If you get an error message "The MNYUI.DLL file is linked to missing export MFC42DLL:6467" after you have installed a software, it is caused due to Microsoft Money Agent loading in the background at the Startup. If you have Windows 98, you can disable this the following way:
1. Click the Start button.
2. Click on "Run".
3. Type in "msconfig" (without the quotation marks) and click OK.
4. Click on the startup tab.
5. Uncheck the line "Money Agent".
6. Click OK.
7. You will be asked to restart the computer; click "Yes".
The root cause of the issue is the corrupted files in the Microsoft Money software. Uninstalling and reinstalling Money software or Upgrading Money to a greater version will solve the issue.
To uninstall Money from your system, perform the following steps:
1. Click Start, Settings, Control Panel.
2. Double Click on Add/Remove Programs.
3. Under Install/Uninstall tab you will find Microsoft Money software.
4. Highlight it and click on Add/Remove.
5. Click OK to any warning message. Click OK.
You can reinstall Money software using the SelectiveRestore Option from the QuickRestore CD. To selectively restore an application or driver from your QuickRestore CD, follow these steps:
1. Place the QuickRestore CD into the CD-ROM drive.
2. Using Windows Explorer, navigate to the QuickRestore CD's directory.
3. Open the CPQS directory, and then open the QUICKSR directory.
4. Double-click the Qrestore file.
5. Wait until the QuickRestore menu is displayed, and then click Selective.
6. Select the application or driver from the menu that follows.
Thursday, November 8, 2007
Error "The MNYUI.DLL file is linked to missing export MFC42DLL:6467"
Securing a Wireless Network
Securing your Wireless Network :
If your wireless LAN is located in a single family home, then you are probably more at risk from intruders coming in via your Internet connection than from folks gaining access to your LAN over the air. But if your LAN has some means of wireless connectivity, you've added another way to access your LAN that doesn't require getting past your router's firewall and doesn't even require physical access!
What can I do?
Actually, there's a lot you can do to secure your wireless LAN. Most of these tips apply to 802.11b based LANs, since they're the most prevalent. But some tips are just good network security practice and can help no matter how you build your LAN:
1) Don't use TCP/IP for File and Printer sharing!
Access Points are usually installed on your LAN, behind any router or firewall you may be using. If someone successfully connects to your Access Point, they'll be on your LAN, just like any of your other clients. But since they'll be using TCP/IP to make the connection, you can easily deny access to MS File and Printer sharing by using a protocol other than TCP/IP for those services. That way, they may get access to your Internet connection, but they won't get access to your files! See this page for instructions on using NetBEUI for File and Printer Sharing.
2) Follow secure file-sharing practices
This means:
Share only what you need to share (think Folders, not entire hard drives)
Password protect anything that is shared with a strong password.
3) Enable WEP Encryption
802.11b's WEP encryption has had a lot of bad press lately about its weaknesses. But a weak lock is better than no lock at all, so enable WEP encryption and use a non-obvious encryption key. Look for and use products that support 128bit WEP. Prices have come down on 802.11b equipment so there's no need to buy something that doesn't support 128bit WEP. See this page if you need help getting WEP to work.
4) Use WEP for data and Authentication
Some products allow you to separately set the Authentication method to "Shared Key" or "Open System". Use the "Shared Key" method so that encryption is used to both authenticate your client and encrypt its data. See this page for more info.
5) Use non-obvious WEP keys and periodically change them
While the limitations that some wireless client utilities have don't help (hexadecimal only support, single keys, forgetting keys, etc.), don't make it easy for potential snoops to get onto your LAN by using simple keys like 123456, all ones, etc. Changing the keys periodically is more difficult, because it requires sending out information about the new keys to users and that can be a security problem in itself. But changing keys periodically can help keep your LAN secure, so consider getting a procedure into place to do it.
6) Secure your wireless router / Access Point (AP)
Your router or Access Point should require a password to access its Admin features. If it doesn't, get one that will!
Also, change your password from the default and use a strong one!
7) Disallow router/ AP administration via wireless
Unfortunately, this feature is usually only present in "Enterprise-grade" APs, and shuts off the ability to administer your Access Point from wireless clients. But if your router/AP has it, use it!
8) Use MAC address based Access and Association control
Previously available only on "Enterprise-grade" products, many routers and Access Points are being upgraded to have the ability to control the clients that can use them. MAC addresses are tied to physical network adapters, so using this method requires a little coordination and maybe a little inconvenience for LAN users. And MAC addresses can be "spoofed" or imitated/copied, so it's not a guarantee of security. But it adds another hurdle for potential intruders to jump. If you already have a product that doesn't include this feature, check your Manufacturer's Web site for a firmware upgrade.
9) Don't send the ESSID
ORiNOCO and Apple call the ability to stop their products from sending out the network ESSID the "closed network" feature. Other manufacturers are adding this ability, so check your Manufacturer's Web site for a firmware upgrade. Note that the feature doesn't have a consistent name, so check your product's documentation.
10) Don't accept "ANY" ESSID
ORiNOCO and Apple's "closed network" feature also won't accept connections from clients using the default "ANY" ESSID. Other manufacturers' products have the ability to not accept clients with an "ANY" ESSID, but you'll need to check your product's documentation, since there's not a consistent name for the feature.
11) Use VPN
Of course, if you really don't want to take chances with your data, then you should run a VPN tunnel over your wireless connection, too. You may take a throughput hit, but isn't your data's security worth it?
Fix hardware and configuration issues common to wireless LANs
Fix hardware and configuration issues common to wireless LANs
Both the money savings and the ease of use of wireless LANs are beneficial to small offices—until something goes wrong. Then it becomes all too apparent that, while wireless networks are growing, troubleshooting resources for wireless LANs are not.
When a wireless network fails, there are a few key areas to look to first. Let's look at some of the more common hardware problems that can cause a wireless network to fail. I’ll also cover the configuration issues that can plague a wireless LAN. With this information, you can troubleshoot your wireless network with confidence. (This article assumes that you’re troubleshooting an infrastructure network, and not an ad hoc network.)
Hardware troubleshooting:
When you have only one access point and only one wireless client that are having connection issues, then you’ve already determined the scope of the problem: Your one client is having trouble attaching to the network. But if you have a larger network, determining the scope of the problem becomes a little more involved.
If lots of users are having trouble connecting but there are still some users who are able to work, the problem is most likely that your network has multiple access points and that one of the access points is malfunctioning. Often, you can take an educated guess as to which access point is malfunctioning by looking at the physical locations of the users who are having the problem, and then figure out which access point serves that portion of the building.
If no one can connect to the wireless network, there are several things that could be going on. If your network uses a single wireless access point, it's possible that the access point could be malfunctioning or could contain a configuration error. The problem could also be related to radio interference or a break in the physical link between the wireless access point and the wired network.
Check connectivity to the access point:
First, you should perform a communications test to see if the access point is responding. Open a Command Prompt window on a PC on your wired network and ping your wireless access point’s IP address. The wireless access point should respond to the ping. If it doesn’t, there’s either a break in the communications link or the access point is completely malfunctioning.
To figure out which is the case, try pinging the access point’s IP address from a wireless client. If the wireless client is able to ping the access point successfully, the problem is almost certainly a broken communications link, such as a damaged cable.
If the wireless client is unable to ping the access point, the access point could be malfunctioning. Try unplugging the access point to reset it and then plug it in again. Wait for about five minutes and then try pinging the access point from both the wireless and the wired clients again.
If both pings still fail, it is likely that the access point is damaged or has an invalid configuration. At this point, I recommend focusing your efforts on getting the access point to communicate with the wired network. Plug the access point in to a known-good network jack using a known-working patch cable. You should also verify the access point’s TCP/IP configuration. After doing so, try pinging the device from a wired client again. If the ping still fails, the unit has probably been damaged and should be replaced.
Configuration issues:
I’ve found that wireless networking equipment is fairly reliable, and the vast majority of problems are related to the network’s configuration rather than a hardware malfunction. With this in mind, let's look at several common hardware configuration problems that lead to a disruption of wireless services.
Test the signal strength:
If you can ping the wireless access point from a wired client but not from a wireless client, the access point is probably just experiencing a temporary problem. If the access point continues to have problems, I recommend checking the signal strength. Unfortunately, there’s no standard method for doing this. Most wireless NIC manufacturers, however, include some mechanism with the NIC for measuring signal strength.
Try changing channels:
If you determine that you’re getting a weak signal but nothing has physically changed in your office, attempt to change channels on the access point and on one wireless client to see if a different channel improves the signal strength. I run a wireless network in my home office, and I’ve found that one of my cordless phones interferes with my wireless network when the phone is in use. 802.11b wireless networks function on the 2.4-GHz frequency, just like many higher-end cordless phones. Changing channels on all of your wireless clients can be a big undertaking, so I recommend testing the new channel with one client first. Remember that your problem could go away as soon as someone hangs up a phone or turns off a microwave oven.
Wireless Common Terms
Radio Frequency
Radio frequencies are high frequency alternating current (AC) signals that are
passed along a copper conductor and then radiated in to the air via an antenna. An
antenna converts/transforms a wired signal and vice versa. When the high frequency AC signal is radiated into the air, it forms radio waves. These Radio waves propagate away
from the source (the antenna) in a straight line in all directions at once.
Spread Spectrum
Spread Spectrum is a communication technique characterized by wide bandwidth and low peak power. Spread Spectrum communication uses various modulation techniques in wireless LANs and possesses many advantages over its precursor, narrow band communication. Spread Spectrum signals are noise-like, hard to detect, and even harder to intercept or demodulate without the proper equipment.
Narrow Band Transmission
A narrow band transmission is a technology that uses only enough of the frequency
spectrum to carry the data signal, and no more. It has always been the FCC's mission
to conserve frequency usage as much as possible, handling out only what is
absolutely necessary. Spread spectrum uses much wider frequency bands than is necessary to transmit the information. A signal is a spread spectrum signal when the bandwidth is much wider then what is required to send the information.
More power is required to send a transmission when using a smaller frequency range.
A compelling argument against narrowband transmission - other than the high peak power required to send it - is that narrow band signal can be jammed or experience
interference very easily. Jamming is the intentional over powering of a transmission
using unwanted signals transmitted on the same band.
Spread Spectrum Technology
Spread Spectrum technology allows us to take the same amount of information that we
previously would have sent using a narrow band carrier signal and spread it out over a
much larger frequency range. For example, we may use 1 MHz at 10 Watts with narrow band, but 20 MHz at 100mW with spread Spectrum. By using a wider frequency spectrum, we reduce the probability that the data will be corrupted or jammed.
SSID (Service Set Identifier)
The Service Set Identifier (SSID) is a unique, case sensitive, alphanumeric value from 2- 32 characters used by wireless LANs as a network name. This naming handle is used for
segmenting networks, as a rudimentary security measure, and in the process of joining
a network. A client station must be configured for the correct SSID in order to join a network.
HomeRF
HomeRF operates in the 2.4 GHz band and uses frequency-hopping technology.
The Home Radio Frequency Working Group developed a single specification (Shared
Wireless Access Protocol-SWAP) for a broad range of interoperable consumer devices. SWAP is an open industry specification that allows PCs, peripherals, cordless telephones and other consumer devices to share and communicate voice and data in and around the
home without the complication and expense of running new wires. The SWAP specification provides low cost voice and data communications in the 2.4GHz ISM band.
Bluetooth
Bluetooth is another frequency technology that operates in the 2.4 GHz ISM band. The
hope rate of Bluetooth devices is about 1600 hops per second, so it has considerably more overhead than 802.11- compliant frequency hopping systems. The high hop rate also gives the technology greater resistance to spurious narrow band noise. Bluetooth systems are not designed for high throughput, but rather for a simple use, low power, and short range. Bluetooth devices have a maximum range of 33 feet (10 meters).
IEEE 802.11
The 802.11 standard was the first standard describing the operation of wireless LANs.
This standard contained all of the available transmission technologies including Direct
Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and infrared. 802.11 compliant products operate strictly in the 2.4 GHz ISM band between 2.4000 and 2.4835 GHz.
IEEE 802.11a
The IEEE 802.11a standard describes wireless LAN device operation in the 5 GHz UNII bands. Operation in the UNII bands automatically makes 802.11a devices incompatible with all other devices complying with the other 802.11 series of standards. The reason for this incompatibility is simple: system using 5GHz frequencies will not communicate with systems using 2.4GHz frequencies.
IEEE 802.11a specifies data rates of only 6, 12 and 24 Mbps. A wireless LAN device must support at lease these data rates in the UNII bands in order to be 802.11a-compliant.
IEEE 802.11b
802.11b is a wireless Ethernet specification by IEEE.IEEE 802.11bis referred to as
"High-Rate" and Wi-Fi. 802.11b was originally designed to enable high performance radio to support roaming in large offices or business campus environments. 802.11b is quiet expensive compared to SWAP. It must be remembered that 802.11b supports voice over Internet protocol.
IEEE 802.11g
80211.g provides the maximum data transfer rate of 54Mbps and is backward compatible
with 802.11b devices. IEEE 802.11g specifies operation in the 2.4 GHz ISM band. IEEE 802.11g utilizes Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. These devices can automatically switch to QPSK modulation to communicate with the slower 802.11b and 802.11- compatible devices.
Thursday, October 18, 2007
Bluetooth -
Products with Bluetooth technology must be qualified and pass interoperability testing by the Bluetooth Special Interest Group prior to release. Bluetooth's founding members include Ericsson, IBM, Intel, Nokia and Toshiba.
What is Bluetooth?
- Bluetooth is a wireless connectivity system
- Bluetooth is an industry initiative founded by Promoter
Companies Agere, Ericsson Technology Licensing AB, IBM
Corporation, Intel Corporation, Microsoft Corporation,
Motorola Inc, Nokia and Toshiba Corporation. - It provides cable replacement and personal area
networking for static and mobile devices. - Global Use in Unlicensed ISM Band.
- Radio designed for low cost and power consumption.
Advantages Of Bluetooth:
- Wireless technology
- Protocol based
- Short Range
- Low Power
- Located in the 2.45GHz ISM Band
- Personal Area Network (PAN) - cable
replacement - Open specification
How Bluetooth started:
History - Harald I Bluetooth (Danish Harald Blåtand) was the King of Denmark between 940 and 985 AD. The name "Blåtand" was probably taken from two old Danish words, 'blå' meaning dark skinned and 'tan' meaning great man. He was born in 910 as the son of King Grom The Old (King of Jutland, the main peninsula of Denmark) and his wife Thyre Danebold (daughter of King Ethelred of England). Like many Vikings, Harald considered it honorable to fight for treasure in foreign lands. When Harald's sister Gunhild was widowed after the death of the violent Norwegian king Erik Blood Axe, she came to Denmark to seek Harald's help in securing control of Norway. Harald took the opportunity to seize control himself. By 960 he was at the height of his powers, ruling over both Denmark and Norway. He was baptized by a priest named Poppo, sent by the German emperor. He then created a monument that read: "King Harald raised this monument to the memory of Grom his father and Thyre his mother. Harald conquered all of Denmark and Norway and made the Danes Christian". These words were also carved in stone called rune stones. Harald was killed in a battle in 985. Harald completed the country's unification begun by his father, converted the Danes to Christianity, and conquered Norway. The expansion begun by Harald in Norway was continued by his son Sweyn I, who conquered England in 1013. Under Sweyn's son Canute there grew up a great Anglo-Scandinavian kingdom that included parts of Sweden.
Old Harald Bluetooth united Denmark and Norway, Bluetooth of today will unite the worlds of computers and telecom (hopefully longer than the few years Harald's Viking kingdom survived). In 1994 Ericsson Mobile Communications initiated a study to investigate the feasibility of a low-power low-cost radio interface between mobile phones and their accessories. In Feb 1998, five companies Ericsson, Nokia, IBM, Toshiba and Intel formed a Special Interest Group (SIG). The group contained the necessary business sector members - two market leaders in mobile telephony, two market leaders in laptop computing and a market leader in digital signal processing technology. It is estimated that before year 2002, Bluetooth will be a built-in feature for more than 100 million mobile phones and several million communication devices ranging from handsets and portable PCs to desktop computers and notebooks.
Why Bluetooth was developed -
- Low cost implementation
- Small implementation size
- Low power consumption
- Robust, high quality data & voice transfer
- Open global standard
Practical use of Bluetooth -
- Mobile phones – PDA – Laptop synchronisation
- Wireless Headsets and Hands Free Kits
- VOIP Cordless phones and intercoms
- PC to printer, fax, scanner
- Connecting household appliances and systems
- Public Information Access Points
Wireless Link between devices -
Bluetooth Protocol Stack -
RF Overview
Frequency Bands and Channels -
- Frequency Range 2.402GHz to 2.480GHz
- 79 Channels
- 1MHz Channel Spacing
- Frequency Hopping Spread Spectrum (FHSS)
- 1600 hops/s
RF Overview
Transmitter Characteristics -
- 3 power classes (*optional power control)
Class 1 = 20dBm
Class 2 = 4dBm*
Class 3 = 0dBm* - Gaussian Frequency Shift Keying (GFSK)
- ±75kHz frequency tolerance.
RF Overview
Receiver Characteristics -
- Sensitivity level of -70dBm or better
- Optional Receiver Signal Strength Indicator
(RSSI) - Co-channel and Adjacent Channel Interference
requirements - Out of Band Blocking performance
requirements - Maximum Usable input Level -20dBm or better
Baseband Layer -
- Sits above the RF layer
- Channel coding and decoding
- Low level timing control
- Management at packet level
Link Manager Layer -
- Attaching slaves to a piconet
- Breaking connections to detach slaves
- Link configuration
- Establishes ACL (data) and SCO (voice) links
- Hold, Sniff and Park modes
- Controls Test Modes
- Power Control
HCI (Host Controller Interface)
Layer -
- Standard interface between upper and lower protocol layers
- Allows the mix and match of Protocol Stack
and RF Chip Sets - Used for test and measurement commands
- Commands are used to control the Bluetooth
module and monitor its status
L2CAP (Logical Link Control and
Adaptation Protocol) Layer -
- Multiplexing between different higher layers
with the lower layers - Segmentation and re-assembly to allow the
transfer of larger packets than the lower
layers support - Group Management - allowing one-way
communication to a group of devices - QOS (Quality of Service) management
RFCOMM Layer -
- Emulation of serial ports over the L2CAP layer
- Based on the ETSI standard TS 07.10
- Support for legacy applications
Service Discovery Protocol (SDP)
Layer -
- Used to discover which services are available
and to determine the characteristics of those available services - A specific Service Discovery protocol is needed in the
Bluetooth environment, as the set of services that are
available changes dynamically based on the RF proximity
of devices in motion, qualitatively different from service
discovery in traditional network-based environments. The
service discovery protocol defined in the Bluetooth
specification is intended to address the unique
characteristics of the Bluetooth environment.
Refer this link for further information - http://en.wikipedia.org/wiki/Bluetooth
Wireless Networking for Peripherals
Wireless Networking Overview
A wireless local area network (WLAN, also known as “wi-fi,” for wireless fidelity) is a collection of two or more computers, printers, and/or other devices linked to each other by radio waves. It uses these radio waves to communicate information from one device to another.
To connect a computer or other device to a wireless network, the device must have a wireless network adapter. The peripherals that support wireless communication use an internal networking component that contains a radio.
No cabling is necessary between networked computers and devices that use wireless technology, although it is highly recommended the use of a cable during setup and installation of any peripherals, and does not support wireless setup.
Network Topology
There are two types of wireless network communication:
In an ad hoc network (also called independent or peer-to-peer networks), all devices communicate directly with one another.
In an infrastructure network, communications are routed through an access point, which handles both communication and security for all devices associated with it. Access points are frequently also connected to an Ethernet LAN with a cable.
Users who are simply trying to print (or scan/copy/fax etc.) from a laptop or PC to a printer or All-in-One may frequently use ad hoc mode, since it simplifies equipment needs. Customers who are trying to connect to another LAN, trying to share an Internet connection, or have a combination of more than six PCs and other devices on the network, will need to set up their networks in infrastructure mode. In either case, connection between the peripheral device and the user’s existing, working wireless network – helping the user to set up a network for the first time is beyond the scope of support.
Standards
Wireless LANs conform to an international group of standards known as 802.11. Standards are simply a set of communication protocols agreed upon so that equipment designed and manufactured by different vendors can talk to each other. Agreed-upon protocols include, for example, such things data transmission rate and encoding method, radio broadcast frequency band, etc.
The Institute of Electrical and Electronics Engineers (IEEE, or “I triple E”) develops standards for a wide variety of computer technologies. Networking standards have been assigned the number 802, while wireless networking standards have been assigned the number 11. Wireless networking standards therefore use the designation 802.11. (Ethernet uses 802.3.)
Improvements have been made upon the first 802.11 standard, which now include 802.11a, 802.11b, and 802.11g. For the most part, equipment on the same network must be built using the same standard. At this time wireless peripherals use the 802.11b standard, which is currently the most commonly used standard. It offers speed and functionality similar to Ethernet, and broadcasts in the 2.4 GHz frequency band.
Note that an 802.11 (wireless) network can connect to an 802.3 (Ethernet) network.
Wireless Network Components
Hardware
- Wireless network adapter: There are three types of wireless network adapters. All include either an integrated antenna, or (as in the case of Mac adapters), connect to an antenna built into the computer.
- A wireless PC card slips into a laptop PCMIA slot.
- A wireless PCI card is installed into an available slot inside a desktop computer. In most cases it consists of a sleeve or card holder, and a PC card radio that slides into the sleeve.
- A wireless USB adapter is a separate device that plugs into a free USB port on the computer (or USB hub).
- Wireless Access Point: A wireless access point is needed for networks set up in infrastructure mode. In cases where a wireless network connects to an Ethernet network, the access point is connected to the Ethernet hub via Ethernet cable.
Software
- A driver is needed for the wireless network adapter and for the attached peripheral.
- The network operating system is included in Windows 2000 and Windows XP.
SSID
To be on the same wireless network, all devices must reference the same Service Set Identifier, or SSID. The SSID, also known as the network name, is a character string that identifies the network and is attached to the header of transmitted data packets. The SSID prevents access to the network by any device that does not have the SSID.
Consult the peripheral’s user guide for information on setting the SSID for the peripheral. The SSID is set on the computer using the configuration utility for the wireless network adapter.
Security
Wireless networks are more vulnerable to hackers than wired networks, because any passer-by with a laptop and a wireless network card can theoretically tap into a wireless network.
Helping a customer to set up security or make decisions about the best kind of security to put in place is beyond the scope of support for the customer support agent. However, it is helpful to know the extent of the potential exposure:
- The contents of any networked drive can be read by a successful attacker. If a printer or All-in-One includes a photocard reader AND is installed on a wireless network, the contents of the card can be read while the card is inserted in the card reader.
- The contents of any file being broadcast from one wireless device to another can also be read by a successful attacker. This means that a document being printed can be read (during the actual transmission only). A document being scanned to the computer can also be read during transmission.
To hinder the success of would-be intruders, peripherals can be configured to use one of two industry standard security options: Wired Equivalent Privacy (WEP), or Wi-Fi Protected Access (WPA) listed below. The security configuration for the peripheral must match that of the existing network.
Wired Equivalent Privacy (WEP) Configuration
Wired Equivalent Privacy (WEP) provides security by encrypting the data sent from one wireless device to another. Devices on a WEP-enabled network use WEP keys to encode data. If your network uses WEP, you must know the WEP key(s) it uses. Use the peripheral’s Embedded Web Server to configure the peripheral to use WEP, and to set the WEP key.
Wi-Fi Protected Access (WPA) Configuration
Wi-Fi Protected Access (WPA) provides security by doing the following:
• Encrypting the data sent from one wireless device to another. WPA automatically changes the encryption keys after a certain time interval, making the wireless network less vulnerable to intrusion.
• Controlling access to network resources through authentication protocols. WPA requires either the use of an authentication server (best suited for enterprise networks) or a pass phrase known to all devices on the network.
Monday, October 15, 2007
PING
ping is a computer network tool used to test whether a particular host is reachable across an IP network. Ping works by sending ICMP “echo request” packets ("Ping?") to the target host and listening for ICMP “echo response” replies (sometimes dubbed "Pong!" as an analog from the Ping Pong table tennis sport.) Using interval timing and response rate, ping estimates the round-trip time (generally in milliseconds although the unit is often omitted) and packet loss (if any) rate between hosts. Ping stands for – Packet Internet Groper.
The word ping is also frequently used as a verb or noun, where it can refer directly to the round-trip time, the act of running a ping program or measuring the round-trip time.
Sample pinging
The following is a sample output of pinging www.google.com under Linux with the iputils version of ping:
$ ping www.google.com
PING www.l.google.com (64.233.183.103) 56(84) bytes of data.
64 bytes from 64.233.183.103: icmp_seq=1 ttl=246 time=22.2 ms
64 bytes from 64.233.183.103: icmp_seq=2 ttl=245 time=25.3 ms
64 bytes from 64.233.183.103: icmp_seq=3 ttl=245 time=22.7 ms
64 bytes from 64.233.183.103: icmp_seq=4 ttl=246 time=25.6 ms
64 bytes from 64.233.183.103: icmp_seq=5 ttl=246 time=25.3 ms
64 bytes from 64.233.183.103: icmp_seq=6 ttl=245 time=25.4 ms
64 bytes from 64.233.183.103: icmp_seq=7 ttl=245 time=25.4 ms
64 bytes from 64.233.183.103: icmp_seq=8 ttl=245 time=21.8 ms
64 bytes from 64.233.183.103: icmp_seq=9 ttl=245 time=25.7 ms
64 bytes from 64.233.183.103: icmp_seq=10 ttl=246 time=21.9 ms
--- www.l.google.com ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9008ms
rtt min/avg/max/mdev = 21.896/24.187/25.718/1.619 ms
This output shows that www.google.com is a DNS CNAME record for www.l.google.com which then resolves to 64.233.183.103. The output then shows the results of making 10 pings to 64.233.183.103 with the results summarized at the end.
- smallest ping time was 21.896 miliseconds
- average ping time was 24.187 miliseconds
- maximum ping time was 25.718 miliseconds
- mean deviation time was 1.619 milliseconds
The following is a sample output of pinging www.google.com under Microsoft Windows XP with its built-in version of ping:
C:\>ping www.google.com
Pinging www.l.google.com [64.233.183.103] with 32 bytes of data:
Reply from 64.233.183.103: bytes=32 time=25ms TTL=245
Reply from 64.233.183.103: bytes=32 time=22ms TTL=245
Reply from 64.233.183.103: bytes=32 time=25ms TTL=246
Reply from 64.233.183.103: bytes=32 time=22ms TTL=246
Ping statistics for 64.233.183.103:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 22ms, Maximum = 25ms, Average = 23ms
This output shows that www.google.com is a DNS CNAME record for www.l.google.com which then resolves to 64.233.183.103. The output then shows the results of making 4 pings to 64.233.183.103 with the results summarized automatically at the end.
- smallest ping time was 22 milliseconds
- average ping time was 23 milliseconds
- maximum ping time was 25 milliseconds
Thursday, October 11, 2007
ATA vs SCSI
Advanced Technology Attachment
(ATA, AT Attachment or "Integrated Drive Electronics", IDE) A disk drive interface
standard based on the IBM PC ISA 16-bit bus but also used on other personal computers. The
ATA specification deals with the power and data signal interfaces between the motherboard
and the integrated disk controller and drive. The ATA "bus" only supports two devices -
master and slave.
ATA drives may in fact use any physical interface the manufacturer desires, so long as an
embedded translator is included with the proper ATA interface. ATA "controllers" are
actually direct connections to the ISA bus.
Originally called IDE, the ATA interface was invented by Compaq around 1986, and was
developed with the help of Western Digital, Imprimis, and then-upstart Conner Peripherals.
Efforts to standardise the interface started in 1988; the first draft appeared in March 1989,
and a finished version was sent to ANSI group X3T10 (who named it "Advanced Technology
Attachment" (ATA) for ratification in November 1990.
X3T10 later extended ATA to Advanced Technology Attachment Interface with Extensions
(ATA-2), followed by ATA-3, ATA-4, ATA-5 and ATA-6.
Small Computer System Interface
(SCSI) A processor-independent standard for system-level interfacing between a computer
and intelligent devices including hard disks, floppy disks, CD-ROM, printers, scanners, and
many more. SCSI-1 can connect up to seven devices to a single SCSI adaptor (or "host
adaptor") on the computer's bus.
SCSI transfers eight bits in parallel (it is an eight-bit bus, but see Wide SCSI) and can operate
in either asynchronous or synchronous modes. The synchronous transfer rate is up to 5MB/s.
There must be at least one target and one initiator on the SCSI bus.
SCSI connections normally use "single ended" drivers as opposed to differential drivers.
Single ended SCSI can support up to six metres of cable. Differential can support up to 25
metres of cable.
A problem with SCSI is the large number of different connectors allowed. Nowadays the
trend is towards a 68-pin miniature D-type or "high density" connector (HD68) for Wide
SCSI and a 50-pin version of the same connector (HD50) for 8-bit SCSI (Type 1-4, pin pitch
1.27 mm x 2.45 mm). 50-pin ribbon cable connectors are also popular for internal wiring
(Type 5, pin pitch 2.54 mm x 2.54 mm). Apple Computer used a 25-pin connector on the
Macintosh computer but this connector causes problems with high-speed equipment.
SCSI was developed by Shugart Associates, which later became Seagate. SCSI was
originally called SASI for "Shugart Associates System Interface" before it became a standard.
Original SCSI implementations were highly incompatible with each other.
The original standard is now called "SCSI-1" to distinguish it from SCSI-2 and SCSI-3,
which include specifications of Wide SCSI (a 16-bit bus) and Fast SCSI (10 MB/s transfer).
Interface Factor | IDE/ATA | SCSI |
Cost | Low | Moderate to high |
Performance | High for single devices or single tasking, moderate to low for multiple devices or multitasking | High in most situations |
Configuration and Ease of Use | High for small number of devices, low for large number of devices | Moderate to high for both small and large numbers of devices |
Moderate to high for both small and large numbers of devices | Moderate to low | High |
Device Type Support | Moderate to low | High |
Device Availability and Selection | High | Moderate |
Software / Operating System Compatibility | High | Moderate to high |
System Resource Usage | Moderate to poor | Moderate to good |
Support for non-PC Platforms | Poor, but growing | Good |
DSL Troubleshooting
Trouble Shooting DSL, Cable, & Dial-up connection & Routing issues
Here are a few simple tools and techniques that we can use to understand where a problem may be with ISP connection & Routing issues "Page cannot be displayed" etc...
- First we need to determine if the computer is even connected to the ISP's Radius server and receiving an IP address.
Using the winipcfg /all command in the RUN box, or in the command prompt does this.
For Dial-up this is simple, there will be only one adapter listed (Dial-up Adapter) or (AOL Dial-up Adapter)
If IP address is 169.254.X.X the computer is not receiving an IP from the server (This is a WIN default IP)
If IP address is 0.0.0.0 they are not connected to ISP
If IP address is anything other than these configurations then they are connected and we can proceed to testing.
NOTE: DSL and cable will have several adapters (2 Ethernet for Cable) (one PPP adapter and one Ethernet Adapter for DSL). We must check all of them for the IP address.
- TESTING
Now that we have determined the computer is connected we can test the DNS & TCP/IP
Functions to see if the computer can compile TCP/IP packets and route them to a particular computer.
Using the PING command in the command prompt does this.
Type PING (space) http://www.(domain/ Name). COM
This will produce several results.
IP address
4 replies w/ the TTL info or Request timed out
How many packets were sent, received, and lost.
If the results produce “Destination host unreachable” or “request timed out” and (4) packets sent (0) received 100% loss. Then there may be a DNS (Domain Naming Service or TCP/IP issue w/ the computer)
We can then try to PING Yahoo by IP address (You may have to PING yahoo from your computer to get the IP address)
IF they can PING the IP address then insert the IP address in their browser to see if it will pull up the web page. If this works then R&R communications in add/remove programs then reboot and test.
If they cannot PING the IP address then R&R TCP/IP, Reseat NIC/modem or Re-install OS.
IF the computer can PING by Domain name & IP address but the browser cannot pull up web pages then R&R Browser.
(Try to use Yahoo they are a major port hole to the Internet and will allow us to PING their domain)
- TESTING NIC & throughput issues
We can test the NIC to see if it is functioning properly by:
Pinging the Loop back address 127.0.0.1
This will use TCP/IP to compile a packet and send it to the NIC causing it to reply back to the OS. If this fails then reseat the NIC into a different PCI slot and test again or replace NIC.
We can test the throughput by running a trace rout to the Domain that the computer is routing slow to. TRACERT http://www.(domain/ Name). COM will produce every hop that the TCP/IP packet makes from the NIC all the way to the Domain server.
If the computer times out on the first hop then the NIC needs to be reseated or replaced.
The second hop is the Gateway router (DSL or Cable Modem)
Every hop is a computer or router and the information of how long the packet took to pass through the router to its next destination. Any hop that times out or the TTL is much greater than the rest indicates a routing issue at that particular router and not in the computer. This helps us distinguish between a COMPAQ problem and an ISP problem.
PC Fundamentals
PC Fundamentals
Binary vs. Decimal Measurements
One of the most confusing problems regarding PC statistics and measurements is the fact that the computing world has two different definitions for most of its measurement terms. :^) Capacity measurements are usually expressed in kilobytes (thousands of bytes), in megabytes (millions of bytes), or gigabytes (billions of bytes). Due to a mathematical coincidence, however, there are two different meanings for each of these measures.
Computers are digital and store data using binary numbers, or powers of two, while humans normally use decimal numbers, expressed as powers of ten. As it turns out, two to the tenth power, 2^10, is 1,024, which is very close in value to 1,000 (10^3). Similarly, 2^20 is 1,048,576, which is approximately 1,000,000 (10^6), and 2^30 is 1,073,741,824, close to 1,000,000,000 (10^9). When computers and binary numbers first began to be used regularly, computer scientists noticed this similarity, and for convenience, "hijacked" the abbreviations normally used for decimal numbers and began applying them to binary numbers. Thus, 2^10 was given the prefix "kilo", 2^20 was called "mega", and 2^30 "giga".
This shorthand worked fairly well when used only by technicians who worked regularly with computers; they knew what they were talking about, and nobody else really cared. Over the years however, computers have become mainstream, and the dual notation has led to quite a bit of confusion and inconsistency. In many areas of the PC, only binary measures are used. For example, "64 MB of system RAM" always means 64 times 1,048,576 bytes of RAM, never 64,000,000. In other areas, only decimal measures are found--a "28.8K modem" works at a maximum speed of 28,800 bits per second, not 29,491.
Storage devices however are where the real confusion comes in. Some companies and software packages use binary megabytes and gigabytes, and some use decimal megabytes and gigabytes. What's worse is that the percentage discrepancy between the decimal and binary measures increases as the numbers get larger: there is only a 2.4% difference between a decimal and a binary kilobyte, which isn't that big of a deal. However, this increases to around a 5% difference for megabytes, and around 7.5% for gigabytes, which is actually fairly significant. This is why with today's larger hard disks, more people are starting to notice the difference between the two measures. Hard disk capacities are always stated in decimal gigabytes, while most software uses binary. So, someone will buy a "30 GB hard disk", partition and format it, and then be told by Windows that the disk is "27.94 gigabytes" and wonder "where the other 2 gigabytes went". Well, the disk is 27.94 gigabytes--27.94 binary gigabytes. The 2 gigabytes didn't go anywhere.
Another thing to be careful of is converting between binary gigabytes and binary megabytes. Decimal gigabytes and megabytes differ by a factor of 1,000 but of course the binary measures differ by 1,024. So this same 30 GB hard disk is 30,000 MB in decimal terms. But its 27.94 binary gigabytes are equal to 28,610 binary megabytes (27.94 times 1,024).
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Windows 95 display of the capacity of an 8 GB hard disk drive. |
One final "gotcha" in this area is related to arithmetic done between units that have different definitions of "mega" or "giga". For example: most people would say that the PCI bus has a maximum theoretical bandwidth of 133.3 Mbytes/second, because it is 4 bytes wide and runs at 33.3 MHz. The problem here is that the "M" in "MHz" is 1,000,000; but the "M" in "Mbytes/second" is 1,048,576. So the bandwidth of the PCI bus is more properly stated as 127.2 Mbytes/second (4 times 33,333,333 divided by 1,048,576).
There's potential good news regarding this whole binary/decimal conundrum. The IEEE has proposed a new naming convention for the binary numbers, to hopefully eliminate some of the confusion. Under this proposal, for binary numbers the third and fourth letters in the prefix are changed to "bi", so "mega" becomes "mebi" for example. Thus, one megabyte would be 10^6 bytes, but one mebibyte would be 2^20 bytes. The abbreviation would become "1 MiB" instead of "1 MB". "Mebibyte" sounds goofy, but hey, I'm sure "byte" did too, 30 years ago. ;^) Here's a summary table showing the decimal and binary measurements and their abbreviations and values ("bytes" are shown as an example unit here, but the prefices could apply to any unit of measure):
Decimal Name | Decimal Abbr. | Decimal Power | Decimal Value | Binary Name | Binary Abbr. | Binary Power | Binary Value |
Kilobyte | kB | 10^3 | 1,000 | Kibibyte | kiB | 2^10 | 1,024 |
Megabyte | MB | 10^6 | 1,000,000 | Mebibyte | MiB | 2^20 | 1,048,576 |
Gigabyte | GB | 10^9 | 1,000,000,000 | Gibibyte | GiB | 2^30 | 1,073,741,824 |
Terabyte | TB | 10^12 | 1,000,000,000,000 | Tebibyte | TiB | 2^40 | 1,099,511,627,776 |
Only time will tell if this standard, which you can read about here, will catch on--old habits die hard. I for one will be doing my share though. As I update various portions of the site, I will be changing places where I used terms such as "kB" and "MB" for binary numbers into "kiB" and "MiB". This may be confusing at first but I think we'll get used to it, and at least it will eliminate the current ambiguity.
Basic Electrical Components
There are several important basic electrical components that are commonly found in the circuits of virtually all PC parts and peripherals. These devices are the fundamental building blocks of electrical and electronic circuits, and can be found in great numbers on motherboards, hard disk logic boards, video cards and just about everywhere else in the PC, including places that might surprise you. They can be used and combined with each other and dozens of other devices, in so many different ways that I could not even begin to describe them all. Still, it is useful to know a bit about how they work, and this page will at least provide you with a basis for recognizing some of what you see on those boards, and perhaps understanding the fundamentals of circuit schematics. Bear in mind when reading the descriptions below that it would really take several full pages to fully describe the workings of most of these components! Fortunately, this level of detail isn't really necessary to provide the background necessary when working with PCs.
For each component, I provide a sample photo, as well as an illustration of the component's symbol in an electrical schematic (diagram showing how a circuit is designed). There are many variants of each of the components shown below; so the diagrams should only be considered examples.
- Battery: A direct current electricity source of a specific voltage, used primarily in small circuits.
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A battery (in this case, a button cell on a PC motherboard.) |
Original photo © Kamco Services |
- Resistor: As you could probably guess from the name, a resistor increases the resistance of a circuit. The main purpose of this is to reduce the flow of electricity in a circuit. Resistors come in all different shapes and sizes. They dissipate heat as a result of their opposing electricity, and are therefore rated both in terms of their resistance (how much they oppose the flow of electrons) and their power capacity (how much power they can dissipate before becoming damaged.) Generally, bigger resistors can handle more power. There are also variable resistors, which can have their resistance adjusted by turning a knob or other device. These are sometimes called potentiometers.
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Magnified surface-mount resistor from a motherboard. |
- Capacitor: A capacitor is a component made from two (or two sets of) conductive plates with an insulator between them. The insulator prevents the plates from touching. When a DC current is applied across a capacitor, positive charge builds on one plate (or set of plates) and negative charge builds on the other. The charge will remain until the capacitor is discharged. When an AC current is applied across the capacitor, it will charge one set of plates positive and the other negative during the part of the cycle when the voltage is positive; when the voltage goes negative in the second half of the cycle, the capacitor will release what it previously charged, and then charge the opposite way. This then repeats for each cycle. Since it has the opposite charge stored in it each time the voltage changes, it tends to oppose the change in voltage. As you can tell then, if you apply a mixed DC and AC signal across a capacitor, the capacitor will tend to block the DC and let the AC flow through. The strength of a capacitor is called capacitance and is measured in farads (F). (In practical terms, usually microfarads and the like, since one farad would be a very large capacitor!) They are used in all sorts of electronic circuits, especially combined with resistors and inductors, and are commonly found in PCs.
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Three capacitors on a motherboard. |
- Inductor: An inductor is essentially a coil of wire. When current flows through an inductor, a magnetic field is created, and the inductor will store this magnetic energy until it is released. In some ways, an inductor is the opposite of a capacitor. While a capacitor stores voltage as electrical energy, an inductor stores current as magnetic energy. Thus, a capacitor opposes a change in the voltage of a circuit, while an inductor opposes a change in its current. Therefore, capacitors block DC current and let AC current pass, while inductors do the opposite. The strength of an inductor is called--take a wild guess--its inductance, and is measured in henrys (H). Inductors can have a core of air in the middle of their coils, or a ferrous (iron) core. Being a magnetic material, the iron core increases the inductance value, which is also affected by the material used in the wire, and the number of turns in the coil. Some inductor cores are straight in shape, and others are closed circles called toroids. The latter type of inductor is highly efficient because the closed shape is conducive to creating a stronger magnetic field. Inductors are used in all sorts of electronic circuits, particularly in combination with resistors and capacitors, and are commonly found in PCs.
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A toroidal core inductor from a PC motherboard. |
- Transformer: A transformer is an inductor, usually with an iron core, that has two lengths of wire wrapped around it instead of one. The two coils of wire do not electrically connect, and are normally attached to different circuits. One of the most important components in the world of power, it is used to change one AC voltage into another. As described above, when a coil has a current passed through it, a magnetic field is set up proportional to the number of turns in the coil. This principle also works in reverse: if you create a magnetic field in a coil, a current will be induced in it, proportional to the number of turns of the coil. Thus, if you create a transformer with say, 100 turns in the first or primary coil, and 50 turns in the second or secondary coil, and you apply 240 VAC to the first coil, a current of 120 VAC will be induced in the second coil (approximately; some energy is always lost during the transformation). A transformer with more turns in its primary than its secondary coil will reduce voltage and is called a step-down transformer. One with more turns in the secondary than the primary is called a step-up transformer. Transformers are one of the main reasons we use AC electricity in our homes and not DC: DC voltages cannot be changed using transformers. They come in sizes ranging from small ones an inch across, to large ones that weigh hundreds of pounds or more, depending on the voltage and current they must handle.
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A transformer from the interior of a PC power supply. |
- Diode / LED: A diode is a device, typically made from semiconductor material, that restricts the flow of current in a circuit to only one direction; it will block the bulk of any current that tries to go "against the flow" in a wire. Diodes have a multitude of uses. For example, they are often used in circuits that convert alternating current to direct current, since they can block half the alternating current from passing through. A variant of the common diode is the light-emitting diode or LED; these are the most well-known and commonly-encountered kind of diode, since they are used on everything from keyboards to hard disks to television remote controls. An LED is a diode that is designed to emit light of a particular frequency when current is applied to it. They are very useful as status indicators in computers and battery-operated electronics; they can be left on for hours or days at a time because they run on DC, require little power to operate, generate very little heat and last for many years even if run continuously. They are now even being made into low-powered, long-operating flashlights.
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A diode (top) and a light-emitting diode (bottom). Note the |
- Fuse: A fuse is a device designed to protect other components from accidental damage due to excessive current flowing through them. Each type of fuse is designed for a specific amount of current. As long as the current in the circuit is kept below this value, the fuse passes the current with little opposition. If the current rises above the rating of the fuse--due to a malfunction of some sort or an accidental short-circuit--the fuse will "blow" and disconnect the circuit. Fuses are the "heroes" of the electronics world, literally burning up or melting from the high current, causing a physical gap in the circuit and saving other devices from the high current. They can then be replaced when the problem condition has been corrected. All fuses are rated in amps for the amount of current they can tolerate before blowing; they are also rated for the maximum voltage they can tolerate. Always replace a blown fuse only with another of the same current and voltage rating.
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A fuse, sitting in its fuse holder, |
WIFI
Wi-Fi, also, WiFi, Wi-fi or wifi, is a brand originally licensed by the Wi-Fi Alliance to describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications.
Wi-Fi was developed to be used for mobile computing devices, such as laptops, in LANs, but is now increasingly used for more applications, including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics such as televisions and DVD players, or digital cameras. There are even more standards in development that will allow Wi-Fi to be used by cars in highways in support of an Intelligent Transportation System to increase safety, gather statistics, and enable mobile commerce IEEE 802.11p.
A person with a Wi-Fi device, such as a computer, telephone, or personal digital assistant (PDA) can connect to the Internet when in proximity of an access point. The region covered by one or several access points is called a hotspot. Hotspots can range from a single room to many square miles of overlapping hotspots. Wi-Fi can also be used to create a Wireless mesh network. Both architectures are used in Wireless community network, municipal wireless networks like Wireless Philadelphia [1], and metro-scale networks like M-Taipei [2].
Wi-Fi also allows connectivity in peer-to-peer mode, which enables devices to connect directly with each other. This connectivity mode is useful in consumer electronics and gaming applications.
When the technology was first commercialized there were many problems because consumers could not be sure that products from different vendors would work together. The Wi-Fi Alliance began as a community to solve this issue so as to address the needs of the end user and allow the technology to mature. The Alliance created another brand "Wi-Fi CERTIFIED" to denote products are interoperable with other products displaying the "Wi-Fi CERTIFIED" brand.
Wi-Fi uses both single carrier direct-sequence spread spectrum radio technology, part of the larger family of spread spectrum systems and multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) radio technology. Unlicensed spread spectrum was first authorized by the Federal Communications Commission in 1985 and these FCC regulations were later copied with some changes in many other countries enabling use of this technology in all major countries. These regulations then enabled the development of Wi-Fi, its onetime competitor HomeRF, and Bluetooth.
The precursor to Wi-Fi was invented in 1991 by NCR Corporation/AT&T (later Lucent & Agere Systems) in Nieuwegein, the Netherlands. It was initially intended for cashier systems; the first wireless products were brought on the market under the name WaveLAN with speeds of 1 Mbit/s to 2 Mbit/s. Vic Hayes, who was the primary inventor of Wi-Fi and has been named the 'father of Wi-Fi,' was involved in designing standards such as IEEE 802.11b, 802.11a and 802.11g. In 2003, Vic retired from Agere Systems. Agere Systems suffered from strong competition in the market even though their products were high quality, as many opted for cheaper Wi-Fi solutions. Agere's 802.11a/b/g all-in-one chipset (code named: WARP) never made it to market, and Agere Systems decided to quit the Wi-Fi market in late 2004.
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Origin and meaning of the term "Wi-Fi"
Despite the similarity between the terms "Wi-Fi" and "Hi-Fi," statements reportedly [3] made by Phil Belanger of the Wi-Fi Alliance contradict the popular conclusion that "Wi-Fi" stands for "Wireless Fidelity." According to Mr. Belanger, the Interbrand Corporation developed the brand "Wi-Fi" for the Wi-Fi Alliance to use to describe WLAN products that are based on the IEEE 802.11 standards. In Mr. Belanger's words, "Wi-Fi and the yin yang style logo were invented by Interbrand. We (the founding members of the Wireless Ethernet Compatibility Alliance, now called the Wi-Fi Alliance) hired Interbrand to come up with the name and logo that we could use for our interoperability seal and marketing efforts. We needed something that was a little catchier than 'IEEE 802.11b Direct Sequence'."
The Wi-Fi Alliance themselves invoked the term "Wireless Fidelity" with the marketing of a tag line, "The Standard for Wireless Fidelity," but later removed the tag from their marketing. The Wi-Fi Alliance now seems to discourage propagation of the notion that "Wi-Fi" stands for "Wireless Fidelity" but includes it in their knowledge base:
To understand the value of Wi-Fi Certification, you need to know that Wi-Fi is short for "Wireless Fidelity," and it is the popular name for 802.11-based technologies that have passed Wi-FI certification testing. This includes IEEE 802.11a, 802.11b, 802.11g and upcoming 802.11n technologies.
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Wi-Fi: How it works
A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant influence on performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client who receives the beacon can communicate at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. Also the firmware running on the client Wi-Fi card is of influence. Say two APs of the same SSID are in range of the client, the firmware may decide based on signal strength to which of the two APs it will connect. The Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than the other. Since Wi-Fi transmits in the air, it has the same properties as a non-switched ethernet network. Even collisions can therefore appear as in non-switched ethernet LAN's.
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Channels
Except for 802.11a, which operates at 5 GHz, Wi-Fi uses the spectrum near 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations vary slightly in different parts of the world, as does maximum permitted power. However, channel numbers are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers.
The frequencies for 802.11 b/g span 2.400 GHz to 2.487 GHz. Each channel is 22 MHz wide yet there is a 5 MHz step to the next higher channel.
The maximum number of available channels for wi-fi enabled devices are 13 for europe, 11 for North America and 14 for Japan
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Examples of Standard Wi-Fi Devices
Wireless Access Point (WAP)
A wireless access point (AP) connects a group of wireless stations to an adjacent wired local area network (LAN). An access point is similar to an ethernet hub, but instead of relaying LAN data only to other LAN stations, an access point can relay wireless data to all other compatible wireless devices as well as to a single (usually) connected LAN device, in most cases an ethernet hub or switch, allowing wireless devices to communicate with any other device on the LAN.
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Wireless Routers
A wireless router integrates a wireless access point with an ethernet switch and an ethernet router. The integrated switch connects the integrated access point and the integrated ethernet router internally, and allows for external wired ethernet LAN devices to be connected as well as a (usually) single WAN device such as a cable modem or DSL modem. A wireless router advantageously allows all three devices (mainly the access point and router) to be configured through one central configuration utility, usually through an integrated web server. However one disadvantage is that one may not decouple the access point so that it may be used elsewhere.
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Wireless ethernet Bridge
A wireless ethernet bridge connects a wired network to a wireless network. This is different from an access point in the sense that an access point connects wireless devices to a wired network at the data-link layer. Two wireless bridges may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes.
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Range Extender
A wireless range extender (or wireless repeater) can increase the range of an existing wireless network by being strategically placed in locations where a wireless signal is sufficiently strong and near by locations that have poor to no signal strength. An example location would be at the corner of an L shaped corridor, where the access point is at the end of one leg and a strong signal is desired at the end of the other leg. Another example would be 75% of the way between the access point and the edge of its useable signal. This would effectively increase the range by 75%.
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Wi-Fi vs. cellular
It has been suggested that this section be split into a new article entitled Mobile VoIP. (Discuss)
Some argue that Wi-Fi and related consumer technologies hold the key to replacing cellular telephone networks such as GSM. Some obstacles to this happening in the near future are missing roaming and authentication features (see 802.1x, SIM cards and RADIUS), the narrowness of the available spectrum and the limited range of Wi-Fi. It is more likely that WiMax will compete with other cellular phone protocols such as GSM, UMTS or CDMA. However, Wi-Fi is ideal for VoIP applications e.g. in a corporate LAN or SOHO environment. Early adopters were already available in the late '90s, though not until 2005 did the market explode. Companies such as Zyxel, UT Starcomm, Sony, Samsung, Hitachi and many more are offering VoIP Wi-Fi phones for reasonable prices.
In 2005, low-latency broadband ISPs started offering VoIP services to their customers. Since calling via VoIP is free or low-cost, VoIP enabled ISPs have the potential to open up the VoIP market. GSM phones with integrated Wi-Fi & VoIP capabilities are being introduced into the market and have the potential to replace land line telephone services.
Currently it seems unlikely that Wi-Fi will directly compete against cellular in areas that have only sparse Wi-Fi coverage. Wi-Fi-only phones have a very limited range, so setting up a covering network would be too expensive. Additionally, cellular technology allows the user to travel while connected, bouncing the connection from tower to tower (or "cells") as proximity changes, all the while maintaining one solid connection to the user. Many current Wi-Fi devices and drivers do not support roaming yet and connect to only one access point at a time. In this case, once you are out of range of one "hotspot", the connection will drop and will need to be re-connected to the next one each time.
For these reasons, Wi-Fi phones are still best suited for local use such as corporate or home networks. However, devices capable of multiple standards, called converged devices, (using SIP or UMA) may well compete in the market. Top-tier handset manufacturers have announced converged dual-radio handsets. Converged handsets present several compelling advantages to mobile carriers:
- Efficient spectrum allocation, as more data-intensive services come online and bandwidth demands increase
- Improved in-building coverage in markets such as the US, where dropped calls are still a major cause of customer dissatisfaction
- Opportunities for mobile operators to offer differentiated pricing and services.
Commercial Wi-Fi
Commercial Wi-Fi services are available in places such as Internet cafes, coffee houses, hotels and airports around the world (commonly called Wi-Fi-cafés), although coverage is patchy in comparison with cellular.
Worldwide Providers:
- There are a small number of aggregators of Wi-Fi hotspots, one of them is BOZII, they allow users to access hotspots in overand password for a flat fee and with no international roaming charges.
In the US:
- T-Mobile provides HotSpots in many partner retail locations including many Starbucks, Borders Books, and a variety of hotels and airports.
- a Columbia Rural Electric Association subsidiary offers 2.4 GHz Wi-Fi service across a 3,700 mi² (9,500 km²) region within Walla Walla and Columbia counties in Washington and Umatilla County, Oregon.
- restaurant chain Panera Bread provides free Wi-Fi access at its restaurants.
- The Pittsburgh International Airport provides free Wi-Fi throughout its terminals, it is believed to be the first airport in the world to have done so back in 2003.
- Other large hotspot providers include Wayport, iPass, and iBahn.
In the UK:
- T-Mobile provides hotspots in many Starbucks and Airports in the UK too.
- BTOpenzone operates hotspots in most commercial areas and lounges.
Universal efforts
Another business model seems to be making its way into the news. The idea is that users will share their bandwidth through their personal wireless routers, which are supplied with specific software. An example is FON, a Spanish start-up created in November 2005. It aims to become the largest network of hotspots in the world by the end of 2006 with 82000 access points. The users are divided into three categories: linus share Internet access for free; bills sell their personal bandwidth; and aliens buy access from bills. Thus the system can be described as a peer-to-peer sharing service, which we usually relate to software.
Although FON has received some financial support by companies like Google and Skype, it remains to be seen whether the idea can actually work. There are three main challenges for this service at the moment. The first is that it needs much media and community attention first in order to get through the phase of "early adoption" and into the mainstream. Then comes the fact that sharing your Internet connection is often against the terms of use of your Internet service provider. This means that in the next few months we can see ISPs trying to defend their interests in the same way music companies united against free MP3 distribution. And third, the FON software is still in Beta-version and it remains to be seen if it presents a good solution of the imminent security issues.
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Free Wi-Fi
While commercial services attempt to move existing business models to Wi-Fi, many groups, communities, cities, and individuals have set up free Wi-Fi networks, often adopting a common peering agreement in order that networks can openly share with each other. Free wireless mesh networks are often considered the future of the Internet.
Many municipalities have joined with local community groups to help expand free Wi-Fi networks (see Mu-Fi). Some community groups have built their Wi-Fi networks entirely based on volunteer efforts and donations.
For more information, see wireless community network, where there is also a list of the free Wi-Fi networks one can find around the globe.
OLSR is one of the protocols used to set up free networks. Some networks use static routing; others rely completely on OSPF. Wireless Leiden developed their own routing software under the name LVrouteD for community wi-fi networks that consist of a completely wireless backbone. Most networks rely heavily on open source software, or even publish their setup under an open source license.
Some smaller countries and municipalities already provide free Wi-Fi hotspots and residential Wi-Fi internet access to everyone. Examples include Estonia which have already a large number of free Wi-Fi hotspots throughout their countries.
In Paris, France, OzoneParis offers free Internet access for life to anybody who contributes to the Pervasive Network’s development by making their rooftop available for the Wi-Fi Network.
Pittsburgh has operated a free Wi-Fi hotzone throughout its 25 block downtown section, southside, Mellon Arena and northshore areas since summer of 2006.
The Pittsburgh International Airport also has provided a free Wi-Fi since 2003 throughout its terminal, it is believed to be the first airport in the world to provide this. Annapolis, Maryland is in the early phases (as of April 2006) of a pilot program to provide free, advertisement-financed Wi-Fi to all its residents. A private company, Annapolis Wireless Internet, will administrate the network. Users will only see local advertisements upon accessing the network. [4]
Unwire Jerusalem is a project to put free Wi-Fi access points at the main shopping centers of Jerusalem.
Many universities provide free Wi-Fi internet access to their students, visitors, and anyone on campus. Similarly, some commercial entities such as Panera Bread and Culver's offer free Wi-Fi access to patrons. McDonald's Corporation also offers Wi-Fi access, often branded 'McInternet'. This was launched at their flagship restaurant in Oak Brook, Illinois, USA, and is also available in many branches in London, UK.
However, there is also a third subcategory of networks set up by certain communities such as universities where the service is provided free to members and guests of the community such as students, yet used to make money by letting the service out to companies and individuals outside. An example of such a service is Sparknet in Finland. Sparknet also supports OpenSpark, a project where people can share their own wireless access point and become as a part of Sparknet and OpenSpark community in return for certain benefits.
Recently commercial Wi-Fi providers have built free Wi-Fi hotspots and hotzones. These providers hope that free Wi-Fi access would equate to more users and significant return on investment.
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Wi-Fi vs. amateur radio
In the US and Australia, a portion of the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. In the US, FCC Part 15 rules govern non-licenced operators (i.e. most Wi-Fi equipment users). Under Part 15 rules, non-licensed users must "accept" (e.g. endure) interference from licensed users and not cause harmful interference to licensed users. Amateur radio operators are licensed users, and retain what the FCC terms "primary status" on the band, under a distinct set of rules (Part 97). Under Part 97, licensed amateur operators may construct their own equipment, use very high-gain antennas, and boost output power to 100 watts on frequencies covered by Wi-Fi channels 2-6. However, Part 97 rules mandate using only the minimum power necessary for communications, forbid obscuring the data, and require station identification every 10 minutes. Therefore, expensive automatic power-limiting circuitry is required to meet regulations, and the transmission of any encrypted data (for example https) is questionable.
In practice, microwave power amplifiers are expensive and decrease receive-sensitivity of link radios. On the other hand, the short wavelength at 2.4 GHz allows for simple construction of very high gain directional antennas. Although Part 15 rules forbid any modification of commercially constructed systems, amateur radio operators may modify commercial systems for optimized construction of long links, for example. Using only 200 mW link radios and high gain directional antennas, a very narrow beam may be used to construct reliable links with minimal radio frequency interference to other users.
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Wi-Fi and its support by operating systems
There are two sides to Wi-Fi support under an operating system. Driver level support and configuration and management support.
Driver support is usually provided by the manufacturer of the hardware or, in the case of Unix clones such as Linux and FreeBSD, sometimes through open source projects.
Configuration and management support consists of software to enumerate, join, and check the status of available Wi-Fi networks. This also includes support for various encryption methods. These systems are often provided by the operating system backed by a standard driver model. In most cases, drivers emulate an ethernet device and use the configuration and management utilities built into the operating system. In cases where built in configuration and management support is non-existent or inadequate, hardware manufacturers may include their own software to handle the respective tasks.
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Microsoft Windows
Microsoft Windows has comprehensive driver-level support for Wi-Fi, the quality of which depends on the hardware manufacturer. Hardware manufactures almost always ship Windows drivers with their products. Windows ships with very few Wi-Fi drivers and depends on the OEMs and device manufactures to make sure users get drivers. Configuration and management depend on the version of Windows.
- Earlier versions of Windows, such as 98 and ME do not have built-in configuration and management support and must depend on software provided by the manufacturer
- Microsoft Windows XP has built-in configuration and management support. The original shipping version of Windows XP included rudimentary support which was dramatically improved in Service Pack 2. Support for WPA2 and some other security protocols require updates from Microsoft. To make up for Windows inconsistent and sometimes inadequate configuration and management support, many hardware manufacturers include their own software and require the user to disable Windows’ built-in Wi-Fi support
- Microsoft Windows Vista is expected to have improved Wi-Fi support over Windows XP. Current betas automatically connect to unsecured networks without the user’s approval. This is a large security issue for the owner of the respective unsecured access point and for the owner of the Windows Vista based computer because shared folders may be open to public access.
Apple Mac OS
Apple was an early adopter of Wi-Fi, introducing its AirPort product line, based on the 802.11b standard, in July 1999. Apple makes the Mac OS operating system, the computer hardware, and the accompanying drivers and configuration and management software, simplifying Wi-Fi integration. All Intel based Mac’s either come with or have the option to included AirPort Extreme cards. These cards are compatible with 802.11g. Many of Apple’s earlier PowerPC models came with Airport Extreme as well, and all Macs starting with the original iBook at least included AirPort slots.
- Mac OS X has excellent Wi-Fi support, including WPA2, and ships with drivers for Apple’s AirPort cards. The built-in configuration and management is integrated throughout the operating system. Many third-party manufacturers make compatible hardware along with the appropriate drivers which integrate with Mac OS X’s built-in configuration and management software and the end user experience is generally seamless. Others include their own software.
- Apple's older Mac OS 9 does not have built in support for Wi-Fi configuration and management nor does it ship with Wi-Fi drivers, but Apple provides free drivers and configuration and management software for their AirPort cards for OS 9, as do a few other manufacturers. Versions of Mac OS before OS 9 predate Wi-Fi and do not have any Wi-Fi support.
Unix-like systems
Linux, FreeBSD and similar Unix-like clones have much coarser support for Wi-Fi. Due to the open source nature of these operating systems, many different standards have been developed for configuring and managing Wi-Fi devices. The open source nature also fosters open source drivers which have enabled many third party and proprietary devices to work under these operating systems. See Comparison of Open Source Wireless Drivers for more information on those drivers.
- Linux has patchy Wi-Fi support[1]. Native drivers for many Wi-Fi chipsets are available either commercially or at no cost[2], although some manufacturers don't produce a Linux driver, only a Windows one. Consequently, many popular chipsets either don't have a native Linux driver at all, or only have a half-finished one. For these, the freely available NdisWrapper and its commercial competitor DriverLoader[3] allow Windows x86 NDIS drivers to be used on x86-based Linux systems but not on other architectures. The FSF has some recommended cards[5] and more information can be found through the searchable Linux wireless site[6] As well as the lack of native drivers, some Linux distributions do not offer a convenient user interface and configuring Wi-Fi on them can be a clumsy and complicated operation compared to configuring wired Ethernet drivers[4].
- FreeBSD has similar Wi-Fi support relative to Linux. Wi-Fi support under FreeBSD is best in the 6.x versions. FreeBSD has "Project Evil'", which provides the ability to use Windows x86 NDIS drivers on x86-based FreeBSD systems as NdisWrapper does on Linux.
- NetBSD, OpenBSD, and DragonFly BSD have similar Wi-Fi support to FreeBSD. Code for some of the drivers, as well as the kernel framework to support them, is mostly shared among the 4 BSDs.
Advantages of Wi-Fi
- Allows LANs to be deployed without cabling, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
- Wi-Fi silicon pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-widening array of devices.
- Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are interoperable and include WPA2 security.
- Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.
- Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.
- Widely available in more than 250,000 public hot spots and millions of homes and corporate and university campuses worldwide.
- As of 2006, WPA and WPA2 encryption are not easily crackable if strong passwords are used
- New protocols for Quality of Service (WMM) and power saving mechanisms (WMM Power Save) make Wi-Fi even more suitable for latency-sensitive applications (such as voice and video) and small form-factor devices.
Disadvantages of Wi-Fi
- Wi-Fi can be interupted by other devices, notably 2.4 GHz cordless phones.
- Spectrum assignments and operational limitations are not consistent worldwide; most of Europe allows for an additional 2 channels beyond those permitted in the US; Japan has one more on top of that - and some countries, like Spain, prohibit use of the lower-numbered channels. Furthermore some countries, such as Italy, used to require a 'general authorization' for any Wi-Fi used outside an operator's own premises, or require something akin to an operator registration. For Europe; consult http://www.ero.dk for an annual report on the additional restrictions each European country imposes.
- EIRP in the EU is limited to 20dbm.
- Power consumption is fairly high compared to some other standards, making battery life and heat a concern.
- The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be breakable even when correctly configured.
- Wi-Fi Access Points typically default to an open (encryption-free) mode. Novice users benefit from a zero configuration device that works out of the box but might not intend to provide open wireless access to their LAN. WPA Wi-Fi Protected Access which began shipping in 2003 aims to solve these problems and is now generally available, but adoption rates remain low.
- Many 2.4 GHz 802.11b and 802.11g Access points default to the same channel, contributing to congestion on certain channels.
- Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g with a stock antenna might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band, as Wi-Fi is no exception to the physics of radio wave propagation. Wi-Fi in the 2.4 GHz frequency block has better range than Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi (and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennas can be several kilometres or more with line-of-sight.
- Wi-Fi pollution, meaning interference of a closed or encrypted access point with other open access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other open access points by others caused by overlapping channels in the 802.11g/b spectrum as well as with decreased signal-to-noise ratio (SNR) between access points. This is a widespread problem in high-density areas such as large apartment complexes or office buildings with many Wi-Fi access points.
- It is also an issue when municipalities or other large entities such as universities seek to provide large area coverage. Everyone is considered equal when they use the band (except for amateur radio operators who are the primary licensee); often this causes contention when one user seeks to claim priority in this unlicensed band. This openness is also important to the success and widespread use of Wi-Fi, but makes Part 15 (US) unsuitable for "must have" public service functions.
- Wi-Fi networks can be monitored and used to read and copy data (including personal information) transmitted over the network when no encryption such as VPN is used.
- Interoperability issues between brands or deviations from the standard can disrupt connections or lower throughput speeds on other user's devices within range. Wi-Fi Alliance programs test devices for interoperability and designate devices which pass testing as Wi-Fi CERTIFIED.
Wi-Fi in gaming
Some gaming consoles and handhelds make use of Wi-Fi technology to enhance the gaming experience:
- The Nintendo DS handheld is Wi-Fi compatible, although there is no built in encryption, most games do not support WPA encryption, only the weaker WEP.
- The Sony PSP includes WLAN to connect to Wi-Fi hotspots or make wireless connections.
- The Xbox 360 features 1 Wi-Fi accessory: A wireless network adapter.
- The PlayStation 3 premium model ($599) features built-in Wi-Fi.
- The Nintendo Wii features Wi-Fi.
Trademark/certification
Wi-Fi and Wi-Fi CERTIFIED are trademarks of the Wi-Fi Alliance the trade organization that tests and certifies equipment compliance with the 802.11x standards.
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Unintended and intended use by outsiders
The wireless access point provides no technological protection from unauthorized use of the network. Many business and residential users do not intend to close (secure) their access points but to leave them open for other users in the area. Some argue that it is proper etiquette to leave access points open for others to use just as one can expect to find open access points while on the road.
Measures to deter unauthorized users include suppressing the AP's service set identifier (SSID) broadcast, allowing only computers with known MAC addresses to join the network, and various encryption standards. Access points and computers using no encryption, or the older (pre-2003) Wired Equivalent Privacy (WEP) encryption are vulnerable to eavesdropping by an attacker armed with packet sniffer software. If the eavesdropper has the ability to change his MAC address then he can potentially join the network by spoofing an authorised address.
WEP encryption can protect against casual snooping but may also produce a misguided sense of security since freely available tools such as AirSnort can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort will determine the encryption password in under a second.[5] The newer Wi-Fi Protected Access (WPA) and IEEE 802.11i (WPA2) encyption standards do not have the serious weaknesses of WEP encryption.
Recreational exploration of other people's access points has become known as wardriving, and the leaving of graffiti describing available services as warchalking. These activities may be illegal in certain jurisdictions, but existing legislation and case-law is often unclear.
However, it is also common for people to unintentionally use others' Wi-Fi networks without explicit authorization. Operating systems such as Windows XP and Mac OS X automatically connect to an available wireless network, depending on the network configuration. A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication. Moreover, a user intending to join one network may instead end up on another one if the latter's signal is stronger. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong destination, as described by Chris Meadows in the February 2004 RISKS Digest. [7]
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