# Adaptive Multi-Channel Clustering in IEEE 802.11s Wireless Mesh Networks +
## 6 Experimental Validation
### Clustering in Static Topologies
#### 6.2.4 Results for Different Grid Sizes
The only exceptions are JOIN messages sent by CFNs to CHs in phase 4 and CHAN_SEL messages exchanged between CHs in phase 5, where endpoints may be several hops apart. Consequently, TCP traffic share is less determined by the network diameter, but significantly by the total node count and the number of neighbors per node. Regarding UDP traffic, the expected dependence on grid size and CH count was confirmed. In the prototype implementation of CHaChA, UDP is used exclusively for broadcast messages that are propagated throughout the network. As the network diameter increases, the average path length between nodes increases as well, so more forwarding steps are caused by each broadcast. From phase 3 onward, the periodic transmission of CH announcement messages is performed, which contributes significantly to the UDP traffic share. With increasing network diameter, there are potentially more PCH candidates, potentially resulting in more final CHs. For example, between the \(4\times 4\) and \(5\times 5\) grids, there is a rise from two to five CHs, causing a corresponding increase in UDP traffic. For both UDP and TCP, the data size trend corresponds to that of the packet count (see right diagram in Figure 18), including any multi-hop forwarding and TCP control messages. This also accounts for the larger increase in TCP traffic compared to UDP, as TCP generates additional handshake and ACK messages. In the \(5\times 5\)-node grid, TCP data size and packet count amounted to 3-4 times the UDP results. In the topologies studied, the increase in individual packet lengths had only little effect on the total data size. Besides the CHAN_SEL messages in phase 5, carrying the list of CHs involved, the periodic CH broadcast announcements are the only messages with their size depending on the network topology, since they contain the list of CMs in the respective cluster. The average total TCP/UDP data size of 2526 kB, generated for parameterization P2 in the \(5\times 5\) grid over an average clustering duration of 55.6 s, can again be simplified as overhead traffic with an effective data rate of only 360 kbit/s. Basically, a trade-off between clustering duration and communication cost has to be found through parameterization. For a low long-term overhead beyond the phase sequence, the choice of a suitable transmission period for the CH broadcast messages is particularly necessary. At the same time, this should preserve the responsiveness of the dynamic cluster adaptation mechanisms, where decisions are partly based on the information provided by the CH announcements. A general reduction of message sizes could be achieved in the future by a more compact encoding or by means of compression methods. Furthermore, depending on the desired degree of reliability, the use of UDP is also conceivable for unicast messages between neighboring nodes. Figure 18: TCP/UDP overhead traffic data size (left figure) and packet count (right figure) depending on grid size/node count (parameterization P2; data points with standard deviation). Reprinted from ref. [18].