“All of the operators are getting creamed by over-the-top services,” said Steven Glapa, Senior Director of Field Marketing at Ruckus. “Mobile device evolution and growing traffic problems are making it ever more clear to carriers that they need to use the right tool for the right job. LTE is well suited for highly-mobile users, but not small high-density wireless cells. Carriers are realizing that Wi-Fi can be a strategic weapon [to fill this need], not just a band aid.”

Not your father’s Wi-Fi

The challenge here is that many carriers do not consider 802.11 products designed for residential or even enterprise deployment suitable for commercial wireless service delivery on a grand scale. To meet carrier requirements for high bandwidth, real-time service-level control, and cost-effective scalability in RF-hostile outdoor environments, Ruckus leveraged its experience in the wide-area Wi-Fi service market to expand its portfolio.

• The ZoneFlex 7731 ($1,199) is a new outdoor point-to-multipoint 5 GHz 802.11n wireless high-speed backhaul bridge. Up to 5 bridges can be deployed with up to 30 degrees apart, with single-hop throughput ranging from 60 Mbps at 12 kilometers to 180 Mbps at 1 kilometer. This bridge is designed for carriers that deploy low density wireless broadband access or for small 3G cell backhaul.
• The ZoneFlex 7762-S ($1,999) is a new outdoor mesh 802.11n AP with a 120 degree “Smart-Sector” antenna designed to deliver 10 dB signal gain over horizontal coverage areas. For example, a carrier might use the ZF7762-S to deliver first-mile access in venues where Wi-Fi needs to reach rooftop customer premises equipment (CPE) throughout a serving area.
• The MediaFlex 7200 (from $99) is a new series of inexpensive 2.4 GHz 802.11n CPE designed to pair well with the ZF 7762-S. Available in three models (indoor/outdoor, internal/external antennas), the ZF7200 can be mounted on a pole or wall to be used as a remotely-managed, two-SSID residential bridge or router.
• Carriers can manage all of these products from a central location using the FlexMaster 9.0 (from $5,000), which Ruckus claims is capable of handling tens of thousands of Smart Wi-Fi network elements and hundreds of thousands of Wi-Fi clients. Features of special interest to carriers include capacity planning, SLA visibility, efficient single-dashboard drill-down trouble-shooting, and compliance reporting.

Carrier-class 802.11

These new products, available immediately, are designed to help carriers use Wi-Fi to tap service delivery opportunities, from triple-play residential services and 3G offload to first/last mile access in developing markets and managed enterprise WLANs. However, according to Glapa, carriers can’t tolerate uncertainty and unlicensed spectrum makes them nervous. “They absolutely must have interference management to deliver reliable services in concrete canyons, and our adaptive antennas are ideal for this.”

But carriers are not easily convinced, so Ruckus ran competitive tests to produce some compelling evidence. The company created a high-interference live test environment consisting of 191 APs in a 3,000 square meter facility to simulate the density of a metro-area like Manhattan.

When an iPhone 3G using Wi-Fi was faced with this interference, its average throughput dropped from 8.7 to 5.5 Mbps over Ruckus. “That’s about 75 percent, which is not perfect, but it’s pretty good when you consider that two other industry-leading APs dropped to 0.3 and 0.1 Mbps,” said Glapa.

Seeing is believing, so Ruckus also intends to use customer case studies to convince potentially skeptical carriers. For example, Tikona has already deployed over 35,000 Ruckus mesh APs to deliver last-mile wireless broadband services throughout India, and plans to continue installing 1,000 new 802.11g APs on rooftops each week. Live network samples show that 80 percent of those APs are now delivering 5 Mbps or better last-mile service – despite running over a non-engineered, self-organized set of 2.4 GHz channels. Other large carrier case studies include Chilean CLEC STEL (metro-area wireless throughout Santiago) and US 4G ISP Towerstream (3G backhaul throughout Manhattan).

The Buffalo WHR-G54S has limited storage; only 4 megabytes of NVRAM, and 16 megabytes of system RAM. So it doesn’t have room for all of the available DD-WRT options. But you get an amazing amount of functionality into this little box, and for the price it’s a steal. It will serve as an Internet router and firewall for 30 or so users, provided they’re not online gambling nuts or BitTorrent addicts. You could also use it as LAN router, a LAN bridge, a dedicated wireless access point, part of a wireless mesh network, or a VPN gateway.

Installation

Let’s take a walk through installing the DD-WRT firmware on the Buffalo WHR-G54S, because there are some tricky bits. These directions also apply to the Buffalo WHR-HP-G54, WZR-HP-G54, and WZR-RS-G54. With a lot of these little routers you can upload new firmware using their factory Web interfaces. But the Buffalo boxes, which are based on Broadcom hardware, accept only special encrypted firmware over the Web interface. So we have to sneak DD-WRT in through the back door, which is a short interval at bootup where the Broadcom flash ROM enters a special mode that allows new firmware to be uploaded via tftp transfer.

Prerequisites

• Make sure you have the tftp command installed
• If any device or computer on your network has the IP address of 192.168.1.1, take it off the network or change the address, because that is the default IP address in the DD-WRT firmware
• Make sure you have the route and ip commands available; these come with the net-tools and iproute packages

Your Buffalo router will plug into your LAN switch just like any other device. For now you want to stick with old-fashioned wired Ethernet; don’t try to do this over a wireless connection. Go ahead and power it up, and point a Web browser at http://192.168.11.1. (For the WZR-RS-G54 it’s 192.168.12.1.) The default login is root, with no password.

If this doesn’t fit your LAN addressing, there is an easy way to get there. Use the ip command to add an address to the network interface of your PC, then add a host route:

# ip address add dev eth0 192.168.11.2
# route add -host 192.168.11.1 gw 192.168.11.2

If you have a WZR-RS-G54, use the 192.168.12.* addresses. Now you should be able to ping your router:

$ ping 192.168.11.1
PING 192.168.11.1 (192.168.11.1) 56(84) bytes of data.
64 bytes from 192.168.11.1: icmp_seq=1 ttl=64 time=0.633 ms

You can also run a ping test from the router; just click the System Info button to find the ping page.

All righty then, you know it works. Unplug the router’s power cord, and go to the Downloads page at DD-WRT.com and download the dd-wrt.v23_mini_generic.bin file, or whatever the latest version is. Make sure it’s mini_generic.bin. Change to the directory that contains the new firmware. Then run these commands:

carla@xena:~/downloads$ tftp
tftp> binary
tftp> trace
Packet tracing on.
tftp> rexmt 1
tftp> connect 192.168.11.1

Now type in the next command, but don’t hit enter:

tftp> put dd-wrt.v23_mini_generic.bin

Hold the Buffalo router so you can see the green Ethernet port LEDS, which are on the back next to the ports. When it’s first plugged in, all of them light up. When they all turn off except for your one connected port, hit ‘enter’ to execute your last tftp command. If it works, you’ll see a lot of

sent DATA
received ACK
sent DATA
received ACK

Sent 2555904 bytes in 3.7 seconds
tftp>

When it’s finally booted up, you’ll see two green LEDs on the front panel; one for power, and a green “g” for wireless G. Now you can point your Web browser to 192.168.1.1 and be greeted by the DD-WRT control panel. If you click on any tabs you’ll be asked for a login. The default is root, admin. Just like before, if this address doesn’t fall into the same range as your LAN, just add a compatible address and route to your PC. Then you can log in to DD-WRT and change it.

I know, we wouldn’t have to go through this silliness if it had a serial port. But it doesn’t, so here we are, and be glad Linux is so flexible and capable.

Initial Setup

Naturally you’ll want to change the login and password to something the whole world doesn’t already know, under the Administration tab. Then you should disable Telnet and enable SSH, Administration -> Services. Don’t worry about keys; just make sure the box for “Authorized Keys” is empty, including no spaces. Then configure networking under Setup -> Basic Setup.

DD-WRT includes only an NTP (Network Time Protocol) client, so you’ll need a separate local NTP server. Enter the IP address of your local time server on the Administration page. Remember to use the pool.ntp.org addresses for your local time server, like this example for North America:

server 0.north-america.pool.ntp.org
server 1.north-america.pool.ntp.org
server 2.north-america.pool.ntp.org
server 3.north-america.pool.ntp.org

Visit www.pool.ntp.org for information for other zones.

Package Management

With the minimal installation, you’ll have a bit less than one megabyte of space to install additional applications. But install them you can with ipkg. First turn on JFFS, the Journaling Flash File System, on the Administration page. Check both “Enable JFFS2″ and “Clean JFFS2″. Then click the “Save Settings” button, and the router will reboot. Once it’s back up, ssh in and see what ipkg can do:

carla@xena:~$ ssh root@192.168.1.1 ~ # df -h Filesystem             Size      Used Available Use% Mounted on /dev/root 1.9M 1.9M0 100% / /dev/mtdblock/4 1.3M    324.0k    956.0k  25% /jffs

OK, you have a little room to play with. Run ipkg with no options to get a list of commands:

~ # ipkg

Now you can generate and view a package list:

~ # ipkg update
~ # ipkg list

And that’s as far we go today. Come back soon to learn some advanced DD-WRT tips and tricks.

Looking forward, the ease-of-use benefits will make it easier for Linux to be shipped as an OEM platform, and installed post-market by technology adopters. More importantly, having a major hardware vendor like Broadcom take a look at Linux and decide to invest the time and effort in creating a Linux driver should mean that other hardware vendors sitting on the fence regarding a Linux driver for their own offerings may come to the conclusion that Linux is something they can no longer ignore.

They may have come to that conclusion already. The success of the Android operating system has pushed a lot of vendors (including Broadcom) to create drivers for Android devices. The BCM4319 and BCM4329 SDIO chipsets were already supported on Android, which is close enough to Linux to get support for those devices into Android’s predecessor. As Android shows up on more devices, you can expect to see more Linux-ready hardware drivers appearing in the near future.

Linux will also be collecting drivers on its own merits, I would expect. Whatever the tipping point was for Broadcom to release this driver, I have a hard time believing other vendors won’t be following suit quickly, especially given how resistant to Linux Broadcom has been in the past.

It is, after all, just one driver among many, and there are indeed many more drivers needed. But Broadcom may the the leader of a driver rush for Linux, which is something the operating system has needed for a long time

The new RackSwitch G8264 delivers up to 1.28 terabits of non-blocking throughput, and includes up to four 40 GbE ports and 64 10 GbE ports. The new Blade switch comes as the company is set to be acquired by IBM in a deal that is expected to close by the end of the year. Blade was set up in 2006 as a spinoff of the now-bankrupt Nortel Networks.

“40 GbE has been too pricey to bring into the data center, until now,” . “This will enable massive adoption of not only 40 GbE, but also will help adoption of 10 GbE as well.”

Tuchler explained that enterprises have been complaining that network uplinks at 10 GbE doesn’t work if they are connecting all their servers at 10 GbE, as they need more upstream bandwidth. In response, Blade is incorporating four Quad Small Form-factor Pluggable (QFSP+) ports for 40 GbE uplinks on the RackSwitch G8264. The 40 GbE standard was ratified in June of this year alongside a 100 GbE standard for core network routing traffic.

Tuchler noted that while 40 GbE makes sense for the uplink side of switches, it doesn’t yet have a place for server-side connectivity.

“I think that the server-side internal structures including the PCI bus aren’t quite fast enough yet,” he said. “The mainstream is using 10 GbE for servers now.”

Virtualization

With the RackSwitch G8264, Blade is also delivering its VMready virtualization technology for virtual machine mobility across network infrastructure. With VMready, the company is delivering something similar to the IEEE 802.1Qbg Edge Virtual Bridging standard, which is still under development.

“The main intent behind the 802.1Qbg is to allow virtual machine traffic to have the right port profiles follow virtual machines as they move across the network,” Tuchler said. “VMready has a structure that is very similar to what is emerging in 802.1Qbg.”

Tuchler explained that VMready is complementary to what VMware does today with its vMotion virtual server mobility technology.

“VMready is the network equivalent of vMotion,” Tuchler said. “So as vMotion moves virtual machines from one server to another, we do the network equivalent and move all the port policies across, so when the virtual machine comes up on a new server it has all the right security and network settings, so the application keeps working.”

Linux-powered OS

Sitting underneath the RackSwitch G8264 is the Blade OS operating system, which has its roots in Linux. Blade is not alone in using Linux as the underlying base for its networking operating system. Alcatel-Lucent, for instance, recently moved its AOS operating system to a Linux base as well.

With IBM’s move to acquire Blade set to close by the end of the year, Tuchler was unable to comment about any roadmap changes that might occur, though he stressed that the two companies already share a lot in common.

“IBM’s view and Blade’s view of the data center are similar and there is a lot of alignment in what we see as the challenges in the data center,” he said. “That was probably a driving reason behind the acquisition, anything more than that I can’t comment until after the close.”

Transmitter types

Generally in communication and information processing, a transmitter is any object (source) which sends information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a transmitter.

In radio electronics and broadcasting, a transmitter usually has a power supply, an oscillator, a modulator, and amplifiers for audio frequency (AF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto the carrier frequency, which is then broadcast. Sometimes a device (for example, a cell phone) contains both a transmitter and a radio receiver, with the combined unit referred to as a transceiver. In amateur radio, a transmitter can be a separate piece of electronic gear or a subset of a transceiver, and often referred to using an abbreviated form; “XMTR”. In most parts of the world, use of transmitters is strictly controlled by laws since the potential for dangerous interference (for example to emergency communications) is considerable. In consumer electronics, a common device is a Personal FM transmitter, a very low power transmitter generally designed to take a simple audio source like an iPod, CD player, etc. and transmit it a few feet to a standard FM radio receiver. Most personal FM transmitters in the United States fall under Part 15 of the Federal Communications Commission (FCC) regulations to avoid any user licensing requirements.

In industrial process control, a “transmitter” is any device which converts measurements from a sensor into a signal, conditions it, to be received, usually sent via wires, by some display or control device located a distance away. Typically in process control applications the “transmitter” will output an analog 4-20 mA current loop or digital protocol to represent a measured variable within a range. For example, a pressure transmitter might use 4 mA as a representation for 50 psig of pressure and 20 mA as 1000 psig of pressure and any value in between proportionately ranged between 50 and 1000 psig. (A 0-4 mA signal indicates a system error.) Older technology transmitters used pneumatic pressure typically ranged between 3 to 15 psig (20 to 100 kPa) to represent a process variable.

Broadcast transmitters

History

In the early days of radio engineering, radio frequency energy was generated using arcs known as Alexanderson alternator or mechanical alternators (of which a rare example survives at the SAQ transmitter in Grimeton, Sweden). In the 1920s electronic transmitters, based on vacuum tubes, began to be used.

Frequency Control

Power output

In broadcasting and telecommunication, the part which contains the oscillator, modulator, and sometimes audio processor, is called the “exciter”. Most transmitters use heterodyne principle, so they also have a frequency conversion units. Confusingly, the high-power amplifier which the exciter then feeds into is often called the “transmitter” by broadcast engineers. The final output is given as transmitter power output (TPO), although this is not what most stations are rated by.

Effective radiated power (ERP) is used when calculating station coverage, even for most non-broadcast stations. It is the TPO, minus any attenuation or radiated loss in the line to the antenna, multiplied by the gain (magnification) which the antenna provides toward the horizon. This antenna gain is important, because achieving a desired signal strength without it would result in an enormous electric utility bill for the transmitter, and a prohibitively expensive transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no more than 20% of the ERP.

For VLF, LF, MF and HF the ERP is typically not determined separately. In most cases the transmission power found in lists of transmitters is the value for the output of the transmitter. This is only correct for omnidirectional aerials with a length of a quarter wavelength or shorter. For other aerial types there are gain factors, which can reach values until 50 for shortwave directional beams in the direction of maximum beam intensity.

Since some authors take account of gain factors of aerials of transmitters for frequencies below 30 MHz and others not, there are often discrepancies of the values of transmitted powers.

Power supply

Transmitters are sometimes fed from a higher voltage level of the power supply grid than necessary in order to improve security of supply. For example, the Allouis, Konstantynow and Roumoules transmitters are fed from the high-voltage network (110 kV in Alouis and Konstantynow, 150 kV in Roumoules) even though a power supply from the medium-voltage level of the power grid (about 20 kV) would be able to deliver enough power.

Cooling of final stages

Low-power transmitters do not require special cooling equipment. Modern transmitters can be incredibly efficient, with efficiencies exceeding 98 percent. However, a broadcast transmitter with a megawatt power stage transferring 98% of that into the antenna can also be viewed as a 20 kilowatt electric heater.

For medium-power transmitters, up to a few hundred watts, air cooling with fans is used. At power levels over a few kilowatts, the output stage is cooled by a forced liquid cooling system analogous to an automobile cooling system. Since the coolant directly touches the high-voltage anodes of the tubes, only distilled, deionised water or a special dielectric coolant can be used in the cooling circuit. This high-purity coolant is in turn cooled by a heat exchanger, where the second cooling circuit can use water of ordinary quality because it is not in contact with energized parts. Very-high-power tubes of small physical size may use evaporative cooling by water in contact with the anode. The production of steam allows a high heat flow in a small space.

Protection equipment

The high voltages used in high power transmitters (up to 40 kV) require extensive protection equipment. Also, transmitters are exposed to damage from lightning. Transmitters may be damaged if operated without an antenna, so protection circuits must detect the loss of the antenna and switch off the transmitter immediately. Tube-based transmitters must have power applied in the proper sequence, with the filament voltage applied before the anode voltage, otherwise the tubes can be damaged. The output stage must be monitored for standing waves, which indicate that generated power is not being radiated but instead is being reflected back into the transmitter.

Lightning protection is required between the transmitter and antenna. This consists of spark gaps and gas-filled surge arresters to limit the voltage that appears on the transmitter terminals. The control instrument that measures the voltage standing-wave ratio switches the transmitter off briefly if a higher voltage standing-wave ratio is detected after a lightning strike, as the reflections are probably due to lightning damage. If this does not succeed after several attempts, the antenna may be damaged and the transmitter should remain switched off. In some transmitting plants UV detectors are fitted in critical places, to switch off the transmitter if an arc is detected. The operating voltages, modulation factor, frequency and other transmitter parameters are monitored for protection and diagnostic purposes, and may be displayed locally and/or at a remote control room.

Building

A commercial transmitter site will usually have a control building to shelter the transmitter components and control devices. This is usually a purely functional building, which may contain apparatus for both radio and television transmitters. To reduce transmission line loss the transmitter building is usually immediately adjacent to the antenna for VHF and UHF sites, but for lower frequencies it may be desirable to have a distance of a few score or several hundred metres between the building and the antenna. Some transmitting towers have enclosures built into the tower to house radio relay link transmitters or other, relatively low-power transmitters. A few transmitter buildings may include limited broadcasting facilities to allow a station to use the building as a backup studio in case of incapacitation of the main facility.

Legal and regulatory aspects

Since radio waves go over borders, international agreements control radio transmissions. In European countries like Germany often the national Post Office is the regulating authority. In the United States broadcast and industrial transmitters are regulated by the Federal Communications Commission (FCC). In Canada technical aspects of broadcast and radio transmitters are controlled by Industry Canada, but broadcast content is regulated separately by the Canadian Radio-television and Telecommunications Commission (CRTC). In Australia transmitters, spectrum, and content are controlled by the Australian Communications and Media Authority (ACMA). The International Telecommunication Union (ITU) helps managing the radio-frequency spectrum internationally.

Planning

As in any costly project, the planning of a high power transmitter site requires great care. This begins with the location. A minimum distance, which depends on the transmitter frequency, transmitter power, and the design of the transmitting antennas, is required to protect people from the radio frequency energy. Antenna towers are often very tall and therefore flight paths must be evaluated. Sufficient electric power must be available for high power transmitters. Transmitters for long and medium wave require good grounding and soil of high electrical conductivity. Locations at the sea or in river valleys are ideal, but the flood danger must be considered. Transmitters for UHF are best on high mountains to improve the range (see radio propagation). The antenna pattern must be considered because it is costly to change the pattern of a long-wave or medium-wave antenna.

Transmitting antennas for long and medium wave are usually implemented as a mast radiator. Similar antennas with smaller dimensions are used also for short wave transmitters, if these send in the round spray enterprise. For arranging radiation at free standing steel towers fastened planar arrays are used. Radio towers for UHF and TV transmitters can be implemented in principle as grounded constructions. Towers may be steel lattice masts or reinforced concrete towers with antennas mounted at the top. Some transmitting towers for UHF have high-altitude operating rooms and/or facilities such as restaurants and observation platforms, which are accessible by elevator. Such towers are usually called TV tower. For microwaves one frequently uses parabolic antennas. These can be set up for applications of radio relay links on transmitting towers for FM to special platforms. For the program passing on of television satellites and the funkkontakt to space vehicles large parabolic antennas with diameters of 3 to 100 meters are necessary. These plants, which can be used if necessary also as radio telescope, are established on free standing constructions, whereby there are also numerous special designs, like the radio telescope in Arecibo.

Just as important as the planning of the construction and location of the transmitter is how its output fits in with existing transmissions. Two transmitters cannot broadcast on the same frequency in the same area as this would cause co-channel interference. For a good example of how the channel planners have dovetailed different transmitters’ outputs see Crystal Palace UHF TV channel allocations. This reference also provides a good example of a grouped transmitter, in this case an A group. That is, all of its output is within the bottom third of the UK UHF television broadcast band. The other two groups (B and C/D) utilise the middle and top third of the band, see graph. By replicating this grouping across the country (using different groups for adjacent transmitters), co-channel interference can be minimised, and in addition, those in marginal reception areas can use more efficient grouped receiving antennas. Unfortunately, in the UK, this carefully planned system has had to be compromised with the advent of digital broadcasting which (during the changeover period at least) requires yet more channel space, and consequently the additional digital broadcast channels cannot always be fitted within the transmitter’s existing group. Thus many UK transmitters have become “wideband” with the consequent need for replacement of receiving antennas (see external links). Once the Digital Switch Over (DSO) occurs the plan is that most transmitters will revert to their original groups, source Ofcom July 2007.

Further complication arises when adjacent transmitters have to transmit on the same frequency and under these circumstances the broadcast radiation patterns are attenuated in the relevant direction(s). A good example of this is in the United Kingdom, where the Waltham transmitting station broadcasts at high power on the same frequencies as the Sandy Heath transmitting station’s high power transmissions, with the two being only 50 miles apart. Thus Waltham’s antenna array does not broadcast these two channels in the direction of Sandy Heath and vice versa.

Where a particular service needs to have wide coverage, this is usually achieved by using multiple transmitters at different locations. Usually, these transmitters will operate at different frequencies to avoid interference where coverage overlaps. Examples include national broadcasting networks and cellular networks. In the latter, frequency switching is automatically done by the receiver as necessary, in the former, manual retuning is more common (though the Radio Data System is an example of automatic frequency switching in broadcast networks). Another system for extending coverage using multiple transmitters is quasi-synchronous transmission, but this is rarely used nowadays.

Main and relay (repeater) transmitters

Transmitting stations are usually either classified as main stations or relay stations (also known as repeaters, translators or sometimes “transposers”.)

Main stations are defined as those that generate their own modulated output signal from a baseband (unmodulated) input. Usually main stations operate at high power and cover large areas.

Relay stations (translators) take an already modulated input signal, usually by direct reception of a parent station off the air, and simply rebroadcast it on another frequency. Usually relay stations operate at medium or low power, and are used to fill in pockets of poor reception within, or at the fringe of, the service area of a parent main station.

Note that a main station may also take its input signal directly off-air from another station, however this signal would be fully demodulated to baseband first, processed, and then remodulated for transmission.

Transmitters in culture

Some cities in Europe, like Mühlacker, Ismaning, Langenberg, Kalundborg, Hörby and Allouis became famous as sites of powerful transmitters. For example, Goliath transmitter was a VLF transmitter of the German Navy during World War II located near Kalbe an der Milde in Saxony-Anhalt, Germany. Some transmitting towers like the radio tower Berlin or the TV tower Stuttgart have become landmarks of cities. Many transmitting plants have very high radio towers that are masterpieces of engineering.

Having the tallest building in the world, the nation, the state/province/prefecture, city, etc., has often been considered something to brag about. Often, builders of high-rise buildings have used transmitter antennas to lay claim to having the tallest building. A historic example was the “tallest building” feud between the Chrysler Building and the Empire State Building in New York, New York.

Some towers have an observation deck accessible to tourists. An example is the Ostankino Tower in Moscow, which was completed in 1967 on the 50th anniversary of the October Revolution to demonstrate the technical abilities of the Soviet Union. As very tall radio towers of any construction type are prominent landmarks, requiring careful planning and construction, and high-power transmitters especially in the long- and medium-wave ranges can be received over long distances, such facilities were often mentioned in propaganda. Other examples were the Deutschlandsender Herzberg/Elster and the Warsaw Radio Mast.

KVLY-TV’s tower located near Blanchard, North Dakota was the tallest artificial structure in the world when it was completed in 1963. It was surpassed in 1974 by the Warszawa radio mast, but regained its title when the latter collapsed in 1991. It was surpassed by the Burj Khalifa skyscraper in early 2009, but the KVLY-TV mast is still the tallest transmitter.

Records

• Tallest radio/television mast:
  • 1974–1991: Konstantynow for 2000 kW longwave transmitter, 646.38 m (2120 ft 8 in)
  • 1963–1974 and since 1991: KVLY Tower, 2,063 ft (628.8 m)

• Highest power:
  • Longwave, Taldom transmitter, 2500 kW
  • Medium wave, Bolshakovo transmitter, 2500 kW

• Highest transmission sites (Europe):
  • FM Pic du Aigu in Chamonix
  • MW Pic Blanc in Andorra

As we’ll discuss in this tutorial, old wireless routers can be turned into access points (APs); they can help increase the Wi-Fi footprint even more. Plus they might even help increase the performance of the 802.11n connections on your network.

Wireless Routers and APs Aren’t the Same

Before going further, it’s important to understand the difference between a wireless router and an AP. First off, wireless routers contain an AP. In addition to the AP functionality, a wireless router provides the routing between clients and the Internet. This makes it possible for multiple computers to access one big network, the Internet. Secondly, routers have a DHCP server. This server gives each client an IP address, which is required for network connectivity. Without the routing and DHCP features, a wireless router would simply be an AP; if a wireless router didn’t have an AP, it would just be a wired router.

On most networks, only one router is needed. Then to extend the wireless coverage, APs can be plugged into the router or switches. These APs aren’t as “smart.” They only provide Wi-Fi access; the router still does most of the network management.

Get Additional Coverage And/or Separate the 802.11G Clients

After we do the magic, we’ll plug the old wireless router into the new one, to serve as another AP. Then if the old router is properly placed (by running an Ethernet cable), it can nearly double the coverage area provided by the new router. Of course, 802.11n clients that connect to the 802.11g router won’t run at 11n rates of speed and performance, but the old router is earning its keep by providing “free coverage.”

There’s a small catch the other way though; it’s better that the 802.11g clients only connect to the 802.11g router. When they connect to 11n routers, the performance of the n clients is negatively effected. However, again, the additional coverage is better than nothing, even just for the old clients.

You can still benefit from keeping your old gear if you don’t have a long Ethernet cable or you don’t want to run it through the building. Even if the old router is placed close to the new one and it doesn’t provide additional coverage, it can still serve as the AP for the 802.11g clients. This way the new router can be set to only allow 802.11n connections, so the old clients won’t connect and degrade the performance.

Performing the Conversion

In addition to changing general settings, turning a wireless router into an access point consists of disabling its DHCP server and hooking it up to the new router correctly. Start by configuring the general settings. Plug in the old router (but don’t connect it to the new router yet) and log into the Web-based configuration utility by typing its IP address into a Web browser. Then at least configure the following settings:

• IP Address: Change the IP address to be within the subnet of the new router. For example, if the new router’s IP is 192.168.0.1, the old router could be set to 192.168.0.2.
• Channel: Change the channel to one of the three non-overlapping channels, 1, 6, or 11, while making sure any coexisting or overlapping routers or APs aren’t set to the same channel.
• SSID: Typically, all the APs of a network should have the same SSID, so roaming works when clients move around and change APs. However, if roaming isn’t crucial, think about setting the old 802.11g router to a different network name. This can help the users distinguish between the g and n access; especially useful if performance is important.
• Security: Remember to set up encryption, preferably WPA or WPA2, on all the wireless routers and APs.

To turn off the DHCP server, find the DHCP settings, usually on the main or network tab. There should be a check box or something similar to toggle the server on and off; disable it. Then make sure to save the changes.

When the configuration is done, put the old router in place. Then connect an Ethernet cable between them, plugging into the regular Ethernet ports of each. Do not connect it to the old router’s Internet/WAN port.

Conversion Complete

We did it; now we should have greater coverage area and/or performance. We disabled the routing features of the old wireless router, turning it into a basic AP. If there are more old routers lying around, consider other projects, too. The DD-WRT replacement firmware, for example, has a repeater feature and CoovaAP includes hotspot features.

1. Use vendor-supplied security – Since the capabilities of each wireless router/access point/bridge differ from brand to brand, it’s best to get the vendor’s recommendation on the best security options for their devices
2. Change the default admin password of your wireless router/access point/bridge – Once a potential attacker detects a wireless network, this is one of the easiest ways to further compromise it.
3. Turn down the power – Some vendor’s wireless router/access point/bridge’s offer the option of changing the power settings so that your wireless network is not broadcasting its signal farther than you really need it to.
4. Use Media Access Control (MAC) address filtering and Wired Equivalent Privacy (WEP) — MAC address filtering will help restrict access to your home wireless network to only those users you authorize. If WEP is the only security option available on your wireless router/access point/bridge, use a key that is hard to guess and change it periodically.
5. Consult the vendor about antenna positioning — Different antennas radiate signal in different patterns. Check your vendor’s documentation to verify optimal antenna positioning for your wireless network.

1. Change SSID and, if possible, disable SSID broadcast – Your wireless router/access point/bridge may come with a default SSID already configured. Change it as soon as you set up your wireless network. Also, some vendor’s may offer the option of not broadcasting this network identifier.
2. Keep your wireless router/access point/bridge firmware up to date – New firmware can help resolve compatibility problems, plug security holes and provide other important fixes. Check the vendor’s Web site for these updates.
3. Use a VPN for working at home – For enterprise users working at home, always check with your enterprise IT department or help desk for best practices regarding accessing the company network over your wireless home network. Often, virtual private network (VPN) software is required for this purpose.
4. Keep your antivirus software up to date – Viruses, worms and Trojans are a continuous threat. Make sure your wireless network is not a haven for these problems.
5. Use a firewall – Either a hardware or software firewall can help protect your computer and the rest of your network from attack.

A DHCP capable wireless router can be used as a wireless media ‘server’. Each PC can see each other’s sharable folders. Music, video and pictures can be streamed from the main PC via the router to any authorized PC/laptop etc in the house.

Steps

For a full-blown file sharing network with easy access straight from boot up, the following five steps are required:

1. Workgroups
2. Sharing Folders
3. Configuring Firewalls
4. Mapping Network Drives
5. Customized O/S’s

1. Workgroups

Configure all PC’s to belong to the same workgroup. This streamlines access issues.

• Under {Control Panel / System / Computer Name / Change} set the workgroup to a useful name like HOME_NETWORK.

2. Share Folders

To share folders you need to access the folder properties and do two things.

• Under the Sharing tab click {SHARE THIS FOLDER}
• Under the Sharing tab also click {PERMISSIONS} and choose the permissions level. This is only necessary if you want remote admin privileges.

You do not need to edit the properties of sub-folders, the root-folder is sufficient. For security, only share a limited number of folders and definitely no system ones.

3. Configure Firewalls

Each respective firewall must allow the other PC access to the shared folders. There are two ways:

• Ensure that the Router DHCP setting is {AUTO}. Configure each firewall {TRUSTED NETWORKS}, or equivalent, to the private range issue eg 192.168.1.2 – 192.168.1.254
• Ensure that the Router DHCP setting is {MANUAL}. AT each PC, under properties for {Wireless Network Connections}, click the properties for {INTERNET PROTOCOL TCP/IP}. Enter a unique IP eg 192.168.1.X where X= 2 to 254

Configure each firewall {TRUSTED NETWORKS}, or equivalent, to allow access inbound/outbound to the other PC unique IP address. This is slightly more secure from casual poking especially if X is midrange.

Important: For security reasons, ensure that you are using maximum WPA encryption on your router.

4. Mapping Network Drives

It is always handy to map a drive letter to the shared folder on another PC.

• Open Windows Explorer
• Under {MY NETWORK PLACES / ENTIRE NETWORK / MICROSOFT WINDOWS NETWORK} click the workgroup eg HOME_NETWORK and select the PC of interest and click the shared folder required.
• Map that folder to a drive letter via TOOLS / MAP NETWORK DRIVE
• If you wish you may tick the choice for {Reconnect on Logon}

5. Customized O/S’s

If you have {FILE & PRINTER SERVICES} and {CLIENT FOR MICROSOFT NETWORKS} installed, then ignore the following:

Rarely, the advanced user may have deliberately installed a custom streamlined version of windows, without some services that would have merely bloated the OS.

• Under {MY NETWORK PLACES} click the properties for {Wireless Network Connections}.
• Select {FILE AND PRINTER SHARING FOR MICROSOFT NETWORKS} and click {INSTALL}.
• Under {MY NETWORK PLACES} click the properties for {Wireless Network Connections}.
• Tick the box for {FILE AND PRINTER SHARING FOR MICROSOFT NETWORKS} and click {INSTALL}.

Do similarly with {CLIENT FOR MICROSOFT NETWORKS}

When Qos are usefull

QoS is useless if you don’t have programs that use it. 99.9% of the usual software doesn’t use it. Practically – if you don’t know you have to install it you don’t need it.

When creating these connections, you must consider:

• Crypto settings
• ACL’s
• Outside interfaces

You can have many SA (security associations) for a crypto map, and inside of a specific SA you can have multiple peers in the list. The VPN engine will process the peers in the order they are listed. This is useful when you are using tracking objects for failover and therefore may have the remote peer coming from multiple IP addresses.

ACL’s will be used to control which traffic will be forwarded through the IPSec connection. This will read as “allow all traffic on my local side to send to any local ip address at the remote side”. This can be adjusted as you see fit. Assume that I am connection two class C networks via an IPSec VPN. My access list may read as:

• 10 permit ip 192.168.0.0 0.0.0.255 192.168.2.0 0.0.0.255

I am sure there is a way to connect when both subnets are the same using NAT; however I feel that this is bad form. In those cases where I have found that both ranges are the same, I will change one of the ranges. This can be a pain in the ass, but in the long run is a best practice.

As you can see from the sample configurations, this is a peer relationship. Regardless of speed or hardware, there is not Master or Secondary. Cisco calls these configurations Mirrors. The configurations are the same with certain variables reversed.

I cannot recommend enough; DO NOT use the SDM for this. Unless you enjoy 400 line ACL’s, you will have a much more pleasurable experience creating these manually. The process is simple and very quick once you get used to it.

I hope this helps you. Please let me know if you spot any typos or mistakes that I made during the creation of this.

LEGEND

• our_key = a key which will be used on both sides. This can be any string of characters.
• Side_A_IP = the public IP address of Side A. This will be the ip address for the interface which has the crypto map attached to it.
• Side_B_IP = the public IP address of Side B. This will be the ip address for the interface which has the crypto map attached to it.
• Crypto_map_name = this is the name of the crypto map. It can be any string of characters.
• Crypto_integer = this is an integer which attaches an ipsec connection to the crypto map.
• ACL_To_Site_B = this is an ACL which will exist at site A to connect to site B.
• ACL_Tp_Site_A = this is an ACL which will exist at site B to connect to site A.
• Public_Interface = this is the public interface which the VPN will be connecting through.
• Site_A_Internal_IP_Range = this is the internal ip range at site A. In the config i am assuming a class C.
• Site_B_Internal_IP_Range = this is the internal ip range at site B. In the config i am assuming a class C.

EXAMPLE Side A Crypto isakmp policy 1   encr 3des   authentication pre-share group 2 Crypto isakmp key our_key address Side_B_IP no-xauth crypto ipsec transform-set trans esp-3des esp-sha-hmac Crypto map crypto_map_name crypto_integer ipsec-isakmp set peer Side_B_IP set transform set trans   match address ACL_To_Site_B Interface Public_Interface crypto map crypto_map_name  ip access-list extended ACL_To_Site_B 10 permit ip Site_A_Internal_IP_Range 0.0.0.255 Site_B_Internal_IP_Range 0.0.0.255 EXAMPLE Side B   Crypto isakmp policy 1   encr 3des authentication pre-share   group 2Crypto isakmp key our_key address Side_A_IP no-xauth crypto ipsec transform-set trans esp-3des esp-sha-hmac Crypto map crypto_map_name crypto_integer ipsec-isakmp set peer Side_A_IP   set transform set trans  match address ACL_To_Site_A Interface Public_Interface   crypto map crypto_map_name ip access-list extended ACL_To_Site_A 10 permit ip Site_B_Internal_IP_Range 0.0.0.255Site_A_Internal_IP_Range 0.0.0.255 

In a typical domain service request, where a computer wants to resolve a domain name to an IP address, it works from right to left. Let’s suppose we want to resolve the domain in www.somewhere.com. First, there is an implied dot just to the right of the “last” word, .com. This implied dot is never needed, because the domain name service automatically fills this in for the address. So, our address is really www.somewhere.com.[blank space]. The blank space is the root domain and contained in the root domain (although a private company may have their own private root servers) are the well-known top level domain names, like: .com, .org, or .net. Other top level domain names have been added in recent years, but these three are the most common.

So, we are resolving a domain, www.somewhere.com.[blank space]. We are already in the root ([blank space]) because we are on the Internet. Working from right to left, the next thing we come to is the .com. The Internet knows how to direct to the .com servers from the information it has stored. The .com servers contain information about the “somewhere” domain and lastly, the “somewhere” servers answer queries for the subordinate addresses such as “www” translating the information into an IP Address.

There are thirteen Internet Root Nameservers, six of which are located in the USA and others which are physically anywhere in the globe. Seven of these are distributed using Anycast software. DNS lookups to the root nameservers are relatively rare, since the information is all cached. The Internet Root Nameservers have names with just one letter, from “a” to “m” and all have an IPV4 address. Nine of these servers have an IPV6 address too.