Internet Speed Differences Wired and Wireless


I have 100 Mbps Internet connection. This is my topology

Internet>>>Cisco Router 1921 >>Cisco Switch 3560 >> Wired and Wireless client

I have desktop PC connected to Cisco Switch and 2 laptops associated with Cisco Wireless Access Points. This AP is also connected to the switch.
When I make speed on Desktop I am getting 90Mbps Download and on laptop I recieved between 15-20Mbps.

Why there is big difference ?

Please help

Many Thanks !!
Who is Participating?
Mohammed RahmanConnect With a Mentor Commented:
Majority of AP manufacturers set APs to operate on channel 6 and 11 as default. (not all but most of them).

During AP configuration, we generally set the security (WEP/WPA...) and leave channel selection to default.

You can login to your AP, browse to Wireless settings or probably advance wireless settings and you may come across a drop down to select channel for your AP.

How to know which off the 11 channels is not over crowded and select the same for our APs?
Simple: Get any wifi channel scanner (google wifi channel scanner and you will get tonnes of results). Use any of them (Like this one: WiFi Channel Scanner  OR inSSIDer

It enables you to quickly view the status of all WiFi wireless hotspots around you and the channels used by them. Based on the results, set your APs on the channel that are least used around you :-) . This will definitely make a difference in terms of data rate to/from APs to workstations and other wifi devices.

** Also, in order to achieve the advertised 54Mbps, you will have to be very close to AP. You can probably plug into the ethernet port and enjoy 93mb if you can get that close to an AP :-)

Also, try to place APs in a way that signals reach maximum floor area and APs overlapping each other (so that connection doesn't drop when you are on move). An example below.
AP placement
Typically, real-world maximum throughput on wireless will be about half the reported connection speed.  So for a reported connection speed of 54Mbps, you would expect to see maximum real-world throughput of about 27Mbps...  do you know what the reported connection speeds were when you made your speed measurements on the laptop?
Except for 802.11n all wireless is half duplex.  On top of that I would also assume that you are protecting your wireless connection  by encrypting it with either WEP or WPA.

Due to it being half duplex and with the encryption you, as Darr247 stated, you are going to get about 50% or less than the advertised bandwidth.

Now, 802.11n can due full duplex, but not all 802.11n devices support it.
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> Except for 802.11n all wireless is half duplex.
Got a cite for your implied claim that 802.11n IS full duplex?

Here's the math for why reported connection speeds don't equal throughput

It works EXACTLY the same for 802.11n, by the way.
English version: Wireless is not cable of connecting at ethernet speeds, but the overhead of wireless also keeps connection speeds lower.
Just do a search on 802.11n MIMO
> Just do a search on 802.11n MIMO
I don't need to. I have a copy of the 802.11n spec from IEEE.  YOU do a search on 802.11n MIMO and find a site you can cite for us where it says 802.11n is full duplex.
Mohammad Aamir QureshiCommented:
change the router duplex setting
duplex auto
Darr247, I stand corrected.  I could swear that I had read with multiple radios and MIMO that 802.11n could do full duplex data transfers.  Guess that was a dream. : )

Aamirg, duplex setting on the router won't make a difference in this case.   Wireless is much slower than the "max" speed due to things like duplex and encryption.
cciedreamerAuthor Commented:
Its a bit bit strange.

When connected to WAP, I recieved 15 MB Speed and with Wired 93 MB !!!!

I am not quite understanding the concept.
It's hard to explain in a small space, but it is working as designed.

Wireless connections are much less efficient than wired connections to start with.  More than likely your wireless connection is also much slower.  So a slower and less efferent connection will cause your through-put to be much slower also.
Did you read the link  Darr247 provided earlier?
15MB would equate to about a 240Mbps connection speed.
What speed was reported when you made that measurement?

To see the current speed, click the wireless icon in the Notification Area, then right-click the SSID of the current connection and choose Status.Currently connected to - Context Menu
Then you can see the connection speed dynamically on the 'Speed' line. e.g.Current Connection - Status - WiFi SpeedCurrent Connection - Status - WiFi Speed
Mohammed RahmanCommented:
To add to points that are already provided above:

Half Duplex

    Used by IEEE 802.11a,b,g and others
    Time Division Duplex (TDD)
    Bi-directional system
    Only one radio transmits at a time
    Radio buffers the data until it is its turns to transmit
    Operates only on one radio channel
    Typically less then half thru-put of the over-the-air data rate

The factors that could be limiting speed:

1. Only one radio transmits at a time (Hence, you can achieve 27Mbps max, provided your wireless device is not effected by below factors)

2. Nearby devices that are working on 2.4Ghz frequency and interfering with your AP.

2.4GHz unlicensed band can get severely affected by the overcrowding of wireless signals to a point where a device will not operate at an acceptable level.

3. Channel on which AP is operating. Its possible that couple of APs are transmitting on same channel as your AP is.

The 2.4GHz band is split up into 11 channels operating on bandwidths of 25MHz each spaced 5MHz apart, within an overall range of 2412MHz to 2462MHz. It doesn't take much maths to work out that the channels have to overlap each other to be able to fit within the overall operating range. This overlapping causes interference if wireless devices are using neighbouring channels and so the only channels recommended for use are 1, 6 and 11 as these do not overlap. However, this means that only 3 wireless devices can used within the same area unless overlapping channels are to be used.

Wireless Networks allow more than 1 person to communicate with another network source at any one time. This sharing of connection means that the more subscribers utilising the network, the more devices the access point has to try and communicate with instantaneously. The point of access has to delegate its resources to each subscriber individually per the amount of transmitting radios it operates on. Half-Duplex equipment can only send or receive at any one time.

4. Antenna strength (Not every laptop has antenna's with same transmitting strength)

Most prominently affecting indoor networks, wall construction properties can be one of the biggest inhibiters of wireless signals. Wire meshing within the walls can cripple signal transmissions and the materials used have different levels of effect; concrete is a usual suspect in badly performing indoor networks. It almost goes without saying that the thicker the walls, the less success the signal will have penetrating through it whilst maintaining a high strength.

5. Distance between AP and Laptops will degrade signal strength

The further apart the networked devices that are trying to communicate with each other are, the more the signal strength drops. This is due to way that wireless signals propagate covering a wider area as they travel further and because of this, as the signal spreads more, the weaker it becomes. The signal strength decreases, roughly, in an inverse cubic relation with respect to the distance between the two devices.

Strength = 1/Distance^3 i.e.
Distance = 1, Strength = 1, Distance = 2, Strength = 1/2^3 = 1/8

Therefore as the distance has doubled; the signal becomes 8 times weaker.

6. Number of devices connected to AP. As the spectrum is shared, more devices connected to AP, less the data rate per device would be.

Note: The wifi data rate is not in range that can be any value between11 to 54Mbps. Its always in the range below.
6, 9, 12, 18, 24, 36, 48, 54 (Hence, based on all these mentioned factors, the speed will always be half of above values)

FINALLY (another Important factor)

Speed Loss Due to Wireless Overheads

Due to encryption, packet translation and partial utilisation of channel bandwidth for user data, advertised throughput speeds are not the actual, real world throughput speeds experienced by the end user. Wireless networking protocol overheads typically result in maximum throughputs of half the maximum theoretical speeds advertised and this can then be further reduced by other factors relating to the makeup of the data packets. Basically, the maximum advertised speeds are in general much higher than what you will probably experience.

Hope this info helps you in understanding why is there such huge difference between wired and wireless connections.
Well, without any research, I see a couple inaccuracies...
e.g. in "3,"  the 2.4GHz ISM band is divided into channels 22MHz wide for the 802.11b/802.11g protocols, and 20MHz wide for 802.11n (Bluetooth uses channels 1MHz wide in the same band).

in "5," the strength of all electromagnetic waves (i.e. including 'light') varies inversely with distance squared, not distance cubed.
Mohammed RahmanCommented:
Thanks for corrections. point 3 has an error as 25MHz against 22MHz and for point 5 (I until now was considering it a cube and not squared). Got to learn something new :-)

Again, thanks for making necessary corrections. (Not every one does that on EE).
cciedreamerAuthor Commented:
My Wireless Connection Speed is 54 Mbps

@mody2579 : You have given a very decent clarification.

I have 2 AP's. I am not quite sure if they are configured with overlapping channels since I am not wireless expert.

Please can you help with recommended configuration and design.

Suggestions only:

(1) You may want to try the speed test on the wireless laptop again but disconnect the desktop before you do that, to see if this makes any difference.

(2) While the desktop is connected, disable wireless on the laptop and connect to the switch directly via RJ45 and repeat the speed test. This test will bypass the AP which could be the bottleneck.
cciedreamerAuthor Commented:
Thanks Mody for your help and suggestions through out this post.

I appreciate it.
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