Le 27/01/2015 18:06, Joe Touch a écrit :
On 1/27/2015 8:45 AM, Emmanuel Baccelli wrote:
Hi Joe
On Tue, Jan 27, 2015 at 4:41 PM, Joe Touch <[email protected]
<mailto:[email protected]>> wrote:
It's far too early to discuss whether this doc could *become* a
useful WG doc; in it's current form, there's simply no hint of
that yet. IMO, the authors should take another shot at it, and then
we can see if there's really anything useful to pursue here. The
current doc does NOT make that case yet.
Can you be more specific?
I've tried. If what I've said so far isn't sufficient, then the draft
needs substantial revision and we'll see from there.
Again, the onus is on the draft to be clear.
Apparently there is some misunderstanding. There are two parts in
this discussion. One part is polemic, another part is non-polemic:
(1) the non-polemic part is about the *physical connectivity* that
is experienced on networks tackled by MANET, ROLL, 6Lo and a slew
of other working groups in this domain. This physical connectivity
is pretty well described in the draft, and I think it should be
easy to get consensus on that, with minimal changes.
I disagree, and have already explained why that's not true in
detail.
(2) the polemic part is about what link model / architecture
/solution applies best to such physical connectivity. This
discussion, as well as previous discussions in AUTOCONF, show that
it is not trivial to agree on something.
If this is just about describing a physical layer, IMO it's not
relevant to the IETF. The implications on L3 and above need to be
part of this doc, otherwise there's no point in discussing it here.
However: the chances of agreeing on a solution for (2) are
significantly lower if (1) has not concluded with a clear
documentation of the *beast* to be tamed.
This is why a document such as the draft discussed -- which
addresses only the *non-polemic* part of the discussion -- would be
useful. Do you disagree with the above? If so, why? This is
unclear.
The current doc is essentially vacuous regarding new information on
wireless subnets. We all already know they are composed of links that
vary highly and that the links can be unidirectional.
Please tell us something we haven't known and dealt with for
decades.
Hi Joe,
I tend to agree with this invitation.
To further support it I would like to point to "Issues in Packet Radio
Network Design", Proceedings of the IEEE, January 1987. I can read this
paper because my employer has an institutional subscription.
The paper tells at some point:
The problem of collisions caused by hidden nodes can be alleviated by
the use of a busy tone which is transmitted by a node on a separate
channel to indicate that it is currently receiving a packet.
That is a recommendation for alleviating hidden terminal problems.
IEEE 802.11 also offers methods to alleviate for the hidden terminal
problems (request to send/clear to send).
If this draft were to describe the hidden terminal problem, and suggest
that the IP networking layer should not be used to solve it, would it be
a satisfactory approach? (instead of saying "may affect the IP layer",
as it currently does).
Another problem described in this draft is the following:
There may be no indication to the IP layer when a previously
established communication channel becomes unusable; "link down"
triggers are generally absent in multi-hop ad hoc wireless networks,
since the absence of detectable radio energy (e.g., in carrier
waves) may simply indicate that neighboring devices are not currently
transmitting. Such an absence of detectable radio energy does not
therefore indicate whether or not transmissions have failed to reach
the intended destination.
This describes a problem. If the solution to it were a link-layer
solution, would you agree with the problem per se?
The paper that I cite above gives a solution to that problem, at the
link layer:
Radio connectivity must be determnined by the two ends of the radio
link (i.e. the two packet radio units which are connected). The
information from each node can be collectd at a central location
where connectivity is then detemrined, or it can be determined by
the nodes themselves through a cooperative mechanism, such as
exchange of the number of transmitted and receveived packets. [...]
One set of methodes that can be used to detemrine the existence of a
link is to directly use measurements made on the radio channel.
These can include such measurements as signal strength,
signal-to-noise ratio and bit-error rate.
Alex
Joe
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