Multi-band Backhaul / AP Dual Radio F.A.Q.

Q1: What is Netkrom NMS?

A: Netkrom NMS stands for Netkrom Network Management System. It is a java client used to configure the MB-ROMB v3with ease and full functionality available.

Q2: Where can I download the NMS?

A: http://www.netkrom.com/supp_drivers.html (Under Windows Utility choose the latest version)

Q3: Where can I download the latest Firmware version for the MB-ROMB v3?

Q4: What is the default IP for the MB-ROMB v3?

A: The Default IP is 192.168.1.3

Q5: What is the Default Password for the MB-ROMB v3?

A: The default password is "admin" (without quotes).

Q6: How many clients can each RF-slot support on the MB-ROMB v3?

A: Each RF-slot of the MB-ROMB v3 can handle 100 simultaneous customers per radio.

Note: while it is possible to have standard users at the max value of 100, Netkrom assumes a setup where the customers are setup with only basic access (email, http)

Q7: What are some reasons why the MB-ROMB v3 is not making a wireless link?

A:

• Check the output power of the MB-ROMB v3 - don’t leave it at default values and test different values. Make sure Diversity is disabled.
• Check the signal from the client as well as going to the client site. Is it an acceptable level? A good signal level can be considered from -75 dBm to -55 dBm and above.
• If your AP is managed by the Netkrom NMS as well, you should check the fade margin of your clients under the Association List Button. A good wireless link have a Fade Margin higher than 20
• Check if you have a clear Fresnel Zone between the AP and the Client

Q8: How am I able to configure the MB-ROMB v3?

A: Available methods to configure the MB-ROMB v3:

Netkrom NMS.
• SSH.

Q9: How do you supply power to the MB-ROMB v3?

A: The MB-ROMB v3 includes an IEEE 802.3af PoE injector - 110/220VAC to 48VDC, 350mA

Q10: Can my MB-ROMB v3 act as a bridge and bridge two networks transparently?

A: Yes, the MB-ROMB v3 can easily bridge two networks. Follow the example below to make your radio work as a bridge.



Notice that Wireless Interfaces (athx) are disabled by default. Remember that in bridge scenarios, the subnet of local network and remote network must match. Notice that after system reboot, the bridge will be the only interface having an IP address

Q11: Can my MB-ROMB v3 act as a router?

A: Yes, the MB-ROMB v3 can act as a router as long as there is not a bridge including all physical interfaces (ethx, athx - enabled). In case you have a radio with the following physical interfaces: eth0, ath0 and ath1. The possible router configuration can be :

Notice that Wireless Interfaces (athx) are disabled by default. Remember that in bridge scenarios, the subnet of local network and remote network must match. Notice that after system reboot, the bridge will be the only interface having an IP


In the above example br0 can be considered as a new physical interface.

The same way as a LAN router works, physical interfaces must be on different subnets; otherwise the MB-ROMB v3 may become unstable.

Q12: How do I configure the Wireless Settings of the MB-ROMB v3?

A: Follow the example below to configure the Wireless settings of the MB-ROMB v3, which is configured in AP mode under IEEE Standard 802.11b/g (2.4 GHz) due to the MiniPCI module (ath0) being configured supports that Frequency Band.


Q13: Can my MB-ROMB v3 be used with encryption?

A: Yes, the MB-ROMB v3 supports WEP 64/128 and WPA, WPA2 with TKIP & AES ciphers.

Q14: Can I run a second Ethernet cable to the second Ethernet port in my MB-ROMB v3 and connect a second device to it?

A: Yes, you can easily run a second Ethernet line to the second Ethernet port and have the data be routed through it (or bridged through from one port to the other).

Q15: What frequency does the MB-ROMB v3 support?

A:The MB-ROMB v3 depending of the MiniPCI module being used can cover the following Frequency Bands:

• IEEE 802.11 b/g Unlicensed Band 2.4 GHz.
• IEEE 802.11 a Unlicensed Band 5 GHz.
• 700 MHz Public Safety Band (760 - 780 MHz)
• 900MHZ Non Line of Sight Unlicensed Band (902 - 928MHz)
• 2.3 to 2.7 GHz MMDS Licensed Band
• 3.4 to 3.6 Ghz Licensed Band
• 3.65GHz Unlicensed Band
• 4.9GHz Public Safety Band
• Special Wideband Range of 4.9 to 6.1GHz

Q16: Does the MB-ROMB v3 support MAC based authentication?

A: Yes, the Netkrom NMS has what is called an "access control list"; this list is what you would use to accomplish the MAC based authentication.

Q17: I can see the link light on the switch from the MB-ROMB v3, but I can’t log in, why?

A: The most likely reason you can’t log into is because your network card isn’t set up on the correct subnet. So you’ll need to change the IP address of your laptop within the same subnet.
e.g. The default IP address of the MB-ROMB v3 is 192.168.1.3 / 24. In order to configure the unit you must configure in your PC an IP address 192.168.1.100 / 24 for instance

Q18: How do you reset the MB-ROMB v3 to default configurations?

A: Please take a look into the following documentation:

Restore to Factory Default Settings Multi-band Backhaul AP Dual Radio

Q19: Will an amplifier improve the speed on my link?

A: It depends on your signal quality and noise. Remember that you can probably get a better link with low output power setting, and a good antenna. Amplifier increases the noise and will only cause problems with the link. The amplifier gets a boost on both the transmitted and received signal.

Thus, in "silent" areas, where you are alone or with very few "noise" or "competition", you might get excellent results. On the other side, in crowded areas, with lots of wireless activity, you will also increase signal received from every other competitor or noise source, which may dramatically lower the overall quality of the link.

Also, take in account the EIRP to see if your link remains in legal limits. You could also get better signal on "11b only" radios, which see most of 802.11g as "noise", thus filtering better the usable signal

Q20: How can I detect RF Interference in my wireless link?

A: The Netkrom NMS through the Site Survey feature can detect the number of APs and the channels being used by them around your Wireless Link. Try using other available and non-overlapping channels.

Q21: What is the recommended separation between two antennas placed in the same tower or pole?

A: The minimum distance recommended is 2 meters. This separation has to be done vertically and horizontally.

Q22: What are possible sources of interference for the radio frequency (RF) link of the MB-ROMB v3?

A: Interference can come from a number of sources, such as:

• 2.4 GHz cordless phones. (In case of 802.11b/g radios).
• Improperly shielded microwave ovens. (In case of 802.11b/g radios).
• Wireless equipment that other companies manufacture
• Electrical motors and the moving metal parts of machinery can also cause interference

RF interference is one of the main causes for poor connection. Interference can be caused by adjacent 802.11 networks or other sources, such as Microwave ovens or cordless phones that operate in the same frequency. Interference caused by adjacent 802.11 networks is of two types:

  • Co-channel interference: When access points, whose coverage area overlaps, are configured in the same channel or channels with overlapping frequencies, it causes connectivity issues for clients in the overlapping coverage area. In order to avoid this issue, either change the channel number to a non-overlapping channel, or move the access point farther away so that their coverage areas do not overlap. For example, in 802.11b/g, network channels 1, 6, and 11 are non-overlapping channels


  • Adjacent Channel interference: When access points are placed too close to each other or use high output power levels, it causes interference, even when the access points are configured on the non-overlapping channels. Decrease the power of the access point to fix this issue.


  • Note: Non-overlapping channels are also called adjacent channels, which explain the name adjacent channel interference.

Use spectrum analyzers to locate interference sources, such as microwave ovens or cordless phones that operate in the 2.4 GHz range, or devices that operate in the 5 GHz range. Remove the interference sources once they are identified. Alternatively, you can change the standard on which your wireless networking operates, for example, from 802.11b/g to 802.11a to avoid interference.

Another important aspect for effective RF communication is signal strength. Poor signal strength leads to intermittent connection. Obstacles, such as walls, metals, absorb and reflect RF energy, which reduces the signal strength. Increase the power to the required level on the access point to provide the adequate coverage. You can also use high gain antennas to extend the range and the signal strength, but ensure that it is FCC approved to operate with the device.

Note: Signal to Noise Ratio (SNR), which is the difference between the signal strength and the RF noise (RF signal or energy from other sources that operates in the same frequency as the wireless network), is a key factor to measure the quality of the link. Higher SNR indicates a good link quality, which results in faster data transfer. A lower value indicates poor quality, which leads to intermittent connectivity or poor performance. Wireless Packet analyzers/site survey software can show you the SNR and throughput at a particular location.

Radio Frequency Interference (RFI) involves the presence of unwanted interfering RF signals that disrupt the original data signals from wireless devices. RFI in a wireless network can lead to adverse effects, for example, intermittent connectivity loss, poor throughput, and low data rates. There are different types of RFI that can occur in a wireless network environment, and you must tale these RFI types into consideration before you implement wireless networks. RFI types include narrowband RFI, all-band RFI, and RFI due to adverse weather conditions.

  • Narrowband RFI—Narrowband signals, depending on the frequency and signal strength, can intermittently interrupt or even disrupt RF signals from a spreadspectrum device, such as a wireless radio. The best way to overcome narrowband RFI is to identify the source of the RF signal. You can use Spectrum analyzers to identify the source of the RF signal.

    Spectrum analyzers are devices that you can use to identify and measure the strength of interfering RF signals. When you identify the source, you can either remove the source to eliminate RFI, or shield the source properly. Narrowband signals do not disrupt original data RF signals (from a wireless radio) across the entire RF band. Therefore, you can also choose an alternate channel for the radio where no narrowband RF interference occurs. For example, if unwanted RF signals disrupt one channel, say channel 11, you can configure the wireless radio to use another channel, say channel 3, where there is no narrowband RFI


  • All-band RFI—As the name suggests, all-band interference involves any unwanted RF signal that interferes with the data RF signal across the entire RF band. All-band RFI can be defined as the interference that covers the whole spectrum that the radio uses. The entire RF band does not point to the ISM band alone. The RF band covers any band of frequencies that the wireless radios use.

    A possible source of all-band interference that you can find commonly is a microwave oven. When all-band interference is present, the best possible solution is to use a different technology, for example, move from 802.11b to 802.11a (which uses the 5Ghz band). Also, the whole spectrum that the radio uses is 83.5 MHz in FHSS (the whole ISM band), while for DSSS it is only 20 MHz (one of the sub-bands). The chances of an interference that covers a range of 20 MHz are greater than the chances of an interference that covers 83.5 MHz. If you cannot change technologies, try to find and eliminate the source of the all-band interference. However, this solution can be difficult, because you have to analyze the entire spectrum to track the source of the interference.


  • RFI Due to Adverse Weather Conditions—Severely adverse weather conditions, for example, extreme wind, fog, or smog can affect the performance of wireless radios, and lead to intermittent connectivity issues. In these situations, you can use a radome to protect an antenna from the environmental effects. Antennas that do not have radome protection are vulnerable to environmental effects, and can cause degradation to the performance of the radios. A common problem that can occur if you do not use the radome is the one due to rain. Raindrops can accumulate on the antenna and affect performance. Radomes also protect an antenna from falling objects, such as ice that falls from an overhead tree.


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