1 Telephony: Internal and External Chapter 6 Copyright 2003 Prentice-Hall Panko’s Business Data...

1

Telephony: Internal and External

Chapter 6

Copyright 2003 Prentice-HallPanko’s Business Data Networks and Telecommunications, 4th edition

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Figure 6.1: Telephony

Telephone Service is Expensive for Corporations

LANs Use Traditional Telephone Building Wiring

Telephone Technology is Basis for Much Wide Area Networking

Telephone Regulation and Carriers Affect Wide Area Networking

Desire for Converged Services: Integrated Management of Voice and Data Networks

3

Figure 6.2: Internal PBX-Based Telephone Network

Multi-floorOffice

Building

4


1. Equipment Room in Ground Floor or Basement

2. ToPhone

Co.

3. EntranceFacility

5. PBXInternal Telephone

Switch

6. WireBundle

(Many Pairs)

7. VerticalRiserSpace

4. TerminationEquipment

5


3. TelecommunicationsCloset on Floor 2. Wire Bundle

4. Cross-Connect Device

5. Horizontal Distribution

1. VerticalDistribution

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1. Horizontal DistributionOne 4-Pair UTP Cord

2. Final DistributionAlong or Through Wall

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Figure 6.3: LAN Building Wiring

1. Equipment Room in Ground Floor or Basement

2. ToWAN

3. EntranceFacility

5. CoreSwitch

(Chassis)

6. VerticalRiserSpace4. Router

8


3. TelecommunicationsCloset on Floor

2. Optical FiberOne Pair per Floor

4. Workgroup Switch

5. Horizontal Distribution

1. VerticalDistribution

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1. Horizontal DistributionOne 4-Pair UTP Cord

Horizontal and Final Distributionare the Same as in Telephony

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Building Cabling Management

Structured Cabling Plans

Testing Inexpensive just to test whether wires are

connected properly

More expensive to test for signal quality

Documentation and Neatness Critical to avoid chaos in wiring

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Figure 6.4: Public Switched Telephone Network (PSTN)

Customer Premises(Residential)

Customer Premises(Business)

Switching OfficeCentral Office

End OfficeDigital

Access LineLocal Loop

Analog SignalingSingle Twisted Pair

12


SwitchingHierarchy

Trunk LineDigital

Class 4

Class 3

Class 5End

Office

Class 5End

Office

13


CircuitEnd-to-End Connection

Between Two Subscribers

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Figure 6.5: Trunk Line Technologies

Trunk Line Speed

North American Digital Hierarchy

56 kbps (DS0 Signaling) 56 kbps (sometimes 64 kbps)

T1 (DS1 Signaling) 1.544 Mbps

T3 (DS3 Signaling) 44.7 Mbps

CEPT Multiplexing Hierarchy

64 kbps 64 kbps

E1 2.048 Mbps

E3 34.4

Connect Pairs of Switches

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Figure 6.5: Trunk Line Technologies

Trunk Line Speed

SONET/SDH*

OC3/STM1 156 Mbps

OC12/STM4 622 Mbps

OC48/STM16 2.5 Gbps

OC192/STM64 10 Gbps

OC768/STM256 40 Gbps

Notes: SONET and SDH speeds are multiples of 51.84 Mbps.OCx is the SONET designation.STMx is the SDH designation.

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Figure 6.6: SONET/SDH Dual Rings

SONET/SDH Ring

SONET/SDH Ring

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

Rings can beWrapped if a

Trunk lineIs Broken

(Ch. 5)

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Figure 6.7: Circuit Switching

3. Circuit Switching:Circuit Reserved for

Duration of Call

2. AcrossMultiple

Access Lines,Switches, andTrunk Lines

1. CircuitEnd-to-End ConnectionSubscriber-Subscriber

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Figure 6.7: Circuit Switching

Dedicated Capacity Full capacity always available to pair of

subscribers during their call

Wasted if not used, and callers pay for whether use it or not

Good for voice, in which there is almost always someone talking

Expensive for data, which is bursty, having short transmissions mixed with long silences

Time

DataBurst

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Figure 6.8: The PSTN: Mostly Digital with Analog Local Loops

Original Telephone Network: All Analog

LocalLoop

(Analog)

ResidentialTelephone(Analog)

Switch(Analog)

Switch(Analog)

Switch(Analog)

LocalLoop

(Analog)

BusinessTelephone(Analog)

Trunk Line(Analog)

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Figure 6.8: The PSTN: Mostly Digital with Analog Local Loops

LocalLoop

(Analog)

ResidentialTelephone(Analog)

Switch(Digital)

Switch(Digital)

Switch(Digital)

LocalLoop

(Digital)

PBX(Digital)

Trunk Line(Digital)

Today’s Telephone Network: Predominantly Digital

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Figure 6.9: Codec at the End Office Switch

Subscriber Access Line is Analog

Switch is Digital

Codec Converts Between Them

Codec

DigitalInternalSignal

DigitalSwitch

Local LoopAccess Line

End Office

AnalogSubscriber

Signal ADC

DAC

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Figure 6.10: Sampling for Analog-to-Digital Conversion (ADC)

Codec First Bandpass Filters the Voice Signal Cuts of all energy below about 300 Hz Cuts off all energy above about 3,400 Hz Bandwidth of about 3.1 kHz

Signal

Energy Distribution forHuman Speech

O Hz 300 Hz ~3,400 Hz 20 kHz

Bandwidth (~3.1 kHz)

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Codec Constantly samples the intensity of the analog

voice signal from the customer

Sample

1/8,000 sec

0110010

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Codec Divides each second into 8,000 sampling periods Only measures intensity of voice signal in each

Sample

1/8,000 sec Sampling Period

IntensityValue

0110010

25


Codec Measures voice intensity as an 8-bit intensity

(loudness) value (0-255) Overall, sends 8 bits 8,000 times per second (64

kbps)Sample

1/8,000 sec Sampling Period

IntensityValue

0110010

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Codec This is why telephone channels are 64 kbps

Designed for digitized voiceCarrier often “steals” 8 kbps for

supervisory signaling, so 56 kbps

8,000 samples/second * 8 bits/sample = 64 kbps

64 kbps – 8 kbps = 56 kbps

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Figure 6.11: Digital-to-Analog Conversion (DAC)

00000100 00000011 00000111

Arriving Digital SignalFrom Telephone Switch(8000 Samples/Second)

Generated Analog SignalFor Subscriber Line

DAC

1/8000Second(8 bits)

Sounds smooth if there are enough samples

per second

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Question

If you have an audio CD player, it contains a(n) _____. a. Analog-to-digital converter

b. Digital-to-analog converter

c. Both

d. Neither

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Figure 6.12: Cellular Telephony

B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

HandoffO

PSTNMobile TelephoneSwitching Office

Cellsite

1. Divide AreaInto Cells

2. CellphoneCommunicatesVia Cellsites,

MTSO

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B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

O

3. UseChannel

47

PSTN

Cellsite

1. Reuse Channels in Non-Adjacent Cells

2. UseChannel 47

In Cell A

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B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

O

PSTN

Cellsite

1. Use A, D, and F

2. ReuseChannel 47

NextIn What Cells?

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Importance of Channel Reuse

Channels are Scarce Only ~800 in First Generation Cellular Systems

Only ~2,500 More for Second Generation Systems

You Can Only Have an Average of 20 Customers per Channel Assumes each will use the system 5% of the time

(generous)

Only 16,000 to 50,000 customers without channel reuse

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Can Reuse Channel in Nonadjacent Cells In adjacent cells, signals will interfere

To tell how roughly how many times you can reuse a channel on average

Divide the number of cells by 7Rough estimate but very useful20 cells / 7 = 3 (Round off: It’s not exact)100 cells / 7 = 14

You can multiply the possible number of subscribers by this factor

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Example 800 channels

20 cells

3 (20/7) channel reuse factors

2,400 effective channels (800 x 3)

20 subscribers/channel maximum for good service

48,000 maximum subscribers (2,400 x 20)

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Example 2,400 channels 100 cells

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Compression

Multiplies Number of Possible Subscribers by About a Factor of 3 2,400 channels 100 cells

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B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

HandoffO

PSTNMobile TelephoneSwitching Office

1.Automatic

Handoff BetweenCellsites as

Phone TravelsBetween

Cells

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Handoffs versus Roaming

Handoff Moving between cells within a single cellular

system

Cellular telephony

802.11 wireless LANs

Roaming Moving between systems

Cellular telephony: use cellphone in another city

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Figure 6.13: Generations of Cellular Service

Generation First 2nd 2.5G 3G

Technology Analog Digital Digital Digital

Data TransferRate

Data TransferIs Difficult

10 kbps*20 kbps to384 kbps

384 kbpsto 2 Mbps

Channels ~800~800 +2,500

~800 +2,500

?

Cells/ ChannelReuse

Large/Medium

Large/Medium

and Small/High

Basedon 2G

?

*Sufficient for Short Message Service (SMS) and wireless Web accessusing the Wireless Access Protocol (WAP) or i-mode

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Figure 6.13: Generations of Cellular Service

Generation First 2nd 2.5G 3G

WorldStandardization(and therefore

roaming)

PoorGood(GSM)

Basedon 2G

? (W-CDMA,CDMA-2000,

and othersystems

may compete)

U.S.Standardization

Good(AMPS)

Poor (GSM,CDM, TDMA,

& CDPD)

Basedon 2G

?

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Figure 6.14: Regulation and Deregulation

Regulation Carriers: carry signals between customer premises

Rights of Way: government permission to lay wire

Monopoly: Service was originally provided by a single telephone carrier

Regulation: This monopoly carrier was regulated to prevent abuse of the monopoly

Tariffs specify a service’s specific service parameters and pricing to prevent discrimination and guarantee service parameters

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Figure 6.14: Regulation and Deregulation

Deregulation Initially, regulated protected monopoly service

Deregulation: remove protections & restrictions

To increase competition, lowering prices

Varies by country

Varies by service within countriesData, long-distance, and customer premises

deregulation is high.Local voice service deregulation is low.

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Figure 6.15: Regulation and Carriers

Carriers Public Telephone and Telegraph (PTT) authority is

the traditional domestic monopoly carrier in most countries.

Domestic transmission: within a countryUK: British TelecomsJapan: NTT

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Carriers In the United States

U.S. is divided into regions called local access and transport areas (LATAs)

About 200 LATAs nationwideSmall states have just one LATALarge states have 10 to 20 LATAs

LATA

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Carriers

In the United StatesLocal exchange carriers (LECs) provide

service within a LATAIncumbent LEC (ILEC) is the traditional

monopoly carrier in the LATACompetitive LEC (CLEC) is a new

competitor

LATA

LEC

ILEC CLEC

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LATA LATAIXC

Carriers In the United States

Inter-exchange carriers (IXCs) provide service between LATAs

LEC versus IXC distinction is used by data carriers as well as voice carriers.

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Carriers

In the United StatesPoint of Presence (POP) is a place in a

LATA where all carriers interconnect to provide integrated service to all customers LATA

POPILEC

CLEC IXCIXC

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International Service (Between Pairs of Countries)

Provided by international common carriers (ICCs)

Allowed carriers, prices, and conditions of service are settled through bilateral negotiation between each pair of countries

Country 1 Country 2ICC

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Figure 6.15: Regulation and Carriers: Recap

U.S. Intra-LATA

LECsILECCLECs

Inter-LATAIXCs

Most of the WorldPTTs for domestic service

ICCs

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Figure 6.16: Converged Services

Integrate Voice and Data Networks Often referred to as voice over IP (VoIP) and IP

telephony

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Provide Voice and Data on a Single Network

Save money compared to traditional telephony Reducing staff and economies of scale in

purchasing with one network

Encoding voice to less than 64 kbps so fewer bits need to be sent

Packet switching to reduce transmission costs for bit sent

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Other advantages Computer-telephony integration (CTI)

Provide integrated voice and data applications

E.g., when a customer calls, their information can be brought up on-screen

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Figure 6.17: PBX-PBX IP Telephony

OrdinaryTelephone

OrdinaryTelephone

Frame Relay, ATM, orthe Internet

IPPacket

PBX withIP Telephony Module

PBX withIP Telephony Module

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Implementation PBX-to-PBX connectivity is easy and saves money

on long-distance calls

LAN implementations are more difficult, less well-developed, and may not save money

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Will Cost Savings be Realized? Convergence justified by gap between high long-

distance and international telephone charges and possible savings through IP telephony

Falling traditional telephone prices are reducing the gap

Packet transmission inefficiency is reducing the theoretical savings and therefore the gap

Does the remaining gap justify convergence?

Telephone Price

VoIP Price

Gap

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Service Quality Availability (less than the PSTN’s 99.999%)

Sound qualitylatency produces pausesMillisecond-to-millisecond inconstancy of

speed produces jitter Sound quality is addressed by using a single ISP to

connect all sitesService Level Agreements (SLAs)

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Figure 6.18: Using a Single ISP for VoIP

ISP 1 Backbone ISP 2 Site A Site B

Site C

No Congestion in Site A-C CommunicationBecause All Traffic Passes through a Single ISP.

It Avoids the Congested Internet Backbone.

Congestion in Site A-B CommunicationBecause of Passage Through Internet Backbone.

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Voice/Data Cultural Concerns

Data Networking Concerns Will all this voice traffic mean that my data cannot

get through well?

Telephony Concerns Will people get the same level of voice quality?

Will they get secondary services (3-party calling, call waiting, etc.)

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1 Telephony: Internal and External Chapter 6 Copyright 2003 Prentice-Hall Panko’s Business Data...

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