Is the USB port in Airport Express a full USB hub?

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AES - 04 Jun 2008 15:09 GMT

Suppose an Airport Express unit (latest version) is set up to talk to
the WiFi LAN provided by a nearby Airport base station.

Does the USB port in that Airport Express unit then provide all the
capabilities of a fully functioning USB hub for laptops who are
communicating wirelessly with that Airport WiFi LAN?

----------

Details:

Situation in question is a third-party all-in-one USB printer-scanner
unit. Connected directly to a laptop's USB port with appropriate
software installed, all functions certainly work.

Connected to a properly designed (and powered) external USB hub which is
connected to that same laptop's port, all functions should also work
exactly the same (right?).

So, if it's connected to the Airport Express unit's USB port, will _all_
functions still work for that same laptop? (And for other laptops with
the same software installed?)

Asking the question here because yesterday afternoon different staffers
in local Apple Store gave flatly contradictory answers ranging from
"Absolutely, yes" to "Absolutely, no" to "Gee, I just don't know".

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Michelle Steiner - 04 Jun 2008 15:33 GMT

> Does the USB port in that Airport Express unit then provide all the
> capabilities of a fully functioning USB hub for laptops who are
> communicating wirelessly with that Airport WiFi LAN?

No. Apple's web site is your friend.
<http://www.apple.com/airportexpress/specs.html>

The USB port on the Airport Express is only for printers.

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Malcolm - 04 Jun 2008 23:50 GMT

>> Does the USB port in that Airport Express unit then provide all the
>> capabilities of a fully functioning USB hub for laptops who are
[quoted text clipped - 4 lines]
>
> The USB port on the Airport Express is only for printers.

The Airport Express USB port can also be used for iTunes remote control
<http://www.keyspan.com/products/urm17a/>

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AES - 05 Jun 2008 01:07 GMT

> >> Does the USB port in that Airport Express unit then provide all the
> >> capabilities of a fully functioning USB hub for laptops who are
[quoted text clipped - 7 lines]
> The Airport Express USB port can also be used for iTunes remote control
> <http://www.keyspan.com/products/urm17a/>

_Very_ interesting.

I'm trying to form a novice user's mental image of what the USB port on
the Airport Express really does . . . ?

Presumably it allows at least some USB-protocol digital signals that
would have been sent out from the USB port on your Mac to be sent out
instead to the USB port on the Airport Express -- enough to at least
make the AE-connected printer think it's connected directly to the
laptop.

But, I'm told, the scanner portion of a remote AE-connected USB
printer-scanner apparently can't send information back to the Mac; and
so one might guess that the USB connection through the AE is unable to
transmit certain USB signals from the AE back toward the Mac . . . ?

But, this Keystone Express Remote gadget, plugged into the USB port of
an AE, _can_ send USB information from the AE back to the Mac, or at
least to iTunes running in the Mac, so there is at least some return
channel and return flow of information.

So, the USB channel is (partially) two-way. But is the channel
partially crippled? Or do some programs in the Mac just not know how to
use it?

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David Empson - 05 Jun 2008 08:57 GMT

> > >> Does the USB port in that Airport Express unit then provide all the
> > >> capabilities of a fully functioning USB hub for laptops who are
[quoted text clipped - 18 lines]
> make the AE-connected printer think it's connected directly to the
> laptop.

Nope.

The Airport Express is a USB master - it acts like a computer. It has
sufficient USB device support to allow a limited set of devices to be
connected. In particular, it supports the Printer class of devices.

As far as USB and the printer are concerned, all this does is provides a
raw data path between the Airport Express and the printer, and allows
identification of the connected printer. The Airport Express doesn't
initiate any printing of its own accord and doesn't know anything about
the data format required by the printer.

The Airport Express then implements one of the network printer sharing
protocols that are supported by Mac OS X (involving Bonjour for
advertising its availability, and some kind of TCP/IP connection for
data transfer). Macs on the network see the Airport Express as a Mac
hosting a shared printer, or as a printer which has a built-in print
server.

The Mac must contain the appropriate printer driver. The driver is
responsible for converting the standard data format used by the Mac OS X
print system (PDF) into something suitable for the printer. This
translated data is then sent over the network to the Airport Express
which forwards it to the printer.

The Mac has no direct knowledge that it is dealing with a USB printer -
it just treats it as a networked printer.

> But, I'm told, the scanner portion of a remote AE-connected USB
> printer-scanner apparently can't send information back to the Mac; and
> so one might guess that the USB connection through the AE is unable to
> transmit certain USB signals from the AE back toward the Mac . . . ?

No "USB signals" are passed to/from the Mac by the Airport Express. A
scanner won't work because there is no standard networked scanner
protocol.

> But, this Keystone Express Remote gadget, plugged into the USB port of
> an AE, _can_ send USB information from the AE back to the Mac, or at
> least to iTunes running in the Mac, so there is at least some return
> channel and return flow of information.

I expect this is tied into the AirTunes mechanism. There is probably
special support in the Airport Express firmware for a class of USB
devices that are recognised as remote controls, and if iTunes is playing
via the Airport Express's audio output then it can get remote control
information from the Airport Express. (This opens up the possibility
that Apple could release a revised Airport Express with a built-in IR
receiver and you could use the Apple Remote to control iTunes via the
Airport Express.)

It all boils down to what USB devices are supported by the firmware in
the Airport Express, and whether there is a method of transferring data
to/from a particular class of devices over a network connection. USB is
entirely local to the Airport Express.

Consider the Airport Extreme (802.11n model) or Time Capsule, which also
supports USB hard drives. Again, the USB connection is entirely local to
the Airport Extreme or Time Capsule. Any access to the hard drive by a
computer involves a network file sharing protocol (typically AFP or
SMB). You can't do things like block-level access to a USB hard drive on
an Airport Extreme (or an external or internal drive on a Time Capsule),
because there is no support for that level of access in standard network
file sharing protocols. This is why Airport Utility has to include
special support for actions like erasing the drive.

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David Empson
dempson@actrix.gen.nz

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Shawn Hirn - 05 Jun 2008 11:59 GMT

> > >> Does the USB port in that Airport Express unit then provide all the
> > >> capabilities of a fully functioning USB hub for laptops who are
[quoted text clipped - 12 lines]
> I'm trying to form a novice user's mental image of what the USB port on
> the Airport Express really does . . . ?

Read the AE's manual. That should provide the information you need.

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AES - 05 Jun 2008 14:18 GMT

Thanks for the extensive and educational replies to my query. It's
clear that my "naive mental picture" of how Airport Express/USB
functions is far too simple: the acronyms"AFP" and "SMB" are not part of
my technical vocabulary.

And, I take the logical point that if three Macs were on an AIrport LAN
together with an Airport Express, and the USB port on the AE were just a
simple USB hub, an external USB device connected to this USB port would
not be able to know just which of the Macs it was looking back into.

Reply to this Message

David Empson - 05 Jun 2008 14:53 GMT

> Thanks for the extensive and educational replies to my query. It's
> clear that my "naive mental picture" of how Airport Express/USB
> functions is far too simple: the acronyms"AFP" and "SMB" are not part of
> my technical vocabulary.

AFP = "Apple Filing Protocol" (self explanatory; it was originally
"AppleTalk Filing Protocol" but doesn't use AppleTalk these days).

SMB = "Server Message Block" (one of the official names of the Windows
file sharing protcol; it is sometimes called CIFS = "Common Internet
File System"; the Mac implementation is provided by an open source
product called SAMBA whose name is derived from SMB.)

Signature

David Empson
dempson@actrix.gen.nz

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Shawn Hirn - 05 Jun 2008 11:58 GMT

> Suppose an Airport Express unit (latest version) is set up to talk to
> the WiFi LAN provided by a nearby Airport base station.
[quoted text clipped - 14 lines]
> connected to that same laptop's port, all functions should also work
> exactly the same (right?).

Its not that simple. Your printer would need to support those functions
wirelessly in the drivers that the manufacturer provides for the
computers that will use it.

For example, suppose you scan a piece of paper. How will you control
which computer that is on your wi-fi network gets the scanned image?
That's up to the drivers on those computers to decide which one will
wake up to handle the scanning request.

I don't know of any scanner or other device that has such drivers;
however, I haven't looked so I won't say they are not out there.

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Mac Forum / Applications / Mac Applications / June 2008

Is the USB port in Airport Express a full USB hub?