ICMP

ICMP (Internet Control Message Protocol) is a part of IP layer. ICMP messages are transmitted within IP datagrams. An IP datagram consists of an ICMP message with IP header.
ICMP communicates either error messages or query messages. To communicate a message it has a type field and a code field. A type field consists of 15 different values viz. 0, 3, 4, 5, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, to identify the type of ICMP message and a code field to specify the condition following the type. e.g. An echo request (ping request) has a type field value 8 and a code field value 0.

Reverse Address Resolution protocol

Reverse address resolution protocol does physical address to logical address mapping. A system with a local disk obtains its IP address from a configuration file when bootstrapped. But RARP is used by diskless systems such as an X terminal or a diskless workstation, to obtain their IP address when bootstrapped.
ARP and RARP both broadcast the request, and receive unicast reply. RARP request is broadcast with sender's hardware address, asking for sender's IP address.

Address Resolution Protocol

Suppose we send an Ethernet frame from our pc on a LAN to another pc. A data link such as an Ethernet or a token ring has its own addressing scheme which is often  48-bit addresses. Information is sent using IP addresses which is 32-bit address. Address Resolution Protocol provides a mapping between two different forms of addresses: 32-bit IP addresses and whatever type of address the data link uses (here 48-bit ethernet address). This logical address to physical address mapping is done by ARP.
ARP does dynamic mapping of addresses. That is, it is neither a concern of the application user or the system administrator to configure anything when this mapping takes place. All work is done automatically.

Ip datagram

Tcp/ip is a combination of tcp(transfer control protocol) which is present in transport layer of tcp model and ip(internet protocol) which is present in network layer. TCP provides reliable connection and ip provides unreliable connection.
Tcp adds TCP header at the beginning of application data which is known as TCP segment. And ip adds ip header at the beginning of this tcp segment which is known as ip datagram.
UDP provides unreliable connection. Udp adds udp header at the begining of application data and is known as udp datagram. And ip adds ip header at the beginning of this udp datagram which is known as ip datagram. Udp stands for user datagram protocol.

Network

A network is a collection of computers. Networks are all around us. A wide variety of networks are available like ethernet, wifi etc.