Chapter 2: Introduction to Analog Telephony 2-1 Copyright © 1998, Cisco Systems, Inc.

2-2CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Objectives Upon completion of this chapter, you will be able to perform the following tasks: Given an analog telephony network, identify the role of each component within the network. The components are telephones, lines, loops, switches, and trunks. Given an analog telephony network, describe the telephony signaling on lines and trunks Given a telephony network, trace the path of a telephone call

Telephone Call Components 2-3 Copyright © 1998, Cisco Systems, Inc.

2-4CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Telephone Call Components Telephone Local loop Voice switch – CO (central office) – PBX (private branch exchange) Trunks

Telephone Components 2-5 Copyright © 1998, Cisco Systems, Inc.

2-6CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Handset (receiver and transmitter) Switch hook Hybrid (2-to-4 wire converter) Sidetone Dialer Ringer Telephone Components Telephone Company Switch Telephone 2-Wire Local Loop Ringer Switch Hook Loop Length Comp. Dialing (Pulse or Tone) Balance Network 2-Wire 4-Wire Hybrid Receiver Transmitter

Telephone Signaling 2-7 Copyright © 1998, Cisco Systems, Inc.

2-8CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Telephone Signaling Supervisory signaling – Release connection (on-hook) – Request for service (off-hook) – Ringing Addressing (dialed digits) – Pulse – DTMF

2-9CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. On-Hook Telephone Switch Local Loop Local Loop -48 DC Voltage (Battery) DC Open Circuit No Current Flow Handset on cradle and switch hook is open

2-10CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Local Loop Local Loop Off-Hook Closed Circuit DC Current Dial Tone Telephone Switch Off-Hook

2-11CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Ringing Local Loop Local Loop Off-Hook Closed Circuit Ring-Back Tone DC Current Ringing Voltage Telephone Switch

2-12CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Ringing (cont.) United States Cadence Europe Cadence Sec 4 Sec

2-13CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Pulse Make (Circuit Closed) Break (Circuit Open) Off-HookDialingInterdigitNext Digit Pulse Period 50 ms 20 pulses per second 100 ms 10 pulses per second US: 60/40 Break/Make 700 ms

2-14CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Dual Tone Multifrequency DTMF *0# Timing: 60 ms Break 40 ms Make

2-15CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Informational SignalingCall Progress Indicators (United States) ToneFrequency (Hz)On Time (sec)Off Time (sec) Dial Busy Ring-back, line Ring-back, PBX Congestion (toll) Reorder (local) Receiver off-hook No such number Confirmation tone to 400 Continuous Continuous, Freq. Mod 1 Hz

Local Loops 2-16 Copyright © 1998, Cisco Systems, Inc.

2-17CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Telephone Company Switch Local Loop Local Loop Local Loops A loop is the physical pair of wires from the subscriber to the telephone company switch

Voice Switches 2-18 Copyright © 1998, Cisco Systems, Inc.

2-19CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Voice Switches Telephone Company PBX CO Intermediate PBX CO CO

2-20CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Central Office Switch All private phones are directly connected to a CO switch Two-wire connection to individual analog phones Calls take one of the following paths – Switched within the CO – Sent to another CO – Sent to an intermediate switch (scalability)

2-21CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Intermediate Switch Switch calls between switches Connects trunks

2-22CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Private Branch Exchange Used in private sector Remote branch subsystem Switches (eXchanges) calls locally – Keeps local calls off public network – Fewer trunks to CO – Private line between PBXs

Trunks 2-23 Copyright © 1998, Cisco Systems, Inc.

2-24CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Trunks Telephone Company PBX PBX CO CO Trunk Interoffice Trunk CO CO CO Trunk Private Trunk Line Interoffice Trunk Intermediate

2-25CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Foreign Exchange Trunks Foreign exchange office – Plugs directly into the line side of a switch – Acts like a phone/switch, thinks it is a phone Foreign exchange station – Sits at the remote site – Acts like a switch/phone, thinks it is a switch

2-26CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. DID/DOD Trunks Telephone Company PBX CO DID You have a call Telephone Company PBX CO DOD XXXX

Trunk Signaling 2-27 Copyright © 1998, Cisco Systems, Inc.

2-28CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Trunk/Line Seizure Signaling Types CO to phone/FXO/FXS – Loop start – Ground start PBX to PBX E&M –Type I to V –Start signaling Wink start Immediate start Delay start

2-29CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Loop Start Signaling CO or FXS Module Telephone, PBX, or FXO Module. Ring Gen. -48 VDC Battery CO or FXS Module Telephone, PBX, or FXO Module. Ring Gen. -48 VDC Battery Idle State (On-Hook): Telephone or PBX has open 2-wire loop. CO or FXS module has battery on ring, ground on tip. PBX Seizure (Off-Hook): Telephone or PBX closes 2-wire loop. CO or FXS module detects current. CO will return dial tone. Tip Ring Tip Ring

2-30CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Loop Start Signaling (cont.) CO Seizure: CO applies AC ring voltage, superimposed over the -48 VDC. When phone goes off- hook, CO removes ring voltage and completes circuit. CO or FXS Module Telephone, PBX, or FXO Module Ring Gen. -48 VDC Battery Tip Ring CO or FXS Module Telephone, PBX, or FXO Module Ring Gen. -48 VDC Battery Tip Ring

2-31CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Ground Start Signaling Idle State (On-Hook): PBX/FXO monitors tip for ground. Battery from CO/FXS appears on ring lead. CO or FXS Module PBX or FXO Module Ring Gen. -48 VDC Battery Tip Ground Detector Tip Ring

2-32CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. PBX Seizure: PBX/FXO senses tip ground from CO/FXS, closes the 2-wire loop, and removes ring ground. CO or FXS Module PBX or FXO Module Ring Gen. -48 VDC Battery Tip Ground Detector Tip Ring PBX Seizure: PBX/FXO grounds ring lead. CO/FXS senses ring ground and then grounds tip lead. CO or FXS Module PBX or FXO Module Ring Gen. -48 VDC Battery Tip Ground Detector Tip Ring Ground Start Signaling (cont.)

2-33CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Idle State (On-Hook): PBX/FXO monitors tip for ground. Battery from CO/FXS appears on ring lead. CO or FXS Module PBX or FXO Module Ring Gen. -48 VDC Battery Tip Ground Detector Tip Ring CO/FXS Seizure: CO/FXS grounds tip lead and superimposes ringing voltage over ring lead battery. CO or FXS Module PBX or FXO Module -48 VDC Battery Tip Ground Detector Tip Ring Gen. Ground Start Signaling (cont.)

2-34CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. PBX Seizure: CO/FXS senses DC current from the PBX and removes the ring ground. PBX Seizure: PBX/FXO tip ground and ringing are sensed, and PBX closes the loop, then removes the ring ground. Note: The PBX must sense the incoming seizure (tip ground) within 100 ms. This timing requirement helps to prevent glare. CO or FXS Module PBX or FXO Module Ring Gen. -48 VDC Battery Tip Ground Detector Tip Ring CO or FXS Module PBX or FXO Module -48 VDC Battery Tip Ground Detector Tip Ring Gen. Ground Start Signaling (cont.)

2-35CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. E&M Signaling PBX to Intermediate Device TypeLeadOn-hook Off-hook IMGroundBattery (-48 VDC) IIMOpenBattery (-48 VDC) IIIMGroundBattery (-48 VDC) IVMOpenGround VMOpenGround Intermediate Device to PBX TypeLeadOn-hookOff-hook IEOpenGround IIEOpenGround IIIEOpenGround IVEOpenGround VEOpenGround Separate signaling leads for each direction E-lead (inbound direction) M-lead (outbound direction) Allows independent signaling

2-36CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. M E&M Type I PBX -48 VDC Off-hook -48 VDC Channel Bank or Cisco Voice Equipment M EE Open On-hook Off-hook E-Lead Detector M-Lead Detector

2-37CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. M E&M Type V PBX -48 VDC M EE Open On-hook Off-hook Open on-hook E-Lead Detector M-Lead Detector Channel Bank or Cisco Voice Equipment

2-38CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. M E&M Type II PBX -48 VDC M EE Battery (closed) off-hook SB SG Open on-hook Ground (closed) off-hook Open on-hook 4-wire, fully looped, nonsymmetrical E-Lead Detector M-Lead Detector Channel Bank or Cisco Voice Equipment

2-39CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. M E&M Type III PBX -48 VDC M EE Battery (closed) off-hook SB SG Ground (open) on-hook Ground (closed) off-hook Open on-hook 4-wire, partially looped SG E-Lead Detector M-Lead Detector Channel Bank or Cisco Voice Equipment

2-40CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. M E&M Type IV PBX -48 VDC M EE Ground (closed) off-hook SB SG Open on-hook 4-wire, symmetrical, least noise Ground (closed) off-hook Open on-hook E-Lead Detector M-Lead Detector Channel Bank or Cisco Voice Equipment

2-41CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Trunk Supervision Signaling Wink Start Digits Forwarded Wink Request for Service Register Found Called Number Answers Local End Hangs Up Remote End Terminated M-Lead -48V 0V E-Lead -48V 0V Local PBX

2-42CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Trunk Supervision Signaling Delay Start Digits Forwarded Request for Service Request Acknowledgement Register Found Called Number Answers Local End Hangs Up Remote End Terminated M-Lead -48V 0V E-Lead -48V 0V Local PBX

2-43CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Trunk Supervision Signaling Immediate Start Wink M-Lead -48V 0V E-Lead -48V 0V Local PBX Request for Service Local End Hangs Up Remote End Terminated Called Number Answers Digits Forwarded Register Found

2-44CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Central Office 2w-4w Hybrid 2- to 4-Wire Conversion and Echo Echo is due to a reflection Impedance mismatch at the 2w-4w hybrid Is the most common reason for echo Receive Direction Transmit Direction Rx and Tx superimposed 2-Wire Local Loop

2-45CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Echo in Voice Networks Delay Talker Listener Talker Echo Listener Echo

2-46CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Echo Is Always Present Echo as a problem is a function of the echo delay, and the magnitude of the echo (dB) Echo Path Loss Echo Path Delay (ms) Echo Is Unnoticeable Echo Is a Problem

2-47CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Echo Suppression Suppresses your voice on the return path Acts as a noise gate, effectively making communications half- duplex

2-48CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Echo Cancellation Most effective means for removing echo Central Office E/C Echo Canceller Block Diagram + Adaptive Filter

Telephone Call Procedure 2-49 Copyright © 1998, Cisco Systems, Inc.

Written Exercise 2-50 Copyright © 1998, Cisco Systems, Inc.

2-51CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc.

2-52CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc.

Lab Exercise 2-53 Copyright © 1998, Cisco Systems, Inc.

2-54CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc.

2-55CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Summary In this chapter you learned how to complete the following tasks: Identify the role of each component within the network. The components are telephones, lines, loops, switches, and trunks. Describe the telephony signaling on lines and trunks Trace the path of a telephone call

2-56CVOICEIntroduction to Analog Telephony Copyright © 1998, Cisco Systems, Inc. Blank for IG Pagination