NET 121b: Essentials of Networking

Chapter 1: Basic Networking Concepts

Objectives:

 

This chapter provides an overview of several network concepts. The topics of this chapter are:

1. Networking fundamentals
2. Servers
3. Topologies
4. Network design

Concepts:

A network can be defined as two or more connected computers that share data or other resources.

Networking can also be defined as:

• users sharing resources (like printers or files)
• across a common medium (like copper wire or fiber optic cable)
• by way of specific rules (like TCP/IP or other network protocols).

Some example of kinds of networks are given in the text.

Networks originated with mainframes, which were typically used from terminals that had no computing power of their own. This kind of computing follows the centralized model. All computing is actually done at a central location (the mainframe) not at the terminals. There are several problems with this model: all processing is done at one place, increasing the computing power of the network is expensive, and the programs that run on these networks tend to be expensive custom made programs.

Some critical terms appear in the chapter:

• Server - not just a computer, but the set of hardware and software used to provide a service.
• Client - any entity on the network that requests a service
• Peer - a network entity that may request and provide services simultaneously.
• Workstation - typically, a personal computer that is attached to a network
• Host - any device assigned an IP address on a network (This takes a lot more explanation, but the book does not offer it at this point. It will be explained soon.)

If entities on a network act as peers, then this is Peer-to-Peer Networking. If entities act in strictly defined roles, as either servers or clients, but not as peers, then this is Server-Centric Networking. Most PC networks are this type. A third term, Enterprise Network, is used to describe a network with some characteristics of each of the other two types.

Most new networks follow a client/server model, which is also a distributed computing model. Clients typically perform some or most of the processing on the network, while servers provide services like data storage, instead of providing all the computing power. Client/server networks are typically easier to upgrade, both on the client side and on the server side.

The text mentions two other phrases, used to describe other computing models. Two-tier computing describes a client at the first tier that only formats information for display, and a server at the second tier that performs processing and data storage. Three-tier computing adds a tier in between the client and the server. The new second tier computer accepts a request from the first tier, and turns it into a request that the third tier computer can understand.

The word workstation is used to describe a computer that acts as a client in a client/server network. It may be a computer with a lot of processing power, which increases the ability of users on such a network to work faster and better.

A third kind of networking is referred to as both web-based networking and as collaborative computing. It is not explained in the text. Collaborative computing can only be done by networking. In this scenario, two or more computers share processing tasks, which they cannot do unless they are in a network. An example is the use of multiple computers to analyze radiotelescope data for the Search for Extraterrestrial Intelligence. The software to do so is currently available from the University of California at Berkeley. A more recent example is the Grid.org Research Program, which uses multiple computers for medical research.

A Local Area Network (LAN) covers a small area, like a building or a campus. A Metropolitan Area Network (MAN) covers a city, linking computers at various locations. A Wide Area Network (WAN) covers an area larger than a MAN. This may be a network between cities or countries. A Virtual Local Area Network (VLAN) is a subset of a LAN. It will not be physically separate from the rest of the LAN, but it will work as though is it a different LAN.

A Network Operating System is used to make a network possible, and to manage the network. Several network operating systems are listed, each of which can exist on a hybrid network:

• Novell NetWare
• Microsoft Windows NT, 2000, and 2003
• Macintosh OSX
• UNIX and Linux

Recent information about current offerings can be found on the Novell and Microsoft web sites. Various vendors sell their own versions of UNIX, and each has web presence.

The chapter lists several functions that servers can perfrom on a network. Some of the important ones are:

• Network Fax Service - Sending a print job to a networked fax machine is more efficient than printing an image, scanning it into the fax and sending it to the recipient. It saves steps and is easily available to more users. It also sends a clearer, cleaner image than the older method
• Electronic Mail - The purpose of e-mail is to send messages. Current applications also include viewers, schedulers, and such. Critical features are the ability to present different file formats, and to transport the message based on where the sender and recipient are in the network.
• Print Services - The functions of print services are listed are varied:
  
  • Providing Multiple Access - A printer has, at best, two interfaces for user input. Most companies will not want to buy a printer for each employee. Sharing printers on a network makes much more sense, because you will use one interface (where the network connects to the printer) and any network user may send print jobs to it.
  • Eliminating Device Constraints - Printer cables are required to be rather short. This limits the location of printers. Network cables eliminate this problem, since they can be longer. Networked printers may be located in central areas.
  • Handling and Queuing Simultaneous Requests - Most users will not send print jobs at the same time, but in any large organization simultaneous requests will happen, due to size or workflow. The network stores requests in queues or buffers, and processes them as the printers become ready for new jobs.

Topology is the study of shapes and configuration. Physical topology is the way a network is wired (or wireless-ed?) together. Networks configurations typically fall into one of several configurations:

• Bus - essentially one continuous cable for each segment, as in the examples of coaxial cable
  
  • Easy to install
  • Moderately difficult to reconfigure. This is because it is difficult to add new devices or move existing ones without sufficient room to tap into the bus.
  • Difficult to troubleshoot
  • Units affected by media failure: All
• Star - using hubs with a individual cable radiating away from it for each node
  
  • Moderately difficult to install
  • Easy to reconfigure
  • Easy to troubleshoot
  • Units affected by media failure: One, unless it is the hub, in which case all nodes are affected.
• Ring - like a daisy chain, going from one station to the next and all the way back to the server
  
  • Moderately simple to install
  • More difficult to reconfigure as the number of stations increases.
  • Easy to troubleshoot
  • Units affected by media failure: All
• Mesh - redundant connections, to survive in case one cable link is broken
  
  • Difficult to install
  • Difficult to reconfigure
  • Easy to troubleshoot
  • Units affected by media failure: Few or none
• Hybrid - combination of more than one type, such as a series of bus networks, connected together in a ring, or a combination of networks running different Network Operating Systems.
  
  • Can be Easy or Difficult to install
  • Easy to reconfigure
  • Easy to troubleshoot
  • Units affected by media failure: All, if the central hub fails. One, if a workstation fails.

   

The last topic in the chapter is the role of planning in network design. The idea here is that a good plan takes all the needs of the network into account before the network is built. A good design results from good planning. A bad design will result from lack of planning, and from lack of understanding of networking priciples.