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Thread: MacBook Air 802.11ac Speeds Hindered by Apple's OS X Mountain Lion

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    MMi Staff Writer Akshay Masand's Avatar
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    Default MacBook Air 802.11ac Speeds Hindered by Apple's OS X Mountain Lion


    We previously reported about an issue with Apple’s latest MacBook Air having Wi-Fi issues. One of the major upgrades found in the new iteration of the hardware was the inclusion of 802.11ac Wi-Fi but a recent discovery points toward an issue in OS X 10.8 Mountain Lion found to be hampering the laptop from reaching peak data transfer speeds. In a review of the mid-2013 13-inch MacBook Air, Anand Lai Shimpi of AnandTech found real world 802.11ac file transfer speed to be artificially slowed by an apparent software issue in OS X Mountain Lion.

    After discovering speeds hitting a cap of 21.2MBps or 169.9MBps over 802.11ac, much lower than the boasted 533Mbps throughput seen with networking testing tool iPerf, Shimp narrowed down the problem to Apple Filing Protocol (AFP) and Microsoft’s Server Message Block (SMB). After investigating the issue further, it was found that OS X doesn’t scale TCP windows to the appropriate size, therefore limiting the performance of the newly implemented Wi-Fi protocol. According to Shimpi:

    The bad news is that in its shipping configuration, the new MacBook Air is capable of some amazing transfer rates over 802.11ac but you won’t see them when copying files between Macs or PCs. The good news is the issue seems entirely confined to software. I’ve already passed along my findings to Apple. If I had to guess, I would expect that we’ll see a software update addressing this.
    A separate report from the folks over at Ars Technica claim an 802.11ac-enabled MacBook Air running Windows 8 in Boot Camp will reach higher file transfer speeds than Apple’s own operating system. While transferring files in Windows is still relegated to Microsoft’s SMB protocol, the publication saw speeds that were roughly 9% faster than OS X over Ethernet, 30% over 802.11n and 218% faster on 802.11ac. The issue presents itself in the Developer Preview build of OS X Mavericks as well, suggesting the TCP limitation wasn’t one that was instituted purposely.

    Source: AnandTech, Ars Technica

    Twitter: @AkshayMasand

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    iPhone? More like MyPhone GooseG's Avatar
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    Are those speeds in megabytes per second (MBps, MB/s) or megabits per second (Mbps, Mb/s. Notice the lower case b, people always confuse this) network speeds are generally measured in Mb/s (Megabits per second). The difference being that there are 8 bits in a byte, so 8 Mb (Megabit), is equivalent to 1 MB (Megabyte). I wish more people understood this, since I see this mistake everywhere.

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    Livin the iPhone Life
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    Quote Originally Posted by Akshay Masand View Post
    After discovering speeds hitting a cap of 21.2MBps or 169.9MBps over 802.11ac, much lower than the boasted 533Mbps throughput
    Nope.
    169.9 MBps is significantly greater than 533Mbps
    169.9 MBps equals 1359.2 Mbps

    1359.2 > 533

    Correct the syntax please.

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    quidam_brujah (06-25-2013)

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