The TCP/IP Protocol Structure
TCP/IP is a protocol that fits into the data frame area of the Ethernet frame. TCP/IP provides three layers of services:
Structure of an Internet Datagram
The packet delivery system is defined as an unreliable (no guaranteed delivery), best effort, connectionless packet delivery system. The protocol that describes this is called the Internet Protocol abbreviated as IP.
The basic packet is called an internet datagram. The structure of the internet datagram is as follows:
Structure of an Internet Datagram
Definitions of the Internet Datagram Structure Headings:
VERS - A version of the protocol.
HLEN - The datagram header length in 32 bit words.
Service Type - This is merely a recommendation to the routing software on the service required.
Total Length - Length of the datagram in bytes (including the header section).
Identification - Each datagram must have a unique number
Fragment Offset - This specifies the offset of the data in the original datagram.
Time to Live (TTL) - As the datagram passes through the network, its time is decremented for each pass of each gateway or host.
Protocol - This specifies the protocol format for the data payload area.
Header Checksum - Complement the result of adding the IP header as a series of 16 bit integers using one's complement arithmetic.
Source IP and Destination IP Addresses - The IP addresses of source and destination nodes.
IP Options - Options used for control purposes.