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Edell, David J. wrote:
<blockquote
cite="mid:FEEF8FE8A931BE478D2538A677C48BED03D1F8F1@aplesjustice.dom1.jhuapl.edu"
type="cite">
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<div dir="ltr" align="left"><font color="#0000ff" face="Arial"
size="2"><span class="019115318-09072008">I ran into a similar issue
when finishing my implementation. </span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial"
size="2"><span class="019115318-09072008"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial"
size="2"><span class="019115318-09072008">I believe the intent was for
the reply method to be inferred from the transport service in that
case--meaning that this is a piece of data missing in the AMS content
itself. In my case, I think the node-id was included which I used in
the absence of TS specified context to infer the reply address in the
APL implementation for unregistered nodes (which uses a direct
mapping). I don't remember if/how I had addressed this for an
unregistered registrar.</span></font></div>
</blockquote>
David's answer is right, and I realize this may not be wholly
satisfactory. There's an implicit expectation that the receiving
entity can figure out the MAMS endpoint name of the sender in a
transport-specific way that is left as an implementation issue. For
example, if you're using UDP as the transport for MAMS traffic then
when you receive the heartbeat you can get the IP address and port
number of the sending socket from the recvfrom() parameters and send
the you_are_dead message back to that socket. You'd have similar
information if you used, say, the DTN Bundle Protocol as your MAMS
transport protocol. This is one of the main reasons that TCP, for
example, is not a particularly good choice as a MAMS transport
protocol: the asymmetry of connect/accept makes this kind of echoing
complex to implement.<br>
<br>
At minimum (I now realize), this implementation responsibility ought to
be made explicit somewhere -- probably in 4.2.7.4.4 and 4.2.7.4.5,
although I guess a case could be made for documenting it in the Green
Book instead.<br>
<br>
Alternatively, we could modify the heartbeat message to carry MAMS
endpoint name. I am not real comfortable with this, as I think it
would be perceived as adding a lot of bandwidth consumption that would
be needed only in two edge cases.<br>
<br>
A third alternative, though, might be simply to ditch the transmission
of you_are_dead messages in these cases, i.e., just ignore the
heartbeats. The only downside of this would be that the unregistered
entity wouldn't receive such prompt notification that it is not
currently registered. But eventually it would drop back into imputed
termination logic and go through the relevant re-registration
procedure, so there's no real harm done.<br>
<br>
On reflection, I like this third alternative pretty well. What do you
all think?<br>
<br>
Scott<br>
<blockquote
cite="mid:FEEF8FE8A931BE478D2538A677C48BED03D1F8F1@aplesjustice.dom1.jhuapl.edu"
type="cite">
<div class="OutlookMessageHeader" dir="ltr" align="left" lang="en-us">
<hr tabindex="-1"><font face="Tahoma" size="2"><b>From:</b>
<a class="moz-txt-link-abbreviated" href="mailto:sis-ams-bounces@mailman.ccsds.org">sis-ams-bounces@mailman.ccsds.org</a>
[<a class="moz-txt-link-freetext" href="mailto:sis-ams-bounces@mailman.ccsds.org">mailto:sis-ams-bounces@mailman.ccsds.org</a>] <b>On Behalf Of </b>Ray,
Timothy J. (GSFC-583.0)<br>
<b>Sent:</b> Wednesday, July 09, 2008 2:51 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:sis-ams@mailman.ccsds.org">sis-ams@mailman.ccsds.org</a><br>
<b>Subject:</b> [Sis-ams] minor heartbeat-related issue<br>
</font><br>
</div>
<div class="Section1">
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Dear WG members,</span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"></span></font> </p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">(Scott: thanks for
posting the latest specs, and for keeping them up-to-date.)</span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"></span></font> </p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Here’s another issue that
I’ve run into. Perhaps I am missing something?</span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"></span></font> </p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;">4.2.7.4.4 - If a server receives a
‘heartbeat’ from an unregistered registrar, it is supposed to send back
a ‘you-are-dead’. In order to do that, it will need to know how to
contact the registrar (i.e. its mams-endpoint-name). That name is not
included in the ‘heartbeat’. How can a server send an MPDU to an
unregistered registrar?</span></font></p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;"></span></font> </p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;">4.2.7.4.5 - Same as previous, but registrar
receives a heartbeat from an unregistered node.</span></font></p>
</div>
</blockquote>
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