In UDP port numbers are positive 16-bit numbers: They are purely abstract: they do not correspond to any physical entity on a host. Port numbers act as mailboxes and help a protocol implementation identify the sending and receiving processes ( Chapter 1).THe following figure shows UDP datagram, including the payload and UDP header (which is always 8 bytes in size): Later in this chapter describes what happens when the size of the UDP datagram exceeds the MTU size and the datagram must be fragmented into more than one IP-layer packet.IPv6 uses the same value (17) in the Next Header field.The IPv4 Protocol field has the value 17 to indicate UDP.The IPv6 encapsulation is similar, but other details differ slightly ( Section 10.5).The following figure shows the encapsulation of a UDP datagram as a single IPv4 datagram. The ability of an application to choose its own unit of retransmission can be an important consideration.Broadcast and multicast operations ( Chapter 9) are much more straightforward using a connectionless transport such as UDP.Because of its connectionless character, it has less overhead than other transport protocols.Given this lack of reliability and protection, we might be tempted to conclude that there are no benefits to using UDP at all. There is no protocol mechanism to prevent high-rate UDP traffic from negatively impacting other network users.UDP provides no error correction as mentioned: it sends the datagrams that the application writes to the IP layer, but there is no guarantee that they ever reach their destination.is the official specification of UDP, and it has remained as a standard without significant revisions for more than 30 years. This is in contrast to a stream-oriented protocol such as TCP ( Chapter 15), where the amount of data written by an application may have little relationship to what actually gets sent in a single IP datagram or what is consumed at the receiver.Each UDP output operation requested by an application produces exactly one UDP datagram, which causes one IP datagram to be sent.Applications wishing to ensure that their data is reliably delivered or sequenced must implement these protections themselves. It provides minimal functionality itself, so applications using it have a great deal of control over how packets are sent and processed.Thus, any modification made to those fields (e.g., by NAT) requires a modification to the UDP checksum. The Checksum field ( figure_10-2.png) is end-to-end and is computed over the UDP pseudo-header, which includes the Source and Destination IP Address fields from the IP header.It can provide error detection, and it includes the true end-to-end checksum at the transport layer.It does not provide error correction, sequencing, duplicate elimination, flow control, or congestion control.UDP is a simple, datagram-oriented, transport-layer protocol that preserves message boundaries: User Datagram Protocol (UDP) and IP Fragmentation ¶ Introduction ¶ ![]() Concurrency with Shared VariablesĬhapter 10. Security: EAP, IPsec, TLS, DNSSEC, and DKIM TCP: The Transmission Control Protocol (Preliminaries) Name Resolution and the Domain Name System (DNS) User Datagram Protocol (UDP) and IP Fragmentation Broadcasting and Local Multicasting (IGMP and MLD) ![]() ICMPv4 and ICMPv6: Internet Control Message Protocol ![]() Firewalls and Network Address Translation (NAT) System Configuration: DHCP and Autoconfiguration I/O Multiplexing: The select and poll Functions If you have any problems with the registration process or your account login, please contact us. Registration is fast, simple and absolutely free so please, join our community today! By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. If you are looking for information about Qt related issue - register and post your question. Over 90 percent of questions asked here gets answered. Qt Centre is a community site devoted to programming in C++ using the Qt framework. Select the forum that you want to visit from the selection below. Before you can post: click the register link above to proceed.
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