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This Lesson isThis Lesson is

UNCLASSIFIED//FOUOUNCLASSIFIED//FOUO

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U-4205L Telephony BasicsU-4205L Telephony BasicsPart 1Part 1

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DisclaimerDisclaimer• The images and media associated with this The images and media associated with this

presentation does not constitute endorsement presentation does not constitute endorsement by the United States Air Forceby the United States Air Force

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OverviewOverview

• Telecommunication SwitchingTelecommunication Switching

• Telecommunication SignalingTelecommunication Signaling

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Objectives and MSBsObjectives and MSBs

• Comprehend telephone switchingComprehend telephone switching– Describe the function of a central Describe the function of a central

officeoffice

– Describe the function of a end office Describe the function of a end office switchswitch

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Objectives and MSBsObjectives and MSBs

• Comprehend telephone switching Comprehend telephone switching (cont.)(cont.)– Describe the function of a tandem Describe the function of a tandem

switchswitch

– Describe hiearchary switchingDescribe hiearchary switching

– Describe dynamic non-hiearchary Describe dynamic non-hiearchary switchingswitching

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Objectives and MSBsObjectives and MSBs

• Comprehend telephone signalingComprehend telephone signaling– Define in band signalingDefine in band signaling

– Define out of band signalingDefine out of band signaling

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Public Switched Telephone NetworkPublic Switched Telephone Network(PSTN)(PSTN)

The worldwide collection of interconnected public The worldwide collection of interconnected public telephone networks that was designed primarily telephone networks that was designed primarily

for voice trafficfor voice traffic

www.linfo.org

PSTN

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Central OfficeCentral Office(CO)(CO)

• A building in which the phone lines in a home A building in which the phone lines in a home or office terminate and connect to a much or office terminate and connect to a much larger switching system larger switching system

• Connected to a much broader switching Connected to a much broader switching system in which switching offices are system in which switching offices are interconnected with trunk lines interconnected with trunk lines

• While the local loop is an analog circuit for While the local loop is an analog circuit for voice calls, once a call gets to the CO, it is voice calls, once a call gets to the CO, it is converted to a 64-Kbit/sec stream of digital converted to a 64-Kbit/sec stream of digital data for routing through the switching systemdata for routing through the switching system

Sheldon

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Telephone SwitchesTelephone Switches

Horack

• Private Branch Exchange– A private switching system normally used in the

commercial sector

• End Office Switch (Class 5)– A telephone central office switch that connects

directly to the customer. • Tandem Switch (Class 4)

– A network switch that serves in partnership with lesser switches (i.e. CO), and serves no end users directly

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Telephone SwitchesTelephone Switches

Freeman

• Primary Center Switch (Class 3)– Processes Calls being made beyond the limits of

a small geographical area

• Sectional Center (Class 2)– Typically connect to major toll centers within one

or two states or provinces• Regional Center (Class 1)

– Last resort" for final setup of calls when routes between centers lower in the hierarchy were not available, serves as an international gateway

Hierarchical SwitchingHierarchical Switching

• A group of interconnected sub-A group of interconnected sub-networks that control traffic through networks that control traffic through segmentationsegmentation

• Provided simplified switch designProvided simplified switch design

• Circuit security Circuit security

• OutagesOutages

X939 X243 X757 X912 X210 X312 X556 X404

4a 4b 4c 4d 4e

3a 3b 3c 3d 3e 3f 3g

2a 2b2d

1a

2c

1bClass 1Region

Class 2State

Class 3County

Class 4City

Class 5Local

850-939-1122 850-939-3344 850-243-5566 912-656-7788 210-756-1111

1c

PBX

50 Users

T1 24 Channels

Company BGI

HIEARCHARY SWITCHING

International Gateway

High Use

Route

High Use

Route

Dynamic Non-Hierarchical RoutingDynamic Non-Hierarchical Routing(DNHR)(DNHR)

• Implemented by AT&T after the Implemented by AT&T after the divestituredivestiture

• Intelligent control and reporting of traffic Intelligent control and reporting of traffic

• Integral for carriers to operate their Integral for carriers to operate their networks at peak efficiencynetworks at peak efficiency

• Introduced flexibility into network traffic Introduced flexibility into network traffic controlcontrol

939 243 656 712

T T

Class 4

Class 5

404

CLEC

Intelligent Network

Uses Switching Points To Access The Signaling Network

Dynamic Non-Hiearchical Routing

T

PBX

50 Users

T1 24 Channels

Company BGI850-939-1122 850-939-3344 850-243-5566 912-656-7788

SSP

SSP SSPSSP SSP

SSPSSP

T

SSP SSP

International Gateway

Telecommunication Signaling Telecommunication Signaling In Band SignalingIn Band Signaling

The exchange of signaling (call The exchange of signaling (call control) information between control) information between switches on the same circuit the switches on the same circuit the voice call rides onvoice call rides on

300 Hz 3400 Hz

Voice Band

2600 Hz

2000 Hz

Telecommunication Signaling Telecommunication Signaling Out of Band SignalingOut of Band Signaling

The exchange of information in order to The exchange of information in order to control a telephone call that is done on control a telephone call that is done on a channel that is dedicated for the a channel that is dedicated for the control purpose and separate from the control purpose and separate from the channels used for the telephone callchannels used for the telephone call

300 Hz 3400 Hz

Voice Band

3700 Hz USA3825 Hz (CCITT)

2000 Hz

Multi-Frequency SignalingMulti-Frequency Signaling

• A method utilizing five or six tone frequencies, two at a A method utilizing five or six tone frequencies, two at a time. time.

• Used for signaling between switchesUsed for signaling between switches

• Examples of multi-frequency signalingExamples of multi-frequency signaling– A A Local Loop to the End Office Switch– SOCOTEL France and Spain– Signaling System 5 (SS5) Country Specific– Inter-register Signaling 1 (R1) USA– Inter-register Signaling 2 (R2) Europe/Asia

Inter-register 1(R1) Inter-register 1(R1) SignalingSignaling USA USA

Frequency HZ

1 700 + 900

2 700 + 1100

3 900 + 1100

4 700 + 1300

5 900 + 1300

6 1100 + 1300

7 700 + 1500

8 900 + 1500

9 1100 + 1500

10 (0) 1300 + 1500

Control Signal 1700 + 700 -1300

System Check 1900

Idle Line 2600300 Hz 3400 Hz

Voice Band

2600 Hz

2000 Hz

In Band Signaling

Signaling System 5

300 Hz 3400 Hz

Voice Band

2000 Hz

3825 Hz (CCITT)

Frequency HZ

1 700 + 900

2 700 + 1100

3 900 + 1100

4 700 + 1300

5 900 + 1300

6 1100 + 1300

7 700 + 1500

8 900 + 1500

9 1100 + 1500

10 (0) 1300 + 1500

Control Signal 1700 + 700 -1300

System Check 1900

Idle Line 2600

Inter-register 2 (R2) Inter-register 2 (R2) SignalingSignaling Asia/Europe Asia/Europe

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Intelligent Network SignalingIntelligent Network SignalingSignaling System 7Signaling System 7

• Developed to meet the needs of an Developed to meet the needs of an all digital network all digital network

• Provides supervision of circuits, Provides supervision of circuits, address signaling, call progress address signaling, call progress signals and alerting notificationsignals and alerting notification

• Data network entirely dedicated to Data network entirely dedicated to inter-switch signalinginter-switch signaling

SS7 NetworkSS7 Network

939 939

Intelligent SignalingSignaling System 7

T

SSPSSP SSP

STP STP

850-939-1122 850-939-3344

Service Switching Point (SSP)Service Transfer Point (STP)Service Control Point (SCP)

Associated Signaling

SSPSSP

T1

Circuit

Signal

Non-associated Signaling

SSPSSP

T3

Circuit

Signal

T1

Non-associated Signaling

SSPSSP

T3

Circuit

Signal

STP STP

•

• The North American Signaling ArchitectureThe North American Signaling Architecture• The North American signaling architecture defines a completely new and separate signaling network. The The North American signaling architecture defines a completely new and separate signaling network. The

network is built out of the following three essential components, interconnected by signaling links: network is built out of the following three essential components, interconnected by signaling links: • signal switching points (SSPs)signal switching points (SSPs)—SSPs are telephone switches (end offices or tandems) equipped with —SSPs are telephone switches (end offices or tandems) equipped with

SS7-capable software and terminating signaling links. They generally originate, terminate, or switch calls. SS7-capable software and terminating signaling links. They generally originate, terminate, or switch calls. • signal transfer points (STPs)signal transfer points (STPs)—STPs are the packet switches of the SS7 network. They receive and route —STPs are the packet switches of the SS7 network. They receive and route

incoming signaling messages towards the proper destination. They also perform specialized routing incoming signaling messages towards the proper destination. They also perform specialized routing functions. functions.

• signal control points (SCPs)signal control points (SCPs)—SCPs are databases that provide information necessary for advanced call-—SCPs are databases that provide information necessary for advanced call-processing capabilities.processing capabilities.

• Once deployed, the availability of SS7 network is critical to call processing. Unless SSPs can exchange Once deployed, the availability of SS7 network is critical to call processing. Unless SSPs can exchange signaling, they cannot complete any interswitch calls. For this reason, the SS7 network is built using a signaling, they cannot complete any interswitch calls. For this reason, the SS7 network is built using a highly redundant architecture. Each individual element also must meet exacting requirements for highly redundant architecture. Each individual element also must meet exacting requirements for availability. Finally, protocol has been defined between interconnected elements to facilitate the routing of availability. Finally, protocol has been defined between interconnected elements to facilitate the routing of signaling traffic around any difficulties that may arise in the signaling network. signaling traffic around any difficulties that may arise in the signaling network.

• To enable signaling network architectures to be easily communicated and understood, a standard set of To enable signaling network architectures to be easily communicated and understood, a standard set of symbols was adopted for depicting SS7 networks. Figure 2 shows the symbols that are used to depict symbols was adopted for depicting SS7 networks. Figure 2 shows the symbols that are used to depict these three key elements of any SS7 network. these three key elements of any SS7 network.

•Figure 2. Signaling Network ElementsFigure 2. Signaling Network Elements

• STPs and SCPs are customarily deployed in pairs. While elements of a pair are not generally co-located, STPs and SCPs are customarily deployed in pairs. While elements of a pair are not generally co-located, they work redundantly to perform the same logical function. When drawing complex network diagrams, they work redundantly to perform the same logical function. When drawing complex network diagrams, these pairs may be depicted as a single element for simplicity, as shown in Figure 3. these pairs may be depicted as a single element for simplicity, as shown in Figure 3.

http://www.iec.org/online/tutorials/ss7/

SSP SSPSSP

Central Office850-939-XXXX

LOCAL CALL

Within an Area Code and LATA

Central Office850-243-XXXX

TANDEM Non-Toll

LOCAL CALL

SSP SSPSSP

STP SCP

PSTN

IN/SS7

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Simplified SS7Simplified SS7

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