Computer Networks

 First Post 

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: 204.160.241.98 -Some networks also provide names that humans can more easily remember than numbers.

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.

Internet Application Protocols 

On top of TCP/IP, several services have been developed in order to homogenize applications of same nature: 

-FTP (File Transfer Protocol) allows the transfer of collection of files between two machines connected to the Internet. 

-Telnet (Terminal Protocol) allows a user to connect to a remote host in terminal mode. 

-NNTP (Network News Transfer Protocol) allows the constitution of communication groups (newsgroups) organized around specific topics. 

-SMTP (Simple Mail Transfer Protocol) defines a basic service for electronic mails. 

-SNMP (Simple Network Management Protocol) allows the management of the network.