Difference Between OSI and TCP/IP Reference Models

Parameter	OSI Reference Model	TCP/IP Model
Clarification between Services, Interfaces and Protocols	OSI Model clearly distinguishes between Services, Interfaces and Protocols. Each layer performs some services to upper layers, layer interfaces tells the processes above it how to access it, and different protocols are used by different layers as per their needs until a job is not finished.	TCP/IP model does not clearly distinguish between Services, Interfaces and Protocols.
Protocol Biasing	This model is not biased for a particular set of protocols and was developed before corresponding protocols invention.	This Model was developed after inventing corresponding protocols and just was description of existing protocols.
Layers	It is a Seven Layered Model. Which are as follows : a)      Physical Layer b)      Data Link Layer c)       Network Layer d)      Transport Layer e)      Session Layer f)       Presentation Layer g)      Application Layer	It is a 4 Layered Model. Which are as follows: a)      Subnet Layer b)      Internet Layer c)       Transport layer d)      Application Layer
Entity Approaches	OSI uses Horizontal approach in creating application entities. I.e. Strict hierarchy of layers is followed by distributed applications which are constructed from common toolbox of Application Service Elements (ASEs).	TCP/IP uses vertical approach in creating application entities. i.e.  In TCP/IP each application entity contains all the functions that it needs to support a distributed communication system.
Sessions	In OSI Model session Layer handles message exchange, data exchange and start and stop of the session. This also monitors session identification.	This Layer is not present in TCP/IP model and ‘Sockets’ and ‘ports’ are used for describing path over which co-operative application operates.
Connections	In OSI network layer supports both connectionless and connection oriented communication, but transport layer supports only connection oriented communication.	In TCP/IP network layer supports only connectionless communication whereas transport layer supports both connectionless and connection oriented communication.
Data Conversion	In OSI Model Presentation Layer converts the data in generic form that can be understood by both the sides.	Presentation layer is not present in TCP/IP Model and data conversion function is performed by application Layer.
Data Reliability	OSI Provides reliable data transfer. Each layer of OSI detects & handles errors, Every Transmitted data contains checksum and Transport Layer checks source to destination reliability.	In TCP/IP data reliability is determined only at Transport layer. This layer uses acknowledgement, checksums and timeout signals to control transmission. Only This layer is responsible for detecting, handling, and recovering all errors.
Role of Hosts	In OSI network operations are not handled by hosts.	In TCP/IP hosts participates in many network operations and handles many operations. I.e. Routing, end-to-end verification, network control.
Addressing	Two types of hierarchical addresses are used in OSI Network Layer Addressing: 1)      Network Service Access Point address (NSAP): It is the location at which network layer provides services to transport layer. Single NSAP is assigned to each transport layer entity. 2)      Network Entity Titles (NET): It is used for addressing intermediate systems (ISs).i.e. Routers, which do not interact with transport layer. If an IS participates in multiple domains or areas, it can have one NET or more than one NETs.	32 bit address known as “IP address” is used for addressing. High- order bits denote network address while lower-order bits denote host address. Any of the three classes of IP can be used to do so.
Layer Merging	OSI model contains both Physical and data link layers separately.	In TCP/IP Model Physical and data link layers are combined to get Subnet Layer which does not distinguish between these two layers. These two layers are totally different from one another. Physical Layer deals with transmission characteristics of Transmission medium i.e. fiber optics, Twisted pair or wireless communication. Data link layer delimits the start and end of frames and transmits them from one side to other with desired reliability.
Price/Popularity	Expensive/Less Popular	Comes free with most of OS which resulted in its wide popularity.

Network Layer Addressing Explanation:

 

Field Name	Description
Authority Format Identifier(AFI)	Provides information Regarding Structure and content of IDI and DSP Fields. e.g.  Length of IDI, Information about Decimal or Binary Notations of DSP.
Initial Domain Identifier(IDI)	It specifies the entity that can assign values t o DSP portion of NSAP Address.
Address Administration	It is used for further administration of addressing by adding a second authority identifier and by delegating address administration to sub authorities.
Area	The Area field is used to identify the specific area within a domain.
Station	The Station field is used to identify a specific station within an area.
Selector	This provides the specific n-selector within a station. The reserved n-selector 00 identifies the address as a network entity title (NET)