Practical Data Communications / Edition 2

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Data communication is the movement of encoded data by electronic means. It is the fastest growing segment of the telecommunications industry and is involved in almost every facet of life today. Written by bestselling telecommunications expert Roger Freeman, this updated edition provides a complete overview of data communications and a comprehensive guide to its practical aspects. Both a tutorial and a practical reference for the design and operation of data networks, this is the most comprehensive and detailed book available on data communications.

Emphasizing practical applications rather than theory, this comprehensive tutorial and reference explores this fast growing segment of the telecommunications field with simple explanations, detailed drawings, and step-by-step discussions of each topic.

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Editorial Reviews

From the Publisher
"Among other valued contributions, the book will serve as a single source of this field s specialized acronyms, terminology, basic concepts and practices." (Choice, Vol. 39, No. 5, January 2002)

"...very well written in a style I found easy to read and understand excellent reference.(CVU - The Journal of the ACCU)

A 45-year veteran of telecommunication system design and operation and a prolific writer of technical books about them, Freeman shifts away from the focus of the 1995 first edition to write primarily for information technologists rather than electrical engineers, and emphasizes the software that makes a data circuit work rather than the electrical data signal itself. He discusses generalized data networks and their protocols rather than proprietary systems, and describes the underlying digital network in order to allow readers to take better advantage of services available from the public network. His work provides a tutorial for students or professionals with only a basic understanding of the field. Annotation c. Book News, Inc., Portland, OR (
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Product Details

Meet the Author

ROGER L. FREEMAN is a veteran of more than forty-five years in telecommunication system design and operation. A senior life member of the IEEE, Mr. Freeman is a frequent lecturer and prolific author with more than fifty articles published in international technical journals. His previous Wiley titles include Reference Manual for Telecommunications Engineering, Telecommunication Transmission Handbook, Telecommunication System Engineering, Radio System Design for Telecommunications, and Fundamentals of Telecommunications.

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Read an Excerpt

Chapter 1: The Enterprise Network Enviroment

An enterprise network is a highway that transports data from one user station to another. An enterprise is an entity, which is either government or industry in the broadest interpretation. Examples of government may be the USAF Rome Laboratory or the Scottsdale, AZ, police department. Examples of industry may be Motorola in Schaumberg, IL, the American Red Cross in Washington, DC, or Len's auto repair shop in Warner, NH. Enterprise networks pervade the world. There are two types of enterprise networks: local area networks (LANs) and wide area networks (WANs). The two types differ in coverage area. The local area network, as its name implies, covers a small, restricted area. Commonly, it covers a portion of one floor, the entire floor, many floors, or the whole building; in some cases, there may be workstations in several buildings. A WAN covers a much larger area, from across town to worldwide.

We can liken a LAN to a wide highway but with just one lane, in most cases. It accommodates large vehicles that move very fast. The WAN, on the other hand, is a comparatively narrow-lane highway, often with one lane coming and another going. Its car-handling capacity is notably smaller than that of a LAN. Another major difference between a LAN and a WAN is that an entire LAN has single ownership. It traverses an area that is under one owner, and the LAN is operated for the exclusive benefit of that owner. A WAN traverses comparatively long distances where right-of-way is required, or it traverses over the network of another entity that is in the telecommunication transport business that will carry the connectivity* to the desired distant end. The connectivity could be carried out over a facility owned by the enterprise.

This would be a private network. With the familiar arrangement, the connectivity could be facilitated by the owner's local telephone company or by a long-distance carrier such as Sprint, MCI, France Telecom, or AT & T. An example of a LAN is illustrated in Figure 1.1, and an example of a WAN is shown in Figure 1.2.

The bit rate capacity of a LAN varies from 4 Mbps to 1000 Mbps; for a WAN, from 56/64 kbps to 1.5/2.0 Mbps up to 45 Mbps or greater. The LAN ordinarily is owned by the enterprise. Therefore there are no recurring costs besides maintenance. The WAN customarily involves leasing, commonly from the PSTN or other common carrier. Leasing is a recurring cost, and it increases exponentially with bit rate and more or less linearly with distance. Maintenance is customarily borne by the carrier leasing the circuits to the enterprise. The exception, of course, is when the enterprise can justify a private network. Power companies have private networks.

Often an enterprise will have many LANs. In some cases they may be interconnected by bridges that contain routing software. Some types of LANs have very severe distance limitations, typically Ethernet* LANs. Even with the 2.5-km maximum extension, such a LAN can accommodate hundreds of accesses. As the number of accesses increases, the efficiency of a LAN, especially an Ethernet LAN, decreases. Transactions slow down; and in the case of Ethernet, collisions and backoffs increase. Somewhere between an 18% to 35%o activity factor, transactions will stop and the entire time is spent with collision resolution.

One method to alleviate the situation is to segment the LAN into areas of common community of interest. A bridge connects segments together. For example, the entire accounting department is on one segment; the operations department on another segment; and engineering on a third segment. Traffic intensity inside a segment is high; among segments it is low.

LAN topologies may differ in many respects with PSTN topologies. Two common topologies dominate in the LAN arena: the bus network and the ring network. We hasten to explain that a tree network is just an extension of a bus network. The most elementary network topology is a point-to-point connectivity, which is illustrated in Figure 1.3. An extension of this scheme is the point-to-multipoint or just multipoint connectivity, illustrated in Figure 1.4...

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Table of Contents


The Enterprise Network Environment.

The OSI Model and the Data-Link Layer.

High-Level Data-Link Control (HDLC) Typical-Data Link Layer Protocol.

Data Network Operations.

Data Transmission I.

Data Transmission II.

The Telecommunications Network as a Vehicle for Data Transport.

The Transmission of Data Over the Analog Voice Channel.

Data Communications in the Office Environment -
Part 1.

Data Communications in the Office Environment -
Part 2.

Wide Area Networks (WANs).

Frame Relay.

Integrated Services Digital Networks (ISDNs).

Building and Campus Wiring and Cabling for Data Communications.

Broadband Data Transport Techniques.

Broadband ISDN (B-ISDN) and the Asynchronous Transfer Mode (ATM).

Last-Mile Data Distribution Systems.

Network Management for Enterprise Networks.

Appendix I: Addressing Conventions.

Appendix II: Acronyms and Abbreviations.


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