Chapter 1
How do LANs differ from WANs, and BNs?
A Local Area Network (LAN) is a group of microcomputers or terminals located in the same general area. A Backbone Network (BN) is a large central network that connects most everything on a single company site. A Metropolitan Area Network (MAN) encompasses a city or county area. A Wide Area Network (WAN) spans cities, states, or national boundaries. Typically, MANs and WANs used leased facilities, while LANs and BNs are often located internally in an organization and used owned facilities.
Why are network layers important?
Communication networks are often broken into a series of layers, each of which can be defined separately, to enable vendors to develop software and hardware that can work together in the overall network. These layers enable simplicity in development and also in the comprehension of complex networks. In the end, the strategy of using more simplistic network layers allows vastly different kinds of equipment to be able to have connectivity over a common platform or network, using protocols and standards that are applicable to each narrow slice of the network.
How can data communication networks affect businesses?
Data communication networks can affect businesses by being the foundations for distributed systems in which information system applications are divided among a network of computers. Data communication networks facilitate more efficient use of computers and improve the day-to-day control of a business by providing faster information flow, aiding strategic competitive advantage. They also provide message transfer services to allow computer users to talk to one another via electronic mail.
Discuss three trends in communications and networking.
First, pervasive networking will change how and where we work and with whom we do business. Pervasive networking means that we will have high speed communications networks everywhere, and that virtually any device will be able to communicate with any other device in the world. Prices for these networks will drop and the globalization of world economies will continue to accelerate. Second, the integration of voice, video, and data onto the same networks will greatly simplify networks and enable anyone to access any media at any point. Third, the rise in these pervasive, integrated networks will mean a significant increase the availability of information and new information services. It is likely that application service providers will evolve that act as information utilities.
How many bits (not bytes) are there in a 10 page text document? Hint: There are approximately 350 words on a double-spaced page.
First, some assumptions must be made. Assume each word averages seven letters and there is one space between each word. Next assume we are using 8-bit ASCII. Multiply 350 words by 8 bytes (7 letters plus a space) to get 2,800 bytes per page. Multiply 2,800 by 10 pages to get 28,000 Multiply 28,000 bytes by 8 bits per byte to get 224,000 bits
Describe two important data communications standards-making bodies. How do they differ?
The International Organization for Standardization (ISO) makes technical recommendations about data communication interfaces. The Telecommunications group (ITU-T) is the technical standards-setting organization of the United Nations International Telecommunications Union (ITU). Postal Telephone and Telegraphs (PTTs) are telephone companies outside of the United States. ITU-T establishes recommendations for use by PTTs, other common carriers, and hardware and software vendors. Although a complicated series of acronyms, it is useful to point out that the ISO created the OSI model! Information technology standards contribute to data communications. In the USA, the National Committee for Information Technology Standards (NCITS) has responsibility (under ANSI) for multimedia (MPEG/JPEG), intercommunication among computing devices and information systems (including the Information Infrastructure, SCSI-2 interfaces, Geographic Information Systems), storage media (hard drives, removable cartridges), database (including SQL3), security, and programming languages (such as C++). The NCITS T3 committee on Open Distributed Processing (ODP) is the US Technical Advisory Group (TAG) to JTC 1/SC 6/WG 7 (Subcommittee 6, Workgroup 7). JTC 1 is the ISO/IEC Joint Technical Committee 1 on Information Technology. Among NCITS/T3's current projects are: Abstract Syntax Notation One (ASN.1), the OSI Directory Services (and protocols), routing information exchange protocols, multicasting (all of considerable interest to the telecommunications industry.) T3 has US TAG responsibility for codes and character sets. IEEE plays an important standards role for data communications, particularly in LAN technology protocols. Note that the HTML specifications state that HTML uses the ISO 8859-1 (Latin 1) character set.
How are Internet standards developed?
The Internet Engineering Task Force (IETF; www.ietf.org) sets the standards that govern how much of the Internet will operate. Developing a standard usually takes 1-2 years. Usually, a standard begins as a protocol developed by a vendor. When a protocol is proposed for standardization, IETF forms a working group of technical experts to study it. The working group examines the protocol to identify potential problems and possible extensions and improvements, and then issues a report to IETF. If the report is favorable, the IETF issues a Request for Comment (RFC) that describes the proposed standard and solicits comments from the entire world. Once no additional changes have been identified, it becomes a Proposed Standard. Once at least two vendors have developed software based on it, and it has proven successful in operation, the Proposed Standard is changed to a Draft Standard. This is usually the final specification, although some protocols have been elevated to Internet Standards, which usually signifies a mature standard not likely to change. There is a correlation of IETF RFCs to ISO standards.
Why has the Internet model replaced the OSI model?
The Internet model is simpler (effectively collapsing the top three layers of the OSI model into a single model) and easier to remember and understand. Further, the ISO OSI Reference Model is the result of a formal standardization process and is technical in its presentation. By contrast, the Internet model is appropriate for those within the networking community with practical needs related to implementing the Internet and networking. However, only a few years ago the Internet model was commonly understood to have only four layers. Today, the transport layer is now separately identified in the Internet model, yielding an important, fifth layer for comprehension. This evolution in presentation may show that at least one technical distinction from the OSI model is now considered practical as the scope, volume of traffic, and complexity of networking (and of the Internet) grows.
What is a server?
The server stores data or software that can be accessed by the clients, or remote users of a hardware input or output device. In client-server computing, several servers may work together over the network to support the business application.
What is the purpose of a data communications standard?
The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time. The software or hardware defined by the standard at one network layer can be easily updated, as long as the interface between that layer and the ones around it remains unchanged.
Discuss three important applications of data communication networks in business and personal use.
Three important applications of data communication networks in business and personal use include email, videoconferencing, and the Internet.
In the 1980s, when we wrote the first edition of this book, there were many, many more protocols in common use at the data link, network, and transport layers than there are today. Why do you think the number of commonly used protocols at these layers has declined? Do you think this trend will continue? What are the implications for those who design and operate networks?
Today there is convergence around the non-proprietary use of TCP/IP as the protocol of choice for all networks. For the most part, network software is designed to interface with networks using this protocol. By non-proprietary, this means that TCP/IP is an interoperable protocol portable to any manufacturer's hardware. All manufacturers are developing their products to use TCP/IP as their protocol of choice. This is of great benefit for those operating networks because they do not have to deal with the incompatibilities of various proprietary networks. In the past, network equipment such as IBM's SNA and Novell's Netware products had retained proprietary protocols that did not interface with as much ease as today's more compatible and TCP/IP based products. The decline of the number of competing protocols is related to the emergence of TCP/IP as the universal connector, along with the rise in competition and subsequently better price availability from those vendors who market to this protocol, thus ensuring the viability of this standard for a long time to come for network managers.
What are three of the largest inter-exchange carriers (IXCs) in North America?
Two of the largest inter-exchange carriers (IXCs) in North America are AT&T and Sprint, and the formerly large MCI was acquired in a post bankruptcy merger with Verizon.
Describe the seven layers in the OSI network model and what they do.
The application layer is the application software used by the network user. The presentation layer formats the data for presentation to the user by accommodating different interfaces on different terminals or computers so the application program need not worry about them. The session layer is responsible for initiating, maintaining, and terminating each logical session between end users. The transport layer deals with end-to-end issues, such as procedures for entering and departing from the network, by establishing, maintaining, and terminating logical connections for the transfer of data between the original sender and the final destination of the message. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer. The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).
Describe the five layers in the Internet network model and what they do.
The application layer is the application software used by the network user. The transport layer deals with end-to-end issues, such as procedures for entering and departing from the network, by establishing, maintaining, and terminating logical connections for the transfer of data between the original sender and the final destination of the message. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer. The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).
Explain how a message is transmitted from one computer to another using layers.
The application layer is the application software used by the network user. The transport layer is responsible for obtaining the address of the end user (if needed), breaking a large data transmission into smaller packets (if needed), ensuring that all the packets have been received, eliminating duplicate packets, and performing flow control to ensure that no computer is overwhelmed by the number of messages it receives. The network layer takes the message generated by the application layer and if necessary, breaks it into several smaller messages. It then addresses the message(s) and determines their route through the network, and records message accounting information before passing it to the data link layer. The data link layer formats the message to indicate where it starts and ends, decides when to transmit it over the physical media, and detects and corrects any errors that occur in transmission. The physical layer is the physical connection between the sender and receiver, including the hardware devices (e.g., computers, terminals, and modems) and physical media (e.g., cables, and satellites).
The number of standardized protocols in use at the application layer has significantly increased from the 1980s to today. Why? Do you think this trend will continue? What are the implications for those who design and operate networks?
The biggest reason that there are more standardized protocols at the application layer is related to the predominant use of the Web and its standardized graphic interface (HTTP, DHCP, for example). In a way, many new protocols ride on top of TCP/IP networks, and some of these new protocols have been developed to enable the retrofitting of new technologies on top of an older networking architecture. On the other hand some proprietary protocols connected with such models as IBM's SNA and DECNet have declined in significance while the importance of Internet-related protocols has grown,
What is a circuit?
The circuit is the pathway through which the messages travel. It can be made up of a copper wire, although fiber optic cable and wireless transmission are becoming more common. A circuit can also pass across many types of physical facilities such as copper wire or fiber optic cable, but the single end-to-end connection, no matter what the equipment, is referred to as the circuit. There are many devices along the circuit's path that perform special functions such as hubs, switches, routers, and gateways.
What is a client?
The client is the input or output hardware device at the other end of a communication circuit. It typically provides remote users with access to the network and the data and software on the server.
Describe the three stages of standardization.
The formal standardization process has three stages: specification, identification of choices, and acceptance. The specification stage consists of developing a nomenclature and identifying the problems to be addressed. In the identification of choices stage, those working on the standard identify the various solutions and choose the optimum solution from among the alternatives. Acceptance, which is the most difficult stage, consists of defining the solution and getting recognized industry leaders to agree on a single, uniform solution. ISO standards development is pursued at the national and international levels. Authorized national technical committees can be designated as Technical Advisory Groups (TAGs) to international subcommittees or workgroups.
