[Sis-csi] Telecon today

[Keith Hogie]

Scott, Keith L. wrote:
> Let's hold the telecon today
>  
> 12:30 Pacific
> 3:30 Eastern
>  
> 703.983.1550 passcode 55555
>  
>         --keith
>  

Sounds good.  We do need to figure out how to converge on words for
the document.  As I was reviewing the current discussion I noticed
a few possible differing views.  I'm trying to figure out if the
following thoughts are the basis of some of our differing views.

There has been lots of discussion on "transport protocols" and
"applications".  I think I have seen things like CFDP mentioned
in the following contexts:

1 - CFDP is a "transport protocol"
2 - CFDP provides "services"
3 - CFDP is an "application"

Here are my thoughts:

1 - CFDP is NOT a transport protocol.  The transport protocols we
have available are TCP and UDP and CFDP (as well as any other
UDP-based, reliable file transfer techniques) live above the
transport layer.

2 - CFDP does provide services for reliable data delivery but
those services are implemented in an application.  I think this
gets into things like FTP which provides services in the same way
but when we talk about FTP we normally mean the FTP application
that implements the FTP protocol.  However, the application does
lots more than just implement the FTP protocol.  It also provides
access to the file system, provides some sort of user interface,
etc.

3 - CFDP in my mind is the application that implements the CFDP
protocol.  Even though rate-control is not part of the CFDP
specification, that does not mean the application implementing
CFDP can't add its own rate-control, add a fancy GUI, interface
CFDP with an email system, or do all sorts of other things.

-------------------------

I wonder if some of the concerns about software development
cost, risk, and non-interoperable systems when people use
UDP are related to these different views.  As I see it,
reliable file transfer over UDP is just an application and
there are already many available.  It's really quite easy
for an end-system to support many different applications.
We all do it all the time on our computers which can easily
have support for Telnet, FTP, SSH, SCP, HTTP, SMTP, POP,
IMAP, NFS, CFDP, MDP, NORM, and many others.  These normally
all run simultaneously.  Adding or changing applications
is really the easiest part of networking because it only
affects the two end systems involved.  Intermediate nodes
in the network do not need to know what protocols any
two end systems are using.

I think the big thing we need
to focus on is getting a basic network infrastructure
with both UDP and TCP over IP and link layer protocols
agreed on.  The individual missions will then pick the
application protocols that meet their needs and issues
like congestion will get worked out between mission
designers and network operations people.

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   Keith Hogie                   e-mail: Keith.Hogie at gsfc.nasa.gov
   Computer Sciences Corp.       office: 301-794-2999  fax: 301-794-9480
   7700 Hubble Dr.
   Lanham-Seabrook, MD 20706  USA        301-286-3203 @ NASA/Goddard
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