response is received only by the client that sent the request. 6.6.10.8 TFTP FTP is the most general file transfer protocol in TCP/IP protocol suite. Many applications do not need the full functionality that FTP offers, nor can they afford its complexity [4]. The TFTP is a simple file transfer protocol that uses UDP, as shown in Figure 6.36, and transmits files in fixed 512-byte blocks. It waits for an acknowledgment for each block before sending the next. UDP is an unreliable packet delivery system and TFTP uses time-outs and retransmissions to ensure that the entire file is received properly. 6.6.10.9 RTP The RTP is designed to improve real-time services, such as digitized audio and video, over the Internet. It is designed to be independent from Data Communications underlying protocols and it cannot guarantee a specific level of service, for example, a certain constant data rate and delay. It uses UDP as a transport layer and cannot ensure timely delivery; such guarantees must be made by the underlying system. However, RTP provides sequence numbering for detection of out-of-order delivery and a timestamp that allows the receiver to control playback [4]. A timestamp defines the exact time at which the first octet of digitized data in the packet was sampled [4]. Protocol information of RTP is inserted into the UDP payload after the UDP header. If some datagrams travel a much longer route and are much more delayed than others, an application layer protocol, such as RTP, cannot help it. For high-quality real-time transmission, additional control of lower layers is required. One proposed protocol for network layer control is the Resource Reservation Protocol (RSVP). The end points send an RSVP message to request resources and all routers on the way have to accept the request. If not, end-to-end QoS is not guaranteed. 6.6.11 www The WWW is an architectural framework for accessing linked documents spread out all over the Internet. Its enormous popularity is the result of a col- orful and easy-to-use graphical interfac