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If 802.11n can operate at 300Mb/s, why does Apple equip the AirPort Express with a 10/100 ethernet port? Doesn't a 100Mb/s port effectively throttle the wireless to 100Mb/s?

AirPort Express specifications

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Attempts to stream a 6GB, 1080P, H.264, MPEG-4 movie from my DLNA server (EyeConnect on Mac mini) to Samsung TV over Wi-Fi resulted in continuous buffering on the TV. After I removed Wi-Fi from the mix, the video streamed w/o incident.

Initial configuration: Mac mini (100/1000BASE-T)-->Gigabit switch-->AirPort Express (10/100)-->802.11n-->Samsung TV  
  Final configuration: Mac mini (100/1000BASE-T)-->Gigabit switch-->Samsung TV (10/100BASE-T)
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So the problem in your particular situation wasn't the 100BASE-TX port on the AirPort Express, since the Samsung TV has the same limitation and it wasn't a problem. The problem was that you weren't even getting 100 megabits/sec out of Wi-Fi, which could due to any number of other problems. What model is the Samsung TV? I'd like to look up its Wi-Fi specs because I'm curious. Was your Express in 2.4 or 5GHz? –  Spiff Dec 6 '11 at 3:52
    
TV: un46c6800ufxa; AE: 2.4GHz –  Craig Dec 6 '11 at 3:59

2 Answers 2

up vote 1 down vote accepted

When hardware products have nonintuitive limitations like this, it's often because at the time the product was designed, there was no good SOC (System-on-a-chip; a single chip with CPU, I/O, and possibly RAM and FlashROM) that met all of the design goals, and no good way to supplement a "close enough" SOC with external chips and still meet the design goals for cost, power, thermal, size, etc. It could be that the only SOCs at that time that had GigE took too much power or dissipated too much heat or plain cost too much to build a successful product around.

Although this particular limitation might mean it's not an ideal product for your situation, I'm not sure it's that big of a deal for most consumers.

Since AirPort Express is one-band-at-a-time, most people are going to put it in 2.4GHz so that their 2.4GHz-only equipment like their iPhones and iPod touches and legacy hardware can still connect. Note here that Apple limits all their 802.11n gear to only use 20MHz-wide channels in 2.4GHz, in order to "be a good neighbor" and leave room in the band for other 2.4GHz devices to use, such as Bluetooth. So a 2x2:2 (2 transmit radios, 2 receive radios, capable of 2 spacial streams) system like the AirPort Express, limited to 20MHz channels, can only get a 144.4 megabits/sec maximum signaling rate. Because wireless Ethernet has a lot more overhead than wired Ethernet, the maximum TCP throughput you could get would be around 72-80 megabits/sec, which 100BASE-T can handle just fine.

There's also an argument to be made that most consumers don't have high-bandwidth needs within their own homes, and care mostly about getting to the Internet, and most home broadband connections are slower than 100 megabits/sec anyway.

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Yes, if you were able to get your wireless network set up to the point that you were approaching the 300mbps maximum theoretical, then it is possible that you could saturate the wired portion of the network.

Achieving these speeds in reality is unlikely. You need 40MHz bandwidth to get 300Mbps which is only possible on the AirPort Express in the 5GHz band which most people don't use their AirPort Expresses for, so you are probably down to 144.4Mbps. Then you have to consider congestion, the 144.4Mbps is shared among all wireless devices. Then consider interference from other radio sources. Then consider that 802.11n is half-duplex, so you can only send or receive, not both simultaneously.

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