Tuesday, April 01, 2008, 08:30 am
Exploring Time Capsule: 10/100/1000 Ethernet vs. 802.11g/n Wireless Networking
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:
Exploring Time Capsule: WiFi 802.11n and the 5GHz band
Exploring Time Capsule: theoretical speed vs practical throughput
Exploring Time Capsule: how it fits into Apple's AirPort family
An in-depth review of Apple's 802.11n AirPort Extreme Base Station
Apple Time Capsule unboxing and preview
A Look Inside Apple's New Time Capsule
Answers to Time Capsule reader questions
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