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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Guys, let’s kick off a new, more specific thread to
discuss this question of network layer scheduling because this is clearly a
major sticking point in our discussions at the moment. To get the ball rolling,
I’ve pulled out a couple of Abhijits’ comments from the reference
model discussion, together with a question I posed a few days ago. To try to
balance things up I’ve also reproduced some statements relating to scheduled
service from the TCONS tutorial (BTW Steve, when are you planning to talk us
through this tutorial?).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>[Abhijits’ comments] <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>I am having some problems
with the scheduling function.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>1. As I understand, the idea
of the scheduling function is to have scheduled access to underlying
sub-networks (bus or spacewire or ethernet) and the scheduling is over the
entire network covering several sub-networks, in general……. I want
to be sure that the scheduling function (essentially a service) is not
conceived as a service on an infrastructure that cannot support it.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>2. The next question is why
do we need the scheduling function anyway?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>3. I fail to see
the need of one big network layer controlling the underlying sub-network
as well. If we assume (just for the sake of<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>argument) that network layer
services are defined that way - this implies separate network layer
functionalities and services for each class of sub-network. I feel
uncomfortable with the scalability of the design.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>[The question I posed a few days ago]<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>Now for the real
question, which is based on Kieths' comments and on the answers I've seen
coming out of TCONS....is it the network layer that entirely controls accesses
to the underlying bus through this so called TCONS scheduling function?<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>If the answer to
that question is yes, then any other protocol that other users might want to
run (SCPS, vanilla TCP/IP, whatever) must go through one or other of the TCONS
services!<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>If the answer is
no, i.e. if access to the underlying medium is controlled in the data link
layer, then the TCONS can merrily co-exist with virtually any other protocol
that might be proposed!<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>[Statements from the TCONS tutorial slides]<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Time Critical?<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>•<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>TCONS must be able to support
real-time applications<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>•<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Delivery time of less than 1 ms must
be supported<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>•<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Priority based media access<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>•<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Deterministic delivery<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>•<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Scheduled Delivery Service<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:54.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>–<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Delivers TCONS Service Data Units to
a destination, in sequence, without error or duplication, and with
deterministic end-to-end delay<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-left:54.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1'><![if !supportLists]><font
size=2 face="Times New Roman"><span style='font-size:10.0pt'><span
style='mso-list:Ignore'>–<font size=1 face="Times New Roman"><span
style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Data is transferred across the
network according to a predefined schedule<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>OK, I think that is enough to start the discussion. Can we
answer the questions above? Can we assuage Abhijits’ concerns? Can we
refute or endorse the TCONS requirements?<o:p></o:p></span></font></p>
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