Reserved—Remains reserved for future use.
6.
Flags—Carries a variety of control information, including the SYN and ACK bits used for connection
establishment, and the FIN bit used for connection termination.
7.
Window—Specifies the size of the sender's receive window (that is, the buffer space available for
incoming data).
8.
Checksum—Indicates whether the header was damaged in transit.
9.
Urgent Pointer—Points to the first urgent data byte in the packet.
10.
Options—Specifies various TCP options.
11.
Data—Contains upper-layer information.
12.
UDP
The User Datagram Protocol (UDP) is a connectionless transport-layer protocol (Layer 4) that belongs to the
Internet protocol family. UDP is basically an interface between IP nd upper-layer processes. UDP protocol ports
distinguish multiple applications running on a single device from one another.
Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP. Because of UDP's
simplicity, UDP headers contain fewer bytes and consume less network overhead than TCP. UDP is useful in
situations where the reliability mechanisms of TCP are not necessary, such as in cases where a higher-layer
protocol might provide error and flow control. UDP is the transport protocol for several well-known
application-layer protocols, including Network File System (NFS), Simple Network Management Protocol
(SNMP), Domain Name System (DNS), and Trivial File Transfer Protocol (TFTP).
UDP Packet Format
The UDP packet format contains four fields: source and destination ports, length, and checksum.
Copyright © 2001
Cisco Systems, Inc.
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