OSI Layers

1. List the layers of the OSI model and the TCP/IP protocol suite (the Internet Model)

Following are the list of OSI model and TCP/IP model:

OSI layers

Layer 7: The application layer. …

Layer 6: The presentation layer. …

Layer 5: The session layer. …

Layer 4: The transport layer. …

Layer 3: The network layer. …

Layer 2: The data-link layer. …

Layer 1: The physical layer

TCP/IP model layers

Application layer

The transport layer

The network layer

The data-link layer

2. How do the layers of the OSI correlate to the layers of the TCP/IP protocol suite?

The TCP/IP protocol suit contains four layers including host-to-network, internet, transport, and application. In case of OSI model, host-to-network layer is merged with combination of the physical and data link layers. The internet layer is merged with network layer, and application layer is merged with session, presentation, and application layers with transport layer in TCP/IP.

3. Which layers of the TCP/IP protocol suite are the network support layers and which layers are the user support layers?

Network support layers are data link layer and network layer. User support layer is application layer.

4. What is data encapsulation (with respect to Questions 1-3)?

Data encapsulation focuses on sending data in which data can be segmented within successive layers of control for transmission across network. Data Encapsulation deals with sending and receiving of data from source. The data encapsulated with protocol information at each OSI reference layer model. Therefore, each layer communicates with it beside layer on the destination. The network device sends a message then it takes a form of data packet. This data packet is added with a header that contains some information regarding destination. Therefore, the data packet is encapsulated under this header file and send to the destination. This also helps in providing security to the data and information stored in the data packet. 

5. What are the responsibilities of the Data Link layer?

Following are the list of responsibilities of data link layer:

• logical linkcontrol
• media access control
• hardware addressing
• error detection
• handling of data

6. What is the difference between Network layer and Transport layer delivery?

The main difference is related to the delivery of packets from source to destination across multiple networks. Transport layer has been responsible for the source to destination delivery of all message.

7. If the Data link layer can detect errors between hops, why do you think we need another mechanism at the Transport layer?

TCP/IP Model Layers

Transport layer helps in becoming a bridge between applications executing in several hosts. Therefore, error detection is required in data link layer.

8. What are the responsibilities of the Network layer?

Following are list of responsibilities of network layer:

• Permitting several networks to be interconnected.
• Forwarding packets to network routers
• Error handling

9. What are the responsibilities of the Transport layer?

Following are list of responsibilities of transport layer:

• Respond to service request form session layer
• Deliver messages between hosts
• Create an end to end connection between source IP and destination IP

10. What is the difference between a port address, a logical address and a physical address?

Logical address is generated by CPU with respect to program. A physical address is an address in a network card. Computer components are addressed by port address.

11. Name some services provided by the Application layer

Following are the services provided by application layer:

• File services, such as the NFS service.
• Simple Network Management Protocol (SNMP), which enables network management.
• File transfer,
• Remote access,
• Shared database management
• Mail services.

12. What are the advantages of combining Session, Presentation and Application layers of the OSI model to a single layer in the TCP/IP protocol suite?

The OSI model consists of seven layers and TCIP/IP has been consisting of five layers. The combination of session, presentation and application layer in TCP/IP helps in reducing complexity of the layers of model. It also helps in increasing the speed of data transfer in the model. It also helps in providing a well-mannered structure to the TCP/IP model.

13. What is an advantage of a hierarchical name space over a flat name space for a system the size of the Internet?

Searching a name in hierarchical structure has been faster that searching in a linear system in case of large name space. The binary search can be used in the hierarchical name space and sequential search is used in the linear name space. Hierarchical name space are flexible and less complex as compared to the flat name space. Therefore, searching can be fast in the hierarchical name space.

14. What is the difference between a primary and a secondary DNS?

DNS refers to the Domain Name System which is the largest database in the world. It contains all registration data and domain name. There are two types of DNS server including primary and secondary DNS. A primary DNS server has been responsible in order to reading data related to domain zone. This server is also responsible for creating a communication bridge with secondary server. Therefore, when request is issued to a server, it starts travelling through primary DNS server and then allocate to secondary server.

The secondary DNS server has been responsible for the slave server that is responsible for obtaining data from server. Secondary DNS server does not obtain data form the primary DNS server.

Correlation between OSI and TCP/IP Layers

15. Why do we need POP3 or IMAP for electronic mail?

IMAP refers to Internet Message Access Protocol. POP refers to Post Office Protocol. Both of these protocols help in reading emails from local access using a third party application. POP helps in downloading emails from the server for permanent storage in local devices. However, IMAP leaves on them on the server and caches the memory in the local storage. Therefore, IMAP helps in implementing cloud computing in the email reading process.

16. What is the purpose of FTP?

File transfer protocol is used for transferring files between computers connected in a network. FTP ca be used for transferring files between an account and commuter and accessing online software module. FTP helps in providing keen approach in downloading the data and files from the server.  The access it the files and documents over the server is done with the help of file transfer protocol.  The use of the FTP ca be done to maintain access to the local server of the computer.

17. What anonymous FTP?

Anonymous File Transfer Protocol helps user to log in to FTP server using a common login procedure and get access to the file over the server. It also helps in downloading files for the FTP server.

18. How is HTTP related to WWW?

HTTP stands for Hyper Text Transfer Protocol. It is a underlying protocol that helps in defining messages in order they are formatted and transmitted over the World Wide Web. It is a file transfer protocol that helps in facilitating access to WWW.

19. What is a URL and what are its components?

URL stands for Uniform Resource Locator has been a specific type of universal resource identifier (URI). It helps in locating an existing resource from the Internet. There are four components of URL:

• Scheme
• Host
• Path
• Query string

20. What is a proxy server and how is it related to HTTP?

A proxy server can be relate with the application level gateway that helps in creating gateway between local network and large scale network including internet. It helps in providing increase in performance and security. A proxy server helps in creating a copy of responses that have been recently requested by the user. Therefore, when client has a request, cache of proxy server is required to check before request transferred to normal server.

21. What does HTML stand for and what is its function?

Network Support and User Support Layers

HTML stands for Hyper Text Markup language. HTML is used for creating webpages for displaying over web browsers.

22. What are the SNMP components?

Following are the SNMP components:

Managed devices

Agents

Network management systems

23. List the SNMP v1 and v2 message types and their function

SNMP v1 helps in providing fundamental functionalities for data polling and is relatively easy to use.

SNMP v2 helps in supporting 64-bit counters but still sends critical data as clear text, so it does not really enhance security.

24. Can two devices connected to the same Frame Relay network use the same DLCIs?

DLCIs refers to a unique interface. A switch connected to a DCLI at each virtual connection in an interface. Therefore, two several connections depending on two various interfaces might contain same DLCI.

25. Compare an SVC with a PVC

PVC” is refered to virtual circuit that is available permanently. It is a category of virtual circuit in which end points do not signal the circuit. However, “SVC” is a circuit that has been on-demand circuit maintained by user signals. “PVC” is a permanent circuit while “SVC” needs to be re-established every time when there is a need for a data transfer.

26. How is an ATM virtual connection identified?

ATM is connected by two virtual numbers including virtual path identifier (VPI) and virtual circuit identifier (VCI)

27. Why is SONET called a synchronous network?

SONET is a standard that helps in optical telecommunication transport formulated by Exchange Carriers Standards Association (ECSA). It helps in reducing the requirements of equipment’s and increase network reliability. IT also helps in synchronizing signals within digital transitions. It is a technology that helps in carrying various signals of several capacities through a synchronous channel. This can be categorized by a byte-interleaved multiplexing scheme.  IN synchronous system, SONET is able to gain average frequency of all clocks in system. Every clock need to be traced back to a highly stable reference.  A single clock is able to handle all timings of equipment and transmission across the entire network.

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