<span style=" font-size:10pt;font-family:sans-serif">John,</span>
<br><span style=" font-size:10pt;font-family:sans-serif">
here may cent waiting whatever additional clarification
Greg or others may add.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">1) Clearly you
refer to EOPP and not to SPP. </span>
<br><span style=" font-size:10pt;font-family:sans-serif">Clause </span><span style=" font-size:11pt;font-family:Calibri"> 3.2.1.2
</span><span style=" font-size:10pt;font-family:sans-serif"> can be
understood considering Table 4-2.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">2) Indeed, a segment
header is required to split packets over multiple frames. VCP Service has
no segment header and therefore can only allow blocking (as per Figure
4-14) while MAP Packet Service allows bot blocking and segmentation (as
per Figure 4-9).</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">TM and AOS have
a first header pointer - in Frame Header and M_PDU respectively - and this
allows "packets spanning over several frames"</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">A first header
pointer is available also in USLP (see clause 4.1.4.2.2.2.1 for TFDZ Construction
Rule ‘000’ indicating a fixed-length TFDZ).
[you do not mention this in your item #2.]</span>
<br><span style=" font-size:10pt;font-family:sans-serif">Conversely, USLPTFDZ
Construction Rules ‘100’, ‘101’, and ‘110’ (indicating
a variable-length TFDZ) can be used "a la TC' for "packets spanning
over several frames" </span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">3) I cannot say
whether it was "</span><span style=" font-size:11pt;font-family:Calibri">intention
of the SLPWG that the multiplexing of Encap packets been done on a FIFO
basis</span><span style=" font-size:10pt;font-family:sans-serif">".
I would simply guess that nobody thought to require a multiplexing there
:o)</span>
<br><span style=" font-size:10pt;font-family:sans-serif">In other words,
I think there is nothing preventing an EPP implementation to implement
a Multiplexing Scheme. I guess that if an agency has this need, SLP WG
could discuss such input.</span>
<br><span style=" font-size:10pt;font-family:sans-serif">Despite limitation
to FIFO looks to me very reasonable for Functional Resources, I think that
absence of a precise statement leaves freedom.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">4) we shall pass
this to Tom Gannett.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Greg and others
are welcome to complement my opinion.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Regards</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Gian Paolo</span>
<br>
<br>
<br>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">From:
</span><span style=" font-size:9pt;font-family:sans-serif">"John
Pietras" <john.pietras@gst.com></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">To:
</span><span style=" font-size:9pt;font-family:sans-serif">"sls-slp@mailman.ccsds.org"
<sls-slp@mailman.ccsds.org></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Cc:
</span><span style=" font-size:9pt;font-family:sans-serif">"Wolfgang
Hell" <wo_._he@t-online.de>, "Holger.Dreihahn@esa.int"
<Holger.Dreihahn@esa.int></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Date:
</span><span style=" font-size:9pt;font-family:sans-serif">18-11-20
17:29</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Subject:
</span><span style=" font-size:9pt;font-family:sans-serif">[Sls-slp]
Questions about Encapsulation Packet Protocol</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Sent
by: </span><span style=" font-size:9pt;font-family:sans-serif">"SLS-SLP"
<sls-slp-bounces@mailman.ccsds.org></span>
<br>
<hr noshade>
<br>
<br>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">SLPWG
colleagues ---</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">As
you may be aware, the Cross Support Services Area is developing a Functional
Resource Model (FRM) that defines the functional resources that abstractly
represent the various functions performed by Earth Space Link Terminals
(i.e., ground stations). The purpose of these functional resources is facilitate
the definition of configuration profiles (used in scheduling) and to support
the monitoring and control of the physical resources that are represented
by those functional resources in cross support situations. (For those of
you familiar with the concept of a Management Information Base (MIB) in
the context of network management protocols such as TCP/IP’s Simple Network
Management Protocol (SNMP) or the ISO/OSI Common Management Information
Protocol (CMIP), the FRM is essentially the “MIB” for space data systems.)</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">We
are in the process of completing the definitions of the functional resources
that correspond to the CCSDS space data link protocol functions: TC SDLP,
TM SDLP, AOS SDLP, USLP, Space Packet Protocol (SPP), and Encapsulation
Packet Protocol (EPP). In exploring the interactions among the Encapsulation
Function defined in the EPP and the various underlying SDLPs, we have developed
a question and several interpretations that I am now posing to you for
comment:</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">1.
Section 3.2.1.2 of the SPP (CCSDS 133.1-B-1) specifies
that “the maximum length of a data unit that can be accommodated in an
encapsulating packet is 4,294,967,287 octets for the Encapsulation Packet.”
Is this just the consequence of that being the size supported by the 4-octet
PACKET LENGTH field (LENGTH OF LENGTHS = ‘11’), or are there identified
operational use cases for this large a packet? <br>
</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">2.
Section 3.2.2.2 confirms that Encap Packets can be
transferred via the Virtual Channel Packet (VCP) service of the TM, TC,
and AOD SDLPs, and via the MAP Packet (MAPP) service of TC SDLP and USLP.
We make the observation that the only time that the underlying SDLP constrains
the size of the Encap packet is when the underlying service is the TC VCP
service, where the maximum size of data unit carried by the Encap Packet
is constrained to be 1015 octets. For the other SDLP services: </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">a.
When Encapsulation Packets are transferred via the
TC MAPP and USLP MAPP services, segmentation is used to break large Encap
Packets in order to fit into TC/USLP transfer frames.</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">b.
When Encapsulation Packets are transferred via the
TM VCP and AOS VCP services, the respective Packet Processing functions
break up the encap packets as necessary to fit them into M_PDUs.</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">If
we have misinterpreted anything here please let us know.<br>
</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">3.
The Encapsulation Function performs a multiplexing
function by forming Encap packets from data units from different “protocol
users”, and multiplexing those packets into a single stream of Encap packets
for the underlying Packet service. We observe that, unlike other CCSDS
SDLP functions that perform multiplexing (Space Packets, Packets, VC Frames,
and MC Frames), there is no mention in the EPP Blue Book of multiplexing
priority. We interpret that as the intention of the SLPWG that the multiplexing
of Encap packets been done on a FIFO basis. We concur with this approach,
as we can see no practical reason for other multiplexing schemes, and we
plan to define this aspect of the corresponding functional resource to
be FIFO only.<br>
</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">4.
Finally, here’s an editorial error that should be
fixed in the next editorial-level update of the EPP Blue Book: although
the title of the book was changed from <i>Encapsulation Service</i> to
<i>Encapsulation Packet Protocol</i>, the heading on each page in B-3still
reads “CCSDS RECOMMENDED STANDARD FOR ENCAPSULATION SERVICE”.</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">Thanks
in advance for any comments that you may have.</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">Best
regards,</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri">John</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri"> </span><tt><span style=" font-size:10pt">_______________________________________________<br>
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