2:30 Eastern it is

[Scott, Keith L.]

I think this is correct.  One step is to ask the question: how fast do
we think we could forward packets in space?  The answer depends on the
hardware/software available, which will probably be (for the near
future) VxWorks or some variant.  I suspect that the whole matter is
moot if we assume that the packet forwarding isn't sharing resources
with the C&DH, as even relatively weak machines can probably outstrip
current uplink rates (of TDRSS' 25Mbps, e.g.) by a factor of 2;
moderate or powerful machines (in a flight-qualifiable context) by
factors of 2-4.

		--keith
 

-----Original Message-----
From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Marc Blanchet
Sent: Thursday, January 25, 2007 4:56 PM
To: Lloyd Wood
Cc: sis-csi at mailman.ccsds.org
Subject: Re: [Sis-csi] 2:30 Eastern it is

Le 07-01-25 à 16:44, Lloyd Wood a écrit :

> At Thursday 25/01/2007 15:45 -0500, Marc Blanchet wrote:
>>> What rates can VxWorks forward at over the past N years?
>>> VxWorks -- how fast can the network stack forward.
>>
>> why bind standards and architecture with specific stack/OS
>> implementation?
>
> because you want implementations, and what good is a standard  
> without implementations?

of course.

>
> The 'real world' choices for operating systems in space hardware  
> tend to be VxWorks or RTEMS. What these two OS architectures have  
> matters for implementation - e.g. RTEMS lacks processes/memory  
> management.

ok. but I can run a vxworks stack on a 3Ghz intel quad cpu or on a  
100Mhz ARM.

>
> I think an appreciation of how much performance you can get out of  
> real-world space hardware is important and has ramifications for  
> architecture/design decisions.

then, the question should be two-fold:
a) hardware current and planned. max throughput
b) penality of stack/OS (preferably on that hardware).

taking b) only to me does not help.

Marc.

> The effects of Moore's law are brutal in space (exponential  
> increase seems slower than on Earth, so there's a gap) and thanks  
> to power/radhard requirements the processors used are slow. You'll  
> be imo lucky to achieve 10Mbps line rate from a stack running on a  
> power-conserving general-purpose processor without hardware assist  
> or brutal performance tweaking.
>
>
> L.

-----
IPv6 book: Migrating to IPv6, Wiley, 2006, http://www.ipv6book.ca



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