The selection and deployment of access point antenna equipment affect network performance and availability. The signal strength or amount of energy radiated from an antenna has to do with antenna type and access point transmit specifications. It is expressed as effective isotropic radiated power (EIRP) and expressed as the sum of access point transmit power plus antenna gain minus cable loss. Cable length will increase signal attenuation or loss and should be minimized. Each antenna type will have a horizontal and vertical beam width specified. The antenna type, gain, cable length, number and mounting is all key to the design. For instance a directional antenna with high gain, no external cable, mounted at proper height will give best performance in an outside deployment with a lot of interference.
The wireless coverage cell on inside deployments can be extended with external antennas that plug into connectors on the access points. Most antennas can be mounted on the ceiling or wall and outside antennas often use a mast to increase height for line of sight.
Effective Isotropic Radiated Power = Transmit Power (dBm) + Gain (dB) - Cable Loss (dB)
Omni-Directional
Omni-directional antenna sends a horizontal radiated pattern of 360 degrees and a vertical pattern of 50 - 70 degrees from its source. From a practical perspective the pattern isn't circular as much as being elliptical. It is a multi-homing antenna that sends signals to several clients in proximity causing some multipath fading that is minimized with antenna diversity. The gain values with 2.4 GHz antenna range from 2.2 dBi - 12 dBi. The higher gain antenna is deployed outside for the most part. Some Cisco access points have an integrated omni-directional dipole antenna or " rubber ducky" that is standard with each device.
Directional
The directional antenna sends out a directed radiated pattern connecting with a distant antenna. The antenna purpose is to send traffic between antennas and not used for multi device homing. There are 3 specific directional antennas: Yagi, Patch and Dish. The Dish antenna has highest gain and narrowest radiation angle beam while Patch antenna has lowest gain and widest radiated beam. Gain values with 2.4 GHz antennas range from 6dBi - 21 dBi. Most antenna from this group are implemented in buildings with there is a lot of signal attenuation such as manufacturing, warehouses, and structures with a lot of steel, concrete, angled designs etc.
Diversity
The diversity antenna implement dual antenna on the access point receiving signals on both. The access point determines what antenna has best gain and transmits on that antenna. Diversity antennas are designed using either omni-directional, directional or dipole styles. Multipath fading occurs in buildings that have a lot of signal reflection. The signal finds multiple paths from source to destination and signal becomes distorted at receiver. This is minimized or eliminated with diversity antennas.
External Antenna
Some Cisco access points such as 1200 series have connectors available for an external antenna. This is available with deployments in environments where the access point is at a maximum 300 feet from the wired switch or signal distortion is excessive. The external antenna with a specified coax cable of 3 - 100 feet allow for placement of the antenna at optimal positioning. Minimizing the cable length will decrease signal attenuation before transmission. Implementing the higher gain diversity patch antenna fixes the problem of clients being out of range. The company could have deployed a repeater as an alternative solution with an 1100 series access point that doesn't support an external antenna.
Building material and structural design will contribute to signal attenuation. The following describes from best to worst building material used with walls, floors and ceilings. Steel and concrete with several feet of construction is most difficult.
• Wood
• Concrete
• Reinforced Concrete
• Steel
Antenna Mounting
Access points should be ceiling mounted if possible at least 17 - 19 feet in height optimizing horizontal and vertical beam width. In some cases the access points will have to be mounted on the wall. Antenna mounting is important and should be implemented with instructions from the hardware installation guide. The Cisco access points utilize the standard RP-TNC 50 ohm type connector.
Outside Bridge Mounting
Companies have implemented a lot of Cisco wireless bridges that connect buildings in a campus network. The line of sight must be available or use a repeater bridge to extend the network where it isn't available. Outside antennas deal with environmental issues and longer distances that require higher gain directional antennas. Mounting is usually with a mast or flat against a wall. Distances can extend around 250 - 500 feet or much further with higher wattage bridges, proper mounting of antenna and deploying repeaters.
Point to point topology is implemented a lot with outside wireless deployments. Point to multipoint topology is implemented both with inside and outside wireless deployments. The root bridge or root access point in a multipoint topology is homed with traffic from several non root bridges or access points. That topology is implemented with several spoke buildings and a hub or core office that must be networked outside. The spoke offices have a point to point connection with the hub office and the hub office has a multipoint connection with all spoke offices. The hub office will implement an omni-directional antenna with a lot of beam width while spoke offices will use a directional antenna.
The inside standard access point designs won't have a group of directional antennas. Most will implement omni-directional antennas and use directional antennas where needed as a means of addressing distances. The outside implementations for the most part imply greater distances and environmental concerns making directional antennas an effective selection.
The book Cisco Wireless Network Design Guide is available at amazon.com.
Shaun Hummel is an author of various technical books and has a web site focused on information technology job search solutions and certifications.
Also called USB thumb drives, USB sticks are highly compact. Thanks to their small size, chances of them getting stolen are high. If your USB drive contains extremely private and sensitive information, go in for USB data security. These measures would help prevent anyone from accessing your personal details.
How to secure USB
Majority of modern USB sticks are now accompanied with specific preinstalled security features enabling users to prevent unauthorized access and password protect their data. If you have private information stored inside, simply password-protect the USB drive.
Using encryption, you can add extra security to the data. Some software use 128-bit AES encryption for maximum security and don't store passwords on removable USB drives.
Data recovery
If your USB doesn't have the password protection option or built-in security, use third party software.
Below are some of the free passwords-protect software to secure USB:-
• FOLDER LOCK: It is one of the fastest ways to password protect and encrypt your folders and files. You can either select to encrypt essential files from techies or lock your private data, pictures and files from casual users. This software comes with plug-and-play support, portability, hack attempt monitoring, stealth mode, shredding, encryption and locking.
Salient Features:
• Folder Encryption, File Encryption, Drive Lock, Folder Lock, File Lock
• Uses 256-bit AES encryption
• Password-protection of USB Drives without the requiring installation at the other end
• Use tool in stealth mode (used while hiding the tool from other system users)
• Move, e-mail, backup or transfer password-protected lockers wherever desired
• TRUE CRYPT: It is open-source software used for creating encrypted folders on USb drives. Its major advantage is that you can install it in USB drive and use it in the form of portable application.
• CRYPTAINER: It is a full freeware utility to password-protect USb drives. You can encrypt folders and files by simply dropping and dragging them into the vault. Additionally, it permits you to form secure-email files which you can send it to anyone.
Even after completely protecting the USB drives, chances that the hackers would crack USB password using keyboard sniffers and keyloggers are high.
Use rechargeable batteries for laptops, one of the advantages of the desktop, it can greatly facilitate a variety of environments using laptops. Introduced the first battery is nickel cadmium batteries (NiCd) battery but has a "memory effect", each charge is required before the evacuation, very easy to use, and soon found himself nickel-metal hydride battery (NiMH ) replaced, NiMH not only failed to "memory effect", but can do more per unit weight of 10% of electricity. The battery most commonly used is lithium-ion battery (Li-Ion), it is also ineffective "memory, compared to NiMH per unit of weight gain more power, the price two times higher than the NiMH . In the same weight, these three kinds battery is 1:1.2:1.9 ratio.
Notebook batteries currently used in three main categories: 1. Nickel-chromium batteries, 2. Ni-MH battery, 3. Lithium, they are generally expressed as: Ni-Cd Ni-Cd, Ni-MH Ni-MH, lithium-ion battery LI.
The purchase or replace the battery when the laptop for many users, "battery" may be unfamiliar. At the outset, batteries and batteries are two concepts. A battery is composed of several slightly bigger than your thumb, cylindrical, up to about 7.8 cm, 3.6 V voltage is small units. They are the batteries, as a small battery, thanks to the combination series, that is, we see that the battery a. Then talk about how to determine if the battery is several nuclei:
One way: Disconnect the battery for the number of contacts to see, there are a few tens of cores. But it is a "minister" approach. Let's take a look at "Cao Chong" is how, "said the elephant": the look of your battery nominal number of v, such that 14.4v, then divided by 3.6 to 4, then turned out to be four batteries together in series. And then take a look at the capacity of the battery pack, for example 3800mAh, then prove that the two aforementioned sets of batteries in series, because the battery capacity is 1500 small - 2000mAh, more importantly, to two to reach 3800mAh. In both cases, the battery is 4 × 2 = 8 cores.
The composition of laptop battery
Notebook battery from the shells, printed circuit boards and batteries belonging lithium ion battery. People talk about batteries in general refers to the number of batteries in the battery mAh refers to the ability of the laptop battery.
Mainly by the protection circuit (or the secondary circuit protection), and the capacity of the circuits in two parts, the laptop battery charge and discharge management and safety.
Time Laptop Battery standby mainly by the value mAh decide. Under normal circumstances, a little more battery, the mAh value is greater than longest standby time. Battery life for notebook mainly by the charge and discharge times to measure the quality of the products are generally eligible to 500-600 times. Therefore, efficient use of laptop batteries within two years expired the battery is aging, standby affect the strong decrease of the mobility of laptops.
Laptop battery advice
Indeed, how to make good use of the battery Batteries, how to extend his schedule and use of living and so on, is undoubtedly the troubled mind of the majority of laptop users, a problem the use of laptop batteries There are many methods and techniques that we use usually requires more learning and application.
(A) quick access to hibernation
No temporary use of portable computers to conserve battery power, you can set the agenda for power management, allowing the system to enter sleep mode after a period of time, but more or shorter will wait a few minutes, there is no way to make the system of the laptop immediately enter the sleep state?
Notebook computer system to allow quick access to the latent state of a simple method is to directly close the display. Press the representation would require little effort, you can make notebook computers to standby mode immediately and effectively save power. When you need to reuse the time, as long as the opening screen, the system automatically returns to pre-condition.
(B) the screen saving mode
TFT is the most important components of portable computer power to reduce its use of the battery when the power consumption, notebook makers have devised ingenious schemes, but generally are based on the screen brightness lower and even off the screen mode.
In some settings management of laptop power you can customize the brightness of the screen, most laptops with a shortcut keys specific adjust the brightness of the screen, typically 6 to 8-setting brightness level.
(C) energy saving settings
Office machines using alternating current, most people may not be the computer attached great importance to energy saving features, but need to use batteries for laptops, using the Energy saving features should be taken seriously. How to design computer hardware more energy efficient, not a user problem to be solved. The user can be installed on the computer of the efficient use of energy saving option.
Energy saving settings require the user to set two: First, the computer BIOS setup program on energy saving in the profile settings, the most important thing is that there Energy savings in many settings of the operating system and operations. In the practical implementation of computer systems, Windows systems should outweigh the energy savings settings in the CMOS settings.
1. BIOS power saving settings
In the CMOS settings, most had a "power savings", which may choose to "Maximum Battery Life" and "Maximum Performance" and other options. "Maximum Battery Life" is the recording power default setting mode. Computer power saving mode phones in several states such as Idle Idle, Standby (standby) mode Suspend mode suspend (sleep) mode. Laptops, these parameters were able to regulate energy consumption, mainly in computer power saving state, the timely closure of some without the use of system equipment. If the wait state, turn off the screen and hard drive, in hibernation, apart from a rigorous monitoring and the hard drive, but also the memory contents can be saved on the hard drive, basic maintenance system throughout the computer closed, once activated, or restart the computer, office will be refurbished and pre-hibernation state. The energy saving settings in the CMOS, mainly determined by mode waiting to enter standby Standby Timeout, set to enter Suspend mode from standby to suspend time Timeout. Travel BIOS Phoenix are the most common. Energy saving various BIOS settings may be somewhat different, it should carefully read the screen.
2. Windows in the energy saving settings
For the average user in the Windows system to operate a better understanding of energy management can be simpler. Windows Help file in the "management hardware and software" entries, there are two laptops equipped with energy-saving elements on "Manage Energy Use" and "use of mobile machinery "in the laptop power management." Energy saving settings in Windows, read the contents.
In the Windows "Control Panel", "power management click, you can open the" Power Management Properties "dialog box. In the" Power Management Properties "dialog should be" power management "is set to "Laptop" and reasonable settlement "system delay", "close the Monitors", "Turn off hard disks" and other options. Another computer can control the opportunity to have some differences, options for the new plant and the latest computer software will be easier to implement, the detailed parameters should be based on characteristics of the computer and Windows files Help to complete.
In addition, if your laptop integrated infrared port, no time to ban it, it can be extended the life of the laptop battery.
(D) alarm settings
Set alarm battery time to prompt the user to record information. Is to click on Open "Control Panel", double-click "Power" option, point "alarm" menu bar, alarm, battery low "column, Windows 98 default is 10%, "a serious shortage of battery alarm" column, Windows 98 default is 3%, which may make appropriate changes as needed. Click the [Alarm Response] button, the warning "voice" and "displays" are selected, the "power level" May of time to select. Alarm limits so that when the battery is used, it will display a warning dialog and the buzzer alarm sounds to alert the user to record information about the delay. Finally click [OK] to exit the settings of power management.
(E) opens the energy save function
In the "technology of extended laptop battery life 'section, we introduce the energy saving feature is the use of processor technology, which allows the performance of laptops are playing with their life stack between the time to achieve the best balance.
Most new notebook models in both the BIOS of the processor energy saving technology have given support, is enabled by default, if not open until the Enter the BIOS will support the option to open OK.
(F) the use of third party software to monitor battery status
In addition to Windows built-in features power management, there are many utilities available to monitor the battery status. For example, PowerCenter is a power monitoring tool available for free download (http://me MBers.xoom.com / TimothyBug / PowerCenter / index.htm). Only 800kb, is designed for computer software notebook services. In addition to the amount of PowerCenter shows the percentage of battery, but also to show the actual time and hours of time can be used.
PowerCenter total of three display types.
(1) FullDisplay: In the window displays detailed information, including the use of battery or AC power, the percentage of the battery and the remaining time available.
(2) CompactDisplay: in use is always above the window.
(3) MinimizeDisplay: PowerCenter reduced to make the Windows taskbar, the display of information is relatively simple.
PowerCenter is also attached to a control center may be composed of six types of warning. When the battery - to a certain level, a warning time user, save the file being processed. In order not to waste electricity and CPU resources, PowerCenter to automatically detect the changes of state of the batteries.
(G) turns deliberately battery
Short battery on a regular basis to ensure a full charge. If you need to run completely out of the battery in the specific practice is as follows: In the box Power Management dialog, select the battery is empty feeding particular, all 3 of its ongoing options batteries are fixed forever, this laptop on the run to continue. Select mode, then enter the Alerts tab, lift the battery low and critical battery Warning check box is a check mark (yes, when the battery is low, the machine will not go into the suspended state). Then leave the computer running the CPU time of tasks, such as the computer automatically perform a number of computational complexity of the 3D demo program, so running out of battery remaining, of course, these disposal N Do not forget to unplug the AC plug.
