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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Bandwidth is the information-carrying capacity of a communication channel. The channel may be analog or digital. Analog transmissions such as telephone calls, AM and FM radio, and television are measured in cycles per second (hertz or Hz). Digital transmissions are measured in bits per second. For digital systems, the terms "bandwidth" and "capacity" are often used interchangeably, and the actual transmission capabilities are referred to as the data transfer rate (or just data rate).

This topic continues in "The Encyclopedia of Networking and Telecommunications" with a discussion of the following:

  • Transmission characteristics and bandwidth of different communication systems
  • How encoding and compression affect bandwidth
  • How different users and applications affect bandwith on shared links
  • How protocols affect bandwidth
  • TCP/IP performance and pipelining
  • Bandwidth reservation and QoS

Refer to the related entries page for other topics, including bandwidth management, throughput, prioritization of network traffic, QoS (quality of service), policy-based management, and traffic management and shaping.

The following RFCs provide interesting information about bandwidth utilization on TCP/IP Networks:

  • RFC 1323 (TCP Extensions for High Performance, May 19920)

  • RFC 2018 (TCP Selective Acknowledgment Options, October 1996)

Bandwidth Requirements and Ratings

In the United States, the Federal Communications Commission (FCC) is in charge of allocating the electromagnetic spectrum and, thus, the bandwidth of various communication systems. In the electromagnetic spectrum, sound waves occupy low ranges, while microwaves, visible light, ultraviolet, and X-rays occupy upper ranges. The bandwidths occupied by various communication technologies are described in "Electromagnetic Spectrum."

The bandwidth requirements of various applications are listed in Table Bandwidth-1. The rates are shown in bits/sec (bits per second), Kbits/sec (thousands of bits per second), Mbits/sec (millions of bits per second), and Gbits/sec (billions of bits per second). Compression and other techniques can reduce these requirements.



Personal communications

300 to 9,600 bits/sec or higher

E-mail transmissions

2,400 to 9,600 bits/sec or higher

Remote control programs

9,600 bits/sec to 56 Kbits/sec

Digitized voice phone call

64,000 bits/sec

Database text query

Up to 1 Mbit/sec

Digital audio

1 to 2 Mbits/sec

Access images

1 to 8 Mbits/sec

Compressed video

2 to 10 Mbits/sec

Medical transmissions

Up to 50 Mbits/sec

Document imaging

10 to 100 Mbits/sec

Scientific imaging

Up to 1 Gbit/sec

Full-motion video

1 to 2 Gbits/sec

Table Bandwidth-1: Bandwidth requirements for various applications

The transmission rates of various communication systems are listed in Table Bandwidth-2. Compression techniques and signal encoding are used to boost data rates. For example, modems use the ITU V.42 bis data compression standard to compress data at a ratio of over 3 to 1. V.42 bis compresses and decompresses on the fly as data is sent and received by connected modems.



Dial-up modem connection

1,200 bits/sec to 56 Kbits/sec

Serial port file transfers

2,000 bits/sec

ISDN (Integrated Services Digital

64 Kbits/sec or 128 Kbits/sec

Fractional T1 digital WAN link

64 Kbits/sec

Parallel port

300 Kbits/sec

DirecPC (satellite) Internet downloads

400 Kbits/sec

DSL (Digital Subscriber Line)

512 Kbits/sec to 8 Mbits/sec

Cable (CATV) modems

512 Kbits/sec to 10 Mbits/sec (or higher)

T1 digital WAN link

1.544 Mbits/sec


2.5 or 20 Mbits/sec

Token ring LANs

4 or 16 Mbits/sec

Ethernet LANs

10, 100, 1,000 Mbits/sec

T3 digital WAN link

44.184 Mbits/sec

HSSI (High-Speed Serial Interface)

52 Mbits/sec

FDDI (Fiber Distributed Data Interface)

100 Mbits/sec

Fibre Channel

1 Gbit/sec

Gigabit Ethernet

1 Gbit/sec

10GE (10 Gigabit Ethernet)

10 Gbits/sec

SONET (Synchronous Optical Network)

51.9 Mbits/sec to 2.5 Gbits/sec

Optical (lambda) networks implementing DWDM

Hundreds (or perhaps thousands) of lambdas per fiber, each running at 2.5 Gbits/sec

Table Bandwidth-2: Transmission rates of various communication systems

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.