OSI vs TCP/IP Model. Which one is best?

OSI Model vs TCP/IP Model

In order to make a comparison and contrast between the two, first, we consider the layered architecture of both models.

Layer by layer comparison of the 2 is reflected in the below figure.

The OSI (Open System Interconnection) and TCP/IP (Transmission Control Protocol/Internet Protocol ) reference models have much in common. Both are supported the concept of a stack of independent protocols. Also, the functionality of the layers is roughly similar.

1.    Session Layer

The Session layer permits two parties to carry ongoing communications called a session across the network.

    ·      Not exist in TCP/IP.

    ·      Session layer features are provided by TCP protocol. (Layer 3)

2.   Presentation Layer

The Presentation Layer handles format information for networked communications.  This is often done by converting data into a generic format that could be understood by both layers.

• ·         Present in OSI Model.
• ·         Its function is provided by the application Layer in TCP/IP.

3.   Application Layer

Although the notion of an application process is common to both, their approaches to constructing application entities are different.

    •    OSI uses a horizontal approach

    •    TCP/IP uses a vertical approach in a sense

4.   Transport Layer

The main function of the transport layer is to ensure that the bits delivered to the receiver are the same as the bits transmitted by the sender; in the same order and without modification, loss, or duplication.

Transport protocols of OSI also provide facilities for ensuring the integrity of network packets and requesting retransmission should the packet become garbled when routed.

Transport protocols of OSI provide the potential for multiple application processes to access the network by using individual local addresses to determine the destination process for each data stream. TCP/IP transport layer do the following:-

•  Defines two standard transport protocols: TCP and UDP

• TCP implements a connection-oriented data-stream protocol which is more reliable.

• UDP implements connection less an unreliable data-stream.

• TCP is liable for data recovery.

• TCP and UDP introduce the concept of ports.

• Common ports and their usage:

·         FTP                       20,21  (File Transfer Protocol)       

·         telnet                    23        (communication)

·         SMTP                   25        (Simple Mail Transfer)

·         http                       80        (Hypertext transmission protocol)

·         POP3                   110     (Post office protocol)

5.   Network Layer

The network layer of OSI provides both connectionless and connection-oriented services. In the TCP/IP architecture is worried, the network interface or internet layer is exclusively connectionless.

This means OSI provides an alternative to network connections and TCP/IP as the only way in use.

6.  Network Addresses

IP Addresses

The internet address is known as the “IP address.” It consists of 32 bits binary number in case of IPV4 and a 128-bit hexadecimal number in case of IPv6 addressing. These numbers are used to represent networks and clients, which means this is a number that identified the network and particular addresses of the nodes.  This system is used in TCP/IP not in OSI conceptual model.

7.    Addressing OSI

International Organizations like ISO/IEC and CCITT jointly administer the worldwide network addressing domain. The initial hierarchical breakdown of the NSAP address is defined by (ISO/IEC 8348).

8.   Routing Tactics Difference

In both models, the routing principle is probably the same but the details are different.

• OSI

·      Computer or devices on networks and intermediate systems like routers use routing protocols to distribute some or all of the knowledge stored in their locally maintained routing information store.

• TCP/IP

·     The TCP/IP routing architecture looks considerably like the OSI routing architecture. Hosts use a discovery protocol to get the identification of gateways and other hosts attached to the same network (subnet).

9.   Link / Physical vs. Subnet

These 2 layers of the OSI correspond on to the subnet layer of the TCP/IP model. The majority of the time, the lower layers below the Interface or Network layer of the TCP/IP model are seldom or rarely discussed.  The TCP/IP model does nothing but highlight the very fact that the host has to connect to the network using some protocol so it can send packets over it.  Because the protocol used isn’t defined, it will vary from host to host and network to network.

10. Grouped Layers

Since these two layers are tailored to functions that are fundamentally specific to each individual networking type, the layering principle of grouping them seems to be irrelevant.

11. Emphasis on Reliability Control

Implementation of the OSI model places emphasis on providing a reliable data transfer service, while the TCP/IP model treats reliability as an end-to-end problem.

·  Each layer of the OSI model detects and handles errors, all data transmitted includes checksums. The transport layer of the OSI model checks source-to-destination reliability.

·         In the TCP/IP model, reliability control is concerted at the transport layer. The transport layer handles all error detection and recovery. The TCP/IP transport layer uses checksums, acknowledgments, and timeouts to normalize transmissions and provides end-to-end verification.

12.       Hosts following the OSI model do not handle network operations but TCP/IP hosts participate in most network operations. These functions include end-to-end verification, routing, and network control. The TCP/IP internet is often regarded as a data stream sending system involving sharp hosts.

13. Legislative and Governing Bodies 

• ·             OSI Reference Model

· The OSI reference model was devised before the protocols were invented. This ordering means the model was not biased toward one particular set of protocols, which made it quite generic. The downside of this ordering is that the designers didn’t have much experience with the subject and did not have a good idea of which functionality to put in which layer.

·   Being general, the protocols within the OSI model are better hidden than in the TCP/IP model and can be replaced relatively easily as the technology changes.

·    More commonly used as a teaching Model for concept building.

• ·                    TCP/IP

·   Standards adopted and are being used today.

·    The protocols came first, and therefore the model was really just a description of the existing protocols. There was no problem with the protocols fitting the model, but it’s hardly possible to be used to describe other models.

·   More popular standard for internetworking for several reasons :

·   Relatively simple and robust compared to alternatives like the OSI model.

·   Available on virtually every hardware and Operating System.

·   Now it is the protocol on which the entire web and networks depend.

14. Conclusion

In OSI a layer's interface tells the processes above it the way to access it. It also specifies what the constraints are and what results to expect. It says nothing about how the layer works inside.  This concept makes each layer a more self-governing object. The OSI reference model was formulated before the protocols were devised. This means the model was not initially biased and favors any individual protocol, which made it quite generic and adaptable.

The downside of this ordering is that the developers and engineers didn’t have much practical knowledge of OSI Model implementation details.

15.  My Opinion

Nothing is ideal in this world every system must be flexible enough to incorporate new concepts and advancements. OSI model is only a reference model which is not practically implemented. Despite its problems, the OSI model (less session and presentation layers) has proven to be exceptionally useful for computer networks. The OSI model is practically not implemented or adapted by any organization, but the protocols are widely used.