[Sis-csi] Basic network diagrams

[Adrian J. Hooke]

I agree that some very simple "networking 101" pictures may be useful. 
Forrest Warthman contributed a very nice tutorial at 
http://www.ipnsig.org/reports/DTN_Tutorial11.pdf which maybe we should 
consider adding to the Green Book as an Annex?

In terms of the slides proposed by Keith Hogie:

Slides 1, 3:

a) That bottom blue-white-pink loop that comes out of the intermediate node 
is not clear; since it doesn't seem to help, maybe it should be removed?

b) What's the key difference between slide 1 and slide 3? They both seem to 
say much the same thing.

Slide 2:

a) This slide (as-titled) seems misleading since the applications interface 
with (not shown) Application services, not directly with IP. One of the 
principal original reasons for adopting/adapting Internet protocols in 
space was to preserve user interfaces with native, unmodified Application 
services. Yet in our quest for "IP purity" we now seem to have inverted 
that logic by advocating the running of custom Applications over native 
networking services. As such, this doesn't seem to represent a very 
"User/Software" friendly view. See 4b below.

Slide 4:

a) DTN is not a peer to applications such as e-mail and file transfer; it 
should sit slightly below them and slightly above the TCP/UDP Transport layer

b) TCP should be fully allowable over RF and optical environments - it can 
be made to work quite well. Why is this slide implicitly advocating 
everything over UDP? Max Repaci and the guys at UMD should have something 
to say here.

c) Informative or not, this is a CCSDS document and as such - to avoid 
confusion - it should only illustrate Link and Physical layer protocols 
that are in the current CCSDS protocol suite and which have either been 
adopted by the CCSDS agencies or are under active consideration. For the 
"RF" domain those should be AOS, TM, TC and Prox-1. Assuming that the 
"Cable" (wired?) domain also embraces LANS on a spacecraft or on a 
planetary surface, the current SOIS candidates such as Spacewire should be 
added . For the "Optical" domain, they should be simply left as "??".

///adrian