【正文】 mber is important because, as mentioned above, datagrams can arrive out of order。ll cover the basic terminology and concepts behind sockets programming in general. Transmission Control Protocol (TCP) When two puters wish to exchange information over a work, there are several ponents that must be in place before the data can actually be sent and received. Of course, the physical hardware must exist, which is typically either a work interface card (NIC) or a serial munications port for dialup working connections. Beyond this physical connection, however, puters also need to use a protocol which defines the parameters of the munication between them. In short, a protocol defines the rules of the road that each puter must follow so that all of the systems in the work can exchange data. One of the most popular protocols in use today is TCP/IP, which stands for Transmission Control Protocol/Inter Protocol. By convention, TCP/IP is used to refer to a suite of protocols, all based on the Inter Protocol (IP). Unlike a single local work, where every system is directly connected to each other, an inter is a collection of works, bined into a single, virtual work. The Inter Protocol provides the means by which any system on any work can municate with another as easily as if they were on the same physical work. Each system, monly referred to as a host, is assigned a unique 32bit number which can be used to identify it over the work. Typically, this address is broken into four 8bit numbers separated by periods. This is called dotnotation, and looks something like . Some parts of the address are used to identify the work that the system is connected to, and the remainder identifies the system itself. Without going into the minutia of the Inter addressing scheme, just be aware that there are three classes of addresses, referred to as A, B and C. The rule of thumb is that class A addresses are assigned to very large works, class B addresses are assigned to medium sized works, and class C addresses are assigned to smaller works (works with less than approximately 250 hosts). When a system sends data over the work using the Inter Protocol, it is sent in discrete units called datagrams, also monly referred to as packets. A datagram consists of a header followed by applicationdefined data. The header contains the addressing information which is used to deliver the datagram to it39。re already familiar with sockets programming, feel free to skip this section. There are two general approaches that you can take when creating a program that uses Windows Sockets. One is to code directly against the API. The other is to use a ponent which provides a higherlevel interface to the library by setting properties and responding to events. This can provide a more natural programming interface, and it allows you to avoid much of the errorprone drudgery monly associated with sockets programming. By including the control in a project, setting some properties and responding to events, you can quickly and easily write an Interenabled application. SocketWrench provides a prehensive interface to the Windows Sockets library and will be used to build a simple clientserver application in the next section of this document. Before we get started with the control, however, we39。s really needed is a reliable, straightforward way to exchange data without having to worry about lost packets or jumbled data. To fill this need, the Transmission Control Protocol (TCP) was developed. Built on top of IP, TCP offers a reliable, fullduplex byte stream which may be read and written to in a fashion similar to reading and writing a file. The advantages to this are obvious: the application programmer doesn39。s destination. This means that the sender and receiver must typically implement their own application protocol on top of UDP. Much of the work that TCP does transparently (such 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。 緒論 隨著 TCP/IP 作為一種獨(dú)立網(wǎng)絡(luò)協(xié)議標(biāo)準(zhǔn)平臺(tái)逐漸的被認(rèn)可，以及互聯(lián)網(wǎng)的激增，在 Windows 環(huán)境下成為網(wǎng)絡(luò)程序設(shè)計(jì)標(biāo)準(zhǔn)的 Windows Sockets API (應(yīng)用程序結(jié)口 )已經(jīng)步入舞臺(tái)。欲了