Subject: [Rserpool] Data transmission

From: "Miguel Angel Nieto Jimenez ECE/TL/NA TU-146 Tlf.91.339.4670" <[email-masked]>
Date: Wed, 25 Jul 2001 10:07:32 +0200

Hi,
   I have some doubts about how data transmission is performed.
Are the associations for data transmission between ASAP endpoints
or between the ASAP under the PU and the PE? Reading the draft I
suppose that is the second one because there is not any ASAP
message defined for data transmission. If this is OK, what would
happen in the following scenario. Suppose we have two nodes, one
has two PU and the other one PE. If both PU want to communicate
with the PE there would be only one association. Then, how would
be the PUs multiplexed? Should be used different streams? Should
be used the SCTP field payloadProtocolId?
   When should the association been closed? Can be supposed that
is going to be only an answer from the PE?

Miguel

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---

From: Randall Stewart at work <[email-masked]>
Date: Wed, 25 Jul 2001 06:55:19 -0500

> is going to be only an answer from the PE?

Hi Miguel:

An answer.. or at least I will attempt an answer since I
am not to sure about your questions :-)

When a PU wants to talk to a PE.. it

1) Asks ENRP where it is.
2) Gets a list back of PE's that are registered under the
   name... the list has the IP address/ports. 

3) The PU sets up an association with the PE and sends data
   directly to the PE with NO ASAP formatting or any intervention.

The idea is that ASAP is a SESSION layer and only handles getting
two endpoints in contact with each other... It does not as such
get involved in the transport of data... for example it does NOT
wrap application data messages with some ASAP wrapper.. but instead
just sends through the data send primitives to the SCTP stack.

Now your question on two PU's and one PE on boxes is quite simple

one PU (PU1) would say have a port 5555 the other PU2
would have a port say 6666 and our friend the PE that both
wants to talk to would have a port 8888

So you would end up with an association between

PU1:5555 <----->PE:8888
and
PU2:6666 <----->PE:8888

It takes two sets of transport addresses each with a port on
the respective peer to create an association.. so even
if PU1 and PU2 are on the same machine the SCTP layer will
know that it has two assocaiations on both sides based
on the differences in port numbers.

In a non-multi-homed machine you have the same situation
as in TCP aka a assocaition is comprised of:

Source Port+Source Address+Destination Port+Destination Address

In a multi homed case it is a bit more complicated and you end up with:

Source Port+[Set of source addresses]+Destination Port+[Set of
destination addresses]

All comprising one associaition..

Hope that helps..

R

-- 
Randall R. Stewart
[email-masked] 815-342-5222 (cell phone)