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Re: TCPng/ multiple addresses per node (was Re: A follow up question)_

2003-04-29 06:30:50


john(_dot_)loughney(_at_)nokia(_dot_)com wrote:

Hi Alain,

I agree with your intro (which I clipped to save space),

Thank you!

one
comment that I have is:

There is a proposal to create an API to enable the
application creating the socket to specify some of the
properties that it desires/requires. This is a step in the right
direction, but I'm not convinced this can go far enough.
So I fully support this idea of lifting the ban on TCPng
(or any transport layer for that matter) to de-couple
the abstraction needed by applications to the one required
by the network. This is in fact introducing some of the semantic
of a session layer between the application and the network.
Can this be done at the transport layer in the form of TCPng
or does this require and actual additional session layer?
I'm not sure at this point in time.

There already something like this, I'm sure you know - SCTP.
I'm actually not trying to promote SCTP, but it might be interesting,
as we have an RFC that does most of the avove, to look at it
critically & see how it performs.
SCTP, as a background, uses sets of addresses/ports to identify a
node. In the usual case, one node will pass all of its addresses(& ports)
to its peer & the peer returns its addresses (&ports) for SCTP traffic. The application has the the option to choose the primary address to be used.
SCTP does not specify how the 'primary' source & destination are chosen,
nor does it explain how to order those lists once it decides to try another pair.

Two possible ways to do that could be:
- use knowledge of the topology, that is pass some of the
  routing information to the end nodes.
- use dynamic measurements.. For example start the connection
using the initial src & dst, and then send regular probes (duplicates?) using
  the other combinations to do measurements and keep statistics.

On top of that you might want to add social/economic information
known by the end points, like this interface is cheap vs expensive
at this particular moment. Similar information for other links
within the network would be valuable but much more difficult
to collect!

Also, there is still a need to enable the application
to specify the desired/required properties of the addresses,
like use temporary vs use stable address, use home address vs
care-of-address,...

SCTP does not do any of that.

   - Alain.






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