Matakuliah : H0122 / Dasar Telekomunikasi
Tahun
: 2008
Sistem Telepon
Pertemuan 11
Learning Outcomes
Mahasiswa dapat menunjukkan konsep telepon,
bagaimana koneksinya serta masalah yang ada pada
sistem telepon.
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Outline Materi
• Terminology
• Central Office
• Switching
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Telephone System
• Terminology
– Local loop
– Central office
– Exchange
– Trunk
– Nodes
– Super trunks
– Tandem switch
– Hierarchy
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Components
• Three major components:
– Local loops: twisted pair, analog signaling
– Trunks: fiber optics or microwave, mostly digital
– Switching offices
Toll Office
End Office
Local
Loop
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Trunk
Switching Office
Intertoll
Trunk
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Hierarchy
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Terminal/Local Loop
•Telephone Terminal
– Local loop and Basic Phone
– Calling sequence in phone
•Talking signals
– Analog voltage
• Outgoing : 1 – 2 V at approx. 3 mA
• Incoming : half of outgoing signals
•Local loop characteristics
– Envelope delay
– Voice grade:
• Dial-up or switched line
• Dedicated, conditioned or leased line
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Terminal/Local Loop
• Loop signal level
– Outgoing : - 10 and 0 dBm (600 )
– Incoming : - 42 to – 4 dBm
– Termination on the Central office : 600 (or 900)
• Dialing
– Pulse
– Tone
• Dual-tone multi-frequency (DTMF)
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Terminal/Local Loop
DTMF tones for each number
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Loop Supervision
• BORSHT is the function of Subscriber loop interface circuit (SLIC) or
line card in interfacing to a local loop
– Battery : - 48 V dc
– Over voltage : protection from excessive voltage
– Ring trip : send 90 V 20 Hz ac signal with on hook : 2 s ; off hook
:4s
– Supervision : monitor the phone loop
– Hybrid:
• Two-wire to four-wire converter or four wire terminating set:
plit the local loop into 2 wire pairs.
• Trans-hybrid loss: – 30 to 50 dB of rejection
– Test
• To test signals on the line and to check quality of loop and
phone performance
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Central Office
• Process calling :
– Recognize the dialed digits
– Make physical connection
• Connection :
– Allow an analog signal voltage
– Switching systems in matrix (crossbar or cross point switch)
– For greater reliability used reed relay
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Common Channel
Signaling
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Echo Cancellation
• Echo parameters:
– Signal travel time and travel distance
– Echo time = (distance/prop.velocity) x 2
• To Cancel
– Insert the reverse path loss
• Echo suppression by insertion of reverse path loss
– Signal subtractions
• Echo suppression using the signal subtraction method
– Digital signal processing
• New version of subtraction method, need arithmetic calculation
(algorithm)
– Four-wire method
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Echo Cancellation
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Four Wire
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Summary
• Telah dipelajari gambaran umum sistem telepon.
• Telah dipelajari komponen telepon.
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