# Mạng và viễn thông P22

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## Mạng và viễn thông P22

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Electronic Mail, Znternet and Electronic Message Services The ability to connect two computers together and, with relative ease, to send information from one to the other, is bringing a revolution in the way in which business and life as a whole is conducted. Today it is possible to run your bank account from home, book your holiday, send electronic messages to your work colleagues or friends, and look up to see what is on at the theatre in London orNew York City.Alternatively companies may make their orders to and pay their bills from their suppliersby computer program and‘electronic data interchange’....

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## Nội dung Text: Mạng và viễn thông P22

7. TCP/IP PROTOCOL 405 address, the Internet address allowed an end user to be identified, no matter how many transit servers, routers or networks would have to be traversed along the way (Figure 22.2). The single network address of the destination port in the destination network does not suffice, because the intermediate networks are unable torecognize this address. A suite of new protocols arrived withInternet. Among others, these included S M T P (simple mail transport protocol), TFTP (trivial $le transfer protocol) and FTP ($le transfer protocol), which together form the basis the Internet electronic mail service. of As the popularity of Internet has grown, so have the number of servers and routers makingupthenetwork.New Internet service providershaveprovidedfordial-up access tothe servers fromprivateindividualsusingtheirPCs athome,and new information providers have provided more Internet pages of information. The Netscape browser, a computer software allowing users to ‘surf theInternet and World Wide Web ( W W W ) , by seeking information from any of the connected servers by means of a menu-driven screen software which drives a hypertext search and browse capability. However, the reason for the rapid growth of the Internet also provides a major challenge for the next stage of its development. The factor enabling rapid growth was the possibility to add further servers and routers to the network at almost any point in the network without considering a master plan. The number of Connected devices could therefore rapidly increase, as the routers (Chapter 19) are always able tofind the desired destination somehow. The problem is the lack of control (and even lack of knowledge) of the path taken. Thetraffic flo& in the network as a whole are therefore largely unmanaged unmanageable. and The onlysolution to slow response or congestion can be to add more capacity. Whether this capacity is added at the most appropriate point is a matter of chance. Messages within the Internet may go undelivered without trace for any number of reasons, and there is no record of whether electronic copies of information have been retained by any of the intermediate parties. Much attention is currently being focussed by the computer industry on solving the security and network management difficulties of the Internet, to stimulate a further surge in demand. 22.7 TCP/IP PROTOCOL STACK Figure 22.3 illustrates the various protocols going to make the TCPIIP stack.At the up heart are the Internet protocol (IP), which is equivalent to an OS1 layer 3 network