Nicolas Montavont

Alberto Blanc

Renzo Navas

Tanguy Kerdoncuff

Handover Triggering in IEEE 802.11 Networks

The current and future IEEE 802.11 deployment could potentially offer wireless Internet connectivity to mobile users. The limited AP radio coverage forces mobile devices to perform frequent handovers while current operating systems lack efficient mechanisms to manage AP transition. Thus we propose an anticipationbased handover solution that uses a Kalman filter to predict the short term evolution of the received power. This mechanism allows a mobile device to proactively start scanning and executing a handover as soon as better APs are available. We implement our mechanism in Android and we show that our solution provides a better wireless connection.

I. INTRODUCTION

Due to the proliferation of Wifi hot-spots and community networks, we have recently observed a great evolution of IEEE 802.11 networks especially in urban scenarios. These 802.11-based networks allow mobile users to get connected to the Internet, providing a high throughput but a limited mobility due to the short coverage area of access points (APs). In our previous work [START_REF] Castignani | Wi2Me: A Mobile Sensing Platform for Wireless Heterogeneous Networks[END_REF] we have shown that community networks appear to be highly dense in urban areas, generally providing several APs (15 in median) per scanning spot. Under this condition, a mobile user may be able to connect to community networks and compensate the low AP coverage area by transiting between APs. We call such AP transition a handover. However, two main issues currently limit mobile users from using community networks in such a mobility-aware scenario. First, operators have not deployed the necessary infrastructure to allow mobile users to perform handovers without being disconnected at the application layer, i.e., after a handover on-going application flows are interrupted. This limitation may be addressed by deploying a Mobile IP [START_REF] Perkins | IP Mobility Support for IPv4[END_REF] infrastructure, in which the application flows may be tunnelled through a Home Agent that belongs to the operator. Second, independently from the first issue, there is still a lack of mechanism to intelligently manage a layer 2 handover between two APs. In current mobile devices, when a handover occurs, we observe a degradation of on-going flows corresponding to a dramatic reduction of the TCP congestion window (CWND) and of the throughput. In this paper, we focus on this latter issue by analyzing the impact of layer 2 handovers on mobile users. We propose Kalman-filter-based HAndover Trigger algorithm (KHAT) that succeeds in intelligently triggering handovers and reducing the scanning impact on the mobile device. We propose a complete implementation of our handover mechanism in Android ICS (4.0) and show a comparative study to show that our approach outperforms the handover mechanism that is currently implemented on these devices.

The paper is organized as follows. Section II presents the litterature on handover optimization and Section III analyzes the handover impact on on-going communications. Section IV introduces KHAT which is evaluated indoor and outdoor in Section V. Section VI concludes the paper.

II. HANDOVER PROCESS AND RELATED WORK

The IEEE 802.11 standard defines a handover as a three steps process: scanning, authentication and association. The standard proposes two different scanning algorithms namely passive and active scanning. In passive scanning, the mobile station (MS) simply tunes its radio on each channel and listens for periodic beacons sent by the APs. In active scanning, the MS proactively sends requests in each channel and waits for responses during a pre-defined timer.

Once candidate APs have been found, the MS selects one of the APs and attempts authentication and association. If the association is successful, the MS can send and receive data through the new AP, if this new AP is on the same IP subnet as the previous AP. If the new AP belongs to another IP subnet, the MS needs additional processing to update its IP address and redirect data flows to its new point of attachment. Such Layer 3 handover may be handled by specific protocols like Mobile IP [START_REF] Perkins | IP Mobility Support for IPv4[END_REF]. Note that in this paper we do not address IP mobility and any layer 3 mobility management protocol can be use on top of our proposal if needed.

In 2012, the IEEE has published new amendments for IEEE 802.11 handover optimization, aimed at reducing its duration and its impact on higher layers. The IEEE 802.11k amendment proposes mechanisms for radio resource measurement for seamless AP transition, including measurement reports of signal strength (RSSI) and load of nearby APs. Additionally, the IEEE 802.11r amendment contains a Fast Basic Service Set Transition (FT), which avoids exchanging 802.1X authentication signaling under special conditions by caching authentication data.

While these features may enhance the handover performance, they heavily rely on a cooperation between APs, which might not always be a viable solution. In addition, users may access various networks operated by different providers. In that case, operators should share network information and performance among them, which is quite an unlikely scenario. In this paper, we focus on MS-based solutions, where the MS itself handles the handover without the help from the network. Several works have been proposed in the literature so far. In general, those studies cover different aspects of the handover mechanism. We may group them into three main categories:

• Handover triggering: when to decide that a disconnection with the current AP will occur.

• AP discovery: how to search for APs on different channels by minimizing the impact on the higher layers.

• Best AP selection: with which AP to associate, among the discovered ones.

The simplest mechanism to trigger a handover is to monitor the RSSI as an estimation of the link quality and start the handover process if the current RSSI is lower than a pre-established threshold (commonly set at -80 dBm). Fig. 1a shows the relationship between the RSSI measured on an MS and the TCP throughput that we have gathered during more than 600 connections to community networks in a urban area in Rennes, France [START_REF] Castignani | Wi2Me: A Mobile Sensing Platform for Wireless Heterogeneous Networks[END_REF]. We observe that the TCP throughput is extremely variable for high RSSI, but starts degrading for RSSI lower than -70 dBm, and it becomes significantly low around -80, dBm. Some works focus on the anticipation of the handover triggering in order to minimize the impact on ongoing communications. Mhatre et al. [START_REF] Mhatre | Using smart triggers for improved user performance in 802.11 wireless networks[END_REF] propose a set of handover algorithms based on continuously monitoring the wireless link, i.e., listening to beacons from the current and neighboring channels. These approaches give handover latencies varying between 150 and 800 ms. However, since these approaches need to listen to beacons from neighboring channels, it is necessary to modify the firmware of the wireless card, which may not always be possible. Yoo et al. [START_REF] Yoo | LMS predictive link triggering for seamless handovers in heterogeneous wireless networks[END_REF] propose a number of handover triggering mechanisms based on predicting RSSI samples at a given future time using Least Mean Square (LMS) linear estimation. In this algorithm, the device continuously monitors the RSSI and computes the LMS prediction if the RSSI is below a certain threshold (P Pred ). Then, if the predicted RSSI value is lower than a second threshold, P Min , the MS starts a handover. Wu et al. [START_REF] Wu | Proactive scan: Fast handoff with smart triggers for 802.11 wireless LAN[END_REF] propose a handover mechanism aiming at decoupling the AP discovery phase from the AP selection and reconnection phase. The MS alternates between scanning phases and a (normal) data mode where the MS is connected to its current AP. The time interval between two scanning phases is adapted depending on the current signal level and varies between 100 and 300 ms. In each scanning phase, the sequence of channels to scan is selected based on a priority list that is built based on the results of a periodic full scanning (i.e., here all channels are scanned).

As far as Android devices are concerned, Silva et al. [START_REF] Silva | Enabling heterogeneous mobility in android devices[END_REF] present a mobility management solution based on IEEE 802.21. They propose a mapping of IEEE 802.21 primitives for handover initiation, preparation, execution and completion to existent Android OS methods and functions.

III. HANDOVER IMPACT

During an L2 handover, the MS is not able to send or receive application flows. This is because, usually, when a MS triggers a handover, the link quality does not allow exchanging frames anymore, and because the MS is often switching operating channel. In this section we evaluate the handover and scanning impact on application flows, and determine which parameters influence the scanning latency and success rate. This testbed consists of nine Cisco Aironet 1040 APs installed in the roof of our building at the locations given in Fig. 2. All APs are connected to a dedicated wired LAN. APs broadcast a single SSID, corresponding to an open-system authentication network belonging to a single IP subnet. We also use a dedicated (fixed) server for traffic generation and tracing. iPerf is used to generate TCP downlink traffic to the MS. For each experiment, we walk from AP 1 to AP 6 and then back again to AP 1 .

A. Operating Systems Benchmark

To illustrate how the handover is currently impacting data flows, we have performed a set of experiments to evaluate the degradation of TCP performance for different devices and Operating Systems (OS). Table I shows the number of handovers and the average TCP As a baseline, we also show the maximum achieved throughput for each device remaining static and connected to a single AP. Using Windows, we observe the best result, since the MS performs up to four handovers, reaching an average throughput of 0.875 M B/s. Additionally we observe that for Windows, the time in which no data is downloaded (i.e., the disconnected time) is relatively short compared to the other OSs. The netbook running Ubuntu reacts slowly to changing channel conditions: in this case the MS is disconnected for more than 20 s and executes only two handovers, indicating that the MS waits until the quality of the radio link is significantly degraded. Fig. 1b shows the evolution of the downloaded data for each case. Additionally, we have observed that for the Windows device, the average round-trip time (RTT) is the lowest one (103 ms) having also a low standard deviation. This differs from the other devices that reach larger RTT values.

B. Scanning Interactions with Data Traffic

We focus on active scanning where an MS sends Probe Requests on each channel to discover potential APs, instead of just waiting for periodic beacons (passive scanning). We chose active scanning because it allows spending less time in each channel to determine the AP availability. If the handover phases are done one after the other, all packets that arrive during the handover process will be lost. In order to reduce the impact of handovers on applications flows, it is possible to introduce a gap between the scanning phase and the other handover steps, i.e., the decision to handover, the authentication and the association, as presented in [START_REF] Wu | Proactive scan: Fast handoff with smart triggers for 802.11 wireless LAN[END_REF]. An MS may use the power saving mode defined in IEEE 802.11 to request its current AP to buffer incoming packets during the time the MS scans other channels. This way, instead of loosing packets during the scanning phase, an MS can receive the packets after the scanning phase, albeit with an extra delay. This behavior is illustrated in Fig. 1c, where we plot the sequence number of the received packets of a TCP flow when an MS is performing one scan of the 13 channels with an active timer set at 50 ms. We can see that the scan is starting just before the time 1 s, at which no more data packets are received from the server. Once the scan is finished, around 850 ms after, the MS comes back to its current AP, and starts receiving TCP packets again.

This technique can also be used to split a scanning phase into several sub-phases where only a subset of channels are scanned. For example, to scan the 13 channels, an MS could sequentially scan three times a subset of 4 (or 5) channels each time, interleaving these sub-phases with the data mode with the current AP to retrieve data packets. The impact of the number of scanned channels, and the timers used in each channel is given in the next subsection.

C. Scanning Parameters

We analyze the scanning performance under different values of timers used to wait for Probe Responses (from 5 ms to 100 ms) and different number of scanned channels during a sub-phase (between 1 and 13). In the standard IEEE 802.11 scanning algorithm, the MS is supposed to scan each channel using two timers We ran 60 scanning sub-phases for each AT and subset of scanned channels and measured the average number of discovered APs, the RSSI distribution of the discovered APs and the average duration of the scanning (i.e., the scanning latency). Results are presented in Table II. As a baseline, we consider that all the available APs are discovered when scanning the full channel sequence (i.e., 13 channels) using AT=100 ms. In the other cases, the MS discovers only a fraction of the APs, since it either does not wait long enough to receive all AP Probe Responses, or because only a subset of channels are scanned.

We have also observed that when using a short AT, even if the MS discovers a low number of APs, those APs have a high RSSI. On the other hand, when using higher AT values, the MS discovers more APs but a large part of them have a low RSSI. This can be observed in Fig. 3a, where we see that for AT=5 ms the average RSSI of candidate APs is -67 dBm, while for AT=20 ms, this decreases up to -76 dBm.

IV. KHAT: PROACTIVE HANDOVER ALGORITHM

We propose a handover algorithm called Kalman Filter-based HAndover Triggering (KHAT for short) that provides link going down detection, optmized scanning strategy, and new AP selection. An MS monitors its link quality with its current AP, and when the signal strength is degrading, it starts alternating between scan periods and data communication with the current AP. The scan periodicity and the timer values are determined according to the current link quality and whether a candidate AP has already been found. Once the candidate AP becomes better than the current AP, the handover is triggered.

A. RSSI modelling

One way of keeping track of the changing radio condition is to track the RSSI on the MS. While far from being perfect, the RSSI has the advantage of being always available, whether the MS is exchanging data or not, as it is updated not only whenever the MS receives data frames but also when it receives beacon frames, which are typically sent every 100 ms by most APs. As the RSSI can fluctuate rapidly, especially when a user is moving, its instantaneous value is not necessarily representative. At the same time, its local average and trend are more useful in deciding whether the radio channel conditions are improving or not and whether they are reaching the point where communication is no longer possible. Using the well known Kalman filter, it is possible to extract this information from the RSSI measurements. Many authors have already use Kalman filter and other time series techniques in order to model radio channels and the received signal strength, see, for example, the works by Jiang et al. [START_REF] Jiang | Kalman filtering for power estimation in mobile communications[END_REF], by Baddour et al. [START_REF] Baddour | Autoregressive modeling for fading channel simulation[END_REF] and references therein.

More formally, let X(t i )

X i be the received signal strength at time t i . In our case, we sample the RSSI roughly every 100 ms; but, as we rely on software timers, there are no guarantees that the t i 's will be equally spaced. Figure 3b shows the empirical distribution of ∆t i = t i -t i-1 for a subset of the traces we collected. The average is 96 ms and the standard deviation is 8.2 ms. Given that roughly 90% of the samples are within less than 100 ms of each other, it seems reasonable to "re-sample" the time series with a time-step of 100 ms.

In all the traces we have collected, it is often the case that several consecutive samples have the same value, indicating that the received signal strength is often constant during periods that are longer than the average distance between samples. The presence of several samples with exactly the same value is an obstacle when one is trying to estimate the local trend of a signal as, in this case, the estimated slope would be exactly 0. The Kalman filter does not perform well in these circumstances. As we rely on the values reported by the 802.11 driver, we wondered whether these consecutive samples with the same values were caused by the driver q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q -100 -90 -80 -70 -60 -50 -40 ∆t /ms CDF q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q qq q q qq q q q q (b) Sampling interval CDF for the original time series Constant Period Length/ms CDF q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q qq q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q qq q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q qq q q q q q q qq q q q q q q qq q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q qq q q q q q q q q q q q q q q q q qq q qq q q q q qq q q q q q q q q q q q q qq q q q q q q q q qq q q q q q q q q q q qq q q q q q q q qqq q (c) The CDF of the length of the periods where all the received power samples are equal for the community networks Fig. 3: RSSI analysis not updating the values often enough. Figure 3c shows the distribution of the length of the periods where the signal strength was constant for several traces collected using a static MS which was not sending or receiving data (note that the distribution was the same whether the test was performed using a laptop running Linux or a smartphone running Android). The median is 305 ms and the standard deviation is 306 ms. In the case of mobile MSs and/or data traffic the median values are smaller (around 110 ms for MS with data traffic, but the standard deviation is always larger). In order to mitigate the effect of these periods, we pre-process the RSSI samples, using a time-varying exponential average, before applying the Kalman filter. In order to further reduce the lag of the smoothed signal, we use a time-varying weight in the exponential smoothing.

Let Y i be the re-sampled RSSI time series. We construct the smoothed series Z i as:

Z i = α i Y i + (1 -α i )Z i-1
where Z 1 = Y 1 and α i = α up if the RSSI is increasing, instead whenever the RSSI starts decreasing α i = α 1 . Whenever the RSSI is constant the value of α i is determined by the last change before the beginning of the constant samples. If the last change was an increase α i = α up , otherwise α i = min(0.8 • α i-1 , α min ). This corresponds to the pseudo-code in Algorithm 1.

We have used α up = 0.5, so that the smoothed time series will react quickly to upward changes, α 1 = 0.4 and α min = 0.01 so that it will, instead, react much more slowly to downward changes. The reason of this asymmetric behavior is that we are interested in having an accurate estimate of the level and, above all, of the trend, only when the signal is decreasing. By using a larger α i when the signal is increasing we assure that Z will quickly reach the value of Y reducing the lag between Y and Z. We have verified that the received power times series of our sample are indeed non-stationary by computing their autocorrelation functions, which were all slowly decreasing (as a function of the lag). We have then decided to use a state-space based model to represent the evolution of the power over time. In particular we have used the local linear trend model (see, for example, Durbin and Koopman [START_REF] Durbin | Time series analysis by state space methods, ser. Oxford statistical science series[END_REF]):

Z i = µ i + ε i ε i ∼ N (0, σ 2 ε ) µ i+1 = µ i + ν i + ξ i ξ i ∼ N (0, σ 2 ξ ) (1) ν i+1 = ν i + ζ i ζ i ∼ N (0, σ 2 ζ )
where Z i is the time series under scrutiny, µ i is the level at time i, ν i is the slope at time i and ε i , ξ i , ζ i are independent identically distributed (i.i.d.) Gaussian random variables with 0 mean and variance σ 2 ε , σ 2 ξ , σ 2 ζ respectively. These variances can be obtained by Maximum Likelihood Estimation from sample realizations of Z.

Once the values for the variances are specified, and given a realization of Z i (i = 0, . . . , n), one can use the well known Kalman filter algorithm to compute µ i and ν i for any value of i (again, see, for example, Durbin and Koopman [START_REF] Durbin | Time series analysis by state space methods, ser. Oxford statistical science series[END_REF]). To be more precise, one can solve the "filtering" problem, where the values of µ i and ν i are computed using the samples Z 0 , Z 1 , . . . , Z i . At first, we have used the dlm [10] R [START_REF]R: A Language and Environment for Statistical Computing[END_REF] package to solve the filtering problem. Note that, as the filtering problem uses only the samples between 0 and i, it can be implemented in real time as it depends only on past values of the time series. The Kalman filter can also be used to predict future values. In the case of the local linear trend model ( 1), the prediction algorithm is extremely simple: one can just model the future values of the time series using a straight line with slope ν i , starting at the value µ i at time i.

We have also implemented the Kalman filter on a Samsung Nexus S smartphone, in the WiFiStateMachine module of the Android Java framework. For the sake of simplicity we have used a straightforward implementation of the Kalman recursion. The general form of the Kalman filter is:

Z i = F Θ i + v v i ∼ N n (0, V i ) Θ i = GΘ i-1 + w i w i ∼ N m (0, W i )
For the local linear trend model Z is a scalar, and so is v, while:

Θ i = µ i ν i , G = 1 1 0 1 , W = σ 2 ξ 0 0 σ 2 ζ , F = (1 0) . We are interested in computing the 2 × 2 vector m i = (E[µ i ] E[β i ]) T ,
containing the expected values of the level (µ i ) and slope (ν i ). It is known [START_REF] Durbin | Time series analysis by state space methods, ser. Oxford statistical science series[END_REF] that one can compute these values using the following equations:

m i = a i + R i F T i Q -1 i e i f i = F i a i C i = R i -R i F T i Q -1 i F i R i Q t = F i R i F T i + V i a i = G i m i-1 R i = G i C i-1 G T i + W i where e i = Y i -f i ,

and the following initial values:

C 0 = σ 2 1 0 0 σ 2 2
, m 0 = (Z 0 0) T are used for C and m. The values of σ 2 1 and σ 2 2 have almost no influence on the computations as the matrices R, F, T, C quickly converge to steady state values which are independent from the initial values.

The local linear trend model 1 is characterized by three parameters:

σ 2 ε , σ 2 ξ , σ 2 ζ .
It is possible to use Maximum Likelihood Estimation (MLE) methods to estimate the values of these parameters from sample realizations of Z. We have used the MLE functions of the dlm package to this end, but in some cases the optimization algorithm used to compute the MLE did not converge. When it converged its estimations for σ 2 ε and σ 2

ζ where not always consistent over all the samples but the order of magnitude was fairly consistent, with σ 2 ε usually smaller than σ 2

ζ and with σ 2 ε often fairly close to 0. It should be stressed that, in this case, there are no guarantees about the convexity of the optimization problem solved by the MLE procedure, which can very well converge to a local minimum instead of a global one. Also it is not uncommon to tune the model parameters in order to improve its performances. In our case we have observed that using σ 2 ε = 0.5, σ 2 ξ = 1 and σ 2 ζ = 2.5, we obtain fairly smooth level and slope values, which can be effectively used by the KHAT algorithm.

B. Algorithm design

KHAT adapts the scanning strategy, the scanning period and the handover trigger by comparing an estimate of the link quality and the quality of candidate AP as presented in Fig. 4. The main process consists in continuously monitoring the RSSI of the current link and detect a link going down event. To achieve this, we use the Kalman filter to obtain the current value of the RSSI (µ) and the slope (ν). After analyzing a large number of RSSI time series, we have estimated that the link going down trigger can be declared if µ < -70 dBm and ν < -0.2 dBm/s. If the link going down condition is satisfied, the MS check on its candidate AP list. If there is not a valid candidate AP, the MS will attempt scanning only if there has not been another scanning instance for the last T Scan seconds. On the other hand, if after triggering a link going down condition, the MS has a valid candidate it will attempt a handover only if the difference between the candidate AP RSSI and the current exponentially smoothed RSSI sample (µ) is greater than ∆, where ∆ is defined as follows:

∆ =          8 , if µ > -70 5 , if -70 ≤ µ < -75 3 , if -75 ≤ µ < -80 2 , if µ ≤ -80. (2)
After a scan completes, an existing candidate AP would be updated with a new RSSI, or a new candidate may be selected. Additionally, in order to avoid The scanning strategy itself is also adapted depending on the current link condition. Each scanning strategy consists in determining a number of channels to scan and the time to wait on each channel (AT in Android system). Based on results presented in section III-C we fixed AT as presented in Table III: the better the current link quality is, the less time the MS will spend scanning, because it still has time to find APs before it disconnects from its current AP. When the signal quality with the current AP is low, we set aside more time for the MS to scan, in order to maximize the probability to find an AP. In order to contain the scanning duration, we propose to use AT in {5 ms, 10 ms, 20 ms}. The reason is that for smaller scan times, we only find APs with high RSSI (as shown in section III-C) and as we are in fairly good condition, the MS would only be interested in AP with high RSSI.

V. EXPERIMENTATION

A. Methodology and implementation

We have implemented our solution on the Android ICS 4.0.3 system working on a Samsung Nexus S (GT-I9023) smartphone. It involves modifications in the Android Java Framework, the WPA Supplicant The mobile user walks at a roughly constant speed and each connection lasts for 120 s. The second set of experiments was performed in the city of Luxembourg, using the HOTCITY Wifi deployment (see [START_REF] Castignani | A study of urban ieee 802.11 hotspot networks: towards a community access network[END_REF] for more details). In all cases, we use iperf to generate the TCP traffic for both MSs and generate several connections for more than one hour.

B. General results

Fig. 5, 6, 7 and 8 show the RSSI and the received TCP data for the two considered environments, over one connection duration, while Table IV shows the average over all connections that we made. We can see that KHAT provides a better RSSI (-69 dBm in average) along the connections and allows the smartphone to have a better throughput than stock Android (222 kB/s versus 146 kB/s). We can also see that KHAT triggers the handover systematically before stock Android to avoid suffering from a poor quality with its current AP. Sometimes, as at Time=400s of the outdoor connection, KHAT manages to find an intermediate AP between those chosen by Stock Android which allows to signigicantly increase both the RSSI and the TCP download. Looking at the zoom of Fig. 8 Time (s.) RSSI (dBm) q q q q q q q q q q KHAT RSSI Legacy RSSI KATH Handover Legacy Handover Time (s.) RSSI (dBm) q q q q q q q q q q q qq q q q q q qq q q q q q q q q q q q KHAT RSSI Legacy RSSI KATH Handover Legacy Handover where the Legacy smartphone is not able to receive any data from the TCP server. On the other hand, KHAT is performing two handovers. The first handover at Time=233s is made prior to the Legacy handover, but still a stagnation in the received data is observed before and after the handover. However the second handover at Time=275s is smooth and does not impact the data reception.

Fig. 9 shows the list of selected APs from the chosen connection in the outdoor environment captured by an MS running Wi2me [START_REF] Castignani | Wi2Me: A Mobile Sensing Platform for Wireless Heterogeneous Networks[END_REF]. The APs are shown in their apparence order along the path. We can see that for the six first APs, the KHAT AP selection is judicious: when the signal strength of one AP is degrading, another AP becomes available. However, between scanning occurence 140 to 200, there is not ideal choice for any AP. Observing that the RSSI is low, KHAT is trying to handover to different AP at this period of time, osciatilling between AP 7 , AP 8 , AP 9 and AP 10 . These are the handovers we can see around Time=625s in Fig 7 . While KHAT avoids to trigger handover when it is not for a significantly better AP, in areas where all APs offer low RSSI, KHAT may trigger several handovers. It finally finds AP 11 at Time=721s which was providing a good coverage area. During this period, we can see that the Legacy phone did not trigger any handover and was unable to receive any data for a long period of time.

VI. CONCLUSION IEEE 802.11 is one of the most popular wireless standard to offer high data rate Internet connection. With the vast number of hot-spots and community networks that are deployed today, there is a potential for users to use Wifi network in mobility scenarios. However, as the AP coverage area is usually limited to few tenths of meters, there is a strong need for optimized mobility support, when users move from one AP to another one. We have shown in this paper that current devices are able to transit between APs, but the handover performance is quite low.

We proposed a handover algorithm called KHAT that anticipates the signal loss from the current AP to preemptively scan for potential APs. The prediction of the link going down is achieved with a Kalman filter which estimates the slope of the RSSI to determine the link condition. If the estimate is below a given threshold (smooth RSSI lower than -70 dBm and slope lower than 0.2), we launch a scanning. Data packets can be buffered (and retrieved later on) by the AP during the MS scanning by exploiting the power saving mode defined in 802.11. Depending on the scanning results, the MS will either handover to a new (better) candidate AP that has been found, or it will loop on the link quality prediction. The scanning period and strategy are adapted depending on the current link condition.

We have implemented KHAT on Android ICS 4.0.3 system working on a Samsung Nexus S (GT-I9023). To address the tradeoff between the scanning latency and the AP discovery, the MS is scanning with AT=20 ms if a handover is imminent, AT=10 ms when the link quality is medium and AT=5 ms when the link quality is good. In two different environments (indoor and outdoor), we compared a Stock Android with a KHAT smartphone. We have shown that KHAT outperforms Stock Android by anticipating handovers, and using more APs available on the path. The average RSSI is 6dBm either in the outdoor environment, and the TCP throughout is 0.22MB/s compared to 0.12MB/s for Stock Android. The perspective of this work is to apply the link quality prediction on candidate APs in order to better choose the target AP when a handover is needed.

2

 2

Fig. 1 :Fig. 2 :

 12 Fig. 1: Various TCP performance

  Fig. 4: Algorithm Flow Chart

Fig. 9 :

 9 Fig. 9: Heatmap of the selected AP in the outdoor environment

  Fig.5, 6, 7 and 8 show the RSSI and the received TCP data for the two considered environments, over one connection duration, while TableIVshows the average over all connections that we made. We can see that KHAT provides a better RSSI (-69 dBm in average) along the connections and allows the smartphone to have a better throughput than stock Android (222 kB/s versus 146 kB/s). We can also see that KHAT triggers the handover systematically before stock Android to avoid suffering from a poor quality with its current AP. Sometimes, as at Time=400s of the outdoor connection, KHAT manages to find an intermediate AP between those chosen by Stock Android which allows to signigicantly increase both the RSSI and the TCP download. Looking at the zoom of Fig.8between Time=200s and

Fig. 5 :Fig. 6 :

 56 Fig. 5: RSSI for Legacy and KHAT smartphones indoor

Fig. 7 :Fig. 8 :

 78 Fig. 7: RSSI for Legacy and KHAT smartphones outdoor

TABLE I :

 I Handover performance of different OS

	Nb. of	AT=5	AT=10	AT=20	AT=50	AT=100
	channels	(%)	(%)	(%)	(%)	(%)
	1	3.11	5.76	10.62	22.28	25.24
	3	6.45	18.28	32.61	58.18	88.24
	5	9.28	21.02	38.83	68.94	89.31
	8	10.44	23.61	40.46	70.43	96.58
	13	11.74	28.62	45.76	79.88	100.00
	RSSI	-67.16	-70.07	-76.02	-81.28	-83.26

TABLE II :

 II Percentage of discovered APs for different values of AT and number of scanned channels namely MinCT and MaxCT (see section II). However, the IEEE 802.11 Android driver uses a single timer, namely Active Timer (AT) for scanning. AT is defined as the time an MS waits for Probe Responses on a channel.

  Algorithm 1 The algorithm used to compute α i

	1: increasing ← FALSE
	2: lastV alue ← Y1
	3: α1 ← α1
	4: i ← 1
	5: while i ≤ length(Y ) do
	6:	if Yi = lastV alue then
	7:	if YI > lastV alue then
	8:	increasing ← TRUE
	9:	αi ← αup
	10:	else
	11:	increasing ← FALSE
	12:	αi ← α1
	13:	end if
	14:	else
	15:	if increasing =FALSE then
	16:	if αi-1 > αmin then
	17:	αi ← 0.8 • αi-1
	18:	else
	19:	αi ← αi-1
	20:	end if
	21:	else
	22:	αi ← αup
	23:	end if
	24:	end if
	25: end while

TABLE III :

 III Scanning Strategies scanning at a very high frequency, we adapt the value of T Scan depending on the scanning results. Each time the MS triggers a link going down, if a candidate AP exists, we double the current value of T Scan (up to 1 s) since it is not necessary to scan at a high frequency if there is at least one candidate AP. On the other hand, if no candidate exists at that time, we set T Scan to its minimum value (250 ms).

TABLE IV :

 IV Performance comparison

	AP 1
	AP 2
	AP 3
	AP 4
	AP 5
	AP 6
	AP 7
	AP 8
	AP 9
	AP 10
	AP 11
	AP 12
	AP 13
	AP 14
	AP 15
	AP 16 AP 17					90
	0	50	100	150 Scan Occurences 200	250	300

978-1-4799-8461-9/15/$31.00 c 2015 IEEE

VII. ACKNOWLEDGMENTS

This work has received a French government support under reference ANR-10-LABX-07-01 (Cominlabs).


Wilson R Lourenço
email: wilson.lourenco@mnhn.fr

Eric Ythier
email: eythier@syntechresearch.com

con commenti su alcune specie correlate (Scorpiones: Buthidae)

Keywords: Scorpion, Tityus, Atreus, Tityus asthenes, new species, Ecuador. Riassunto Scorpione, Tityus, Atreus, Tityus asthenes, nuova specie, Ecuador

Description of Tityus (Atreus) cisandinus sp. n.

Introduction

The buthid scorpion Tityus asthenes was originally described by [START_REF] Pocock | Notes on the classification of scorpions, followed by some observations upon synonymy, with descriptions of new genera and species[END_REF] from Poruru in Peru, in a paper devoted to the classification of scorpions in general and including description of several new genera and species. No precision, however, about the collector of the studied specimen was supplied, situation not uncommon in the publications of Pocock (Lourenço & Ramos, 2004). The description of T. asthenes was brief, based on a single female specimen and not followed by any illustrations. The type locality of Tityus asthenes, supposedly in Peru, remains unclear since no present locality with this name, including in river systems, exist in this country. [START_REF] Francke | Escorpiones y escorpionismo en el Peru VI: Lista de especies y claves para identificar las familias y los géneros[END_REF] suggested that the correct locality is Paruro in southern Peru, however this corresponds to an arid region not compatible with many species of Tityus placed in the subgenus Atreus. Consequently, the specimen described by Pocock could have been collected in quite different regions in tropical America. Probably in relation to its general morphology, Tityus asthenes was associated to the group of Tityus americanus (= Scorpio americanus Linné, 1754) by [START_REF] Pocock | Notes on the classification of scorpions, followed by some observations upon synonymy, with descriptions of new genera and species[END_REF]. In fact, this group corresponds to scorpions defined by a large size, 80 to 110 mm in total length, presenting long and slender pedipalps, in particular in males and with an overall dark coloration. This group corresponded well to the Tityus asthenes group of species as defined by Lourenço (2002a), this until the more precise definition of subgenera within Tityus (Lourenço, 2006), which placed these large scorpions in the subgenus Atreus Gervais 1843. 2012). The subsequent discovery and description of several new species belonging to this group of scorpions in the last 30 years changed the past opinion about their models of distribution and showed that most species could have less extended and much more localised ranges of distribution (Lourenço, 1997(Lourenço, , 2002b(Lourenço, , 2011(Lourenço, , 2017)).

A recent study on some scorpions from Ecuador (Ythier & Lourenço, 2017) reopened the question about the true identity of some Tityus from this country, and in particular that of Tityus asthenes. In an old paper on scorpion fauna of Ecuador, Lourenço (1988) suggested that Tityus asthenes was the most common species of the subgenus Atreus, being present in both the cisAndean and transAndean regions of the country. The type specimen of Tityus asthenes was examined by the senior author early in the 1970s, while yet a student, without any final resolution about its true identity (Figs. 13). The recent reanalysis of the female holotype of T. asthenes clearly demonstrates that this species does not belongs to the subgenus Atreus but rather to the subgenus Tityus and to the group of species Tityus bolivianus (Lourenço & Maury, 1985; of two new specimens collected in the Amazon region of Ecuador, close to the Peru border and associated to T. asthenes in Lourenço & Ythier, 2013, led us to consider this Tityus population as a new species. Until now the cisAndean and transAndean populations of Tityus (Atreus) found in Ecuador were considered as a single one (Lourenço, 1988;[START_REF] Brito | A checklist of the scorpions of Ecuador (Arachnida: Scorpiones), with notes on the distribution and medical significance of some species[END_REF], however we now consider these as possibly different and separated by the Andean mountain system. The material cited by Lourenço (1988) from the Napo province was not restudied, but most certainly corresponds to the new species described here. The transAndean populations of Tityus subgenus Atreus in Ecuador, in particular those from the Province of Esmeraldas, will require some further studies to have their status clearly redefined, since it may correspond to a not described species.

The Amazon region of Ecuador, known as the Oriente, is exceptionally rich in biodiversity of both flora and fauna. Much of the Oriente is tropical rainforest (Fig. 6.), starting from the east slopes of the Andean mountains (upland rainforest) and descending into the Amazon basin (lowland rainforest). It is crossed by many rivers rising in the Andean mountains and flowing east towards the Amazon River. The lowlands in the Oriente, where the new species was found (type localities going from 250 m (Kapawi) to 310 m (Yaupi) above sea level), have a warm and humid climate year round, and typically receives more than 2000 mm (average 3500 mm) of rain each year, April through June being the wettest period. Temperatures vary little throughout the year and averages 25° C, with variation between daytime (up to 28° C) and nighttime (about 22° C). Lowland rainforests contain the tallest trees of all types of rainforest, with the largest variety of species. The tree canopy typically sits 2040 m above the ground where vegetation is sparse and comprises mainly small trees and herbs that can experience periodical flooding during heavy rains. For several sections of the lowland rainforest such as the canopy, knowledge of the scorpion fauna is still almost nonexistent (Lourenço & Pézier 2002). Consequently, the effective number of species in the Amazon region of Ecuador may be much greater than what is presently estimated.

Material and Methods

Illustrations and measurements were produced using a Wild M5 stereomicroscope with a drawing tube and an ocular micrometer. Measurements follow [START_REF] Stahnke | Scorpion nomenclature and mensuration[END_REF] and are given in mm. Trichobothrial notations follow [START_REF] Vachon | Etude des caractères utilisés pour classer les familles et les genres de Scorpions (Arachnides)[END_REF], while morphological terminology mostly follows [START_REF] Vachon | Etude sur les Scorpions[END_REF] and [START_REF] Hjelle | Anatomy and morphology[END_REF].

Comparative material:

• Tityus obscurus (Gervais, 1843): French Guiana, Réserve de la Trinité, XII/2010 (C. Courtial), 2 males, 1 female.

• Tityus apiacas Lourenço, 2002: Brazil, Pará, Itaiatuba, Bacia do Rio Jamanxim, 5/XII/2007 (J. Zuanon, 1 male; Amazonas, BR319, km 350, trilha 1, ponto 500 (5°16'11.28" S 61°55'46.8" W), 25/VII:2001, pitfall (H. Guariento & L. Pierrot), 1 male.

• Tityus dinizi Lourenço, 1997: Brazil, Amazonas, Anavilhanas, X/1999 (J. Adis), 2 males. Etymology. The specific name refers to the geography of the region where the new species was found, between Amazon and Oriental Andes in Ecuador. Diagnosis. A moderate species when compared with the average size of other species in the subgenus Atreus: male 72.8 mm and female 70.1 mm in total length (see Table I). General pattern of pigmentation reddishbrown to brown overall. Basal middle lamella of female pectines dilated, but less conspicuous when compared with that of several other species of the subgenus Atreus. Subaculear tooth moderately long and spinoid. Pectinal tooth count 1919 in male and 2120 in female. Fixed and movable fingers of the pedipalp with 1516 oblique rows of granules. Ventral carinae of metasomal segments II to IV parallel in configuration. Pedipalps and in particular chela fingers with a strong chetotaxy. Trichobothriotaxy Aα orthobothriotaxic. The new species may be an endemic element to the occidental region of Amazon. Description based on male holotype and female paratype. Measurements in Table I. Coloration. Basically reddishbrown to brown overall. Prosoma: carapace reddishbrown with some dark pigment on the carinae. Mesosomal tergites reddishbrown with one darker transverse stripe on the posterior edge of tergites IVI. Metasoma: segments I to V reddishbrown; IV and V darker than the others and with some blackish regions over carinae. Vesicle: dark reddishbrown; aculeus reddish at the base and dark reddish at the tip. Venter reddishyellow; sternites with dark zones on lateral and posterior edges; sternite V with a white triangular zone on posterior edge, better marked on male; pectines pale yellow to white. Chelicerae reddishyellow with a dark thread; fingers blackish with dark reddish teeth. Pedipalps: reddishbrown; fingers dark, almost blackish with the extremities yellow. Legs reddishbrown to brown.

Morphology. Carapace moderately to strongly granular; anterior margin with a moderate to strong concavity. Anterior median superciliary and posterior median carinae moderate to strong. All furrows moderately to strongly deep. Median ocular tubercle distinctly anterior to the centre of carapace. Eyes separated by more than one ocular diameter. Three pairs of lateral eyes. Sternum subtriangular. Mesosoma: tergites moderately to strongly granular. Median carina moderate in all tergites. Tergite VII pentacarinate. Venter: genital operculum divided longitudinally; each half with a semioval to semitriangular shape. Pectines: pectinal tooth count 1919 in male holotype and 2120 in female paratype; basal middle lamellae of the pectines dilated in the female and inconspicuously dilated in male. Sternites with a thin granulation and elongate spiracles; VII with four carinae better marked on female. Metasomal segments with 108885 carinae, crenulated, better marked on female. Dorsal carinae on segments I to IV with one to three spinoid granules, better marked on female. Lateral inframedian carinae on segment I complete, crenulate; represented by 13 granules on II; absent from III and IV. Ventrolateral carinae moderate to strong, crenulated on female, smooth on male. Ventral submedian carinae crenulate. Intercarinal spaces weakly granular. Segment V with dorsolateral, ventrolateral and ventromedian carinae crenulated on female, inconspicuous in male. Lateral intercarinal spaces moderately granular on female, smooth on male. Telson granular on female, smooth on male, with a long and strongly curved aculeus on both sexes. Dorsal surface smooth in both sexes; ventral surface weakly granular in females; subaculear tooth spinoid, shorter in male. Cheliceral dentition characteristic of the family Buthidae [START_REF] Vachon | De l'utilité, en systématique, d'une nomenclature des dents des chélicères chez les Scorpions[END_REF]; movable finger with two well formed, but reduced, basal teeth; ventral aspect of both fingers and manus with long dense setae. Pedipalps: femur pentacarinate; patella with seven carinae; internal face of patella with several spinoid granules; chela with nine carinae and the internal face with an intense granulation; other faces weakly granular. Femur, patella and chela fingers with a strong chetotaxy. Fixed and movable fingers with 1516 oblique rows of granules. Trichobothriotaxy; orthobothriotaxy Aα [START_REF] Vachon | Etude des caractères utilisés pour classer les familles et les genres de Scorpions (Arachnides)[END_REF][START_REF] Vachon | Sur l'utilisation de la trichobothriotaxie du bras des pédipalpes des Scorpions (Arachnides) dans le classement des genres de la famille des Buthidae Simon[END_REF]. Legs: tarsus with numerous short fine setae ventrally.

Relationships. Taking into account the fact that previous populations of Tityus (Atreus) from Ecuador and, in particular, those from the Amazon region were associated to Tityus asthenes (Lourenço, 1988, Lourenço & Ythier, 2013), it would be logical to associate the new species to this one. However, the type locality of Tityus asthenes, supposedly in Peru, remains unclear, and the specimen described by Pocock could have been collected in quite different regions in tropical America. Moreover, the reanalysis of the general morphology of the female holotype brings confirmation that T. asthenes does not belongs to the subgenus Atreus, but rather to the subgenus Tityus and to the Tityus bolivianus group of species. It has a rather small size with only 53 mm in total length and a tegument strongly smooth with weakly marked carinae and granulations; the subaculear tubercule is small and very sharp (see Lourenço & Maury, 1985). These considerations led us to rather associate the new species to other Tityus (Atreus) distributed in the Amazon basin such as Tityus obscurus, Tityus dinizi, Tityus apiacas and Tityus tucurui Lourenço 1988(Figs. 2328). Tityus cisandinus sp. n. can however be distinguished from these cited species by: I) a rather smaller global size (see Table 1) with marked different morphometric values; II) better marked carinae and granulations; III) stronger chetotaxie on pedipalps. Moreover the geographical range of distribution appears as quite different (see Lourenço, 2011Lourenço, , 2017)). The new species is a possible endemic element to the Andean/Amazon region of Ecuador and Peru. In our opinion, the material listed by Teruel (2011) from Loreto in Peru and associated to Tityus asthenes, corresponds in fact to the new species described here. No confirmation is however possible since the cited material is deposited in the private collection of this author and not accessible.

Figs. 13 .

 13 Figs. 13. Tityus asthenes, female holotype. 12. Habitus, dorsal and ventral aspects. 3. Detail of ventral aspect, showing coxapophysis, sternum, genital operculum and pectines. Black & white photos taken in 1972.

Figs. 45 .

 45 Figs. 45. Tityus asthenes, female holotype. Habitus, dorsal and ventral aspects. Recent colour photos taken in 2017. Labels attest that the type was examined by F. Matthiesen, while in the Muséum in Paris during 1972. (Scale bar = 1 cm).

  All specimens are now deposited in the collections of the Muséum national d'Histoire naturelle, Paris, France.

Fig. 6 .

 6 Fig. 6. The natural habitat of Tityus cisandinus sp. n. (rio Capahuari, Pastaza province), covered by rainforest.

Figs. 710 .

 710 Figs. 710. Tityus cisandinus sp. n., male holotype and female paratype. Habitus, dorsal and ventral aspects.

Figs. 1114 .

 1114 Figs. 1114. Tityus cisandinus sp. n. Male holotype (1113) and female paratype (14). 11. Chelicera, dorsal aspect. 12. Cutting edge of movable finger showing rows of granules. 1314. Metasomal segment V and telson, lateral aspect.

Figs. 1520 .

 1520 Figs. 1520. Tityus cisandinus sp. n. Male holotype (1519) and female paratype (20). Trichobothrial pattern. 1516. Chela, dorsoexternal and ventral aspects. 1718. Patella, dorsal and ventral aspects. 1920. Femur, dorsal aspect.

Fig. 21 .

 21 Fig. 21. Tityus cisandinus sp. n. Female paratype alive.

Fig. 2324 .

 2324 Fig. 2324. Tityus obscurus from French Guiana. Habitus of male, dorsal and ventral aspects.

Fig. 2526 .

 2526 Fig. 2526. Tityus dinizi from Brazil. Habitus of male, dorsal and ventral aspects.

Fig. 2728 .

 2728 Fig. 2728. Tityus apiacas from Brazil. Habitus of male, dorsal and ventral aspects.

  see taxonomic section; Figs 45). Moreover, the study

Table I .

 I Measurements (in mm) of the male holotype and female paratype of Tityus cisandinus sp. n. and males of Tityus dinizi (Brazil), Tityus apiacas (Brazil) and Tityus obscurus (French Guiana).

		Tityus cisandinus sp. n. Tityus dinizi	T. apiacas	T. obscurus
		♂	♀	♂	♂	♂
	Total length:	72.8	70.1	96.1	81.8	90.5
	Carapace:
	Length	7.6	8.1	9.1	8.4	8.1
	Anterior width	5.7	5.6	6.7	6.2	6.3
	Posterior width	7.9	9.0	9.5	9.1	8.7
	Mesosoma length	16.9	19.2	19.8	20.2	24.4
	Metasomal segment I.
	length	5.8	5.2	8.7	6.6	7.6
	width	3.8	4.2	4.1	4.2	4.2
	Metasomal segment II.
	Length	7.8	6.3	10.8	8.5	9.2
	Width	3.6	4.1	3.8	4.3	4.0
	Metasomal segment III.
	Length	8.7	7.1	12.2	9.6	10.1
	Width	3.6	4.2	3.9	4.4	4.1
	Metasomal segment IV
	Length	9.4	8.2	13.6	10.5	10.6
	Width	3.8	4.1	4.0	4.7	4.4
	Metasoma, segment V.
	length	9.9	8.8	13.5	10.7	10.9
	width	4.0	4.1	4.1	4.8	4.6
	depth	3.8	3.9	4.1	4.4	3.9
	Telson length	6.7	7.2	8.4	7.3	9.6
	Vesicle:
	width	3.2	2.9	3.3	3.2	3.2
	depth	3.0	2.9	3.2	3.2	3.1
	Femur:
	length	9.8	8.4	13.3	13.2	13.3
	width	2.2	2.4	2.4	2.2	2.3
	Patella:
	length	10.1	9.1	13.8	13.8	14.0
	width	2.6	3.0	3.1	2.8	2.8
	Chela:
	length	17.4	15.7	21.5	21.8	23.1
	width	2.5	2.9	2.8	2.6	2.5
	depth	2.3	2.8	2.6	2.5	2.3
	Movable finger:
	length	11.3	10.8	13.2	13.4	13.5

Acknowledgements

We are most grateful to Janet Beccaloni (NHM, London) for useful information on the type specimen of Tityus asthenes and for providing colour photos of the type. We are also grateful to EliseAnne Leguin (MNHN, Paris) for the preparation of several photos and plates.

List of the Ecuadorian species of Tityus

Genus Tityus C. L. Koch, 1836


Wilson R Lourenço
email: wilson.lourenco@mnhn.fr

nuove specie dal parco nazionale 'Serra da Mocidade' nello stato di Roraima (Scorpiones: Buthidae, Chactidae)

Keywords: Scorpiones, Buthidae, Chactidae, Broteochactas, Taurepania, new species, Serra da Mocidade National Park, mountain range, State of Roraima, Brazil Scorpiones, Buthidae, Chactidae, Broteochactas, Taurepania, nuova specie, parco nazionale Serra

Scorpions belonging to the genera Tityus C. L. Koch, 1836 (subgenus Atreus Gervais, 1843) and Broteochactas Pocock, 1893 (subgenus Taurepania GonzálezSponga, 1978) are studied and two new species are described: Tityus (Atreus) generaltheophiloi sp. n. and Broteochactas (Taurepania) mauriciodiasi sp. n., based on specimens collected in the mountain range of Serra da Mocidade National Park in the State of Roraima, Brazil. Both new species are most certainly endemic elements of these mountain ranges. Moreover, the discovery of these new elements confirms the poor knowledge available for most of the summits in the Amazon region.

Introduction

As outlined in several previous papers (Lourenço, 2002a(Lourenço, , b, 2012[START_REF] Lourenço | The genus Broteochactas Pocock, 1893 in Brazilian Amazonia, with a description of a new species from the State of Amazonas (Scorpiones: Chactidae)[END_REF]Lourenço et al., 2010[START_REF] Lourenço | New species of Chactidae (Scorpiones) from the upper Rio Negro in Brazilian Amazonia[END_REF], contributions to the knowledge of the Amazonian scorpion fauna and in particular of the elements belonging to the families Buthidae C. L. Koch, 1837 and Chactidae Pocock, 1893 have been the subject of several previous studies (e. g. [START_REF] Lourenço | The distribution of noxious species of scorpions in Brazilian Amazonia: the genus Tityus C. L. Koch, 1836, subgenus Atreus Gervais, 1843 (Scorpiones, Buthidae)[END_REF][START_REF] Lourenço | The genus Brotheas C. L. Koch, 1837 in Brazilian Amazonia, with a description of a new species from the State of Pará (Scorpiones: Chactidae)[END_REF][START_REF] Lourenço | The genus Broteochactas Pocock, 1893 in Brazilian Amazonia, with a description of a new species from the State of Amazonas (Scorpiones: Chactidae)[END_REF][START_REF] Lourenço | The geographical pattern of distribution of the genus Teuthraustes Simon (Scorpiones, Chactidae) in South America and description of a new species[END_REF][START_REF] Lourenço | New species of Chactidae (Scorpiones) from the upper Rio Negro in Brazilian Amazonia[END_REF]. However, the Amazon region remains one of the world's most diverse areas for its scorpion fauna. Inventory on the Amazonian scorpion fauna began in the second half of the 19 th century, and was for the first time synthesized in a monograph by [START_REF] Melloleitão | Escorpiões sulamericanos[END_REF]. Since then, other contributions have been published, e. g. [START_REF] Gonzálezsponga | Escorpiofauna de la region oriental del Estado Bolivar, en Venezuela[END_REF][START_REF] Gonzálezsponga | Guía para identificar escorpiones de Venezuela[END_REF] and Lourenço, (2002a, b). On account of the diversity and richness of the Amazonian scorpion fauna, the discovery and description of new species is by no means unusual (e. g. Lourenço, 2002aLourenço, , b, 2012[START_REF] Lourenço | The genus Broteochactas Pocock, 1893 in Brazilian Amazonia, with a description of a new species from the State of Amazonas (Scorpiones: Chactidae)[END_REF][START_REF] Lourenço | The geographical pattern of distribution of the genus Teuthraustes Simon (Scorpiones, Chactidae) in South America and description of a new species[END_REF]Lourenço et al., 2010[START_REF] Lourenço | New species of Chactidae (Scorpiones) from the upper Rio Negro in Brazilian Amazonia[END_REF].

Since [START_REF] Melloleitão | Escorpiões sulamericanos[END_REF] published his monograph on South American scorpions, the number of known Amazonian species, in particular from Brazil, was much less significant than it is today. In fact, most species known in Amazonia have been described only in recent years (e. g. [START_REF] Gonzálezsponga | Escorpiofauna de la region oriental del Estado Bolivar, en Venezuela[END_REF][START_REF] Gonzálezsponga | Guía para identificar escorpiones de Venezuela[END_REF]Lourenço, 2002aLourenço, , b, 2014;;Lourenço et al., 2010[START_REF] Lourenço | New species of Chactidae (Scorpiones) from the upper Rio Negro in Brazilian Amazonia[END_REF].

In fact, many different regions within the Amazon basin, including those nearby the Rio Negro, and in particular the various summits of the northern range of Amazonia were among the last to attract the attention of investigators because most of the pioneer work in Amazonia was carried out along the Solimões and Amazon rivers, in some cases up to Peru [START_REF] Papavero | Essays on the history of neotropical dipterology[END_REF][START_REF] Papavero | Essays on the history of neotropical dipterology[END_REF]. In so far as scorpions are concerned, only in recent decades more intensive collecting was possible in most of these summits composed by the Tepuys or Inselbergs (e. g. GonzálezSponga, 1978;[START_REF] Lourenço | Scorpion biogeographic patterns as evidence for a NeblinaSão Gabriel endemic center in Brazilian Amazonia[END_REF][START_REF] Lourenço | Description of Tityus (Atreus) neblina sp. n. (Scorpiones, Buthidae), from the 'Parque Nacional do Pico da Neblina' in Brazil/Venezuela, with comments on some related species[END_REF][START_REF] Lourenço | New species of Chactidae (Scorpiones) from the upper Rio Negro in Brazilian Amazonia[END_REF]. This has resulted in several new discoveries and descriptions. One exception among the elder expeditions is the one performed by an English Team composed of Messrs F. V. McConnell and J. J. Quelch in Mount Roraima (British Guiana), in the period from August to October 1898, which resulted in the description of two scorpion species [START_REF] Pocock | Myriopoda and Arachnida. In: Report on a collection made by Messrs F. V. McConnell and J. J. Quelch at Mount Roraima in British Guiana[END_REF], most certainly endemic to this summit. See also [START_REF] Lourenço | The genus Vachoniochactas GonzálezSponga (Scorpiones, Chactidae), a model of relictual distribution in past refugia of the Guayana region of South America[END_REF]. In this contribution, two new species are described from the Mountain range of 'Serra da Mocidade ' National Park (Figs. 12) in the state of Roraima, Brazil. These belong to the genera Tityus C. L. Koch, 1836(subgenus Atreus Gervais, 1843) and Broteochactas Pocock, 1893(subgenus Taurepania GonzálezSponga, 1978). Both new species are most certainly endemic elements of these summits which have been explored for the first time during the INPA's Team expedition of 2016.

Methods

Illustrations and measurements were made using a Wild M5 stereomicroscope with a drawing tube and an ocular micrometer. Measurements follow those of [START_REF] Stahnke | Scorpion nomenclature and mensuration[END_REF] and are given in mm. Trichobothrial notations are those developed by [START_REF] Vachon | Etude des caractères utilisés pour classer les familles et les genres de Scorpions (Arachnides)[END_REF] and the morphological terminology mostly follows [START_REF] Hjelle | Anatomy and morphology[END_REF]. Patronym: name honors the Brazilian Army General Guilherme Cals Theophilo Gaspar de Oliveira, based in Brasilia, Brazil, who strongly supported the field expedition to the Serra da Mocidade National Park.

Diagnosis: a moderate species when compared with the average size of the other species in the subgenus Atreus: female up to 70.5 mm in total length. General pattern of pigmentation blackishbrown to dark blackish overall (a type of velvet blackish). Basal middle lamella of female pectines moderately to strongly dilated. Subaculear tooth moderately long and strongly spinoid. Pectinal tooth count 19/20 in female. Fixed and movable fingers of the pedipalp with 16/16 oblique rows of granules. Ventral carinae of metasomal segments II to IV parallel in configuration. Basal tooth of chelicera fixed finger with a trifid (trifidus) morphology. This new species is a possibly endemic element to the mountains of Serra da Mocidade National Park.

Description: based on female holotype. Measurements after the description. Coloration. Basically blackishbrown to dark blackish overall (velvet blackish). Prosoma: carapace blackishbrown; eyes surrounded by dark blackish pigment. Mesosoma: tergites blackishbrown with reddishbrown confluent stripes on the posterior edges of tergites I VI. Metasomal segments blackishbrown; V very dark, almost blackish. Vesicle dark, almost blackish; aculeus reddish at the base and blackish at the tip. Ventral aspect blackishbrown with diffused reddish spots; sternite V with a white triangle; pectines pale yellow. Chelicerae dark yellow with a dark thread; fingers blackish with dark reddish teeth. Pedipalps globally blackish with the extremities of fingers reddish. Legs globally blackish. Morphology. Carapace strongly granular; anterior margin with a moderate concavity. Anterior median superciliary and posterior median carinae moderate. Furrows moderately to strongly deep. Median ocular tubercle distinctly anterior to the centre of carapace. Eyes separated by a little more than one ocular diameter. Three pairs of lateral eyes. Sternum subtriangular. Mesosoma: tergites strongly granular. Median carina moderate in all tergites. Tergite VII pentacarinate. Venter: genital operculum divided longitudinally; each half with a semitriangular shape. Pectines: pectinal tooth count 19/20 in female holotype; basal middle lamellae of the pectines moderately to strongly dilated in the female. Sternites weakly granular with elongate spiracles; VII with four carinae. Metasomal segment I with 10 carinae, crenulate; segment II with 8 carinae, crenulate; segment III with 8 carinae, crenulate; segment IV with 8 carinae, crenulate; segment V with 5 carinae, crenulate. Dorsal carinae on segments II to IV with 23 strong spinoid granules. Lateral inframedian carinae on segment I complete, strongly crenulate; on II represented by only 3 distal granules; absent from III and IV. Ventrolateral carinae strong, crenulate. Ventral submedian carinae strongly crenulate. Intercarinal spaces weakly to moderately granular. Segment V with dorsolateral, ventrolateral and ventromedian carinae strongly crenulated. Lateral intercarinal spaces moderately granular. Telson, moderately to weakly granular, with a long and strongly curved aculeus. Dorsal surface smooth; ventral surface moderately granular in female; subaculear tooth moderately long and strongly spinoid. Cheliceral dentition characteristic of the family Buthidae [START_REF] Vachon | De l'utilité, en systématique, d'une nomenclature des dents des chélicères chez les Scorpions[END_REF]; movable finger with two wellformed basal teeth; fixed finger with a trifid (trifidus) basal tooth; ventral aspect of both fingers and manus with long dense setae. Pedipalps: femur pentacarinate; patella with 7 carinae; chela with 9 carinae; all faces moderately granular. Fixed and movable fingers with 16/16 oblique rows of granules. Trichobothriotaxy; orthobothriotaxy Aα [START_REF] Vachon | Etude des caractères utilisés pour classer les familles et les genres de Scorpions (Arachnides)[END_REF][START_REF] Vachon | Sur l'utilisation de la trichobothriotaxie du bras des pédipalpes des Scorpions (Arachnides) dans le classement des genres de la famille des Buthidae Simon[END_REF]. Legs: tarsus with numerous short fine setae ventrally. Relationships: from its general morphology, the new species belongs to the subgenus Atreus. Because of its morphological features and also because of the closest area of distribution, it can be associated with Tityus dinizi Lourenço 1997, described from the Rio Negro area. The two species can, however, be distinguished from each other by a number of features: I) the new species has a darker blackish coloration overall, particularly on the legs and pedipalps; II) the basal middle lamella of the pectines is less dilated in the new species than it is in T. dinizi; III) body and appendages are less elongated in the new species; IV) basal tooth on fixed finger of chelicera has a particular trifid morphology in the new species. Moreover, the habitat of both species is quite distinct. Tityus dinizi is found in flooding areas (Igapos) in the region nearby the Rio Negro margins whereas the new species was collected in the mountain range of 'Serra da Mocidade' National Park, at altitudes of 600 700 m.

Morphometric values of the female holotype of Tityus (Atreus) generaltheophiloi sp. n. Total length (including the telson), 70.5. Carapace: length, 8.0; anterior width, 5.9; posterior width, 9.1. Mesosoma length, 19.6. Metasomal segments. I: length, 5.2; width, 4.3; II: length, 6.2; width, 4.3; III: length, 7.1; width, 4.2; IV: length, 8.1; width, 4.1; V: length, 8.9; width, 3.9; depth, 3.7. Telson length, 7.4. Vesicle: width, 2.9; depth, 3.0. Pedipalp: femur length, 8.5, width, 2.2; patella length, 8.8, width, 3.1; chela length, 15.8, width, 2.8, depth, 2.7; movable finger length, 10.7 Diagnosis. Small to moderate sized scorpions with respectively 34.7 and 32.9 mm in total length for the biggest female and male examined. Coloration reddishyellow to reddish brown. Body and appendages moderately to strongly granulated with some smooth and lustrous zones. Metasomal carinae moderately to strongly marked; segment V with several spinoid granules on ventral aspect; segments I to IV with strong posterior spinoid granules on dorsal carinae. Pectines with 89 teeth (mode 8/9). Dentate margins on fixed and movable fingers of pedipalps with 6/7 more or less delimited rows of granules. Rows not separated by clearly larger accessory granules, but rather by a conglomeration of small granules. Trichobothrial pattern of type C, majorante neobothriotaxy.

Description: (based on female holotype and paratypes). Coloration. Basically reddish yellow to reddishbrown. Prosoma: carapace reddishbrown. Tergites reddishbrown, as the carapace. Metasomal segments reddishyellow, paler than tergites; vesicle reddish yellow; aculeus dark red. Chelicerae yellowish marked with diffused variegated spots; fingers yellow with diffused variegated spots; teeth reddish. Pedipalps reddishbrown; femur and patella with blackish zones over the carinae; chelae reddishbrown; granulations over the dentate margins of fingers blackish. Legs yellow without spots. Venter yellow to reddishyellow; sternite V with a pale, almost white triangle; coxapophysis brownish; pectines and genital operculum pale yellow in female to pale brown in male. Morphology. Carapace moderately granular; furrows shallow. Sternum pentagonal, wider than long. Tergites almost acarinate, moderately granular, with granulations better marked on male. Pectinal tooth count 9/8 for female holotype (see diagnose for variation), fulcra absent. Sternites weakly granulated, better marked on male, VII acarinate; spiracles with an ovalshape. Only metasomal segment V longer than wide; metasomal tegument lustrous with some minute granulations; segment V with conspicuous spinoid granulations ventrally. Dorsal and laterodorsal carinae strongly marked on segments IIV; other carinae equally strong; ventral carina present on all segments; vestigial on segment I of female. Pedipalps: femur with dorsal internal, dorsal external and ventral internal carinae moderately to strongly marked; ventral external carina weak; tegument with very few granulations, almost smooth; internal aspect very weakly granular. Patella almost smooth; all carinae moderate to strong. Chela with minute granulations; all carina weakly to moderately develop; internal aspect with a few granules. Dentate margins on fixed and movable fingers of pedipalps with 6/7 more or less delimited rows of granules. Rows not separated by clearly larger accessory granules, but rather by a conglomeration of small granules. Chelicerae with a dentition typical of Chactidae [START_REF] Vachon | De l'utilité, en systématique, d'une nomenclature des dents des chélicères chez les Scorpions[END_REF], and with dense setation ventrally and internally. Trichobothrial pattern of type C, majorante neobothriotaxy. [START_REF] Vachon | Etude des caractères utilisés pour classer les familles et les genres de Scorpions (Arachnides)[END_REF].

Relationships: Broteochactas (Taurepania) mauriciodiasi sp. n. can be distinguished from other species in the subgenus Taurepania and in particular from Broteochactas (Taurepania) porosa [START_REF] Pocock | Myriopoda and Arachnida. In: Report on a collection made by Messrs F. V. McConnell and J. J. Quelch at Mount Roraima in British Guiana[END_REF] which occurs in the nearby region of the Monte Roraima, by the following features: I) some distinct morphometric values; II) carapace and tergites more intensely granulated; III) a slightly inferior number of teeth on pectines; IV) a particular granulation on chela fingers, randomly arranged and without the presence of conspicuous accessory granules. Moreover, the two cited species are most certainly endemic elements to their respectively summits.

Morphometric values of the female holotype and male paratype of Broteochactas (Taurepania) mauriciodiasi sp. n. Total length (including the telson), 34.7/32.9. Carapace: length, 4.8/4.4; anterior width, 3.2/2.8; posterior width, 5.0/4.5. Mesosoma length, 9.8/8.3. Metasomal segments. I: length, 2.0/1.8; width, 3.0/3.1; II: length, 2.2/2.0; width, 2.8/2.9; III: length, 2.3/2.2; width, 2.7/2.9; IV: length, 2.5/3.1; width, 2.6/2.8; V: length, 5.5/5.6; width, 2.5/2.6; depth, 2.2/2.2. Telson length, 5.6/5.5. Vesicle: width, 2.4/2.4; depth, 1.8/1.8. Pedipalp: femur length, 4.0/3.5, width, 1.7/1.5; patella length, 4.6/4.1, width, 1.9/1.7; chela length, 8.6/7.7, width, 2.7/2.8, depth, 3.2/3.2; movable finger length, 5.2/4.4. Taxonomic comments on the subgenus Taurepania stat. n.

The genus Taurepania was created by [START_REF] Gonzálezsponga | Escorpiofauna de la region oriental del Estado Bolivar, en Venezuela[END_REF] based on the species Broteochactas porosus [START_REF] Pocock | Myriopoda and Arachnida. In: Report on a collection made by Messrs F. V. McConnell and J. J. Quelch at Mount Roraima in British Guiana[END_REF], one of the two species described by this author from Mt. Roraima. [START_REF] Gonzálezsponga | Escorpiofauna de la region oriental del Estado Bolivar, en Venezuela[END_REF], erroneously attributed the type locality of this species to Estado Bolivar in Venezuela. [START_REF] Sissom | Family Chactidae Pocock, 1893[END_REF] in the 'Catalog of the scorpions of the world', confirmed the type locality to Venezuela, but stated that [START_REF] Pocock | Myriopoda and Arachnida. In: Report on a collection made by Messrs F. V. McConnell and J. J. Quelch at Mount Roraima in British Guiana[END_REF] cited Guyana instead. In fact the field expedition performed by Messrs F. V. McConnell and J. J. Quelch in Mount Roraima, was a British expedition and a priori took place in British Guiana. The matter may be problematic since Mt. Roraima is located in a trifrontier location, between Brazil, Guyana and Venezuela.

Since the genus Taurepania and several other genera of Chactidae are very closely related to the genus Broteochactas, their status changed during the last decades. [START_REF] Lourenço | Diversité de la faune scorpionique de la region amazonienne; centres d'endémisme; nouvel appui à la théorie des refuges forestiers du Pléistocène[END_REF] considered Taurepania and several other genera as only groupofspecies within Broteochactas. In subsequent years some of these genera were rehabilitated as valid genera [START_REF] Lourenço | Scorpion biogeographic patterns as evidence for a NeblinaSão Gabriel endemic center in Brazilian Amazonia[END_REF]. Taurepania was maintained as a valid genus by [START_REF] Sissom | Family Chactidae Pocock, 1893[END_REF], but again invalidated by [START_REF] Soleglad | Highlevel systematics and phylogeny of the extant scorpions (Scorpiones: Orthosterni)[END_REF]. In reality, the species associated to Taurepania remain extremely poorly studied. All these species apparently are associated to several summits of Northern Amazonia. For this reason and until better studies may be possible on these summit populations, Taurepania is considered here as a subgenus of Broteochactas.

Biogeographic considerations

Because of their low vagility, scorpions have frequently been used as biogeographic tools [START_REF] Lourenço | The biogeography of scorpions[END_REF]. The two new species described here were collected in the summits of Serra da Mocidade National Park, an area located E to the Imeri Endemic Centre (Figs. 25 26) as defined by [START_REF] Lourenço | Diversité de la faune scorpionique de la region amazonienne; centres d'endémisme; nouvel appui à la théorie des refuges forestiers du Pléistocène[END_REF][START_REF] Lourenço | Scorpion biogeographic patterns as evidence for a NeblinaSão Gabriel endemic center in Brazilian Amazonia[END_REF]. These new descriptions provide further evidence of the very high biodiversity and the important levels of endemism around the Rio Negro region [START_REF] Lourenço | Scorpion diversity and endemism in the Rio Negro region of Brazilian Amazonia, with the description of two new species of Tityus C. L. Koch (Scorpiones, Buthidae)[END_REF][START_REF] Lourenço | A new species of Brotheas (Scorpiones, Chactidae) from the Rio Negro region in the State of Amazonas, Brazil[END_REF]. The Serra da Mocidade National Park may be considered as a subcentre of endemism related both to Imeri and Imataca centres.

Although several endemic centres of scorpions have been established within Amazonia, only a few can be considered to be well known. The best known centre is unquestionably Manaus in Brazil, but even in this area new species are continuously being discovered and described (e. g. [START_REF] Lourenço | Addition to the scorpion fauna of the Manaus region (Brazil), with a description of two species of Tityus from the canopy[END_REF]Lourenço & Araujo, 2004;[START_REF] Lourenço | A new synopsis of the scorpion fauna of the Manaus region in Brazilian Amazonia, with special reference to the 'Tarumã Mirim' area[END_REF][START_REF] Monod | A new species of Broteochactas Pocock, 1890 from Brazilian Amazonia (Scorpiones, Chactidae)[END_REF][START_REF] Pinto Da Rocha R | Broteochactas fei, a new scorpion species (Scorpiones, Chactidae) from Brazilian Amazonia, with notes on its abundance and association with termites[END_REF].

Since the region around the Rio Negro is much more vast than that of Manaus, many new taxonomic elements, mainly at the level of species, but also even of genera, may be expected to be discovered and described in coming years. Any final conclusions regarding the actual composition of the scorpion faunas of both Manaus and specifically of the Rio Negro region should be interpreted with caution because the results obtained may well be biased in consequence of insufficient collecting and field work. The inventory of scorpions may present difficulties because these animals are often extremely cryptic and some species remain known only from a single locality. Until better methods of sampling are used, precautions must be taken into consideration in the interpretation of all biogeographical results [START_REF] Prance | Forest Refuges: evidence from Woody Angiosperms[END_REF][START_REF] Lourenço | Diversité de la faune scorpionique de la region amazonienne; centres d'endémisme; nouvel appui à la théorie des refuges forestiers du Pléistocène[END_REF][START_REF] Lourenço | The biogeography of scorpions[END_REF].

The new evidence presented in this paper, based on scorpion studies, supports the conclusion that the upper Rio Negro and surrounded areas such as the 'Serra da Mocidade' National Park may represent important endemic centres.

Fig. 1 .

 1 Fig. 1. General view of the 'Serra da Mocidade' National Park, showing the typical vegetation (photo by T. Laranjeiras).

Fig. 2 .

 2 Fig. 2. A typical Inselberg formation in the 'Serra da Mocidade' National ark (photo by T. Laranjeiras).

Figs. 37 .

 37 Figs. 37. Tityus (Atreus) generaltheophiloi sp. n. Female holotype. 3. Chelicera, dorsal aspect. 4. Idem, fingers and teeth in detail. 5. Metasomal segment V and telson, lateral aspect. 6. Pecten. 7. Cutting edge of movable finger showing series of granules.

Figs. 812 .

 812 Figs. 812. Tityus (Atreus) generaltheophiloi sp. n. Female holotype. Trichobothrial pattern. 89. Chela, dorso external and ventral aspects. 1011. Patella, dorsal and external aspects. 12. Femur, dorsal aspect.

Fig. 13 .

 13 Fig. 13. Habitat of Tityus (Atreus) generaltheophiloi sp. n., showing typical vegetation (photo F. F. Xavier Filho).

Figs. 1417 .

 1417 Figs. 1417. Broteochactas (Taurepania) mauriciodiasi sp. n. Female holotype (14, 16) and male paratype (15, 17). 14. Chelicera, dorsal aspect. 1516. Metasomal segments IIIV and telson, lateral aspect. 17. Cutting edge of movable finger, showing granulations.

Figs. 1823 .

 1823 Figs. 1823. Broteochactas (Taurepania) mauriciodiasi sp. n. Female holotype. Trichobothrial pattern. 1819. Chela, dorsoexternal and ventral aspects. 2022. Patella, dorsal, external and ventral aspects. 23. Femur, dorsal aspect.

Fig. 24 .

 24 Fig. 24. Habitat of Broteochactas (Taurepania) mauriciodiasi sp. n., showing typical vegetation (photo F. F. Xavier Filho).

Fig. 25 .

 25 Fig. 25. Map of Northern South America Amazonian and Guayana regions showing the known distribution of the most important Tityus (Atreus) species, including the type locality of Tityus (Atreus) generaltheophiloi sp. n.

Fig. 26 .

 26 Fig. 26. Map of Northern South America Amazonian and Guayana regions showing the type localities of Broteochactas (Taurepania) mauriciodiasi sp. n. and Broteochactas (Taurepania) porosa (Mount Roraima).

Acknowledgements

I am most grateful to Marcio Oliveira from INPA, Manaus, Brazil, who arranged facilities for the study of the material related to the new species described here, to Thiago Laranjeiras and Francisco Felipe Xavier Filho, INPA, Manaus, Brazil, for the permission to use several personal photos in the article, to Lucienne Wilmé (Missouri Botanical Garden, Madagascar) for preparing the maps and to Michael M. Webber, University of Nevada, Las Vegas, USA, for her review of an earlier version of the manuscript.

The Expedition 'Biodiversity of the Serra da Mocidade' was the result of a collaboration between the Instituto Nacional de Pesquisas da Amazônia (INPA), Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio), Comando Militar da Amazônia (CMA), and Grifa Filmes. We extend our acknowledgements to all these partners.