INTERNET & WORLD WIDE WEB (UNIT-1) MECHANISM OF INTERNET 1. INTRODUCTION Hello friends are topic is Internet and World Wide Web the most popular services of our topic is social networking and online shopping today we are going to discuss Internet mechanism in this we will discuss Data transmission mechanism Data processing Security over network Working model of E-Mail 2. DATA TRANSMISSION MECHANISM Data transmission mechanism Internet layer TCP IP Internet layer TCP IP comprises of 5 intermediate layers Physical layer Data link layer Network layer Transport layer Application layer TCP IP layer communicate with each other from top to bottom and bottom to top by the help of interfaces coming from the top layer and going to the bottom layer then it is called services and if information is going from bottom to top then it is called Information. 1
Physical Layer Physical layer transmit data in form of Bits over a physical medium that defines the method of Transmission for devices. The physical layer receives the data from upper layer that is called data link layer. At physical layer data is converted in form of bits and these bits were transmitted over transmission medium these transmission medium are cables and transmitted to the sender, sender receives the data from transmission and convert it back into bits. Characteristics of Physical Layer Responsible for data transfer from source to destination. Representation of bits by encoding into signals. Physical layer comprises of devices and cables it is responsible for converting data inform of Signals and this conversion is called encoding at the receiver end when data is received inform of signals decoded and converted into bits Data Link Layer Framing: Divides the data received from the network layer into data units called frames. Physical Addressing: This layer adds a header to the frame. Header defines the physical address of the sender and receiver of the frame. At data link layer data is converted into frames. These frames were transmitted to lower layer that is physical layer. Physical layer convert data into bits and it is also responsible for converting into Signals and transmitted to transmission medium Physical addressing is also done at data link layer by adding header and trailer, Data link adds 2 header first source address and second destination address and that the trailer it uses data recovery techniques data traversal with header and trailer in the diagram data is coming from network services data link layer as a header and trailer and transmit the data to the physical layer, physical layer is 2
responsible for conversion of data in form of bits whereas conversion of data at Data Link Layer is in form of frames. 3. DATA TRANSMISSION Nodes / Computers connected in a network Physical address of each node Data with Header and Trailer I would like to share that all the computers connected in a network. Each computer have a physical address and data is transmitted from one to another means from source to destination.in this diagram computer having physical address 10 want to communicate with the computer having physical address 87 at data link layer header part contain source address as well as destination address and the data part with the trail node T2 trailer contain recovery technique network layer receives message and convert it into packets at header as logical address of receiver address of router.at network layer the data is coming from the upper layer that is transport layer. Network layer also add a header which contain logical address of the receiver and sender now it sends the data to data link layer where converted into frames data link layer send the frame to lower layer that is physical layer which converts data into bits, these bits were transmitted to the cables in form of signals. data transmission with logical addresses, In this diagram I would like to share that the computer having physical address 10 and logical address A wants to communicate with computer having physical address 95 and logical address P. At this layer data is attached with 2 header first one the source address and second one is the destination address Source address with a Logical address destination with logical address these logical address were added by the network layer and trail bit. Trail bit is responsible for data recovery. Data is transmitted over the network, the logical address of a router to collect the data and send it to the address having the logical address P and physical address 95. 3
Transport Layer The transport layer is responsible for delivery of message from one process to another. Transport Layer receives the data from application layer it adds its own header which called ports and transmit it again to its lower layer network layer. 4. DATA PROCESSING AT SENDER AND RECEIVER Data processing at sender and receiver, sender A wants to communicate with the receiver P here in this example a sends data to the application layer. Application layer convert data into segments these segment converted into packets and these packets were transmitted inform of bits and signal. Application the application layer is responsible for providing services to the user. User directly interacts with applications in this example I would like to show SMTP telnet and http are the user interaction part. SMTP (Simple mail transfer protocol) is used for sending e-mails. Telnet is used for remote login and HTTP (Hyper Text Transfer Protocol) is used for browsing. The applicationlayer converts the data in messages and transfers it to the next layer that is Transport Layer. Quick Look at Layers The application layer: allow access to network resources. Transport Layer: to provide reliable process to process message delivery and error recovery Network layer: To move packets from source to destination to provide internetworking Data link Layer: To organize bits into frames, to provide Hop-Hop delivery. Physical layer: to transmit bits over medium, to provide mechanical and electrical specifications 4
5. SECURITY OVER NETWORK Security over network what is security prevention from unauthorised access is called security. Who need security? Financial Institutions and banks Everyone on Internet Banks and Financial Institutes holds are personal data, So they need to be secured and our data on Internet should be secured. TCP Hijacking: Prevention by Authentication Packet sniffing: Prevention by Encryption (SSL, HTTPS) TCP Hijacking is a technique used by hackers, So prevention is by authentication only authenticated users can access the data by providing passwords. Packet sniffing prevention by encryption data should be encrypted so that no hacker can access the data. The Encryption techniques are https or SSL. SSL or HTTPS is the certificate given by the authority TCP Hijacking in this diagram I would like to share that a communication is established between 2 users a hijacker look at the communication link and hijack the data and send it to sender to prevent from hijacking the authentication mode is required. The authentication mode is done at user end. Packet Sniffing: With the packet sniffing we can prevent or protect our self by selecting secure applications like if you re browsing website http. Bankname.com instead of using http we should use https as a secure network Packet Sniffing is blocked by the services Http over SSL during online shopping with credit cards. While doing shopping using credit card we should use the secure connection https or FTPS. 5
6. WORKING OF E-MAIL E-Mail is an Electronic Mail Sending data / information in secure manner from one location to another Now a day s email is very popular we all use e-mail services of Internet and due to this our topic is also popular. User Agent (UA) Message Transfer Agent (MTA) Message Access Agent (MAA) Messaging Protocols (SMTP and POP) Multipurpose Internet Mail Extension (MIME) Structure of E-Mail Message Header MIME Header Message Body Message header contain sender address, receiver address time of sending message, time of receiving message mime header contains the information about text image or any other audio-video attached e-mail message body contain only the part of text or image or audio or video message access agent simple mail transfer protocol SMTP post office protocol POP works on application layer of TCP model SMTP protocol is used for sending mails it works on port number 110 and post office protocol is used for receiving mail now a days the version of POP is POP3 it works on layer of TCP model multipurpose Internet mail extension it is a supplementary protocol allows non ASCII data to be sent through e-mail it is a supplementary protocol of TCP IP it allows users to send text images videos and graphics user agent Scenario 1: when sender and receiver of an e-mail are on same email server we need only two user agents message 8 bit message 7 bit message 1 bit for address I this scenario I would like to show you that two persons ALICE and BOB want to communicate with the help of Email. A mail server is between for the communication user agent is an application which works under email a mail server maintain the queue of email. E-mail header contains sender address, receivers address date time with IP address of the network that is a logical address. 6
MIME header contains MIME version contains type content transfer content ID. An email body content text, image, video or audio. If sender attached an image or audio or video then MIME header automatically convert its content type by encoding the content type once email is transferred to the next layer that is physical layer the physical layer converted into bits and send it to the receiver. 7. SUMMARY Hello viewers to conclude this unit we have discussed about TCP / IP protocols, Layers that are physical layer network layer transport layer data link layer and presentation layer. We have also discussed about e- mails sending and receiving of data from sender end to receiver end we have also discussed about the harder part of the email and in the end we discuss about MIME header, hope you must have enjoyed the lecture thank you. 7