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মঙ্গলবার, ৩ ডিসেম্বর, ২০১৩

UDP (User Datagram Protocol) and Transmission Control Protocol (TCP) Detail Port .

User Datagram Protocol (UDP):
UDP Stand for (User Datagram Protocol) is a simple OSI transport layer protocol for client/server network applications based on IP (Internet Protocol). UDP is the main alternative to TCP and one of the oldest network protocols in existence, introduced in 1980.
UDP is often used in videoconferencing applications or computer games specially tuned for real-time performance. To achieve higher performance, the protocol allows individual packets to be dropped (with no retries) and UDP packets to be received in a different order than they were sent as dictated by the application.
 The User Datagram Protocol (UDP) is a transport layer protocol defined for use with the IP network layer protocol. It is defined by RFC 768 written by John Postel. It provides a best-effort datagram service to an End System (IP host).

TCP/IP Transport Layer Protoco:
Internet Protocol (IP) addresses are the universally-used main form of addressing on a TCP/IP network. These network-layer addresses uniquely identify each network interface, and as such, serve as the mechanism by which data is routed to the correct network on the internetwork, and then the correct device on that network. What some people don't realize, however, is that there is an additional level of addressing that occurs at the transport layer in TCP/IP, above that of the IP address. Both of the TCP/IP transport protocols, TCP and UDP, use the concepts of ports and sockets for virtual software addressing, to enable the function of many applications simultaneously on an IP device.



Incidentally, I describe UDP before TCP for a simple reason: it is simpler. UDP operates more like a classical message-based protocol, and in fact is more similar to IP itself than is TCP. This is the same reason why the section on TCP is much larger than that covering UDP: TCP much more complex and does a great deal more than UDP

Very Important Port :

Ports

Generally, clients set the source port number to a unique number that they choose themselves - usually based on the program that started the connection. Since this number is returned by the server in responses, this lets the sender know which "conversation" incoming packets are to be sent to. The destination port of packets sent by the client is usually set to one of a number of well-known ports. These usually correspond to one of a number of different applications, e.g. port 23 is used for telnet, and port 80 is used for web servers.
A server process (program), listens for UDP packets received with a particular well-known port number and tells its local UDP layer to send packets matching this destination port number to the server program. It determines which client these packets come from by examining the received IP source address and the received unique UDP source port number. Any responses which the server needs to send to back to a client are sent with the source port number of the server (the well-known port number) and the destination port selected by the client. Most people do not memorise the well known ports, instead they look them up in table (e.g. see below).

20 FTP-DATA File Transfer [Default Data]
21 FTP File Transfer [Control]
23 TELNET Telnet
25 SMTP Simple Mail Transfer
37 TIME Time
69 TFTP Trivial File Transfer
79 FINGER Finger
110 POP3 Post Office Protocol v 3
123 NTP Network Time Protocol
143 IMAP2 Interim Mail Access Prot. v2
161 SNMP Simple Network Man. Prot.
Some well-known UDP/IP port numbers
(a full list is provided in the link at the bottom of this page).

If a client/server application executes on a host with more than one IP interface, the application needs to ensure that it sends any UDP responses with an IP source address that matches the IP destination address of the UDP datagram that carried the request.

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