Mesh-Network VoIP Call Capacity Scott Travis and Stan Komsky

Context and Problem The prevalence of 802.11 access points allows for many wireless communication needs, but VoIP suffers when the wireless channel becomes full and QoS cannot be sustained VoIP technology is quickly becoming mainstream. Also, mesh-networks are being employed in areas where traditional networks would be more difficult to implement, such as large metropolitan areas On a wireless network, VoIP call capacity is reduced significantly. Over a mesh-network, this capacity should be reduced even further

Context and Problem Mesh networking allows for continuous connections and reconfiguration as data hops from one node to another until the destination is reached. They have advantages of being low cost, having robust coverage, and having the ability to natural scaling. Mesh Networking uses multi-hop Ad Hoc network which can lower the QoS of VoIP calls. Our project consists of determining the effect of increasing the number of VoIP calls on a 2 hop mesh network. We will determine the VoIP call capacity on this network and compare it to the call capacity of a traditional wireless network.

Work Outline Work Status Preliminary Research Completed Traditional Test Bed Configuration Traditional Test Bed Testing Multi-hop Test Bed Configuration Multi-hop Test Bed Testing Result Analysis Further Multi-hop Testing To Be Done

Router/Wireless Acces Point Work Done Traditional Wireless Test Bed 1 hop VoIP Client 1 VoIP Client 2 Router/Wireless Acces Point Internet

Router/Wireless Access Point Work Done Multi-hop Mesh Network Wireless Test Bed 2 hops VoIP Client 1 Ad-Hoc Laptop Router Router/Wireless Access Point VoIP Client 2 Internet

Work Done Completed in both traditional and multi-hop mesh network testbeds: Connection between machines achieved using SJPhone for Windows iperf used to monitor connection quality In the traditional network, iperf monitored Jitter, packet loss, average bandwidth In the multi-hop mesh network, iperf was only able to reliably test jitter; average bandwidth and packet loss remained the same at 73.6Kb/s and 0%, respectively

Work Done The multi-hop network used a laptop running Linux with two network cards acting as router between the second VoIP client and the wireless access point Used the Linux IPTables “firewall” to intelligently forward packets between the two VoIP clients Wifi_A Wifi_B IPTables

Work Done Wifi_A Wifi_B IPTables Using this setup, VoIP client 2 connected to the Linux laptop using an ad-hoc network, the Linux laptop connected to the AP using the AP’s wireless network, and VoIP client 1 connected to the AP via a standard Cat-5 cable This setup also allows for scalability since any other VoIP clients could connect to the Linux laptop using the same ad-hoc network Also, this setup guarantees the 2 hops we were looking to achieve to test our VoIP call capacity

Results Traditional Network Test Bed Measurements 2 3 4 5 6 Noticeable Calls Avg. Bandwidth Avg. Jitter Avg. Packet Loss 2 73.6K 3.287 ms 0.017% 3 73.5K 5.302 ms 0.009% 4 4.234 ms 0% 5 71.2K 6.037 ms 0.45% 6 68.2K 20.345 ms 6.8% Noticeable QoS Loss Declared Unusable

Results 2 Multi-hop Mesh Network Test Bed Measurements 3 4 5 6 Calls Avg. Bandwidth Avg. Jitter 2 73.6K 1.67 ms 3 73.5K 3.71 ms 4 5.89 ms 5 71.2K 10.77 ms 6 68.2K 16.89 ms Noticeable QoS Loss Declared Unusable

Avg. Jitter Traditional Results Side By Side Comparison Calls Avg. Jitter Traditional Avg. Jitter Multi-hop 2 3.287 ms 1.67 ms 3 5.302 ms 3.71 ms 4 4.234 ms 5.89 ms 5 6.037 ms 10.77 ms 6 20.345 ms 16.89 ms

Results Multi-hop networks, since they travel over multiple wireless hops, lose the QoS needed for a VoIP call at a faster rate The chances of extra traffic across the path is also harder to calculate since there may be several nodes and wireless hops the VoIP packets traverse However, since the multi-hop network may have multiple possible paths between any two destinations, using multi-path routing could increase useable bandwidth and available QoS

Results Traditional Wireless Network Wireless Mesh-Network Pros: Cons: Ease of setup Easier to provide QoS over a single known wireless hop Cons: Scalability Reliability (if the AP goes down, the wireless cannot be used) Wireless Mesh-Network Ease of scalability Reliability (If your AP goes down, there may be others in the area. Or, if an AP along the path goes down, several others may be available to get to your destination) Original setup may be complicated Trying to provide QoS across multiple wireless links can quickly degrade call capacity

Summary/Lessons Learned Increasing the number hops increases the rate at which QoS is lost due to errors and delays in wireless transmissions Multi-hop networks can be easily scaled, but the original setup can be much more complicated than traditional networks VoIP across a wireless link is something that will likely become more widespread in the coming years. However, current technologies do not allow for an adequate number of VoIP calls in either a traditional or multi-hop wireless setup. More research is needed in this area on what exactly is causing the problems and how and where to address these issues.

Future Work Testing could be expanding by comparing QoS with the number of hops in the network, we could also increase the bandwidth per call to see if that changes the results Our multi-hop testbed is only one of several ways to setup a multi-hop network; testing different setups could show if there are differences in available QoS as each setup increases the number of hops