You connect to the Internet through a network adapter card or other network device, such as a modem or ISDN card. Internet bandwidth is measured in bits per second (bps).
Your Internet bandwidth determines how fast data gets to your computer and also how many requests can be serviced simultaneously. As more computers get data through your Internet connection simultaneously, delays or failures can occur if you do not have enough bandwidth.
When you lease an Internet connection, your ISP installs a network cable to your site. Leased connection speeds range from 56,000 bps (or 56 kilobytes per second) with Frame Relay to 45,000,000 bps (or 45 megabytes per second) with a T3 connection. A dial-up ISDN line can offer speeds up to 128,000 bps (or 128 kilobytes per second).
The connection types described in Table 2.2 represent typical levels of service for full Internet connections in North America and Japan. The Internet services offered through Internet service providers in your country might differ significantly.
Table 2.2 Common Internet Service Connection Types
Connection type | Maximum bandwidth | Approximate number of users supported |
Dedicated PPP/SLIP | Modem speed | 2-3 |
56K (Frame Relay) | 56,000 bps | 10-20 |
ISDN (using PPP) | 128,000 bps | 10-50 |
T1 | 1,540,000 bps | 100-500 |
Fractional T1 | Varies as needed | Varies as needed |
T3 | 45,000,000 bps | 5,000+ |
To understand these speeds in practical terms, assume a page of text is 42,240 bits. (One character is 8 bits. Therefore, 8 bits x 80 characters in a line x 66 lines per page = 42,240 bits per page.) A 28.8 Kbps modem can transfer .67 pages per second. A 128,000 bps ISDN line can transfer three pages per second. A 1,500,000 bps T1 line can transfer 35.5 pages per second.
For example, a light-duty server can use a 56 Kbps link or ISDN. A server with medium traffic might have a T1 line or some fraction of a T1 line installed. Large businesses that expect heavy Internet traffic might need fractional or multiple T1 lines or even T3 service in order to handle thousands of users.
Modem connections to the Internet are available, but are typically used for individual client browsing and are not recommended for servers. A connection to the Internet that uses a phone line and modem can service only two or three users simultaneously. (Modem connections might be used for text-only Internet servers with only a small number of potential users.) Modem connections are often called "slow links" because data is transmitted at the speed of the modem, typically from 9600 to 28,800 bps. This is far too slow for efficient operation of a World Wide Web server, for example.