25-UDP

Dr. John P. Abraham

Professor

UTPA

User Datagram Protocol

• A Datagram transport service• IP alone can’t distinguish among multiple

application programs running on a given host. Another words, once the datagram is delivered to the computer, how does the computer use it? Is it an email datagram? Is it a web datagram?

• Transport layer protocols are known as end-to-end protocols (rather than host-to-host), because they deliver to the application on each end.

Features of UDP (thin protocol)

• End-to-end• Connectionless• Message oriented. Programmers may choose a

message size that produces datagrams that fit in a standard MTU (1400 to 1450 octets of data).

• Best effort• Arbitrary interaction: allows an application to

send to many other applications (1 to many), or many-to-1 or many-to-many, or 1 to 1.

• Operating system independent.

Position of UDP in the TCP/IP protocol suite

UDP communication semantics

• UDP uses IP to send messages, as such problems of IP are inherited. An application must be immune to these problems or programmers should take additional steps to handle these problems.

Well-known ports used with UDPWell-known ports used with UDP

Endpoint identification with protocol numbers

• Protocol port numbers (sockets) are independent of underlying operating system. Each computer that supports UDP must map port numbers and program identifiers that the OS uses.

User datagram format

Encapsulation and decapsulation