ZOverLord
Premium
join:2003-10-20
Minneapolis, MN
edit:
February 17th, @04:57PM
| reply to HotelOne
Re: How Much Speed Loss Due to Wireless Overhead?
Actually, when using WEP or WPA, overhead is more based on what CPU is in the card or AP.
With a little research on your card or AP, you can find out what the CPU is in your card or AP.
How Fast is it? How Slow is it? ("Compared to others")
Once encryption is added, the CPU's in your cards and AP's will become the bottle neck of bps.
This can be proven by disabling any encryption and testing rates, and then enabling encryption and testing rates.
It becomes impossible then, because of the differences in these CPU's to make a blanket statement that for example WEP or WPA will cause a speed loss of X%, because it can be smaller or greater depending on the SPEED of the processors involved at the given moment using these algorithms.
Because they are on both ends of the equation, they both effect the outcome. Worse is an AP which has a SLOW CPU, now no matter what CPU's the interface cards have, the AP CPU is SWAMPED with encryption/decryption overhead and slows EVERYBODY down who interfaces with it via a Wireless Device it is hosting.
Other overhead obviously can be attributed to packet retransmission, due to Receiver Sensitivity and Transmitted Signal strength, and Noise, but when compared to the above, in most cases, it's the CPU's that make the biggest CHUNK of lost Bandwidth/Time when using encryption.
You can put 40 foot parabolic antennas on both ends and the CPU's in your Interface cards and AP's are the ONLY constants you can't change, even firmware and HACKED TX power patches can't change that, only a Soldering Iron can 
Bottom line, more focus should be placed on how fast the CPU's in AP's and Interface cards are, because as encryption algorithm's change, and we know they will, how much Bandwidth/Time do you want to give up when you implement them?
As Stated by VincentFox, some of the newer AP's and cards use faster CPU's. It is Interesting that NONE of the name brand manufactures list the SPEED of their processors in their consumer specs.
They may say they use an ARM processor, and you can find out which models run how fast, but they NEVER post the RAW Mhz per second numbers of the processor inside.
Buyer BEWARE, because in some cases this is where the manufactures SKIMP, and sadly, this is the only thing the average person can't change. |
DrTCP
Yours truly
Premium,ExMod 1999-04
join:1999-11-09
Round Rock, TX
| said by ZOverLord  :
They may say they use an ARM processor, and you can find out which models run how fast, but they NEVER post the RAW Mhz per second numbers of the processor inside.
I just saw this thread and wanted to add a couple of points.
First Mhz is really a bad indicator. For example AMD Athlon processors outperform the Intel counterparts at the same physical clock speeds. Besides making comparisons acrosss architectures is even more difficult. That is why all those complex benchmarks are developed to have meaningful tests for particular uses.
The CPU speed of the AP may or may not be that relevant at all even for the two AP using the same CPU. It depends on the design. Some AP implement encryption dedicated hardware. You might have a 33Mhz processor but with dedicated hardware doing the encryption/decryption your performance would perhaps equal to 233Mhz processor or maybe even more.
Also there are two types of AP design. One implements most 802.11b MAC functions (including encryption) in the CPU (SoftAP or HostAP) while the other type firmware AP implements most in the wireless module. Obviously, HostAP design is more vulnerable to Host CPU clocking...
There are some newer cards that can do functions partially on the host CPU (most of the MAC) and partially on the wireless module (encryption assist) as a balance of function vs future upgradeability. |
