# Time Series Analysis to Predict End-to-End Quality of Wireless Community Networks +
## 3 Experimental Dataset
### Dataset Description  
FunkFeuer [6] is a non-commercial project maintained by computer enthusiasts that installs Wi-Fi antennas across rooftops in several places of Austria that are relatively close to each other (Vienna, Graz, Weiniertel and Bad Ischl). Currently, there are around 2000 wired and wireless links, and every week new antennas are added to the network. FunkFeuer uses a new version of the OLSR routing protocol [49], which expands the capabilities of the original OLSR protocol [50] and makes it highly scalable. The chosen dataset is composed of OLSR information such as routing tables and network topology data, collected during eight days in the period from 28 March to 4 April.  
As stated before, FunkFeuer uses OLSR, a link-state routing protocol. The nodes in an OLSR network periodically exchange routing information to maintain a map of the network topology. The Multi Point Relays (MPRs) are the network nodes selected for propagating the topology information. The use of MPRs reduces the number and size of the messages to be flooded during the routing update process. The key issue is that every node maintains a connectivity map for all the network. Exploiting this OLSR property, FunkFeuer publishes its complete network information from the point of view of a single node (ego-network).  
OLSR, as other routing protocols, needs to propagate link status over the whole network. Data collection on these protocols suffers a delay in this process. Funkfeuer dataset presents a similar behavior in the sense that the dataset is biased and does not represent the real network state, since the time for event propagation throughout the network is not negligible. In other words, the higher is the distance between a node and an event that happens in the network, the later this event will be present in the nodes global view. The largest of the shortest paths in the network (diameter) is 18. This means that there are several paths where packets have to go through a relatively high number of Hops to reach their destination. Figure 1 shows the histogram of distance in hops between network nodes during the period from 28 March to 4 April. If there is a change in the topology at the edge of the network, this change may take 16 hops to fully propagate. If the MPR nodes are configured to propagate topology information every 5 s, the change may take up to 80 s to fully propagate.  
The OLSR protocol uses ETX [34] (ETX is an active-probing link metric, designed for MANETs and widely used in mesh protocols, based on estimating the bidirectional loss ratios of a link) to choose, for each device and packet, the next hop. The ETX value of a link is the number of expected transmissions needed to send a packet over the link and it is calculated as follows: \(ETX=1/(LQ*NLQ)\), where LQ and NLQ stand for the \"Link Quality\" and the \"Neighbor Link Quality\" of that link, respectively. Concerning physical links, the LQ assumed by OLSR is defined as the fraction of successful packets (HELLO) that were received by a node from a given neighbor within a certain time window, while the NLQ is the fraction of successful packets that were received by the neighbor within a time period. Concerning paths, OLSR computes the ETX of a path as the sum of the ETX values of the links that form the path, and chooses the one with minimum ETX value. That is to say, the ultimate decision to be made by OLSR will be about the selected paths; therefore, the final metric value that will be the subject of comparison will relate to the whole path. As a result, prediction of the path ETX will allow more efficient routing decisions in an unstable environment, taking also into account the ego-network measurement effect previously explained. It is important to point out here that LQ as defined by ETX and studied in this work ignores the parameters of transmitted-packets size as well as link transmission rate. Consequently, this work considers that the significant Path Quality parameter is packet loss.