Computer Networks work based on Two type protocols.TCP and UDP. They are  collection of different communication protocols.Here give TCP/IP and its different protocols.

TCP ( Transmission Control Protocol)
   TCP is used for transmission of data from an application to the network.It is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive.
IP ( Internet Protocol)
    IP takes care of the communication with other computers.It is responsible for the sending and receiving data packets over the Internet.
HTTP ( Hyper Text Transfer Protocol)     HTTP takes care of the communication between a web server and a web browser.It is used for sending requests from a web client  to a web server, returning web content  from the server back to the client.
SMTP ( Simple Mail Transfer Protocol)
    SMTP is used for transmission of e-mails.
MIME ( Multi-purpose Internet Mail Extensions )
     The MIME protocol lets SMTP transmit multimedia files including voice, audio, and binary data across TCP/IP networks.
IMAP ( Internet Message Access Protocol)
     IMAP is used for storing and retrieving e-mails.
POP (Post Office Protocol)
      POP is used for downloading e-mails from an e-mail server to a personal computer.
FTP (File Transfer Protocol)     FTP takes care of transmission of files between computers.
NTP ( Network Time Protocol)      NTP is used to synchronize the time (the clock) between computers.
DHCP ( Dynamic Host Configuration Protocol)      DHCP is used for allocation of dynamic IP addresses to computers in a network.
SNMP ( Simple Network Management Protocol)       SNMP is used for administration of computer networks.
LDAP ( Lightweight Directory Access Protocol)       LDAP is used for collecting information about users and e-mail addresses from the internet. 
ICMP - Internet Control Message Protocol
     ICMP takes care of error-handling in the network.Its is responsible to display error message when a link down.
 ARP ( Address Resolution Protocol)
       ARP is used by IP to find the hardware address of a computer network card based on the IP address. 
BOOTP ( Boot Protocol )
       BOOTP is used for booting  computers from the network.
PPTP (Point to Point Tunneling Protocol )
        PPTP is used for setting up a connection  between private networks

Open system interconnection (OSI)  developed by ISO in 1974. It is not a physical model, its a set of guide lines for how to data transfer.OSI consist 7 layers. each layers have different functions.  OSI communicate with various hardware and software networks.Each layer functions are given.

OSI Model

   Layer 7 :Application Layer
      It is responsible for providing networking services to user. eg. HTTP,FTP,DNS,DHCP...etc.It is hardware software interface.its also known as desktop layer.Identification of services is done using port numbers.Ports are entry and exit unit of layer.
  Layer 6 :Presentation Layer
      It is Responsible for converting data into standard format.eg MPEG , JPEG , MP3 ,ASCII...etc.Presentation layer is responsible for Encoding and Decoding , Encryption and Decryption , Compression and Decompression.
 Layer 5 :Session Layer
      It is responsible for establishing ,maintaining and terminating session.it also provide dialog control between devices.it coordinate communication by offering 3 different modes simlex , half duplex , full duplex.
 Layer 4 :Transport Layer
     It is responsible for an end to end connection.Data from upper layer is cut from this layer called segments. .Following tasks are performed at transport layer

• Identifying Services
• Multiplexing and Demultiplexing
• Segmentation
• Sequencing and Reassembling
• Error Correction
• Flow control

Layer 3 :Network Layer
    This layer create packets from segments by adding header and recreate segments. Its responsible to find the best path for packets to destination.This layer mainly use TCP/IP protocol .
Layer 2 :Data link Layer
     Datalink layer is divided into 2,
         Media Access Control(MAC)
         Logical Link Control(LLC)
 Media Access Control(MAC) : It define how packets are placed on the media. Physical addressing
 (MAC address) and logical topologies are defined here.
 Logical Link Control(LLC) : It is responsible for identifying network layer protocol and encapsulating
  packets.
Layer 1 :Physical Layer
  It is used to perform data transmission in  the help of media. Hub,Cables,Modems are working at physical layer.                             

There are 3 type of cables available.they are
1.Straight  cable
2.Cross Over cable
3.Rolled Over cable

Straight cable

Straight Cable:
         This type of cables are used between different devices. Such as Pc to Hub, Pc to Switches, Switch to Riuter ,Hub to Router ...etc.Fig shows how to connect straight cables

Cross Over Cable

Cross Over Cable:
     
  The cross over cable can used to connect switch to switch , Hub to Hub , Pc to
Pc,Hub to Switch , Router to Host.Fig shows how to connect a cross cable.


 

Rolled Over Cable
      

Rolled Over Cable

       Rolledover Cable is used to connect Router or Switch to Pc through consol (COM) port.And is used to configure switch or Router