Open Systems Interconnection (OSI) Reference Model is an architectural model commonly used to illustrate the function and structure of communication protocols of data. International Organization for Standardization (ISO) originally developed OSI in 1978 but today it manages it (OSI) jointly with International Telecommunication Union-Telecommunication Standardization Sector (ITU-T).  The model is made up of seven layers that identify the functions of communication protocols of data. Every layer is a representation of a role played when there is a transfer of data between collaborating applications across an interceding data. "The layers are: Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data-link layer, Physical layer. "(Peeters, 2010).This paper will however focus on Network and Transport layers.

Peeters (2010) asserts that this is layer 3 of the model and its responsibility is to address messages and interpret valid addresses names and addresses into physical addresses. The layer is also establishes the route to the target computer, from the source. This is done by the layer determining the path the data should take depending on among other factors, conditions of network and service's priority. Additionally, the layer controls the network's traffic problems, for instance managing data congestion and routing and switching of packets.

The network layer situated on the router is also important in model due to its function of compensating the failure of the router's network adapter to transmit a huge chunk of data originating from the source through breaking it (data) into manageable units. This layer is similar to the data at the destination end.  Examples of protocols of network-layer are Packet Exchange (IPX) and Internet Protocol (IP).

This is layer 4 of the model and gives an additional connection level underneath the session layer.  This layer makes sure that all the delivered packets are free of errors, devoid of duplication or losses and in sequence. The layer also repackages messages at the source computer, sorting long messages into a number of packets and gathering small packets into one package. Consequently, the layer discloses the packets, is similar to the original messages, and, normally, sends a feedback that the message was conventional, at the receiving computer (Peeters, 2010).

The transport layer offers flow control and handles errors other that taking part in solving of problems involving reception and transmission of packets. Examples of transport-layer protocols are Sequenced Packet Exchange (SPX) and Transmission Control Protocol (TCP).

Comparison of TCP/IP model to the OSI model

There are many similarities that can be drawn between TCP/IP and OSI models. First of all, there architecture is similar, a fact that can be witnessed through both of them being made up of layers. Secondly, both TCP/IP and OSI have a common application layer even though in practice, the layer is made up of different services in reference to each model. Additionally the two models have similar network and transport layers. This is witnessed in the similar functions played by OSI model's presentation and network layers and those ones played by TCP/IP model's transport layers. Another similarity in both models is that their knowledge is a prerequisite to being a networking professional. Lastly both models have an assumption that their packets are usually switched. This means that specific packets may use dissimilar paths in order to get to the same target/destination (Mann, 2001).

Mann (2001) observes that the first difference exhibited by TCP/IP and OSI is that the latter is viewed as the standards upon which the internet has developed. On the other hand, the former is considered as ""generic, protocol-independent standard...." Secondly, as opposed to OSI, TCP/IP model's application layer is made up of   the session and presentation layer issues. Additionally, its network access layer is combination of physical and OSI data link layers. Another difference comes in line with simplicity where TCP/IP model seems to be more because it has fewer layers (4) as opposed to seven in OSI model. Lastly TCP/IP model is regarded as more reliable because its protocols are the standards that determined the development of internet; contrastingly, the OSI model is only made use of as a guiding tool.