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<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004>All,</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>We spent time at the
recent CCSDS meetings addressing interoperability and capability issues with
SCPS-TP. </SPAN></FONT><FONT face=Arial size=2><SPAN
class=829081917-30112004>In addition to the SCPS Transport Protocol (SCPS-TP),
there are three other protocols in the SCPS suite:</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> SCPS Network
Protocol (SCPS-NP) (<A
href="http://www.ccsds.org/CCSDS/documents/713x0b1.pdf">http://www.ccsds.org/CCSDS/documents/713x0b1.pdf</A>)</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> SCPS Security
Protocol (SCPS-SP) (<A
href="http://www.ccsds.org/CCSDS/documents/713x5b1.pdf">http://www.ccsds.org/CCSDS/documents/713x5b1.pdf</A>)</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> SCPS File
Protocol (SCPS-FP) (<A
href="http://www.ccsds.org/CCSDS/documents/717x0b1.pdf">http://www.ccsds.org/CCSDS/documents/717x0b1.pdf</A>)</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>These protocols were
approved as CCSDS Recommendations a little over five years ago, and reviewing
them falls under the Cislunar Space Internetworking Working Group's
charter. Possible actions for these protocols include:</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> o Approving
the standards 'as-is' for another five years.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> o Updating /
clarifying aspects of the specifications (as is being done for the
TP)</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> o Retiring
some or all of the standards</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> o
...?</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>It is my personal
belief that while there has not been as much commercial interest in the above
standards as there has been in the SCPS Transport Protocol (SCPS-TP), they are
still relevant for space use, at least for certain mission sets. Below is
a brief reprise of the various protocols' capabilities, comparisons with their
Internet counterparts, and comments about their continued applicability to
CCSDS.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004>SCPS-NP</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>The SCPS Network
Protocol allows for very compact representation of end system addresses and
groups of addresses (the latter via the path address feature). SCPS-NP
also provides mechanisms for priority handling of datagrams, as well as
per-packet control of routing mechanisms. Per-packet routing control is
used to signal that certain packets should be flooded to improve
reliability. The smallest SCPS-NP header is 4 octets, significantly
smaller than IPv4's 20-byte header. The main disadvantage of SCPS-NP is
that it is not bit-interoperable with IPv4/v6 -- SCPS-NP headers would
have to be translated into and out of IPv4/v6 to allow interoperation with an
IPv4/v6-based network. Translating between SCPS-NP and IP is possible,
with the possible loss in IP of some of NP's capabilities such as the ability to
select different routing treatments as mentioned above. Other differences
between SCPS-NP and IP include:</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 1) SCPS-NP
has a 8191-byte maximum packet size limit and no
fragmentation</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 2) SCPS-NP
supports a maximum of 16 upper-layer (transport) protocols</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 3) SCPS-NP
supports 16 levels of precedence, independent of the IP TOS
field</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 4) SCPS-NP's
version of ICMP (SCMP) supports explicit signaling of congestion, corruption,
and link outage if such information can be acquired from the link
layer.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Its lower overhead
and ability to signal per-packet routing options make SCPS-NP an attractive
alternative to straight IPv4 (IPv6) for bandwidth-constrained
missions.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>SCPS-SP</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>SCPS-SP provides
capabilities similar to IP Security (IPSEC) in the Internet world. The
main differences between SCPS-SP and IPSEC are:</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 1) SCPS-SP
incurs two bytes of overhead per packet, whereas IPSEC requires
10</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 2) SCPS-SP
only allows one active security association per address pair, while IPSEC allows
multiple simultaneous SAs.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>For some mission
scenarios the overhead savings of SCPS-SP are probably not worth the
effort. If the mission is pushing HDTV streams around at tens or hundreds
of Mbps, a few extra bytes for IPSEC will likely be tolerable. Smaller,
lower bandwidth missions might still be able to capitalize on the
savings.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 3) SCPS-SP
does not provide replay protection, instead it relies on transport sequence
numbers.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Because of its lower
overhead, SCPS-SP is still relevant to bandwidth-constrained missions that
require security services.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004>SCPS-FP</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>The SCPS File
Protocol supports low-bandwidth file transfers. The main features of
SCPS-FP that have NOT been implemented in modern FTP implementations
are:</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 1) Record
read, update</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 2) Integrated
file integrity checking</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004> 3)
Suppression of reply text</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>The ability to read
and update pieces of a file without reading/sending the entire file could be of
significant benefit to bandwidth-constrained (or asymmetric bandwidth)
missions.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>In short, SCPS-NP,
SCPS-SP, and SCPS-FP provide bit-efficient services that will be needed on
future space missions. While some missions will likely have bandwidth to
burn, others that are not so lucky will be able to reap significant benefits
from NP, SP, and FP. For that reason I would suggest that these protocols
be reaffirmed as Recommendations within CCSDS.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Again, I invite
discussion on any/all of the protocols.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Best
Regards,</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004>
--keith</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Dr. Keith
Scott</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004><A
href="mailto:kscott@mitre.org">kscott@mitre.org</A></SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004>+1.703.883.6547</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=829081917-30112004>Chair, CCSDS
Cislunar Space Internetworking Working Group</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=829081917-30112004></SPAN></FONT> </DIV></BODY></HTML>