How fast is fast?
This chart puts into
perspective line speeds
used in Internet backbones,
LANs, and WANs.
DS-3 North America
||Category 4 cable
category 3 cable,cable
||T-2, DS-2 North America
||Standard ADSL downstream
||E-1, DS-1 Europe
DS-1 North America
||DS-0, pulse code modulation
||56flex, U.S. Robotics x2 modems,
||56flex, x2 modem communications rate
||V.34, Rockwell V.Fast Class modems
||Level 1 cable, minimum cable data speed
||V.32bis modem, V.17 fax
||modem speed circa early 1990s
||modem speed circa 1980s
Units of Measurement
bit= smallest unit of digital information, i.e. ones & zeros
byte= a set of 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
*Editor's note: individual components in the bandwidth measurement chart have not been separated by Open Systems Interconnect (OSI) protocol layer or media.
Short for Optical Carrier, used to specify the speed of fiber optic networks conforming to the SONET standard.
The table shows the speeds for common OC levels.
Abbreviation of Copper Data Distribution Interface, a network technology capable of carrying data at 100 Mbps over unshielded twisted pair (UTP) cable.
CDDI is a trade name of Crescendo Communications (acquired by Cisco Systems in 1993) and commonly used instead of the general term Twisted Pair Physical Layer Medium (TP-PMD).
TP-PMD is the general ANSI standard name for this FDDI -like service.
Abbreviation of Fiber Distributed Data Interface, a set of ANSI protocols for sending digital data over fiber optic cable.
FDDI networks are token-passing networks, and support data rates of up to 100 Mbps (100 million bits) per second. FDDI networks are typically used as backbones for wide-area networks. An extension to FDDI, called FDDI-2, supports the transmission of voice and video information as well as data. Another variation of FDDI, called FDDI Full Duplex Technology (FFDT) uses the same network infrastructure but can potentially support data rates up to 200 Mbps.
100 BASE-T (Fast Ethernet)
A networking standard that supports data transfer rates up to 100 Mbps (100 megabits per second). 100BASE-T is based on the older Ethernet standard. Because it is 10 times faster than Ethernet, it is often referred to as Fast Ethernet.
Officially, the 100BASE-T standard is IEEE 802.3u. Like Ethernet, 100BASE-T is based on the CSMA/CD LAN access method. There are several different cabling schemes that can be used with 100BASE-T, including:
Category 5 describes network cabling that consists of four twisted pairs of copper wire terminated by RJ45 connectors. Cat-5 cabling supports frequencies up to 100 MHz and speeds up to 1000 Mbps. It can be used for ATM, token ring, 1000Base-T, 100Base-T, and 10Base-T networking.
Computers hooked up to LAN s are connected using Cat-5 cables, so if you're on a LAN, most likely the cable running out of the back of your PC is Category 5.
Cat-5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard developed by the Electronics Industries Association as requested by the Computer Communications Industry Association in 1985.
A dedicated phone connection supporting data rates of about 43 Mbps.
A T-3 line actually consists of 672 individual channels, each of which supports 64 Kbps.
T-3 lines are used mainly by Internet Service Providers (ISPs) connecting to the Internet backbone and for the backbone itself.
T-3 lines are sometimes referred to as DS3 lines.
A dedicated phone connection supporting data rates of 1.544Mbits per second.
A T-1 line actually consists of 24 individual channels, each of which supports 64Kbits per second.
Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access.
T-1 lines are a popular leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet backbone itself consists of faster T-3 connections.
T-1 lines are sometimes referred to as DS1 lines.
(1) A type of computer network in which all the computers are arranged (schematically) in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then lets it continue to travel around the network.
(2) When capitalized, Token Ring refers to the PC network protocol developed by IBM. The IBM Token-Ring specification has been standardized by the IEEE as the IEEE 802.5 standard.
Thin Ethernet (10Base-2)
One of several adaptations of the Ethernet (IEEE 802.3) standard for Local Area Networks (LANs). The 10Base-2 standard (also called Thinnet) uses 50 ohm coaxial cable (RG-58 A/U) with maximum lengths of 185 meters. This cable is thinner and more flexible than that used for the 10Base-5 standard.
The RG-58 A/U cable is both less expensive and easier to place. Cables in the 10Base-2 system connect with BNC connectors.
The Network Interface Card (NIC) in a computer requires a T-connector where you can attach two cables to adjacent computers. Any unused connection must have a 50 ohm terminator.
The 10Base-2 system operates at 10 Mbps and uses baseband transmission methods.
A modem designed to operate over cable TV lines. Because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, a cable modem can be used to achieve extremely fast access to the World Wide Web.
This, combined with the fact that millions of homes are already wired for cable TV, has made the cable modem something of a holy grail for Internet and cable TV companies. There are a number of technical difficulties, however.
One is that the cable TV infrastructure is designed to broadcast TV signals in just one direction - from the cable TV company to people's homes. The Internet, however, is a two-way system where data also needs to flow from the client to the server.
In addition, it is still unknown whether the cable TV networks can handle the traffic that would ensue if millions of users began using the system for Internet access.
Despite these problems, cable modems that offer speeds up to 2 Mbps are already available in many areas.
Short for Asymmetric Digital Subscriber Line, a new technology that allows more data to be sent over existing copper telephone lines (POTS).
ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). ADSL requires a special ADSL modem.
ADSL is growing in popularity as more areas around the world gain access.
Abbreviation of Integrated Services Digital Network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).
Most ISDN lines offered by telephone companies give you two lines at once, called B channels. You can use one line for voice and the other for data, or you can use both lines for data to give you data rates of 128 Kbps, three times the data rate provided by today's fastest modems.
The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.