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Application Guide For Mesh AP – MAP-3120 How to optimize the backhaul performance? F/W: 3.1.4
Page 2 of 17 Preface This guide help to configure the MAP-3120 to have the optimal setting from Web The concepts also can apply to MAP-3100 and the previous model MAP-2000/MAP-2100
Page 3 of 17 Topics Network Hypothesis Backhaul Concepts How to check the connections How to maintain the connections
Page 4 of 17 Network Hypothesis Assumes the network is as the topology right-hand side Three Nodes, 1st Floor, 2nd floor 1F: GW253 & Relay252 2F: Relay251 2F 1F 1F 2.4GHz b/g Wireless Coverage 5.8GHz a Wireless Backhaul Link 5.8GHz a Wireless Backhaul Indirect Link Note: Please also refer to MAP3K_AppGuide1 for some more information about this example.
Page 5 of 17 Wireless Ad-Hoc Network Each nodes’ wireless coverage should at least reach one of the Mesh other nodes Line-of-Sight For non Line-of-Sight, there will need to have field test for the signal strength That is, should hear other Mesh nodes! Backhaul Concepts 2F 1F 2.4GHz b/g Wireless Coverage 5.8GHz a Wireless Backhaul Link 5.8GHz a Wireless Backhaul Indirect Link 5.8GHz a Wireless Backhaul wireless coverage
Page 6 of 17 The Backhaul use the same ESSID Channels Security This Backhaul use the same bandwidth IEEE802.11a/g: 54Mbps IEEE802.11b: 11Mbps TurboA/TurboG available automatically only at certain channels Turbo A: channel 42, 50, 58, 152, 160 Turbo G: channel 6 Backhaul Concepts 5.8GHz a Wireless Backhaul Link 5.8GHz a Wireless Backhaul Indirect Link The same Backhaul Ad-Hoc domain
Page 7 of 17 Check the Connections A Good Link is both ends can hear each other clearly instead of one with powerful output power yet weak at listening to its link partner A Good Clear Link is At least RSSI can be at range 30 ~ 50dbm Or receive sensitivity -35 ~-65dbm Or the SOM (System Operation Margin) > 20dbm RSSI below 20dbm or SOM below 10dbm, the link will not stable RSSI above 60dbm, the voice could too loud to hear clearly Note: 1. To check the SOM, please also refer to the URL page: 2. A simple way to convert RSSI to sensitivity is roughly: (RSSI value) - 95 = (Receive Sensitivity)
Page 8 of 17 Check the Connections You can check the connectivity in advanced through the URL link etcalc/wlan_budgetcalc.html
Page 9 of 17 Check the Connections From Web page, click on Status -> Neighboor Example on Gateway 253 Gateway hear itself Gateway hear Relay Too Weak!! Unstable Link. 60 Too Strong!! Too loud to transmit data 48 30~50 OK! Note: This RSSI value could change. It could be changed due to the environment factors, say, other wireless radio frequency in the air or reflections, dust, humidity changes or there could be walking people, objects moving around etc.
Page 10 of 17 Check the Connections Gateway 253 Web page 1F 1F Relay 252 Web page 48dbm Relay 252 Receive Signal Strength Indication Gateway 253 RSSI 45dbm Good Links toward Gateway and Relay Example Reference Table: IEEE802.11a, Channel:160 TX: 20dbm RX: 54Mbps Antenna: 10dbi Space loss: 50m =81dbm; Cable loss 0.3m = 0.1dbm – 0.2 = -51.8dbm > - 67dbm (SOM >16dbm) Ceiling mount, no objects / fence / wall in between
Page 11 of 17 Maintain the Connections Physically Check the angle of the Antenna Both ends Empower the Antenna Could be one end or both ends Check if there is loosen cable/connector that cause cable loss Could be one end or both ends Check if there is objects that cause the space loss Logically Fix the data rate, say, manual set to lower rate to gain more sensitivities One end 1F 1F 48dbm 20dbm Hint: Check the spec. of the antenna. Wrong antenna say, 11g 2.4G antenna can not be applied to 11a frequency and without doubt will get a weak connection. In this example, could need to check GW’s antenna!! Weak Connections
Page 12 of 17 Maintain the Connections Physically Reduce the antenna power Logically Reduce the TX power 1F 1F 60dbm 45dbm Strong Connections
Page 13 of 17 Maintain the Connections The Neighbor Listing All the RSSI are in the range of 30 ~ 50dbm If there are some links too weak, consider to remove it from the list (refer to App Guide 4) Compare both ends Due to backhaul is using the same CSMA/CA domain, to have an optimal performance, make sure both ends’ RSSI is close to each other, say in 10db difference 1F 1F 48dbm 45dbm Good Links toward Gateway and Relay Example Reference Table: IEEE802.11a, Channel:160 TX: 20dbm RX: 54Mbps Antenna: 10dbi Space loss: 50m =81dbm; Cable loss 0.3m = 0.1dbm – 0.2 = -51.8dbm > - 67dbm (SOM >16dbm) Ceiling mount, no objects / fence / wall in between Good Connections 30~ 50dbm A dbm B dbm (A –B) < +/-10
Page 14 of 17 Summary To have the optimized backhaul performance Check the RSSI from Web page -> Status -> Neighbor The RSSI should not exceed 60 The RSSI should not below 20, at least above 30 A fair connection should be in the range 30 ~50dbm The RSSI subtract between one nodes and its link partner should with in 10db, no more then 20db 1F 1F 48dbm 45dbm Good Links toward Gateway and Relay
Page 15 of 17 Summary Overall backhaul bridging throughput 1024byte on this example Tested via IXIA1600, total 128 MAC address
Page 16 of 17 One more Questions Question: IF the three nodes got an average RSSI level to 30dbm, can I still have a good connection? Answer: Yes, if ALL the RSSI level is close to each other (in at least below 10db), the link should be fine. BUT, if one of the node got a strong RSSI or TX power, that raise the RSSI to, say, 50dbm and the other end is 29 (50-29 > 30db), then the performance could be unstable. Suggestions: Please consider to increase the power to make it better, like TX power (from web page) or powerful antenna. Each nodes, in average up to 35 or 40dbm could much more better. Also can consider to fix the data rate to make the link more stable. For example, due to the RSSI is stable in this example, we can set it to fixed 54Mbps. And if the RSSI is not so high, then, can fixed at 24Mbps or 36Mbps.
Page 17 of 17 Appendix Performance Result on this example SNMP Statistic Packet size: 1024byte Simulate 128 nodes / MAC Simulate 25Mbps injects to backhaul from gateway and 12.5Mbps to backhaul from relay 25Mbps 12.5Mbps Castle Rock SNMPc Monitor Point