Moving Between Network Connections

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Jason Koesters - 29 Apr 2004 02:33 GMT

Hi Everyone,
Got a complaint/question here. I've got a 1GHz AlBook (10.3.3) with
the Airport Extreme and Gigabit ethernet. I use both at home. Mostly
the Airport, but when transferring large files I plug into my 10/100
switch with my other comps.
On occasion, I will want to transfer a file over the network and I'm
not plugged in, so the file starts to transfer, quite slowly, over the
wireless. Instead of stopping the transfer, turning off the airport,
and plugging in the ethernet (I guess I'm supposed to), I just plug in
the ethernet cable. Showing my ignorance perhaps, I would assume OS X
would bridge the two connections, or something similar, and begin
transferring data over the ethernet. But it doesn't.
Beyond this, I stop the transfer and turn off the airport, and now
OS X tells me I've disconnected from the host (SMB share connection) and
asks whether I would like to keep trying to connect or disconnect. I
say OK to keep trying, and I guess it is only trying the Airport where
it originated, because although the ethernet is working for everything
else, it won't connect for that host.
My question is whether this is expected, normal behavior?
In anticipation of a certain response, my second, slightly more
irate question is why Apple would not do a better job of being able to
switch between network connections? If you've got a connection (no
matter the connection) why not use it?!?
Just thinking a bit longer here, maybe this is an issue directly
with the SMB (Samba) protocol. Anybody a Samba guru and know?
I was just bothered and curious. Thanks for listening and any
responses.

Jason

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Geoffrey - 29 Apr 2004 08:44 GMT

> I've got a 1GHz AlBook (10.3.3) with the Airport Extreme and Gigabit
> ethernet. I use both at home. Mostly the Airport, but when transferring
[quoted text clipped - 4 lines]
> wireless. Instead of stopping the transfer, turning off the airport,
> and plugging in the ethernet (I guess I'm supposed to) ...

Yes, you are.

> I would assume OS X would bridge the two connections, or something
> similar, and begin transferring data over the ethernet. But it doesn't.

No, you're right, it doesn't. And bridging wouldn't solve your problem
either.

> My question is whether this is expected, normal behavior?

As far as I can tell, yes it is.

> In anticipation of a certain response, my second, slightly more irate
> question is why Apple would not do a better job of being able to switch
> between network connections? If you've got a connection (no matter the
> connection) why not use it?!?

Any network connection is built to run over a single hard connection,
unless the serving/sharing protocols allow for split-session multilink
(the ability to share a single connection over more than one physical
network connection). Even then, multilink doesn't allow you to switch a
network connection from one hard link to another, or split a single
network connection session over more than one hardware connection.

Virtually *all* networking protocols for all OSes are designed to work
over one connection, Apple is no exception.

> Just thinking a bit longer here, maybe this is an issue directly
> with the SMB (Samba) protocol.

No, because TCP and AppleTalk do the same thing -- without an extra
multilink API layer, once you've made a connection to a remote server
you're stuck with using whichever hardware method you used initially.

If you want to change from AirPort to cabled ethernet, you have to close
the connection to your remote server, then re-open the connection once
you've plugged your cable in.

Geoffrey

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Barry Margolin - 29 Apr 2004 15:49 GMT

> > In anticipation of a certain response, my second, slightly more irate
> > question is why Apple would not do a better job of being able to switch
[quoted text clipped - 10 lines]
> Virtually *all* networking protocols for all OSes are designed to work
> over one connection, Apple is no exception.

I think you two are using the word "connection" to mean different
things. The OP used it to mean "interface", you're using it to mean
"TCP connection".

Most Macintosh applications *do* seem to be able to handle the situation
when there are changes at the network layer, by closing existing
connections and reopening them. For instance, if you leave your browser
running while you release your DHCP lease and get a new IP, the browser
will typically recover. And the OP claimed that he didn't have problems
if he disabled the wireless interface before plugging in the Ethernet.

The strange thing is that his file sharing application even claimed that
it was going to try to reconnect. This seems like it *should* have
adapted to the new interface configuration, but for some reason it
didn't.

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Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

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Pete Verdon - 29 Apr 2004 16:40 GMT

> I think you two are using the word "connection" to mean different
> things. The OP used it to mean "interface", you're using it to mean
[quoted text clipped - 5 lines]
> running while you release your DHCP lease and get a new IP, the browser
> will typically recover.

Except that when the browser is open and displaying a page, there is no open
TCP connection. Broadly speaking[1] a new connection is opened for each
thing that is downloaded.

Pete

[1] Ie one of those things oh-so-common in this field that's not quite true
but to explain it all is not worth it.

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Mac Forum / General / Portable Macs / April 2004

Moving Between Network Connections