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Lesson 5 Bandwidth
Objective Explain how bandwidth is measured and how a client's bandwidth needs are evaluated.

What is bandwidth and how is it measured?

How many visitors come to your web site every day? How many visitors do you expect in the future?
The answers to these questions determine a key decision in network architecture: how much bandwidth to deploy.
Understanding the concept of bandwidth is important because bandwidth affects the performance of a site. Bandwidth is a measure of how much data can pass through a transmission wire in a given amount of time. Think of the communication path as a common water pipe. The size of the pipe determines how much water (traffic) can flow through the pipeline during a specific period of time. Bandwidth is a function not of the size of the copper used in a wire, but its quality. The higher the quality of copper, along with the shielding and filtering circuit used along its length, the higher its "bandwidth". Bandwidth is generally measured in Kbps (thousands of bits per second) or Mbps (millions of bits per second, or megabits per second). When you are making decisions about how much bandwidth to deploy on your e-commerce site, you need to consider the following inputs:
  1. Maximum download time and other performance requirements. You should ask: Is it important that your users get a speedy display of your web page(s), or is it OK for them to wait 5 or 20 seconds on a busy day?
  2. Page size, which includes all files: HTML files, images, and multimedia files. A text file takes up a lot less memory than an image, and a lot less than a video file. The page size is, therefore affected by the material it contains.
  3. Current or projected volume of users. Remember, more users mean more data must
  4. be transmitted.

Planning for later needs

If you expect to see a significant increase in volume of traffic to your web site, you need to plan for a bandwidth solution that can be upgraded without having to replace hardware. The table below can be used as an aid in determining what kind of connection you will need for a given Web site. You should note faster connections, such as OC-12 and OC-48 do exist, but due to cost, these are not typically used for most Web sites.

Connection Speed Cost
Fractional T1 Up to 1.544 Mbps Low
T1 1.544 Mbps Medium
E1 (in Europe) 2.048 Mbps Medium
Fractional T3 Up to 45 Mbps Medium
T3 45 Mbps High
OC-3 (optical fiber) 155.52 Mbps Highest
You may also combine two pipelines (such as two T1s) to meet bandwidth needs. In many cases, two T1s may be preferable to a fractional T3 because they provide redundancy, which means they provide several components that perform the same function, a good thing when trying to avoid problems in network communications: if one component fails, the redundant (or double) takes over, so the communication does not break. Question: How does bandwidth affect the development of a site?
Answer: Bandwidth refers to how much data can pass through a transmission wire in a given amount of time. The amount of bandwidth available will determine how much traffic will be able to flow at any given time.
In the next lesson, you will learn how to evaluate a network's capacity.
Question: How does bandwidth affect the development of a site?
Answer: Bandwidth refers to how much data can pass through a transmission wire in a given amount of time. The amount of bandwidth available will determine how much traffic will be able to flow at any given time.