Department of Information Technology. CS6551 Computer Networks. Anna University - Two Mark Questions

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Department of Information Technology CS6551 Computer Networks Anna University - Two Mark Questions 1. What are the functions of application layer?

1 Department of Information Technology CS6551 Computer Networks Anna University - Two Mark Questions 1. What are the functions of application layer? The application layer is the top-most layer of OSI model. It provides services directly to user applications. It enables the user to access the network. It provides user interfaces and support for services such as , remote file access and transfer, shared database management and other types of distributed information services. 1 File Transfer: It allows a user to access, retrieve and manage files in a remote computer. 2 Mail services: It provides the basis for forwarding and storage facilities. 3 Directory services: It provides distributes database sources and access for global information about various objects and services. 2. Define Bit Stuffing. Bit stuffing is the process of inserting non information bits into data to break up bit patterns to affect the synchronous transmission of information. It is widely used in network and communication protocols, in which bit stuffing is a required part of the transmission process. Bit stuffing is commonly used to bring bit streams up to a common transmission rate or to fill frames. Bit stuffing is also used for run-length limited coding. 3. Mention some of the physical properties of Ethernet. Repeater: Amplifies and forwards electric signals. No more than 4 between any two hosts determines a maximum reach of 2500m. Terminators: Placed at the end of a segment to avoid signals from bouncing back. Medium: Broadcast. Maximum number of hosts: What are all the different kinds of multicast routing? In multicast routing, the router may forward the received packet through several of its interfaces. Every group member should receive only one copy of the m/c packet Nonmembers must not receive a copy A packet must not visit router more than once (no loops). Paths from the source to each destination must be optimal (shortest path).

5. List out the difference between circuit switching and packet switching. 6. What is the difference between Congestion control and Flow control?

2 5. List out the difference between circuit switching and packet switching. 6. What is the difference between Congestion control and Flow control? Flow control and congestion control are two network traffic control mechanisms used in computer networks, they have their key differences. Flow control is an end to end mechanism that controls the traffic between a sender and a receiver, when a fast sender is transmitting data to a slow receiver. On the other hand, congestion control is a mechanism that is used by a network to control congestion in the network. Congestion control prevents loss of packets and delay caused due to congestion in the network. Congestion control can be seen as a mechanism that makes sure that an entire network can handle the traffic that is coming to the network. But, flow control refers to mechanisms used to handle the transmission between a particular sender and a receiver. 7. Give the approaches to improve QOS? Scheduling FIFO Queuing Priority Queuing Weighted Fair Queuing Traffic Shaping Leaky Bucket 8. List out the function of POP3. POP3 is an Internet based standard used for retrieving by a user from an e- mail server. POP is an acronym for Post Office Protocol. POP3 allows mail clients to connect and download their messages; these messages are generally removed from the server and stored on the clients local machine. One of the most important features of POP3 is its ability to check the size of the mailbox and the message count.

3 9. What is the difference between port address, logical address and physical address? Logical Address: An IP address of the system is called logical address. This address is the combnation of Net ID and Host ID. This address is used by network layer to identify a particular network (source to destination) among the networks. This address can be changed by changing the host position on the network. So it is called logical address. Physical address: Each system having a NIC(Network Interface Card) through which two systems physically connected with each other with cables. The address of the NIC is called Physical address or mac address. This is specified by the manficture company of the card. This address is used by data link layer. Port Address: There are many application running on the computer. Each application run with a port no.(logically) on the computer. This port no. for application is decided by the Karnal of the OS. This port no. is called port address. 10. What is the average size of an Ethernet frame? The minimum length of an Ethernet frame is 64 bytes. Therefore the minimum length of data from the upper layer is (64 bytes 18 bytes) 46 bytes. You must add (46 bytes 42 bytes) 4 bytes of padding to the data. 11. What is the access method used by Wireless LAN? Stations on wireless LANs normally use CSMA/CA. 12. Define Slow Start. Slow-start is part of the congestion control strategy used by TCP, the data transmission protocol used by many Internet applications. Slow-start is used in conjunction with other algorithms to avoid sending more data than the network is capable of transmitting, that is, to avoid causing network congestion.

13. When can an application make use of UDP? Applications such as: DNS, DHCP, TFTP, SNMP, RIP, VOIP uses UDP. UDP has no inherent order as all packets are independent of each other.

There is no guarantee that the messages or packets sent would reach at all. No Acknowledgment No handshake (connectionless protocol) 14. Give the purpose of layering?

4 13. When can an application make use of UDP? Applications such as: DNS, DHCP, TFTP, SNMP, RIP, VOIP uses UDP. UDP has no inherent order as all packets are independent of each other. If ordering is required, it has to be managed by the application layer. UDP is faster because there is no errorchecking for packets. There is no guarantee that the messages or packets sent would reach at all. No Acknowledgment No handshake (connectionless protocol) 14. Give the purpose of layering? The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create willinteroperate, and to facilitate clear comparisons among communications tools. Change Design Learning Troubleshooting Standards 15. Mention the advantage and disadvantage of error correction by receiver, as compared to error detection. Send additional information so incorrect data can be corrected and accepted. Error correction is the additional ability to reconstruct the original, error-free data. 16. Differentiate between Connection oriented operation and Connectionless operations.

5 17. What are the major duties of Network Layer? Connection model: connectionless communication Host addressing Message forwarding 18. What are the two different types of errors occurred during the data transmission? Insertion Deletion Duplication Distortion Reordering 19. List out any four IEEE 802 standards with its name. IEEE Bridging (networking) and Network Management IEEE LLC IEEE Ethernet IEEE Token bus IEEE Wireless LAN (WLAN) & Mesh (Wi-Fi certification) IEEE Wireless PAN IEEE Bluetooth certification 20. Define Bridge and Switch. Bridges: A bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet ortoken ring)..in bridging networks, computer or node addresses have no specific relationship to location. Switches: A switch is a network device that selects a path or circuit for sending a unit of data to its next destination. A switch may also include the function of the

6 router, a device or program that can determine the route and specifically what adjacent network point the data should be sent to. 21. Draw TCP Header Format. 22. What do you meant by QOS? Quality of Service (QoS) refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and networks, SONET, and IProuted networks that may use any or all of these underlying technologies. The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. 23. What is PGP? Pretty Good Privacy or PGP is a popular program used to encrypt and decrypt over the Internet, as well as authenticate messages with digital signatures and encrypted stored files. 24. What is Flow Control? In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. Too much data arriving before a device can handle it causes data overflow, meaning the data is either lost or must be retransmitted. 25. What is meant by CSMA/CD? Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier transmission access in Ethernet networks. On Ethernet, any device can try to send a frame at any time. Each device senses whether the line is idle and therefore available to

7 be used. If it is, the device begins to transmit its first frame. If another device has tried to send at the same time, a collision is said to occur and the frames are discarded. Each device then waits a random amount of time and retries until successful in getting its transmission sent. 26. Define Subnetting. A subnetwork, or subnet, is a logical, visible subdivision of an IPnetwork. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. 27. What is TCP? TCP (Transmission Control Protocol) is a standard that defines how to establish and maintain a network conversation via which application programs can exchange data. TCP works with the Internet Protocol (IP), which defines how computers send packets of data to each other. 28. What is Telnet? Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user canaccess someone else's computer remotely. 29. What is the use of two dimensional parity in error detection? Detects up to 3-bit errors Good for burst errors 30. What are the issues in data link layer? Network layer services Framing Error control Flow control Reliable Delivery Best Effort Acknowledged Delivery

8 31. Differentiate fast Ethernet and gigabit Ethernet. Speed of the Fast Ethernet is 100Mbps, whereas it is 1000Mbps in Gigabit Ethernet. Better performance and reduced bottlenecks are expected due to higher bandwidth in Gigabit Ethernet than Fast Ethernet. Upgrade from Ethernet to Fast Ethernet is easy and cheaper than upgrading Fast Ethernet to Gigabit Ethernet. Needs specific network devices, which can support 1000Mbps data rate, in Gigabit Ethernet. Devices connected to Gigabit Ethernet needs manual configuration up to some extent, whereas most of the devices connected to Fast Ethernet configure automatically themselves negotiate the optimum speed and duplexity. 32. What are the silent features of IPv6? Larger Address Space Simplified Header End-to-end Connectivity Auto-configuration Faster Forwarding/Routing IPSec - Built-in security No Broadcast Anycast Support 33. List out the various features of Sliding window protocol. The key feature of the sliding-window protocol is that it permits pipelined communication to better utilize the channel capacity. The sender can send a maximum N frames without acknowledgement. N is called the window size of the sliding window. The sliding window maps to the frames in sender s buffer that are to be sent, or have been sent and now are just waiting for acknowledgement. 34. What is SMTP? Most systems that send mail over the Internet use SMTP to send messages from one server to another; In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your application.

9 35. Define DNS? The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites. DNS implements a distributed database to store this name and address information for all public hosts on the Internet. 36. What is the function of router? Router has generally three main functions. Packet Forwarding Packet switching and Packet filtering 37. What is meant by Framing? Break stream of bits up into discrete chunks Break down a stream of bits into smaller, digestible chunks called frames 38. Differentiate persistent and non-persistent CSMA. The main difference between persistent and non-persistent carrier sense protocol is that in non-persistent if a station finds the channel busy, it waits random amount of time and start retransmission again. 39. How performance is improved in CSMA/CD protocol compared to CSMA protocol? In CSMA scheme, a station monitors the channel before sending a packet. Whenever a collision is detected, it does not stop transmission leading to some wastage of time. On the other hand, in CSMA/CD scheme, whenever a station detects a collision, it sends a jamming signal by which other station comes to know that a collision occurs. As a result, wastage of time is reduced leading to improvement in performance. 40. Define BGP. Border Gateway Protocol (BGP) is a routing protocol used to transfer data and information between different host gateways, the Internet or autonomous systems. BGP is a Path Vector Protocol (PVP), which maintains paths to different hosts, networks and gateway routers and determines the routing decision based on that.

10 41. Define a Layer. The layers are stacked this way: Application Presentation Session Transport Network Data Link Physical 42. List the main two limitations of Bridges. Reduces the traffic on other network segments, since it does not send all packets. Bridging occurs at the data link layer of the OSI model, which means bridging cannot read IP addresses, but only the outermost hardware address of the packet. 43. Define Source Routing. Source Routing is a technique whereby the sender of a packet can specify the route that a packet should take through the network. Remember that as a packet travels through the network, each router will examine the "destination IP address" and choose the next hop to forward the packet to. 44. What is the need for ARP? Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address that is recognized in the local network. Suppose a station A wants to send to Station B. Station A knows Station B's IP address. But Station A would still send out an ARP to request for B's MAC address before sending. And then after having B's MAC address, A would then send the data with B's MAC address as destination address. 45. Differentiate between delay and jitter. Delay: Is the amount of time data(signal) takes to reach the destination. Now a higher delay generally means congestion of some sort of breaking of the communication link.

11 Jitter: Is the variation of delay time. This happens when a system is not in deterministic state eg. Video Streaming suffers from jitter a lot because the size of data transferred is quite large and hence no way of saying how long it might take to transfer. 46. What are the components of a Network? Sender Receiver Medium Message Protocols 47. What is meant by Sockets? Sockets is a method for communication between a client program and a server program in a network. A socket is defined as "the endpoint in a connection." Sockets are created and used with a set of programming requests or "function calls" sometimes called the sockets application programming interface (API). 48. Define TTL. Socket = IP address + Port Number Time-to-live (TTL) is a value in an Internet Protocol (IP) packet that tells a network router whether or not the packet has been in the network too long and should be discarded. 49. Define Hop count. The number of point-to-point links in a transmission path. Since each link is terminated at a network device such as a router or gateway, the processing performed within the device to determine how to forward the packet adds overhead to the transmission. 50. Compare Piconet and Scatternet. Scatternets can be formed when a member of one piconet (either the master or one of the slaves) elects to participate as a slave in a second, separate piconet. The devices participating in both piconet scan relay data between members of both ad hoc networks. 51. What is mean by data communication? Data communication is the exchange of data (in the form of 1s and 0s) between two devices via some form of transmission medium (such as a wire cable).

12 52. What are the three fundamental characteristics determine the effectiveness of the data communication system? The effectiveness of the data communication system depends on three fundamental characteristics: Delivery: The system must deliver data to the correct destination. Accuracy: The system must deliver data accurately. Timeliness: The system must deliver data in a timely manner. 53. Why are protocols needed? In networks, communication occurs between the entities in different systems. Two entities cannot just send bit streams to each other and expect to be understood. For communication, the entities must agree on a protocol. A protocol is a set of rules that govern data communication. 54. What is redundancy? It is the error detecting mechanism, which means a shorter group of bits or extra bits may be appended at the destination of each unit. 55. Define checksum. The error detection method used by the higher layer protocol is called checksum. Checksum is based on the concept of redundancy. 56. What are the network support layers and the user support layers? Network support layers: The network support layers are Physical layer, Data link layer and Network layer.these deals with electrical specifications, physical connection, transport timing and reliability. User support layers: The user support layers are: Session layer, Presentation layer, Application layer.these allow interoperability among unrelated software system. 57. What are the functions of MAC? MAC sub layer resolves the contention for the shared media. It contains synchronization, flag, flow and error control specifications necessary to move information from one place to another, as well as the physical address of the next station to receive and route a packet. 58. What is a virtual circuit? A logical circuit made between the sending and receiving computers. The connection is made after both computers do handshaking. After the connection, all packets follow the same route and arrive in sequence. 59. What are the duties of the transport layer? The services provided by the transport layer End-to- end delivery Addressing Reliable delivery Flow control Multiplexing

13 60. What are the four aspects related to the reliable delivery of data? The four aspects are, Error control, Sequence control, Loss control, Duplication control. 61. Define Gateway. A device used to connect two separate networks that use different communication protocols. 62. How does MIME enhance SMTP? MIME is a supplementary protocol that allows non-ascii data to be sent through SMTP. MIME transforms non-ascii data at the sender site to NVT ASCII data and deliverers it to the client SMTP to be sent through the Internet. The server SMTP at the receiving side receives the NVT ASCII data and delivers it to MIME to be transform feed back to the original data. 63. Define CGI. CGI is a standard for communication between HTTP servers and executable programs. It is used in crating dynamic documents. 64. List out the available detection methods. There are 4 types of redundancy checks are used in data communication. a) Vertical redundancy checks (VRC). b) Longitudinal redundancy checks (LRC). c) Cyclic redundancy checks (CRC). d) Checksum. 65. Write short notes on VRC. The most common and least expensive mechanism for error detection is the vertical redundancy check (VRC) often called a parity check. In this technique a redundant bit4called a parity bit, is appended to every data unit so, that the total number of 0 s in the unit(including the parity bit) becomes even. 66. Write short notes on LRC. In longitudinal redundancy check (LRC), a block of bits is divided into rows and a redundant row of bits is added to the whole block. 67. Write short notes on CRC. The third and most powerful of the redundancy checking techniques is the cyclic redundancy checks (CRC) CRC is based on binary division. Here a sequence of redundant bits, called the CRC remainder is appended to the end of data unit. 68. Write short notes on CRC checker. A CRC checker functions exactly like a generator. After receiving the data appended with the CRC it does the same modulo-2 division. If the remainder is all 0 s the CRC isdropped and the data accepted. Otherwise, the received stream of bits is discarded and the dates are resent.

14 69. What are the steps followed in checksum generator? The sender follows these steps a) The units are divided into k sections each of n bits. b) All sections are added together using 2 s complement to get the sum. c) The sum is complemented and become the checksum. d) The checksum is sent with the data. 70. List out the steps followed is checksum checker side. The receiver must follow these steps a) The unit is divided into k section each of n bits. b) All sections are added together using 1 s complement to get the sum. c) The sum is complemented. d) If the result is zero. Anna University Big Questions 1. Layering Protocols and Internet Architecture (OSI & TCP/IP Model) * 2. Error Detection and Error Correction Mechanism 3. Flow Control Mechanism (ARQ Mechanism)* 4. Media Access Control ( CSMA/CD, CSMA/CA)* 5. Ethernet and Bluetooth* 6. Dynamic Host Configuration Protocol (DHCP) 7. Subnetting 8. ARP and RARP 9. Intra domain Routing (RIP) and Inter domain Routing (OSPF)* 10. IPv4 and IPv6* 11. TCP and UDP * 12. TCP Congestion Control Mechanism 13. QOS 14. SMTP and POP3* 15. DNS* Note: * very important questions. We should expect 90% of the above questions in your University question.

5105: BHARATHIDASAN ENGINEERING COLLEGE NATTARMPALLI UNIT I FUNDAMENTALS AND LINK LAYER PART A

5105: BHARATHIDASAN ENGINEERING COLLEGE NATTARMPALLI 635 854. NAME OF THE STAFF : R.ANBARASAN DESIGNATION & DEPARTMENT : AP/CSE SUBJECT CODE : CS 6551 SUBJECT NAME : COMPUTER NETWORKS UNIT I FUNDAMENTALS