Review Questions

1.         What does the OSI model standardize?

The OSI model standardizes:

-          seven-layer presentation of systems interconnection in packet-switched networks;

-          functionality of each layer;

-          names of all layers.

2.         Is it possible to present another variant of OSI containing a different number of layers, e.g., five or eight?

Yes, the seven-layer decomposition is one of possible versions of such an approach. In particular, TCP/IP model appeared before the OSI model defines 4 layers.


3.         Is the protocol the software module that solves the problem of interaction between systems, or does it represent a formalized description of the interaction rules, including the sequence of message exchange and their formats?

Both statements are true.


4.         Are the terms interface and protocol synonymous?

Yes, they are.


5.         At which layer of the OSI model do application programs operate?

The OSI model describes only system functions, i.e. those that are implemented by a network operating system, system utilities or system hardware. The model doesn’t consider functions implemented by user applications/software. Therefore user applications can’t be referred to any of the OSI model layers; actually user applications work on top of the OSI layers, using their functionality. However some user applications implement functions of some layer(s) of the OSI model instead of using system tools; in this case one can say that   an application works on respective layer(s) of the OSI model.

6.         On which network elements are transport-layer protocols installed?

Usually transport-layer protocols are installed on end nodes of a network in order to provide appropriate quality of data transmission on ‘end-to-end’ basis. Transit nodes (i.e. routers) don’t have necessarily to support transport-layer protocols; however, they can support such protocols for support of auxiliary functions, for example:

-          Remote control over a transit node as in this case a transit node becomes an end node relatively to control node;

-          Intervention of a transit node into process of control of data transmission quality (i.e. to achieve congestion avoidance). For example, a router can use a transport-layer protocol to slow down a data transmission of  some end node creating congestion of a network.


7.         At which layer of the OSI model do network services operate?

At application layer.


8.         Which of the devices listed below implement the physical-layer functions of the OSI model? Which implement the data link layer?

A.     Router

B.     Switch

C.     Bridge

D.     Repeater

E.      Network adapter

The physical-layer functions of the OSI model are implemented by all kinds of network devises; the data-link layer functions are implemented by all kinds of devises but repeater.


9.         Which names are traditionally used for the protocol data unit at each layer? Fill in the table.








Data link layer






Network layer






Transport layer






Session layer






Presentation layer






Application layer







10.    Give examples of open systems.

11.    Suppose a small company, which is not widely known, offers a product that you need, characterized by parameters that exceed the parameters of similar products supplied by well-known companies. You could accept the offer after reviewing the manufacturer's documentation and ensuring that it does specify parameters that exceed the similar parameters of well-known products. Or you could accept the offer only after careful testing that confirms the technical parameters of the product under consideration are better than those of similar products available on the market. Or you could choose the product of a world-known company, since the latter is guaranteed to comply with the standards, and there is no risk of it going out of business and, consequently, no risk of experiencing problems with technical support. In which case will your action comply with the principle of open systems?

12.    Which organization has developed the Ethernet standards?

Ethernet standards were initially developed by Digital Equipment (DEC), Intel and Xerox; after a while they were accepted (slightly modified) by IEEE as a national standards; then they were accepted by ISO as international ones.


13.    Which of the administrative forces of the Internet is directly involved with standardization?

The Internet Engineering Task Force (IETF).


14.    Are the terms standard, specification, and RFC synonyms?

Although sometimes these terms can be used as synonyms generally they are none not; each term has its specific meaning. For example, specification might be standardised or non-standardised; RFC might represent standard or might be just an informational document.


15.    Which type of standards do contemporary RFCs represent (if they are standards)?

A.     Proprietary standards

B.     Governmental standards

C.     National standards

D.     International standards - Yes

16.    Which organization originated the creation and standardization of the TCP/IP stack?

US Department of Defense (DoD)


17.    Specify the main properties of the TCP/IP stack.

18.    Compare the functions of lowest layers of the TCP/IP and OSI reference models.

19.    Define transport and information services.

20.    Which protocols belong to Control Plane? Which belong to Management Plane?

21.    Is it necessary for routers to support the transport-layer protocols? – See the answer 6.


1.         Suppose that you have two computers connected to the network using Ethernet adapters. Adapter drivers installed on these computers support different interfaces to the IP network-layer protocol. Will these computers interact normally?

Yes, a difference in inter-layer interfaces of a protocol stack of computers doesn’t impede their network communications.

2.         How can you organize interaction between two computers if they use different protocols of the following layers:

·         Physical and data link?

·         Network?

·         Application?

This problem goes beyond the topics of the book; the purpose of including it into the book was to encourage creative thinking of students.

3.         Describe the steps that you will need to take if you have to check the state of the process of standardizing the MPLS technology?

Use materials on and sites.

4.         Find the area in which the IETF has concentrated its activities (for instance, by the number of workgroups).