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Technical Guide For Mesh AP – MAP-3120 What’s the difference between Mesh Bridge and AP WDS Bridge?
Page 2 of 14 Preface This guide shows the difference between AP bridge modes (AP + WDS mode) to MAP-3120 A standard AP only get two interfaces, LAN and WLAN, the two interfaces comes into a 2-port like switch With AP+WDS support, it provides a easy yet cost-effective way to expand the wireless coverage, being an AP and a Bridge But, there are something need to know at this mode, the limitations and what Mesh can help
Page 3 of 14 Topics What a Bridged AP do The facts & limitation How the MAP-3120 helps for this Summary
Page 4 of 14 Wireless AP in Bridge Mode Assumes the network is as the topology Two WAP-4033 configured as AP + WDS mode By now, only one mobile user WDS Bridge Link Mobile User The situation are: If only one WAP-4033 AP existed in the network. The Mobile Uses can get a true 54Mbps Wireless connection. Since the Wireless packet is just one hop. That is data packet send to AP. (Wireless) AP make the bridge to the Server. 54Mbps for 1 user. Now, add a new AP: If the mobile user still attached to the same AP, then it is still one hop. However, when this user moved to the second AP and attached, then the result will be changed. The same data packets will existed in this blue Wireless coverage twice. Since the AP#2 repeat the packet again back to AP#1. Two hops now. The bandwidth will be 27Mbps left (54 / 2 hop) for one user.
Page 5 of 14 The Fact – 1/2 WDS expand the Coverage But, Hopping reduce the performance Those wireless users attached in AP#2 (say, 3 users) without doubt, the bandwidth is cut due to the hopping WDS Bridge Link Mobile User Other Fact: AP#2, though all the Wireless setting is the same Yet, this wireless coverage is a reduced performance area. All the users in this blue wireless coverage need to sacrifice the bandwidth due to the same packet need to go into this 54Mbps wireless pool to compete again. AP#2 The performance with more users: So, actually, the average performance will like this: Users in AP#1 coverage = 54Mbps / (Users attached to AP#1 + 1 ) Users attached to AP#2, then share the left bandwidth. In this example, User in AP#1 get 13.5 Mbps (54 / 4) User in AP#2 get 3.3 Mbps (13.5 / 4)
Page 6 of 14 The Fact – 2/2 The performance result, is that true? Yes. But, could be worse. Because actually, the whole blue cycle is in the same CSMA/CA domain that share same 54Mbps. In a CSMA/CA network, the network efficiency could vary on the wireless physical and logical factors Be reminded, 54Mbps is in theory, the real DATA throughput is lower to this theory bandwidth WDS Bridge Link Mobile User The factors: It can be: The transmit power of each AP or users The channel conflicts (or interference) of the wireless network The real application of the users, WWW / FTP data packets or small voice packets Some others …. Please also refer to the previous Application guide for some ideas of this Hint: Now, we knows, WDS bridging (hopping) will effect the overall performance just because of a standard AP is with ONE antenna as the AP and bridging at the same time. 3.3Mbps!! We are in the same Wireless coverage, why there is such a result for me to the file server?! What’s more: In our example, we just assume two hopping. How about multiple hopping! We will discuss it in Application Guide 7. Well, 13.3Mbps in theory. It is not so acceptable yet, it fair.
Page 7 of 14 How MAP-3120 help this? Now, we replace the AP to MAP- 3120, Layer 2 Mesh AP With dual RF interface, AP#2 can still keep its bandwidth a 5G or b/g 2.4GHz as the 54Mbps Backhaul AP#1 keep its 54Mbps for its coverage AP#2 keep its 54Mbps for its coverage Mobile users can walk around with the same setting WDS Bridge Link Mobile User Backhaul Connection 50Mbps MAP-3120
Page 8 of 14 Wireless AP Bridge Again Assumes the network is changed as the topology Now, Three WAP-4033 configured as AP + WDS mode Each cell is with three mobile Users All the users access the file server and let’s see the result again WDS Bridge Link Mobile User WDS Bridge Link Simple Calculate: The average bandwidth for those 9 users are 54Mbps / (9 users + 3 APs) = 4.5Mbps In the view of bridge: The average bandwidth for AP# 1 users is: 54Mbps / 5 = 11Mbps The average bandwidth fro AP# 2, AP#3 is: 11Mbps / 4 = 2.75Mbps AP#2AP#3
Page 9 of 14 AP changed to MAP-3120 Assumes MAP-3120 is applied again Now, Three MAP-3120 is applied to replace WAP-4033 The average bandwidth for AP#2 and AP#3 now is stable 6Mbps (6Mbps v.s. 2.7Mbps) WDS Bridge Link Mobile User WDS Bridge Link Simple Calculate: Average Backhaul bandwidth: 54Mpbs / 3 Mesh AP = 18Mbps Average Node bandwidth: 18Mbps / 3 Users = 6Mbps Why it is more stable: 1.In the view of Backhaul Connection, only three nodes share the 54Mbps, less competition and interference factor then bridge mode 2.At the mean time, each AP node utilize its own 54Mbps coverage, also less interference and competition Backhaul 54Mbps 18Mbps 6Mbps
Page 10 of 14 Summary – 1/3 As the two examples above, Mesh AP all get better performance to single RF Access Point and also provides the same mobility Due to the native limitation, single RF AP may be a cost effective solution for wireless coverage expanding, yet it increase performance issues and also management issues With dual RF interfaces, Mesh AP – MAP-3120 provides a stable, manageable wireless coverage than single RF Access Point
Page 11 of 14 Summary – 2/3 Mesh AP - MAP-3120AP + WDS bridge Easy Install YES, can be plug and playNO, need to key in Bridge MAC address one by one and maintain it Easy Management YES, with NMS, that can help to monitor node status and wireless client status NO, traditional AP do not support central management for the whole Wireless coverage Better Performance YES, better to AP/Bridge. Each Mesh AP have its own SSID where just share the same backhaul bandwidth NO, all AP nodes and clients using same SSID (same collision domain), same Wireless Channel and shared bandwidth Better Security YES. Backhaul have its security, yet each node can also have its own security setting NO, all AP nodes and clients using same encryption QoS YES. VLAN supports that connected switch can priority the packets NO. Only one SSID, can not add-on VLAN and priority setting The comparison toward AP+WDS bridge and MAP-3120
Page 12 of 14 Summary – 3/3 Bandwidth Table - Mesh AP to WDS AP If we make sample on 4 APs, 20 users per nodes The average bandwidth will as like below, 670Kbps v.s. 110Kbps The average performance drops as the number of users grows yet Mesh should much better to WDS AP
Page 14 of 14 Appendix For more about VLAN, please refer to App Guide 6. For more about NMS management, please refer to App Guide 3