Original post:
http://simhq.com/forum/ubbthreads.php/topics/3666854/Getting_the_best_wireless_spee.html#Post3666854I will start by mentioning a few facts of how 802.11 wireless communication works and then explain the list from the original post.
Some 802.11 Facts:
01. It uses half-duplex communication. Only one device on the same frequency can transmit at any point in time. You and neighbors that are on the same channel need to take turns transmitting and receiving.
02. Each Unicast frame sent to another device requires an acknowledgment (ACK), a confirmation of receipt. If a packet is sent and no confirmation of receipt is returned the packet needs to be resents. Too many resends will cause a degradation in performance.
03. After the transmission of each frame there is a short wait time called an Interframe Space (IFS). The ISF is used to allow time for the radio signal to propagate and allow time for the ACK to be received.
04. If an ACK frame is not received the sending device will assume the sent frame did not reach its destination and will resend the frame until it receives an ACK frame or till the retry threshold had been reached.
05. Every device needs to be on the same frequency and use the same modulation such as a,b,g,n. Devices on different modulations need to take turns communicating if they are on the same SSID.
06. Wi-Fi is a certification given to equipment that conforms to a Wi-Fi Alliance standard. It is used to certify that all Wi-Fi certified equipment will be able to communicate with other Wi-Fi certified equipment using 802.11.
07. In 802.11 the term Bandwidth means the size of the channel measured in Megahertz. For example in the United States, the 2.4 GHz ISM band has 11 usable channels and each channel is 22 MHz wide. The
5.0 GHz UNII band has 23 usable channels and each channel is 20 MHz wide. There is a single ISM channel in the UNII-3 band with a frequency range of 5.825-5.875 with a bandwidth of 150 MHz
08. The amount of transmit power is regulated by the FCC. If you want to use an add-on antenna you have to make certain it does not exceed the power amplification limit set by the FCC. The antenna either has to be certified by the FCC for use with the equipment you plan to use or you have to be certain it does not amplify the signal beyond strength allowed. I will discuss this topic further. It is against the law to transmit a signal beyond the limit set by the FCC.
09. Your throughput (Actual Data Rate) will usually be half of what is advertised by the manufactured.
10. The best solution to increase throughput it to reduce retransmissions and ACK (Acknowledgment) errors.
11. Increased signal amplification will not increase throughput. It only makes a signal go further.
These are some of the more common facts people deal with on a daily basis. All the information discussed is for equipment used in the United States.
_______________________________________________________________________________
Advanced properties of the wireless device (all settings are default)
01. 802.11n Channel Width for band 2.4..... Options are 20 MHz only or auto (std is 20 MHz only)
02. 802.11n Mode..... Options are on or off (set to on)
03. Ad Hoc Channel 802.11b/g.....Options 1-13 (set at 11)
04. Ad Hoc QoS Mode.....Options are WMM on or off (set to off)
05. Bluetooth(R) AMP.....Options are on or off (set to on)
06. Fat Channel Intolerant.....Options are on or off (set to off)
07. Mixed Mode Protection.....Options are CTS-to-self Enabled or RTS/CTS Enabled (first option on)
08 . Roaming Aggressiveness.....Options 1-5 (set to 3)
09. Transmit Power....Options 1-5 (set at 5)
10. Wireless Mode.....Options are 1-802.11b 2-802.11g 3-802.11b/g (3 is selected)
The settings on the router are a little simpler.
802.11 b/g/n
802.11 b/g
802.11 b/g/n 40 MHz
Channel selection 1-13 (default is 11 but this only gives an 'actual data transfer speed' of 65 Mbps as reported by the router.
If I manually select channel 1 it shows a transfer speed of 150 Mbps.
Does security make a difference? It's set to 'WPA & WPA2 (Recommended)'
If you can make any sense out of it I take my hat off to you. Any reply greatly appreciated.
_______________________________________________________________________________
01. 802.11n Channel Width for band 2.4..... Options are 20MHz only or auto (std is 20 MHz only)
802.11n uses two frequencies. The 2.4 GHz ISM Band (Industrial Scientific and Medical Band) and the 5.0 GHz UNII Band (Unlicensed National Information Infrastructure Band). Each channel on the ISM band is 20MHz wide. There needs to be a separation of five channels to avoid Adjacent Channel Interference. The most common and recommended configuration for an ISM in a Multi-Channel Architecture (MCA) is the use of channels 1, 6, and 11. For home use select the channel that is been used the least at your location.
In 5 GHz UNII band. Each channel is 20MHz wide. The modulation is Orthogonal Frequency Division Multiplexing (OFDM) with 56 subcarriers per channel. 52 are used for data and 4 are used for control signals.
On the 2.4 GHz ISM Band using 802.11b each channel will be MHz wide. The modulation would be High Rate - Direct Sequence Spread Spectrum (HR/DSSS).
802.11n allows you to combine two 20MHz channels to create a single 40Mhz channel. That allows you to double the amount of data sent to another 802.11n receiver that is configured for 20/40 Mhz and using 40Mhz Channel Bonding.
It is possible to bond two 2.4 GHz ISM channels but it will give you a single 40-MHz channel . It will also interfere with any nearby 2.4 GHz 1,6, & 11 channel.
2.4 GHz Channel Bonding is not allowed in Corporate Equipment.
02. 802.11n Mode..... Options are on or off (set to on)
The 802.11n-209 Amendment adds a variety of features not found in legacy 802.11a,b,and g. The only 802.11n feature I see mentioned is the “Fat Channel”. A more proper name is Channel Bonding. High Throughput (HT) the name for 802.11n, allows two 20MHz channels to be bonded together to create the 40-Mhz Channel in the UNII band. The bonded channel uses OFDM modulation with 114 subcarriers. This bonding creates a single logical channel with a bandwidth of 40Mhz essentially doubling the amount of data that can be sent in each packet.
The 802.11n has a mode called Greenfield Mode. In this mode only other 802.11n radios will be able to understand the transmission. 802.11a,b, and g will no be able to communicate with the 802.11n radio in Greenfield Mode. You use Greenfield when you know communication will occur only with other 802.11n radios. This allows you to use all the features available only on 802.11n without the performance degradation caused by setting a compatibility mode for communicating with 802.11a,b,g and n radios.
03. Ad Hoc Channel 802.11b/g.....Options 1-13 (set at 11)
Ad-Hoc is also called an Independent Basic Service Set (IBSS). It is used to create a Basic Service Area (BSA) among a group of computers without an Access Point or a Wireless router. To create an IBSS you manually select the same channel on each computer and give each computer the same Service Set Identification (SSID). Make certain you configure the security so only the computers with the proper credentials are allowed to join the BSA. If a rouge computer joins your network it can steal information from your computer and/or add malicious software.
04. Ad Hoc QoS Mode.....Options are WMM on or off (set to off)
Qos means Quality of Service and WMM means Wi-Fi Multimedia. Qos is a means to allow data with higher priority such as voice and video to be given higher priority to the medium. WMM is a Wi-Fi certification based on the IEEE 802.11e Quality of Service Amendment. WMM allows computers such as a laptop top to conserve power by putting the radio into a sleep mode for brief periods of time.
Qos also relates to a Medium Contention function called Hybrid Coordinated Function (HCF). HCF is divided into two methods. The first is called Enhanced Distributed Coordinated Function (EDCF). It allows Qos through software and The second is HCF Coordinated Channel Access. It allows Qos through hardware.
HCF Coordinated Channel Access is not in use by any existing device. I mention it in case some software or hardware claims compatibility with it.
05. Bluetooth(R) AMP.....Options are on or off (set to on)
I don’t know what Bluetooth AMP means. Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) on the 2.4 GHz ISM Band. Too many Bluetooth devices in a small area can interfere with other devices using the 2.4 GHz band. The interference can be noticed by a lot of retransmissions due to lack of acknowledgments (ACK). The retransmissions can be seen with a Protocol Analyzer. Because Bluetooth works on the 2.4 GHz frequency it might cause contention issues with 802.11 devices. I read that newer Bluetooth devices can skip a channel that is senses been used in the area.
06. Fat Channel Intolerant.....Options are on or off (set to off)
This is called 40-MHz Channel Intolerance. It only applies to the 2.4Ghz band. 40-MHz Channel Intolerance is not allowed in the 5 GHz. If you are using a 40-MHz channel on the 2.4Ghz ISM Band and your device hears a signal from another device that is 40-MHz Channel Intolerance your device will switch back to using a single 20 MHz channel to prevent interfering with the other device. A 20Mhz ISM channel in used on 802.11n devices. Older 802.11a,g also use the 20Mhz channels. 802.11b uses the 22Mhz channels. 802.11a,g uses the OFDM modulation. 802.11b uses the HR-DSSS modulation.
07. Mixed Mode Protection.....Options are CTS-to-self Enabled or RTS/CTS Enabled (first option on)
A mixed mode means there are 802.11b,g and 802.11a,n devices accessing the same Wireless Router or Access Point. 802.11b and 802.11g use the 2.4 GHz frequency and use different Modulations.
802.11b uses Direct Sequence Spread Spectrum (DSSS) modulation to transmit at 1 and 2 Mbps. Or High Rate Direct Sequence Spread Spectrum with Complimentary Code Keying (HR/DSSS CCK) to transmit at 5.5 and 11 Mbps.
802.11g-ERP (Extended Rate Physical) uses Orthogonal Frequency Division Multiplexing (OFDM) modulation to transmit at rates of 6,9,12,18,24,36,48, and 54 Mbps on the 2.4Ghz Band. 802.11a also uses the same modulation but it transmits on the 5Ghz Band.
Since a,b,g,n can be on the same Channel they might no be able to understand each others signal because of the different modulations. They need a way to co-exist.
CTS-To-Self is a protection mode sent as a broadcast signal to all the devices in the same Basic Service Set (BSS) to let them know that a device is about to transmit and the length of the transmission based on time. The broadcast signal is sent at a basic rate so it can be understood by all devices. When 802.11b want to transmit it first sends a CTS-To-Self and then it transmits its signal. 802.11g will do the same. 802.11b and 802.11g take turns transmitting and listening for each others signal to avoid collisions.
Ready-To-Send / Clear-To-Send (RTS/CTS) is a polling contention method. RTS/CTS works only if there is an Access Point. When a device wants to transmit it sends a Ready-To-Send to the Access Point. The Access Point then sends a Clear-To-Send signal that can be heard by all the stations. This prevents other stations from transmitting for the amount of time indicated inside the CTS signal and lets first station know that it can begin transmitting. The CTS has information letting all the other station know how long they need to wait before they can request a RTS of their own. CTS/RTS should only be used under two circumstances. First it is used to test for what is called a Hidden Node and second in a Point-To-Multipoint configuration where multiple clients are too far away to hear each other and cannot receive a CTS-To-Self signal.
08 . Roaming Aggressiveness.....Options 1-5 (set to 3)
Roaming means you are re-associating to another SSID. The decision to roam is done by the client and not by the Access Point. Whether to roam or not depends on the received Signal Strength, Bit-Error Rate, or Noise Level.
As you move about, your laptop can switch to the other Access Point (AP) automatically. Two things will happen, your computer will have to Authenticate and Re-associate at the new SSID which means that if you were downloading a file when the roaming accorded you will lose the session and will have to reconnect and restart the file download at the new BSS (Basic Service Set). The re-association might give a new IP address.
09. Transmit Power....Options 1-5 (set at 5)
The transmit power on most laptops is 30mw. The transmit power on most Residential Wireless Gateway (RWG) vary by chipset and manufacturer. If you have multiple devices, you want two things to happen. First you want each device to hear each other’s signal and be able to take turns transmitting. Second, you want the devices to be able to hear and communicate back to the RWG. If you set the power too high on the router the devices will be able to hear the router but they might not be to communicate back to the router because they are too far away for their transmit power. This can cause two problems a hidden node problem and a near far problem.
The hidden node is caused by the devices been able to hear the router but not each other. Since a device does not know that the other device exist it might transmit at the same time as the first device and causing a collision at the router. The problem can also be caused by a Power Mismatch. A hidden node is usually when a signal is been blocked by an object. All devices need to take turns transmitting. If they can’t hear each other because of a power mismatch or signal blockage they can transmit at the same time causing a collision which causes a corrupt packet that will not be acknowledged and will have to be resent.
The Near/Far problem is when one device is closer to the router sending a strong signal and the other devices signal is too far and its signal is too weak when it arrives at the router. Because both signals are on the same channel the stronger signal will drown out the weaker signal.
The best way make a signal go further is to use an antenna with a higher gain. A higher gain antenna will also detect a signal at a longer distance, it is called receive amplification.
Try to keep all devices at the same power level to avoid power mismatches.
10. Wireless Mode.....Options are 1-802.11b 2-802.11g 3-802.11b/g (3 is selected)
Unless you have devices that require backward compatibility with 802.11b the best choice is 2-802.11g. 802.11g allows a maximum data rate of 54Mbps. After all the overhead you should get a steady 20 to 30 Mbps. If you also enable 802.11b your throughput can go down to 5Mbps which if about half the maximum data rate of 802.11b HR-DSSS which is 11Mbps.
Security:
WPA is a Wi-Fi Certification. WPA the name for TKIP (Temporal Key Integrity Protocol). TKIP is an enhanced version of WEP. WEP can be cracked with a brute force attack within minutes. To combat this problem on hardware that is not powerful enough to support CCMP the Wi-Fi Alliance created TKIP to be added as a firmware update to secure older hardware before the completion of the 802.11i amendment.
WPA2 is the Wi-Fi Alliance name for Counter Mode with Cipher Block Coding Message Authenticated Protocol / Advance Security Encryption CCMP-AES. The CCMP is used to for Authentication and AES is used for Encryption.
Use only CCMP-AES with a Pre-Shared Key of maximum size whenever possible.
Comment:
I did not see any advance HT features for the Intel Centrino Wireless-N130 Wireless adapter:
http://www.intel.com/support/wireless/sb/CS-030709.htmFrom the information given the modulation used is ERP-OFDM and the frequency used is the 2.4 GHz ISM Band. None of the 802.11n HT technology features are available. And the maximum data rate is 54Mbps.
There is no mention of: 40-Mhz Channel or Multiple Spatial Streams. It appears to have only one Radio Chain with one antenna. And no mention of Aggregated MAC Service Data Unit (A-MSDU) or Aggregated MAC Protocol Data Unit (A-MPDU). It also lacks any information on Block Acknowledgments (Block ACK).
Without more information about the Wireless Card and the Router I cannot determine whether or not the Data Rate can be increased.
If both devices are Wi-Fi certified there will be a list for each device at the Wi-Fi web site listing all the technology tested and all features available on each device.
If the proper 802.11n technology is available on both devices the maximum Data Rate with one Radio Chain and one Data Stream is 75Mbps which averages to about 37Mps of throughput.
_____________________________________________________________________________________
A warning about transmit power.
The strength of the 802.11 radio signal you transmit with your home equipment has to be carefully calculated. I will make reference only to home equipment because that is what most people reading this post will be using. Residential Wireless Gateway is the proper name for what the consumer industry calls a Wireless Router. Combined, the radio and amplifier inside the router is called a Radio Chain. The point where an antenna is attached to the router is called the Intentional Radiator.
If you plan on adding a different antenna and /or attaching an amplifier here are some rules that need to be follows according to the FCC.
The maximum power allowed on the 2.4 GHz ISM Band and the 5GHz UNII band is 1,000 mW ( +30dBm). The antenna on most home routers is a Dipole Antenna. Most home Dipole Antennas have a passive amplification of 6dB EIRP (Equivalent Isotropically Radiated Power). The maximum EIRP allowed for home equipment is 4,000 Mw (+36dBm).
For every 3dB you double the power. That means 1,000mw x 2 = 2,000mw and 2,000mw x 2 = 4,000mw. So connecting a +6db antenna to a +30dBm IR give you 4 watts of power transmitted (EIRP) from the antenna.
If you attach a +9db antenna you will be transmitting 8,000mw of power or +39dmw of EIRP. By law you will have to reduce the power at the IR by 3db to once again equal +36db of EIRP at the antenna. If you don’t and the FCC decides they want to take action against you they can fine you, confiscate your equipment or worst.
With the proper equipment it is legal to use more than +36dBm of EIRP. It requires the use of a specialized antenna and/or a particular Band. The topic deals with an outdoor Point-To-Point or Point-To-Multipoint connections using Semi-Directional Antennas or Highly Directional Antennas.
If you don’t follow the rules for wireless communication you can jam other peoples signal and prevent equipment from functioning properly. Radio frequency management is of enough concern that many hospitals have someone in charge just for that purpose. If you live across the street from a hospital and your signal is too strong you can cause their medical equipment to not function properly. The 2.4Ghz and 5 GHz frequency is free to use and available to anyone but there are rules that must be followed.
