What is a KVM Switch?

A KVM Switch allows the connection of a Keyboard, VDU (Video Display Unit) and mouse to multiple computers. The user determines which one of a number of computers they would like to take control of. It is a hardware device that allows selection of individual computers or servers by means of a simple control system using a simple dial or button.

Some KVM Switches can have the added capability to control associated USB devices and even speakers. Products utilising Category 5 twisted pair cable can be used to control equipment at distances up to 300 metres, often using some form of manufacturers proprietary protocols.

A later innovation has been KVM over IP, where the KVM Switch conveys the control information and captured keyboard, video and mouse signals via an IP over Ethernet link to a remote application. This greatly increases the range and scope of control over LAN, WAN and Serial Point-to-Point links. The common method is to connect via a web browser using some form of proprietary software, but security is an obvious issued. This is dealt with by implementing SSL (Secure Sockets Layer) with 128-bit encryption.

Organisations that have a number of dedicated servers may well opt to use KVM Switches to enable the servers to be monitored and controlled individually from a single device. Administrators and operators can switch between physical server devices at the flick of a switch or push of a button.

Keyboard, Video and Mouse Switches come in various formats including Desktop and Rackmounted models. These products come as Direct Connect systems, Networked systems and those that are controlled from a dedicated console. In addition to the KVM Switches most major manufacturers will normally have an extensive range of accessories such as interface modules, cable adapters and cable kits.

For some time now, VGA based switches have probably been the most popular format, but HDMI (High-Definition Multimedia Interface) and DVI (Digital Visual Interface) are quickly becoming efficient digital alternatives to VGA.

DVI is a common digital standard that is popular for PC connections to display units and HDMI is an uncompressed digital standard for audio and video signals. It is able to pass both the video and audio down a single cable between such devices as DVD Players, Set-Top boxes and a digital television.

Control connections on KVM switches are commonly PS/2, which was the common standard for mouse and keyboard connections for many years, and USB which is simpler and more flexible. A lot of Switches have the option of either. The user just has to remember to purchase the right cable types, unless they are supplied with the switch.

KVM Switches are manufactured by a large number of manufacturers. If you are looking to purchase then I recommend the manufacturer that has a good reputation for providing an extensive range of accessories and a good range of switches themselves.

David Christie is MD at NSTUK Ltd, a Technical Training and Consultancy company based in the Northeast of England. David delivers technical training in the area of Data Communications and Telecoms and also provides consultancy and Training Needs Analysis. The company runs an ecommerce website specialising in the sale of Networking hardware and consumer electronics. Website: http://www.ipexpress.co.uk

For a Great range of KVM Switches and Accessories follow:

http://www.ipexpress.co.uk/Tripp-Lite-KVM-Switches/b/931344031?ie=UTF8&title=Tripp%20Lite%20KVM%20Switches

What type of WiFi Antenna do I need?

When deciding to deploy a Wireless LAN (WLAN) solution within a building or facility, there are many factors to consider. The first most obvious consideration is the radio or RF coverage required within the facility, the size and design of the facility will determine the number of wireless access points required to provide that coverage. Another consideration will be selection of the appropriate wireless antennas to provide the desired coverage.

The wireless antenna is one of the most important components of any wireless access point or wireless client device, because it is the antenna that determines how the radio signals are propagated, what type of radiation pattern they produce and how much gain they produce. The radiation pattern may be isotropic, meaning that the antenna radiates the signal equally in all directions, and we often refer to these antennas as omni-directional. Depending on the siting of the antenna, we may need a radiation pattern than is not isotropic, but radiates in a pattern that maximises the radio signal in a certain direction.

Before we get into a description of different types of WiFi antenna, how much gain they produce and what type of radiation pattern they typically provide, I must stress that when deploying a wireless LAN for the first time, it is very important to have a wireless site survey conducted to determine the siting of the access points and also highlight any problem areas where specialist wireless antennas may be required.

A Wireless Antenna will normally be designed to work efficiently over a narrow band of frequencies, the wider the range of frequencies the antenna will operate over, the more “Broadband” the antenna is said to be. WiFi Antennas will operate either in the 2.4Ghz ISM band or the 5Ghz band, so the antenna must be designed to operate within those specific frequency ranges.

In most countries there will be a restriction on the amount of power a wireless antenna can transmit, and this is usually in the region of 1 Watt, with a 6dBi gain for omni-directional antennas and somewhere in the region of 23dBi for directional antennas. The reasons for the restrictions being mainly to reduce interference with other users within a particular frequency band.

Antenna gain is the measure of how much effective signal power is increased by an antenna for a given input power, and is measured in decibels (dB). Decibels are calculated on a logarithmic scale, and an example would be a 3dB increase represents a doubling of power ie. 25 milliwatt input would produce a 50 milliwatt output. EIRP or Effective Isotropic Radiated Power is determined by the Transmit Power and Antenna Gain ie 15 dBm transmit power with 6 dB gain would produce an EIRP of 21 dBm

Lets take a look at some of the antenna types available and how they typically perform:

Omni-Directional Antennas                                                                                                                               

This type of Antenna, as previously stated normally produces an isotropic radiation pattern that is often referred to as a “Doughnut” shape. It is worth bearing in mind that true isotropic antennas tend to be purely theoretical and other types of omni-directional antennas are compared to that of an isotropic design.

Vertical Omni

A vertical omi-directional antenna is usually based on a dipole design where the radiation pattern of a dipole antenna is 360 degrees in the horizontal plane, with the vertical plane varying depending on whether the dipole is vertical or not. A vertically orientated dipole antenna normally has a 75 degree radiation pattern. Dipole antennas are normally said to have a gain, on average of a little over 2Db.  

Ceiling domes

These antennas are designed to be mounted on the ceiling, above false ceilings or even on walls. Because of their less obstructed view, they tend to have a higher gain of around 3Db.

Rubber Ducks

Rubber duck wireless antennas were first used with early walkie talkies as a cut down whip aerial designed at one quarter wavelength. Because of this they are termed electrically short antennas, usually having a wire type element covered with a rubber sheathing, making them flexible and robust. They are vertically mounted and have a 360 degree radiation pattern similar to that of a half-wave dipole. These are the antennas that you see on most mass produced wireless routers for the home market.

Directional Antennas

Reflecting and radiating elements are added to the standard di-pole design to concentrate the signal energy in a specific direction. Directional antennas can give a gain over the standard isotropic antenna of between around 3dB as much as 20Db.

Yagi

Yagi antennas are referred to as high gain antennas and have multiple reflector  and radiating elements to give a typical gain of between 12 and 20dB. They are often used as outdoor antennas and will have a typical horizontal beamwidth of around 30 degrees and 15-25 degrees vertical beamwidth.

Dish

The most common  type of dish Wireless Antenna is the parabolic dish, which uses a curved parabola shaped dish to direct the wireless radio waves to a narrow beamwidth. These type of antennas are extremely highly directive and can also have extremely high gain, as much as 40 or 50dB. One of the design factors is that the dish will be larger than the wavelength of the design radio frequency. Most often used for point to point wireless communications links. Outdoor wireless bridges will often use a Parabolic Dish Antenna.

Patch Antenna

You will often find Patch Antennas deployed in office type environments, normally attached high up on a wall, or sometimes ceiling mounted. Typical horizontal beamwidth is around 70-80 degrees, but this can extend to around 100 degrees. Construction is normally a pair of metal plates that are actually the antenna elements, which together make up the transmission line. They are normally of half-wavelength design, with typical gain being around 2dB, similar to a traditional dipole antenna.

Of course, there are many other variations of wireless antenna which have not had a mention here, but this article was designed to give the layman a simple explanation of basic Wireless Antenna types.

Following a successful Wireless Site Survey, the majority of access points in anything but the smallest office environment will normally employ dome antennas or vertical dipoles. Problem areas may be better served by Patch or Sector wireless antennas to maximise the coverage area.

This article on Wireless Antennas was written by David Christie, MD at NSTUK Ltd,  Website http://www.ipexpress.co.uk .  For Wireless Antenna Products, visit  http://www.ipexpress.co.uk/Wireless-Antennas-Wireless-Networking-Products/b/681707031

What is Broadband?

The term Broadband has been used to describe a number of things over the years, but when you mention Broadband to most people these days, they think of high-speed Internet. The term Broadband Internet is used by service providers to describe the high speed services on offer to connect to the Internet using either DSL (Digital Subscriber Line) services or Cable. A Broadband Router is a device that routes data packets to and from a Local Area Network and the Internet via an interface supporting one of a number of DSL Broadband technologies.

The first time I heard the term Broadband was when studying to be a Radio Officer and learning Radio Theory. A Broadband Antenna was one which was not resonant at a particular frequency but would work over a range of frequencies. We used to discuss methods of “Broadbanding an Antenna”.

In the early 1980s, the ISDN (Integrated Services Digital Network) was devised with what was known as Basic Rate Access with fixed 64Kbps channels and Primary Rate Access with either 1.544Mbps or 2.048Mbps. Broadband was used to describe ISDN Services above the Primary Rates, and normally referred to Optical Networking with the ITU-T G.707 and G.709 standards.

Most households in Western Europe and the US now have some form of Broadband Service for connection to the Internet, and will employ some form of Broadband Router or Broadband Modem to provide that service. What about the technology behind it? The majority of Broadband Internet Services are provided by means of Digital Subscriber Line, and more specifically Asynchronous Digital Subscriber Line (ADSL).

Telephone cables have traditionally carried our analogue telephone signals and the associated signalling within the first 4Khz of available frequency response on the cable. ADSL uses more of the available bandwidth on the cable to support both an Uplink and Downlink high-speed modem. The term ADSL comes from the fact that the Uplink and Downlink modems run at different speeds, with the Downlink significantly faster than the Uplink. This is because we often request content from the Internet such as web pages and therefore we need a faster downlink connection to bring that content to us.  In most cases we employ a Broadband Router or Modem to provide these services, while at the same time maintaining our traditional telephony service.

The first true High Speed ADSL standard known as ANSI T1.413-1998 Issue 2  was released in 1998 and provided for a downstream signal of up to 8Mbps and upstream signal of up to 1Mbps. The speed was dependent upon the length of copper cable on the local loop, with 10,000 – 12,000 feet being common. Further standards continued to be developed to provide these broadband services, and in 2002 the ADSL2 standard was first introduced, which increased the downstream rates to around 12Mbps. This was quickly followed in 2003 by the ADSL2+ Standards which saw a massive increase in Broadband downstream data rates to around 24Mbps.

How does ADSL2 and ADSL2+ manage to achieve these faster data rates? They use a type of modulation known as DMT or Discrete Multi Tone which is a form of FDM (Frequency Division Multiplex) where the available bandwidth is split into smaller sub channels that each have a subcarrier which used a form of Phase Shift Keyed Modulation. ADSL2 uses 256 of these sub-channels, each containing a modulated subcarrier with the upper frequency range being around 1.1Mhz. ADSL2+ effectively doubles Broadband speeds by using a wider frequency range up to an upper limit of around 2.2Mhz with 512 sub-channels. The data is fed to the sub-carriers and transmitted in parallel to provide Broadband Speeds of up to 24Mbps.

Most service providers in the developed countries are either already providing a Broadband service up to 24Mbps, or will be in the near future, and it will be a version of ADSL2+ that they are using. If you want to take advantage of these fast Internet services then you really need a Broadband Router that supports this technology. Obviously a Broadband Router manufactured before the standards were introduced will not support these faster Broadband speeds, so you may want to consider upgrading your Broadband Router if you are not using a device supplied by your Service Provider.

This article on Broadband was written by David Christie, MD at NSTUK Ltd, Website http://www.ipexpress.co.uk

How to Connect a Wireless Router

When connecting a Wireless Router to the Internet and to provide a WLAN (Wireless Local Network) for local connectivity, it is important that you firstly have a working Broadband DSL connection to the Internet via a DSL modem. A lot of non-technical people get confused about the difference between a wireless router and an Internet Gateway Router, which has a built-in modem and so does not need a standalone DSL modem.

Let us assume you already have a DSL Modem and you have tested connectivity to the Internet through the modem with a PC. Now we need to connect the wireless router to the DSL Modem and also set up the local Wireless LAN to enable local devices to connect wirelessly with the device. If you have a cable modem, because your broadband service from your Internet Service Provider is a cable service then the setup is very similar, having already tested the functionality of the Cable Modem. In order to connect to the wireless router, your PCs, Notebooks or even Gaming Consoles need to support the IEEE 802.11 wireless standards. In other words they must have a wireless NIC card either built-in to the Motherboard or you will need to purchase a wireless adapter, the most common being USB Wireless Adapters which are largely Plug and Play.

Another important thing to remember when purchasing your wireless router, is to make sure it is not a wireless access point, otherwise it will not have the routing function which essential to connect your wireless devices to the Internet.

We are almost ready to start connecting our wireless device, so it would be a good idea to have a copy of any setup instructions that came with the device. They will be very similar, regardless of the manufacturer, but there will be subtle differences.

Switch off or unplug your existing DSL Modem or Cable Modem. If it is a DSL Modem then it will be connected to a telephone point with a supplied telephone cable, usually via an ADSL filter. Next take the network cable supplied with your wireless router and plug one end into the RJ-45 receptacle on the DSL Modem (there will usually only be one). Connect the other end of the cable into the WAN port on your wireless router. Most wireless routers also have 4 ports to enable you to connect 4 separate PCs via cables. The WAN port is normally distinct from the computer ports my means of colour coding or due to the fact that it is separate from the other 4 ports.

The next step is to plug in and switch on the DSL Modem and wait few minutes to enable it to boot and then synchronise with the Service Provider network via the telephone cable. Your DSL Modem will normally have a visible LED indicating a successful connection to the Internet.

Now switch on your wireless routing device that you previously connected to the DSL Modem, and shortly a green LED will normally indicate successful connection to your Modem. We are now almost ready to start configuring the Wireless Router itself.

Use a network patch cable to connect a working PC to one of the usually 4 network ports on the wireless device. A built in DHCP Server in the wireless router should allocate an appropriate IP Address to the PC being used for configuration. Open up a browser window on your PC and type in the URL provided by the manufacturer in the address bar. For example Linksys routers normally use the URL http://192.168.1.1 . Success should result in the router default configuration page becoming visible in your browser window. Your router instructions should give you the default username and password required to access the main wireless router configuration. This will often be admin and admin, or whatever your router instructions informs you. Once you have successfully entered the Username and Password, then navigate to the section that allows you to change the settings and configure an admin Username and Password that you can remember. Save the settings!!

You should now be able to test the connection to the Internet by disconnecting the cable and connecting to the wireless network by using your PC wireless connection. Bring up a browser window and try connecting to a favourite website, maybe a search engine like Google. If successful then the final step is to secure your wireless network by configuring wireless security settings, normally WPA or WPA2.

Either via your wireless connection or by reconnecting the cable between the PC and the wireless router, navigate back to the wireless router’s default configuration page and find the wireless security settings section. You will be required to configure the SSID of the wireless router. Your router will have a default SSID, but you should change it to a name that you remember. When you or your family are trying to connect a PC to the wireless router in the future, this name will ensure they attempt to connect to the correct wireless network instead of a neighbours network. Now select WPA or WPA2 settings from the configuration (WPA2 is more secure, if available). Configure a unique pass phrase that you can remember and the wireless router will use this pass phrase to generate a secure network key that is used to authenticate devices and to encrypt data passing over the wireless network. Remember to save this configuration again.

You will now need to reconnect your wireless enabled PC to the wireless network and you will be asked for the same pass phrase when your PC attempts to connect to the wireless network with the SSID you configured earlier.

If no mistakes have been made then you should now be able to connect to the Internet from the wireless enabled PC. Any other PCs that require wireless access just need to be configured with the correct SSID and pass phrase and connectivity should be quick and efficient. Good Luck.

This article on configuration of wireless routers was written by David Christie, MD at NSTUK Ltd, Website http://www.ipexpress.co.uk

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