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1. 1. Computer Networks Labs Manual FETR, ISROLI COMPUTER NETWORKS LAB MANUAL For V SEMESTER DEPT.: COMPUTER SCIENCE & ENGINEERINGFACULTY OF ENGINEERING TECHNOLOGY AND RESEARCH ISROLI-AFWA, BARDOLIDept : Computer Science & Engineering
2. 2. Computer Networks Labs Manual FETR, ISROLI NETWORKS LABORATORY Sub Code: 150702 Note: Student is required to solve one problem from PART-A and one problem from PART-B. Both the parts have equal weightage. PART A – Simulation Exercises The following experiments shall be conducted using either NS228/OPNET or any other simulators. 1. Simulate a three nodes point-to-point network with duplex links between them. Set the queue size vary the bandwidth and find the number of packets dropped. 2. Simulate a four node point-to-point network, and connect the links as follows: n0-n2, n1-n2 and n2-n3. Apply TCP agent between n0-n3 and UDP n1-n3. Apply relevant applications over TCP and UDP agents changing the parameter and determine the number of packets by TCP/UDP. 3. Simulate the different types of Internet traffic such as FTP a TELNET over a network and analyze the throughput. 4. Simulate the transmission of ping messaged over a network topology consisting of 6 nodes and find the number of packets dropped due to congestion. 5. Simulate an Ethernet LAN using N-nodes(6-10), change error rate and data rate and compare the throughput. 6. Simulate an Ethernet LAN using N nodes and set multiple traffic nodes and determine collision across different nodes. 7. Simulate an Ethernet LAN using N nodes and set multiple traffic nodes and plot congestion window for different source/destination. 8. Simulate simple ESS and with transmitting nodes in wire-less LAN by simulation and determine the performance with respect to transmission of packets. PART B The following experiments shall be conducted using C/C++. 1. Write a program for error detecting code using CRC-CCITT (16-bits). 2. Write a program for frame sorting technique used in buffers. 3. Write a program for distance vector algorithm to find suitable path for transmission. 4. Using TCP/IP sockets, write a client-server program to make client sending the file name and the server to send back the contents of the requested file if present. 5. Implement the above program using as message queues or FIFOs as IPC channels. 6. Write a program for simple RSA algorithm to encrypt and decrypt the data. 7. Write a program for Hamming Code generation for error detection and correction. 8. Write a program for congestion control using Leaky bucket algorithm.Dept : Computer Science & Engineering
3. 3. Computer Networks Labs Manual FETR, ISROLI PEN: NAME: SUBJECT: 150702 (Computer Networks)Sr. Page Signatur Date Title GradeNo No. ePART A: Simulation using NCTUns.1 Simulate a three nodes point-to-point network with duplex links.2 Simulate a four node point-to-point network and apply relevant application over TCP/UDP Agents.3 Simulate the different types of Internet traffic such as FTP a TELNET over a network.4 Simulate the transmission of ping messaged over different network topology.5 Simulate an Ethernet LAN using N-nodes (6-10), change error rate and data rate and compare the throughput. Simulate an Ethernet LAN using N nodes and set6 multiple traffic nodes and determine collision across different nodes. Simulate an Ethernet LAN using N nodes and set multiple7 traffic nodes and plot congestion window for different source/destination.8 Simulate simple ESS and with transmitting nodes in wire-less LAN by simulation and determine the performance. Dept: Computer Science & Engineering
4. 4. Computer Networks Labs Manual FETR, ISROLISr. Page Date Title Grade SignatureNo No.PART B: Perform Experiments using C/C++.9 WAP for error detecting code using CRC-CCITT (16-bits).10 WAP for frame sorting technique used in buffers. WAP for distance vector algorithm to find suitable path for11 transmission.12 Write a client server program using TCP/IP sockets. Write a client server program using as message queues or13 FIFOs as IPC channels. WAP for simple RSA algorithm to encrypt and decrypt the14 data. WAP for Hamming Code generation for error detection and15 correction.16 WAP for congestion control using Leaky bucket algorithm. Dept: Computer Science & Engineering
5. 5. Computer Networks Labs Manual FETR, ISROLI PART A – NCTUNS SIMULATION Introduction to SimulationTo study the network performance two things you can use.They are:  Emulator  SimulatorEmulatorA device on the [LAN], Real network, actual equipment, real software or a part of the realsystem is replaced by a model. This model is called Emulator. Properties of an existingpart are simulated (only the part of the real system). A network emulator emulates thenetwork .Imitates the behavior of application traffic.Objective:  To test control systems, under realistic condition.  To do analysis.  To access the performance.  To predict the impact of change  To optimize technology decision-making.Advantage:  Reflect results preciselyDisadvantage:  Must run in real time  Expensive  Requires a lot of setup  We won’t use emulation for experimentation.Simulator  Network simulators are typically programs which run on a single computer, take an abstract description of the network traffic (such as a flow arrival process) and yield performance statistics (such as buffer occupancy as a function of time).Dept: Computer Science & Engineering
6. 6. Computer Networks Labs Manual FETR, ISROLIObjective:  To test and develop different solutions and finally to arrive at a best solution.Advantage:  Cost effective  Flexible.  No risk involved. Extensive experiments can be done.  Easier to analyze.Disadvantage:  Not just a part but a complete network simulator needs to simulate networking devices and application programs.  Needs network utility programs to configure and monitor.  Simulation model maintains its own simulation clock. When a decision is taken within the model, the simulation clock does not advance until the necessary calculations have been performed.  Results are not convincing.Different types of simulators:  REAQL  NS  OPNET  NCTUns NCTUns  Open source,  high quality  support many type of networks  Extensible. Can be used as emulator also.  Uses real-life Linux’s TCP/IP protocol  Uses real-life unix network configuration.  Can simulate various networking devices.  Can simulate various network protocols  Simulation speed is high.  It uses kernel re-enter methodology. For this it uses tunnel network interface. Tunnel devices are available in most UNIX machines.  NCTUns modifies the kernel to use a special virtual timer . kernel code is modified. Each kernel on which NCTUns runs need to be patched. Kernel needs to be patchedDept: Computer Science & Engineering
7. 7. Computer Networks Labs Manual FETR, ISROLI on all simulation machines.NCTUns ArchitectureNCTUns uses distributed Architecture.NCTUns has following components. They are: 1. GUI Operating Environment (nctunsclient) 2. Simulation Engine 3. Protocol and job Dispacher 4. Coordinator 5. kernel modification 6. User-level daemon and real world application program 7. Remote, concurrent and Parallel simulation 1) GUI Operating Environment: a) It is a GUI program which generates the simulation job. b) It uses TCP/IP sockets to communicate with other components. c) The simulation job generated is submitted to remote simulation machine for execution. When the simulation is finished, the simulation results and generated log files are transferred back to the GUI . The user then examines the logged data and plot the graphs, play back packet transfer animations. 2) Simulation Engine: a) It is a userlevel program. It is compiled along with Protocols to form Simulation server. Simulation server takes simulation job and generates data and log files. 3) Protocol and job Dispatcher: a) It is a userlevel program. It takes simulation jobs from the GUI user and dispatches it to the simulation server machine. b) It coordinates large number of GUI users and a large number of simulation machines. 4) Coordinator: a) It is a userlevel program. b) It is executed on every simulation machine where simulation server resides. c) It takes simulation jobs from the dispatcher and executes the simulation server to process the simulation job. d) Coordinator informs the dispatcher whether machine is busy or not. e) It communicates with the dispatcher and GUI on behalf of server.Dept: Computer Science & Engineering
8. 8. Computer Networks Labs Manual FETR, ISROLI f) Message exchange between simulation server and GUI are performed through coordinator. 5) Kernel Modification 6) User-level Daemon and real-world application program: The NCTUns real-world application programs run at the user level to either generate network traffic, configure network, or monitor network traffic, etc. For example, the tcpdump program can run on a simulated network to capture packets flowing over a link and the trace route program can run on a simulated network to find out the routing path traversed by a packet. 7) Remote, concurrent and parallel simulations. NCTUns uses a distributed architecture, by which simulation machines can be far away from the machines where the GUI programs are run. For example, the simulation service machines may reside at NCTU in Taiwan while the GUI users come from many different places of the world. Multiple simulation jobs can be concurrently simulated on different machines (one machine serves one job) to increase the total simulation throughput. When the NCTUns simulation jobs are run on multiple machines, we say that NCTUns is operating in the “multiple machine‟ mode [13]. This mode supports remote and concurrent simulations. In the “single-machine‟ mode, the simulation jobs run on the same machine. With the inter-process communication (IPC) design, NCTUns can be used for eitherDept: Computer Science & Engineering
9. 9. Computer Networks Labs Manual FETR, ISROLI mode without changing its program code. Only the mode parameter in its configuration file needs to be changed.STEPS TO START NCTUNSThree things we are going to start. They are:  Dispatcher (With ADMIN privilege)  Coordinator (With ADMIN privilege)  Nctunsclient (With ADMIN or user privilege)But after drawing the topology, you should submit the simulation with user privilege onlyWe need three terminals. 1st terminal to execute ./dispatcher at the server 2nd terminal to execute ./coordinator at the server 3rd terminal to execute ./nctunsclient at the clientSTEP 1: # cd /usr/local/nctuns/binSTEP 2: #. /dispatcher <enter key> Right click on the blank space of the screen and select open tabSTEP 3: #. /coordinator <enter key> Right click on the blank space of the screen and select open tabSTEP 4: #. /nctunsclient <enter key>Dept: Computer Science & Engineering
10. 10. Computer Networks Labs Manual FETR, ISROLITo submit the simulation, you should be the normal userDept: Computer Science & Engineering
11. 11. Computer Networks Labs Manual FETR, ISROLIWORKING WITH NCTUNSThere are 4 steps in doing the NCTUNS experiments. They are as below. 1. Drawing a network topology D 2. Editing node’s properties E 3. Running the simulation R 4. Post analysis P1.5.1 Drawing a network topology: 1.5.2 Identification of tools on the toolbar: Select Draw topology D Edit property E Run Simulation R Play back P Delete X Label A Point – to – point link Moving path Hub (Blue color)Dept: Computer Science & Engineering
13. 13. Computer Networks Labs Manual FETR, ISROLIEditing Node’s Properties:A network node (device) may have many parameters to set. Some parameters are  Bandwidth  Queue size  IP addressThe GUI automatically finds subnets in a network and generates and assigns IP andMAC addresses to layer 3 network interfaces.If the user switches the mode back to the “Draw Topology” mode and when theuser again switches the mode back to the “Edit topology” mode, node’s IP andMAC addresses will be regenerated and assigned to layer 3 interfaces.Therefore the application programs now may use wrong IP addresses to communicatewith their partners.Dept: Computer Science & Engineering
14. 14. Computer Networks Labs Manual FETR, ISROLI PART A Programs Start up 1. Open three terminals a) in terminal 1 at command prompt run dispatcher( root@localhost# dispatcher) b) in terminal 2 at command prompt run coordinator( root@localhost# coordinator) c) in terminal 3 at command prompt run nctunsclient( root@localhost# nctunsclient) 2. After the above steps NCTUns starting screen will appear. 3. To draw the network topology perform the following steps Choose Menu-> File-> Operating Mode-> D(draw mode), draw the required topology or change the existing simulation topology.(drag and drop) 4 Once topology is drawn , set the node property by switching to “Edit property” mode E 5 Configure the node with appropriate commands at source and destination 6 Run the Simulation menu simulation run 7 Play back the simulation.Dept: Computer Science & Engineering
15. 15. Computer Networks Labs Manual FETR, ISROLI Experiment No 1 1. Simulate a three-node point-to-point network with a duplex link between them. Set the queue size and vary the bandwidth and find the number of packets dropped. Topology:- STEPS: To draw a network topology, do the following steps: 1. Select the host icon on the toolbar and drag it onto the working window. Repeat this for another host icon. Select the link icon on the toolbar and drag it on the screen from host [node 1] to the hub and again from host [node2] to the hub. Here the hub acts as node 3 in the point-to-point network. This leads to the creation of the 3-node point-to-point network topology. [We can see the ip address of the host by moving the mouse pointer on host] 2. Save this topology as a filename.tplDept: Computer Science & Engineering PAGE :
16. 16. Computer Networks Labs Manual FETR, ISROLI To configure the network devices, do the following steps: At Sender 1. Double click on host [node-1], a host dialog box will open up 2. Click on the Add button and enter the command (at the sender) stg [-u udp][-t duration (sec)] [-p port number]HostIPaddr and set the simulation time 0 to 40 sec then click okDept: Computer Science & Engineering PAGE :
17. 17. Computer Networks Labs Manual FETR, ISROLI 3. Click on the node editor and you can see the different layers-interface, ARP, FIFO, MAC, TCPDUMP, Physical layers. 4. Select MAC and then select full-duplex for switches and routers and half- duplex for hubs, and check the log packet statistics check box ,Dept: Computer Science & Engineering PAGE :
18. 18. Computer Networks Labs Manual FETR, ISROLI 5. Select output throughput log file etc (at sender), select the number of drop packets, number of collisions. Click the OK button. At Receiver: Steps 1. Click on the Add button and enter the command (at the receiver) rtg [-t] [-w log] [-p port number] and click OK.Dept: Computer Science & Engineering PAGE :
19. 19. Computer Networks Labs Manual FETR, ISROLI 2. Click on the node editor and you can see the different layers-interface, ARP, FIFO, MAC, TCPDUMP, Physical layers. 3. Select input throughput log file etc (at receiver), select the number of drop packets, number of collisions. Click ok.Dept: Computer Science & Engineering PAGE :
20. 20. Computer Networks Labs Manual FETR, ISROLI To RUN the Simulation 1. Now click on the R button (Run simulation). By doing such a user can run/pause/continue/stop/abort/disconnect/reconnect/submit a simulation. No simulation settings can be changed in this mode. 2. Now go to the Menu->Simulation->Run. Executing this command will submit the current simulation job to one available simulation server managed by t h e dispatcher. When the simulation server is executing, the user will see the time knot at the bottom of the screen move. The time knot reflects the current virtual time (progress) of the simulation case.Dept: Computer Science & Engineering PAGE :
21. 21. Computer Networks Labs Manual FETR, ISROLI To PLAYBACK the simulation To start the playback, the user can left-click the start icon ( |>) of the time bar located at the bottom. The animation player will then start playing the recorded packet animation. . The results are stored in file.results folder(“file” is the same name given by the user to the simulation file). You will see the following log files in the folder: file.results Filename.8023_N2_P1_OutThrput.log Filename.8023_N3_P1_InThrput.log Filename..8023_n2_p1_coll.log Filename.8023_N2_P1_Drop.log Here the drop and collision files do not have data, because of point to point connection no drop, no collisionDept: Computer Science & Engineering PAGE :
22. 22. Computer Networks Labs Manual FETR, ISROLI Graph can be plotted during the play mode To plot the graph on menu Tools plot graph open file name Graph for 10 mbps bandwidthDept: Computer Science & Engineering PAGE :
23. 23. Computer Networks Labs Manual FETR, ISROLI Change the bandwidth say, 9 Mbps or less , and run the simulation and compare the two results. To view the results go to the filename. results folder.Dept: Computer Science & Engineering PAGE :
24. 24. Computer Networks Labs Manual FETR, ISROLI To change the setting of the graph and X-values and Y-values, go to options general setting Inference: Since it is a point to point connection and numbers of nodes are only 2, so there is no chance of drop and collision, whatever the data sent from source is received by the receiver.Dept: Computer Science & Engineering PAGE :
25. 25. Computer Networks Labs Manual FETR, ISROLI Experiment No 2 2. Simulate a four-node point-to-point network and connect the link as follows: Apply a TCP agent between n0 to n3 and apply a UDP agent between n1 and n3. Apply relevant applications over TCP and UDP agents changing the parameters and determine the number of packets sent by two agents. Topology:- Sender:- stcp –p 3000 –l 1024 1.0.1.3 stg –u 1024 1.0.1.3 Receiver:- rtcp –p 3000 –l 1024 rtg –u 3000 Parameters:- Throughput of incoming and outgoing PacketsDept: Computer Science & Engineering PAGE :
26. 26. Computer Networks Labs Manual FETR, ISROLI Experiment No 3 3. Simulate the different types of Internet traffic such as FTP, TELNET over a network and analyze the throughput. To draw a network topology, do the following steps: Step 1: Select the host icon on the toolbar and drag it onto the working window. Repeat this for another host icon. Select the link icon on the toolbar and Draw the topology as shown above. [We can see the ip address of the host by moving the mouse pointer on host ] Step 2: Save this topology as a filename.tpl To configure the network devices, do the following steps: Step 1: click on host , a host dialog box will open upDept: Computer Science & Engineering PAGE :
27. 27. Computer Networks Labs Manual FETR, ISROLI Step 2: Click on the Add button and enter the command (at the sender) node 1: For FTP stcp –p 21 –l 1024 1.0.1.4 node 2: For Telnet stcp –p 23 –l1024 1.0.1.4 and set the simulation time 0 to 40 sec then click ok Step 3: Click on the node editor and you can see the different layers- interface, ARP, FIFO, MAC, TCPDUMP, Physical layers. Step 4: Select MAC and then select full-duplex for switches and routers and half-duplex for hubs, and check the log packet statistics check box ,Dept: Computer Science & Engineering PAGE :
28. 28. Computer Networks Labs Manual FETR, ISROLI Step5: Select output throughput log file etc (at sender), select the number of drop Packets, Output ThroughPut. Click the OK button. Step 6: At Receiver: Click on the Add button and enter the command (at the receiver) node 4 For FTP rtcp -p 21 –l 1024 For TELNET rtcp -p 23 –l 1024 and click OKDept: Computer Science & Engineering PAGE :
29. 29. Computer Networks Labs Manual FETR, ISROLI Step 7: Click on the node editor and you can see the different layers- interface, ARP, FIFO, MAC, TCPDUMP, Physical layers. Step 8: Select input throughput log file etc (at receiver), select the number of drop packets, number of collisions. Click ok.Dept: Computer Science & Engineering PAGE :
30. 30. Computer Networks Labs Manual FETR, ISROLI To RUN the Simulation Step 1: Now c l i c k o n t h e R b u t t o n ( Run s i m u l a t i o n ). By d o i n g s o a user can run/pause/continue/stop/abort/disconnect/reconnect/submit a simulation. No simulation settings can be changed in this mode. Step 2: Now go to the Menu->Simulation->Run. Executing this command will submit the current simulation job to one available simulation server managed by the dispatcher. When the simulation server is executing, the user will see the time knot at the bottom of the screen move. The time knot reflects the current virtual time (progress) of the simulation case. To playback the simulation To start the playback, the user can left-click the start icon ( |>) of the time bar located at the bottom. The animation player will then start playing the recorded packet animation. The results are stored in fil e.resul ts folder (“file” is the same name given by the user to the simulation file). You will see the following log files in the folder: file.results Filename.8023_N1_P1_OutThrput.logDept: Computer Science & Engineering PAGE :
31. 31. Computer Networks Labs Manual FETR, ISROLI Filename.8023_N4_P1_InThrput.log Filename..8023_n4_p1_coll.log Filename.8023_N4_P1_Drop.log Here the drop and collision files do not have data, because of in point to point connection no drop, no collision Graph can be plotted during the play mode To plot the graph on menu Tools plot graph open file name Graph for output Thruput FTP Traffic Graph for Input Thruput , FTP TrafficDept: Computer Science & Engineering PAGE :
32. 32. Computer Networks Labs Manual FETR, ISROLI Graph For output Thrput, TELNET Traffic Graph for input Thrput (Telnet Traffic)Dept: Computer Science & Engineering PAGE :
33. 33. Computer Networks Labs Manual FETR, ISROLI To change the setting of the graph and X-values and Y-values ,go to options general settingDept: Computer Science & Engineering PAGE :
34. 34. Computer Networks Labs Manual FETR, ISROLI Experiment No 4 4. Simulate the transmission of ping messages over a network topology consisting of 6 nodes and find the number of packets dropped due to congestion. Topology:- Sender:- stcp –p 2000 –l 1024 1.0.1.4 Receiver:- rtcp –p 2000 –l 1024 Command Console:- Goto tools-> simulation time and change Simulation time to 100. During run mode, double click host 2 and then click command console. And execute the following command. ping 1.0.1.4 Parameters:- Drop Packets and Collision Packets.Dept: Computer Science & Engineering PAGE :
35. 35. Computer Networks Labs Manual FETR, ISROLI Experiment No 5 5. Simulate an Ethernet LAN using N nodes (6-10), change error rate and data rate and compare throughput. Topology:- Sender:- stcp –p 2000 –l 1024 1.0.1.4 Receiver:- rtcp –p 2000 –l 1024 Double click on receiver link and change BER to 0.000001, Run Again. Parameters:- Throughput of outgoing PacketsDept: Computer Science & Engineering PAGE :
36. 36. Computer Networks Labs Manual FETR, ISROLI Experiment No 6 6. Simulate an Ethernet LAN using N nodes and set multiple traffic nodes and determine collisions across different nodes. Topology:- Sender:- stcp –p 2000 –l 1024 1.0.1.4 Receiver:- rtcp –p 2000 –l 1024 Parameters:- Collision Packets and Drop Packets (Optional)Dept: Computer Science & Engineering PAGE :
37. 37. Computer Networks Labs Manual FETR, ISROLI Experiment No 7 7. Simulate an Ethernet LAN using N nodes and set multiple traffic nodes and plot congestion window for different source/destination. Topology:- Sender:- stcp –p 2000 –l 1024 1.0.1.4 Receiver:- rtcp –p 2000 –l 1024 Parameters:- Receiver side Collision Packets and Drop PacketsDept: Computer Science & Engineering PAGE :
38. 38. Computer Networks Labs Manual FETR, ISROLI Experiment No 8 8. Simulate simple BSS and with transmitting nodes in wireless LAN by simulation and determine the performance with respect to transmission of packets. Topology:- Click on “access point”. Goto wireless interface and tick on “show transmission range and then click OK. Double click on Router -> Node Editor and then Left stack -> throughput of Incoming packets Right stack -> throughput of Outgoing packets Select mobile hosts and access points then click on. Tools -> WLAN mobile nodes-> WLAN Generate infrastructure. Subnet ID: Port number of router (2) Gateway ID: IP address of router Mobile Host 1 ttcp –t –u –s –p 3000 1.0.1.1 Mobile Host 1 ttcp –t –u –s –p 3001 1.0.1.1 Host(Receiver) ttcp –r –u –s –p 3000 ttcp –r –u –s –p 3001 Run and then play to plot the graph.Dept: Computer Science & Engineering PAGE :
39. 39. Computer Networks Labs Manual FETR, ISROLI Part B Experiments Experiment No 1 CRC Problem Statement Write a program for error detecting code using CRC-CCITT (16-bits). Theory It does error checking via polynomial division. In general, a bit string bn-1bn-2bn- 3…b2b1b0 As bn-1Xn-1 + bn-2 Xn-2 + bn-3 X n-3 + 2 b X1 b …b2 X + 1 + 0 Ex: - 1001010111 0 As X10 + X7 + X5 + X3 + X2 + X1 All computations are done in modulo 2 Algorithm:- 1. Given a bit string, append 0S to the end of it (the number of 0s is the same as the degree of the generator polynomial) let B(x) be the polynomial corresponding to B. 2. Divide B(x) by some agreed on polynomial G(x) (generator polynomial) and determine the remainder R(x). This division is to be done using Modulo 2 Division. 3. Define T(x) = B(x) –R(x) (T(x)/G(x) => remainder 0) 4. Transmit T, the bit string corresponding to T(x). 5. Let T’ represent the bit stream the receiver gets and T’(x) the associated polynomial. The receiver divides T1(x) by G(x). If there is a 0 remainder, the receiver concludes T = T’ and no error occurred otherwise, the receiver concludes an error occurred and requires a retransmission.Dept: Computer Science & Engineering PAGE :
40. 40. Computer Networks Labs Manual FETR, ISROLI Experiment No 2 Frame Sorting Problem Statement Write a program for frame sorting technique used in buffers.Theory The data link layer divides the stream of bits received from the network layer intomanageable data units called frames. If frames are to be distributed to different systems on the network, the Data link layeradds a header to the frame to define the sender and/or receiver of the frame. Each Data link layer has its own frame format. One of the fields defined in theformat is the maximum size of the data field. In other words, when datagram isencapsulated in a frame, the total size of the datagram must be less than this maximumsize, which is defined by restriction imposed by the hardware and software used in thenetwork. IP Datagram Header MTU Trailer The value of MTU differs from one physical network to another In order to make IP protocol portable/independent of the physical network, the packagers decided to make the maximum length of the IP datagram equal to the largest Maximum Transfer Unit (MTU) defined so far. However for other physical networks we must divide the datagrams to make it possible to pass through these networks. This is called fragmentation. When a datagram is fragmented, each fragmented has its own header. A fragmented datagram may itself be fragmented if it encounters a network with an even smaller MTU. In another words, a datagram may be fragmented several times before it reached the final destination and also, the datagram referred to as (frames in Data link layer) may arrives out of order at destination. Hence sorting of frames need to be done at the destination to recover the original data.Dept: Computer Science & Engineering PAGE :