The OSI is reference/conceptual model and accordingly multiple practical models (such as TCP/IP, AppleTALK, etc) exits. Which fundamental functionalities necessarily needs to considered while implementing any network model?

The fundamental functionalities necessarily needs to considered while implementing any network model are (1) Scalability, (2)The quality of service (3) Fault tolerance (4) Security.

Explanation:

Solution:

Network must help a wide area of applications and administrations, just just as work over various sorts of links and devices that make up the physical infrastructure. The term network refers to the innovations that help the infrastructure and the customized administrations and rules, or protocols, that move messages over the network.

The following are some  fundamental functionalities necessarily needs to considered while implementing any network model which is stated below:

(1) Scalability :

A huge number of users and service providers connect with the Internet every week. All together for the Internet to help this fast measure of development, it must be scalable.

A scalable network can extend rapidly to help new clients and applications without influencing the performance of the administration being conveyed to existing clients.  

(2)Quality of Service :

Networks must provide predictable, quantifiable, and, now and again, ensured administrations.  

Networks also need mechanisms to carry on congested network traffic. Network bandwidth is the estimate of the data-transfer size of the network. As such, what amount of data can be transmitted inside a particular measure of time? Network data transfer capacity is estimated in the quantity of bits that can be transmitted in a solitary second, or bits every second (bps).  

(3) Fault Tolerance :

The Internet is consistently accessible to the a huge number of users who depend on it. This requires a network design that is worked to be fault tolerant.

A fault-tolerant network is one that constrains the impact of a failure, with the goal that the least number of devices are influenced by it. It is likewise worked in a manner that empowers fast recuperation when such a failure happens.

Faults-tolerant networks rely upon various ways between the source and destination of a message. On the off chance that one way comes up short, the messages can be immediately sent over an alternate connection.

(4) Security:  

The Internet has advanced from a firmly controlled inter network of instructive and government associations to a generally open methods for transmission of business and individual interchanges.

Subsequently, the security necessities of the network have changed. The network infrastructure, the system administrations, and the information contained on arrange appended gadgets are vital individual and business resources. Bargaining the respectability of these benefits could have genuine outcomes.