[en ligne]. Addis Abbeba : Centre français des études éthiopiennes, 2018. Disponible sur Internet : <http://books.openedition.org/cfee/1341>. ISBN : 9791036523786. DOI : https://doi.org/10.4000/books.cfee.1341.

The weak military activity in Yemen during World War I and the maintenance of the status quo between the British in Aden -who first settled in Aden in 1839 -and the Ottomans -who re conquered the northern country in 1849 -has led historians to suggest that no important events occurred in the country at the time. The overall situation during the war, however, should not conceal what was a period of "high dispersion of powers" 2 and of deep political tension. The general context is one of imperial competition about Yemen and of continuous blockades of the Yemeni coast, by first the Italians, and then by the British. Just after the invasion of Tripolitania the 29 September 1911, the Italians began to organize the blockade to prevent the numerous Ottoman troops 3 stationed on this side of the Red Sea to attack Eritrea. 4 This measure promoted reconciliation between the Ottomans and their main opponent in Yemen, Imām Yaḥyā, who succeeded to his father at the head of the Zaydī population in 1904, and had kept leading a blooding war until then. The Da''ān agreement, signed on 9 October, gave him legal control of the Zaydī region in Upper Yemen in return for the recognition of Ottoman sovereignty. Thereafter, Ottoman enemies more or less became Yaḥyā's one's. These included first the Italians and the British-whom the Imam identified as an infidel people occupying sacred Islamic land-, but also the Emir Muḥammad 'Alī al-Idrīsī, who had issued a da'wa (summons to follow his Islamic leadership) in northern 'Asīr in 1909 and gained Italian support against the Ottomans at the beginning of the Libyan war in October 1911 and until the Peace agreement at Lausanne a year after. 5 After the declaration of war against the Ottoman Empire in November 1914, the British, in turn, imposed a severe blockade on the Yemeni coasts to prevent dhows smuggling food, materials and arms into Turkish Arabia. On 30 April 1915, they succeeded in signing an alliance treaty in Aden with al-Idrīsī 6 against the Ottomans-including the objective of avoiding direct conflict with Imam Yaḥyā. 7 Thus, the conflict between the Ottomans and the British essentially consisted of a single major Ottoman attack on the British position at the gates of Aden in Laḥj in May 1915 8 , skirmishes on the littoral of the Red Sea following Yemeni and Ottoman attempts to break the British blockade, and the bombing of al-Ḥudayda in June 1917 and of some Ottoman posts, namely in and around al-Luḥayya in 1918. 9 As for Emir al-Idrīsī, he made progress toward southern Tihāma, primarily after 1917, but after the Ottoman withdrawal in 1919-1920 he lost power against Imam Yaḥyā, who led the first independent Arab state of the 20th century. The evolution of the balance of power in Yemen during the war invites to consider the political dispositions of the Shāfi'īs -and the traditional elite of ulemas and sayyid-s (normal plur. Sādā': Hashemite people, i.e. descendants of the Prophet) among them in particular-either vs. the Ottomans or the local competing leaders. How did those who satisfied with the Ottoman occupation accommodate the growing power of Emir al-Idrīsī, and then Imam Yaḥyā's final control all over the country?

This article proposes to explore the idea of an extended social and political affirmation of the Yemeni local elite, namely the sayyid-s, on the ground of the local context of World War I, and from a perspective that goes beyond the sole empowerment of Imam Yaḥyā. It is based on the analysis of the now well known but still understudied chronicle of Ismā'īl b. Muhammad al-Washalī (1867/1868 -1937), a sayyid and Shāfi'ī scholar of the Tihāma. Al-Washalī's began to write this chronicle in 1911, under the title "Disseminating the Finest Praises about Yemen's Masters of Generosity and Goodness and Reporting the Events that Occurred During This Time" -which is now the most important Yemeni source on the wartime. 10 The author, from his residence in al-Munīra, reveals a number of points on a multitude of small local conflicts between the Ottomans and the "British-Idrīsī side", and on the effects of the blockade on the daily life of the region's inhabitants and its weakening of the Ottoman forces. Yet the most interesting aspect of this chronicle is not the insight it provides on the military situation and the end of Ottoman rule in Yemen, which are already well known. 11 Rather, it is how it deals with the instability of power, and with the status given to the ulemas and sayyid-s in an unsecure context such as the World War. In the first part of this paper, I analyze how, as an ulema and a sayyid, al-Washalī delivers more than a simple chronicle of events. The context of writing, the tributes he pays to the different authorities and the selected events of the time he witnessed invite us to consider his chronicle as a political stand, or even a claim in favor of the social group he belongs to. The objective is not to determine the veracity of what al-Washalī writes. Rather, the argument defended here is that the chronicle can be seen-following Quentin Skinner's interpretation of historical writing as taking a political stand 12 -as a performative means for allowing the author to ensure his own shift away from Ottoman allegiance, in a way that could be both understood and perhaps emulated by the common people. Al-Washalī is, although without any weapon except his pen, an actor of the war, who defends the social order threatened by overwhelming development of modern liberalism. His arguments and justifications, which introduce the moral and ethical aspects of the shifting attitudes of some of the Tihāmīs, shall form the core of my analysis because they reveal his own authority to formulate them as a religious scholar. His chronicle makes it then possible to understand how he tried to provide a comprehensive account of the shifting attitudes of people in the Tihāma as the war progressed and as the Ottomans lost their authority. This can help explain how the Shafi'ī elite participated in the handover of Ottoman power, first to Emir al-Idrīsī's state and then to the Zaydī Imām, Yaḥyā.

Writing the Ottoman History of the Tihāma: Asserting the sayyid-s' Authority

If we accept the idea that a chronicle can fall into the category of plot, it is important to take into account the project that motivated al-Washalī to engage in such a work in 1911. Of course, al-Washalī was a learned man and as such, it is not surprising that he engaged himself in such a traditional form of writing. 13 But what has to be stressed, is also the particular political context of the Yemeni province at that time that could have incited him to this work. After many years of administrative attempts to control the country, what Thomas Kuehn has called a "politics of difference" was experimented in the Zaydī zones, that opened the way to a more radical conciliatory attitude towards Imām Yaḥyā, and then to the Da''ān agreement. 14 The historical analysis of this 1911 event should also consider that it took place in a more general context of political contest led by Islamic reformism from Cairo but also from Indonesia, against the traditional elites of the Muslim world and their privileges -who in turn may have been led to react by promoting their status. In Yemen, as early as 1905, some sayyid ulemas had tried to present themselves to the Ottoman authorities as "keys" to local society, and already in 1910, two sayyids, representatives for Sana'a in the Ottoman Parliament had made suggested to the imperial government that the sayyids and the ulemas be put in charge in the province judiciary and as district and subdistrict governors. 15 Beyond Yemen and all over the mega-region covering the Indian Ocean, the sayyid-s were challenged by new and modern educated people and were reacting by asserting their Hashemite genealogy and the value of their Yemeni or Hadramī origins -sometimes by developing the educational structures of their original region 16 . Then, the chronicle should be read as a conceivable means for its author -also a sayyid -of taking a stand, or even a political act tracing some of the positions he possibly defended aloud in public in support to the social group he was belonging. 17

The monthly account of events-be they political, military, or linked to the death of individuals and to natural, climatic occurrences-lends the chronicle the status of a neutral document that could serve as evidence in the event that the episodes related were politically evaluated and judged. Yet, as with all historical testimonies, there were still specific pro-sayyid intentions behind its writing. 18 Al-Washalī situated himself at the political center of the southern region of the Tihāma. To support this statement, one might stress the importance of his choice to link the chronicle to the previous three volumes of what the editor Ibrāhīm al-Maqhafī describes as the "encyclopedia of the biographies and families of well-known scholars and za'īms in the Tihāma." 19 Al-Washalī thus considers the chronicle as a "chapter [faṣl] on the amazing, unusual, and strange events" that occurred in the Tihāma and a continuation of the 'encyclopedia' on the pretext that "historical science ['ilm altārīkh] could never be complete without an account of events [dhikr al-ḥawādīth]." 20 Indeed, both projects also complete each other through the "historical facts" that appear in the encyclopedia instead of appearing in the chronicle, 21 and the biographical data provided in the chronicle on important 13 See Rosenthal 1969, on what he calls the "Annalistic form" made famous by 'Alī Ṭabarī in the 9th Century, p. 71-86. 14 See Kuehn 2011. The so-called "Rule of Difference" refers to the political model the Ottomans tended to apply time to time in Yemen since the end of the 1870's, aiming to rule according to the "Customs and Dispositions" of the Yemenis, instead of the Ottoman imperial centralization principle. It came to demarcate the Province of Yemen as a subordinate and colonial space. 15 Ibid., p. 222-224. 16 See Freitag and Clarence-Smith 1997, Freitag 2003, Boxberger 2002. We also refer to the case of a great Hadrami scholar from Zanzibar (under British protectorate since 1890), Bā Kāthir (1855-1925), who decided in 1911 (the year of the Treaty of Da''ān) and on the advice of a shaykh of Hadramaut, to write the story of a trip he made fifteen years before between Egypt, the Hijaz and its region of origin. As was shown by Friedhelm Hartwig, the goal of the narrative was not to describe the trip in itself, but to highlight the social space in which the Sayyid-s of Hadramaut evolved, the faith that motivated them and the extent of their religious knowledge. See Hartwig 2001. 17 Indeed, the text is sometimes closer to "oral speech" than to a "written text," the author addressing the reader with interjections like "look!": see al-Washalī,, p. 159. 18 Renaud Dulong has convincingly proposed this by distinguishing between historical "documents" and "monuments"the latter being linked to "society's capacity to testify about itself as well as its capacity to anticipate the memory of future generations"; see Dulong 2002. 19 figures of the Tihāma.

The historical methodology that al-Washalī champions allows him to insert an autobiographical note in his work. In it, he details the high quality of the education he received from the famous Tihāmī ulemas in the town of al-Zaydiyya thanks to his maternal uncle and Shaykh al-Islām Muḥammad b. 'Abd Allah al-Zawwāk, a sayyid who cared for him as a child following his father's death and who thereafter employed him as his mulāzim (secretary). After the death of the Shaykh in 1311/1893-1894, he worked as a mulāzim and a children's tutor for two other famous ulemas and sayyid-s, 'Abd al-Raḥmān al-Qudaymī, and Muḥammad b. Yaḥyā al-Ahdal, in the town of al-Munīra, where he also worked on his historical project. 22 The objectives of the biographical encyclopedia also allowed al-Washalī to insert an entry on himself among the prestigious hierarchy of the Yemeni sayyid families. Al-Washalī's nasab (genealogy) linked him to the large family of the Ḥasanī-s (descendants from al-Ḥasan b. 'Alī, the Prophet's eldest grandson). It also linked him to the broader society of Yemeni sayyid-s-be they Shafi'is or Zaydis-who had disputed power in Yemen for centuries and who had been familiar to the intellectual overcoming of their doctrinal antagonism since Muḥammad b. Isma'īl al-Wazīr in the fifteenth century, and more accurately in the time of Muḥammad al-Shawkānī in the eighteenth century. 23 Obviously, the place al-Washalī attributes to his own status within the sociological framework of Yemen is a way for him to proclaim his intellectual authority to speak about the region and its current political situation by asserting the specific identity of the Tihāma at a time when different local political projects are emerging in the southern Arabian Peninsula to the detriment of the Ottoman Empire. When he began work on his chronicle at the end of 1911,24 the Italians had weakened the Ottoman positions in Yemen, and al-Washalī seems to have been particularly aware of the growing authority of the local dissidents-and perhaps of a possible partition of the Ottoman province of Yemen into various small protectorates. In 1911-if not in 1909, when he probably began taking notes on the events he witnessed25 -he duly points out al-Idrīsī's da 'wa in northern 'Asīr in 1909. 26 This led to a threatening situation for the Ottomans in the Tihāma in May 1911, when, as he reports, an Idrīsī attack on the Ottoman garrison of al-Ḥafāyir near Jāzān killed two thousand Ottomans and injured five hundred. 27 As for Imām Yaḥyā, al-Washalī also carefully reports how he threatened the Ottoman authorities with the support of important tribes (including the powerful 'Alī al-Miqdād clan) as early as February 1911, in addition to how he himself was prey to local attacks. 28 What has to be highlighted however is that the mention of the Da''ān agreement in October does not give Imām Yaḥyā the advantage in the chronicle. Hereafter the latter will be referred to in the chronicle as "the Imām of Shahāra", a reference to the town where he settled, but above all a title that had been negotiated by the Ottomans in Da''ān in order to contain his ambitions as "Commander of the Faithful", a title that he was claiming until then. 29 And according to the chronicle, the Ottoman mushīr (marshal) 'Izzat Pasha who came to sign the agreement was only accompanied by fifteen "individuals," whereas Yaḥyā had to prove his power with an entourage of ten thousand men. Al-Washalī then mentions that 'Izzat Pasha not only gave to the Imam the qadā' (district) "of the Mountains", but also a monthly salary of 30,000 riyals, as a way of underlining that the imam became the sultan's obligé. Furthermore, he details the fact that Yaḥyā was in charge of collecting taxes on behalf of the Ottoman state, namely the dues on mīrī ("public") lands and the zakāt, but also those related to camels and cows that were up until that point considered matrūk ("abandoned" or untaxed). 30 While these details were not in fact mentioned in the treaty, 31 it must be stressed that they are part of the arguments of the chronicle that tend to present it as much more advantageous to the Ottomans. Yet by adding that, after the treaty, "security spread throughout the mountains, Islamic rules were applied [qāmat al-aḥkām al-shar'īyya], and controversies came to an end [sakinat al-fitan]," 32 al-Washalī shows how the alliance between the Ottomans and an educated sayyid could bring about peace and justice. Thus, al-Washalī is stressing how political stability of the Tihāmī region improved under a combined rule of the local sayyid-s and their Ottoman protector.

Ottoman legitimacy in Yemen is presented using a political argument that al-Washalī develops throughout his narrative, based on the idea-one that was rather classical and not specifically Islamic-33 that social and moral chaos leads to the introduction of a political leader who can bring about stability. It is obviously not insignificant that the event chosen to open the chronicle takes place forty years before, in the year 1287/1871. Here, al-Washalī reports "a famous event," which he claims is known as "the year of the 'Asīr." 34 Referring to previous historians' accounts, he considers it one "of the most significant and the most terrible [events] that took place in Yemen." 35 It concerns the attack on the Ottoman position in Ḥudayda led by Muḥammad b. 'Āyid, the Emir of 'Asīr, along with thirty-five thousand combatants, which provoked the fury of "the Sultan Lion" (al-Sultan al-asad aldarghām), Abdülaziz 36 . The Ottomans retaliated a few months later in 1872 by invading the Yemeni coasts, occupying what would become-at the time when al-Washalī is writing-the Ottoman province of Yemen. 37 The combatants of the aggressive emir of 'Asīr's are not justified in their attack, being only "brutish people" (akhlāṭ) from the Sirāt Mountains and Qahtān. Al-Washalī does not mention the Ottoman presence in Ḥudayda since 1849, presenting it instead as unquestioned and legitimate fact that was further bolstered by the authority of the Ottoman sultan-whom the unjust barbarians tried to defeat in Yemen for no justified reason in 1871. This historical account, in which local disorder obliged the Ottomans to re-assert their power in upper Yemen, lends real legitimacy to their presence in Yemen. Al-Washalī pursues his argument by showing how Turkish occupation was beneficial to a country that was undermined by conflict and fitna (the divisiveness among the Muslims condemned by the Koran). 38 The social order and civil peace the Ottomans imposed on the Muslim populations were their primary means of securing power and ensuring that it was effective. Whereas, according to the Zaydī historical accounts, the imams (al-Manṣūr Muḥammad, 1890-1904 and then Yaḥyā, 1904-1948) vol. 4,part 2, This is particularly apparent in Muḥammad 'Abd Allah al-Zawwāq's poem, which is quoted by al-Washalī and evokes a correlation between the arrival of Sa'īd Pasha and the end of the fitna-s: ibid., p. 15.

against them, and continued to do so after the Ottomans withdrew, 39 al-Washalī shows that the Ottomans provided the Yemenis with peace and order against the instability of the local political conflicting powers.

The argument of the internal stability provided by the Ottomans rests on the Islamic legitimacy of the empire. Whether al-Washalī aims at flattering them or at promoting them among the Yemenis, he also presents them as the most capable Islamic force when it came to challenging adversity in general and western hostility in particular. He praises this enduring empire and its leaders, who succeeded in both imposing their "superiority" over "impious countries" and respecting "the requirements of the high words of Islam"-leaders who "magnified Islamic rites," were always ready to serve the Holy places, and "guaranteed the subsistence of all those who the Koran and the religious sciences." 40 Abdülhamid is presented as "a vigorous, courageous, and enterprising ruler to whom men and countries, along with godless communities (al-ṭawā'if al-kufriyya), were subjugated." 41 In his text, al-Washalī prays that God ensures the Ottomans "victory, success and strength, [that He] helps them to triumph over enemies in a resounding victory." 42 He also shows a real interest in the technical innovations the Ottomans introduced in Yemen: the telegraph, printed books of hadiths (along with biographies of the Prophet and historical books in Turkish!), imported fruits thanks to the railroad they had built and which extended to Medina, and prepared the construction of a railroad between the Red Sea and Sana'a with the assistance of French experts. [START_REF][END_REF] The classical ideal of governance and justice embodied by the Ottomans meant that the liberal Young Turks-who instituted the consultative regime (amr al-shūrā) in 1908 and left the sultan with "only his name"-did not find a favorable position in al-Washalī's work. 44 He denounces these supporters of liberty and equality ("horrible things," or umūr qabīḥa) as profiteers, corrupt people, and traitors to the Islamic cause, finally excluding them-along with the leaders of the Committee of Union and Progress (CUP) -from those he generally refers to as "the Ottomans" and who are led by Sultan Muḥammad Rashshād. 45 In his account, al-Washalī makes it understood that the Ottomans in Yemen were not influenced by the CUP's political orientation in favor of centralization, but that they adapted to the local power.

Indeed, the third important idea emerging from al-Washalī's text is that the Ottomans were ruling in accordance with the local elites. He was himself clearly involved in this, since he portrays himself as having direct contact with Ottoman administrative and military elites-saying, for example, that he received information for his chronicle from "reliable Turkish leaders" (al-thiqqāt min ru'asā' al-Turk). 46 In addition, he makes evident that the moral objective of bringing peace and order to a country divided by conflicts between tribal clans and families and subject to the hostility of "brutish" 47 tribal people accustomed to violence and looting was widely supported thanks to the interventions of important local sayyids serving the Ottoman authority. Among them was Sayyid Ḥusayn b. 'Alī al-Ahdal, who had led a counter-offensive against Imam Yaḥyā around Sana'a in February 1911, meaning before he signed the Da''ān agreement. 48 But the most influential sayyid on the Ottoman side was undoubtedly al-Washalī's protector, Sayyid Muḥammad b. Yaḥyā al-Ahdal, 49 who regularly intervened between conflicting clans as a mediator and whom al-Washalī accompanied during a dangerous conflict. 50 Muḥammad al-Ahdal, presented as the "Master of al-Munīra" (Ṣāḥib al-Munīra), was keen collaborator with the Ottoman administration throughout the Tihāma. More than that, he is presented as the holy spirit of the Ottoman sultan when al-Washalī mentions the dream of 'Abd al-Qādir "Abū Sirrayn" ("He Who Has the Two Secrets"), a "just man" (rajul ṣāliḥ) living in Mawr, in 1909:

Sultan 'Abd al-Ḥamīd-who was deposed-and his brother Sultan Muḥammad Rashshād-his successor-were sitting, at the home of Sayyid al-'Allāma Muḥammad b. Yaḥyā al-Ahdal, Master of al-Munīra. The latter left them for a while, being called away by the Prophet-may God bless him-who then took the hand of Sultan Muḥammad Rashshād, and told the Sayyid: "Place this one (meaning Muḥammad Rashshād) under the of this (meaning 'Abd al-Ḥamīd) and be careful." 51 The idea presented here by al-Washalī is that not only did the sayyid-s help the Ottomans to bring peace to Yemen, but that they finally became the real protectors of the original Ottoman spirit distorted by the CUP's leaders in Istanbul. Then, if the political role al-Washalī attributes to the Ottoman power and the local sayyid-s is to be taken seriously, then his presentation of how power struggles evolved during World War I deserves particular attention.

World War I and the Shifting Balance of Power: A Historical Challenge

The favorable light al-Washalī shed on the growing power of Emir (and Sayyid) al-Idrīsīwho is already at war against the Ottomans when al-Washalī begins the chronicle-is quite intriguing. Instead of criticizing the emir's da'wa, he appears to legitimize it, particularly when he declares that the da'wa was accompanied by "wonderous facts and strange things" (umūr 'ajība wa ashyā' gharība), as if inexplicable (and perhaps divine) factors were involved. 52 He explains that, just after Sultan Abdülḥamid was deposed in April 1909, coalitions of tribes violently attacked different Tihāmī towns and their civilians because "the rumor had been spread that al-Idrīsī ordered assaults on the soldiers of the [Ottoman] state, who were present in the towns, and the besieging of the garrisons." 53 Indeed, in August, "Idrīsī tribesmen" are reported to have occupied the towns of al-Qanāwīṣ, al-Zaydiyya and al-Luḥayya. 54 The author, who witnessed one of these attacks, corroborates the explanation given by al-Idrīsī in November 1909, in which he disclaimes all responsability for the uprising, and accuses the Turkish mal-administration. 55 Al-Washalī, who may have heard about this declaration, states that this order could never have been given by the Emir, whom he portrays as a learned man and an honorable sayyid. Furthermore, in order to clear al-Idrīsī's name, al-Washalī mentions that the Emir had connections with the Ottomans when he was in Cairo, some few years before. [START_REF]Al-Washalī states that Muḥammad Tawfīq, an Ottoman who had studied for eight years with al-Idrīsī in Egypt, was sent to mediate during the crisis with the Emir[END_REF] Thus, in al-Washalī's view, al-Idrīsī could not have been an enemy of "the Turks", and he accuses "the tribes," who, "due to their ignorance and their iniquitous nature, believed that it was true. They fought the soldiers and then attacked the people in the cities, and what happened happened, and praise be to God for what He wanted and did, whether it was sweet or bitter." 57 Al-Washalī finally explains that al-Idrīsī never wanted independence for the territory of 'Asīr, but that, in fact, he simply wanted to "cooperate with the Ottoman state." 58 Two years later, in December 1911 and particularly from January 1912 onwards, the beginning of the Italian blockade on the Tihāmī coast modifies al-Washalī's appreciation about the Ottomans and al-Idrīsī. In April he indicates, as a consequence of the blockade, a doubling of prices, and in July the heavy toll paid by the poor fishermen who were not allowed to carry out their activity. 59 The situation was worrying for the Yemenis, as well as for the Ottomans, and may have required moral support from al-Washalī for the latter. But the Italian blockade appears to have been the first step of his disenchantment towards them. From then he expresses compassion for the poor people who were about to die of starvation, through expressions like Lā ḥawla wa lā quwwata illā bil-Lāh ("there is neither change nor power except by means of Allah"). 60 He also reports assassinations outside the cities, and the fact that during a strong bombing attack of Ḥudayda in July, the civilians ran away from the town, and that they were robbed by the tribes on their way out. 61 Al-Washalī's report coincides with the information given to the French Consul in Djeddah in May. 62 For the Consul, who wrote also that insubordination was spreading all over the country and that the tribes were taken a full advantage of the blockade through smuggling activities, the balance of power was not any more in favour of the Ottomans. 63 Far from giving neutral information, al-Washalī in turn introduces for the first time the idea that the Ottomans could not protect the common people anymore. In opposition to this, he duly notes, during these events, the growing power of Emir al-Idrīsī, who led many attacks on the Ottomans, thanks to his ability to provide food, money, ammunitions and weapons to his supporters despite of the blockade. Al-Washalī avoids putting into question the agreement between the emir and the Italians, only reporting that it was difficult to know the identity of the emir's suppliers, since "the information provided by the people were confused". 64 The remark raises the question of how information, and also propaganda, was circulating from here and there to the people of Yemen, but still, it also suggests that al-Washalī was free to present things as he wanted. At the end of the year 1912, when the Italian blockade ended, he finally raised the question of why the blockade had been set. Relaying on "news" and "journals" (we do not know where they were published, but surely from an Arab editor outside Yemen) he denounces for the first time some of "the Ottoman leaders" (umarā' al-dawla al-'uthmāniyya) in Istanbul. He holds responsible those people who had "bought Tripoli to the Italians and who had made people believe that they did it with the authorization of the Ottoman Sultan, Mehmet Rashshād." He relates the war that followed in Libya between the Italians and the sayyid Muhammad al-Sanūsī, which lasted "almost a year" before Sultan Mehmet got aware of what was happening and reacted by prohibiting Italy from delivering food and products coming from the Ottoman provinces. This is what would have caused, following al-Washalī, the Italian blockade of the Yemeni coast. What we understand from this explication is that the "Ottoman leaders" who "bought Libya" to Italy were people from the CUP, whom al-Washalī denounces as traitors and impious people who gave their soul to the Europeans. 65 This denunciation did not undermine the idea, for al-Washalī, that the absolute enemies of Islam were the impious countries (that is to say the Europeans), and that the unique safeguard against them was the Ottoman Islamic State. But it suggests that the "liberals" who were at power in Istanbul were not representative of the Ottoman society, and especially of the Ottoman society in Yemen, which was still loyal to the old Islamic order of Sultan 59 Ibid, p. 91-97. 60 Ibid., p.100. 61 Ibid. 62 The Administrator of the French consular agency in Hodeidah relates also that the police had no means of handling robberies in town, specially by night, and that local people were forced to organize their own collective defense, with guns and jambya-s (traditional Yemeni knives). He added that the tribes were encouraged by the Italians in order to incite them to join with al-Idrīsī, and that in these conditions, the Ottomans were forced to "distribute privileges" to their opponents, and to carry out a sort of "reconciliation policy" with them, with the result that the Ottoman troops and the civil servants were "demoralized": Note from to the French Consul in Djeddah, 3 May 1912, CADN, Djeddah, Consulat and Légation de France (1908[START_REF][END_REF]), vol. 59 (Hodeida 1908-1912), 2 MI 3253. 63 This situation will last at least until 1914, when Sultan 'Alī in Laḥj relates that Governor Maḥmūd Nadīm "is serving the wishes of the Imam more than the provisions of the convention, so much so that he by his behaviour has incurred the displeasure of the Turkish officers"; see the Letter of Sultan 'Alī to Jacob, Resident in Aden, 19 August 1914, in Records of Yemen, 1798-1960, vol. 6, p. 7. 64 Al-Washalī, vol. 4, part 2, p. 98. 65 For al-Washalī, "religion got lost in the desert like in the first times of Islam", and "ignorance increased and knowledge reduced" with the liberals of the CUP: Ibid., p. 103.

Abdülhamid.66 Al-Washalī then shows how, as early as 1913, and at a time when some Tihāmīs started expressing their disappointment at the Ottoman rule more or less openly,67 the conflict shifted toward negotiations in order to implement an agreement similar to the one Yaḥyā had signed, but this ultimately failed in the summer of 1914. 68 The emir of 'Asīr remains difficult to defend, mainly after it becomes apparent that he had allied with the British in the spring of 1915. Did al-Idrīsī manage to hide the agreement? Al-Washalī for his part ignores it. One of his justifications for this is to try to show that al-Idrīsī was not always on good terms with this "impious community." He reports that, in June 1915, when the emir arrived in Mīdī from Jāzān in the night, cannons were fired against him from the boat, which had landed him. 69 Al-Washalī doesn't mention that, since the British controlled the Red Sea, the boat could only have one of their own, but in case, he suggests that the Emir had left the British on bad terms. In the aftermath of these events, al-Idrisi, suddenly determined to fight the Ottomans, is portrayed as just, loyal in battle, and respectful of the rules of war as well as Islam. 70 Al-Washalī's extremely accommodating attitude toward al-Idrīsī progressively increases as the Ottomans' situation deteriorated in both Yemen and the rest of the empire. The Arab revolt led by the Hashemite Sharif Ḥusayn in October 1916 marks an important step, and is presented as severely affecting the Ottomans. Al-Washalī describes this event in a very singular way when he records it in his chronicle on 10 November 1916, of course not mentioning the British initiative to which Sharif Ḥusayn had responded positively. Al-Washalī completely relies on the account that has been related to him by people from Hejaz and is careful to emphasize that "the responsibility (of the narrative) lies squarely with the person who has seen" the events. In his version of how the revolt broke out, he observes an initial error on the part of the Ottomans when they replaced Sharif Ḥusayn with Emir 'Alī Ḥaydar Pasha -a Sayyid also, but originated from the Bosphorus. The argument, which targets the Ottoman government in Istanbul, follows Ḥusayn's proclamation diffused in the entire region [START_REF]and Abyssinia at the end of[END_REF] , carrying out the idea that the revolt was caused by the C.U.P. Government's betrayal of Islam and the Muslims 72 , instead of arguing with the idea of Arab independence, which success was limited to the northern Arab provinces of Syria and Iraq.

The second reason proposed by al-Washalī to explain the revolt allows him to justify what appears as a manipulated (and then acceptable) British support. He reports that Ḥusayn revolted also against the fact that the Ottomans had opened their ranks to a foreign and ungodly community, the Germans, by allying with them. [START_REF]On the German-Ottoman alliance in the Arab Peninsula during the war[END_REF] He writes that seven Germans had come to the Sharīf (from Sana'a) in order to propose that he leaves for Germany with them (why? -it is not explained), but that instead of following them, Sharīf Ḥusayn ordered their beheading, and that he eventually had the seven heads sent to the British. 74 According to al-Washalī, this wartime gift made the British indebted to the authoritative and powerful Sharif of Mecca:

The English were grateful to him, and they began to attach value to him. They were in constant contact with him by telegraph, and they sent him gold so that he could wage war against the Turks settled in Mecca and Jeddah. The Sharif then gathered a large number of tribes and told them: "You know that you are the people of the Sacred House (the Holy Places). The Turks mixed with the Germans, so that they could take their railway to Medina and Rabīgh [South of Medina], with the ultimate goal of extending to Mecca. They forbade you to live on your camels. But should you live away from your religion and your sanctuary?" 75 The Germans' interference in the Ottoman Empire's internal affairs in 1916 -an idea, which had spread in popular milieus in the Hedjaz, as the French Consul in Jeddah noticed it-, [START_REF]Hedjaz the Turks were called "Germans" by the Bedouins: see Letter of Col. Brémond to the French Minister of Foreign Affairs[END_REF] offers a clue about al-Washalī's gradual criticism of Ottoman presence in Yemen. The denunciation is rather implicit-and may be linked to the observation of the severe punishment the Ottomans inflicted on those who turned against them. 77 It emerges in his presentation of how the Ottomans dealt with the British blockade, which intensified after the Arab Revolt. [START_REF] Baldry | notes that the British patrols were quite ineffective until 1917[END_REF] Al-Washalī conscientiously highlights the terrible situation, which the people had to endure that year as a result of the "impious English State blockade," and how they were forced to live on wild berries, and sell their children-even noticing a man who had "sold his mother" [START_REF] Baldry | [END_REF] The shortage of food and arms seriously affected the military Ottoman positions. Since communications were cut, the Ottomans failed to pay the soldiers' salaries-a situation that, according to al-Washalī, forced the central administration to send two officers from Istanbul to Sana'a by land transport and even foot, with pockets full of money for the Ottoman army in Yemen in 1917. 80 The author highlights that many tribes who were allied with the Ottomans and Imam Yaḥyā ended up turning away from them, while for his part, al-Idrīsī made a series of new alliances: he succeeded in bringing 10,000 combatants over to his side in the fall of 1917, paying and feeding them well. He distributed weapons, flour, and money to those around him. 81 As far as the British were concerned, they could rely on the Zarānīqs. They also managed to buy the support of people in northern "Yemeni ports" like Jeddah (sic) in July 1916 andin Salīf in April 1917. 82 According to al-Washalī, the application of additional taxes, notably affecting the merchants of the Tihāma, was another result of the blockade. Although the taxes were increasingly unbearable, the Ottomans did not hesitate to brutally punish those who refused to pay them. Women fell victim to repression, a growing number of freed slaves were sold, 83 , and the town of Zabīd was bombed, killing seventeen people, after merchants refused to lend the Ottomans 16,000 rials. 84 Rural areas were also affected by the Ottoman reaction to the situation. Al-Washalī mentions small details to demonstrate how they also terrorized the people of the Tihāma by burning the villages of al-Idrīsī's supporters, 85 seizing their goods, 86 or plundering the local merchants (namely the wealthier Indians). 87

Al-Washalī also relates a serious situation concerning division among the Ottomans, when he attributes the British attack on the town of Salīf in June 1917 to the complicity "of some officers of the [Ottoman] State in Salīf. They apparently corresponded with them [the British] secretly and have received a lot of gold coins, selling their religion, seeking to rely on the impious Muslim countries." 88 Whereas, in al-Washalī's presentation, Sharif Husayn had shown his political and personal force by heading seven Germans, so that he could submit the British to his authority, these Ottoman officers had no means, in al-Washalī's narrative, to be presented differently but as traitors. What could be expected then from a state which was plagued by division and which adopted forms of violence usually associated with tribes, when its legitimacy was based precisely on its ability to establish order and harmony? Unlike Sharif Ḥusayn, the Ottomans certainly offered no further evidence of their honor, and their defeat seemed more and more inevitable -if not desirable. Al-Washalī notices that they left the city of Luḥayya, taking the "diwan's notebooks" with them (a sign of their escape), 89 and that they were also unable to hit and damage the British planes flying over their positions. 90 As for al-Idrīsī, it no longer matters that he was supported by the British, for it is as if his growing Islamic leadership justifies the means. From this period onward, al-Washalī calls his combatants "the Army" (al-jaysh)-lending his supporters a form of legality. Thereafter, "al-jaysh" alone suffices to designate al-Idrīsī's army.

In al-Washalī's chronicle, the end of the war in October 1918 is marked by the British bombing and occupation of the city of Ḥudayda, from then on occupied like the Kamarān Island (June 1915) and Luḥayya (June 1918). [START_REF] Also | 162 for the occupation of Kamarān, which remained under British administration until[END_REF] For him, this is a huge event that affected Islam and all Yemeni Muslims. [START_REF]The British eventually left Luhayya, Ḥudayda, and Kamarān Island permanently in 1919[END_REF] Associated with "one of those impious communities called Amīrīkān [Americans]," the British imposed "forty conditions" on the Ottoman State, one of which was "the sale of Yemen, Syria, and Iraq": 93 probably referring to the armistice of Mudros (30 September 1918), [START_REF]Although the Mudros Agreement contains only 25 articles. Cf. "Art. VXI: Surrender of all garrisons in Hedjaz, Assir, Yemen, Syria, and Mesopotamia to the nearest Allied Commander[END_REF] al-Washalī provides an interpretation that condemns both the British and the Ottoman attitudes toward these previous Ottoman provinces. Following the agreement, the Ottoman army was to surrender in Yemen without leaving any regrets.

Al-Washalī fails to mention that the fall of Luḥayya was the result of an Anglo-Idrīsī cooperation but instead, underlines that the Ottomans in 'Asīr handed over all their weapons to al-Idrīsī, now referred to as Mawlanā al-Imām (Our Lord the Imam) or as Imam Amīr al-Mu'minīn (Commander of the Faithful)-a title that had hitherto been reserved for the Ottoman sultan. As for Imām Yaḥyā, al-Washalī does not mention that he had already taken possession of Sana'a, and that he was also handed over many weapons from the Ottomans. 95 Obviously, the chronicler had definitively chosen his side. This is confirmed by the way he refers to Yaḥyā's title, which shifts from Imam of Shahāra to the slightly more restrictive Sayyid al-'Allāma ("Very Learned Sayyid"). Yaḥyā, who was believed to have lost the war at the same time as the Ottomans, ends up simply considered as an important religious scholar expected to pledge allegiance to the new leader, al-Idrīsī, along with al-Washalī, who would be placed in charge of the district (Qaḍā) of al-Ḥudayda in 1921. 96 After the emir's death in 1923 and the deterioration of his emirate, however, al-Washalī will defect to the new authority of Imam Yaḥyā, becoming the town mufti in addition to the head of the district. [START_REF] Al-Maqhafī | introductory note to Nashr al-thanā[END_REF] Following his previous allegiance to the Ottomans, one can imagine that he had little difficulty dealing with the numerous "ex-Ottomans" who stayed on in Yemen and now served Imam Yaḥyā's new State. 98

Conclusion

The years of World War war, following the Young Turks Revolution (1908) and sultan Abdülhamid's dismissal (1909), were years of profound upheaval for the Yemenis-particularly for those who, like al-Washalī, had sworn allegiance to the Ottomans. The "Rule of Difference" carried out by the latter had enhanced the local powers of the sayyid-s, and al-Washalī shows how the pan Islamic ideology developed by Sultan Abdülhamid contributed to the recognition of their social and political ascendency and, finally, to their alliance with the Empire.

But like so many sources examined by historians, al-Washalī's chronicle is far from being neutral. The author was obviously captivated by the leadership of Emir al-Idrīsī as soon as 1909, and was aware of the growing power of Imam Yaḥyā after the treaty of Da''ān in 1911. Time had come to try to assert the unity of the Tihāma behind its noble and educated leaders, the sayyid-s, the group he belonged to, and to secure their future. The chronicle was certainly the sole tool to achive this goal, and al-Washalī made it a document claiming the recognition-implicit or explicit-of all forms of sovereignty -sunnī or zaydī-, provided that they were framed as an Islamic power that was strong enough to ensure security and bolster the social authority of the local elite. The Ottoman administrators' fears that the Shafi'īs' loyalty was not secure because of the Zaydī rebels' capacity to diffuse their rebelliousness 99 may have been totally unfounded. Al-Washalī's defection to al-Idrīsī was not a repudiation of the Ottomans' former authority. Rather, he validated the idea of a natural continuity between two opposing Muslim sides that were not actually enemies: al-Idrīsī was simply able to support the Islamic values of peace and security that the Ottomans could no longer honor and uphold because of their defeat in World War I, and his ties with the "impious" British deserved to be ignored. Al-Washalī's chronicle can be seen as means of revealing the qualities of a new Yemeni state, the contours of which while still variable are nonetheless characterized by peace and justice thanks to its educated elite, and by a rejection of all forms of Christian and occidental influence. In this sense, al-Washalī took a stand as a sayyid in the debates of his time in order to define and elaborate the nature and structures of the future government of Yemen. In these, his chronicle emphasized and demonstrated how the ulemas could -or even, should-play an essential role in the application of justice, and it also provided a template for structuring the political sphere, in which sayyid-s were expected to dominate society. After all, the author illustrated and continuously underscored the crucial part he was playing as a sayyid and scholar in guiding the people to accept the authority of their leaders. By doing so, he is also, maybe, one of the Shāfi'ī actors of the model's revival articulated around the alliance of ulemas and rulers that the Qāsimī dynasty had developed from the beginning of the eighteenth century, and that Imam Yaḥyā will reassert while creating the first modern State of Yemen after the 1920's.

  , CNRS, IREMAM UMR 7310, 13094 Aix-en-Provence, France Références de l'article publié : HONVAULT, Juliette. World War I and the Perspective of a Hashemite Order in Yemen. Study of the Chronicle of Ismā'īl b. Muḥammad al-Washalī, In : The First World War from Tripoli to Addis

  Ibrāhīm Aḥmad al-Maqhafī, introduction to Nashr al-thanā, by al-Washalī 1982, vol. 1, part 1, p. 11. The book is composed of two parts, each divided into two volumes: genealogy and biographies of great scholars descending from al-Ḥusayn b. 'Alī (vol. 1); genealogy and biographies of great scholars descending from al-Hasan b. 'Alī (vol. 2); biographies of other great scholars of the Tihāma (vol. 3); and the chronicle (hawādith al-waqt wa nawādīrihi) (vol. 4). 20 Al-Washalī, vol. 4, part 2, p. 5. 21 For example, see what occurred around the time of Abdallah b. Aḥmad Bawnī Pasha; al-Washalī, vol. 3, part 2, p. 92.

  argued that the Ottomans' inability to apply the sharia justified the jihād29 Kuehn, op.cit., vol. 4, part 2, p. 93. 31 For a complete account in English of the Revolt of 1911, seeBaldry 1976b. 32 Al-Washalī, "Ahdāth 'ām 1330," vol. 4, part 2, p. 93. 33 See JocelyneDakhlia 1998, p. 103. 34 Al-Washalī, general introduction to Nashr al-thanā, vol. 1, part 1, p. 13. This was probably written after the biographical encyclopedia. vol. 4, part 2, p. 5. 36 Abdülazīz was the Sultan of the Ottoman Empire from 1861 to 1976.37

This paper was first presented under the title "Fighting With the Ottomans: The Islamic Cause in Yemen During World War I" at the International Conference of Istanbul, "Not All Quiet on the Ottoman Fronts: Neglected Perspectives on a

 vol. 2, part 1,

'Abd al-Bārī Ṭāhir also highlights this in his preface: see al-Washalī, Nashr al-thanā, vol. 1, part 1, p. 8. On this issue, see Bernard Haykel (2003). Al-Washalī, refers to and quotes Muḥammad al-Shawkānī in his chronicle: see al-Washalī, vol. 4, part 2, p. 23

The author seemingly began to write the biographical part of the book and the chronical simultaneously at the end of 1911: as underlines 'Abd al-Bārī Ṭāhir it in the general introduction, al-Washalī indicates that someone who was born in 1296/1879 is 33 years old at the time when he writes his history, i.e. around1330/1912 (p. 36); and he indicates the year when he is writing in the chronicle,1329/1911, vol. 4, p. 10.

The year 1327/1909 is the first year to be reported in detail in the chronicle. Just like the reports for the years that follow, it contains eleven pages, whereas those for the years prior to this rarely exceed two pages and only provide a summary of the most important events. After 1339/1920, events were observed in less detail, perhaps due to the author's new administrative and religious responsibilities.

 vol. 4, part 2,

Ibid., vol. 4, part 2, p. 85. See also Anne[START_REF] Bang | The Idrisi State in 'Asir, 1906-1934: Politics, Religion and Personal Prestige as State Building Factors in Early Twentieth-Century Arabia[END_REF], p. 90-94. Al-Washalī does not mention that al-Idrīsī signed a treaty with the Ottomans in al-Hafā'ir, which was ratified in Istanbul in January 1910. The Ottomans recognized al-Idrīsī as the qā'im maqām (representative of the Sultan) of 'Asīr, provided that he acknowledged their right to collect taxes in the port cities and to maintain garrisons in the territory. Al-Washalī does mention, however, al-Idrīsī's campaign against the Ottomans in 1910 and how, despite the support of Sharīf Ḥusayn from Mecca, the latter did not succeed in driving him back.

 vol. 4, part 2, p. 82-93.

On the weak impact of the Young-Turk Revolution on Yemen in1908[START_REF][END_REF], see Juliette Honvault 2012.

The French Vice-Consul in Ḥudayda to the French Minister of Foreign Affairs reports, in the end of 1912, a discussion with a local "notable" stressing what he presents as a shared opinion among the "Arabs", that, "at this point, the common


Ons Aouedi

Kandaraj Piamrat

Benoît Parrein

Decision tree-based blending method using deep-learning for network management

Keywords: Blending, traffic classification, ensemble learning, machine learning, deep learning, decision tree

Network traffic classification is a key component for network management, Quality-of-Service management, as well as for network security. Therefore, developing machine learning (ML) methods, which can successfully distinguish network applications from each other, is one of the most important tasks. However, among the classification methods applied to network traffic classification so far, there is no one method that outperforms all the others. They all have advantages and inconveniences depending on the application domain. Therefore,this paper proposes an intelligent traffic management model by using deep learning (DL) that incorporates multiple Decision Treebased models. Our model deploys a blending ensemble learning method to combine tree-based classifiers in order to maximize generalization accuracy. Using two datasets, we show that our proposed ensemble model is efficient for network traffic classification. Furthermore, the proposed approach is also compared against other representative machine-learning and deep-learning models and the results demonstrate that our approach provides better performance compared to others.

I. INTRODUCTION

Traffic classification is a subgroup of traffic management strategies that aim to classify the traffic into predefined categories, such as normal or abnormal traffic, the type of application (e.g., streaming, Web browsing, etc.) or the name of the application (e.g., YouTube, Netflix, Google, etc.) [START_REF] Pacheco | Towards the deployment of machine learning solutions in network traffic classification: A systematic survey[END_REF]. Identifying different applications from traffic is critical to manage bandwidth resources and to ensure Quality of Service requirements. Consequently, traffic classification helps Internet Services Providers to manage their infrastructures efficiently and hence improve the service offered to their customers. However, traditional techniques such as port-based classification and deep packet inspection are becoming less efficient to handle and classify heterogeneous traffic (i.e., various applications). In this line, ML is opening the ways to develop powerful network traffic classifiers, which achieve an acceptable tradeoff between complexity and accuracy.

ML models can be broadly divided into two categories, which are simple (i.e., individual) machine models and ensemble models. Ensembles are well-established ML techniques that can obtain more accurate prediction results by integrating various base learners [START_REF] Polikar | Ensemble based systems in decision making[END_REF]. Considering the risk and the difficult task of choosing the suitable model for traffic classification, ensemble learning can be a promising solution as it aims to combine heterogeneous or homogeneous ML models (commonly classifiers) in order to obtain a model that outperforms every one of them and overcome their limitations [START_REF] Li | A novel ensemble deep learning model for stock prediction based on stock prices and news[END_REF]. Ensemble learning can be generally divided into two groups: (i) homogeneous ensemble (like bagging or boosting) and (ii) heterogeneous ensembles such as blending. The blending takes advantage of different ML models. Through the use of a learning method in the combination stage (i.e., meta-classifier), the blending model is much more powerful than single models. However, little attention has been paid to the application of the blending ensemble to integrate multiple types of classifiers in the network context. Moreover, it is well-known that DL techniques outperform the other ML methods in several fields and have shown success in network traffic classification [START_REF] Pacheco | Towards the deployment of machine learning solutions in network traffic classification: A systematic survey[END_REF]. In addition, DT-based models are the most suitable learning algorithm for network traffic classification [START_REF] Amaral | Machine learning in software defined networks: Data collection and traffic classification[END_REF] as they can produce solutions in the form of models, which can be easily understood by human experts.

For the aforementioned reasons, in this paper, we focus on the non-linear blending model based on DL as a nonlinear meta-classifier using DT-based models as the base classifiers. We propose this ensemble because the non-linear blending performs better than uniform blending (majority voting) and linear blending [START_REF] Chen | Comparison and improvement of the predictability and interpretability with ensemble learning models in qspr applications[END_REF]. Consequently, during the process of blending construction, model selection and model combination are explored. Then, several DT-based classifiers are used as base classifiers including simple DT, Random Forest (RF), AdaBoost, and XGBoost, and then DL is used as a meta-classifier in order to learn the non-linear relationship among the base classifiers. To the best of our knowledge, this investigation of the non-linear blending method is performed in network traffic classification for the first time.

The rest of the paper is organized as follows. Section II discusses related works. Section III presents the proposed models. In Section IV, experimental results and performance of the proposed model are presented. Finally, conclusions and future works are given in Section V.

II. RELATED WORK

This section presents an overview of state-of-the-art approaches that are proposed to solve the traffic classification problem using ML/DL models.

Using Machine learning methods, many solutions have been proposed for network traffic classification. In this context, Cherif et al. [START_REF] Cherif | On using extreme gradient boosting (xgboost) machine learning algorithm for home network traffic classification[END_REF] used the symmetric uncertainty feature selection method then XGBoost for traffic classification. Peng et al. [START_REF] Peng | Effectiveness of statistical features for early stage internet traffic identification[END_REF] tested ten well-known classifiers includes Adaboost, DT, RF, Naive Bayes classifiers. Also, Belavagi et al. [START_REF] Belavagi | Performance evaluation of supervised machine learning algorithms for intrusion detection[END_REF] have compared several ML models for intrusion detection which are Logistic Regression, Gaussian Naive Bayes, SVM, and RF. The results were indicated obtained that RF outperforms the other classifiers. Qazi et al. [START_REF] Qazi | Application-awareness in sdn[END_REF] presented a mobile application detection framework, called Atlas. This framework enables fine-grained application classification using DT as a classifier.

DL models have advanced considerably and are being widely adopted in several domains. Several studies show that it completely outperforms traditional methods in most areas. Thus, researchers have tried to apply DL for traffic classification and it has been used as semi-supervised and supervised learning based on the amount of label data. In such context, Aouedi et al. [START_REF] Aouedi | A semisupervised stacked autoencoder approach for network traffic classification[END_REF] have used DL as semisupervised learning for network traffic classification with the help of dropout and denoising code hyper-parameters in order to improve the classification performance.

Moreover, the increasing demand for user privacy and data encryption has tremendously raised the amount of encrypted traffic on today's Internet. Consequently, encrypted traffic classification has become a challenge in modern networks. In this context, DT-based classifier and DL can be good classifiers for encrypted traffic characterization. For instance, Draper et al. [START_REF] Draper-Gil | Characterization of encrypted and VPN traffic using time-related[END_REF] have used two common ML models, which are DT and KNN (K-nearest neighbor), to distinguish between VPN and non-VPN network traffic. The results show that DT has achieved better results. Also, Alshammari et al. [START_REF] Alshammari | learning based encrypted network traffic classification in SDN home gateway[END_REF] show that DT performs much better than Genetic Programming and Ad-aBoost algorithms in classifying VoIP Skype network traffic. In addition, in this field, DL models have been used in order to accurately classify the encrypted network traffic [START_REF] Wang | Datanet: Deep Conference on Network Protocols (ICNP)[END_REF] [START_REF] Lotfollahi | Deep packet: A novel approach for encrypted traffic classification using deep learning[END_REF].

The current literature shows that it is promising to classify network applications using ML-based approaches. Additionally, strategies such as bagging and boosting are widely used as ensemble models. From the above review, it can be seen that heterogeneous ensemble-learning models' potential in network traffic classification is not fully studied, despite, they achieved a remarkable generalization performance [START_REF] Xiao | A deep learningbased multi-model ensemble method for cancer prediction[END_REF]. Moreover, although the efficiency of DT-based classifiers and DL for network traffic classification, to the best of our knowledge no paper exploits them together in one model. Consequently, our approach leverages their successful experiences and creates a new model to perform a better classification.

III. PROPOSITION

This paper introduces a new decision tree-based ensemble learning method for network traffic classification. In this section, the architecture of the proposed ensemble model and its principle design are presented. Figure 1 summarizes the methodology of this model. For the training data, data pre-processing is performed. It includes data normalization using Min-Max as well as the feature selection process. After extensive experiments, we decide to deploy a blending ensemble learning to improve the performance and generalization capability for network traffic classification.

A. Data pre-processing

Data pre-processing is a data mining technique that is used to transform the data and makes it suitable for another processing use (e.g. classification, clustering). It is a preliminary step that can be done with several techniques among which feature selection. This task was done in our preliminary work [START_REF] Aouedi | Performance evaluation of feature selection and tree-based algorithms for traffic classification[END_REF], in which we have compared Recursive Feature Elimination (RFE) against Information Gain attribute evaluation (IG). RFE is a wrapper method that recursively evaluates alternative sets by running some induction algorithms. Starting from all the feature sets, the method recursively removes the less relevant features. After the optimal subset has been selected by RFE, we use these features as input of the proposed ensemble model.

B. Blending ensemble learning

As shown in Figure 1, our model is mainly composed of two levels, which are base-classifiers using DT-based models (level-1) and meta-classifiers using DL (level-2). The principal purpose of level-1 is to construct base classifier models utilizing the training set and to produce the meta-data for the meta-classifier (i.e., DL in our case) using the validation set. Then, the meta-classifier model is used to make the final classification. In other words, we use a hold-out method to divide the training set into a new training set and validation set. Then, the base classifiers models are constructed through the new training set and their predictions on the validation set to generate the meta-data. Next, the meta-classifier uses this meta-data for the training process and to make the final classification on the test set.

In order to construct an ensemble model with both good generalization and classification performance, (as discussed in the literature review), DT, RF, Adaboost, and XGBoost models were our choice as base classifiers (level-1). Since, the base classifiers need to be accurate, diverse, and complementary as possible in order to provide highly discriminative meta-data for classification [START_REF] Sesmero | Generating ensembles of heterogeneous classifiers using stacked generalization[END_REF], a comparative analysis has been done on seven DT-based models with respect to the algorithm on which it is based (e.g., gradient boosting or bagging). Here, we compute the average of the evaluation metric from ten runs. Next, in level-2, we used the DL model to combine the prediction output of the base classifiers (level-1), and explore the non-linear relationship among the base classifiers and in turn, get a non-linear blending model. This step is known as the combination phase where the DL learns from the metadata generated by the level-1 classifiers to find one and final decision. As DL acts as a combination method and its inputs are the prediction of the base-classifiers, known as meta-data, we use a simple neural network architecture (i.e., three hidden layers). Algorithm 1 explains the steps involved in designing a blending-based ensemble, and Table I explains the notations used in the algorithm. IV. EXPERIMENTAL STUDY AND RESULTS ANALYSIS In this section, we evaluate the performance of the proposed ensemble model by performing extensive experiments. The obtained results are analyzed and discussed as well as we show on the used datasets that our proposed model improves the classification performance (e.g., accuracy and generalization).

A. Experiment setup

Here, we compute the average of the evaluation metric from ten runs. Also, there are different evaluation models as k-fold cross-validation and train/validation/test split. In this research, we used the train/validation/test split because the validation set is an essential part to build our blending ensemble.

The code is made available online1 .

• Dataset description

We evaluate the different classifiers on a real-world traffic dataset. This dataset was presented in a research project and collected in a network section from Universidad Del Cauca, Popayán, Colombia [START_REF] Rojas | Personalized service degradation policies on OTT applications based on the consumption behavior of users[END_REF]. It was constructed by performing packet captures at different hours, during the morning and afternoon over six days in 2017. We chose this dataset because it can be useful to find many traffic behaviors as it is a real dataset and rich enough in diversity and quantity. It consists of 87 features, 3,577,296 instances, and 78 classes (Facebook, Google, YouTube, Yahoo, Dropbox, etc.). In this experiment, we have separated the dataset into 80% for training, 10% for validation, and 10% for testing.

B. Ensemble-based deep learning classifier

In order to find the optimal model, we conduct base classifiers selection as explained below.

1) Feature Selection: Using RFE, we have derived a method to identify the best 15 features out of 87 features in our preliminary work [START_REF] Aouedi | Performance evaluation of feature selection and tree-based algorithms for traffic classification[END_REF]. The 15 selected features are listed hereafter : DestinationIP, sourceIP, sourcePort, destination-Port, FlowIATMax, FwdIATTotal, Timestamp, FlowDuration, InitWin-BytesBackward, InitWinBytesForward, FwdPacketLengthMax, Bwd-PacketLengthMax, SubflowFwdBytes, BwdPacketLengthMean, Fwd-PacketLengthStd.

2) Base classifiers selection:

To start, we first randomly partitioned the data into a ratio of 80% for training, 10% for validation, and 10% for testing the different models. Table III shows the accuracy of different DT-based methods. It can be seen that RF has the best accuracy as a bagging method Based on these results, to improve the generalization performance of Tree-based models and based on the above results, we will use DT, RF, XGBoost, and AdaBoost as base classifiers (i.e., level-1 of the blending). DT is a simple and classical model, RF is a bagging model that improves the classification performance and builds different versions of the training set by sampling with replacement, and XGBoost and AdaBoost as boosting models can help to avoid the problem of underfitting (bias). We have chosen XGboost and Adaboost as they perform better than the other boosting models (i.e., LightGBM, CatBoost) and their boosting process is different. Although all the base models in this study are based on DT, they work in a different way (e.g., their training process does not use the same training set) and guarantee the diversity of level-1 models.

3) Results of the proposition: In this subsection, different results are presented along with their analysis and discussion.

• Classification performance The classification performance of the proposed ensemble using training and test set is presented in Table II. Note that the DL (meta-classifier) hyper-parameters is as follows, number of hidden layer=3, activation function=ReLu, learning rate=0.001, and optimizer=Adam.

It can be seen that using the training set AdaBoost gives the best results, followed by RF and XGBoost, our model, and DT. The accuracy achieved by the base classifiers, which are DT, RF, AdaBoost, and XGBoost on the training set is 87.56%, 94.68%, 97.13%, and 92.59%, respectively. However, the classification performance of these models using the test set is different where their accuracies are 82.24%, 85.28%, 88.51%, and 88.70%, respectively. It is important to note here that ML models need to perform very well on the test set (i.e., unseen data during the training). In contrast to the base classifiers, the difference between classification results using the training and test set of our ensemble model is almost negligible (Table II andFigure 7), where the training and test accuracy are 89.78% and 89.77%. This demonstrates that our ensemble does not have an overfitting problem. This may be attributed to the generalization ability of the blending ensemble. Moreover, its accuracy is 1.07%, 1.26%, 4.49%, 7.53% better than XGBoost, AdaBoost, RF, and DT, respectively. Similarly, in terms of the other measures, the proposed model also outperforms its base classifiers.

• Impact of the hold-out validation set Figure 2 shows the impact of the hold-out validation set on the performance of the blending method as well as the base classifiers. The hold-out method is used to divide the training set into a new training set and a validation set. Here, the ratio of the validation set varied between 10% and 40% with a step size of 10% (we stopped because the performance started to decrease). Also, we evaluated the impact of this ratio in terms of several evaluation metrics. It can be seen that the blending method maintained a better prediction performance than the base classifiers in all cases in terms of different evaluation metrics. Moreover, when the ratio of the hold-out validation set is 10%, the blending method can obtain the best results. In addition, we can notice that the performance of the base classifiers decreases with more validation sets (i.e., less training set), and hence the performance of the blending method decreases. This is because increasing the hold-out validation set (i.e., the training data for the meta-classifier) means decreasing the training set of the base classifiers. Therefore, the performance of the blending method depends on the quality of the base classifiers and that is why choosing the appropriate models for the ensemble is a crucial step.

• Impact of the base classifiers

To find the base classifiers that can impact the performance of the proposed ensemble model, some experiments have been conducted. We tried to evaluate the performance of the proposed model with different combinations of base classifiers. Figure 3 presents the accuracy of different combinations of three base classifiers and the one with all the base classifiers Fig. 2: Effect of hold-out validation set ratio (proposed model). It is important to note here that with all the cases, we used DL as a meta-classifier.

The proposed model that integrates all the base classifiers has a better result than the three base classifiers. This means that no model negatively impacts the performance of the proposed ensemble. Moreover, as shown in this figure when we drop out one of the boosting models (AdaBoost and XG-Boost) the accuracy of our ensemble decreases significantly. Specifically, XGBoost plays the most critical role in achieving good performance. The accuracy of the blending decreases notably without XGBoost, which means that this model is an important component of our ensemble-learning method. • Comparative analysis over various ML algorithms In order to further validate the effectiveness of the proposed ensemble, which demonstrated the best performance against the base classifiers, we compared this framework with some representative ML algorithms. The optimal hyper-parameters of these algorithms have been used. These classifiers include (i) simple classifiers such as SVM and KNN, (ii) ensemble models such as Extra-Trees, LightBGM, and CatBoost, (iii) neural network classifier, which is Multi-layer Perceptron (MLP) classifier. We select these classifiers as our baselines because Extra-Trees, DT, and KNN are easy to train, SVM is widely used and proved to be useful in several applications [START_REF] Kilincer | Machine learning methods for cyber security intrusion detection: Datasets and comparative study[END_REF], and MLP is a neural network model (we have used the optimal architecture which is two hidden layers, the same learning rate, and the activation function as our metaclassifiers), as well as CatBoost and LightBGM because they are recent models for the classification task.

Figure 4 shows the accuracy of the proposed ensemble and the various ML models. In this case, a clear hierarchy of models emerges from best to worst. We can see from the results that the proposed model performs well when compared with the different ML algorithms. Its accuracy is 4.9%, 5.2%, 11,98%, 14.29%, 16.11%, 42.75% better than Extra-Trees, LightBGM, CatBoost, MLP, KNN, and SVM, respectively. This may be attributed to the fact that the combination of DTbased models and DL helps to yield far superior results compared to several ML models. Consequently, we can conclude that our model is a good model and can better differentiate the applications. All experiments were run using four core Intel® Core™ i7-6700 CPU@3.40GHz processor, and 32.00 GB of RAM. One of the advantages of this model is that the base classifiers: DT, RF, AdaBoost, and XGBoost can be trained in parallel. Consequently, since boosting models take a long time to train (Table III), thus they can impact more the training time of the proposed model than RF and DT.

As shown in Figure 5 and Figure 6, we have compared classification time (CT) per sample and the training time (TT) taken by respective models. In the case of AdaBoost, TT is 7921s and CT is 149.38µs. Whereas, for XGBoost, TT is 52×10 3 s and CT is 550.89µs. Finally, for the blending model, TT is 53 × 10 3 s and CT is 581.6µs. Moreover, as shown in Figure 7, that the meta-classifier (i.e., DL) converges quickly and its accuracy starts to be stable after 20 epochs, indicating that the training process of the DL is time-efficient. Thus, although we used a large amount of data, DL (level-2 of the blending) requires just a few epochs to converge. This is because the new features used by the DL are the output of the base classifiers. Consequently, the features deployed by the meta-classifier are relevant features and can help it to converge fast and very well.

As explained in Section III, our model consists of two main phases (level 1, and level 2 process) and it trains data more than the base classifier (training set+validation set). Thus, this can explain its high training time. In addition, there is a slight difference with XGBoost. However, the training time can be proceeded offline and thus does not impact the realtime utilization of the classification process.

C. Experiments on other datasets

Recently, as many solutions have been proposed for encrypted traffic classification, we also implemented experiments based on another dataset, called VPN-nonVPN dataset in order to validate the effectiveness of the proposed ensemble on encrypted traffic. The VPN-nonVPN dataset consists of encrypted traffic characterized only by time-related features [START_REF] Draper-Gil | Characterization of encrypted and VPN traffic using time-related[END_REF].

• The proposed ensemble with VPN-nonVPN dataset To evaluate the performance of the proposed ensemble, four scenarios of different classification tasks were proposed in experiments (for more details on the captured traffic and the traffic generation process, refer to [START_REF] Draper-Gil | Characterization of encrypted and VPN traffic using time-related[END_REF]). Scenario A (Sc A) is a binary classification to indicate whether the traffic flow is VPN or not. Both scenario B (Sc B) and scenario C (Sc C) are 7-classification tasks. Scenario B is to distinguish between seven non-VPN traffic services like audio, browsing, etc. Scenario C is similar to Scenario B, while its target labels are seven traffic services of the VPN version. Scenario D (Sc D) mixes all the fourteen types mentioned in scenario B and scenario C to perform the 14-classification task. Similar to the first dataset, we have used the RFE as a feature selection method for each scenario. It can be seen from Table IV that our ensemble achieved the best results with the VPN-nonVPN dataset in all scenarios. This can explain the performance of our model using only time-related features. Specifically, for example, in Scenario A, the accuracy of model is (8.31%, 13.29%, 34.84%, 26.83%, 5.74%, 5.47%, 4.51%, 3.9%, 5.5%, 3.64%) better than DT, KNN, SVM, MLP, Extra-Tree, RF, CatBoost, LightGBM, Ad-aBoost, XGBoost, respectively. On the other hand, in scenario D, the accuracy of our model is (15.19%, 21.31%, 49.83%, 39.39%, 9.9%, 9.83%, 8.82%, 7.12%, 10.38%, 7.32%) better than DT, KNN, SVM, MLP, Extra-Tree, RF, CatBoost, LightGBM, AdaBoost, and XGBoost models, respectively. These results illustrate the high performance of our model with both binary and especially for multi-classification scenarios.

V. CONCLUSION AND FUTURE RESEARCH

In this paper, ensemble learning based on deep learning and four DT-based models has been proposed in order to provide efficient solutions for network management. The proposed ensemble consists of pre-processing tasks and classification tasks. For the base classifiers selection, a comparative analysis has been conducted based on the complexity and the accuracy of the classifiers. Next, an ensemble model that incorporates several DT-based models and deep learning is applied to improve overall classification accuracy. By using deep learning as a meta-classifier, the non-linear relationships among the base classifiers are learned automatically, thus enabling the ensemble method to achieve a better classification. Using two datasets, the simulation results show that the proposed ensemble model outperforms other traditional machine learning models (DT, SVM, KNN) and ensemble learning models (e.g., RF, MLP).

For future work, we will investigate further the performance of our model in another context (e.g., intrusion detection) and compare its performance with other ensemble models such as majority voting and linear blending.

Fig. 1 :

 1 Fig. 1: Flowchart for the proposed traffic classification model

Fig. 3 :

 3 Fig. 3: Results of base classifier experiments.

Fig. 4 :

 4 Fig. 4: Comprehensive comparison of well-known classifiers • Time cost of the proposed modelWe now analyze the computational efficiency of the proposed model against other ML models. This comparison has been done in terms of training and classification time. All experiments were run using four core Intel® Core™ i7-6700 CPU@3.40GHz processor, and 32.00 GB of RAM. One of the advantages of this model is that the base classifiers: DT, RF, AdaBoost, and XGBoost can be trained in parallel. Consequently, since boosting models take a long time to train (TableIII), thus they can impact more the training time of the proposed model than RF and DT.As shown in Figure5and Figure6, we have compared classification time (CT) per sample and the training time (TT) taken by respective models. In the case of AdaBoost, TT is 7921s and CT is 149.38µs. Whereas, for XGBoost, TT is 52×10 3 s and CT is 550.89µs. Finally, for the blending model, TT is 53 × 10 3 s and CT is 581.6µs. Moreover, as shown in Figure7, that the meta-classifier (i.e., DL) converges quickly and its accuracy starts to be stable after 20 epochs, indicating that the training process of the DL is time-efficient. Thus, although we used a large amount of data, DL (level-2 of the blending) requires just a few epochs to converge. This is because the new features used by the DL are the output of the base classifiers. Consequently, the features deployed by the meta-classifier are relevant features and can help it to converge fast and very well.

Fig. 5 :Fig. 6 :Fig. 7 :

 567 Fig. 5: Training time comparison

TABLE I :

 I List of notations used in ensemble learning model.

	List of notations	Meaning
	X	Set of features
	Y	Class label set
	M	Base classifier
	H	Ensemble classifier
	n	Number of training samples
	D train	training set of the base classifier (level-1)
	Dval	validation dataset
	P	Base classifier prediction using D val
	D ′	meta-data used to train the meta-classifier (level-2)

TABLE II :

 II Statistical measures of the base classifiers and blending methods using Training and Test sets.

	Dataset	Model	Accuracy	Precision	Recall	F1-score
		DT	87.56	87.55	87.56	87.36
		RF	94.68	94.81	94.68	94.59
	Training set	AdaBoost	97.13	97.18	97.13	97.11
		XGBoost	92.59	92.71	92.59	92.43
		Proposed model	89.78	89.74	89.78	89.95
		DT	82.24	82.06	82.24	81.99
		RF	85.28	85.57	85.28	84.71
	Test set	AdaBoost	88.51	88.72	88.51	88.16
		XGBoost	88.70	88.72	88.70	88.47
		Proposed model	89.77	89.70	89.76	89.93
	with 85.28% accuracy whereas the accuracy of Extra-Tree is
	84.87%. Also, it is more efficient in terms of training and
	classification time compared to Extra-Trees. Coming to the
	boosting models, where the AdaBoost and XGBoost outper-
	form the LightGBM and CatBoost. The accuracy of these
	models is 88.51% and 88.70%, respectively (they outperform
	LightGBM in terms of classification time and CatBoost in
	terms of training time).

TABLE III :

 III Comparison of different methods

	Methods Learning Algo-	Accuracy	Training time (s)	Test time (s)
		rithms	(%)
	Single	Decision Tree	82.24	110.21	0.24
	classifier
	Bagging	Random Forest Extra Tree	85.28 84.87	193.67 205.874	9.63 150.544
		AdaBoost	88.51	7921.74	53.44
	Boosting	XGBoost CatBoost	88.70 77.79	52423.84 231064.01	197.07 15.54
		LightGBM	84.57	6292.55	987.50

TABLE IV :

 IV The classification accuracy (%) of baseline and ensemble methods on VPN-nonVPN Dataset.

	Model	Sc A	Sc B	Sc C	Sc D
	DT	87.85	89.85	84.52	78.83
	KNN	82.87	86.39	80.79	72.71
	SVM	61.32	69.49	58.41	44.19
	MLP	69.33	78.40	75.80	54.63
	Extra-Tree	90.42	92.89	87.77	84.12
	RF	90.69	93.24	88.78	84.19
	CatBoost	91.65	94.61	88.26	85.20
	LightGBM	92.26	94.87	89.59	86.90
	AdaBoost	90.66	93.67	89.23	83.64
	XGBoost	92.52	94.71	89.45	86.70
	Proposed model	96.16	95.76	92.86	94.02

https://github.com/aouedions11/Decision-tree-based-blending-methodusing-deep-learning-for-network-management.git