Introduction

A network can be defined as a group of computers and other devices connected in some ways so as to be able to exchange data.
-Each of the devices on the network can be thought of as a node; each node has a unique address.
-Addresses are numeric quantities that are easy for computers to work with, but not for humans to remember.
Example: 64.31.12.11
-Some networks also provide names that humans can more easily remember than numbers.
Example: www.cmscomputer.in, corresponding to the above numeric address.

Addressing

Internet address

Consists of 4 bytes separated by periods
Example: 136.102.233.49
-The R first bytes (R= 1,2,3) correspond to the network address;
-The remaining H bytes (H = 3,2,1) are used for the host machine.

-InterNIC Register:

organization in charge of the allocation of the address ranges corresponding to networks.
-Criteria considered:
→ Geographical area (country)
→ Organization, enterprise
→ Department
→ Host

Domain Name System (DNS):

-Mnemonic textual addresses are provided to facilitate the manipulation of internet addresses.
-DNS servers are responsible for translating mnemonic textual Internet addresses into hard numeric Internet addresses.

Ports

-An IP address identifies a host machine on the Internet.
-An IP port will identify a specific application running on an Internet host
machine.
-A port is identified by a number, the port number.
-The number of ports is not functionally limited, in contrast to serial
communications where only 4 ports are allowed.
-There are some port numbers which are dedicated for specific
applications.

Applications	Port numbers
HTTP	80
Telnet	23
POP3 (e-mail)	110
SMTP (e-mail)	25
Gopher	70
FTP	20 and 21
Finger	79