TCP/UDP
By: Rogger
Transmission Control Protocol (TCP)
TCP provides a highly reliable, connection oriented, end-to-end transport service between processes in end systems connected to the subnet. TCP only assumes that the layer below offers an unreliable datagram service. TCP provides the types of facility associated with the ISO Class 4 transport service, including error recovery, sequencing of packets, flow control by the windowing method, and the support of multiplexed connections from the layer above.
Format of TCP header
The sender's TCP layer communicates with the receiver's TCP layer using the TCP protocol data unit. It defines parameters such as the source port, destination port, sequence number and so on. Its descriptions are given below:
Source and destination port number - which are 16 bits values to identify the local port number
Sequence number - which identifies the current sequence number of the data segment. This allows the receiver to keep track of the data segments received. Any segments that are missing can be easily identified.
Data offset - which is a 32 bit value and identifies the start of the data.
Flags the flag field is defined as UAPRSE, where U is the urgent Flag, A the acknowledgement flag, P the push function, R the reset flag, S the sequence synchronize flag and F the end - of transmission flag.
Windows - which is a 16 bit value and gives the number of data blocks that the receiving host can accept at a time.
Checksum - which is a 16 bit checksum for the data and header.
UrgPtr - which is the urgent pointer and is used to identify an important area of data.
User Data Protocol (UDP)
The Internet Protocol suite also supports a connectionless transport protocol, UDP (User Data Protocol). UDP provides a way for applications to send encapsulated raw IP datagrams and send them without having to establish a connection. Many client-server applications that have one request and one response use UDP rather than go to the trouble of establishing and later releasing a connection.
A UDP segment consists of an 8-byte header followed by the data. The two ports serve the same function as they do in TCP; to identify the end points with the source and destination machines. The UDP length field includes the 8-byte header and the data. The UDP checksum includes the same format pseudo-header, the UDP header, and the UDP data, padded out to an even number of bytes if need be. It is optional and stored, as 0 if not computed.
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Source - TAIOC.com