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NOORUL ISLAM COLLEGE OF ENGINEERING, KUMARACOIL DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING TWO MARKS AND SIXTEEN MARKS QUESTIONS & ANSWERS SEMESTER VI CS 65-COMPUTER NETWORKS B.E ELECTRICAL AND ELECTRONICS ENGG PREPARED BY Mr.GIRIDAS.K.L. Research Scholar Dept of CSE. TWO MARKS UNIT-1 1. Define network architecture. A network architecture guide the design and implementation of networks. It is used to help deal with this complexity; network designers have developed general blueprints. 2. Draw an example of layered network system. 3. List the layers of OSI architecture. The layers of OSI architecture are, Physical layer, Data link layer, Network layer, Transport layer, Session layer, Presentation layer, Application layer. 4. Differentiate between transport layer and network layer. Transport Layer It is responsible for the end-to-end delivery of the entire message. It provides service point addressing. Network Layer It is responsible for the end-to-end delivery of individual packet. It provides logical addressing. 5. List the categories of network. The categories of network are, Local Area Network (LAN), Metropolitan Area Network (MAN), Wide Area Network (WAN). 6. Define data link layer. Data link layer is the layer of control present in each communicating device that provides functions such as flow control and error control. 7. What is the use of flow control and error control? Flow control is a technique for assuring that a transmitting entity does not overwhelm a receiving entity with data. Error control allows the sender to know about the damaged or lost frame. 8. Give the frame format of BISYNC. 9. List the types of errors. The types of errors are, Single-bit error, Burst-bit error. 10. What is redundancy? Redundancy is an error detecting mechanism, which means a shorter group of bits or extra bits can be appended at the destination of each unit. Some of the extra bits are added with the original data for error detection. 11. List out the error detection methods. The error detection methods are, Vertical Redundancy Check (VRC), Longitudinal Redundancy Check (LRC), Cyclic Redundancy Check (CRC), Checksum. 12. List the types of error correcting methods. The types of error correcting methods are, Single-bit error correction, Burst error correction. 13. List the categories of flow control. The categories of flow control are, Stop and wait, Sliding window. 14. What is an ARQ? ARQ means Automatic repeat request. If the sender does not receive an ACK for a packet after a certain time period, it assumes that the packet did not arrive (or was delivered with bit errors) and retransmits it. Stop-and-wait and sliding window are two example ARQ protocols. 15. What is bit stuffing? Bit stuffing is a technique used to distinguish control sequences and data on the bit level. Used by the HDLC protocol. 16. What is the use of checksums? Checksums are used to detect errors in a packet and may also be used to verify that the packet has been delivered to the correct host. The term checksum is sometimes used to refer generically to error-detecting codes. 17. Define HDLC. HDLC is a bit-oriented data link protocol designed to support both half-duplex and full-duplex communication over point-to-point and multipoint links. 18. List the types of parity check. The types of parity check are, Simple parity check, Two-dimensional parity check. 19. What is the purpose of hamming code? A hamming code can be designed to correct burst errors of certain length. So the simple strategy used by the hamming code to correct single bit errors must be redesigned to be applicable for multiple bit correction. 20. What is data link flow control? What are the two approaches of link level flow control? Data link flow control is a set of procedures which says the amount of data to be transmitted for a sender. The two approaches of data link flow control are, Feedback based flow control, Rate based flow control. UNIT-2 1. Define carrier sense protocol. List its versions. Protocols in which stations listen for a carrier and act accordingly are called carrier sense protocol. The versions of carrier sense protocols are, 1_persistent CSMA, Nonpersistent CSMA, P-persistent CSMA. 2. What are the key assumptions of dynamic channel allocation? The key assumptions of dynamic channel allocation are, Station model, Single channel assumption, Collision assumption, Continuous time and slotted time, Carrier sense or no carrier sense. 3. Define Ethernet. An Ethernet is a multiple-access network, meaning that a set of nodes send and receive frames over a shared link. A popular local area network technology that uses CSMA/CD and has a bandwidth of 10 Mbps. An Ethernet itself is just a passive wire; all aspects of Ethernet transmission are completely implemented by the host adaptors. 4. What is CSMA/CD? CSMA/CD means Carrier Sense Multiple Access with Collision Detect. CSMA/CD is a functionality of network hardware. “Carrier sense multiple access” means that multiple stations can listen to the link and detect when it is in use or idle; “collision detect” indicates that if two or more stations are transmitting on the link simultaneously, they will detect the collision of their signals. Ethernet is the best-known technology that uses CSMA/CD. 5. List the types of Ethernet. The types of Ethernet are, Fast Ethernet, Gigabit Ethernet, Switched Ethernet. 6. List the physical properties of Ethernet. The physical properties of Ethernet are, An Ethernet segment is implemented on a coaxial cable of up to 500 m. Hosts connect to an Ethernet segment by tapping into it; taps must be at least 2.5 m apart. A transceiver—a small device directly attached to the tap. An Ethernet adaptor, which is plugged into the host. Multiple Ethernet segments can be joined together by repeater 7. What is 10Base2? The “10” in 10Base2 means that the network operates at 10 Mbps, “Base” refers to the fact that the cable is used in a baseband system, and the “2” means that a given segment can be no longer than 200 m. 8. Give the frame format of Ethernet. 9. Write short notes on Ethernet address with an example. Ethernet addresses are typically printed in a form humans can read as a sequence of six numbers separated by colons. Each number corresponds to 1 byte of the 6-byte address and is given by a pair of hexadecimal digits, one for each of the 4-bit nibbles in the byte; leading 0s are dropped. For example, 8:0:2b:e4:b1:2 is the human-readable representation of Ethernet address 00001000 00000000 00101011 11100100 10110001 00000010. 10. What is runt frame? If an adaptor sends only 96 bits then it is called a runt frame. It is possible if the two hosts are close to each other. 11. What is exponential backoff? 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 retransmission attempt is a general technique known as exponential backoff. 12. List the advantages of Ethernet. The advantages of Ethernet are, Ethernet is best under lightly loaded conditions, It is extremely easy to administer and maintain No switch, Router and configuration table It is easy to add a new Host It is Inexpensive. 13. Define token rings. Token ring is a direct link network. It is also a kind of shared media network. Here the data are transferred in the form of packet, so it is also known as packet switching. 14. Give the frame format of 802.5/token ring. 15. Differentiate between baseband and broadband. Baseband Broadband The word base specifies The word broad specifies a digital signal. an analog signal. Manchester encoding is PSK encoding is used used here. here. 16. What are the types of bridges? The types of bridges are, Simple bridge, Multiport bridge, Transparent bridge. 17. List the two kinds of traffic in FDDI. The two kinds of traffic in FDDI are, Synchronous traffic, Asynchronous traffic. 18. Define THT. THT means Token Holding Time. It gives the amount of time the node is allowed to hold the token. 19. What is MSAU? Several relays are usually packed into a single box, known as a multistation access unit (MSAU). It also makes it very easy to add stations to and remove stations from the network, since they can just be plugged into or unplugged from the nearest MSAU, while the overall wiring of the network can be left unchanged. In practice, MSAUs are almost always used because of the need for robustness and ease of station addition and removal. 20. What are the features of wireless LANs? The features of wireless LANs are, Time Bounded Services, Power Management, Security Management. UNIT-3 1. Define packet switch. A packet switch is a device with several inputs and outputs leading to and from the hosts that the switch interconnects. The core job of a switch is to take packets that arrive on an input and forward them to the right output so that they will reach their appropriate destination. 2. Define datagram. Datagram is the basic transmission unit in the Internet architecture. A datagram contains all of the information needed to deliver it to its destination. Datagram networks are connectionless. 3. What are the stages in virtual circuit switching? The stages in virtual circuit switching are, Connection setup, Data transfer. 4. Define virtual circuit identifier. A virtual circuit identifier (VCI) uniquely identifies the connection at this switch and that will be carried inside the header of the packets that belong to this connection 5. Give the frame relay packet format. 6. What is source routing? An approach to switching that uses neither virtual circuits nor conventional datagram is known as source routing. Source routing can be used in both datagram networks and virtual circuit networks. 7. What is a bridge? Bridge is a node in promiscuous mode, accepting all frames transmitted on either of the Ethernets, so it could forward them to the other. 8. List the informations available in configuration messages. The informations available in configuration messages are, The id for the bridge that is sending the message, The id for what the sending bridge believes to be the root bridge, The distance, measured in hops, from the sending bridge to the root bridge. 9. What is ATM? The switching technology that deserves special attention is asynchronous transfer mode (ATM). ATM is a connection-oriented, packet-switched technology. In ATM terminology, the connection setup phase is called signalling. 10. What is LSP? In link state routing, a small packet containing routing information send by a router to all other router by a packet called Link State Packet (LSP). 11. What is segmentation and reassembly? Fragmenting the high-level message into low-level packets at the source, transmit the individual low-level packets over the network, and then reassemble the fragments back together at the destination. This general technique is usually called fragmentation and reassembly. In the case of ATM, however, it is often called segmentation and reassembly (SAR). 12. Define throughput. Throughput is the observed rate at which data is sent through a channel. The term is often used interchangeably with bandwidth. Throughput = pps × (BitsPerPacket) 13. Define internetwork. An internetwork is often referred to as a “network of networks” because it is made up of lots of smaller networks. An internet is a logical network built out of a collection of physical networks. 14. Give the IPv4 packet format. 15. What is an ARP? ARP means Address Resolution Protocol. It is the protocol of the Internet architecture, used to translate high-level protocol addresses into physical hardware addresses. Commonly used on the Internet to map IP addresses into Ethernet addresses. 16. What is subnetting? The use of a single IP network address to denote multiple physical networks. Routers within the sub network use a subnet mask to discover the physical network to which a packet should be forwarded. Subnetting effectively introduces a third level to the two-level hierarchical IP address. 17. What is reliable flooding? Reliable flooding 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. As the term “flooding” suggests, the basic idea is for a node to send its link-state information out on all of its directly connected links, with each node that receives this information forwarding it out on all of its links. This process continues until the information has reached all the nodes in the network. 18. Give the IPv6 packet format. 19. What is multicast? Multicast is a special form of broadcast in which packets are delivered to a specified subgroup of network hosts. 20. Write short note on routers. The nodes that interconnect the networks are called routers. They are also sometimes called gateways. They relay packets among multiple interconnected networks. UNIT-4 1. Define UDP. UDP means User Datagram Protocol. It is a transport protocol of the Internet architecture that provides a connectionless datagram service to application-level processes. 2. Give the packet format of UDP header. 3. Define TCP. TCP means Transmission Control Protocol. Connection-oriented transport protocol of the Internet architecture. TCP provides a reliable, byte-stream delivery service. 4. Differentiate between flow control and congestion control. Flow Control Flow control involves preventing senders from overrunning the capacity of receivers. Congestion Control Congestion control involves preventing too much data from being injected into the network, thereby causing switches or links to become overloaded 5. What is meant by segment? At the sending and receiving end of the transmission, TCP divides long transmission into smaller data units and packages each into a frame called a segment. 6. Show how TCP manages a byte stream. 7. What is three-way handshake algorithm? The algorithm used by TCP to establish and terminate a connection is called a threeway handshake. We first describe the basic algorithm and then show how it is used by TCP. The three-way handshake involves the exchange of three messages between the client and the server. 8. What is silly window syndrome? Silly window syndrome is a condition occurring in TCP that may arise if each time the receiver opens its receive window a small amount, the sender sends a small segment to fill the window. The result is many small segments and an inefficient use of bandwidth. 9. What is meant by congestion? Congestion in a network occurs if user sends data into the network at a rate greater than that allowed by network resources. 10. Define QoS. QoS means Quality of Service. It is a packet delivery guarantees provided by a network architecture. Usually related to performance guarantees, such as bandwidth and delay. The Internet offers a best-effort delivery service, meaning that every effort is made to deliver a packet but delivery is not guaranteed. 11. What is the use of slow start? Slow start is used to increase the congestion window rapidly from a cold start. Slow start effectively increases the congestion window exponentially, rather than linearly. 12. Differentiate between TCP and UDP. TCP It is a connection oriented protocol. It provides a reliable delivery. UDP It is a connectionless protocol. It provides unreliable service. 13. List the approaches to support QoS. The approaches to support QoS are, Fine-Grained Approaches, which provide QoS to individual applications or flows, Coarse-Grained Approaches, which provide QoS to large classes of data or aggregated traffic. 14. Give the header format of TCP. 15. What are the two things that have to be done in packet classifying and scheduling? The two things that have to be done in packet classifying and scheduling are, Associate each packet with the appropriate reservation so that it can be handled correctly, a process known as classifying packets. Manage the packets in the queues so that they receive the service that has been requested, a process known as packet scheduling. 16. Draw the UDP message queue. 17. List the fields of a pseudo header. The fields of a pseudo header are, Protocol number, Source IP address, Destination IP address, UDP length field. 18. What is sliding window algorithm? Sliding window algorithm is an algorithm that allows the sender to transmit multiple packets before receiving an acknowledgment. As acknowledgments are returned for those packets in the window that were sent first, the window “slides” and more packets may be sent. The sliding window algorithm combines reliable delivery with a high throughput. 19. Draw the timeline for three-way handshake algorithm. 20. Define RED. RED means Random early detection. It is a queuing discipline for routers in which, when congestion is anticipated, packets are randomly dropped to alert the senders to slow down. UNIT-5 1. What is World Wide Web? World Wide Web is a hypermedia information service on the Internet. It is a repository or information spread all over the world and linked together. 2. What is Uniform Resource Identifier? Uniform resource identifier is a generalization of the URL. It is used in conjunction with SIP to set up multimedia sessions. 3. What is name resolution? Name resolution is the action of resolving host names (which are easy for humans to read) into their corresponding addresses (which machines can read). 4. What is mean by zone? Zone is a partition of the domain name hierarchy, corresponding to an administrative authority that is responsible for that portion of the hierarchy. Each zone must have at least two name servers to field DNS requests for the zone. 5. What is mean by SNMP? SNMP means Simple Network Management Protocol. It is an Internet protocol that allows the monitoring of hosts, networks, and routers. 6. What is mean by SMTP? SMTP means Simple Mail Transfer Protocol. It is an electronic mail protocol of the Internet. It is a standard protocol for transferring mail between hosts in the TCP/IP suite. 7. What is mean by HTTP? HTTP means Hyper Text Transport Protocol. It is an application-level protocol based on a request/reply paradigm and used in the World Wide Web. HTTP uses TCP connections to transfer data. 8. What is mean by DNS? DNS means Domain name system. It is a client/server application that identifies each host on the internet with an unique user friendly name. 9. What is mean by telnet? Telnet is a Remote terminal protocol of the Internet architecture. Telnet allows you to interact with a remote system as if your terminal is directly connected to that machine. 10. What is mean by FTP? FTP means File Transfer Protocol. It is the standard protocol of the Internet architecture for transferring files between hosts. It is built on top of TCP. 11. What is mean by IMAP? IMAP means Internet Message Access Protocol. It is an application-layer protocol that allows a user to retrieve his or her email from a mail server. 12. What do you meant b PGP? PGP means Pretty Good Privacy. It is a collection of public domain software that provides privacy and authentication capabilities using RSA and that use a mesh of trust for public key distribution. 13. In what way HTTP is similar to SMTP? HTTP is like SMTP because the data transfer between the client and server look like SMTP messages. 14. List some of the security services. Some of the security services are, Authentication, Access control, Data confidentiality, Integrity. 15. List the types of HTTP messages. The types of HTTP messages are, Request message, Response message. 16. What are the functions of User Agent? The functions of User Agent are, Prepares the message, Creates the envelope, Puts the message in the envelope. 17. What are the functions of a browser? The functions of a browser are, Fetches the page requested, Interprets the text and formatting commands it contain, Displays the page. 18. Define the terms Cryptanalysis and Cryptology. Cryptanalysis : The art of breaking ciphers is called Cryptanalysis. Cryptology : The art of devising ciphers and breaking them collectively is called as Cryptanalysis. 19. Define URL. URL means Uniform resource locator. It is a text string used to identify the location of Internet resources. It is a standard for specifying any kind of information on the internet. 20. What are the types of security attacks? The types of security attacks are, Passive attacks, Active attacks. SIXTEEN MARKS UNIT- 1 1. Explain OSI Architecture. The ISO was one of the first organizations to formally define a common way to connect computers. Their architecture, called the Open Systems Interconnection (OSI) architecture. Open Systems Interconnect (OSI) Architecture International Standards Organization (ISO) International Telecommunications Union (ITU, formerly CCITT) X dot series since the protocols are given names like X.25, X.400, X.50. Different layers of it are: Application : Application specific protocols Presentation : Format of exchanged data Session : Name space to tie together potentially different transport streams Transport : Process-to-process channel (end-to-end) Network : Host-to-host packet delivery (routing) Data Link : Framing of data bits (single hop issues) Physical : Transmission of raw bits 2. Explain Internet architecture. An alternative view of internet architecture is, First Layer: A wide variety of network protocols are defined. These protocols are implemented by combination hardware. Second layer: Contains a single protocol called IP This Protocol supports the interconnection of multiple networking technologies into a single, logical internetwork. Third Layer: Contains two main protocols TCP and UDP are sometimes called end to end protocols. TCP and UDP provide alternative logic channels to application programs. TCP provides a reliable byte stream channel. UDP provides an unreliable datagram delivery channel. Fourth Layer: Contains a range of application protocols such as FTP, TFTP, Tel net and SMTP. These protocols enable the inter operation of popular applications. 3. Explain Framing in detail. FIG: Bits flow between adaptors, frames between hosts TYPES: Byte-oriented protocol (PPP), Bit-oriented protocol (HDLC), Clock-based framing. Byte-oriented protocol (PPP): It includes, Sentinel-based approach, Byte-count approach. Bit-oriented protocols (HDLC): Unlike these byte-oriented protocols, a bit oriented protocol is not concerned with byte boundaries—it simply views the frame as a collection of bits. These bits might come from some character set, such as ASCII, they might be pixel values in an image, or they could be instructions and operands from an executable file. Clock-based framing (SONET): A third approach to framing is exemplified by the Synchronous Optical Network (SONET) standard. For lack of a widely accepted generic term, we refer to this approach simply as clock-based framing. 4. Explain error detection techniques. Error detection algorithms allow the recipient to reconstruct the correct message even after it has been corrupted; such algorithms rely on error-correcting codes. Bit errors in communication links occur due to noise of various kinds Error detection vs error correction Best choice for low error probability? Basic idea in error detection: together with n-bit message, send k “redundant” bits that can detect many possible errors k/n determines efficiency of error detecting code Checksums: Add up all words of message, and transmit sum together with message. Receiver performs same calculation. If received sum is different, discard message Internet checksum: Split message in 16-bit words. Perform ones complement arithmetic in 16-bit words Negative number x: binary complement of positive –x If sum generates carryout, increment result. 16-bit overhead for arbitrary large message. Cyclic Redundancy Check (CRC): Represent (n+1)-bit message x with n-th degree binary polynomial M(x) e.g., 10011010: x7+x4+x3+x Sender & receiver agree on divisor polynomial C(x) of degree k e.g., C(x) = x3+x2+1 (k=3) Multiply M(x) with xk : T(x) T(x) = 10011010000 Divide T(x) by C(x) in mod-2 polynomial arithmetic quotient Q(x), remainder R(x) Send T(x) – R(x) = C(x) * Q(x) to receiver If no errors, T(x)-R(x) should be divisible by C(x) 5. Explain Link Level Flow Control. It is one of the main function of data link layer. It is a technique for assuring that a transmitting entity does not overwhelm a receiving entity with data. This is a set of procedures which says the amount of data has to be transmitted for a sender. There are two approaches. They are, Feedback based flow control Rate based flow control Feedback flow control The receiver sends back information to the sender giving it permission to send more data or at least telling the sender how the receiver is doing. Rate based flow control The protocol has a built in mechanism that limits the rate at which the senders may transmit data without using feed from the receiver. There are many feedback based flow control schemes. The protocol has well defined rules about when a sender may transmit the next frame. These rules often prohibit frames from being sent until the receiver has granted permission, either implicitly or explicitly. UNIT- 2 1. Explain Ethernet in detail. The Ethernet is easily the most successful local area networking technology of the last 20 years. The Ethernet is a multiple-access network, meaning that a set of nodes send and receive frames over a shared link. Physical Properties: An Ethernet segment is implemented on a Coaxial cable of up to 500m. Hosts connects to an Ethernet segment by tapping in to it, taps must be at least 2.5m apart. A transceiver is a small device directly attached in the tap and detects when the line is idle and drives the signal when the host is transmitting. The transceiver in turn connected to an Ethernet potential adaptor, which is plugged into the host. Multiple segments can be jointed together by repeater. A repeater is a device that forwards digital signals, much like an amplifier that forwards analog signals. Access Protocol: It is a algorithm that controls access to the shared Ethernet link. This algorithm is commonly called Media Access Control (MAC). It is typically implemented in hardware on the network adaptor. Frame Format: Address: Every Ethernet host in the world has a unique Ethernet address. Each address belongs to the adaptor not the host; it is usually burned in to ROM. Ethernet addresses are typically printed in a form; it can read as a sequence of six numbers separated by colons. Eg: 8: 0 : 2b: c4 : b1: 2 An Ethernet adaptor receives all frames and accepts Frames addressed to its own address. Frames addressed to the broadcast address. Frames addressed to a multicast address, if it has been instructed to listen to that address. All frames, if it has been placed in promiscuous mode. 2. Explain Token ring in detail. Token ring are the significant class of shared media network. Fig: A Token Ring network Physical properties: One of the problems with ring topology is that any node or link failure would render the whole network useless. This problem is addressed by connecting each station in to the ring using an electro magnetical relay. If the relay is open, it is included in the ring. If the relay is closed then the ring automatically bypasses the station. The data rate may either 4Mbps or 16 Mbps. The encoding bit uses Manchester encoding. IBM Token ring may have up to 260 stations per ring. 802.5 Token rings sets the limit at 250. The physical medium used in IBM is twisted pair. 3. Explain FDDI in detail. FDDI is a high speed token ring fiber optical cable based technology. Fig: Dual-fiber ring: (a) normal operation; (b) failure of the primary ring 4. Explain learning bridges and spanning tree algorithm. Learning Bridges: Do not forward when unnecessary Maintain forwarding table Learn table entries based on source address Table is an optimization; need not be complete Always forward broadcast frames Fig: Forwarding table maintained by a bridge Spanning Tree Algorithm: Bridges must be able to correctly handle loops. This problem is addressed by having the bridges run a distributed spanning tree algorithm.. Specifically, the configuration messages contain three pieces of information: The id for the bridge that is sending the message The id for what the sending bridge believes to be the root bridge The distance, measured in hops, from the sending bridge to the root bridge 5. Explain wireless LANs. Wireless technologies differ in variety of dimensions, most notably in how much bandwidth they provide and how far apart communicating nodes can be. The most widely used wireless technologies are, Bluetooth, Wi=Fi, WinMAX, 3G cellular. Wireless LANs can operate in two configurations. They are, With base band station Without base band station UNIT- 3 1. Explain Packet switching and circuit switching. Packet Switching: Instead of allocating resources statically the data is put in variable length packets that are sent over the network. The deficit is that congestion may occur and therefore it is very hard to provide quality guarantees and real-time properties. A packet switched network may need some connection setup phase for establishing paths. Datagram switching is a special case where packets contain full source and destination address. The advantage is that there is no need for a setup phase at all. Circuit Switching: During a connection setup phase the switches are signaled and made to establish a path between the endpoints. Resources are allocated statically along the path for the whole duration of the call. Circuit switching naturally offers a connection oriented service, while it is less suited for datagram service due to setup delays. The advantage is that no congestion occurs and that service quality and real-time properties can easily be guaranteed. The problem is that there is no sharing of unused capacity and therefore the utilization can be very low during periods when sources need less than the allocated capacity. 2. Explain the following routing algorithms. i) Distance vector routing algorithms ii) Link state routing algorithms. Distance vector routing Sharing information Routing Table (Creation, updation - algorithm) Example Link state routing Information sharing Link state packet Link state database Dijkstra’s algorithm Routing table construction Example 3. Explain packet switched networks. A switch is a multi-input, multi-output device, which transfers packets from an input to one or more outputs. Thus, a switch adds the star topology. A star topology has several attractive properties: A switch has a fixed number of inputs and outputs. We can connect switches to each other and to hosts using point-to-point links. Adding a new host to the network by connecting it to a switch does not necessarily mean that the hosts already connected will get worse performance from the network. Fig: A switch provides a star topology It includes the following, Datagram, Virtual circuit, Source routing. Datagram: Connectionless (datagram) networks have the following characteristics: A host can send a packet anywhere at any time When a host sends a packet, it has no way of knowing if the network is capable of delivering it or if the destination host is even up and running. Each packet is forwarded independently of previous packets that might have been sent to the same destination. A switch or link failure might not have any serious effect on communication. Virtual circuit: It is a connection-oriented model, requires that we first set up a virtual connection from the source host to the destination host before any data is sent. One entry in the VC table on a single switch contains A virtual circuit identifier (VCI), An incoming interface , An outgoing interface, A potentially different VCI that will be used for outgoing packets. Source Routing: A third approach to switching that uses virtual circuits nor conventional datagrams is known as source routing. The name derives from the fact that all the information about network topology that is required to switch a packet across the network is provided by the source host. 4. Explain the service model of IPv4. A good place to start when you build an internetwork is to define its service model, that is, the host-to-host services you want to provide. The IP service model can be thought of as having two parts: An addressing scheme, A datagram. Datagram delivery: The IP datagram is fundamental to the Internet Protocol. Every datagram carries enough information to let the network forward the packet to its correct destination; there is no need for any advance setup mechanism to tell the network what to do when the packet arrives. Packet Format: Fragmentation and Reassembly: There are two important points: Each fragment is itself a self-contained IP datagram, Each IP datagram is re-encapsulated for each physical network over which it travels. Implementation: We conclude this discussion of IP fragmentation and reassembly by giving a fragment of code that performs reassembly. #define FRAGOFFMASK 0x1fff #define FRAGOFFSET(fragflag) ((fragflag) & FRAGOFFMASK) #define INFINITE_OFFSET 0xffff /* structure to hold the fields that uniquely identify fragments of the same IP datagram */ typedef struct fid { IpHost source; IpHost dest; u_char prot; u_char pad; u_short ident; } FragId; typedef struct hole { u_int first; u_int last; } Hole; 5. Explain DHCP and ICMP in detail. Dynamic Host Configuration Protocol (DHCP): DHCP means Dynamic Host Configuration Protocol. It contains many methods for automated configuration. It relies on the existence of a DHCP server that is responsible for providing configuration information to hosts. There is atleast one DHCP server for an administrative domain. Goal of DHCP is to minimize the amount of manual configuration required for a host to function. Packet format: Internet Control Message Protocol (ICMP): ICMP means Internet Control message protocol, Defines a collection of error message that are sent back to the source host whenever a router or host is unable to process an IP datagram successfully. It defines a handful to control message that a router can send back to a source host. ICMP – Redirect _ It is a useful control message tell how best route to the source host. UNIT- 4 1. Explain UDP in detail. It is the simplest transport protocol that extends the host to host delivery service of the n/w into a process to process communication service. So, the protocol needs to add a level of demultiplexing to allow multiple application processes on each host to share the network An example for transport protocol is UDP (User Datagram Protocol). In UDP, the host’s address contain one additional field called process –id (pid) to identify the processes directly which is assigned by the OS process –id unique. UDP uses port (or) mailbox to indirectly identify the processes. The basic idea is, source process sends messages to a port/ mailbox and the destination process will receive the information from that port. Packet Format: Src Port : Identifies the Source Process / Port, Dst Port : Identifies the Destination Process / Port, Length : Length of the UDP header, Check Sum : Used to detect transmission errors, Data : Original data / message have to transfer. 2. Explain TCP in detail. TCP is a transport protocol which offers a reliable, connection oriented byte stream service.TCP is a full duplex protocol meaning that each TCP connection supports a pair of byte streams, one following in each direction. TCP also includes flow – Ctrl mechanism for each byte streams that allows the receiver to limit how much data the sender can transmit a given time. TCP supports demultiplexing mechanism (like UDP) that allows multiple application programs on any given host to simultaneously carry on a conversation with their peers. TCP also includes, Flow control, Congestion control. RTT (Round Trip Time) is the time takes for a bit of information to propagate from one end to other and back again. Frame format: Advertised window Flag SYN & FN ACK URG URG Ptr : Carry enough information about the flow of data. : It contains SYN, FIN, RESET, PUSH, URG and ACK. : Indicates connection establishment & termination. : Means that Acknowledgement field is valid : Urgent data. : Starting point of urgent data. 3. Explain sliding window in detail. Sliding window algorithm serves several purposes: It guarantees reliable delivery of data. It ensures that data is delivered in order. It enforces flow control between sender and Receiver. The three pointers maintained by the send buffer are: LastByteAcked, LastByteSent, LastByteWritten. Flow control: Receiver Side: LastByteRCVD – Last Byte Read < Max RCV Buffer AdvertisedWindow = Max RCV Buffer – ( (Next Byte Expected – 1)- Last Byte Read) AdvertisedWindow --> Represents amt of free Space remaining in its buffer Sender Side: LastByteSent – Last Byte Acked < Advertised window EffectiveWindow = Advertised window – (Last Byte Sent – Last Byte Acked) 4. Explain Adaptive retransmission. Original algorithm: Theory Estimate RTT Multiply by 2 to allow for variations Practice Use exponential moving average (A = 0.1 to 0.2) Estimate = (A) * measurement + (1- A) * estimate Problem Did not handle variations well Ambiguity for retransmitted packets Was ACK in response to first, second, etc transmission? Karn/Partridge Algorithm: Algorithm Exclude retransmitted packets from RTT estimate For each retransmission Double RTT estimate Exponential backoff from congestion Problem Still did not handle variations well Did not solve network congestion problems as well as desired. Fig: (a) original transmission (b) retransmission Jacobson/Karels algorithm: Algorithm Estimate variance of RTT Calculate mean interpacket RTT deviation to approximate variance Use second exponential moving average Deviation = (B) * |RTT_Estimate – Measurement| + (1–B) * deviation B = 0.25, A = 0.125 for RTT_estimate Use variance estimate as component of RTT estimate Next_RTT = RTT_Estimate + 4 * Deviation Protects against high jitter Notes Algorithm is only as good as the granularity of the clock Accurate timeout mechanism is important for congestion control 5. Explain congestion control in detail. When there are too many packets present in the subnet, performance degrades. This is said to be congestion. Slow processors can also make congestion, Low bandwidth lines also make congestion. Congestion control: Congestion control involves preventing too much data from being injected into the network, thereby causing switches or links to become overloaded. General principles of congestion control are, Closed loop control, Open loop control. Approaches to congestion control are, End to end congestion control, Network assisted congestion control. UNIT- 5 1. Explain the functions of SMTP. 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 email addresses. SMTP provides mail exchange between users on the same or different computers. It requires, System for sending messages to other computer users based on email 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. Explain the WWW in detail. WWW means World Wide Web. A hypermedia information service on the Internet. World Wide Web is a hypermedia information service on the Internet. It is a repository or information spread all over the world and linked together. It includes the following concepts, Hypertext & Hypermedia Browser Architecture Categories of Web Documents HTML CGI Java 3. Explain IMAP in detail. IMAP means Internet Message Access Protocol. It is an application-layer protocol that allows a user to retrieve his or her email from a mail server. IMAP is an alternative final delivery protocol which is defined in RFC 2060. IMAP assumes that all the e-mail will remain on the server indefinitely in multiple mail boxes. IMAP provides extensive mechanisms for reading messages or even parts of messages a feature when using a slow modem to read the text part of a multipart message with large audio and video attachments. IMAP provides mechanisms for creating, destroying, and manipulating multiple mail boxes on server. IMAP State Transition: When the server says ‘ok’, then client can send commands like LOGIN AUTHENTICATION SELECT EXAMINE CLOSE LOGOUT FETCH If the user needs to fetch a message, then the server returns it in MIME format. The message attributes may be, Message size, Flags like seen, deleted, recent. 4. Explain HTTP in detail. HTTP means Hyper Text Transport Protocol. It is an application-level protocol based on a request/reply paradigm and used in the World Wide Web. HTTP uses TCP connections to transfer data. The data transferred by protocol are, Plain text, Cipher text, Audio, images or any internet accessible information. The types of HTTP messages are, Request message, Response message. Headers: It is used to exchange the information in-between the client and server, It has one or more number of header lines, Every header line consisting of name of the header, a colon, a space and a header value. Uniform Resource Identifier: Uniform resource identifier is a generalization of the URL. A URI is a character string which finds a resource. The resource can be anything that has the identity like, Document, Image, A service. 5. Explain security in detail. Security involves the privacy of the message. Cryptography is the heart of security. Four factors needed for a secure network. Privacy: The sender and the receiver expect confidentiality. Authentication: The receiver is sure of the sender’s 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. Some of the security services are, Authentication, Access control, Data confidentiality, Integrity. -----END----