Communications Protocol

• All communications between devices require that the

devices agree on the format of the data. The set of rules defining a format is called a protocol. At the very least, a communications protocol must define the following:

• rate of transmission (in baud or bps) • whether transmission is to be

synchronous or asynchronous • whether data is to be transmitted in

half-duplex or full-duplex mode • In addition, protocols can include sophisticated

techniques for detecting and recovering from transmission errors and for encoding and decoding data.

TCP/IP Model1-25-06

LayerName

CommonComponents

OSI Reference

Application HTTP, SMTP, POP3FTP, DNS

ApplicationPresentationSession

Transport TCP, UDP Transport

Network IP, ICMP Network

Physical Ethernet, FDDI Data LinkPhysical

TCP/IP Protocols

• Hypertext Transfer Protocol (HTTP)– Web servers implement this protocol. Short

for HyperText Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.

TCP/IP Protocols

• Simple Mail Transfer Protocol (SMTP)– Used by e-mail servers (and sometimes Web servers)

to send e-mail. Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.

TCP/IP Protocols

• Post Office Protocol Version 3 (POP3)– A protocol used to retrieve e-mail from a mail server.

Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).

– There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.

TCP/IP Protocols

• IMAP - Short for Internet Message Access Protocol, a protocol for retrieving e-mail messages. The latest version, IMAP4, is similar to POP3 but supports some additional features. For example, with IMAP4, you can search through your e-mail messages for keywords while the messages are still on mail server. You can then choose which messages to download to your machine.

• IMAP was developed at Stanford University in 1986.

TCP/IP Protocols• File Transfer Protocol (FTP)

– The protocol for exchanging files over the Internet. FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser and SMTP for transferring electronic mail across the Internet in that, like these technologies, FTP uses the Internet's TCP/IP protocols to enable data transfer.

– FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server).

• DNS– Short for Domain Name System (or Service or

Server), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

– The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

TCP/IP Protocols

TCP/IP Protocols

Transmission Control Protocol (TCP)– Creates a reliable connection between two

computers. TCP is one of the main protocols in TCP/IP networks. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

• Internet Protocol (IP)– Provides addressing scheme.. IP specifies the format of packets,

also called datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transmission Control Protocol (TCP), which establishes a virtual connection between a destination and a source.

– IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time.

– The current version of IP is IPv4. A new version, called IPv6 or IPng, is under development.

TCP/IP Protocols

• Internet Control Message Protocol (ICMP)– Provides error messages. an extension to the Internet

Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The PING command, for example, uses ICMP to test an Internet connection.

– RFC - Short for Request for Comments, a series of notes about the Internet, started in 1969.An Internet Document can be submitted to the IETF by anyone, but the IETF decides if the document becomes an RFC. Eventually, if it gains enough interest, it may evolve into an Internet standard.

TCP/IP Protocols

TCP/IP Protocols

• User Datagram Protocol (UDP)– Does not establish a connection, just sends

messages.

– a connectionless protocol that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP provides very few error recovery services, offering instead a direct way to send and receive datagrams over an IP network. It's used primarily for broadcasting messages over a network.

Connecting Your LAN to the Internet

• Your ISP connects to the Internet

• A WAN connection is used between your building and the ISP

• A T-Carrier connection is often used– A digital connection for voice and data

Common T-Carrier Connections

Other ways to Connect to the Internet

• Integrated services digital network (ISDN)– Dial-up access– Basic Rate Interface (BRI) up to 128 Kbps– Primary Rate Interface (PRI) up to 1.544 Mbps

• Digital Subscriber Line (DSL)– Often differing speeds for uploads and downloads– Depending on type, up to 6.1 Mbps for downloads

and 1.544 Mbps for uploads• Cable Modem

– Shared access cable provided by cable TV company With the addition of users in the area transfer speeds will be reduced.

Web Hosting Solutions

• Standard hosting– Your site resides on the same computer with many

other sites– Cheapest solution

• Dedicated server– You have a server that only you use

• Co-location– Your own server is physically located at the company

that does your Web hosting

Web BrowsersBrowser Wars

• A software application used to locate and display Web pages. The two most popular browsers are Netscape Navigator and Microsoft Internet Explorer. Both of these are graphical browsers, which means that they can display graphics as well as text. In addition, most modern browsers can present multimedia information, including sound and video, though they require plug-ins for some formats.

Web BrowsersNetscape

• The creation• Netscape Navigator was developed by the team

who had created the Mosaic web browser at the National Center for Supercomputing Applications. The company they created was initially named "Mosaic Communications Corporation" and their web browser "Mosaic", but a legal challenge from NCSA over the rights to the name resulted in the company and the product being renamed. The name "Netscape" was invented by sales representative Greg Sands.

Web BrowsersMosaic Netscape 0.9

Web BrowsersNetscape

• Release history• Mosaic Netscape 0.9 – October 13, 1994 • Netscape Navigator 1.0 – December 15, 1994 • Netscape Navigator 1.1 • Netscape Navigator 1.22 • Netscape Navigator 2.0 – September 18, 1995 • Netscape Navigator 2.01 • Netscape Navigator 2.02 • Netscape Navigator 3.0 – August 19, 1996 • Netscape Navigator 3.01 • Netscape Navigator 3.02 • Netscape Navigator 3.03 • Netscape Navigator 3.04 – October 4, 1997 • Netscape Navigator 4.0 – June 1997

Web BrowsersNetscape

The rise of Netscape• When the consumer internet revolution arrived in

the mid to late 1990s, Netscape was well positioned to take advantage of it. With a good mix of features and an attractive licensing scheme that allowed free use for non-commercial purposes, the Netscape browser soon became the de facto standard, particularly on the Windows platform.

Web BrowsersNetscape

The fall of Netscape • Microsoft saw Netscape's success as a clear

threat to the dominant status of the Microsoft Windows operating system. It began a wide-reaching campaign to establish control over the browser market. Browser market share, it was reasoned, leads to control over internet standards, and that in turn would provide the opportunity to sell software and services. Microsoft licensed the Mosaic source code from Spyglass, Inc., an offshoot of the University of Illinois, and turned it into Internet Explorer.

Web BrowsersNetscape

• The resulting battle between the two companies became known as the browser wars. Versions of IE were markedly inferior to contemporary versions of Netscape Navigator; IE 3.0 (1996) began to catch up to its competition; IE 4.0 (1997) was the first version that looked to have Netscape beaten, and IE 5.0 (1998) with many bug fixes and stability improvements saw Navigator's marketshare plummet below IE for the first time.

Web BrowsersNetscape

• In March 1998, Netscape released most of the code base for Communicator under an open source license. The product named Netscape 5, which was intended to be the result, was never released, as managers decided that the code needed a complete rewrite. This product, taking growing contributions from the open-source community, was dubbed Mozilla, once the codename of the original Netscape Navigator. Netscape programmers gave Mozilla a different GUI and released it as Netscape 6 and later Netscape 7. After a lengthy public beta, Mozilla 1.0 was released on June 5, 2002. The same code base, most notably the Gecko layout engine, became the basis of several standalone applications, including Firefox and Thunderbird.

• These products, however, came too late for Netscape as a business. Eventually Microsoft emerged victorious in the browser wars, and Netscape was acquired in 1999 by AOL.

Web BrowsersInternet Explorer

• Internet Explorer 3 was the first major browser with Cascading Style Sheets (CSS) support released in August, 1996 and it could handle the PICS system for content metadata. The improvements were significant, compared to its main competitor at the time, Netscape Navigator.

Web BrowsersInternet Explorer

• The browser was not widely used until version 4, which was released in October 1997 and was integrated with the Windows 98 operating system. This integration, however, was subject to numerous criticisms (see United States v. Microsoft). Version 5, released in September 1998, was another significant release that supported bi-directional text, ruby characters, XML and XSL.

Web BrowsersInternet Explorer

• Version 6 was released on August 27, 2001, a few weeks before Windows XP. This version included DHTML enhancements, content restricted inline frames, and better support of CSS level 1, DOM level 1 and SMIL 2.0. The MSXML engine was also updated to version 3.0. Other new features included a new version of the IEAK, Media bar, Windows Messenger integration, fault collection, automatic image resizing, P3P, and a new look-and-feel that is in line with the style of Windows XP

• For version 7.0 of Internet Explorer, set to ship with Windows Vista and as a separate download for Windows XP with Service Pack 2, large amounts of the architecture, including the security framework, have been completely overhauled. Partly as a result of these security enhancements, the browser will be a stand-alone application, rather than integrated with the Windows shell, and it will no longer be capable of acting as a file browser. The "beta 1" (build 5112) and "beta 2 preview" (build 5299) pre-releases both operate in this new stand-alone manner.

Web BrowsersInternet Explorer

Web BrowsersDeveloping Web sites For

• Browsers have been criticized for implementing non-standard HTML markup extensions such as the BLINK tag, which is sometimes referred to as a symbol for Netscape's urge to develop extensions not standardized by the W3C, and even mentioned in the fictional Book of Mozilla. Both IE and Netscape have also been criticized for following actual web standards poorly, often lagging behind or supporting them very poorly or even incorrectly. This criticism wasn't very loud during the days of its popularity as web masters then often simply developed for Netscape Navigator, but came to be an increasing annoyance to webmasters who wish to provide backward and cross-browser compatibility. Today, many web masters still struggle with cross-browser compatibility do not choose to support old versions, due to their poor and invalid web standard implementations.