wireless g, external disk, 2Mbit/s

J

jhd

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My MBP hooks up wirelessly to my router (Netgear dg834g), they are in the same room about 12 ft apart and according to AirStatz and the icon at the top right of my MBP screen; i have a perfect signal.

However, i only get a 2Mbit/s transfer rate to a external hard disk (Buffalo Linkstation) that is connected to the Netgear router via an ethernet cable. Any ideas why it is so slow?

My router is configured to only accept wireless g connections, so i would expect it to be running at least 10x faster.

I connect to the external disk by mounting it via finder>go>connect to server. Does this have any limitations?
 
54 megabits/second (802.11g) would yield a maximum throughput of 6.75 megabytes per second (54 / 8 = 6.75). Considering that wireless transfers need a whole lot more "synchronization" than wired connections (due to interference, ACK/SYN packets, etc.), 2 megabytes per second is about normal.

Expecting to see 10 times that transfer rate (eg., 20 megabytes per second) is unrealistic. A wired 100 megabit connection (100 baseT) can only transfer at 12.5 megabytes per second at its best, and you're running a link that is essentially half that speed, not to mention it's wireless, so there's a lot more dropout involved.

Short answer: you're seeing normal speeds. If you want to try and eek out every last bit of speed out of your connection, and possibly see 2.25 megabytes per second, try fiddling with your router's channel settings and packet sizes... be warned, though, that packet sizes can have adverse effects on your connection, possibly rendering your wireless connection useless until you change them back to acceptable values.
 
Thanks for the explanation. I didn't realise that there was a x8 difference between megabits and megabytes.
 
It is even more than that: You can expect a factor of 10 because you have to take all the framing on the bit and the various packet levels (Ethernet, IP, TCP) into account. 1MB/s over a 10Mbit/s ethernet is a good value. With Gigabit ethernet, the theoretical limit is at about 100 MB/s. You need a high powered processor to reach this level of performance, because networking costs computing power.

For wireless connections, you have the added problem that the medium is shared. No other traffic on the same channel can occur while a station is sending data. On a wired connection, you have a dedicated link with two independed routes for sending and receiving data, given that your connection is switched and does not pass a simple hub.
 
mvcube said:
With Gigabit ethernet, the theoretical limit is at about 100 MB/s. You need a high powered processor to reach this level of performance, because networking costs computing power.
Click to expand...
The theoretical maximum throughput of gigabit ethernet is exactly 125MB/sec. You do not need a "high powered processor" to reach this level of performance -- you need high-speed disks to feed the data to the ethernet port fast enough. The throughput of the network adaptor (ethernet, in most cases) is hardly dependent on processor power at all (we have a 900MHz Celeron processor machine @ work with a 750GB striped RAID connected via SATA-II and gigabit ethernet, and it reaches very fast transfer speeds... rivaling and sometimes exceeding our dual-Xeon servers).

The original MacBooks with 1.83GHz Core 2 Duo processors have very capable gigabit ethernet ports, and 1.83GHz is, by no means, a "high powered processor".
 
My experience may be a bit older. Windows is rarely able to use the full GB bandwith, because its TCP/IP implementation isn't "perfect".

I'll check the transfer rate between my iMac and my Macbook with ftp. Both habe GB ports and the Dell switch shouldn't be a bottleneck. I'll keep you posted.
 
Here are some results for FTP of an 976MB (1024182272) binary file:

iMac (10.4.11) to Windows 2003 Server (to disk): 11 s, 84.69 MB/s
iMac to Macbook (10.5.2) (to disk): 33 s, 29.38 MB/s
iMac to Macbook (10.5.2) (to /dev/null): 10s, 94.56 MB/s
iMac to itself (localhost) (to /dev/null): 6 s, 156.80 MB/s

Disk I/O seems to be a limiting factor. Due to caching, my first tries -not shown here- were noticably slower. What you see here are values which seem to come from reading the data from the disk cache.

I cant get anywhere near 125 MB/s, even if sending data in the bin. Only the local interface is a little faster: This seems to be the theoretical limit for my iMac.

Marcus
 
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