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Exploring Time Capsule: 10/100/1000 Ethernet vs. 802.11g/n Wireless Networking

Time Capsule, like most of Apple's earlier AirPort base stations, can handle both wired and wireless networked devices, but is optimized for serving wireless clients. This segment, the fourth of six exploring Time Capsule in depth, highlights the differences between wired and wireless networking on Time Capsule and the AirPort Extreme.

Time Capsule and the AirPort Extreme are designed primarily to serve wireless clients, providing a convenient and minimally invasive way to network systems in a home or small office to support centralized backups, file sharing, and media streaming. Wired Ethernet networking is nearly always going to be much faster, but also requires running wires through walls and tethering mobile devices to an Ethernet jack.

For the purposes Time Capsule is designed, including Time Machine backups and simple file and print sharing, the speed advantages of Ethernet are less of a factor compared to the needs of users who want a blazing, hard wired RAID array supplying high speed Network Attached Storage.

All of Apple's recent AirPort base stations have included an Ethernet switch, which allows user to directly plug in devices using an Ethernet cable; the base station bridges those wired clients to any devices attached wirelessly, so all can appear on the same AirPort created network.

However, while the AirPort base stations support full speed Ethernet switching, the shared disk file serving capacity of Time Capsule and AirPort Extreme is not tuned to saturate a big Ethernet pipe. That means the effective speed of the base stations' wired networking jacks are not competitive with a standalone NAS or dedicated file sharing computer. The numbers below (and chart on page 2) help outline that fact.

Real World Tests: Gigabit Ethernet vs 802.11n WiFi

Connected via Gigabit Ethernet to Time Capsule from a MacBook Pro, it took 1:38 to copy a gigabyte folder of mixed media to its internal drive. Including the few seconds it took for the sleeping Time Capsule drive to spin up, the operation took 1:45.

Wirelessly, it initially took a whopping 13:10 for the MacBook Pro to copy the same files to Time Capsule. In a parallel test, it took 8:18 to wirelessly copy the files to a drive connected via USB to an AirPort Extreme. The odd difference in speed was apparently related to the fact that in both tests, the MacBook Pro was wirelessly attached to the AirPort Extreme base station, which then wirelessly relayed the data to the Time Capsule, which was setup to "Extend a Wireless Network."

In that configuration, the MacBook Pro was skating across the wireless network twice to reach Time Capsule. With Time Capsule configured as the primary base station, the MacBook Pro took just 2:55 to copy the same files, a huge difference. Repeating the test again, it took 4:36 to perform the same action.

Repeating the gigabyte file copy test using a 5 GHz configuration took 8:17 and then 9:38 on the second try, suggesting that the 5 GHz setting itself isn't likely to make a huge improvement for typical users, and may instead just reduce their range and signal strength due to its worse signal penetration and radio power limitations. However, using wide channels, the same copy took just 2:11, indicating that in optimal conditions, 802.11n can easily compete with running wires in many applications.

The wild fluctuations in copy times over our wireless network links makes it harder to empirically compare wired to wireless times in a way that offers users with different configurations and different circumstances (such as the degree of outside interference, and the user's specific needs for wireless coverage area) a simple "rule of thumb" answer.

Below, we outline and present the results of various tests we performed to show you the range in performance you can expect to get wirelessly, compared to a wired network using Gigabit Ethernet, using Fast Ethernet (such as on previous 2007 models of the AirPort Extreme) and using 802.11g (on WiFi clients that do not support the full speed of 802.11n).

WiFi N vs Gigabit Ethernet and Multiple Users

In ideal conditions, 802.11n can perform at around three quarters the speed of Time Capsule's Gigabit Ethernet for a single user. However, if there are multiple users, each will eat into the limited, shared wireless bandwidth available. In a small office network, this favors setting up non-mobile machines to use Gigabit Ethernet rather than share the wireless network with mobile machines such as laptops. An Ethernet switch will allow each wired user to enjoy a fast, independent connection to the Time Capsule or shared AirPort Extreme drive, although at some point, concurrently connected users will eventually hit the limits of the drive and the data serving hardware itself.

For home users, an individual doing more than one thing, such as streaming AirTunes while running Time Machine, may similarly see a blip in their music playback performance every time Time Machine kicks in. Time Machine seems to momentarily overwhelm the wireless network when it first begins and again when it wraps up the backup session at the end, but counterintuitively, does not seem to excessively tax the network while it's actually backing up files in the middle of its session.

The design of Time Machine makes this issue easy to work around; if you're doing intensive network file operations or streaming media, simply turn Time Machine off to prevent any interruptions, and turn it back on again when its greedy use of the network no longer matters. Time Machine automatically accounts for lost time and catches up.

In our tests, configuring the network to use wide channels over the 5 GHz frequency made the network fast enough to accommodate both AirTunes and Time Machine at the same time without any hiccups. Attempting to dump the gigabyte of test files on the Time Capsule at the same time that both background operations where actively going on resulted in an estimate of 17 minutes from the Finder file copy, but didn't interrupt AirTunes playback. Time Machine took longer to perform its back up, but everything played along cooperatively, even as the reported signal strength fell down to around 216 Mbits/sec. The test files actually took 8:51 to copy during the AirTunes and Time Machine wireless smack down.

That indicates that for casual home and small office users, Time Capsule and the AirPort Extreme can support typical file sharing and Time Machine operations without any noticeable lag, if conditions are ideal, the configuration is optimized, and expectations are set realistically. For users with more demanding needs, a standalone NAS or dedicated file server connected to Time Capsule's Gigabit Ethernet switch might make more sense.

On page 2 of 2: Real World Tests: Gigabit Ethernet vs Fast Ethernet vs Wireless; and Real World Tests: WiFi 802.11n vs WiFi 802.11g.

Real World Tests: Gigabit Ethernet vs Fast Ethernet vs Wireless

If you have a Fast Ethernet version of the AirPort Extreme base station, you might be worried that you need to upgrade to Time Capsule in order to gain the faster speed advantage of Gigabit Ethernet. There is a small speed advantage, but it isn't the factor of ten that the theoretical throughput numbers suggest. Copying the gigabyte of test files via Fast Ethernet (10/100 Mbit/sec) to the AirPort Extreme disk from the same MacBook Pro took 2:45.

That's just 50% longer than using Gigabit Ethernet to access the Time Capsule, which may also enjoy a slight advantage in being directly connected to its internal drive over SATA rather than via USB; in other words, the difference in Fast Ethernet and Gigabit Ethernet isn't that dramatic. It also explains why Apple left Gigabit Ethernet off the original revision of the AirPort Extreme base station; Gigabit Ethernet sounds good, but the base station hardware can't take full advantage of the much bigger pipe.

Copying the same gigabyte of files to a PowerMac G5 acting as an AFP file server, the operation took 1:45 via Fast Ethernet. Using Gigabit Ethernet, the same files copied in 0:38. That indicates that the Time Capsule and AirPort Extreme are not the most ideal file servers for high performance users who have little need for wireless connectivity.

If you have an extra machine sitting around, it would no doubt make a much faster wired file server, although both of the base stations are much more compact and energy efficient than a PC or Mac set up primarily to perform file sharing; the base stations are designed primarily to serve wireless clients. And of course, Time Machine currently does not support backing up to other file server shares outside of the AirPort Extreme and Time Capsule, although this should be remedied soon in updates to Mac OS X Leopard.

Repeating the same file copy test to Time Capsule over Gigabit Ethernet, it took 1:37, almost three times longer than coping the files to the PowerMac G5 over Gigabit Ethernet. Wirelessly, copying files to the PowerMac G5 file server took 2:51; wirelessly copying directly to Time Capsule using the same network setup took 2:49. That means the standalone server was slower over wireless than Time Capsule, but considerably faster when using Gigabit Ethernet. Incidentally, in each of these tests, Time Capsule served as the wireless and Ethernet router between the MacBook Pro and the PowerMac G5 (which did not have its own wireless card).

While a standalone server can easily offer a significant edge in performance as a Gigabit Ethernet (or even a Fast Ethernet) file server, Time Capsule and AirPort Extreme are both equally as fast compared to a dedicated standalone server when serving the purpose they were designed for: wireless backups and effortless file sharing in a simple and efficient compact form factor. For users with needs for the performance of a wired network, there are more appropriate server solutions to choose from, from designating a machine as a file sharing host or setting up a dedicated server.

The chart below shows copy times in minutes:seconds, seconds, and megabytes per second, and graphs the performance on the right. We performed many of the tests twice to show the variance we saw in wireless performance even in back to back tests with no obvious variables changing. The results indicate that when used as a wireless device, Time Capsule is nearly as fast as when accessed by a wired client.

Again, note that these time reflect the performance of Time Capsule with little background competition from other clients. As multiple devices or background activities consume its wireless bandwidth, the performance of wireless networking will rapidly fall in comparison to wired clients, so while stringing cables can be unnecessary in an AirPort home, a small office using Time Capsule might want to diversify their network with an Ethernet backbone to support non-mobile clients.

Real World Tests: WiFi 802.11n vs WiFi 802.11g

Unlike the wireless networking tests, copying files over Ethernet resulted in far more consistent test results; there was no significant divergence between test times as there was when testing wireless connections. The variable results related to wireless networking times also suggests why reviewers reported a wide difference in the usefulness of wireless disk sharing on the MacBook Air.

With a poorly configured network, even 802.11n can be unusable slow, and in our tests, even older 802.11g devices could beat it in copy times. Set to optimize data throughput, base stations using a wide 40 MHz channel of the 5 GHz band should greatly improve the experience of users tied to WiFi, particularly Air users.

What about older clients that can't wring the wide channel performance from 5 GHz 802.11n networks? Using a PowerBook G4 with 802.11g, it took 7:21 minutes to copy the test files to Time Capsule, and that was through a secondary 802.11g router connected to the Time Capsule via Fast Ethernet.

That's no match for the 2 to 3 minute average of 802.11n in ideal settings using wide channels, but is actually better than the default configuration times experienced with 802.11n out of the box in b/g compatibility mode. The sweet spot of wireless networking is clearly targeted on 802.11n, but earlier devices can make reasonable use of Time Capsule and Airport Extreme shared drives.

The main advantage of upgrading to 802.11n for users with mixed wireless equipment is signal range; 802.11n devices use MIMO antenna technology to dramatically expand the coverage area of a base station. Even in situations where 802.11n isn't demonstrably faster than 802.11g, its wider range of coverage means the signal will not only be accessible to a greater area, but its speed will also hold up better on the peripheral edges of service.

Once you upgrade enough of your wireless devices to move to 802.11n exclusively (or create a hybrid base station network as described earlier with dedicated 802.11n service), you can take advantage of the other 802.11n trick: wide channels in the 5 GHz band that supply a major boost in network speed. Don't tell your neighbors or they'll flock into the 5 GHz band behind you and turn it into the same overpopulated wasteland that currently plagues many 2.5 GHz WiFi users in urban areas. Also note that in mixed mode, 802.11n networks momentarily slow down to g or even b speeds when older devices are actively transmitting data on the network.

The next segment will look at how the wired and wireless networking of Time Capsule and AirPort Extreme compares against performing Time Machine backups to a directly connected USB drive.

Previous articles related to Time Capsule and its AirPort Extreme cousin: