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BE-CSE/IT Regulations-2008/2010 CS2302 COMPUTER NETWORKS

UNIT-I

Network architecture layers Physical links Channel Access on links Hybrid multiple access techniques Issues in the data link layer Framing Error correction and detection Link-level flow control.

PART A - TWO MARKS

1. Define line configuration and give its types. May/June 2013 It refers the way two or more communication devices attach to a link. A network consists of 2 or more computers directly connected by a physical medium. Types: i. Point to point physical links are limited to a pair of nodes. ii. Multipoint more than two nodes share a single physical link.

2. Group the OSI layers by function. May/June 2012 Seven layers of OSI model belonging to three subgroups: Physical, Data link and Network layers : network support layers; moving data from one device to another. Session, Presentation and Application layers: user support layers; allow interoperability Transport layer : ensures end-to-end reliable data transmission. 3. What are the features provided by layering?

It decomposes the problem of building a network into more manageable components. It provides more modular design. To add new service, modify the functionality at one layer.

4. Why are protocols needed? What are the two interfaces provided by it? Nov/Dec 2010 A protocol is a set of rules that govern data communication. Provides communication service used to exchange messages.

Service interface- defines operations that local objects can perform on the protocol.

Peer interface- defines form and meaning of messages exchanged between protocol peers to implement the communication service.

5. Mention the different physical media. May/June 2013 Twisted pair (the wire that phone connects to) Coaxial cable (the wire that TV connects to) Optical fiber (the medium most commonly used for high-bandwidth, long-distance links)



Space (the stuff that radio waves, microwaves and infra red beams propagate through) 6. Define topology and mention the types of topologies. Nov/Dec 2010 Topology defines the physical or logical arrangement of links in a network. Types of topology : - Mesh - Star - Tree - Bus - Ring 7. What are the two types of duplex? Full duplex-two bit streams can be simultaneously transmitted over the links at the same time, one going in each direction. Half duplex-it supports data flowing in only one direction at a time.

8. What are the issues in data link layer? Nov/Dec 2012 a) Framing b) Physical addressing c) Flow control d) Error control e) Access control.

9. Define Error Detection and Correction. Mention the types of errors. Nov/Dec 2011 Data can be corrupted during transmission. For reliable communication, errors must be detected and

corrected. Single bit error: The only one bit of a given data unit (such as byte character/data unit or packet) is changed from 1 to 0 or from 0 to 1. Burst error: 2 or more bits in the data unit have changed from 1 to 0 from 0 to 1.

10. Write short notes on error correction. Nov/Dec 2011

It is the mechanism to correct the errors and it can be handled in 2 ways.

When an error is discovered, receiver can have the sender retransmit the entire data unit. A receiver can use an error correcting coder, which automatically corrects certain errors. 11. Write short notes on VRC and LRC. Error detection - vertical redundancy check (VRC) often called a parity check. In V R C , a redundant bit called a parity bit, is appended to every data unit so that the total number of 0s in the unit (including the parity bit) becomes even. 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. 12. Write short notes on CRC checker. Nov/Dec 2010

After receiving the data appended with the CRC it does the same modulo-2 division. If the remainder is all 0s the CRC is dropped and the data accepted. Otherwise, the received stream of bits is



discarded and the data are resent. 13. Define checksum. What are the steps followed in checksum generator?

The error detection method used by the higher layer protocol is called checksum. Checksum is based on redundancy.

a) Units are divided into k sections each of n bits. b) All sections are added together using 2s

complement to get the sum. c) The sum is complemented and become the checksum. d) The checksum is sent with the data.

14. Define flow control. Mention the categories of it. Nov/Dec 2011

Flow control refers to a set of procedures used to restrict the amount of data. The sender can send data before waiting for acknowledgment.

There are 2 methods to control flow of data across communication links: a) Stop and wait- send one frame at a time. b) Sliding window- send several frames at a time.

PART B

1. Draw the OSI Network architecture and explain the functionalities of each layer in detail.

Nov/Dec 2012, Nov/Dec 2010, May/June 2013

Physical layer Data link layer



Network layer Transport layer Session layer Presentation layer Application layer

2. Draw the Internet architecture [TCP/IP architecture] and explain the functionalities of each layer in detail. May/June 2013

NET1, NET2, and so on. combination of hardware (e.g., a network adaptor) and software(e.g., a network device driver).

Ethernet or Fiber Distributed Data Interface (FDDI) protocols.

Internet Protocol (IP). Interconnection of multiple networking technologies into a single, logical

internetwork.

Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP): end-to-end protocols,

TCP - reliable byte-stream channel UDP - unreliable datagram delivery channel.

Application protocols, FTP, TFTP (Trivial File Transport Protocol), Telnet (remote login), and SMTP (Simple Mail Transfer Protocol, or electronic mail), enable interoperation of popular

applications.



3. Write about Channel Access on links. Multiple Access Techniques Frequency Division Multiple Access In frequency-division multiple access (FDMA), the available bandwidth is divided into frequency

bands. Each station is allocated a band to send its data. When any one frequency level is kept idle and another is used frequently leads to inefficiency.

Time Division Multiple Access In time-division multiple access (TDMA), stations share the bandwidth of the channel in time. Each station is allocated a time slot during which it can send data. The main problem with TDMA lies in achieving synchronization between the different stations.

Code Division Multiple Access CDMA differs from FDMA because only one channel occupies the entire bandwidth of the link. It differs from TDMA because all stations can send data at the same time without timesharing. CDMA simply means communication with different codes. CDMA is based on coding theory. Each station is assigned a code, which is a sequence of numbers

called chips. Chips will be added with the original data and it can be transmitted through same medium.



4. Write about the Issues in the data link layer. May/June 2012 Framing

To transmit frames over the node it is necessary to mention start and end of each frame. There are three techniques to solve this frame

Byte-Oriented Protocols (BISYNC, PPP, DDCMP) Bit-Oriented Protocols (HDLC)

Clock-Based Framing (SONET)

Byte Oriented protocols

View each frame as a collection of bytes (characters) rather than a collection of bits. Byte-oriented approach BISYNC (Binary Synchronous Communication) protocol and the

DDCMP (Digital Data Communication Message Protocol). Sentinel Approach

Fig: BISYNC Frame format

Point-to-Point Protocol (PPP)

Fig: PPP Frame Format Byte-Counting Approach



Fig: DDCMP frame format Bit-Oriented Protocols (HDLC)

Fig: HDLC Frame Format

Clock-Based Framing (SONET)

5. Explain about CRC. Nov/Dec 2012 Calculating a CRC, a sender and receiver have to agree on a divisor polynomial, C(x). C(x) is a polynomial of degree k. For example, suppose C(x) = x3 + x2 + 1. In this case, k = 3.



6. Explain flow control mechanisms. Nov/Dec 2012

Stop and wait. Sliding window.

Four different scenarios for the stop-and-wait algorithm. (a) The ACK is received before the timer expires; (b) the original frame is lost; (c) the ACK is lost; (d) the timeout fires too soon. Sliding Window Algorithm

First, the sender assigns a sequence number, denoted SeqNum, to each frame.

Sender maintains three variables: send window size, SWS; LAR - sequence number of the last acknowledgment received; and LFS - sequence number of the last frame sent. The sender also maintains invariant: LFS LAR SWS

Sliding window on sender



Sliding window on receiver

Receiver maintains three variables: The receive window size, RWS; LAF - sequence number of the largest

acceptable frame; and LFR - the sequence number of the last frame received.

The receiver also maintains invariant: LAF LFR RWS

UNIT-II

Medium access CSMA Ethernet Token ring FDDI - Wireless LAN Bridges and Switches.

PART A TWO MARKS

1. What is MAC? May/June 2012

MAC-Medium Access Control. Some network topologies share a common medium with multiple nodes. At any time, there may be a number of devices attempting to send and receive data using the network media. When two or more nodes are sending data at the same time, data may be unusable due to collision. There are rules that govern how these devices share the media to solve the collision problem.

2. What is CSMA/CD? Nov/Dec 2011

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) When a station has a frame to transmit: 1) Listen for Data Transmission on Cable (Carrier Sense) 2) When Medium is Quiet (no other station transmitting):

a) Transmit Frame, Listening for Collision. b) If collision is heard, stop transmitting, wait random time, and transmit again.

3. What is CSMA/CA?

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is a protocol for carrier transmission in 802.11 networks.

CSMA/CA acts to prevent collisions before they happen. In CSMA/CA, as soon as a node receives a packet that is to be sent, it checks to be sure the

channel is clear. 4. What is exponential back off?



Once an adaptor has detected a collision and stopped its transmission, it waits a certain amount of time and tries again. Each time it tries to transmit but fails, the adaptor doubles the amount of time it waits before trying again. This strategy of doubling the delay interval between each transmission attempt is a general technique known as exponential back off.

5. What is Ethernet? Nov/Dec 2012

Local area networking technology that uses CSMA/CD and has a bandwidth of 10 Mbps. Ethernet is a multiple-access network, meaning that a set of nodes send and receive frames over a shared link. Problem faced by the Ethernet is how to mediate access to a shared medium fairly and efficiently.

6. What is meant by bridge? Nov/Dec 2011

It is a collection of LANs connected by one or more bridges is usually said to form an extended LAN. In their simplest variants, bridges simply accept LAN frames on their inputs and forward them out on all other outputs.

7. Write short notes on FDDI. Nov/Dec 2010

FDDI is similar to 802.5 and IBM Token Rings but it uses optical fiber cable instead of copper cables. A FDDI network consists of a dual ringtwo independent rings that transmit data in opposite directions. The second ring is not used during normal operation but instead comes into play only if the primary ring fails.

8. What is the advantage of FDDI over a basic Token Ring? Nov/Dec 2010

Fiber distributed Data Interface. A high speed token ring networking technology designed to run over optical fiber.

FDDI is able to tolerate a single break in the cable or failure of one station due to dual ring.

Hosts are connected in a ring. A token (bit pattern) circulates around the ring. A given node must possess the token before it is allowed to transmit. 802.5 and FDDI are examples of token ring networks.

9. Differentiate fast Ethernet and gigabit Ethernet. Nov/Dec 2012

100-Mbps version called Fast Ethernet. 1000-Mbps version called Gigabit Ethernet. Both 100-Mbps and 1000-Mbps Ethernets are designed to be used in full-duplex, point-to-point configurations, which mean that they are typically used in switched networks.



10. What is the difference between switch and bridge? Nov/Dec 2012

It is used to forward the packets between shared media LANs such as Ethernet. Such switches are sometimes known by the obvious name of LAN switches.

It is a collection of LANs connected by one or more bridges is usually said to form an extended LAN. Bridges simply accept LAN frames on their inputs and forward them out on all other outputs. Pair of Ethernets is interconnected by using repeater. A node between the two Ethernets and have the node forward frames from one Ethernet to the other, this node is called bridge. 11. What is Spanning tree?

It is for the bridges to select ports over which they will forward frames. A spanning tree is a subgraph of this graph that covers (spans) all the vertices, but contains no cycles. It keeps all of the vertices of the original graph, but throws out some of the edges. BIG QUESTIONS

1. Explain CSMA/CD and CSMA/CA. May/June 2013

CSMA- resolving the media contention.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Listen for Data Transmission on Cable (Carrier Sense)

When Medium is free

a) Transmit Frame, Listening for Collision b) If collision is heard, stop transmitting, wait random time, and transmit again.

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) Nov/Dec 2012

Carrier transmission in 802.11 networks

CSMA/CD- deals with transmissions after a collision has occurred. CSMA/CA- prevent collisions before they happen. If the channel is clear, packet is sent. If the channel is not clear, node waits for a randomly chosen period of time, checks again to see if the channel is clear.

2. Explain the timers and time registers in FDDI. Nov/Dec 2011

Time registers _ Synchronous allocation(SA) _ Target token rotation time(TTRT) _ Absolute maximum time(AMT)



Timers _ Token rotation timer(TRT) _ Token holding timer(THT)

3. Explain about Ethernet. Nov/Dec 2012 Ethernet is a multiple-access network, set of nodes send and receive frames over a shared link. _ Access method : CSMA/CD _ Addressing _ Electrical specification _ Frame format

Implementation:

_ 10 base 5 : Thick Ethernet _ 10 base 2 : Thin Ethernet _ 10 base T : Twisted-pair Ethernet _ 1 base 5 : Star LAN ADVANTAGES

Easy to administer and maintain. No switches that can fail, no routing or configuration tables to be kept up-to-date. Easy to add a new host to the network. It is inexpensive: Cable is cheap, only cost is the network adaptor on each host.

End-to-end flow-control mechanism.

DRAWBACKS Too much of the networks capacity is wasted by collisions. Most Ethernets are far shorter than 2500 m.

4. Explain the frame format for token ring and token bus.

Access method: Token passing

_ Priority and reservation

_ Time limits

_ Monitor stations

5. Explain about HDLC. May/June 2013



Station types:

_ Primary station

_ Secondary station

Configurations:

_ Unbalanced configuration

_ Symmetrical configuration

_ Balanced configuration

Modes of communication:

_ Normal Response Mode(NRM)

_ Asynchronous Response Mode(ARM)

_ Asynchronous Balanced Mode(ABM)

Frames :

_ Flag field

_ Address field

_ Control field

_ Information field

_ FCS field

6. Briefly explain FDDI(Fiber Distributed Data Interface) May/June 2012

Dual ringtwo independent rings that transmit data in opposite directions. The second ring is not used during normal operation, comes into play only if the primary ring fails. single attachment stations (SAS) dual attachment stations (DAS)

Physical characteristics

At most 500 stations. Maximum distance of 2 km between any pair of stations. Network is limited to a total of 200 km of fiber, due to dual nature of the ring; the total amount of cable



connecting all stations is limited to 100 km. FDDI uses 4B/5B encoding.

UNIT-III

Circuit switching vs. packet switching / Packet switched networks IP ARP RARP DHCP ICMP Queueing discipline Routing algorithms RIP OSPF Subnetting CIDR Interdomain routing BGP Ipv6 Multicasting Congestion avoidance in network layer.

PART A TWO MARKS 1. What is circuit switching and packet switching? Nov/Dec 2010

Circuit Switching is a strategy for switching data through a network. It involves establishing a dedicated path (circuit) between the source and destination.

Packet Switching is also a strategy for switching data through a network. A packet switch is a device with several inputs and outputs leading to and from the hosts that the switch interconnects. It uses store and forward switching of discrete data units called packets.

2. What is a virtual circuit? May/June 2013

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.

3. What are data grams?

In datagram approach, each packet is treated independently from all others. It contains all of the information needed to deliver it to its destination. Packets in this technology are referred to as datagram. Datagram networks are connectionless.

4. Differentiate switched virtual circuit and Permanent virtual circuit. May/June 2011

Switched virtual circuit format is comparable conceptually to dial-up line in circuit switching. In this method, a virtual circuit is created whenever it is needed and exits only for the duration of specific exchange.

Permanent virtual circuits are comparable to leased lines in circuit switching. In this method, the same virtual circuit is provided between two uses on a continuous basis. The circuit is dedicated to the specific uses.



5. Define ICMP. Nov/Dec 2012

Internet Control Message Protocol is a collection of error messages that are sent back to the source host whenever a router or host is unable to process an IP datagram successfully.

6. Define Routing. What is distance vector routing?

The process by which nodes exchange topological information to build correct forwarding tables.

A lowest cost path algorithm used in routing. Each node advertises reachability information and associated costs to its immediate neighbors, uses the updates it receives to construct its forwarding table. RIP uses it.

7. What is link state routing? Nov/Dec 2012

A lowest cost path algorithm used in routing. Information on directly connected neighbors and current link costs are flooded to all routers; each router uses this information to build a view of the network on which to base forwarding decisions. OSPF uses it.

LSP: In link state routing, a small packet containing routing information sent by a router to all other router by a packet called link state packet.

8. Define Reliable flooding. May/June 2013

It is the process of making sure that all the nodes participating in the routing protocol get a copy of the link state information from all the other nodes.

9. Define BGP. Nov/Dec 2011

Border Gateway Protocol. An interdomain routing protocol by which autonomous systems exchange reachability information. Recent version-BGP-4.

10. Define Subnetting. Nov/Dec 2012, Nov/Dec 2011

Subnetting provides an elegantly way to reduce the total number of network numbers that are assigned. It takes a single IP network number and allocate the IP address with that network to several physical networks, which are referred as subnets.

11. Write short notes on the following Nov/Dec 2012 i. Broadcasting -send a single packet to all connected nodes. ii. Multicasting- packets are delivered to a specified subgroup of network hosts. iii. ARP-maps IP addresses and link level addresses. iv. RARP- logical address for a machine that only knows its physical address. 12. What is meant by congestion? Why the congestion occurs in network? Nov/Dec 2011



Congestion in a network occurs if user sends data into the network at a rate greater than that allowed by network resources. Congestion occurs because the switches in a network have a limited buffer size to store arrived packets.

PART B - BIG QUESTIONS

1. Explain the two approaches of packet switching techniques. May/June 2013 _ Datagram approach _ Virtual circuit approach _ Switched virtual circuit(SVC) _ Permanent virtual circuit(PVC) _ Circuit switched connection versus virtual circuit connection _ Path versus route _ Dedicated versus shared 2. Explain IPv6. May/June 2013 _ Internetwork protocol (IP) _ Addresses and routing _ Address space allocation _ Address notation _ Packet format _Auto configuration

3. Discuss DHCP in detail. Nov/Dec 2012 Dynamic Host Configuration Protocol. A protocol used by a host, as it boots, to learn various network information, such as its IP address. - relies on the existence of a DHCP server -centralized repository for host configuration information -problem faced by DHCP is server discovery -relay agent receives DHCPDISCOVER message - unicast to DHCP server and awaits the response - send back to the requesting client -DHCP relay agent receives a broadcast DHCPDISCOVER message from a host - sends a unicast DHCPDISCOVER message to the DHCP server



4. Explain distance vector routing and link state routing. May/June 2013

Distance vector routing

_ Sharing information _ Routing table _ Creating the table _ Updating the table _ Updating algorithm

Link state routing

_ Information sharing _ Packet cost _ Link state packet _ Getting information about neighbors _ Initialization _ Link state database

5. Explain RIP and OSPF in detail.

RIP- routing protocol built on the distance-vector algorithm

OSPF-used link-state routing protocols

OSPF header format OSPF link-state advertisement



6. Explain subnetting Nov/Dec 2012 _ Three levels of hierarchy _ Masking _ Masks without subnetting _ Masks with subnetting _ Finding the subnetwork address _ Boundary level masking _ Non-boundary level masking

UNIT-IV

UDP TCP Adaptive Flow Control Adaptive Retransmission - Congestion control Congestion avoidance QoS

PART A TWO MARKS 1. Write the main idea of UDP. May/June 2013

User Datagram Protocol. Transport protocol that provides a connectionless datagram service to application level processes. The basic idea is for a source process to send a message to a port and for the destination process to receive the message from a port.

2. What are the different fields in pseudo header?

Protocol number Source IP address Destination IP addresses.

3. Define TCP. May/June 2013

Transmission Control Protocol. Connection-oriented transport protocol. It guarantees reliable, byte-stream delivery service. It is a full-duplex protocol, each TCP connection supports a pair of byte streams, one flowing in each direction.

4. Define Congestion Control. Nov/Dec 2012

It involves preventing too much data from being injected into the network, thereby causing switches or links to become overloaded. Thus flow control is an end to an end issue, while congestion control is concerned with how hosts and networks interact.

5. State the two kinds of events trigger a state transition.

A segment arrives from the peer. The local application process invokes an operation on TCP.



6. What is meant by segment? What is meant by segmentation? Nov/Dec 2011

At the sending and receiving end of the transmission, TCP divides long transmissions into smaller data units and packages each into a frame called a segment.

When the size of the data unit received from the upper layer is too long for the network layer datagram or data link layer frame to handle, the transport protocol divides it into smaller usable blocks. The dividing process is called segmentation.

7. What is meant by Concatenation?

The size of the data unit belonging to single sessions are so small that several can fit together into a single datagram or frame, the transport protocol combines them into a single data unit. The combining process is called concatenation.

8. Define Gateway. Nov/Dec 2011

A device used to connect two separate networks that use different communication protocols.

9. What is meant by quality of service? What are the two categories of it? Nov/Dec 2013

The quality of service defines a set of attributes related to the performance of the connection. For each connection, the user can request a particular attribute each service class is associated with a set of attributes.

The two main categories are,

User Oriented Network Oriented

10. What is RED?

Random Early Detection in each router is programmed to monitor its own queue length and when it detects that congestion is imminent, to notify the source to adjust its congestion window.

11. What are the three events involved in the connection? May/June 2013

For security, the transport layer may create a connection between the two end ports. A connection is a single logical path between the source and destination that is associated with all packets in a message. Creating a connection involves three steps:

Connection establishment Data transfer Connection release




1. Explain the duties of transport layer. Nov/Dec 2012

End to end delivery Addressing Reliable delivery Error control Sequence control Loss control Duplication control Flow control Multiplexing

2. Explain UDP & TCP. May/June 2012

User Datagram Protocol(UDP)

Source port address Destination port address Total length Checksum

Transmission Control Protocol(TCP)

Source port address Destination port address Sequence number Acknowledgement number Header length Reserved Control Window size Check sum Urgent pointer Options and padding

3. Explain about congestion control. Nov/Dec 2012

Congestion avoidance BECN FECN Four situations Discarding

4. Explain the Congestion Avoidance techniques in detail. Nov/Dec 2013

_ Leaky bucket algorithm _ Token bucket algorithm



_ Switch controlling the output rate _ Flowchart 5. Explain how QoS is provided through Integrated Services & Differentiated Services.

May/June 2013 -To transmit audio and video over a network, provide sufficient bandwidth. -Sensitive to the timeliness of data as real-time applications. - Integrated Services, a QoS architecture developed in the IETF and often associated with RSVP (Resource Reservation Protocol). -Differentiated Services, which is undergoing standardization in the IETF at the time of writing.

UNIT-V

Email (SMTP, MIME, IMAP, POP3) HTTP DNS- SNMP Telnet FTP Security PGP - SSH

PART A TWO MARKS 1. What is the function of SMTP? Nov / Dec 2012, May / June 2013

The TCP/IP protocol supports electronic mail on the Internet is called Simple Mail Transfer (SMTP). It is a system for sending messages to other computer users based on e-mail addresses. SMTP provides mail exchange between users on the same or different computers.

2. What is the difference between a user agent (UA) and a mail transfer agent (MTA)?

Nov / Dec 2012

The UA prepares the message, creates the envelope, and puts the message in the envelope. The MTA transfers the mail across the Internet.

3. 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 transformed back to the original data.

4. Why is an application such as POP needed for electronic messaging?

Workstations interact with the SMTP host, which receives the mail on behalf of every host in the organization, to retrieve messages by using a client-server protocol such as Post Office Protocol, version 3(POP3). Although POP3 is used to download messages from the server, the SMTP client still needed on the desktop to forward messages from the workstation user to its SMTP mail server.

5. Give the format of HTTP request and response message. May / June 2013



6. What is Domain Name System? What are the

divisions of it? May / June 2013

Domain Name System can map a name to an address and conversely an address to name.

Generic domain: Define registered hosts according to their generic behavior, uses generic suffixes.

Country domain: Uses two characters to identify a country as the last suffix.

Inverse domain: Finds the domain name given the IP address.

7. How the TCP connections are needed in FTP? Nov / Dec 2010

FTP establishes two connections between the hosts. One connection is used for data transfer, the other for control information. The control connection uses very simple rules of communication. The data connection needs more complex rules due to the variety of data types transferred.

8. What are the basic components of FTP?

The client has three components: the user interface, the client control process, and the client data transfer process. The server has two components: the server control process and the server data transfer process. The control connection is made between the control processes. The data connection is made between the data transfer processes.

9. Name four factors needed for a secure network.

Privacy: The sender and the receiver expect confidentiality.

Authentication: The receiver is sure of the senders identity and that an imposter has not sent the message.

Integrity: The data must arrive at the receiver exactly as it was sent.

Non-Reputation: The receiver must able to prove that a received message came from a specific sender.



10. What is a digital signature?

Digital signature is a method to authenticate the sender of a message. It is similar to that of signing transactions documents when you do business with a bank. In network transactions, you can create an equivalent of an electronic or digital signature by the way you send data.

11. What are the advantages & disadvantages of public key encryption?

Advantages:

a) Remove the restriction of a shared secret key between two entities. Here each entity can create a pair of keys, keep the private one, and publicly distribute the other one.

b) The no. of keys needed is reduced tremendously. For one million users to communicate, only two million keys are needed.

Disadvantage:

Calculating the cipher text using the long keys takes a lot of time. So it is not recommended for large amounts of text.

12. What is SNMP? What are the requests messages support SNMP? Nov/Dec 2011

Simple Network Management Protocol. An internet protocol that allows the monitoring of hosts, networks and routers.

GET - used to retrieve a piece of state from some node. SET - used to store a new piece of state in some node.

13. Define PGP and SSH. Nov/Dec 2010

Pretty Good Privacy is used to provide security for electronic mail. It provides authentication, confidentiality, data integrity, and non repudiation. A collection of public domain software that provides privacy and authentication capabilities using RSA and that uses a mesh of trust for public key distribution.

Secure Shell is used to provide a remote login, and used to remotely execute commands and transfer files and also provide strong client/server authentication / message integrity.


1. Explain the functions of SMTP. Nov/Dec 2010

System for sending messages to other computer users based on e-mail addresses. SMTP provides mail exchange between users on the same or different computers.



User Agent Mail Transfer Agent Multipurpose Internet Mail Extensions Post Office Protocol

2. Illustrate the features of FTP and its operation. Nov/Dec 2012

Transfer a file from one system to another. TCP connections Basic model of FTP

3. Explain about HTTP. May/June 2013

HTTP transactions HTTP messages URL

4. Explain the WWW in detail. May/June 2013

Hypertext & Hypermedia Browser Architecture Categories of Web Documents HTML CGI Java

5. Explain about DNS in detail. Nov/Dec 2010 - Domain hierarchy - Name server - Name resolution 6. Explain about RSA algorithm.

Public key Encryption technique. Encryption algorithm Decryption algorithm Security in RSA

7. Explain about telnet. Nov/Dec 2012 Remote terminal protocol. It allows to interact with a remote system as if terminal is directly connected to that machine.

- working procedure - applications

cn q&a

Documents

data communication

network layers

single physical link

network support layers

physical medium

given data unit

osi layers

error detection