Internet Bandwidth – How Much is Enough?

What is bandwidth?

Bandwidth refers to the amount of information that can be carried in a given time period (usually a second) over a wired or wireless communication link. In digital systems, bandwidth is expressed as bits per second (bps). For example, a modem that runs at 56,000 bps has twice the bandwidth of a modem that runs at 28,800 bps. The higher the bandwidth, the more data can be transferred in bits per second. A good analogy is to think of your Internet connection as a pipe. The term bandwidth describes the diameter of the pipe and how much water (data) can flow through it. If you don’t have enough available bandwidth, then the pipe becomes clogged and data does not flow properly.

Available bandwidth becomes very important when you’re running servers for web-delivery platforms.If data does not flow fast enough or freely enough, the performance of internet will suffer and the end user may see error messages. But what if your equipment and network do meet or even exceed system requirements and the performance of internet is still very slow?

Bandwidth bottlenecks

A communication path for information that travels to and from your location and internet location is typically made up of several communication links, each with its own bandwidth. If one of these communication links is much slower than the rest, it is a bandwidth bottleneck. A bottleneck results in data transmission delays. Delays typically occur when bandwidth cannot support the amount of information being relayed at the speed it is being processed. Data cannot flow through the pipe fast enough. If data cannot flow through the pipe fast enough, internet will run very slowly and web pages will take a long time to load.

Because the lowest bandwidth at all communication links dictates your effective, available bandwidth, you may have less available bandwidth than you think.

Have you taken a close look at your actual network capacity and performance? The following variables affect your network performance and available bandwidth:
Proxy servers and caching
Firewalls and content filtering
Using daisy chain hubs instead of switches
Quality of bandwidth provided by your Internet Service Provider
But I have plenty of bandwidth! Are you sure the amount of bandwidth you think you have is really what is available? Let’s take a look at a case study at one school. The school connects to the District Technology Center, which has an OC3 connection to the Internet. The connection speed of an OC3 connection is 155.52 Mbps (megabits per second). The network administrator wants to connect 50 workstations to web server simultaneously. The administrator knows that web server requires an average data transfer speed of 40 kbps (kilobits per second) for each workstation connecting simultaneously. The administrator does the math and believes he has more than enough bandwidth to run web server and internet on 50 workstations simultaneously:

1. The administrator converts the unit of measurement for data transfer speed from Mbps to Kbps: 155.52 Mbps is equal to 159,252 Kbps.
2. The administrator divides the Kbps transfer speed by the number of workstations to get the data transfer speed available for each workstation: 159,252/50 = 3,185 Kbps available per workstation. It looks like the school has more than enough bandwidth to run 50 workstations simultaneously; 3,185 Kbps is available for each workstation when only an average of 40 Kbps is required. But does the school really have enough

A closer look

Let’s take a closer look.
The lowest bandwidth at all communication points dictates your effective bandwidth—the bandwidth you actually have available to run web server. Although the school has an OC3 (155.52 Mbps) connection from the District Technology Center to the Internet, the connection from the school to the Technology Center is a T1 connection, which only connects at a speed of 1.544 Mbps.

The T1 connection reduces the available bandwidth to 1.544 Mbps, or 1,581 Kbps (1.544 Mbps = 1,581 Kbps). The T1 connection from the school to the Technology Center is already being 60% utilized without running web server. Approximately 949 Kbps of the 1,581 Kbps total is already being used. This reduces bandwidth available for web server from 1,581 Kbps to 632 Kbps. Subtract utilized bandwidth from the total bandwidth: 1,581 Kbps – 949 Kbps = 632 Kbps available The school’s network has half-duplex hub architecture, which further delays the transmission of data. Why? A hub is a device that connects segments of a network. It can transmit or receive data, but it can’t do both simultaneously. Data can only flow in one direction at a time, which greatly reduces throughput, or the rate at which data can be transferred. With less than 632 Kbps of bandwidth available, and 40 Kbps calculated for each simultaneous workstation connection, the school can only run about 15 workstations simultaneously — not 50: 632 Kbps/40 Kbps = 15 workstations The calculation of 15 workstations doesn’t include the effects of using half-duplex hubs, which reduce throughput because data can only flow in one direction at a time. Therefore, an estimated range for the number of workstations can effectively run web server is 10 to 14.

Bandwidth solutions

After consulting with one of internet Field Engineers, here’s what the network administrator did to increase the school’s available bandwidth and the number of workstations they could run simultaneously:
The administrator made sure that the school’s network and computers met all of the system requirements to run web server.
The school was using filtering software, which slowed the delivery of data from internet. The administrator reconfigured the content filtering system to trust all content from the domain.
The administrator disabled the caching of web pages at the proxy server so that users would receive dynamic, current content at all times.
The administrator reduced the utilization of the T1 connection from the school to the District Technology Center by no longer allowing students to surf the Internet or run non-essential applications when web server classes were in session.
The administrator installed 100 Mbps switches instead of using passive daisy chain hubs. A switch is a device that routes data between network segments, and it allows data to flow both ways. Data can be transmitted and received at the same time.

What are web server client system requirements?

In general, we recommends 1.2 Mbps of available bandwidth for every 40 workstations that connect simultaneously to web-delivery platforms. Most internet require an average connection of 40 Kbps per workstation; Normal internet client requires 128 Kbps per workstation. The following guidelines for bandwidth requirements are for concurrent users at one location:

Do your home users need DSL or cable?

Before you have students connect to servers web-delivery platforms from home, find out if they have a dialup modem. Analog, dialup modems utilize nearly the full bandwidth of the present day phone system. A speed of 33.6 Kbps is pushing the speed limit of the current analog phone system. Many users who have 28.8 or 33.6 Kbps modems will never achieve connections at those rates due to phone line conditions. Many phone connections do not support speeds this high, so buying a 56K modem may not bring substantial improvement. A connection speed of 28.8 Kbps is not fast enough to run internet at a satisfactory performance level. Most internet require an average connection speed of 40 Kbps. internet client requires a 128 Kbps minimum connection speed – a speed much faster than a dialup modem can reach. For these reasons, students who are home users may need a DSL or cable Internet connection instead of a dialup modem to run internet. DSL and cable Internet connections are capable of much higher data transmission speeds than a modem and telephone line.

Find your connection type and speed

How fast is fast? This chart puts into perspective line speeds used in Internet backbones, LANs, and WANs. Find the potential connection speed (data transfer rate) for your connection type.

Speed Connection type
155.52 Mbps OC-3, STS-3
100.0 Mbps CDDI, FDDI, Fast Ethernet, Category 5 cable
51.84 Mbps OC-1, STS-1
44.736 Mbps T-3, DS-3 North America
34.368 Mbps E-3 Europe
20.0 Mbps Category 4 cable
16.0 Mbps Fast Token Ring LANs
10.0 Mbps Thin Ethernet, category 3 cable, cable modem
8.448 Mbps E-2 Europe
6.312 Mbps T-2, DS-2 North America
6.144 Mbps Standard ADSL downstream
4.0 Mbps Token Ring LANs
3.152 Mbps DS-1c
2.048 Mbps E-1, DS-1 Europe
1.544 Mbps ADSL, T-1, DS-1 North America
128 Kbps ISDN
64.0 Kbps DS-0, pulse code modulation
56.0 Kbps 56flex, U.S. Robotics x2 modems,
33.6 Kbps 56flex, x2 modem communications rate

Units of Measurement

In digital systems, bandwidth is expressed as bits (of data) per second (bps). Here are the units of measure for bandwidth or data transfer speeds:
bit= smallest unit of digital information (ones and zeros)
byte= a set of 8 bits
bps= bits per second
Kbps= kilobits per second =1000 bits per second
Mbps = Million bits per second =1,000,000 bits per second
Gbps = Gigabits per second = 1,000,000,000 (one billion) bits per second
Tbps = Terabits per second = 1,000,000,000,000 (one trillion) bits per second