Unlike traditional analog signalling systems,
SS7 separates the signalling channel from the rest of the media channels. Signalling
refers to the exchange of information between call components required to provide
and maintain service, mainly Central Office Exchanges. If at any time the signalling
of a currently allocated call becomes non-existent, the exchanges remove the
associated media connection between the interconnected call components.
Chapter 1
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Integrated Services Digital Network (ISDN)
While ISDN utilizes the same methodologies as a circuit-switched network, to
provide better voice and data exchange between end terminals, it utilizes the
same infrastructure as a regular telephony network. ISDN consists of two separate
connectivity interfaces??”Basic Rate Interface (BRI) and Primary Rate Interface (PRI).
ISDN Basic Rate Interface (BRI)
An ISDN BRI connection consists of two bearer channels (B-channels), each one
capable of carrying a maximum throughput of 64kbps, and a single data channel
(D-channel) of 16kbps. B-Channels carry either voice or data, while the D-Channel
carries signalling information. When utilized in voice mode, a BRI can carry two
phone calls at the same time. When utilized in data mode, a BRI would be able to
combine the two channels into a single data path of 128kbps.
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