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Tuesday, April 01, 2008, 05:30 am PT (08:30 am ET)

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.