多階層行動隨意網路之設計及實作---子計畫三:多階隨意網路上位置衍生的服務與應用(II)
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(2) 行政院國家科學委員會補助專題研究計畫期末報告 ※※※※※※※※※※※※※※※※※※※※※※※※※ ※ ※ ※ 多階層行動隨意網路之設計及實作—子計劃三： ※ ※ 多階隨意網路上位置衍生的服務與應用（2/2） ※ ※ ※ ※※※※※※※※※※※※※※※※※※※※※※※※※ 計畫類別：□個別型計畫 5整合型計畫 計畫編號： NSC 93－2219－E－009－002 執行期間： 93 年 8 月 1 日至 94 年 7 月 31 日 計畫主持人： 簡 榮 宏. 本成果報告包括以下應繳交之附件： □赴國外出差或研習心得報告一份 □赴大陸地區出差或研習心得報告一份 □出席國際學術會議心得報告及發表之論文各一份 □國際合作研究計畫國外研究報告書一份. 執行單位： 國立交通大學 資訊科學系. 中 華 民 國 94 年 7 月 27 日. I.
(3) 行政院國家科學委員會專題研究計畫期末報告 多階層行動隨意網路之設計及實作—子計劃三：多階隨意網路上 位置衍生的服務與應（2/2） Location-Base Services and Applications for Multi-tier Ad Hoc Networks 計畫編號：NSC 93-2219-E-009-002 執行期限：93 年 8 月 1 日至 94 年 7 月 31 日 主持人：簡榮宏 國立交通大學資訊科學系 計畫參與人員：蔡嘉泰、李奇育、張瑋倫、盧牧英 國立交通大學資訊科學系 中文摘要 隨著無線區域網路的普及，影響了人們對無線網路服務與應用的需求，其中位置衍 生(location-based)的服務與應用是最為重要的網路服務之一。在本計畫中，我們分別設 計了(1)定位技術(2)位置閘道器(3)地理位置資訊 (4)位置追踪服務等四個模組來提供位 置追踪服務應用系統。所開發的系統具有相容性、擴充性、模組化及不限使用環境的特 性。. 關鍵詞：無線區域網路、位置閘道器、位置追踪服務. Abstract With the development of Wireless Local Area Networks (WLANs), people are interested in developing the location-based services for WLAN users. In this project, we design and integrate a location-based service system with four modules: location determination technologies, location gateway, geographic location provisioning and location tracking service, to provide a location tracking service and application. This system has the ability of compatibility, extensibility, module, and unlimited circumstance. Keywords: Wireless local area networks, Location gateway, Location tracking service. II.
(4) 目錄 一、前言……………………………………………………………………1 二、研究目的………………………………………………………………1 三、文獻探討………………………………………………………………2 四、研究方法………………………………………………………………3 五、結果與討論……………………………………………………………7 六、參考文獻……………………………………………………………...12 附件一 附件二 附件三 附件四. III.
(5) 一、前言 隨著無線網路的發展及手持式設備成本的降低，不論是機場、學校、咖啡店、速食 店等公共場所亦或是個人的家中都有採用無線網路，如此普及的無線區域網路也促使了 中小型的設備，如筆記型電腦、個人數位助理器、手機，甚至是資訊家電等都具備無線 網路傳輸功能。尤其是小型的手持式設備，可以讓使用者攜帶在身邊隨時使用而不受限 制的在任何場所、地點及時間。正由於其可移動、方便攜帶及無線上網的特性，衍生出 許多的應用，如旅遊資訊導覽[1]、行車導航[2]及路況資訊的提供、緊急救援服務[3]等， 而這麼多應用服務(application services)的開發其背後均需要位置資訊的提供才能完成該 服務，然而所提供的位置資訊是否正確，精確度是否適合，都會影響著應用程式的服務 品質及正確性。因此，位置資訊的研究便成了開發以位置資訊為導向(Location-based Services)應用程式的重要技術。 在提供位置資訊技術的研究方面，已有不少的研究結果可供參考，然而這些技術都 有其適用的範及使用限制，例如全球衛星定位技術(Global Positioning System) [4, 5]，是 在行動裝置上加裝接收器來達成高定位精確度，而其最大的缺點在於室內的環境中無法 接收到訊號，而喪失定位功能；反之，也有只適用於室內的定位技術，如訊號特徵(signal fingerprinting)[6]定位方法，須事先在室內環境內量測訊號特徵值，並儲存於資料庫中， 但在室外環境下，由於量測區域龐大，此一定位方法就顯得不適用。除了上述兩種定位 系統外，尚有 DV-Hop[7]、質心定位法[8]、可移動參考點[9]、訊號到達基地台的夾角 (Angle of Arrival, AOA) )[10,11]、訊號到達基地台的時間差(Time Difference of Arrival, TDOA)[10,11]、輔助全球衛星定位系統(Assisted-GPS) [12, 13]、細胞識別定位系統等， 這些常見的方法將在文獻探討中加以詳細說明。因此，由上述可知發展一個可用於室內 及室外的定位技術是一個值得深入探討的研究課題。 另外，要發展一個適合室內及室外的定位技術要考慮的因素很多，影響定位系統準 確度的變因也很多，想要將這樣的系統設計得完善是很不容易，以目前所有已經提出的 定位技術中並沒有這樣的定位系統。所以，本計畫將考量各種定位技術、優缺點及其限 制條件後，開發新的定位技術，來達成能在室內及室內環境下都具有定位功能的系統， 並以此定位系統為基礎實作一個位置資訊為導向的應用程式，以驗證理論的可行性，及 分析實際定位系統的準確度。. 二、研究目的 定位技術的重要性已成為無線網路研究的重要項目之一，以目前定位技術的發展狀 況，使用者在不同的環境下，所能使用的定位技術也有所不同，這是由於定位技術的適 用範圍及其精確度的影響所致。然而這樣的差異對於開發位置資訊為導向應用程式的人 員會造成很大的困擾，需要額外的花費來偵測目前使用者環境的是否變化，程式開發的 複雜度也因此大大的升高。若程式開發者要求使用者自行設定其所在的環境，則會造成 使用者的不便，使用者必須明確知道其所在的環境，當其變換了所處的環境就要更動設 定。因此，為了降低開發位置資訊為導向應用程式的複雜度及提升使用者的便利性，發 展出適用於室內及室外的定位系統是必要的。本計畫的目標在發展一個適用於室內及室 外的定位系統。 然而直接發展一個適用於室內及室外的定位系統困難度及系統複雜度非常的高，因 此，利用適當的決策模組來整合現有的室內及室外的定位技術是一個有彈性且具模組化 的可行方法。具有彈性的優點是在於可以整合各種定位系統，或開發出新的定位技術後 可以加以替換而不需更動已開發完成的應用程式及定位系統。具有模組化的優點是能讓 1.
(6) 程式開發者專注於應用程式的領域來發展所需的位置資訊為導向應用程式，而不必再額 外考慮使用者所在的環境，有助於降低位置資訊為導向應用程式發展的複雜度及困難 度，也可讓專門研究定位技術的人員，針對其專長設計或改良出較好的室內或室外的定 位方法後，就可輕易的合併、替換或整合到此定位系統內。 然而在整合室內及室外的定位技術中，對於定位技術的切換時機及無接縫切換的問 題必需加以探討，因為若是切換時機不對或切換而造成長時間的延遲，都會造成位置資 訊的誤差、延遲(delay)或中斷。因此，定位技術的切換時機與無接縫切換的問題也是我 們在發展整合室內及室外的定位系統必需加以考量的重要因素。 綜合上述的各項因素，我們在本計畫中發展出一個整合室內及室外的無接縫定位系 統，並以此系統為基礎，再建立所需的地理資訊系統，如此便可發展成一個位置追踪服 務的應用系統，實作此位置追踪服務的應用系統所產生雛型系統可提供將來研究位置資 訊為導向的服務來參考。. 三、文獻探討 目前已有多種的定位技術及其應用被提出來，我們將其簡單分成三大類，分述如下： 1. 自行定位系統(Self-positioning system)：行動裝置能透過接收來自特定裝置所發送出 來的位置相關訊號，自行收集、處理後可獲得自身的位置資訊。 z DV-Hop[7]：利用計算從開始的節點至目的節點的 Hop 數目，並收集參考點的 位置資訊，來估計節點的位置。 z 質心定位法[8]：利用參考點的涵蓋區域重疊的特性，若使用者在某一涵蓋的重 疊區域內，則計算此區域的質心位置來當成使用者的位置。 z 全球衛星定位系統(Global Positioning System, GPS)[4, 5]：利用環繞地球的 24 顆衛星，將衛星精確的速度、高度、經度、緯度傳送到使用者的全球衛星定位 系統接收器，然後再由手機自行計算自己的位置。 z 可移動參考點[9]：利用數個可移動且週期性散佈其位置資訊的參考點，使用者 可以收集參考點的位置並加以分析，以獲得使用者的位置資訊。 2. 遠端定位系統(Remote positioning system)：在網路設備中加裝特別的無線電頻率功 能的裝置，經由測量訊號來源的方向或訊號來源的時間差。這此的量測資訊由中央 伺服器負責收集，並計算出位置資訊。 z 訊號到達基地台的夾角(Angle of Arrival, AOA)[10, 11]：基地台需額外建置一個 能辨別訊號送至基地台時的角度的天線，利用使用者與其所有相臨的基地台的 訊號夾角，再利用三角測量來獲得使用者的位置資訊。 z 訊號到達基地台的時間差(Time Difference of Arrival, TDOA)[10,11]：基地台需 額外建置一個設備，它能辨別訊號送至基地台時的時間差，利用使用者與其所 有相臨的基地台的訊號時間差，來獲得使用者的位置資訊。 3. 間接定位系統(Indirect positioning system)：此定位系統是整合自行定位系統與遠端 定位系統。欲定位的裝置先自行量測訊號資料，然後再將訊號資料送至遠端定位系 統。遠端定位系統收集這些量測的訊號資料及處理位置資訊的偏差值，便能計算出 位置資訊。 z 輔助全球衛星定位系統(Assisted-GPS) [12, 13]：方法頪似全球衛星定位系統，但 在網路端加入一個位置修正伺服器。因為衛星傳送的資訊會因為地表空氣的折射 干擾而產生誤差，故透過此位置修正伺服器將所計算出的位置資訊加以修正，以 獲得較精確的位置資訊，並節省手機的電力消耗。 z 訊號特徵(signal fingerprinting)[6]定位技術，利用已存在的網路架構，事先量測訊 2.
(7) 號強度的特徵值，並分析儲存至資料庫中，啟動此定位後，使用者只需傳回其目 前所接收到的訊號特徵給位置伺服器，位置伺服器便能依據事先定義的規則從資 料庫中取出其所對映的位置資訊。最著名的應用即為利用無線網路來定位的 RARDAR[14]系統。 z 細胞識別定位系統：利用基地台發出個別的識別記號(Cell ID)，根據使用者接收 到不同的識別記號群組，並透過網路的中央位置伺服器來決定其所在的位置，例 如以細胞格為主的定位方法(cell-based position method)[15, 16]。 在愈來愈多的研究定位的方法被提出來，提升了定位系統的準確度，有了適當的定 位系統，便可以發展位置衍生的服務與應用： 如 Active Badge[17]的辦公室人員電話轉 接系統，每個人員配帶一個小型的發射器，每個發射器能發出一個唯一的識別碼，在辦 公室內裝設適當的接收器，來判別使用者目前所在的地點，當有電話進來時，若人不在 坐位上，便可以此系統找到人員所在位置，並將電話轉接到距其最近的話機，以方便人 員接聽；利用無線電訊號強度的特性所發展的定位系統，如：RADAR[14]、SpotON[18]， 其中 RADAR 是應用在二維平面的室內定位，而 SpotON[18]則可用在三維平面的室內定 位；Cricket[19]定位系統是在室內的適當位置放置超音波發射器，使用者端安裝接收器， 使用者就能根據所接收到不同的超音波發射器所發出的資料來決定位置資訊；同樣採用 超音波發射器及接收器的原理，也發展出智慧家庭的居家老人追踪系統[20]，以監控其 是否需要即時的照顧或是協助；旅遊導覽系統[1]的應用，則是讓遊客手持一個具有網路 存取功能的數位助理器，將遊客目前所在位置周圍的特殊景點顯示在數位助理器上供遊 客參考，可以再點選選項以提供詳細解說。. 四、研究方法 本計畫將整合已發展的定位系統、位置閘道器及地理資訊系統來發展位置追踪服 務，基本架構如圖一所示，共可分為四個主要的模組，(1)定位技術(Location Determination Technologies) (2)位置閘道器(Location Gateway) (3)地理位置資訊(Geographic Location Provisioning)(4)位置追踪服務 (Location tracking service)，各區塊內基本功能概述如下： 1. 定位技術(Location Determination Technologies)模組：負責接收位置資訊的需求，並根 據位置閘道器的協助來決定所需啟動的定位技術，並參考資料庫內所存之無線網路存 取器(Access point)的位置資訊及網路環境來計算位置資訊，並回傳其結果。而本模組 內包含室內定位技術子模組與室外定位技術子模組，透過此二子模組的運作可以使此 定位技術模組能應用在各種不同的環境。 2. 位置閘道器(Location Gateway)模組：負責接收位置追踪服務的位置要求(location request)並轉送給定位技術模組。在轉送位置要求前會先啟動一個決策子模組，它會根 據網路系統的狀況及使用者的裝置來通知定位技術模組所需的適當定位技術，當定位 技術模組回傳位置資訊後，本模組會將此結果回傳給位置追踪服務模組。 3. 地理位置資訊(Geographic Location Provisioning)模組：提供位置追踪模組所須之地理 位置資訊，如地圖、座標、相對位置或經緯度等資訊。 4. 位置追踪服務 (Location tracking service)模組：在行動裝置上開發位置追踪服務應用 程式，向位置閘道器提出位置資訊之需求，取得後再依位置資訊向地理位置資訊模組 取得對應的地理位置資訊。. 3.
(8) 定位技術 z 室內定位 z 室外定位. Location data 位置閘道器 Location request Location request. 地理位置 資訊系統. Map data changes Subscriber information. Latitude Longitude. 位置追踪 服務. 圖一：本計畫基本架構圖. 本計畫根據所提之計畫書內容逐步完成上述各模組，並加以整合各模組之功能，完 成位置追踪服務的應用系統，本系統架構的優點如下： 1. 本架構的模組化設計，讓各種不同功能的模組能獨立開發互不干擾，使得研發人員可 以專心針對特定的模組研究，而所開發的模組之間又能相互溝通傳遞訊息，協力完成 定位目標。 2. 位置閘道器內的決策子模組能根據位置追踪服務所提供的有限資訊來決定使用者目 前所在的環境，讓使用者不必理會其所在環境都能獲得其位置資訊。 3. 定位技術模組包含有室內及室外的定位技術，使得本系統能在大部分的環境下正常運 作。另外，藉由位置閘道器的協助，本模組可以輕易加入各種已開發或新開發的定位 技術而不會影響整個系統的運作，相容及擴充性頗高。 本系統整合地理位置資訊，所呈現的位置資訊可讀性高，配合使用者的程式介面， 讓位置追踪的操作更便利。 本計畫之系統開發將針對(1)定位技術(Location Determination Technologies) (2)位置 閘道器(Location Gateway) (3)地理位置資訊(Geographic Location Provisioning)(4)位置追 踪服務等四個模組的開發分別說明如下： 1. 定位技術模組：本模組包含四種定位技術 (1) 我們針對以細胞格為主的定位方法(cell-based positioning method)[15,16]研究、分析 及改進，將訊號重疊的區域與面積的質心理論相結合，原本的定位精確度以訊號 重疊區域的表示方式，改由該區域的質心來表示(如圖二所示)，並探討精確度的變 化及系統的效能。另外，將原本集中式細胞格為主定位方法（位置資訊傳至位置 伺服器處理）經由我們設計的訊框格式(beacon frame)夾帶位置訊息的方式，使得 每個使用者可以利用本身的裝置，藉由簡單的數學運算即可自行定位，完成分散 式的定位技術。然而，由於多階訊號強度的特性在細胞格為主的定位方法下可以 提升定位的準確度(如圖三所示)，因此我們也在本模組內加以考量； (2) 權重式多角定位(multilateration) [21]的方法，分成兩個階段：第一階段是以節點的 DV-hop的方式計算出初始的位置;第二階段則利用節點的鄰居位置與距離，反覆地 更新與交換資訊，並根據資訊的可靠程度給予不同權重來進行多角定位； 4.
(9) (3) 訊號特徵(signal fingerprinting)定位方法，是根據訊號在不同的位置會有不同的訊 號強度，因此藉由事先量測訊號強度並記錄在資料庫中，便可利用訊號比對的方 式來完成定位； (4) 全球衛星定位系統(Global Positioning System)是利用環繞地球的24顆人造衛發射 其位置訊號，使用者接收此訊號並加以處理便能獲得其位置資訊。. P1 (x8, y8). (0,1) (x7, y7). P6 (-. C1. 3 1 , ) 2 2. B1. B6 A1 P 0 (0,0). C6. 3 1 (- , - ) 2 2. 3 1 , ) 2 2. B4. (x1, y1). C4. C2. (x2, y2). B2. A1 (x6, y6). C6. B3 C5. B6. C3. B5 P5. (. B2. B1. C1. P2. C2. (x9, y9). P3. (x3, y3). B3. B5 (x5, y5) (x4, y4). 3 1 ( ,- ) 2 2. P4. C5. (0, -1). B4. (a). (b). 圖二：(a)重疊區域(b)轉換成質心的表示方式. 圖三：多階訊號強度所形成之區域 5. C3. C4.
(10) 2. 位置閘道器模組：本模組主要的功能是整合不同性質定位方法，利用我們所設計的一 個決策子模組，它會根據現行網路的環境及使用者的裝置來通知定位技術模組所需的 適當定位技術，當定位技術模組回傳位置資訊後，本模組會將此結果回傳給位置追踪 服務模組。 在此我們先討論兩種常見的定位方式來實做整合，一個是室外的全球衛星定位(GPS) 技術；另一個則是室內的訊號特徵(signal fingerprinting)定位技術，這是因為室外的全 球衛星定位(GPS)技術，若使用在室內的環境下會完全失效，反之，室內的訊號特徵 定位技術若使用在室外會因為沒有事先建立資料庫來比對而失效，藉由這兩個較特殊 的定位技術來驗證系統的靈敏度及準確度。也因此，我們將提供一個無接縫的位置換 手模式，使得當使用者所在的位置(室內或室外)改變時，系統能作適當的轉換並讓使 用者不會感覺有任何異狀，即系統不因環境的改變而使其定位應用程式中斷服務。無 接縫換手(seamless handoff)定位系統整體架構如圖四所示。 此系統是一個主從式(client-server)的架構，每個部分由數個模組所組成，在客戶端 (client)的主要工作：(1)進行環境的偵測及收集有關的位置訊息，並將此位置訊息送至 伺服端(server)；(2)將使用者的位置呈現在網頁上。而伺服端(server)的主要工作也有兩 項：(1)將客戶端送來的位置訊息配合定位的技術來估計使用者目前所在的位置，並將 此位置資訊儲存在資料庫中；(2)查詢資料庫來取得使用者的位置資料，並將其回傳給 使用者，讓使用者端能以網頁的方式呈現位置資訊。 3. 地理位置資訊模組：本模組內容為地理位置的資訊，我們將實作環境下的地圖資訊（交 通大學校園地形圖）以經緯度均分的方式將其切割成數個小區域圖，並分別儲存在資 料庫中，當位置追踪服務模獲得其位置資訊（室內參考位置或室外的經緯度資料）後， 便以此向地理位置資訊模組要求適當的地圖資訊，並以網頁的方式呈現地圖結合使用 者位置。 4. 位置追踪服務模組：使用者透過網路存取的方式與位置追踪服務模組溝通，以取得位 置追踪服務。使用者依其權限成功的登入本模組後，管理者權限的使用者可以進入監 控畫面，監控(追踪)本系統上所有使用者的位置資訊，而一般權限的使用者僅能看到 個人位置資訊的畫面。所有的畫面呈現都會根據使用者的位置改變來動態的調整使用 者目前所在的位置。. 6.
(11) Web Display User Location. Other. personal location information. Web Server APACHE PHP. query. Login ID PW. Monitor. WEB. monitor locatoin information. Database. MySQL. (geolocation) user pic_table data_1fap. access 1.Register 2.Location metrics 3.HO msg. Location Client. Decisio n Kernel. WLAN. expire. register. handoff. outdoor. indoor. GPS Location Server. ( Client Part ). ( Server Part ). 圖四：整合室內及室外的無接縫換手(seamless handoff)定位系統之架構圖。. 五、結果與討論(含結論與建議) 本年度計畫所完成的工作項目除了根據所提之計畫書內容逐步整合各模組之功 能，完成位置追踪服務的應用系統外，也持續針對定位的方法加以研究、改進，我們觀 察出多階訊號強度的特性應用在細胞格為主的定位方法下可以提升定位的準確度，因此 我們作了相關的研究（如表一及表二）。根據模擬的結果顯示（表一），多階訊號強度 在 10% (20%)的參考點損壞情況下, 平均位置估計誤差只有 11.92%R (18.48%R)，其中 R 為參考點訊號涵蓋範圍的半徑。另外，多階訊號強度在 20%的訊框遺失率情況下, 平均 位置估計誤差只有 10.65%R（請參考表二）。 表一：在不同比率的參考點損壞情況下，平均位置誤差 參考點損壞率. 無法定位. 平均位置誤差. 0% (Optimal). 0. 5.869%R. 1%. 2. 6.425%R. 5%. 66. 8.769%R. 10%. 280. 11.917%R. 20% 1310 18.482%R *R 是參考點的訊號涵蓋範圍的半徑. 7.
(12) 表二：在不同的訊框遺失率下，平均位置誤差 訊框遺失率. 平均位置誤差. 0% (Optimal). 5.869%R. 1%. 6.092%R. 5%. 6.99%R. 10%. 8.161%R. 20% 10.65%R *R 是參考點的訊號涵蓋範圍的半徑 實作位置追踪服務的應用系統其顯示介面如圖五～十所示。圖五是位置追踪服務系 統主畫面，當管理者登入本系統後，就可以看到此一畫面（系統設定登入後顯示室內的 人員追踪），可由左方的選項選擇位置資訊的呈現（如圖六所示）亦或是室外位置資訊 的呈現（如圖七所示）。其中室外的定位呈現方式是將大地圖按其經緯度分割，不會因 為大地圖的關係而造成人員追踪時無法適時的反應其位置變化的結果。 另外，我們將此實作的系統搭配特殊設計的自走車及系館所提供的網路監控影像， 除了可以達成位置追踪的功能外，也可以利用自走車移動至指定的地點並傳回影像。此 特殊設計的自走車是結合無線網路模組[22]、無線攝影機模組、RS232/UART 轉換介面 模組以及 8051 單晶片自走車。我們利用 C 語言和 C++寫作 Socket 網路程式，在無線網 路模組與監控者間建立伺服器端(Server)與使用者端(Client)的連線。而 8051 單晶片是利 用組合語言來直接控制自走車的行進。藉由整合這兩者的功能，使得監控者能夠遠端遙 控自走車，並透過無線網路即時回傳現在環境影像給監控者。 圖八是利用交通大學工程三館四樓之網路攝影機所監控的畫面。而圖九是我們特殊 設計的自走車實物，該自走車與使用者連線後，配合使用者介面的控制便可以直接利用 無線網路加以控制其行進方向（前進、左轉及右轉），亦可同時傳回自走車前方影像， 傳回之即時影像監控畫面如圖十所示。. 8.
(13) 圖五：系統主畫面. 圖六：室內位置資訊的呈現. 9.
(14) 圖七：室外位置資訊的呈現. 圖八：交通大學工程三館四樓網路攝影機之監控畫面. 10.
(15) 無線網路攝影機. RS232/UART 轉換介面. 自走車. 無線網路模組 圖九. 無線監控自走車實物. 圖十：即時影像監控畫面. 11.
(16) 七、參考文獻 [1] N. Davies, K. Cheverst, K. Mitchell and A. Efrat, “Using and determining location in a context-sensitive tour guide”, Computer, vol. 34(8), Aug. 2001, pp. 35-41. [2] T. S. Rappaport, J. H. Reed, and B. D. Woerner, “Position location using wireless communications on highways of the future,” IEEE Communications Magazine, pp. 33-41, Oct. 1996. [3] J. M. Zagami, S. A. Parl, J. J. Bussgang, and K. D. Melillo, “Providing universal location services using a wireless E911 location network”, IEEE Communications Magazine, vol.36(4), Apr. 1998, pp. 66-71. [4] E. G. Masters, C. Rizos, and B. Hirsch, “GPS...more than a real world digitizer”, IEEE Position Location and Navigation Symposium, 1994, pp. 381-387. [5] K. Chadha, “The Global Positioning System: Challenges in Bringing GPS to Mainstream Consumers”, Proc. of IEEE International Conf. on Solid-State Circuits, 1998, pp. 26-28. [6] Rong-Hong Jan and Yung Rong Lee, "An indoor geolocation system for wireless LANs," ICPP Workshops 2003, pp. 29-34. [7] D. Niculescu and B. Nath, “DV based positioning in ad hoc networks,” Kluwer Journal Telecommun. Systems, vol. 22, no. 1, Jan. 2003, pp. 267–280. [8] N. Bulusu, J. Heidemann, and D. Estrin, “GPS-less Low Cost Outdoor Localization For Very Small Devices,” IEEE Personal Communication, vol. 7, Oct. 2000, pp.28-34. [9] K.-F. Ssu, C.-H. Ou and H. C. Jiau, “”Localization with mobile anchor points in wireless sensor networks,” IEEE Transactions on Vehicular Technology, vol. 54, no. 3, May 2005, pp. 1187-1197. [10] C. Drane, M. Macnaughtan, and C. Scott, “Positioning GSM telephones,” IEEE Communications Magazine, vol. 36(4) , Apr. 1998, pp.46-54. [11] J. Bensche, J. Cooke, E. Job, T. Luke, J. Kvaal, and N. Swatland, “Investing in The Wireless Location Services Market,” Lehman Brothers Report, Sep. 2000. [12] G.M. Djuknic, and R.E. Richton, “Geolocation and assisted GPS”, Computer, vol. 34(2), Feb. 2001, pp. 123-125. [13] E. Kotsakis, A. Caignault, W. Woehler, and M. Ketselidis “Integrating Differential GPS data into an Embedded GIS and its Application to Infomobility and Navigation”, 7th EC-GI & GIS WORKSHOP EGII -Managing the Mosaic Potsdam, Germany, June 13-15, 2001. [14] P. Bahl, and V. Padmanabhan, ”RADAR: An In-Building RF Based User Location and Tracking System,” Proc. of IEEE INFOCOM, vol. 2, Mar. 2000, p.775-784. [15] H.-C. Chu, and R.-H. Jan, "A cell-based location- sensing method for wireless networks," Wireless Communications and Mobile Computing, vol. 3, no. 4, pp. 455-463, June 2003.(SCI) [16] R.-H. Jan, H.-C. Chu, and Y.-F. Lee, "Improving the accuracy of cell-based positioning for wireless networks", Computer network, vol. 46, pp. 817-827, Dec. 20, 2004. [17]R. Want, A. Hopper, V. Falcao, and J. Gibbons, ”The Active Badge Location System,” 12.
(17) ACM Transactions on Information Systems, vol. 40, January 1992, pp.91-102. [18] J. Hightower,G. Boriello, and R.Want, “SpotON: An indoor 3D location sensing technology based on RF signal strength,” Univ. of Washington, Tech. Rep. UW CSE 00-02-02, Feb. 2000. [19] N. B. Priyantha, A. Chakraborty, and H. Balakrishnan, “The cricket location-support system,” in Proc. ACMInt. Conf. Mobile Computing Networking (MOBICOM), Boston, MA, Aug. 2000, pp. 32–43 [20] S. Helal, B. Winkler, C. Lee, Y. Kaddoura, L. Ran, C. Giraldo, S. Kuchibhotla and W. Mann, “Enabling location-aware pervasive computing applications for the elderly”, Proc. of the First IEEE International Conference on Pervasive Computing and Communications, 2003, pp. 531 - 536. [21] Y.-H. Gau, H.-C. Chu, and Rong-Hong Jan, "A Weighted Multilateration Positioning Method for Wireless Sensor Networks," Workshop on Wireless, Ad Hoc, and Sensor Networks(WASN), National Central University, Session A1, pp.3-8, Taiwan, August 1-2, 2005. [22] Host AP driver for Intersil Prism2/2.5/3, hostapd, and WPA Supplicant. Available: http://hostap.epitest.fi 本年度已發表之論文如下： [A1] Rong-Hong Jan and Wen-Yueh Chiu, "An approach for seamless handoff among mobile WLAN/GPRS integrated networks," accepted and to appear in Computer Communications. (附件一) [A2] Rong-Hong Jan, Ching-Peng Lin, and Maw-Sheng Chern, “An optimization model for Web content adaptation,” accepted and to appear in Computer Networks. (附件二) [A3] Hung-Chi Chu and Rong-Hong Jan, "A GPS-less positioning method for sensor networks," Proc. of the 1st International Workshops on Distributed, Parallel and Network Applications(DPNA) 2005. (附件三) [A4] Yu-He Gau, Hung-Chi Chu, and Rong-Hong Jan, "A Weighted Multilateration Positioning Method for Wireless Sensor Networks," Workshops on Wireless, Ad Hoc, and Sensor Networks(WASN), National Central University, Taiwan, 2005. (附件四). 13.
(18) ARTICLE IN PRESS. DTD 5 附件一. 1. 57. 2. 58. 3 4. Computer Communications xx (xxxx) 1–10 www.elsevier.com/locate/comcom. 59 60. 5. 61. 6. 62. 7. 63. 8 9 10. An approach for seamless handoff among mobile WLAN/GPRS integrated networks*. 11 12. 65 66 67 68. Rong-Hong Jan*, Wen-Yueh Chiu. 13. 64. 69. 14. Department of Computer and Information Science, National Chiao Tung University, Hsinchu, 30050 Taiwan, ROC. 70. 15. Received 8 October 2003; revised 4 March 2005; accepted 16 March 2005. 71. 16. 72. 17. 73. 22 23 24 25. Wireless local area networks (WLAN) and General Packet Ratio Service (GPRS) networks are two of the most widely used wireless network systems. In this paper, we propose a mobility support for mobile host roaming between WLAN and GPRS networks. In addition, a handoff decision model is presented to reduce the latency of the handoff procedure. The experimental results, including throughput, packet delay and handoff latency are given to show the performance of our approach. q 2005 Published by Elsevier B.V.. F. 21. 74. Abstract. O. 19 20. O. 18. Keywords: Wireless LAN; GPRS; Seamless hand-off. 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47. 51 52 53 54 55 56. *This research was supported in part by the Communications Software Technology Project of Institute for Information Industry and in part by the National Science Council, Taiwan, ROC, under grant NSC 93-2219-E-009002 and NSC93-2752-E-009-005-PAE. * Corresponding author. Tel.: C886 3 5731637; fax: C886 3 5721490. E-mail address: [email protected] (R.-H. Jan).. U. 50. N. 48 49. D. mobility and ‘always on’ connectivity for mobile users. However, the GPRS data rate is only up to 115 Kbit/s, and the cost of data transmission is much greater than that for WLANs. Therefore, mobile users like to have the two systems in their mobile hosts (MH). This lets people use the WLAN to access the Internet wherever it is available, yet switch to a GPRS network when they leave the hot spot. A procedure that enables roaming between GPRS network and WLAN is known as vertical handoff. In order to achieve vertical handoff, several issues, such as handoff decision making, authentication, and mobility management, have to be addressed. Some work on handoff decision making for WLAN/GPRS integrated networks has been reported in the literature. In [1], the physical layer parameters, such as received signal strength and signal decay, are used as decision criteria to trigger the handoff. In [2], they present a roaming scheme based on the relative bandwidth of WLAN and GPRS. In addition to physical layer parameters and network bandwidth, the network conditions, such as user preference, packet delay and packet loss, may also be the criteria for handoff decision. After vertical handoff decision is made, we face the authentication issue. The authentication for WLAN/GPRS integrated networks can be divided into two approaches, SIM-based and WLAN-based. In SIM-based authentication, the roaming users are authenticated and charged using GSM Subscriber Identity Module (SIM) [3]. The SIM-based. EC TE. 32. Over the past decade, Internet use has exploded with people gaining rich information from the World Wide Web. Meanwhile, technology has made wireless devices smaller, less expensive and more powerful. Wireless networks have become increasingly popular for accessing the Internet because they enhance mobility. People can connect to the Internet and remain on-line while roaming. Wireless local area networks (WLAN) are the most widely-used local wireless network system in schools, offices, airports, etc. Some organizations provide free WLAN service for their members. Although the data rate for WLAN can run up to 54 Mbit/s based on the IEEE 802.11a standard, its coverage area, known as its hot spot, is too small. There is no WLAN service outside of the hot spot. Thus, users cannot leave the hot spot until all transmissions are complete. On the other hand, General Packet Ratio Service (GPRS), based on the GSM system, provides high. R. 31. R. 30. 1. Introduction. O. 29. C. 27 28. PR. 26. 0140-3664/$ - see front matter q 2005 Published by Elsevier B.V. doi:10.1016/j.comcom.2005.03.004. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112.
(19) ARTICLE IN PRESS. DTD 5. 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168. 2. System architecture. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 170 171 172 173 174 175 176 177 178. 181 182. In this section, we describe the proposed seamless service framework including system architecture, the functionality of each component, and the message sequence chart of the process. 2.1. Seamless handoff agent and proxy. F. 125. 169. 179 180. O. 123 124. Note that a host can be reached by other hosts on the Internet, depending on its IP address. If all hosts are fixed on the Internet, the packets can be routed to their destinations by examining the prefix of the destination IP address at each router. However, this mechanism limits the host’s mobility. For example, once an MH with a home IP address visits a foreign network, two problems will occur. One, there is no node in the home network to deal with packets destined to the MH. And two, no node in the home network knows where the MH is. One way to make the MH reachable is to give the MH a new IP address with the foreign network’s prefix. However, all previous connections are broken. In order to provide mobility support for the MH, as shown Fig. 1, a seamless handoff proxy (SH proxy) server is added to the home network for forwarding the packets destined to the MH. In addition, a software agent, called as seamless handoff agent (SH agent), is installed in the MH for tunneling mechanism and handoff management. Now, follows a brief description of the system’s operation. As shown in Fig. 2, let H address denote the home IP address of the MH. SH agent binds H address to a virtual NIC. Note that the MH has two physical NICs, the WLAN NIC and the GPRS NIC. When MH moves to WLAN, it receives a new IP address, denoted as W address, from the foreign network. SH agent binds W address to the WLAN NIC and registers address pair (H,W) to the SH proxy. Similarly, when the mobile host moves to the GPRS network, it registers address pair (H,G) to the SH proxy where address G represents the new IP address received from GPRS. The applications in the MH use H address as the source address to send the packet. The virtual NIC in the SH agent accepts the packet and then the SH agent tunnels the packet to the SH proxy. The SH proxy decapsulates the packet and transfers it to the CN. If CN has a packet ready to send to. O. 122. PR. 121. proposed in this paper. By properly setting, both the threshold and hysteresis, the MH can handoff before leaving the hot spot, thus avoiding the so-called ping-pong effect. A pre-handoff mechanism is proposed to place the GPRS in a ready state before handoff occurs. The remainder of this paper is organized as follows. In Section 2, we describe our system architecture, the message flow chart, and handoff decision model. Section 3 discusses the implementation and performance of the proposed method, and a conclusion is given in Section 4.. EC TE. 120. R. 119. R. 118. O. 117. C. 115 116. authentication works well if the WLAN system is owned by the GPRS operator. In [4], a WLAN-based authentication is proposed for the WLAN/GPRS integrated networks in which WLAN and GPRS networks can be owned by different service providers or operators. In WLAN-based authentication approach, an Authentication, Authorization, and Accounting (AAA) server, which is installed in both WLAN and GPRS networks, is required. Next, the mobility management scheme that maintains a connection’s continuity should be considered during vertical handoff. Two major theories for mobility support have been proposed: routing-based approach and pure-end system approach. In the routing-based approach, the home network has an agent responsible for transferring packets between the correspondent node (CN) and the MH. Mobile IP [5], a standard of mobility support for IPv4 [6] that was drawn up by the Internet Engineer Task Force (IETF), is the most common solution for offering roaming in IP networks. Many studies [7–9] are based on mobile IP to support the host’s mobility. This approach does not require modifying the correspondent nodes or its applications. However, mobile IP does have some problems. First, an inefficient data flow, called a triangular routing problem, exists in this kind of approach. Second, mobile IP may not cooperate with network address translation (NAT) protocol because the IP address information was encapsulated in its registration packet. In [10], a number of network-layer (IP-layer) handoff optimization techniques, such as fast router advertisement, fast router caching, and soft handoff, that can improve handoff performance WLAN/GPRS integrated networks are proposed. In [11], a UDP tunneling method is presented to solve the NAT problem for Mobile IP. In the pure-end system approach, the current TCP/IP structure should be modified to support host mobility. The Migrate Internet Mobility Project [12] is one of this studies proposed by the Laboratory for Computer Science at MIT. By modifying the transport layer and its applications at the end users, no agent to transfer the data is needed and better performance is achieved, compared to the routing-based approach. Clearly, the pure-end system approach is not compatible with the current network environment and is difficult to promote. The paper applies a routing-based approach to integrate WLAN and GPRS networks to provide roaming service. The proposed method can be simply applied to the current network system without updating hardware or software. Thus, the method can be promoted easily. The architecture of our proposed system differs from the standard mobile IP. We use a virtual network interface card (virtual NIC) instead of a foreign agent. Since IP address starvation is a serious problem, NAT protocol [13] is used widely. In order to inter-operate with NAT, the UDP tunneling method is applied in this system. A handoff decision model which is designed to reduce the packet loss rate and increasing throughput is also. N. 114. U. 113. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. D. 2. 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224.
(20) ARTICLE IN PRESS. DTD 5. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. 3. 225. 281. 226. 282. 227 228. 283 284. Home Network CN. 229. 285. 230. 286. 231. 287 SH Proxy. 232. 288. INTERNET. 233. 289. 234. 290. 235 236. 291 292. 237. 293 Access Point. 238 GGSN. 239. SGSN. 294 295. WLAN. 240. 296. 241. 297. 242 HLR. BSS. Mobile Host. Base Station. F. VLR. 243 244. GPRS Network. O. 245 246 248 250. 254 255 256 257 258 259 260 261 262 263. MH, it uses H address as the destination address. The packet will be delivered to the home network. The SH proxy intercepts the packet destined to the H address and checks the address binding table to see if the MH is connecting to the WLAN or the GPRS. If the MH is connecting to WLAN, then the SH proxy tunnels the packet with the W address as the destination address to MH. After the MH receives the packet, the SH agent decapsulates the packet and forwards to the application via the virtual NIC. In the following, we give a detailed description of the SH agent and SH proxy.. 269. R. 267 268. 2.1.1. SH agent The functions of the SH agent can be divided into five modules: the virtual NIC, sending module, receiving module, control module, and user interface. Each module is a thread independently operating in the system. Fig. 3. O. 266. R. 264 265. 271. U. 275 276. N. 272 274. 1. The virtual NIC is software that simulates a physical network adapter. The MH’s home IP address is bound with this virtual NIC. The connections established by applications in MH use this virtual adapter to communicate with other nodes. The existing connections will not be broken while roaming because the virtual NIC would never change its IP address. 2. The sending module is responsible for transmitting packets to the SH proxy. It catches packets from the virtual NIC sent by applications, and then encapsulates the packets as payload for new UDP packets (known as UDP tunneling). Finally, it sends those tunneling packets to the SH proxy with port number 5150 via physical network adapters using existing routing rules set by the control module.. 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325. 328. W SH H Agent. Application. 329 SH Proxy. G. CN. 330 331 332 333. Mobile Host. 279 280. 301. 327. 277 278. 299 300. 326. C. 270. 273. depicts the relationships of modules in the SH agent. Descriptions of the modules are given as follows:. D. 253. Fig. 1. System architecture.. EC TE. 251 252. PR. Mobile Host. 249. O. 247. 298. 334 335. Fig. 2. Brief account of the system operation.. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 336.
(21) ARTICLE IN PRESS. DTD 5. 4. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. 337. 393. 338. 394. Control flow Packet flow. 339 340. 395 396. Tunneling. 341. 397. 342. 398. 343. APP1. 344. APP2. 399. APP 3. 400. ARP Cache. 345. 401. 346. 402. 347 348. Control Module. 349. 403 404. Routing Table. 405. Virtual NIC SH Proxy. 350 351. Sending Module. User Interface. 352. 409 410. SH Agent. F. Receiving Module. Information. 355 356. GPRS. 358. O. 357 Mobile Host. 360. Fig. 3. Modules in SH agent.. 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392. D. 5. Finally, a user interface lets the user assign some system parameters, such as the SH proxy IP address, home IP address, priority of each NIC, and so on. The user interface also shows the states of the system. To manage all available NICs in MH, we built a table to record necessary information for each NIC. Each entry in the table includes the following fields: the NIC’s name, description, current IP address of the NIC, gateway information, connection type, priority of the NIC, current state, and its index in the operating system. Note that the connection type and priority of the NIC should be provided by the user; this helps one to adopt a proper handoff policy, and other information can be collected by the SH agent itself.. EC TE. 371 372. R. 370. R. 369. O. 368. C. 367. N. 366. U. 365. 3. The receiving module is responsible for receiving packets from the SH proxy. It receives tunneling packets with port number 5051 from the SH proxy, and then performs UDP decapsulation to get original packets. Finally, it forwards the packets to the virtual NIC; after that, the packets can be received by the corresponding application. 4. The control module is responsible to monitor all states of NICs, to select the working NIC and to execute corresponding procedures such as registration, handoff, and pre-handoff procedures. After the SH agent starts operation, the control module initializes the routing table and ARP cache. The routing table is modified according to the NICs’ priority provided by the user. The WLAN or GPRS NIC is assigned as the working NIC for the tunneling packet. The control module also keeps an eye on each NIC’s connection state until the SH agent stops the service. If the working NIC is disconnected, the control module should find another connectable NIC to communicate with the SH proxy. If a NIC with a higher priority than the current working NIC becomes connectable, the control module should switch to the NIC with the higher priority. The control module sends control messages using the UDP channel established by the receiving module. Thus, the SH proxy can collect both the IP address and port number from the receiving channel when the registration request or handoff request arrives. Even if the IP address or port number is changed by the NAT gateway, the SH proxy can still get a routable address to tunnel packets back to the SH agent.. PR. 361. O. 359. 363 364. 407. WLAN. 354. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 406 408. 353. 362. CN. 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434. 2.1.2. SH proxy Similarly, functions of the SH proxy can be divided into four modules as given below and each module is a thread operating independently in the system (see Fig. 4).. 435 436 437 438 439. 1. The ‘FromSHAgenttoCN’ module receives tunneling packets from the SH agent, decapsulates those packets, and sends the original packets to their target CNs. 2. The ‘FromCNtoSHAgent’ module catches packets destined to the MH that has registered to the SH proxy, and it also encapsulates these packets and tunnels them back to the corresponding SH agent. 3. The control module deals with control messages like registration or handoff requests. It collects necessary. 440 441 442 443 444 445 446 447 448.
(22) ARTICLE IN PRESS. DTD 5. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. 5. 449. 505. 450. 506. Control flow Packet flow Tunneling. 451 452. 507 508. 453. 509. 454. 510. 455. 511. APP. FromSHAgenttoCN Module. 456 457. 512 513. 458. 514. 459 460. 515 516. 461. 517. 462. 518. 463 464. SH Agent. 465. CN. FromCNtoSHAgent Module Module. 520 521. 466. 472 473. Fig. 4. Modules in SH proxy.. 480 481 482 483 484 485 486 487. R. 488 489. 495 496 497 498 499 500. R. O. 494. C. 493. The packet format for the proposed method is introduced as follows. As shown in Fig. 5, four fields, the type, ID, code, and flag are defined. The type field gives the indication of packet types. The packet types and related information are summarized in Table 1. The ID field contains the SH agent’s home IP address. We use this field to identify the source node for the packet. The code field records the SH proxy’s reply. The default value is zero.. N. 491 492. 2.2. Packet structure. U. 490. 501 502. IP header. UDP header. Type. ID. Code. Flags. Extension. 503 504. 528 529 530. The fourth field is reserved now. Depending on different packet types, some extension is attached to the packet.. Fig. 5. Packet fields.. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 531 532 533 534. 2.3. Handoff decision model. D. 479. 527. 535. The Handoff Decision Model is designed in the control modular of the SH agent. The goal of this model is to decide when to handoff so as to improve system performance. We assume the following: One, that GPRS is always available anywhere. And two, if WLAN is available, WLAN is chosen as the access network, because it has both a higher data rate and lower cost. The received signal strength (RSS) of WLAN varies with many factors, including landforms, obstacles, power strength of access point, etc. In general, RSS is related to the distance between the transmitter and the receiver.. EC TE. 478. information to update SH agent information, and sends corresponding messages back to SH agent. The SH proxy stores information for registered SH agents in a table called ‘SH agent information’. Each entry in the table contains the registered SH agent’s Home IP address, current IP address, and port number. Note that the current IP address and port number are obtained from the header of registration request or handoff request by the SH proxy itself. The packet does not carry this information in its payload. 4. The system administrator can configure the SH proxy by user interface, and it also shows internal information like the states of currently registered SH agents.. 526. PR. 474. 525. O. SH Proxy. 471. Control Module. O. 470. 523 524. F. Information. 469. 477. 522. User Interface. 467 468. 475 476. 519. Table 1 Packet types. 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550. Packet name. Type. Code. Extension. Tunneling packet Registration request Registration reply. 0 1 2. Original packet. Pre-handoff request Pre-handoff reply Handoff request Handoff reply SH agent deregistration SH proxy stop. 3 4 5 6 7 8. 0 0 1Zaccept 2Zreject 0 1 0 1 0 1. MAC address of gateway. 551 552 553 554 555 556 557 558 559 560.
(23) ARTICLE IN PRESS. DTD 5. 6. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. 561. 617 RSS of WLAN [dbm]. 562 563 564. 0. Tc. 618. Max. Ta. Tb. 619 620. 565. 621. 566. 622. 567. 623. 568. 624. 569. 625. 570. 626. 571 572. C. B. A. 627 628. AP. Distance [m]. 573. 629. 574. 630. 575. 631. 576. 632. 577. 633. 578. 634 Use WLAN Network. 581. Border Area. O. 582. F. 579 580. Use GPRS Network. 643 644. 589 590. PðrÞ Z Pðr0 Þ K 10a logðr=r0 Þ. (1). 591. 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616. Dbc Z th !vh. where vh is the moving speed of MH and th is the time for performing the pre-handoff mechanism. A reference point A with distance Da to the access point is selected to measure the RSS in WLAN, say, Ta. One can then estimate the distance Dc between AP and the point C by applying (1) as follows.. EC TE. 599. R. 598. R. 597. O. 595 596. C. 594. N. 593. where P(r) is signal power, in dbm, received by a given MH whose distance to the transmitter is r meters; P(r0) is the signal power at a reference point whose distance to transmitter is r0; the parameter a called the exponent value, indicates the rate of path loss. As shown in Fig. 6, suppose that an MH moves out from the access point, and if the RSS is lower than threshold Tc, the MH should perform handoff from WLAN to GPRS. In a GPRS network, if MH requests to be active, then SGSN moves the MH from standby to ready state. In ready state, the MH is attached to GPRS mobility management (GMM) and thus MH can receive and send data for all relevant service types. Thus, before the RSS decreases to Tc in the WLAN, MH should send a request to GPRS for activating. Otherwise, the MH must wait until SGSN moves it from standby state to ready state. This causes both longer packet delay and packet loss. In our decision model, prior to data transmission handoff from the WLAN to the GPRS networks, the SH agent sends a pre-handoff request to the SH proxy via the GPRS network. This causes the SGSN to move the MH from standby to ready state. We call this procedure ‘pre-handoff.’ Suppose that (1) when MH reaches point B (see Fig. 6), it sends a pre-handoff packet, and (2) when MH reaches point C, a handoff occurs (i.e. the RSS is Tc). The distance Dbc. U. 592. PR. According to [20], the following signal propagation model may hold:. D. 587 588. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 639. between points B and C can by determined by:. Fig. 6. Variables in decision model.. 586. 638 640. 584 585. 637. O. 583. 635 636. Dc Z Da 10ð1=10aÞðTaKTc Þ :. Similarly, one can apply (1) to find RSS Tb for the point B by: Tb Z Tc C 10a logðDc =ðDb K Dbc ÞÞ Therefore, when MH is moving and measures the RSS of AP, if the RSS decreases to Tb, the pre-handoff request should be sent periodically. This keeps GPRS NIC and the state of HM in SGSN in a ready state. When the RSS decreases to Tc, every thing is ready for handoff. This way, one can reduce both the packet delay and packet loss.. 641 642. 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666. 2.4. Message sequence chart. 667 668. Below is an example to illustrate all of the message sequences in this current approach. As shown in Fig. 7, the IP address of the home network is 140.113.167.0. The two visited networks are the WLAN network with an address of. 669 670 671 672.
(24) ARTICLE IN PRESS. DTD 5. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10 673. 1. 674. record data send proxy ARP. Start in GPRS Mobile host IP :211.79.33.*. Tunneling. 736 Port 5150. 681. tunneling packet. 4. 682 683 684. tunneling packet. 686 687. Handoff RSS>T.p From GPRS to WLAN Mobile host IP : 140.113.24.*. Port 5151. Pre-Handoff. pre-handoff request. 8 pre-handoff reply. Handoff. 9. 702. 11. SH Proxy stop. 709. 713. 725 726 727 728. 758 759 760 761. Stop Proxy ARP. 762. Port 5151. 763 764 765. SH Proxy. CN. Fig. 7. Message sequence chart.. N. C. O. R. 140.113.27.0 and the GPRS network with 211.79.33.0. All IP addresses for MH are given by the dynamic host configuration protocol (DHCP) servers. Assume that MH starts from the GPRS network, moves to the WLAN network and finally returns to the GPRS network. All messages in this approach are listed below: 1. When the SH proxy starts service in the home network, it sends an ARP request to get the gateway’s MAC address. Then, two UDP channels are opened for the SH agent. Ports 5150 and 5151 are assigned to receive tunneling packets and control packets, respectively. Note that the SH proxy also uses port 5151 to send tunneling packets back to the SH agent.. U. 723 724. 757. D. R. 712. 722. SH Agent. Mobile Host. 711. 721. 755 756. SP Proxy stop. Application. 710. 720. 754. Port 5151. SP Agent stop Port 5151. EC TE. 10. 706. 719. 753. Port 5151. 705. 718. 752. handoff reply. SH Agent off-line. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 749 751. update data. Repeat 3~6. 703. Port 5151. 747 748 750. PR. handoff request. Mobile host IP:211.79.33.*. 717. Port 5151. RSS < T.p. RSS < T.h From WLAN to GPRS. 715 716. 746. handoff reply. Repeat 3~6. 701. 714. 745 Port 5151. update data. 698. 707 708. 742. 7. 697. 704. 741. encapsulation. 743. handoff request. 694. 699 700. 739 740. 744. 689. 696. 738. decapsulation. 6. 688. 695. 737. decapsulation. Port 5151. 5. 685. 693. 735. encapsulation. 680. 691 692. 734. registration reply. 679. 690. 733. Port 5151. 3. F. 678. 731 732. Port 5151. O. 677. 730. registraton request. 2. Registration. 729. start service. O. 675 676. 7. 766 767 768 769 770. 2. The MH starts at the GPRS network and its SH agent sends registration request to the SH proxy. If the SH proxy accepts the request, it creates a new entry in the ‘SH agent information’ table to record related information. The SH proxy then sends proxy ARP to inform other nodes of the substitution for this MH, and sends the registration reply to the SH agent. 3. After a successful registration, the application in MH can communicate to CN. The application uses virtual NIC to send packets. Thus, the source IP address of the packets is 140.113.167.*. Next, the sending module of the SH agent encapsulates the packets into a UDP tunneling packet with a source IP address of 211.79.33.* and destination port 5150, and sends. 771 772 773 774 775 776 777 778 779 780 781 782 783 784.
(25) ARTICLE IN PRESS. DTD 5. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10. 789 790. 4.. 791 792. 5.. 793 794 795 796 797 798 799 800. 6.. 801 802 803 804. 7.. 805 806 807 808 809. 8.. 810 811 812. was Microsoft windows XP professional. We used a desktop PC as the SH proxy. The operating system in the SH proxy was NT4.0. The CN was a desktop PC with some endpoint testing software. The IP address of the home network was 140.113.167.0. The SH proxy’s IP address was 140.113.167.205 and the mobile host’s home address was 140.113.167.242. Two networks visited were the WLAN network with an address of 140.113.27.0 and the GPRS network with 211.79.33.0, respectively. The MH’s IP address in the visiting network was automatically assigned by the DHCP server. The operator of the GPRS network was Chunghwa Telecom, is the largest telecommunications company in Taiwan. Note that the ready timer of the GPRS mobility management system expired after the MH idled more than 44 s, and the transit time from standby to ready was 1–2 s. The CN was at National Central University, ChungLi City, Taiwan, with an IP address of 140.115.83.240. The distance between the MH and CN was 40 km. 3.2. Performance analysis. F. 787 788. the tunneling packets to SH proxy via GPRS NIC. After tunneling packets are received by the SH proxy, the ‘FromSHAgenttoCN’ module decapsulates the packets. Then, the original packets are transmitted to their destination using normal routing method. CN receives the packets and transmits them back to the MH. The SH proxy collects the packets that destined to the MH. By checking the IP address, the SH proxy finds the corresponding entry in the ‘SH agent information’ table and retrieves the current IP address for the MH. The ‘FromCNtoSHAgent’ module encapsulates these packets with a destination IP address of 211.79.33.* and sends the tunneling packets to the SH agent via the established UDP channel. When the tunneling packets arrive at the SH agent, the receiving module decapsulates these packets and then delivers them to applications via virtual NIC. If the control module decides to perform a handoff from GPRS to WLAN, it changes the routing table and sends a handoff request via WLAN NIC to the SH proxy. This way, the SH proxy can update the IP address and port number. After the handoff is complete, the SH agent uses WLAN network for transmission. When the RSS of WLAN is lower than Tb, the control module decides to start the pre-handoff mechanism. Thus, the SH agent sends the per-handoff message to the SH proxy via GPRS NIC to prepare handoff. The SH proxy simply returns this message to the sender. Note that the pre-handoff mechanism is done to change the MH state in the GPRS network from standby to ready. The control module performs a handoff from WLAN to GPRS if RSS of WLAN is lower than Tc. After a successful handoff, the SH agent uses GPRS NIC to send packets. If the SH agent decides to go off-line, it sends an ‘SH agent stop’ message to the SH proxy. Then, the SH proxy removes the entry of the SH agent from the ‘SH agent information’ table. If the SH proxy wants to stop the service, it sends an ‘SH proxy stop’ message to all registered SH agents.. O. 786. A laptop PC with two physical NICs, an Audiovox RTM 8000 GPRS card and a Lucent Orinoco volt 3.3 802.11b WLAN card, were used as the MH. An SH agent was developed in this PC. The operating system in the MH. 3.2.2. Handoff latency Handoff latency is the latency caused by the handoff procedure. Comparing the handoff latencies between GPRS and WLAN, the latency for a handoff from a WLAN to. 818 819 820. 10.. 821 822 823 824 825. 11.. EC TE. 817. R. 9.. 832 833 834. 838 839 840. O. The following section describes the developing environment, test bed and performance evaluation for the proposed system.. C. 831. 3. Implementation and evaluation. N. 830. U. 829. R. 826 827 828. D. 837. 816. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862. 893. 3.1. Developing environment. 815. 843 844. 869. 835 836. 814. 842. 863. 3.2.1. Packet delay The packet delay of this method is caused mainly by the tunneling mechanism. Since our method is based on the routing-based approach, the triangular routing problem exists. The round trip time (RTT) between the MH and CN was measured in the experiment. The RTT was composed of the packet transmitting time between the NH and SH proxy, the time of performing encapsulation/decapsulation mechanism, and the RTT of the connection between the SH proxy and CN. Both the quality of access network and the CPU load significantly influences the RTT. Figs. 8 and 9 show the RTTs of our method from the MH to CN using the WLAN and GPRS networks, respectively. When the MH was in the WLAN, the RTT varied from 109 to 1999 ms, with an average RTT of 595 ms. (The one-way average was 297.5 ms.) When the MH was in the GPRS, the RTT varied from 992 to 11571 ms, with an average RTT of 2330.7 ms and a one-way average of 1165.4 ms. Compared to the system without mobility support, the one-way delays caused by the mobility support mechanism were 280.5 ms for WLAN and 615.44 ms for GPRS. Table 2 lists the oneway packet delays for the systems with/without mobility support.. 813. 841. The following experiment shows the packet delay, the amount of packet loss caused by handoff latency, and the benefit of the handoff decision model. In addition, the compatibility of this approach with existing applications is examined.. O. 785. PR. 8. 864 865 866 867 868 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 894 895 896.
(26) ARTICLE IN PRESS. DTD 5. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10 897. 2000. 898. 901. 1400 3.5. 958. 3. 959. 1200 1000 800. 906. 600. 907 908 909. 960 2.5. 961. 2. 962. 400. 1.5. 963 964. 200. 1. 965. 0.5. 966. 910. average 595. 0 0. 911. 100. 200. 300. 400. 500. 600. 700. 800. 900. 1000. 967. packet sequence. 912 913. 0. 0. 920 921 922 923 924 925 927 929. 935 936. 6000. 2000. 941. 0. 0. 100. 200. O. 939 940. R. 938. 300. 942. 800. 900 1000. C U. Type. WLAN GPRS. F. handoff. System with mobility support. 10–20 ms 550–600 ms. 297.5 ms 1165.4 ms. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10. 976 977 978 979 980 981 982 983. 986 987 988 989. 992 WLAN. GPRS. WLAN. 993. 4. 994. 3.5. 995 996. 3. 997. 2.5. 998 999. 2. 1000 1001 1002. 1. 1003 1004. 0. 1005 0. 10. 20. 30. 40. 50. time(s). 60. 1006 1007. Fig. 11. Average packet lost with RSS decision model.. 952. 975. 991. 0.5. System without mobility support. 974. 990 handoff. 1.5. Table 2 Packet delays for the systems with and without mobility support. 949 951. 700. N. 945. 950. 600. Fig. 9. RTT in GPRS.. 944. 947 948. 500. packet sequence. 943. 946. 400. 973. 985. 4.5. average 2330.7. 971 972. 984. 5. 4000. 937. threshold, the handoff procedure starts. Method 3, our proposed method uses a handoff-decision model. Figs. 10–12 show the average numbers of packets lost for methods 1, 2 and 3, respectively, during the handoff procedures. Table 3 summarizes the average number of packets lost and handoff latencies for three methods. Packet loss is serious in Method 1 (see Fig. 10), with an average of 3.1818. In stark contrast, however, the average packet loss for Method 3 was a scant 0.1391. The average handoff delays for Methods 1–3 were 13032.9, 4542.3 and 570.1 ms, respectively. Clearly, Method 3, the proposed pre-handoff method promises far better performance.. R. 934. 8000. RTT (ms). 933. 970. 3.2.3. Throughput evaluation The throughput of the system is affected by the network bandwidth, the performance of the NIC and the MH CPU. We used ‘Qcheck’ software to generate UDP streams with. 10000. 968 969. Fig. 10. Average packet lost with no decision model.. EC TE. 12000. 931 932. 60. D. 926. 930. 50. O. a GPRS network is longer. This is because (1) the transition time from standby to ready in GPRS should be considered; (2) the bandwidth of WLAN is much higher than that of GPRS, and (3) the handoff procedure via WLAN is faster than that of GPRS. In the experiment, the MH sent ICMP echo request messages (ping packets) to the CN every 4096 ms. Three methods for handoffs from WLAN to GPRS network are compared below. Method 1 has a handoff procedure that does not start until the WLAN is unavailable. In Method 2, if the RSS of the WLAN is lower than a given. 928. 40. O. 919. 30. PR. 918. 20. time(s). packet lost. 917. 10. Fig. 8. RTT in WLAN.. 914 915 916. 955 956 957. packet lost. RTT(ms). 905. WLAN. GPRS. 4. 902 904. 953. handoff. 954 WLAN. 4.5 1600. 903. handoff. 5. 1800. 899 900. 9. 1008.
(27) ARTICLE IN PRESS. DTD 5. 10 1009. R.-H. Jan, W.-Y. Chiu / Computer Communications xx (xxxx) 1–10 handoff. 5. 1010. GPRS. WLAN. 4.5. 1011 1012. mobile equipment, and all existing applications can still be run. Looking ahead, developing both a security mechanism and billing system for integrated WLAN and GPRS networks might be interesting future work.. handoff WLAN. 4. 1013 3.5. 1021 1022 1023 1024. 1073 2. [14–19].. 1075 1076. 1. References. 1078. 0 0. 10. 20. 50. 60. Table 3 Packet loss and handoff latency for methods 1—3. 1031 1033. 40. Fig. 12. Average packet lost with our decision model.. 1030 1032. 30. time(s). 1026. 1029. Method 1 Method 2 Method 3. Avg. number of packet loss. Handoff latency. 3.1818 1.1089 0.1391. 13032.9 ms 4542.3 ms 570.1 ms. 1034 1035 1036 1037 1038. 600 kbps in WLAN and 50 kbps in GPRS. The average throughput of WLAN was 481.14 kbps, and in GPRS networks, the average throughput was 16.82 kbps.. 1039 1041 1042 1043 1044 1045. 3.2.4. Compatibility test Finally, we tested the compatibility of our system. Most of the applications worked normally in our system. Due to the high packet delays in GPRS networks, however, realtime application such as VoIP, did not work well. We hope such delays can be reduced in the future.. 1046 1047. 4. Conclusion. R. 1048 1049. 1055 1056 1057 1058 1059 1060 1061. R. O. 1054. C. 1053. N. 1051 1052. This paper presents a mobility support method to integrate WLAN and GPRS networks. This approach contains an SH proxy in a home network and an SH agent installed in the MH. A handoff decision model is designed to improve overall performance. From the operator’s point of view, our approach reduces the need to modify the existing environment, and the decision model also reduces the handoff latency from the WLAN to GPRS networks. Hence, operators can simply use this approach to provide roaming services for the integrated networks. From the user’s point of view, only an SH agent is needed to install in his or her own. U. 1050. [1] Q. Zhang, C. Guo, Z. Guo, W. Zhu, Efficient mobility management for vertical handoff between WWAN and WLAN, IEEE Commun. Mag. 41 (2003) 102–108. [2] K. Pahlavan, et al., Handoff in hybrid mobile data networks, IEEE Person. Commun. 7 (2000) 34–47. [3] J. Ala-Laurila, J. Mikkonen, J. Rinnemaa, Wireless LAN access network architecture for mobile operators, IEEE Commun. Mag. 39 (2001) 82–89. [4] M. Jiang, J. Chen, Y. Liu, WLAN-centric authentication in integrated GPRS-WLAN networks, Vehicular Technology Conference (VTC), vol. 3, 2003 pp. 2242–2246. [5] C. Perkins, IP Mobility Support, IETF RFC 2002, 1996. [6] J. Postel, Internet Protocol, STD 5, IETF RFC 791, 1981. [7] First Steps Towards UMTS: Mobile IP Services. A European Testbed (FIT-MIP), [online]. Avaliable: http://www.eurescom.de/wftproot/ web-deliverables/public/P1000-series/P1013/. [8] M. Ylianttila, M. Pande, J. Makela, P. Mahonen, Optimization scheme for mobile users performing vertical handoffs between IEEE 802.11 and GPRS_EDGE networks, IEEE Global Telecommun. Confer. 6 (2001) 3439–3443. [9] I. Wu, W. Chen, H. Liao, F. Young, A seamless handoff approach of mobile IP protocol for mobile wireless data networks, IEEE Trans. Consumer Electron. 48 (2002) 335–344. [10] R. Chakravorty et al., Performance Issues with Vertical Handovers— Experiences from GPRS Cellular and WLAN Hot-spots Integration, Proceeding of the Second IEEE Annual Conference on Pervasive Computing and Communications, March 2004, pp. 155–164. [11] H. Levkowetz, S. Vaarala, Mobile IP NAT/NAPT Traversal using UDP Tunneling, draft-ietf-mobileip-nat-traversal-07.txt, work in progress, IETF Internet-Draft, Nov. 2002. [12] Migrate Internet Mobility Project [online]. Available: http://nms.lcs. mit.edu/projects/migrate/. [13] K. Egevang, P. Francis, The IP network address translator (NAT), IETF RFC 1631, 1994. [14] C. Perkins, IP in IP Tunneling, IETF RFC 2003, 1996. [15] C. Perkins, Minimal Encapsulation within IP, IETF RFC 2004, 1996. [16] S. Hanks, T. Li, D. Farinacci, P. Traina, Generic Routing Encapsulation (GRE), IETF RFC 1701, 1994. [17] S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6) Specification, IETF RFC 1883, 1995. [18] C. Pollini, Trends in handover design, IEEE Commun. Mag. 34 (1996) 82–90. [19] Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, ISO/IEC 8801-11, ANSI/IEEE Std. 802.11, 1999 Edition. [20] Y. Chen, H. Kobayashi, Signal strength based indoor geolocation, IEEE Int. Confer. Commun. 1 (2002) 436–439.. EC TE. 1040. 1077. 0.5. 1025 1027 1028. 1074. 1.5. F. 1019 1020. 1069. 1072. O. 1018. 2.5. O. 1017. 1067 1068. 1071. 5. Uncited references. PR. 1016. 1066. 1070. 3. D. 1015. packet lost. 1014. 1065. 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117. 1062. 1118. 1063. 1119. 1064. 1120. COMCOM 2758—26/4/2005—19:15—SHYLAJA—145014—XML MODEL 5 – pp. 1–10.
(28) 附件二 COMPNW 3174. No. of Pages 13, DTD = 5.0.1. ARTICLE IN PRESS. 3 August 2005 Disk Used. Computer Networks xxx (2005) xxx–xxx www.elsevier.com/locate/comnet. An optimization model for Web content adaptation Rong-Hong Jan. 3. a,*. , Ching-Peng Lin a, Maw-Sheng Chern. a. b. q. b. Department of Computer and Information Science, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30050, Taiwan, ROC Department of Industrial Engineering and Engineering Management, National Tsing Hua University, Hsinchu 30043, Taiwan, ROC. PR. 4 5 6 7. OO F. 2. Received 18 December 2003; received in revised form 7 June 2005; accepted 16 June 2005. ED. Responsible Editor R. Boutaba. 11 Abstract. CT. This paper considers Web content adaptation with a bandwidth constraint for server-based adaptive Web systems. The problem can be stated as follows: Given a Web page P consisting of n component items d1, d2, . . . , dn and each of the component items di having Ji versions d i1 ; d i2 ; . . . ; d iJ i , for each component item di select one of its versions to compose the Web page such that the fidelity function is maximized subject to the bandwidth constraint. We formulate this problem as a linear multi-choice knapsack problem (LMCKP). This paper transforms the LMCKP into a knapsack problem (KP) and then presents a dynamic programming method to solve the KP. A numerical example illustrates this method and shows its effectiveness. 2005 Published by Elsevier B.V.. RE. 12 13 14 15 16 17 18 19. UN CO R. 20 Keywords: Content transcoding; Knapsack problem; Dynamic programming 21. q This research was supported in part by the Communications Software Technology Project of Institute for Information Industry and in part by the National Science Council, Taiwan, ROC, under grant NSC 93-2219-E-009-002 and NSC 93-2752E-009-005-PAE. * Corresponding author. Tel.: +886 3 573 1637; fax: +886 3 572 1490. E-mail address: [email protected] (R.-H. Jan).. 1389-1286/$ - see front matter 2005 Published by Elsevier B.V. doi:10.1016/j.comnet.2005.06.006. 1. Introduction. 22. Over the past decade, Internet use has exploded with people gaining rich information from the World Wide Web (WWW). With traditional wired-line Internet, users can only access the Internet in fixed places. Recently, however, due to the technology explosion in wireless communication and portable communication devices, e.g., cellular phones, personal digital assistants, and pagers, it. 23 24 25 26 27 28 29 30.
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