User data submitted to agreement
UDP is ISO reference model a connectionless transport layer protocol, provide oriented affairs of simple unreliable transmit information service. UDP protocol is basically the IP protocol and the upper level protocol interfaces. UDP protocol for ports in the same device distinguish operation on multiple applications.
introduction
UDP protocol's full name is the user data submitted to agreement, in the network it with TCP protocol as used for handling packets. In the OSI model, in the fourth layer - the transport layer, in the IP protocol of a layer. UDP have not provide data submitted to grouping, assembly and unable to sort of data packets faults, that is, when messages are sent after, not know whether its safety integrity to arrive. UDP used to support those who need the data transfer between computers network application. Including the network video conference system, the numerous client/server model of network application all need to use the UDP protocol. UDP protocol from published so far has been used for many years, although its original luster has been some similar agreement covered, but even today, UDP can still be a very practical and feasible network transport layer protocol.
With known TCP (TCP) agreement is same, UDP protocol is located directly Internet protocol (IP) agreement of top. According to the OSI (OSI) reference model, UDP and TCP belong to the transport layer protocol.
UDP protocol's main function is to network data flow compressed into data submitted to form. A typical data submitted to is a binary data transmission units. Each data submitted to the first 8 bytes to contain header information, the remaining byte is used to contain specific data transmission.
Use the UDP
In choosing use agreement when the choice of UDP must careful. In the network quality is not quite satisfied with the environment, UDP protocol packet loss may be more severe. But because the UDP characteristics: it does not belong to connection type agreement, thus has the resource consumption is small, processing speed advantage, so usually audio, video and common data in transmission when use the UDP more, because they even the occasional lost one or two packets, also won't receiving results too much influence. For instance we chat using ICQ and OICQ is to use the UDP protocol.
UDP header
UDP header composed by four domain which each domain each occupy 2 bytes, specific as follows:
The source port
Target socket
Data submitted to the length
Calibration value
UDP protocol use socket for different applications retain their respective data transmission channel. UDP and TCP protocol is using this mechanism to achieve the same hour within several applications also sending and receiving data support. Data sending party (can be client or server) will UDP data submitted to send out through the source port, and data receiving side is through the target port receive data. Some network applications can be used for its reserved in advance or registered static port, Other network applications can be used is not registered dynamic port. Because the UDP header using two bytes deposit socket, so the socket of the valid range is 0 to 65535. Generally speaking, than 49151 the socket all represent dynamic port.
Data submitted to the length of refers to include header and data section, total bytes. Because header length is fixed, so this domain is mainly used to calculate variable length of data section (also called data load). Data submitted to the maximum length according to operating the different environmental and each different. Theoretically, contains header, data submitted to the maximum length to 65535 bytes. However, some practical applications tend to limit the size of the data submitted, sometimes reduced to 8192 bytes.
UDP protocol used in the calibration value to ensure header data security. Calibration value first in data sending by special algorithm calculated, the relay to the receiving party after, also need to recount. If a data reported during transmission by a third party distort or due to reasons such as circuit noise were damaged, sending and receiving party calibration calculation values will not agree, thus UDP protocol can check whether errors. This is different with TCP protocol, the latter requiring calibration value must have.
Many of the link layer protocols will provide error check, including pop the Ethernet protocol, perhaps want to know why UDP must also provide inspection and. Its reason is the link layer under the agreement between the source end and terminal some of the channel may not provide error detection. Although UDP provide error detection, but detect the error, error correction, UDP don't do simply the damaged news section throw away, or give application provides the warning message.
UDP protocol several characteristics
(1) the UDP is a connectionless protocol, transmission data before the source end and terminal not establish a connection, when UDP
It wants to teleport simply to grab from the application's data, and as quickly as you can throw it to the web. After the sender, UDP transmits data speed is merely by applications to make data speed, computer ability and transmission bandwidth limit, In the receiver, each news section on UDP queue, application every time from the queue read a news section.
(2) the data transmission not establish a connection, and therefore do not need maintenance connection status, including transceiver state, so a service machine can simultaneously to multiple clients transmission of the same message.
(3) UDP packets title is very short, only 8 bytes, relative to TCP 20 bytes packets of overhead is small.
(4) throughput from congestion control algorithm of adjustment, only by their application software generated data rate, transmission bandwidth, the source end and terminal host performance restrictions.
(5) UDP use do your utmost to consign, i.e. not to ensure reliable delivery, so host does not need to maintain complex link status table (there are many parameters).
(6) UDP is facing a message. The sender UDP on application into down message, first in add after downward delivery to the IP layers. Neither separation, merger, but also not keep these messages boundary, therefore, applications need to choose the appropriate message size.
Although UDP is not a reliable agreement, but it is distributed information of an ideal agreement. For example, on the screen reports stock markets, on the screen aviation information, etc. UDP is also used in Routing Information Protocol RIP (Protocol) modify ccna Information Routing table. In these applications, if there is a message lost, in seconds after another new news will replace it. UDP widely used in multimedia applications, for example, Progressive grow independently developed by our RealAudio software, which is on the Internet to advance the recorded music or the spot to client real-time transmission of a kind of software, the software use RealAudio numerous - on - protocol agreement is running in the rest of the agreement, most UDP over the Internet phone software products are run on UDP above all.
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