Computer Science 9618 Paper 3: Communication

Communication COMPUTER SCIENCE 9618 PAPER 3 Communication And Internet Technologies Protocol What is meant by Protocol ? Set Of Rules For Successful transmission and receipt of the data Explain why protocols are essential for communication b/w computers Provid...

Communication COMPUTER SCIENCE 9618 PAPER 3 Communication And Internet Technologies Protocol What is meant by Protocol ? Set Of Rules For Successful transmission and receipt of the data Explain why protocols are essential for communication b/w computers Provides a set of standard for transmission of data that basically gives accepted set of rules for transmitting and receiving data. This enable communication between different platforms They are able to communicate because of the same protocol Types Of Protocol With Their Uses TCP / IP Protocol Suite Application Transport Network Data Link  It is a conceptual model for networking It consists of 4 layers How these layers are implemented ? By Code / Program Describe TCP/IP Protocol Suite ? A layered model with 4 layers Transmission Control Protocol with Internet Protocol uses a set of protocols for transmission of data Application Layer, Transport Layer, Network Layer, Data Link Layer.  Application Layer E.g Web Browser It sends files to transport layer Contains all programs that exchange data (1) HTTP Explain what happens when a user access a website ? 1) User types in URL 2) HTTP transmit URL from Application Layer to Transport Layer 3) TCP breaks the URL into Data Packets and sends the packet which contains domain name to DNS. DNS checks for matching IP. 4) Server sends back an acknowledgment 5) Web server sends back the web pages in HTML format 6) Browser Interpret the HTML file.  (2) FTP FTP (File Transfer Protocol) is a standard network protocol used to transfer files between a client and a server over a TCP- based network, such as the internet. It allows users to upload, download, rename, delete, move, and copy files on a server. 1) SERVER : In FTP, the server is the central computer that stores files available for users to download. It manages the storage and distribution of files. 2) Command : This refers to the set of instructions a user can send to the FTP server, such as commands to delete, copy, or move files. These commands are executed on the server. 3) Anonymous : Anonymous FTP allows users to access files on a server without needing to identify themselves with a username and password. It is typically used for public file sharing (3) SMTP SMTP stands for Simple Mail Transfer Protocol. It is used for sending emails from a client (like an email app) to a mail server. SMTP "pushes" outgoing emails from the sender to the recipient's mail server. The protocol works by breaking the email message into commands and responses. These commands ensure the email is routed correctly to its destination. SMTP is for sending mail, while IMAP or POP are for receiving mail. Note : Does not handle binary files such as images and videos and to send binary files we need MIME ( Multipurpose Internet Mail Extension ) (4) POP 3/4 AND IMAP POP (Post Office Protocol) and IMAP (Internet Message Access Protocol) are "pull" protocols used for receiving emails from an email server to a client. What is the difference between POP and IMAP Synchronization Note : On IMAP email does not get deleted and can be accessed from different devices.  Transport Layer Data are broken into packets and are sent to network layer uses TCP Ensures that packets arrive in sequence without error Transmission Control Protocol It uses positive acknowledgment with re-transmission It automatically resends the data packets if it has not received positive acknowledgment It is connection oriented which means that a connection is required b/w both the devices Re transmits missing packets Re assembles packets in correct order State the function of TCP part of TCP/IP protocol suite ? Allows application to exchange data Establishes and maintain the connection until exchange of data is completed Determines how to break application data into packets and add sequence / packet number to TCP header Sends packets to and accepts packets from the network layer Manages flow control of data to avoid congestion Acknowledges all packets that arrives Detects when a packet has not arrived at destination Handles re-transmission of dropped packets Re-assembles packets in correct order  Network / Internet Layer The Network Layer in the TCP/IP model uses Internet Protocol (IP) to manage data movement. It helps route and forward data across different networks. This layer is responsible for identifying and addressing devices on the network. It ensures data packets are sent to the correct destination across interconnected networks. State the function of Internet Protocol ? Ensures correct routing of packets of data over over the internet. Takes a packet from your transport layer and add its own header Which includes IP address of recipient and sender both Encapsulate data into datagram Passes datagram to the link layer for transmission on the LAN Link Layer The protocol in this layer provides the means for the system to deliver data to the other devices Ethernet Protocol Wifi Protocol Bluetooth Protocol  Concept Of Packets Application Layer SENDER Transport Layer Network Layer Link Layer Application Layer RECEIVER Transport Layer Network Layer Link Layer Describe the purpose of packet header ? To store data about packets And its routing to ensure that it reaches its destination To ensure that message can be properly reconstructed What does TCP protocol header might contain ? To store data about packets And its routing to ensure that it reaches its destination To ensure that message can be properly reconstructed What does IP data packet might contain ? Message Data IP version Size of Packet Sequence Number Protocol Source IP address Destination IP address Bit-Torrent Protocol What does seed 16236 means Peer Computer That has 100 % of file and is uploading downloaded content What is the function of Swarm ? All the connected peer computer that have all or part of the file to be uploaded/ downloaded they share a torrent Who is Tracker ? Central server that stores details of other computers that have all / part of files to be downloaded. Stores IP addresses of other peers in swarm allowing them to connect Who are Leachers ? Peers who download much more data and upload less data negative impact on network Explain how data is exchange using Bit-Torrent ? Torrent file is made available File to be shared is split into pieces Bit-Torrent client software is made available to other peers which allows them to work as seed or leaches A peer can act as a seed and a peer downloading file can get different pieces form other seed simultaneously Once a peer has a piece of a file it can become a seed for the parts downloaded and leaches download much more than they upload. Tracker keep record of all the peers and the parts of the file they have and can pause and restart at any time. Network Model : Peer To Peer Used for : File Sharing Email Communication Which protocols are used in Email Communication ? POP : Post Office Protocol Downloading Email SMTP : Simple Mail Transfer Protocol Sending Email IMAP : Internet Message Access Protocol Downloading Email HTTP : Hypertext Transfer Protocol Accessing email using a browser  Packet Switching Vs Circuit Switching Circuit Switching If third person wants to join he/she would have to wait until one of them hangs up Packet Switching Question : Describe Circuit Switching ? A circuit is established at the start of the communication Between sender and receiver This lasts for the duration of the call / data transfer Then the link that make up the circuit are removed Question : Describe Packet Switching ? A circuit does not have to be established at the start of the communication The data to be sent is divided into packet That can travel along different routes from node to node Packets are reassembled in the correct order at the receiver’s end Must wait until the last packet is received to put the data together Benefits Of Packet Switching Packets can be re-routed if there are problems Packets can take the least congested route transmission error can be detected missing / corrupt packets can be resent Drawbacks Of Packet Switching Packets can be dropped / delayed Real time conversation is not possible  Benefits Of Circuit Switching The person communicating can see each other in real time better synchronization / full bandwidth available Drawbacks Of Circuit Switching Bandwidth / channel not available to other users Extra time required to set up circuit at start of conversation alternative route not available without restarting the conversation Less secure as easier to intercept data if only one channel used failure in single route used means failure of transmission Scenario Based Question a) A large video file is shared ? Packet Switching File is divided into packets and necessary data is added to the packet e.g Header which are sent independently of each other and do not need to take the same route Packets are reassembled at the destination Missing / Corrupt packets can be resent b) Person A and Person B wants to have a video conversation ? Circuit Switching The circuit can easily be set up for the duration of the conversation set up before communication starts maintained throughout the transmission All data travels down the same route Dropped at the end of transmission complete bandwidth used Question : Describe what happens when the LAN transmit data from Computer X to Computer Y using circuit switching Computer X sends a connection request to computer Y If computer Y is busy then Computer X waits and then resends the connection request to Computer Y If available, Computer X sets up path between nodes Computer X sends the data Computer Y sends the receipt signal The sender signals node to deallocate resources Question : Describe what happens when the LAN transmit data from Computer X to Computer Y using Packet switching Message is split into packets Each packet is a fixed size Each packet is given a header Including destination IP, sequence number Packets are forwarded from one LAN to another Packets may take different routes Missing Packets are requested to be resent Packets re-assembled into each order at destination Question : State two problems that could arrive if video conferencing were to use packet switching. Picture and sound not synchronized // real time conversation is not possible. Interruption, data can be delayed by the other computing traffic.  Communication And Network Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Question 8 Question 9 Question 10 Question 11 Question 12 Question 13 Question 14 Question 15 Question 16 Question 17 Question 18 Question 19 Question 20 Question 21 Question 22 Question 23 Question 24 Question 25 Question 26 Question 27 Question 28 Question 29  Answers Answer 1 Answer 2 Answer 3 Answer 4 Answer 5 Answer 6 Answer 7 Answer 8 Answer 9 Answer 10 Answer 11 Answer 12 Answer 13 Answer 14 Answer 15 Answer 16 Answer 17 Answer 18 Answer 19 Answer 20 Answer 21 Answer 22 Answer 23 Answer 24 Answer 25 Answer 26 Answer 27 Answer 28 Answer 29