Protocols

What is a Protocols???

• Protocols define how messages are sent and received.

• A set of rules that defines how data is formatted and processed on a network.

Types of Protocols

• TCP/IP• HTTP• FTP• SMTP

Internet Protocol• Internet Protocol (IP) is the principal

communications protocol in the Internet Protocol Suite for relaying datagram across network boundaries.

• In other words, it is a set of rules used to send and receive messages at the Internet address level.

• IP provides the method of distributing data in packets, can distribute packets to a destination via different routes, and can handle congestion in this manner.

Transmission Control Protocol

• The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocols suite (IP), and is so common that the entire suite is often called TCP/IP.

• TCP provides for virtual circuits, error detection and correction, automatic repeat requests, and other reliable end-to-end communications, using the IP protocol for transmission

• TCP handles reassembling packets at the destination, as they can arrive out of order due to the IP routing scheme to avoid congestion.

• TCP/IP together provide for the most commonly used functions on the internet, namely e-mail, file transfer, and the basis of the HTTP protocol for web page documents.

TCP Ports:

Hypertext Transfer Protocol

• The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.

• Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text. HTTP is the protocol to exchange or transfer hypertext.

Working of HTTP

File Transfer Protocol

• File Transfer Protocol (FTP) is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet.

• A typical FTP session operates using two channels: a command (or control) channel and a data channel.

• Command channel --transmitting commands and replies to those commands (Port 21)

• Data channel --transferring data.  (Port 20)

FTP Modes• Two modes that FTP can run in:– Active FTP– Passive FTP

Active FTP

• A user connects from a random port on a file transfer client to port 21 on the server. It sends the PORT command, specifying what client-side port the server should connect to. This port will be used later on for the data channel and is different from the port used in this step for the command channel.

• The server connects from port 20 to the client port designated for the data channel. Once connection is established, file transfers are then made through these client and server ports.

Passive FTP

• The client connects from a random port to port 21 on the server and issues the PASV command. The server replies, indicating which (random) port it has opened for data transfer. 

• The client connects from another random port to the random port specified in the server's response. Once connection is established, data transfers are made through these client and server ports.

Active Vs. Passive FTP

Simple Mail Transfer Protocol

• Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. 

• SMTP uses TCP port 25.

WEB PORTAL

• A web portal is most often one specially-designed Web page at a website which brings information together from diverse sources in a uniform way.

• In other words, a website or service that offers a broad array of resources and services, such as e-mail, forums, search engines, and online-shopping malls.

• Usually, each information source gets its dedicated area on the page for displaying information; often, the user can configure which ones to display.

Types of Web Portals

Domain Name System

• The Domain Name System (DNS) is an hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.

• It associates various information with domain names assigned to each of the participating entities.

• rarely do applications deal directly with IP addresses

• top level domains: edu, com, gov, org, net, …• hostname.domain_name.top_level _domain

e.g., csc.liv.ac.uk

DNS (Continue…)

Host numberThe part of the IP address that specifies a particular host (machine) on the network.

Domain nameThe specifies a specific organization or group.

Top-level domain (TLD)The last section of a domain name that specifies the type of organization or its country of origin.

SEARCH ENGINES

• Search Engines are basically a type of program that uses keywords to search for documents that relate to these keywords and then puts the results found in the order of relevance to the topic that was searched for.

• Examples:– Google– Alta Vista

Importance• Search engines are important because with over 8

billion web pages available, it would be impossible to search for the information that is specifically needed.

• That is why search engines are used to filter the information that is on the internet and transform it into results that each individual can easily access and use within the matter of seconds.

Types of Search Engines

• Crawler based search engines (e.g.: Google, Yahoo, Ask.com)

• Directories (e.g.: dmoz.org, Yahoo.com)• Specialty search engines (e.g.: Askjeeves)• Hybrid search engines (e.g.: Yahoo.com)• Meta search engine (e.g.: Metacrawler)

WEB Browsers

• A web browser is a software application for retrieving, presenting, and passing over information resources on the World Wide Web.

• In other words, it is an software application to access information provided by web browsers.

• It brings information resources to the user.

• Retrieve, present, and traverse information resources on the WWW.

Famous Web Browsers

• Internet Explorer• Mozilla Firefox• Safari• Opera• Google Chrome