CECS 5460Computer Networks for Educational Environments
Bandwith by Services
ISDN = Integrated Services Digital Network (Symmetrical)
ISDN is a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. There are two levels of service: the Basic Rate Interface (BRI), intended for the home and small enterprise, and the Primary Rate Interface (PRI), for larger users. Both rates include a number of B-channels and a D-channels. Each B-channel carries data, voice, and other services. Each D-channel carries control and signaling information.
DSL = Digital Subscriber Line (Asymmetrical Connection (Recv/Xmit))
DSL refers to different variations of DSL, such as ADSL, HDSL, and RADSL. Assuming your home or small business is close enough to a telephone company central office (around 18,000 feet) that offers DSL service, you may be able to receive data at rates up to 6.1 megabits (millions of bits) per second (of a theoretical 8.448 megabits per second). Typically, individual connections will provide from 1.544 Mbps to 512 Kbps downstream and about 128 Kbps upstream.
CableModem (Asymmetrical Connection (Recv/Xmit))
A cable modem is a device that enables you to hook up your PC to a local cable TV line and receive data at about 1.5 Mbps. The actual bandwidth for Internet service over a cable TV line is up to 27 Mbps on the download path to the subscriber with about 2.5 Mbps of bandwidth for interactive responses in the other direction. However, since the local provider may not be connected to the Internet on a line faster than a T-carrier system at 1.5 Mpbs, a more likely data rate will be close to 1.5 Mpbs.
The T1 (or T-1) carrier is the most commonly used digital line in the United States, Canada, and Japan. In these countries, it carries 24 pulse code modulation (PCM) signals using time-division multiplexing (TDM) at an overall rate of 1.544 million bits per second (Mbps). T1 lines use copper wire and span distances within and between major metropolitan areas. A T1 Outstate System has been developed for longer distances between cities.
OC-1 = Optical Carrier (Sync)
The Synchronous Optical Network (SONET) includes a set of signal rate multiples for transmitting digital signals on optical fiber. The base rate (OC-1) is 51.84 Mbps. Asynchronous transfer mode (ATM) makes use of some of the Optical Carrier levels.