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<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2>Scott,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2>There is a two steps to processing a delivery point
name:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2>1. Do I support the underlying transport
service</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2>2. If 1 is true, then can I use it to transfer to the
destination</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma size=2>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT face=Tahoma
color=#0000ff size=2>Step 2 is particular to the underlying transport service -
this allows for different formats etc for different underlying transport service
types.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT
color=#0000ff></FONT></SPAN> </DIV></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT color=#0000ff>
<DIV dir=ltr align=left><SPAN class=698082910-11112008><FONT
color=#0000ff>"vxmq2113451256:11311876" merges the two together whereas
</FONT></SPAN>"vxmq:2113451256:11311876" separates these two steps into
independent information</FONT></SPAN></DIV></DIV>
<DIV><FONT face=Tahoma color=#0000ff size=2></FONT> </DIV>
<DIV><SPAN class=698082910-11112008><FONT face=Tahoma color=#0000ff size=2>FYI,
this is the mechanism that CORBA uses, with an ID for each transport type so
that a particular ORB implementation only needs to process those transport types
that it supports.</FONT></SPAN></DIV>
<DIV align=left>
<DIV align=left><FONT face=Tahoma size=2></FONT> </DIV>
<DIV align=left><FONT face=Tahoma size=2>Stuart D. Fowell BEng MBCS</FONT></DIV>
<DIV align=left><FONT face=Tahoma size=2>Distributed, Real-Time Embedded (DRE)
Consultant</FONT></DIV>
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<FONT face=Tahoma size=2><B>From:</B> sis-ams-bounces@mailman.ccsds.org
[mailto:sis-ams-bounces@mailman.ccsds.org] <B>On Behalf Of </B>Scott
Burleigh<BR><B>Sent:</B> 08 November 2008 00:24<BR><B>To:</B>
sis-ams@mailman.ccsds.org<BR><B>Subject:</B> [Sis-ams] notation for delivery
point names<BR></FONT><BR></DIV>
<DIV></DIV>Hi, gang. At the October meetings we left one spec issue
unresolved, because it seemed subtle and complex enough to deserve some off-line
thought and discussion by email. That issue was the notation we use for
delivery point names.<BR><BR>The spec currently says that a delivery point name
is the concatenation of a transport service name, an equals ('=') sign, and an
endpoint name in transport-service-specific format. Currently the syntax
of the transport service name for TCP is the intuitively obvious "tcp", and
endpoint names are in the similarly obvious format
<I>hostname</I>:<I>portnumber</I>; likewise for UDP. But for VxWorks
message queues the spec says the transport service name is
"vxmq<I>hostnumber</I>", with <I>msgqID </I>as the endpoint name. The idea
under discussion, as I recall, was to simplify the protocol by using the general
structure <I>protocolname</I>:<I>qualifier</I>:<I>qualifier</I>:...:<I>qualifier
</I>for all delivery point names, e.g. "tcp:amroc.jpl.nasa.gov:5453" and
"vxmq:2113451256:11311876".<BR><BR>I've given this some thought and have
concluded that, while I agree that the proposed notation's generality is
appealing, this is one of those rare cases where the more intuitively elegant
approach is disadvantageous in implementation.<BR><BR>The intent of the current
design is to simplify the processing of delivery vectors in MAMS messages: a
receiving MAMS entity can always know whether or not a given delivery point is
one that it can use for message transmission to the sending entity, simply by
looking for the '=' character and then comparing the preceding character string
to the names of the transport services to which it has access.<BR><BR>The
proposed design is, paradoxically, more complex. In the case of
"tcp:amroc.jpl.nasa.gov:5453" the receiving entity would know that the delivery
point is usable if "tcp" -- the token preceding the first colon -- is one of its
transport services. But in the case of "vxmq:2113451256:11311876" the
delivery point would be usable only if "vxmq:2113451256" -- the string preceding
the *second* colon -- was one of its transport services, because message-queue
transport is possible only between tasks residing on the same machine.
Tasks residing on different computers running VxWorks cannot exchange messages
among themselves via message queue; "vxmq" alone would not be enough to assure
connectivity.<BR><BR>In order to make the proposed syntax work, we would have to
build transport-service-specific rules into the code that processes delivery
vectors in inbound MAMS messages, indicating how much of the delivery point name
constitutes the transport service name. To avoid adding any more
complexity to an already complex specification, I think we should stick with the
current notation. Does anyone have strong feelings
otherwise?<BR><BR>Scott<BR></BODY><!--[object_id=#scisys.co.uk#]--><FONT face=Tahoma size=2><FONT color=#0000ff>
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