Structured Network Design Methodology PDIOO

While the roles of a network designer are indeed varied, and different general approaches to network design exist, the entire concept of designing a network is greatly simplified through the use of structured design methodologies. Although it sounds rather fancy, a structured design methodology is really nothing more than a set of distinct steps that help to ensure that all of the necessary tasks in the network design process are completed.

Cisco uses a methodology known as PDIOO as part of designing networks. PDIOO is an acronym that describes some of the major elements in a network design process, namely:

  • Planning
  • Design
  • Implementation
  • Operation
  • Optimization

Instead of concentrating on memorizing these elements, you should instead focus on recognizing them as the key elements to any network design project. More than anything, PDIOO represents a theme that comes up again and again over the course of designing not only a network, but also just about any system you can think of.

For the purpose of designing networks, Cisco recommends an 8-step process that constitutes the structured network design methodology mentioned earlier. Each of these 8 steps represents a specific network design task that much be completed as part of a project. The specific steps involved in any network design project include:

  1. Identifying customer requirements
  2. Identifying and analyzing the current network
  3. Designing network topologies and services
  4. Planning the network implementation
  5. Proof of concept (building pilots or prototypes)
  6. Documenting the network design
  7. Implementing and verifying the network design
  8. Monitoring and revising the network design

Each of these elements is looked at in more detail in upcoming articles.

Advantages and Disadvantages of Different Network Design Approaches

Although a top-down approach is preferred to the bottom-up method, both have associated advantages and disadvantages. The lists below take a look at some of the relative advantages and disadvantages of each method.

Top-down Network Design:

Advantages: Begins with a focus on an organization’s specific goals and requirements for network applications and services, while allowing potential future needs to be considered and accounted for.

Disadvantages: Requires thorough initial needs analysis in order to determine specific requirements, and ensure that all possible applications and services have been considered.

Bottom-up Network Design:

Advantages: Generally a faster approach based on past projects and implementations that works within an existing environment.

Disadvantages: The approach may not take all necessary applications and services into consideration, leading to a design that ultimately may not meet the needs of an organization, and may need to be redesigned in the future.

Network Design Approaches

Two very general approaches exist to developing a network design, known as top-down and bottom-up. In this case, the “down” and “up” being discussed relate to a concept you are already familiar with, namely the OSI model.

The Top-Down Approach

In a top-down approach, a network designer looks at a project starting with the general applications required. In this sense, the term “application” does not necessarily mean things like a web server or Internet Explorer, although they may certainly be factors. Instead, this approach focuses on determining what the goals of the network are from an Application Layer perspective, namely the applications or services required. For example, an organization might want to implement or upgrade a network to support new applications like Voice over IP (VoIP), IP multicasting, and so forth. Along the same lines, the goal of the customer might be to interconnect to a partner network to enable an e-commerce platform. Notice that the top-down approach doesn’t begin by focusing on any particular technical elements. No discussion of Gigabit Ethernet, fiber optic cabling, or routing protocols occurs at this level. Instead, the top-down approach is solution-oriented, focusing on the specific business and technical goals of an organization. Of course technologies do need to be considered, but this typically happens later in the design process.

The Bottom-Up Approach

The alternate approach, known as bottom-up, is more commonly employed, but is far from optimal. Instead of focusing on the applications that drive the need for a new or redesigned network, this approach tends to start lower in the OSI model, worrying about issues like specific technologies, protocols, network media, and so forth. Generally speaking, this is the “stuff” that networking professionals are most familiar with. They have a tendency to begin the design process at this level, leaving applications and services as an afterthought to be considered later. After all, the network won’t do anything without the necessary equipment, or so popular thinking goes. In most cases, taking a bottom-up approach tends to require a less thorough initial analysis, and is easier to implement as a quick fix. Ultimately, however, the bottom-up approach is seldom truly successful, as it tends to rely on a number of fixes along the way in order to deal with issues that were not initially considered.

The Role of the Network Designer

Prior to taking a look at the various tasks involved in designing a network infrastructure, it’s important to be familiar with the role that a network designer or architect plays. Although the exact responsibilities that a network designer will take on for the duration of a specific project can vary based on the size or scope of the undertaking, common themes apply to almost all projects.

Certainly most network designers start their careers on some network engineering-related path; foundation knowledge and hands-on experience in these areas is critical. However, the main goal of a network design professional is to map an organization’s main business and technical goals to a functional network design that meets all stated needs. In some cases this can be a relatively simple undertaking, but in many cases, the process is much more complex. On a typical network design project, the designer handles roles that include needs analysis, data gathering, producing documentation, designing an appropriate solution, overseeing implementation, troubleshooting, verification, and more.

Quite simply, network designers wear many hats; they not only have to be able to effectively determine the true business and technical requirements driving a project, but also deal with a range of non-technical issues including personnel, politics, scheduling, and even “selling” their concept. At the end of the day, however, a good network designer will still be able to roll up their sleeves, get in there, and configure equipment if necessary. Their approach may seem very high-level in some ways, but a thorough understanding of how systems function, interrelate, and are configured is equally crucial.

Changing Image Thumbnail Settings on Windows XP

Windows XP makes it easy to browse through images stored in folders on your system by way of its “thumbnail” view option. When thumbnail view is selected for a folder (by clicking View > Thumbnails in My Computer), Windows XP displays images as miniature thumbnails rather than as traditional file icons, making it easier to differentiate between images.

While thumbnail view makes it easier for most users to sort their pictures, the default thumbnail image size (96 pixels) may be a little too small for some users. If you find yourself squinting at the screen to see thumbnail images, then you should consider increasing XP’s default thumbnail size.

The easiest way to make the switch to a larger size is by using Microsoft’s free Tweak UI PowerToy. After downloading and installing the program, open it and browse to Explorer > Thumbnails. Increase the Thumbnail size to a new larger value like 200 pixels and click OK. After doing this, all folders that you switch to thumbnail view will display thumbnails in this larger size. Note that increasing the thumbnail size results in higher memory and disk space usage.

Changing Mouse Scroll Wheel Settings on Windows XP

Chances are good that the mouse connected to your PC includes a scroll wheel between the right and left mouse buttons. Using the scroll wheel to navigate up and down within programs like Microsoft Work or your web browser is certainly helpful, much easier than grabbing for the vertical scroll bar at the right-hand side of the screen.

While most users are familiar with the purpose of the scroll wheel itself, many don’t realize that the manner in which the wheel performs can actually be customized to better suit one’s needs and preferences. By default, scrolling the wheel will scroll the screen three lines at a time in the direction you specify. This can be changed to a higher number of lines for faster scrolling, or even to a page at a time if that’s your preference.

To change the scroll wheel settings for your mouse, open Control Panel, open the Mouse applet, and then click the Scroll tab. Use the settings on this tab to adjust how your scroll wheel mouse performs to better suit your preferences.

Disable Balloon Messages on Windows XP

Tired of Windows XP displaying those warning balloon messages on your taskbar? While they do help to keep less experienced users a little more informed about the state of their Windows XP system than they might otherwise be, they can get annoying, especially for experienced users who would rather not be disturbed.

As with most system settings, balloon messages can be disabled by a Registry tweak. However, a safer option for most users is to make the change via Microsoft’s free Tweak UI PowerToy instead. To disable balloon messages with this tool, open it and then head to the Taskbar and Start menu section. Uncheck the Enable balloon tips item and click OK to stop these “helpful” balloon messages from bothering you.

Disable Low Disk Space Warning Messages on Windows XP

Running out of hard disk space? When Windows XP detects that a drive has 200 MB or less free disk space left, it begins alerting you to the situation by displaying the following message:

You are running out of disk space on X (where X is the drive letter in question). To free space on this drive by deleting old or unnecessary files, click here.

The “solution” to this problem is obviously to delete unneeded personal files, or uninstall unused programs in a bid to free up space.While the message is there to help, it can also become annoying, especially once you’re aware of the situation. If you want to disable these warnings and keep tabs on your disk space situation as you see fit, then changing one simple setting will get the job done. While the message can be disabled via a Registry edit, a safer option is to use Microsoft’s free Tweak UI PowerToy to make the change.

To disable the low disk space warning with Tweak UI, open the program, click Taskbar and Start menu, uncheck the Warn when low on disk space option, and click OK.

Disable AutoPlay on Windows XP Drives

One of the more annoying “features” of Windows XP is its insistence on launching AutoPlay when you insert or attach certain types of media to your PC, like CD discs or USB thumb drives. While AutoPlay can be temporarily disabled by holding down the Shift key after inserting a CD, for example, you may want to consider disabling the feature completely.

AutoPlay can be disabled via a Registry hack, but an easier method also exists. The free Tweak UI PowerToy from Microsoft makes it easy to disable AutoPlay for the drive letters of your choice at the click of a button. After installing Tweak UI, just expand My Computer > AutoPlay > Drives and uncheck any drive letters for which you want AutoPlay disabled. Click OK and then never worry about being harassed by AutoPlay settings on those drives again. If you change your mind, you can always re-enable AutoPlay by checking the associated driveusing Tweak UI.

Modifying XP’s PATHEXT Variables to Include Saved MMC Files

Windows XP’s Run command provides a quick and easy way for experienced users to open files without the need to navigate through the Start menu or browse folders looking for a file. For example, if you type cmd.exe at the Run command and press Enter, a Command Prompt windows will open. Type msconfig.exe and the System Configuration Utility does the same.

You may also be aware of the fact that its not always necessary to enter certain file extensions when using the Run command. For example, entering just the filename portion of the command – say, cmd rather than cmd.exe – if OK because the EXE file extension is one of those tried by XP when an extension isn’t supplied. XP will attempt to use a number of file extensions when you don’t provide one, as dictated by it’s declared PATHEXT variables.

By default, the following PATHEXT system variables are declared by XP: .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH. One notable one that isn’t present is the .MSC extension used by saved MMC consoles. If you want pre-built consoles like the Services MMC to open without needing to type its full filename – services.msc – at the Run command, then you’ll need to add .MSC to the XP’s PATHEXT variable.

To add a new file extension to XP’s PATHEXT system variable, follow these steps:

1. Open the System applet in Control Panel.

2. Click the Advanced tab, and then click the Environment Variables button.

3. Double-click the PATHEXT variable in the System variables section and then click Edit.

4. After the .WSH entry, type a semi-colon and then type .MSC (no spaces required) and then click OK.

5. Reboot your system and then attempt to open the Services MMC from the Run command by simply typing services and then click OK.