🚀 go-pugleaf

AES <siegman@stanford.edu> wrote:

> I recently configured an Airport Express unit as a client on our home
> Airport system (complete setup summarized below).  
> 
> The instant we began playing music from one of our laptops to our living
> room stereo system through this AE client, doing so seemed to soak up
> essentially all the bandwidth capacity of our Airport base station --
> connections from a second laptop thru the Airport LAN to the Internet
> slowed to a crawl.  
> 
> Is this normal?  Or do we need to upgrade part of our setup?

To stream audio to the Airport Express, iTunes uses the Apple Lossless
codec. This will generate data at a rate of approximately 0.7 Mbps on
average (assuming 50% compression, which will be somewhat variable).

That isn't going to tax even the slowest 802.11b (11 Mbps theoretical
limit), as long as the signal is good.

If you are getting bad Internet performance while streaming music then
there is something wrong with your wireless network, such as a very weak
signal which is limiting the throughput, or interference from another
transmission source in the same band (e.g. neighbouring wireless
networks on the same channel or less than five channels removed, or a
2.4 GHz cordless phone).

> Full setup:
> 
> AT&T DSL comes into house through a Cayman 3220-H modem/router unit (DSL
> installation is very low data rate, maybe 130 KB, due to 25,000 foot 
> distance to local office; Cayman router is ancient, was part of original
> installation 7 or 8 years ago)
> 
> One of the Cayman's 4 ports goes to Airport Extreme base station that's
> a year or so old via 100' of Cat 4 cable; second port goes to an 
> Ethernetted printer; third and fourth ports not connected.

I assume that Airport Extreme is an 802.11n model? (The flat rectangular
one.)

Which wireless protocol (802.11a/b/g/n) and frequency (2.4 GHz or 5 GHz)
are you using?

You can find out the signal/noise ratio for each client of each base
station by going to the Logs & Statistics section in Airport Utility's
manual setup for the base station. It is in the "Base Station" menu, if
I remember right. It shows a nice graph with different coloured lines
for each client (which you will need to identify the clients by finding
out their MAC address or Airport ID).

You may find that the noise is very high, or the signal is very low
(there should be a clear gap between signal and noise; if I remember
right, noise is typically around -90 dBm on my network, signal should be
-70 dBm or higher).

If you look at the stats on the Airport Extreme, any client which is
showing a bad signal/noise ratio would explain the problem. Given the
evidence, I suspect you will find that either the music source or
Airport Express has a very bad signal.

> Airport Express unit is new; I configured it as a client on the Airport
> Extreme network following instructions in user's guide.  Nothing except
> an audio cable to the stereo system is connected to it.

Assuming the music source is also connected wirelessly, then that
configuration will result in two "hops" to the Airport Express. If the
signal is bad enough that you are only getting in the order of 1.5 Mbps
to any client, then that might explain what you are seeing. All of the
available wireless network transmission time will be taken up by
streaming the 0.7 Mbps audio to the Airport Extreme, then forwarding it
to the Airport Express.

If the music source was connected via Ethernet, or the Airport Extreme
and Airport Express were connected via Ethernet, that would halve the
wireless network transmission time, leaving more time for other clients.

The above numbers are somewhat of a simplification. You may need a fair
amount more bandwidth for all clients to have enough "headroom",
especially if two or more clients are trying to send data at the same
time.

> Music source is iTunes on a MacBook Pro running OS 10.5; second laptop
> is MacBook running OS 10.4.  Both laptops see the Airport Express as a
> remote speaker choice in iTunes speaker selection menu.
> 
> Observed behavior is that Internet response time for second laptop 
> attempting to read email with Eudora or surf with Safari drops to a 
> crawl as soon as first laptop starting sending music through the AE unit.

-- 
David Empson
dempson@actrix.gen.nz