On 07 Aug 2010, at 03:29 , Patrick Frejborg wrote:
> My guess is that
> multi-path connectivity for vanilla TCP&UDP is that the node have one
> identifier attached with several locators so you can have several
> transport connections available,
There is only one transport-layer session,
but multiple paths can be used concurrently by the
ILNP packets handling that one transport-layer session.
> even simultaneously (wondering how
> the application asks to setup several transport connections).
When ILNP is in use, then the transport-layer is decoupled
from the Locator. For example, the transport-layer pseudo-header
checksum only includes the Identifier values, never the Locator
values. Hence, a single transport-layer session can be
carried in ILNP packets using multiple Locators concurrently
(obviously: one Locator pair in any single given packet).
> But there is no demultiplexing/multiplexing of packets at the stack,
> the stack chose one path at the time - if one fails the stack
> switches to the another path.
I am not sure what you mean above.
The ILNP implementation can send TCP segments (or TCP ACKs,
or other TCP information) using different Locator pairs.
As an example, if one considers TCP with an originator using
Locators (A, B, C) and a responder using Locators (W, X, Y),
then the originator can choose which Source Locators to use
and also which Destination Locators on a packet-by-packet
basis.
Again, purely as an example, the originator could send
packets using these Locator values in this simple sequence:
(A, W)
(B, X)
(C, Y)
or any other sequence that it wishes to. Similarly, the
responder can use any valid combination of Locators that it
wishes to use.
In any case, the TCP implementations at either end are unaware
that multiple Locators are being used (i.e. because the
transport-layer pseudo-header checksum only includes Identifiers,
never Locators). In turn, this is why not special multi-path
TCP (or UDP or SCTP or other) transport-layer modifications
are required. (Caveat: Of course, the ILNP stack upgrade is
needed in the first place.)
The same concepts apply to UDP and/or SCTP.
I will look over the ILNP I-Ds and try to clarify this a bit;
apparently they aren't clear enough right now in this area.
Yours,
Ran
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