Thursday, 17 September 2015

Internet protocol

Network Protocols



The DOD model is a Brief version of the OSI model, it has four layers.

     1.       Application layer

   2.       Host to Host Layer

   3.       Internet Layer

   4.       Network Access layer  
                                                 
                                
   DOD and OSI Layers






















TCP/IP Model Protocols

















Application Layer Protocols


Telnet:- It is a protocol that allows a user to access Telnet server or machine remotely through command line.

TFTP:-  TFTP (Trivial File Transfer Protocol) is used to transfer file over the network. It does not provide the directory browsing feature. So to use this protocol we must know the exact file name and location of file.

FTP:-  FTP(File Transfer Protocol)  is actual file transfer protocols. We can transfer data or file using the FTP protocol. FTP is not just a protocol, It is a program also that provide directory browsing feature and let users select data what they need to transfer.

SMTP:- SMTP(Simple Mail Transfer Protocolis used to send E-mail messages. It is responsible for successful message delivery. It continuously check queue for messages, as message comes in queue it process that message to deliver.

LPD:- (Line Printer Daemon) is designed for printer sharing. It allows to send print command over the network.

X Window:- X Window defines a protocol for writing client/server applications
based on a graphical user interface (GUI). The idea is to allow a program, called a client,
to run on one computer and have it display things through a window server on another computer


SNMP:- (Simple Network Management Protocolis used to collect information about network. It is also called watchdog over the network. When any problem occur in network SNMP send alert to the management machine.

NFS:- NFS(Network File Systemis used for file sharing. It allows to different file systems to share data.


                                        Transmission Control Protocol

TCP:- TCP(Transmission Control Protocol) take data payload from upper layers and break them into segments.TCP is a connection oriented protocol , it means tit create a virtual circuit before transfer data segments. It is also called hand shaking.   During this initial handshake, the two TCP layers also agree on the amount of information that’s going to be sent before the recipient’s TCP sends back an acknowledgement. With everything agreed upon in advance, the path is paved for reliable communication to take place.













Destination port :- The port number of the application requested on the destination host.

Sequence number :- Puts the data back in the correct order or retransmits missing or damaged
data, a process called sequencing.

Acknowledgement number:- Defines which TCP octet is expected next.

Header length:-  The number of 32-bit words in the TCP header. This indicates where the data
begins. The TCP header (even one including options) is an integral number of 32 bits in length.

Reserved:- Always set to zero.

Code bits :- Control functions used to set up and terminate a session.

Window :- The window size the sender is willing to accept, in octets.

Checksum :- The cyclic redundancy check (CRC), because TCP doesn’t trust the lower layers
and checks everything. The CRC checks the header and data fields.

Urgent :- A valid field only if the Urgent pointer in the code bits is set. If so, this value indicates
the offset from the current sequence number, in octets, where the first segment of non-urgent
data begins.

Options:- May be 0 or a multiple of 32 bits, if any. What this means is that no options have to be
present (option size of 0). However, if any options are used that do not cause the option field to total
a multiple of 32 bits, padding of 0s must be used to make sure the data begins on a 32-bit boundary.

Data :-  Handed down to the TCP protocol at the Transport layer, which includes the upper layer
headers.

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