EMC Corporation Technical Questions and Answers


Posted on :10-02-2016
EMC Corporation Technical Questions:-

Q1. What is Protocol Data Unit?

ANS: The data unit in the LLC level is called the Protocol Data Unit (PDU). The PDU contains of four fields a Destination Service Access Point (DSAP), a Source Service Access Point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is an information frame (I - frame) or a supervisory frame (S -frame) or a unnumbered frame (U - frame).


Q2. What are the data units at different layers of the TCP / IP protocol suite?

ANS: The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.


Q3. What is a router? 

ANS: Routers are machines that direct a packet through the maze of networks that stand between its source and destination. Normally a router is used for internal networks.


Q4. What is difference between base band and broad band transmission?

ANS: In a base band transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.


Q5. What MAU?

ANS: In token Ring, hub is called Multistation Access Unit (MAU)


Q6. Why should you care about the OSI Reference Model?

ANS: It provides a framework for discussing network operations and design.


Q7. What is attenuation?

ANS: The degeneration of a signal over distance on a network cable is called attenuation.


Q8. List out few of the applications that make use of Multilinked Structures?

ANS: Sparse matrix, Index generation.


Q9. What is IP?

ANS: IP is Internet Protocol. It is the network protocol which is used to send information from one computer to another over the network over the internet in the form of packets.


Q10. What is the difference between routable and non- routable protocols?

ANS: Routable protocols can work with a router and can be used to build large networks. Non- Routable protocols are designed to work on small, local networks and cannot be used with a router.


Q11. What is mesh network?

ANS: A network in which there is a multiple network links between computers to provide multiple paths for data to travel.


Q12. What is MAC address?

ANS: The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.


Q13. What is bit rate? 

ANS: Bit rate is the number of bits transmitted during one second.


Q14. What is subnet?

ANS: A generic term for section of a large networks usually separated by a bridge or router.


Q15. Explain 5-4-3 rule?

ANS: In an Ethernet network, between any two points on the network, there can be no more than five network segments or four repeaters and of those five segments only three of segments can be populated.


Q16. How Gateway is different from Routers?

ANS: A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats.


Q17. What is a gateway?

ANS: A gateway acts a door for the packet to reach the outside of the internal network.


Q18. What is baud rate?

ANS: Baud rate refers to the number of signal units per second that are required to represent those bits. Baud rate = bit rate / N, Where N is no-of-bits represented by each signal shift.


Q19. What is cladding?

ANS: A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.


Q20. What is SAP?

ANS: Series of interface points that allow other computers to communicate with the other layers of network protocol stack.


Q21. What is a Multi-homed Host?

ANS: It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.


Q22. How do cryptography-based keys ensure the validity of data transferred across the network?

ANS: Each IP packet is assigned a check sum, so if the check sums do not match on both receiving and transmitting ends, the data was modified or corrupted.


Q23. What is data link layer in the OSI reference model responsible for?

ANS: Data link layer is located above the physical layer, but below the network layer. Taking raw data bits and packaging them into frames. The network layer will be responsible for addressing the frames, while the physical layer is responsible for retrieving and sending raw data bits.


Q24. What is difference between ARP and RARP?

ANS: The Address Resolution Protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. The Reverse Address Resolution Protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.


Q25. What are the types of Transmission media?

ANS: Signals are usually transmitted over some transmission media that are broadly classified in to two categories.

a) Guided Media: These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. 

b) Unguided Media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.


Q26. What are the different types of networking / internetworking devices?

ANS: Repeater: Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link. 

Bridges: These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipient and control congestion. 

Routers: They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enables them to determine which of the several possible paths the best for a particular transmission.
Gateways: They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.


Q27. What is Semaphore? 

ANS: Semaphore is synchronization tool to solve critical-section problem, can be used to control access to the critical section for a process or thread. The main disadvantage (same of mutual-exclusion) is requiring busy waiting. It will create problems in a multi programming system, where a single CPU is shared among many processes. Busy waiting wastes CPU cycles.


Q28. What is deadlock?

ANS: Deadlock is a situation when two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting Processes.


Q29. What are major types of networks and explain?

ANS: Server-based network, Peer-to-peer network.

Peer-to-peer network: Computers can act as both servers sharing resources and as clients using the resources.

Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration.


Q30. What is the range of addresses in the classes of internet addresses?

ANS: Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255




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