le," that is a bit of a misnomer. For applications that require nothing more than a simple query and response, UDP is ideal Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Chapter 7 Figure 7-40 IP Source Address The UDP header IP Destination Address Unused Protocol Type UDP Datagram Length Source Port Number Destination Port Number UDP Datagram Length UDP Checksum because it involves minimal protocol overhead. UDP's primary responsi- bility is to add a port number to the IP address to create a socket for the application. The fields of a UDP message (see Figure 7-40) are described here. The Source Port field identifies the UDP port used by the sender of the datagram, while the Destination Port field identifies the port used by the datagram receiver. The Length Field field indicates the overall length of the UDP datagram. The Checksum field provides the same primitive bit error detection of the header and transported data as we saw with TCP. The Internet Control Message Protocol (ICMP) The Internet Control Message Protocol (ICMP) is used as a diagnostic tool in IP networks to notify a sender that something unusual happened during transmission. It offers a healthy repertoire of messages, including Destination Unreachable, which indicates that delivery is not possible because the destination host cannot be reached; Echo and Echo Reply, used to check whether hosts are available; Parameter Problem, used to indicate that a router encountered a header problem; Redirect, which is used to make the sending system aware that packets should be for- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Transport Technologies warded to another a