OSI MODEL

Q1- What is OSI layer ?
Ans- OSI layer is a conceptual model developed by ISO which describes the flow of data between sender and receiver in a network. It describes the changing in data unit on each layer. There are seven layer in OSI model . All layer perform a specific task.

Q2- Tell me three network layer Protocols ?
Ans-  IP (internet Protocol)
         ARP ( Address Resolution Protocol )
         RARP ( Reverse Address Resolution Protocol )

Q3-  What is different between TCP and UDP ?
Ans- TCP and UDP both protocol works on Transport layer of OSI model. Both are responsible for               data delivery but there are some difference between them.

     TCP - 
It is a connection oriented protocol . It is a reliable protocol which gives acknowledgement after delivery a data to destination. It transfers data after making connection between source and destination computers. It is slower than UDP because it checks connection before sending any segment of data. HTTP, FTP, SMTP, RDP are works with TCP

   UDP- 
UDP is connection less protocol . It is unreliable because it does not give acknowledgement after delivering data. It is faster than TCP .  TFTP, DNS and DHCP works with UDP.

Q4- Which layer adds header and trailer ?
Ans- Data Link Layer.

Q5- Hub, switch, router, bridge, repeater , NIC , MAC , IP  works on which layer of OSI model.

Ans.  HUB           -         Physical Layer
          Switch        -         Data Link Layer
          Repeater     -         Physical Layer
          Bridge        -         Date Link Layer
          Router        -         Network Layer
          NIC            -         Data Link Layer
           MAC         -         Data Link Layer
           IP              -         Network Layer


Q6- Which layer is responsible for framing ?
Ans. Data link layer is responsible for framing. HDLC, PPP  and frame-relay are the data link layer protocol.

Q7- What is Port number ? Which layer adds port number ?

Ans- Port number is the address of protocol which is used to identify services working of any host in network. It is assigned by IANA ( Internet Assign Network Authority ) . Transport Layer adds port numbers in segment that is called service point addressing. There are some important protocol and their Port numbers.

HTTP ( Hyper Text Transfer Protocol )  -      80 (SSL-443)
SMTP ( Simple Mail Transfer Protocol ) - 25  (SSL-465)
POP  ( Post Office Protocol )                    -110  (SSL-995)
FTP  ( File Transfer Protocol )                  - 20 and 21
Telnet                                                         -23
RDP ( Remote Desktop Protocol )             -3389
ICMP ( Internet Control Message Protocol ) - 1 and 7