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OSI Model - Open System Interconnection reference model.

Provides Guidelines on how computers communicate over a network .It does

n't define specific procedure /protocols how the communication happens.
Protocols: Protocols is a formal set of rules and procedures computer must under
stand accept and used to be able to communicate over network. E.g TCP, SNMP,IMAP
OSI Model Stacks: Application ,Presentation, Session, Transport, Network, Datali
nk and Physiscal Layers
TCP/IP Model ( 4 Layers ) Application, Transport, Internet and Network Access la
yer . It's a simpler 4 Leyer model defines specific protocols for each layer.
5 layer reference model is the combination of OSI model and TCP/IP model where w
e have below 4 layers copied from OSI reference model and above 3 layers of OSI
model are combined called Application layer .Hence in 5 layer reference model we
have Application ,Transport, Network, Datalink,Physical.
Specific Job of Each Layer :
Application Layer: Application Layer protocols specifies detail like How
data should be encoded,compressed, or encrypted, and how session should be mana
ged. Appl^ layer protocols are :HTTP,SMTP,DNS,FTP
Transport : Transport Layer Specifies which Application layer protocols
should be used to process the data on receiving compuers. Each Appl^ layer proto
cols uses specific numerical identity, called port .which is used to identify th
e protocols . HTTPS
80, SMTP-25, DNS -53, TFTP-69,FTP -21,SFTP -22
Transport Layer protocols are of 2 types UDP / TCP where UDP is best effort delive
ry service providing no delivery notification, error checking or recovery proced
ures to source computer. E.g DNS, Online Gaming, VOIP or streaming Videos . TCP
on the other hand a robust protocols proving Delivery notification ,error checki
ng ,and recovering procedures. With TCP the receiving computer tell the sending
computers when the data was received. E g.: HTTP, FTP ,SMTP are kind of TCP prot
ocols .TCP accepts data from application protocols and cuts the data into smalle
r pieces called segments .
Network Layer: It received the data segments from transport layer and ad
d a header to create Packets.Layer 3 header contains source and Destination IP a
ddress .Network Layer also identify the upper layer transport layer protocols th
at is being used .Each transport layer protocols is assigned a unique identifier
s UDP -17 and TCP- 6
Datalink Layer: Layer 2 received the packets and add its own header to e
ach packet to create Frame .This layer usually include another address call MAC
address / physical address. It also perform the data integrity check ,this check
is done by adding a checksum in the trailer at the end of the frame .finally la
yer 2 converts entire data into zeros and one ( 0 and 1) for digital communicati
Physical Layer: layer 1 converts bit into electrical signals and sends t
hem across the physical medium which can be telephone wire, fiber-optic cable ,o
r even wireless environment .Physical layer specification defines characteristic
such as voltage specification ,voltage lavel ,physical data rate , max^ transmi
ssion distance etc