Basic Trouble-Shooting Guide

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Troubleshooting a wireless network can be challenging, especially when one considers the overall complexity of computer networks in general, coupled with the nuances of the nature of RF (radio frequency) applications. Certain problems may be simplistic with obvious cause. In these cases, a simple parameter change may solve the issue. However, it is more often the case that a problem requires a more detailed review and systematic approach to identify the cause and the cure.

Consider that a problem may be related to any one of the following:

• IP / Ethernet Network or computer (at either end of the wireless link)
• Network Application
• Physical interfaces (cables, connectors)
• Poor Installation
• User Error
• Interference

This page will cover three of the most common types of problems reported to our Technical Support Department:

• Problem #1: No TCP/IP access to the radio for management purposes
• Problem #2: Can't establish a wireless link
• Problem #3: Poor throughput or packet loss

Wireless networks are complex, but with proper installation, maintenance, and documentation most problems can be resolved quickly, if avoided all together. Here are some very general guidelines:

• Look for the common causes first
• Make only one change at a time
• Divide and conquer
• Work from the known to the unknown
• If it worked before, look for what might have changed
• Use quantitative tests
• Record everything

There are many tools available in the Trango radios which facilitate troubleshooting. For a complete list of troubleshooting tools, please refer to the Access5830 User Manual and specifically Appendix D for the complete list of Command Line Interface commands.

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Problem #1:

No TCP/IP access to the radio for management purposes

Trango radios offer three IP based management systems: CLI, HTTP, and SNMP. Each interface requires TCP/IP connectivity to the radio.

Consider that Trango radios are classified (according to the OSI networking model) as layer two bridges. They forward all frames between the Ethernet port to the Wireless port, except IP packets with the IP address of the radio itself. That is, if a packet with the IP Address of the radio is received, it is regarded as a management packet. This packet must be one of the following types, ICMP, SNMP, TFTP, Telnet, or HTTP.

Since connecting to the radio requires basic IP connectivity, and IP connectivity across wireless links requires radios to be associated, these are the first things to look at.

Common IP Management Problems

Cause	What to look for
Incorrect IP Stack in radio, or PC.	Is the IP Address, Subnet Mask, and Default Gateway of the Radio compatible with the Management PC, server or router? For example, a PC must be on the same subnet as the radio in order to access it via Telnet or HTTP.
Physical Connectivity	Poor cabling is a very common problem. Try to narrow the search for a cable problem by pinging to some intermediate point in the network. Check all connections. Check cable and connector quality. Use a cable tester to test all cables.
Crossover vs. Straight-Thru cable	Check the following: Straight-thru cable between Jbox and radio Straight-thru cable between jbox and Switch, Hub, or Router Cross-over cable between Jbox and Computer or Server.
SU switch 2	To Access the SU via the AP, wireless link must be UP and Switch 2 in SU must be ON.
AP and SU switch 5	AP and SU switch 5 controls HTTP browser function. If SW 5 is off, the HTTP browser is disabled. If SW 5 is off, you can still access the radio via Telnet.
SU Opmode and SU switch 6	To Access the SU from the Ethernet side, while the SU is operating (in opmode SU), SW 6 must be on. Older versions of firmware (prior to 1.61 for Acces5800 and 1.1 for Access5830) do not include SW 6, thus TCP/IP connectivity is not possible to an SU (from the Ethernet Port) while the SU is in opmode SU. For older versions of firmware, and for SUs with SW 6 off, TCP/IP access is possible to SU only while it is in opmode OFF. If you suspect this is the problem, reboot the SU and Telnet or HTTP into it within 30 seconds while the SU is still in opmode OFF. If you successfully gain access to the radio within 30 seconds, the radio will remain in opmode OFF.
Wrong IP address	If you are not sure of the radio's IP address, you can use the serial port (Access5830) to access the radio. For FOX5800/5300 radios, press the reset button to reset the radio to default factory IP setting 192.168.100.100.
Wrong SNMP Community Strings	If connecting via SNMP management software, confirm the Community String is the same on the radio and in the SNMP management software

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Problem #2:

Can't establish a wireless link

Consider that in order to establish a wireless link, the following minimum criteria must be met:

1. Radios must be receiving adequate signal strength (at least -78 dBm) at each end.
2. BASE ID listed in SU must match with the Base ID listed in the AP.
3. AP's SU database must contain the correct SU ID and MAC addresses of the SU(s) in its subscriber database.
4. Channel and polarization must be set the same in both the AP and SU.
5. SU's opmode must be set to "SU".
6. AP's opmode must set to "AP".

To identify SU's which are not associating either go to the HTTP interface LINK CONTROL page. This page will show the status of currently associated SUs. Any SU which is in "Powered Off" status is not associated. Alternatively, use the su live command on the command line.

The following table lists some common causes of Link issues, and what symptoms to look for.

Some Common Causes of Link Issues

Cause	What to look for, What to do
Physical Connectivity	Something may be disconnected. Try to ping to some intermediate point in the network. Check all connections. Are devices powered up?
SU database in AP contains erroneous SU info.	Review AP's SU database. SU's MAC address and SU ID must be correct in SU database. Double check the MAC address as it is easy to make a mistake.
AP and SU on different channels	Confirm that the AP's Active Channel is present in the SU's channel scan table. It may be useful to turn off the SU's autoscan feature or to remove all frequencies from the scan table other than the AP's current channel.
Inadequate signal strength	Poor signal strength can be caused by a number of factors. Poor Antenna Alignment Low power setting on AP Lack of line-of-sight (Fresnel zone infringement) RFRX Threshold Setting on AP and SU set too low. Target RSSI for powerleveling may be set to low Check and adjust each of these parameters. Performing the SSRSSI command at the SU end will establish the signal strength being received by each radio. An RSSI less than -78 dBm is considered too marginal for a reliable link. To check the RSSI from SU at the AP, use telnet su ping <su id> command. To check the RSSI from AP at th SU, use apsearch <seconds> <channel> <polarization> To align antenna, use Type command ssrssi <channel> <polarization> command and move antenna until optimal signal strength is received.
AP and/or SU not in appropriate opmode.	AP must be in opmode AP to be transmitting SU must be in opmode SU to be transmitting Remember that if you Telnet or HTTP into a radio within 30 seconds of booting up you will stop the radio's normal process of progressing to its default opmode.
AP and SU on different Base ID	Ensure that the Base ID in SU match that of AP. The Base ID is the key parameter used by the SU in the association process. If the Base ID in the SU does not match the base ID in the AP, the radios will not associate.

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Problem # 3:

Poor throughput or packet loss

Performance issues, often called "packet loss" or "dropped packet" problems result in degredated throughput, and occasionally dropped links. Poor throughput is often a sign of packet loss, which can occur either over the air or on the wired Ethernet portion of the network.

Normal Throughput, or Bandwidth

The Access5830 Access Point will deliver sustained throughput of 10 Mbps as measured by various FTP programs and Smartbits™. More typical results, due to varying packet sizes, various packet headers, and other variables will yield test test results in the 8.5 - 9.2 Mbps range. As more subscriber units are added to a the Trango Point to Multipoint (PMP) system, they will share the aggregate throughput of the AP thus affecting the throughput to any one SU. In order to determine if a specific SU is exhibiting a throughput problem, it is necessary to consider the number of SUs associated with the AP, and the traffic demands of all the SUs.

When trouble-shooting performance issues it is important to consider whether the packet-loss is occurring over-the-air (RF packetloss) or on he Ethernet portion of the network.

Over the Air packet loss can be caused by:

• Inadequate Signal Strength at either end
• RF Interference from another device
• Multipath interference created by bounced signals

Packet loss can occur in the radio if:

• The radio is not properly grounded
• There is Poor Power to radio
• The antenna cableis damaged
• The radio is damaged

Packet loss can occur on the Ethernet portion of the network if there is:

• Slow or Bad Network Equipment
• Bad Cabling
• Bad RJ45 Connectors
• Ungrounded equipment

Over-the-air packet loss

To check the quality of the wireless link, perform the following steps.

1. Calculate expected RSSI and fade margin at each end of link
2. Check Signal Strength (RSSI) at each end of the link. Record results. Compare to calculated values.
3. Perform RF Loopback test (su testrflink <su id>).
4. On Access5830 v1.1 firmware perform linktest <su id>
5. Record results

Some common causes of Performance Problem / Packet loss

Cause	What to look for / What to do
Inadequate Signal Strength	Perform Link Budget Calculation to determine expected RSSI reading at each end based on radios and antennas and distance.
	Does the actual RSSI match or approximate the calculated RSSI?
	Does the calculated link allow sufficient fade margin?
	Is there unobstructed Line-of-Site between the AP and SU?
	Is the Fresnel zone clear?
	Are the antennas optimally aligned?
	During the antenna alignment process, did you consider down-tilting and up-tilting, as well as right-to-left alignment for both the AP and SU? Up and down tilt of the AP is an often overlooked consideration.
	Was the link working before? Did the antenna move due to wind or other forces?
	Is the SU outside, or on the fringe of the AP's 60° service area
	Check the AP's output power. Is the AP set at MAX TX power?
	What is the target RSSI at AP from SU? This target must be higher than the RFRX Threshold setting.
RF Interference	Perform a Site Survey at each end of the link. Perform the survey at different times of the day and for extended periods. Are you using a noisy channel / Polarization? If so, this is very likely the cause of the packet loss.
	If there is interference present, try a clear channel and/or antenna polarization. Keep in mind that you are not limited to the radio's default channel. You can create your own channels in single MHz increments anywhere within the band.
	Utilize the radio's RFRXThreshold feature. This feature will blockout signals below the threshold. For example, if your channel is showing interference at -78 dBM, set the RFRX Threshold to block signals below -75 dBm. Although this will reduce the range of the radio, the feature will effectively block the interference.
	Try moving the radio away from the interference source. Sometimes moving the radio a few feet will help.
	For interference from the sides and rear, shield the radio with metal and/or RF absorbent material.
	Channel Planning. Is Interference coming from an adjacent sector or adjacent cell-site? If so, refer to our Access5830 Colocation Application Note.
	Do not over extend power or PoE cables. Use a UPS, or minimally a surge. Did you check the DC power going into the Jbox?
Multipath Interference	On very short links (less than ½ mile) it is sometimes possible to cause packet loss due to bounced or multipath signals. If multipath is suspected, is is very possible that switching the antennas' polarity (from V to H, or H to V) will solve the problem. For very close range installations turn down the AP's TX power to the minimum possible to achieve a working link. This will reduce the multipath problem.
Radio Grounding	Are your radios properly grounded? Poor / or non-existant grounding has been known to cause performance problems. Ground shield of Ethernet cable prior to entering building. Ground radios from lug bolt marked GND.
Damage to Radio and/Cables	Look for visible damage to the radio. Does Jbox light up when radio is plugged in? If you suspect a bad radio, perform a bench test with another known good radio. If problem persists, contact Technical Support.
Damage to RF Cables	Carefully inspect the RFcable and SMA connectors on SU's with external antennas.
Incorrect Settings	Double Check everything, but specifically on the radio check RFRXTHRESHOLD, TX POWER, POLARIZATION
Slow Network Gear	Connect radios to 100 Mbps Full-Duplex devices
MIR Setting	If throughput to a specific SU is lower than expected it may be useful to check the MIR (Maximum Information Rate) setting.
Ethernet Cabling	Did you check the cable and connector with a Cable Tester? Ethernet cabling must be outdoor-rated, shielded, and <300 feet inclusive of run from radio to Jbox and from Jbox to network or computer. Do not splice cables. Incorrect wiring can cause performance problems.