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Its used to detect an error if the packet may be mis-routed. I'm not 100% sure.
Only TCP will automatically discard a packet with a bad checksum. UDP packets have a checksum field, but it is rarely used, and then only by the application (not UDP itself)
in tcp header (32 bits) we have a field that is called options and padding that has variable in length and the header length shows the actual header size i.e size of 20 octets+size of options and padding field and in UDP we dont have any field like that and its header is fixed of 8 OCTETS (32 bits header size) refrence: WIRELESS COMMUNICATIONS AND NETWORKS by William Stallings Second Edition pg 91(see fig)
In the commonly used TCP/IP communications, that would either be a TCP header, or a UDP header.In the commonly used TCP/IP communications, that would either be a TCP header, or a UDP header.In the commonly used TCP/IP communications, that would either be a TCP header, or a UDP header.In the commonly used TCP/IP communications, that would either be a TCP header, or a UDP header.
code bits
The protocol field, in the IP header, identifies what kind of data is in the IP packet - the upper-layer protocol. For example, if the code is 6, that means that the data is a TCP segment.
An Ethernet frame has a 14 byte header, a data section, and a 4 byte trailer 14 byte header consist of destination address, source address and type The trailer is for CRC (Cyclic redundancy Check) An Ethernet frame can contain an IP and TCP PDU. IP header most important parts consists of (Version,IHL, Total length,Protocol, source and destination address) In details (Version,Header length,Differentiated services field, total Length, Identification, Flags, fragment offset, Time to live, protocol, header checksum, source and destination address). TCP header most important parts consists of (Source port, Destination port and header Length) In details (Source Port, Destination Port, Sequence number, Acknowledgment number, Header length,Flags,Window and check sum). The details of the IP and TCP header have been taken from a Network protocol Analyzer Wireshark on my own pc.
It is a TCP Header
window
a tcp header contains the information of the source and destination networks and well as what port to access with out it the packet would not know where to go
both tcp and udp
no, service of UDP