WLAN vs Ethernet Speed

[Mrwest]

How come you loose about 5Mbit in your WLAN.
When I run a TP-test my WLAN speed shows about 12-13Mbit but when I run it over the Ethernet ports it will show 18-19Mbit.
Why do I loose 5-6Mbit? Throughput? Fallback?

[YeOldeStonecat]

A lot more overhead with wireless, add to that..not a perfect connection...so often more repeat attempts made. Various interference. Encryption for security adds even more overhead.

[Mrwest]

Thanx for a quick answer!!

[Mrwest]

By the way... What kind of overhead are we talikng about. What is added to the protocols?

Does it hlep to change MTU and if it does, why? Same with RWIN?

Lot of questions....:)

[TonyT]

802.11 Protocol—The IEEE 802.11 standard defines various physical-layer rates for different types of WLANs, such as 1, 2, 5.5 and 11 Mbps for 802.11b and 802.11g. Rates for 802.11a and 802.11g include 6, 9, 12, 18, 24, 36, 48 and 54 Mbps. The user throughput is less than these link rates for several reasons:

• Each packet includes additional data, such as preambles, headers (MAC, IP, TCP, etc.) and checksums.
• When every directed (unicast) packet is received, the receiver transmits a short acknowledge packet back to the sender.
• Transmitters wait for short random times between packets to allow other users to contend for and share the channel.

Given these reasons, the theoretical maximum user-level performance for the various 802.11 systems is:
........................Maximum TCP Rate.........Maximum UDP Rate
802.11b...........................5.9 Mbps..........7.1 Mbps
802.11g (with 11b)...........14.4 Mbps..........9.5 Mbps
802.11g (11g-only mode)...24.4 Mbps.........30.5 Mbps
802.11a...........................24.4 Mbps.........30.5 Mbps
802.11a TURBO.................42.9 Mbps.........54.8 Mbps

Assumes 1500-byte packets, encryption enabled, default 802.11 MAC configurations,
zero packet errors, and maximum available channel bandwidth (that is, operating at close range).
Note that some 802.11 implementations use tricks such as reducing backoff times between
packets to improve throughput performance. Such tricks can result in interoperability problems
with other vendors' systems (mixing manufacture devices).

http://www.atheros.com/pt/whitepapers/Methodology_Testing_WLAN_Chariot.pdf

[Mrwest]

Thanks for the explanation TonyT!!