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Transcript of © The McGraw-Hill Companies, Inc., 2006© The McGraw-Hill Companies, Inc., 2007 Chapter 3...
© The McGraw-Hill Companies, Inc., 2006© The McGraw-Hill Companies, Inc., 2007
Chapter 3底層技術
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目標
本章結束後,您將能夠: 了解不同版本的有線乙太網路 了解無線乙太網路 了解各種類型的點對點廣域網路 了解各種類型的交換式廣域網路,尤其是 ATM 區別訊號增益器、橋接器、路由器、及集線器之間的差異
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3.1 區域網路
本節所討論的主題包括: 有線區域網路:乙太網路 無線區域網路: IEEE 802.11
區域網路 ( Local Area Network, LAN ) 是指在一個有限的區間內的資料通訊系統,如一個部門、一棟建築物或是一個校園的網路。它可以讓一定數量的設備彼此直接通訊,而大型的機構往往需要數個相連的 LAN 。
最受歡迎的區域網路包括乙太網路 ( Ethernet ) 及無線區域網路 ( wireless LAN ) 。我們在本節會簡短的介紹這兩種區域網路。
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3.2 點對點廣域網路
本節所討論的主題包括: 實體層 資料鏈結層
在 Internet 中,我們遇到的第二種網路類型是點對點廣域網路 ( point-to-point WAN ) 。
一個點對點廣域網路使用公眾網路,如電話線以連接 2 個遠端裝置。我們在此將會介紹這些技術的實體層與資料鏈結層。
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ADSL 是針對住宅式消費者所設計的一種非對稱式通訊技術;
ADSL 並不適用於商業性消費者。
請注意:請注意:
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3.3 交換式廣域網路
本節所討論的主題包括: X.25 訊框轉送 ATM
Internet 的骨幹網路通常為一交換式廣域網路 ( Switched WAN ) 。
交換式廣域網路為一個涵蓋面積可達一州或一個國家之大的廣域網路,並且提供很多地點給使用者存取。
在 WAN 內部,由眾多交換器連接點對點網路以構成一個網狀連結。交換器為一種多埠的連接器,允許數個輸入與輸出間的連接。
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資料胞網路使用 Cell 作為資料交換的基本單元。一個 Cell 為一固定大小的資料區塊。
請注意:請注意:
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注意,一條虛擬連線用 VPI 和 VCI 來定義。
請注意:請注意:
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IP 通訊協定使用 AAL5 子層。
請注意:請注意:
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我們將在第 23 章討論在 ATM 上執行 IP 的相關議題。
請注意:請注意:
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3.4 連接裝置
本節所討論的主題包括: 訊號增益器 集線器
橋接器 路由器
LAN 或 WAN 通常不會單獨的運作,它們會與其他網路或與 Internet 連接在一起。因此,我們使用連接裝置 ( connecting device ) 將各個LAN 或 WAN 連接在一起。連接裝置可以運作在網路模型中的不同層次。
在此,我們討論 3 種類型的連接裝置:訊號增益器 ( Repeater ) 或集線器 ( Hub ) 、橋接器 ( Bridge ) 或第二層交換器 ( Two-layer Switch ) 、及路由器 ( Router ) 或第三層交換器 ( Three-layer Switch ) 。
訊號增益器或集線器運作在網路模型中的第一層。 橋接器或第二層交換器運作在網路模型中的前兩層。 路由器或第三層交換器運作在網路模型中的前三層。
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訊號增益器連接一個 LAN 中的不同區段。
請注意:請注意:
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訊號增益器轉送每一個位元,但它並沒有過濾的功能。
請注意:請注意:
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訊號增益器是重建訊號,而不是放大訊號。
請注意:請注意:
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橋接器使用一張表格來做封包過濾的決定。
請注意:請注意:
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橋接器無法改變在訊框中的實體 (MAC) 位址。
請注意:請注意:
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路由器是一個三層裝置 ( 實體層、資料鏈結層、與網路層 ) 。
請注意:請注意:
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訊號增益器或橋接器連接一條 LAN 的各區段。路由器連接獨立的 LAN 或 WAN 以形成互連網路。
請注意:請注意:
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路由器改變封包內的實體位址。
請注意:請注意: