[Sois-tcons] TCONS rationale

[Chris Plummer]

Just a follow up. Looking at this again I think it is actually important
that we do not use TCOA as a justification for TCONS...that would be open to
the criticism that we are artificially creating our own need for TCONS.

 

Chris.

 

  _____  

From: sois-tcons-bounces at mailman.ccsds.org
[mailto:sois-tcons-bounces at mailman.ccsds.org] On Behalf Of
dstanton at keltik.co.uk
Sent: 01 April 2005 13:06
To: sois-tcons at mailman.ccsds.org
Subject: [Sois-tcons] TCONS rationale

 


My initial thoughts were to look to the TCOA documentation to find the
services which they are demanding of the underlying transfer layer and which
are not provided by current transport services. However, there isn't much to
be got from their documents.

We need to identify very succinctly the TCONS USPs (Unique Selling Points)
in bullet form and to identify the arguments for and against existing
protocols which may already have them. So, a first cut would be:

Bit efficiency (arguments about IP header compression etc.)
Priority (does Diffserv do the job?)
Scheduling (Why?, Which applications?)

The fundamental arguments against are likely to be (and I'm playing devils's
advocate here):

Are we really likely to need to have to provide these services across
hetereogeneous busses? Are we compensating for bad spaceraft design and
(flameproof suit on) the failure of OBL to arrive at a standardised bus/LAN?

Are these services actually required by real applications? 

Can these services be provided by other transport/network layers?

Can these issues be solved by using conventional protocols across high
capacity busses? The space link guys have the laws of physics working
against them. We don't have such an excuse for having limited bandwidth. Do
the power or availability of rad hard devices arguments wash? If we have
spacewire why are we worried about bit efficiency and priority?

Fundamentally we are missing a SOIS concept of operations and policies (one
such policy issue is why are we prepared to be iconoclastic at the network
layer and yet pander to entrenched positions at the bus/lan level, trying to
accommodate every flavour of bus that has ever flown or likely to be flown).
Looking at the documentation, ther's a lot of assertion without much in the
way of justification. This may be because I haven't seen some of the earlier
work.

I'm not trying to shoot everyone down here. It's just that if we aren't
clear in our own minds on these issues, it will be very difficult to defend
TCONS/SOIS at the CESG. 

Any thoughts?

Dai



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