Web Engineering Notes
Web engineering is way of developing and organising knowledge about Web application development and applying that knowledge to develop Web applications, or to address new requirements or challenges. It is also a way of managing the complexity and diversity of Web applications.
Web engineering is specifically targeted toward the successful development, deployment and maintenance of large, complex Web-based systems.
It advocates a holistic and proactive approach to developing successful Web applications. As more applications migrate to the Web environment and play increasingly significant roles in business, education, healthcare, government, and many day-to-day operations, the need for a Web engineering approach to Web application development will only increase. Further, as we now place greater emphasis on the performance, correctness, and availability of Web-based systems, the development and maintenance process will assume greater significance.
Web engineering has been successfully applied in a number of Web applications. A well engineered Web system is:
• Functionally complete and correct
• Universal accessibility (access by people with different kinds disabilities)
• Perform satisfactorily even under flash and peak loads
• Interoperable with other Web and information systems
Web Engineering is an emerging discipline having both theoretical and practical significance. It is gaining the interest among researchers, developers, academics, and clients. This is evidenced by increased research activities and publications in this area, hosting of dedicated international conferences and workshops, publication of new journals devoted to Web Engineering, and universities offering special courses and programmes on the subject. It is destined for further advancement through research, education, and practice.
SLIP (Serial Line Internet Protocol)
SLIP is a packet framing Protocol, it defines a sequence of characters that frame IP packets on a serial line. It provides no addressing, packet type identification, error detection/correction, or compression mechanisms. It is used for the same purpose as PPP, which is the encapsulation of IP packages over Modem lines. SLIP does not have PPP’s configuration negotiation or Authentication schemes, which can make the configuration of SLIP connections more complicated.
SLIP modifies a standard Internet datagram by appending a special SLIP END character to it, which allows datagrams to be distinguished as separate. SLIP requires a port configuration of 8 data bits, no parity, and EIA or hardware flow control. SLIP does not provide error detection, being reliant on other high-layer protocols for this. Over a particularly error-prone dial-up link therefore, SLIP on its own would not be satisfactory.
It is commonly used on dedicated serial links and dial-up connections that operate at speeds between 1200bps and 19.2Kbps or higher.
PPP (Point-to-Point Protocol)
PPP is designed for simple links which transport packets between two peers. These links provide full-duplex simultaneous bi-directional operation, and are assumed to deliver packets in order. Although PPP is not tied to a particular type of packets it transports, its most common use is the encapsulation of IP packages over Modem lines. Basically, PPP is similar to SLIP, but it has the advantages of not being limited to one type of Protocol it can transport, a configuration negotiation phase at the start of a connection (for determining connection configuration parameters automatically), and the possibility to use standardized Authentication procedures for automated login.
The two authentication schemes supported by PPP are PAP(Password Authentication Protocol) and CHAP(Challenge Handshake Authentication Protocol).
PPP Frame Format:
The following descriptions summarize the PPP frame fields illustrated in Figure:
• Flag—A single byte that indicates the beginning or end of a frame. The flag field consists of the binary sequence 01111110.
• Address—A single byte that contains the binary sequence 11111111, the standard broadcast address. PPP does not assign individual station addresses.
• Control—A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame.
• Protocol—Two bytes that identify the protocol encapsulated in the information field of the frame.
• Data—Zero or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the information field is found by locating the closing flag sequence and allowing 2 bytes for the FCS field. The default maximum length
of the information field is 1,500 bytes. By prior agreement, consenting PPP implementations can use other values for the maximum information field length.
• Frame check sequence (FCS)—Normally 16 bits (2 bytes). By prior agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS for improved error detection.