[Sis-csi] Telecon today

[Weiss, Howard]

Keith,

I'll let Scott Burleigh correct me ("Mr. CFDP"), but the way that I
understand it, CFDP as it is currently implemented is more than a
application implementing the CFDP protocol.  It cast aside the layering
that we have grown to know and love and instead mashed into the
application layer the file transfer protocol with various services,
transport-layer-like reliability services, etc running over your
favorite underlying network/link services (e.g., UDP/IP, CCSDS AOS,
etc). So, while its probably best described in the same vein as Internet
FTP (application layer cruft implementing a file transfer protocol), it
really is much more as it stands today - until such time that the spec
is revisited and layered.

Howie

> -----Original Message-----
> From: sis-csi-bounces at mailman.ccsds.org [mailto:sis-csi-
> bounces at mailman.ccsds.org] On Behalf Of Keith Hogie
> Sent: Thursday, April 20, 2006 10:02 AM
> To: sis-csi at mailman.ccsds.org
> Subject: Re: [Sis-csi] Telecon today
> 
> 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.
> 
> ----------------------------------------------------------------------
>    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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