On-Line Encyclopedia - C

The Maui Communications Networks
On-Line Encyclopedia

Alphabetical List Of Definitions For Technical Terms

C
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CDMA
"Code Division Multiple Access" - Originally developed for use by the military in the 1970's, CDMA is a digital signal multiplexing technique where each signal is split into a number of small transmission units called "chips". The chipping codes are spread over a band of frequencies then reassembled at the receiving end. In this way, many different signals can be transmitted in the same frequency band. CDMA is defined in International Standard 95 (IS-95) and a second generation of the standard (CDMA-1) was developed by Qualcomm. In 3G cellular, an additional, evolved CDMA standard (CDMA-2000) is used for base-to-mobile communications.

Captive Portal
A captive portal is a web page on which a user logs in to a network. In the implementation of a HotSpot or visitor access system a gateway device called an access controller presents a user with a captive portal web page that presents a login dialog box when the user first attaches to the network. The portal (the web page serving as the entry point for access to the network) is "captive" because the user's initial attempt to connect to their default browser home page is "hijacked" (told to go somewhere it didn't intend to go.). and redirected to the web page where the user logs in. This is accomplished through DNS redirection by which the user's browser's initial attempt to resolve the URL of the user's default home page is not sent to a DNS server but, rather, the access controller returns the IP address of the captive portal web server. Once the user has authenticated the access controller connects the user to their default home page.

Co-Location
The term refers to multiple radio transmitters being located on the same tower or rooftop. The concern is that co-located transmitters may interfere with each other because their antennas may be so close that they electrically couple and cause signal degradation.

Converting MOS to R-Values
The Mean Opinion Score (MOS) and the R-Value (Impairment Value) in the ITU E-Model are, respectively, a subjective and an quantitative measure of telephone call quality. These values are used to measure quality on both analog and VoIP circuits. The International Telephony Union (ITU) has provided a conversion formula in the G.107 specification. The following chart shows the result of applying that formula to the conversion of MOS and R values.
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