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Telos Zephyr Xstream Two-Way Radio User Manual

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USER’S MANUAL

Section 7: ISDN BASICS 134

Withthedigitalnatureofthemoderntelephonenetworkishiddenfromsubscribers,voiceand

signalinghasbeendeliveredjustastheyhavebeensincetheeraofwoodenphonesetsand

mechanicalbells.Intheageofdigitalcommunication,this“lastmile”bottleneckhasbecome

increasinglyfrustratingforthosewhohaveneedtose

nddigitalinformationthroughMs.Bell’s

wires.

Withmostofthenetworknowdigital,itisclearlyoddthatwehavebeenusingmodemsto

convertdigitalinformationtoanalogbeepsjusttoaccommodatethemileortwoofancient

analoglinkageateachendofathousand‐milelongdi

gitalconnection.

ISDNisthetechnologywhichhasevolvedtoeliminatethisanalogbottleneckyetstillutilize

existingcopperinfrastructure.Itiscurrentlytheonlytechnologythatallowsfullydigitalaccess

tothePublicSwitchedTelephoneNetwork.

7.2 The ISDN Basic Rate Interface (BRI)

OnoneISDNBRIcircuit,therearethreesimultaneouschannels:Tw

o64kbps“bearer”channels

forthetransmissionofuserinformationandone16kbpssignalingchannelforcallset‐upand

statuscommunication.ThisisBasicRateInterface(BRI),2B+Dservice.InEuropeandother

countriesitisalsoreferredtoasISDN‐2orSØ.Itcanbeimplementedovermostofthemillio

ns

ofstandardcoppertwo‐wirephonecircuitsalreadyinservice.

?

CURIOSITY NOTE!

While the D channel is always present for signaling, it can, in theory, be used for connections

to the public packet network. ISDN lines where the D channel is used only for signaling are

sometimes referred to as 2B+0D rather than 2B+D service. D channel packet service is not

widely available and is not used by Zephyr Xstream.

ISDNBRIsareperfectlymatchedtoZephyrXstream’stransmissioncapabilities.Onechannel

provideshighqualitymono,whilethetwochannelscancarrynear‐CDqualitystereo.

i

ISDN TIP!

In some cases, your ISDN line, while having 2 B channels, will only have only one phone

number. This is the case of the AT&T Custom PTP protocol, and may be the case with ETS

300 (Euro-ISDN) and INS 64 (Japanese ISDN). This does not generally present a problem.

This works as if the lines are assigned to a short “hunt group” i.e.; the first incoming call

will be assigned to Line 1, and the second incoming call will be assigned to Line 2. Of course

you have the option of which line to use on outgoing calls.

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