Week 1 Flashcards
Briefly outline the OSI Reference Model for data communications
networks.
OSI is short for Open System Interconnection, an ISO standard for worldwide communications that
defines a networking framework for implementing protocols in seven layers. Control is passed from one layer
to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the
next station and back up the hierarchy.
7 Application Layer Program-to-program communication.
6 Presentation Layer Manages data representation conversions. For example, the Presentation Layer would be
responsible for converting from EBCDIC to ASCII.
5 Session Layer Responsible for establishing and maintaining communications channels. In practice, this layer is often combined with the Transport Layer.
4 Transport Layer Responsible for end-to-end integrity of data transmission.
3 Network Layer Routes data from one node to another.
2 Data Link Layer Responsible for physical passing data from one node to another.
1 Physical Layer Manages putting data onto the network media and taking the data off.
Outline the basic design principles of the
Internet.
- Interoperability. Systems from different vendors using different operating systems and application software must be able to work together. Hence different implementations of the underlying Internet protocols had to be compatible.
- Layering. Internet protocols are designed as a series of layers, with each layer building on the services and capabilities provided by the lower layers. This principle is also the basis of the OSI reference model. However, Internet applications do not fit the OSI model exactly. We do not assume a prior knowledge of networking and the OSI model in this subject and for most purposes the simplified model is adequate when considering the design of an Internet application.
- Simplicity. A major benefit of the layered approach is that at the application level developers are presented with a relatively simple logical view of the data communications process. Thus they are insulated from the complexities of the hardware, different kinds of routers, different kinds of physical networks and network topologies that are present at the physical layer. The IP layer is simple, providing only rules for formatting packets and for addressing. At the next level up, the transport protocols provided service abstractions that applications programmers are then able to easily understand and make use of.
- Uniform Naming and Addressing. The IP layer provides a standard addressing convention that enables each computer or other device connected to the Internet to be uniquely identified by a 32 bit word. The usual way of writing such addresses is as a set of four integers separated by dots; for example 130.194.208.3 is the IP address of a particular host machine at Monash.
- End-to-end protocols. In between the sender of the data and its receiver, the only thing that the network needs to examine is the destination addressed of the packets it must deliver. The actual route taken by a packet is of no particular interest to the sender or the receiver and no data in the packets is processed in any way along the way.
Describe the basic purpose and function of the following network protocols: TCP, UDP, IP, DNS
TCP: Abbreviation of Transmission Control Protocol, and pronounced as separate letters. 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.
UDP: Short for User Datagram Protocol, a connectionless protocol that 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.
IP: Abbreviation of Internet Protocol.. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transport 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.
DNS: Short for Domain Name System (or Service), 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.
Explain what is meant by the World Wide Web.
World Wide Web is a system of Internet servers that support specially formatted documents. The documents are formatted in a language called HTML (HyperText Markup Language) that supports links to
other documents, as well as graphics, audio, and video files. This means you can jump from one document to
another simply by clicking on hot spots.
There are several applications called Web browsers that make it easy to access the World Wide Web; Two of the most popular being Google Chrome and Microsoft’s Internet Explorer.
Why do you think that the number of WWW hosts has grown so quickly?
Until recently Electronic Commerce meant Electronic Data Interchange (EDI) between organisations. Today it often means the communication of information and the carrying out of transactions between businesses, or between a business and a consumer, over the Internet. Generally the Internet application that supports such communication is the World Wide Web. In fact it is the World Wide Web, with its extreme ease of use, which has led to the rapid growth of Internet, based electronic commerce. The impact of the WWW can be compared to that of the railways in the nineteenth century.
Discuss three basic Web protocols.
SSL: Short for Secure Sockets Layer, a protocol developed by Netscape for transmitting private documents via the Internet. SSL works by using a private key to encrypt data that’s transferred over the SSL connection. Both Netscape Navigator and Internet Explorer support SSL, and many Web sites use the protocol to obtain confidential user information, such as credit card numbers.
SMTP: 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.
POP: Short for Post Office Protocol, 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).
IMAP: Short for Internet Message Access Protocol, a protocol for retrieving e-mail messages. Like POP,
IMAP uses SMTP for communication between the e-mail client and server. IMAP was developed at Stanford
University in 1986.
Explain what is meant by an intranet and and extranet.
Intranet: A network based on TCP/IP protocols (an Internet) belonging to an organisation, accessible only by the organisation’s members, employees, or others with authorisation. An intranet’s Web sites look
and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorised access. Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary
protocols.
Extranet: It refers to an intranet that is partially accessible to authorised outsiders. An extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view.
Discuss three ways in which the Internet and the WWW are enabling electronic new commerce applications.
a. The lower cost of communication over the Internet, compared to proprietary private networks means that participation can be cost effective for many more organisations. The more organisations that are connected the Internet, the more opportunities there are for new applications that take advantage of this.
b. The intuitive and familiar user interface provided by Web browsers means that users can come up to speed more quickly. This lowers training costs and reduces employee resistance to participation.
c. Consumers are on-line. The rapidly growing number of private individuals and consumers on-line has created the opportunity for business to consumer electronic commerce.
d. Web enabled applications are generally fairly inexpensive to implement, making participation cost effective for a larger number of organisations.
