Page 130 - Handout Computer Network.

• Checksum—Calculated checksum of the header and data fields

• Urgent Pointer—Indication of the end of the urgent data

• Options—One option currently defined—maximum TCP segment size

• Data—Upper-layer protocol data.

6.2.3. UDP

User Datagram Protocol (UDP), the segment format for which is shown in Figure (6-4), is
the connectionless transport protocol in the TCP/IP protocol stack.
UDP is a simple protocol that exchanges datagrams without acknowledgments or
guaranteed delivery. This simplicity is evident when comparing the UDP segment format with
that of TCP.

Error processing and retransmission must be handled by upper-layer protocols. For
example, if a TFTP download gets interrupted for some reason, the human operator can just
retry until it is successfully done.

Figure 6-4 shown a UDP Segment Format

The following list defines the fields in the UDP segment shown in Figure 6-4 shown a UDP
Segment Format:

• Source Port—Number of the calling port
• Destination Port—Number of the called port
• Length—Number of bytes, including header and data

• Checksum—Calculated checksum of the header and data fields
• Data—Upper-layer protocol data
UDP uses no windowing or acknowledgments; therefore, application layer protocols
provide reliability.

UDP is designed for applications that do not need to put sequences of segments together.
These protocols use UDP:

• Trivial File Transfer Protocol (TFTP)
• Simple Network Management Protocol (SNMP)

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