The Header Checksum provides a verification that the information used in processing internet datagram has been transmitted correctly. The data may contain errors. If the header checksum fails, the internet datagram is discarded at once by the entity which detects the error.
The internet protocol does not provide a reliable communication facility. There are no acknowledgments either end-to-end or hop-by-hop. There is no error control for data, only a header checksum. There are no retransmissions. There is no flow control.
Errors detected may be reported via the Internet Control Message Protocol (ICMP) [3] which is implemented in the internet protocol module.
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2. OVERVIEW
2.1. Relation to Other Protocols
The following diagram illustrates the place of the internet protocol in the protocol hierarchy:
+--------------------------+----+ Internet Protocol & ICMP +--------------------------+----+
+---------------------------+ Local Network Protocol +---------------------------+
Protocol Relationships
Figure 1.
Internet protocol interfaces on one side to the higher level host-to-host protocols and on the other side to the local network protocol. In this context a "local network" may be a small network in a building or a large network such as the ARPANET.
2.2. Model of Operation
The model of operation for transmitting a datagram from one application program to another is illustrated by the following scenario:
We suppose that this transmission will involve one intermediate gateway.
The sending application program prepares its data and calls on its local internet module to send that data as a datagram and passes the destination address and other parameters as arguments of the call.
The internet module prepares a datagram header and attaches the data to it. The internet module determines a local network address for this internet address, in this case it is the address of a gateway.
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It sends this datagram and the local network address to the local
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