【正文】 as generating checksums, acknowledging the receipt of packets, retransmitting lost packets and so on) must be performed by the application itself. With the limitations of UDP, you might wonder why it39。s destination intact, and as a result it exchanges a fairly high number of packets over the work. UDP doesn39。 緒論 隨著 TCP/IP 作為一種獨立網絡協議標準平臺逐漸的被認可，以及互聯網的激增，在 Windows 環(huán)境下成為網絡程序設計標準的 Windows Sockets API (應用程序結口 )已經步入舞臺。 Socketwrench 是 Catalyst 軟件開發(fā)的其中一部分，稱之為 SocketTools Visual Edition。欲了解更多關于 sockettools 軟件包，請訪問 Catalyst網站 。其中一個就是使用 API 函數編寫代碼。它提供了一種更加適 當的編程接口，使用 sockets編程可以避免許多易錯點。 socketwrench 提供了 比較 全面的 Windows Sockets 類庫 ，并且 在 文章中的下一部分會被用來建立一個簡單的客戶機 服務器應用。 傳輸控制協議 當兩臺電腦之間想通過網絡交換信息，在真正傳輸和接收數據之前，有幾個組成部分是必須的。盡管如此，在這些物理連接之外，計算機之間同樣也需要定義一些參數傳遞的協議。在當今最流行的協議 就是 TCP/IP， 也即傳輸控制協議。不像一個單一的本地網， 每個系統(tǒng)是直接連接到對方，互聯網是一個網絡的集合，結合了單個的、 虛擬的網絡。每個系統(tǒng)，通常被稱為主機，分配一個唯一的用來辨別的 32 位數字。這就是所謂的 點分法 ，類似 “ ” 。不對 Inter 地址進行詳細的了解 了 ，只 要 知道 主要的 3“ 類 ” 地址，如 “ A” ， “ B” 和 “ C” 。 當一個系統(tǒng)通過互聯網 協議發(fā)送數據時，所發(fā)送的不連續(xù)的單位即所謂的數據報，也被稱為信息包。報頭包含了數據報要傳遞的目的地址的 信息，就像一個信封，是用來書寫地址、郵件處理。事實上，數據報在網絡傳輸過程中也 可能會 出現丟失、 重復或無序 現象 。那怎么樣才可以實現可靠的、直接的交換數據，而不出現信息報丟失或者 無序的現象 。建立在 IP 基礎上，TCP 提供了一個可靠的 、全雙工的字節(jié)流可讀可寫類似于對文件的讀寫操作。因為數據是作為一個字節(jié)流來保存的，使用 TCP可以更加容易的修改和 使用 現有的代碼。在換句話說，在兩個程序開始進行數據交換之前，他們必須 建立 一個連接 。當建立連接后，其中一個程序要作為客戶端 的角色，而另 一個要在作為服務器。當連接建立成功，雙方可以發(fā)送和接收數據，直到連接關閉為止。以離散單元的形式交換的數據稱之為數據報，類似于 IP 數據報。 UDP 有時被稱為是一個不可靠的協議，因為在網絡上一個程序發(fā)送一 UDP數據報，是沒有辦法知 道它是否確實到達它的目的地。 TCP 的 許多工作（如生成校驗，確認收到的數據包，轉發(fā)丟包等）必須由應用程序本身來體現出來。 UDP 與TCP 相比 存在 著 兩個關鍵領域優(yōu)勢：速度和數據包開銷。 UDP 并沒有這種開銷，比起 TCP來要快的多 。 Client Server Programming with Winsock Author . Ahmed . Ahmed is a senior IT Professional and works for a web and software development firm. Ahmed specializes in creating database driven dynamic web sites. He has been working with SharePoint for the last 34 years. He develops customized SharePoint solutions. Ahmed enjoys travelling and has been to many parts of the world. Web: Blog: Introduction Winsock control es with VB6 and is used to create applications that access the lowlevel functions of the Transmission Control Protocol/Inter Protocol (TCP/IP). Most of you might have worked with Inter Transfer Control which is very handy control when it es to Inter Programming but there is another control which even more robust and helps programmers creating more flexible applications. Winsock control es with VB6 and is used to create applications that access the lowlevel functions of the Transmission Control Protocol/Inter Protocol (TCP/IP). TCP/IP is a specification that defines a series of protocols used to standardize how puters exchange information with each other. TCP/IP provides munication across interconnected works that use diverse hardware architectures and various operating systems. The protocols in TCP/IP are arranged in a series of layers known as a protocol stack. Each layer has its own functionality. Winsock is a standard that is maintained by Microsoft. This standard is basically a set of routines that describe munications from the TCP/IP stack. These routines reside in a dynamic link library that runs under Windows. The winsock DLL is interfaced with TCP/IP and from there through the Inter. In this article, I am going to show how to use the winsock in a client server environment, we will create two separate applications, one of which will be a server and the other will be a client. Both client and server will interact with each other to exchange data. Client will send a request to the server and the server which will be connected to a database will retrieve the information requested by the client from the database and will return the requested information back to the client. You will base a database with this article, the database contains the item numbers and their prices. In real life situations, database might be located on a machine different from the one that hosts and client application. Ports amp。 Events Winsock enables you to create clients and servers using the same control. This dual functionality enables you to specify through property setting the type of application you will be building. The Winsock control uses a number of the same properties, whether