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kết thúc chậm trễ cho các gói cá nhân. Cũng không dịch vụ thực hiện bất kỳ lời hứa về sự biến đổi của sự chậm trễ pakcet trong một dòng gói tin. Như chúng ta đã học được trong Chương 3, bởi vì TCP và UDP chạy trên IP, không phải của các giao thức này có thể làm cho bất kỳ sự chậm trễ nào đảm bảo các ứng dụng gọi. | Introduction end delay for an individual packet. Nor does the service make any promises about the variation of pakcet delay within a packet stream. As we learned in Chapter 3 because TCP and UDP run over IP neither of these protocols can make any delay guarantees to invoking applications. Due to the lack of any special effort to deliver packets in a timely manner it is extermely challenging problem to develop successful multimedia networking applications for the Internet. To date multimedia over the Internet has achieved significant but limited success. For example streaming store audio video with user-interactivity delays of five-to-ten seconds is now commonplace in the Internet. But during peak traffic periods performance may be unsatisfactory particularly when intervening links are congested links such as congested transoceanic link . Internet phone and real-time interactive video has to date been less successful than streaming stored audio video. Indeed real-time interactive voice and video impose rigid constraints on packet delay and packet jitter. Packet jitter is the variability of packet delays within the same packet stream. Real-time voice and video can work well in regions where bandwidth is plentiful and hence delay and jitter are minimal. But quality can deteriorate to unacceptable levels as soon as the real-time voice or video packet stream hits a moderately congested link. The design of multimedia applications would certainly be more straightforward if their were some sort of first-class and second-class Internet services whereby first-class packets are limited in number and always get priorities in router queues. Such a first-class service could be satisfactory for delay-sensitive applications. But to date the Internet has mostly taken an egalitarian approach to packet scheduling in router queues all packets receive equal service no packets including delay-sensitive audio and video packets get any priorities in the router queues. No matter how much .
