Chapter Twelve Voice and Data Delivery Networks. 2 Introduction General, we used to go into either – data communications or voice communications Today,

Chapter Twelve

Voice and Data Delivery Networks

2

Introduction

• General, we used to go into either– data communications or voice communications

• Today, the two fields are mergingReasons:

1. Voice systems transfer computer data and

2. data networks support voice

• Thus, we need to the basic of voice telecommunications too!– Basic concept (to p3)

3

Basic conceptIt has:• The local loop is the telephone line that runs from the telephone

company’s central office to your home or business• Central office – building that houses the telephone company’s switching equipment and provides a local dial tone on

your telephone

• For a local call, it has such a layout• If you place a long-distance call, the central office passes your

telephone call off to a long-distance provider, a nation wide telephone system

• Trunk – special telephone line that runs between central offices and other telephone switching centers– Usually digital, high-speed, and carries multiple telephone

circuits– Typically a 4-wire circuit, while a telephone line is a 2-wire

circuit

• How to classify a call is a long distance or local call?– LATA concept

(to p4)

(to p5)

(to p7)

(to p6)

(to p8)

4

FIGURE 5-8 It is more efficient to connect telephones to a central office switch and then connect the central office switches together than to connect all telephones to each other.

A Local Environment

building that houses the telephone company’s switching Equipment and provides a local dial tone on your telephone

(to p3)

5

FIGURE 5-11 Residential telephone cabling.(to p3)

6

FIGURE 5-10 The connection of the central offices in the nationwide telephone network.

A nation-wide environment

Local Central Offices

(to p3)

7

FIGURE 5-7 Diagram of a telephone call involving toll trunks and toll offices.

Note: can be replacedby a switch office

(to p3)

8

LATA concept

• The country is divided into a few hundred local access transport areas (LATAs)– If your call goes from one LATA to another, it is a

long-distance call and is handled by a long-distance telephone company

– If your call stays within a LATA, it is a local call and is handled by a local telephone company

– (note: This concept applied in USA only and not HK)

Installing a telephone system/line(to p9)

9

Telephone System/Line

• When telephone company installs a line, it must not proceed any further than 12 inches into the building – This point is the demarcation point, or demarc

• Modular connectors, such as the RJ-11, are commonly used to interconnect telephone lines and the telephone handset to the base

• When handset is lifted off base (off-hook), an off-hook signal is sent to the central office

(to p10)

10

Telephone System/Line (continued)

• When off-hook signal arrives at central office, a dial tone is generated and returned to telephone

• When user hears the dial tone, they dial (or press) number

• The central office equipment collects dialed digits, and proceeds to place appropriate call

• Types of telephone systems (to p11)

11

Types of telephone systems

• Private Branch Exchange (PBX)• Automated Attendant• Automatic Call Distributor• Interactive Voice Response• Key Telephone System

• Basic Telephone Systems Services– That offered by local operators

• Other Players in the Market

(to p20)

(to p21)

(to p24)

(to p16)

(to p15)

(to p12)

(to p18)

12

PBX

• Private Branch Exchange (PBX) – common internal phone switching system for medium- to large-sized businesses– Provides advanced intelligent features to users,

such as:• 4-digit internal dialing• Special prefixes for WATS, FX, etc (private dialing

plans)• PBX intelligently decides how to route a call for

lowest cost

(to p13)

13

PBX (continued)

• More PBX features:– Voice mail

– Routes incoming calls to the best station set (automatic call distribution)

– Provides recorded messages and responds to touch-tone requests (automated attendant)

– Access to database storage and retrieval (interactive voice response)

– VoIP

(to p14)

14

PBX (continued)

• PBX components: – CPU, memory, telephone lines, trunks

– Switching network

– Supporting logic cards

– Main distribution frame

– Console or switchboard

– Battery back-up system

(to p11)

15

Automated Attendant

• Plays a recorded greeting and offers a set of options

• Lets the caller enter an extension directly (touch tone or voice) and bypass an “operator”

• Forwards the caller to a human operator if the caller does not have a touch tone phone

• Available as an option on a PBX

(to p11)

16

Automatic Call Distributor

• When you call a business and are told all operators / technicians / support staff / etc. are busy and that your call will be answered in the order it was received

• Used in systems where incoming call volume is large, such as customer service, help desk, order entry, credit authorization, reservations, and catalog sales

• Early systems used hunt groups– Original systems routed call to first operator in line

(kept person very busy!)

(to p17)

17

Automatic Call Distributor (continued)

• Modern systems perform more advanced functions, such as:– Prioritize the calls– Route calls to appropriate agent based on the

skill set of the agent– If all agents busy, deliver call to waiting queue

and play appropriate message (like how long they may have to wait)

– Forward calls to another call center, or perform automatic return call

(to p11)

18

Interactive Voice Response

• IVR is similar to automated attendant except:– IVR incorporates a connection to a database (on

a mainframe or server)

– IVR allows caller to access and/or modify database information

– IVR can also perform fax on demand

(to p19)

19

Interactive Voice Response (continued)

• Common examples of IVR include:– Call your bank to inquire about an account

balance

– University online registration system

– Brokerage firm taking routine orders from investors

– Investment fund taking routine requests for new account applications

– A company providing employees with info about their benefit plans

(to p11)

20

Key Telephone System

• Used within a small office or a branch office, a key telephone system (KTS) is an on-premise resource sharing device similar to a PBX

• Example – key system might distribute 48 internal telephone sets over 16 external phone lines– The business would pay for the 16 individual lines

but have 48 telephone sets operating

• User selects outside line by pressing corresponding line button on key set (phone)

(to p11)

21

Basic Telephone Systems Services

• Foreign exchange service (FX) - customer calls a local number which is then connected to a leased line to a remote site– It can serve as discounted IDD for service agents

• Wide area telecommunications services (WATS) – discount volume calling to local- and long-distance sites

• Off-premises extensions (OPX) – dial tone at location B comes from the PBX at location A

(to p11)

(to p22)

22

Wide Area Telecomm Services

• Wide Area Telecomm Services (WATS)– offers quantity discounts to high volumes of calls

– there are 3 basic categories:

– a) call direction (that is in-WATS or out-WATS)• In-WATS (only allow users to call in to company)• Out-WATS(only allows users to call out to

company)

(to p23)

23

– b) Coverage • The charges depends on band zone to which

company has prescribed.• In USA, it has 5 bands (1-5)

– c) Geographic regions• three types• 1) Intra-state (service provides on either in or

out WATS, within subscriber’s home state)• 2) Inter-state (applies to outside state boundary

but within the country)• 3) International (applies similar to IDD calls)

(to p21)

24

Other Players in the Market

• Alternate operator services – Pay phones, hotel phones

• Aggregator – pulls a bunch of small companies together and goes

after phone discounts• Reseller

– rents or leases variety of lines from phone companies, then resells to customers

• Specialized mobile radio carriers – mobile communication services to businesses and individuals, including dispatch, paging, and data services

HK Telecomm Revolution ! (to p25)

25

Telecomm and Deregulation in HK Environment

• Prior 1995, all telecomm services in HK are franchised (why need to cater for franchising?)

• HK Government opens up the telecomm markets of fixed network services in 1995.

• Franchised right to HK telecomm (now PCCW) expired on 1995.

• New operators fixed line tel line registered in 1995• HK telecom (PCCW) licensed on June 29, 1995• Hutchison Telecomm Ltd licensed on June 30,

1995• New World licensed on June 20, 1995•

(to p26)

26

Telecomm and Deregulation in HK Environment (cont.)

• Deregulation of Mobile comm services

– In 23 Feb 1999, OFTA (Office for Telecomm Authority) announced the regulation of MNP (Mobile number portability) started on 1 March 1999, that a customer could retain of his/her mobile phone number as personal identity.

• Worldwide Regulatory agencies • Limitations of voice telecomm!

(to p27)

(to p28)

27

Worldwide regulatory agency

USA Federal Communications Commission (FCC)

Hong Kong Office for Telecommunications Authority (OFTA) (to p26)

28

Limitations of Telephone Signals

• POTS lines were designed to transmit the human voice, which has a bandwidth less than 4000 Hz

• A telephone conversation requires two channels, each occupying 4000 Hz

• A 4000 Hz analog signal can only carry about 33,600 bits per second of information while a 4000 Hz digital signal can carry about 56,000 bits per second – ie the use of mulltiplexing

• How to make it faster? (to p30)

(to p29)

29

Limitations of Telephone Signals (continued)

(to p28)

30

Limitations of Telephone Signals (continued)

• If you want to send information faster, you need a signal with a higher frequency or you need to incorporate more advanced modulation techniques

• POTS cannot deliver faster signals– What will?

• The 56k Dial-Up Modem• Other High speed data networks

(to p31)

(to p36)

31

The 56k Dial-Up Modem

• A 56k modem (56,000 bps) achieves this speed due to digital signaling as opposed to analog signaling used on all other modems

• Would actually achieve 64k except:– Local loop is still analog, thus analog signaling

– Analog to digital conversion at the local modem introduces noise/error

– Combined, these shortcomings drop the speed to at best 56k

(to p34)(to p33)

(to p32)

32

The 56k Dial-Up Modem (continued)

(to p31)

33


(to p31)

34


• In reality, it does not achieve 56k either – FCC will not let modem transmit at power level

necessary to support 56k, so the best modem can do is approximately 53k

• Will not even achieve 53k if connection between your modem and remote computer contains an additional analog to digital conversion, or if there is significant noise on line

• Two standards in the market(to p35)

35


• Based upon one of two standards:– V.90

• Upstream speed is maximum 33,600 bps

– V.92 • Newer standard • Allows maximum upstream speed of 48 kbps

(under ideal conditions) • Can place a data connection on hold if the

telephone service accepts call waiting and a voice telephone call arrives

(to p30)

36

High Speed data networks

• Digital Subscriber Line (DSL)• Cable Modems• T-1 Leased Line Service• Frame Relay

– Committed Information Rate (CIR)

• Asynchronous Transfer Mode (ATM)

– Comparison

• Convergence

(to p48)

(to p60)

(to p64)

(to p42)

(to p37)

(to p65)

(to p44)

37

Digital Subscriber Line

• Digital subscriber line (DSL) is a relative newcomer to the field of leased line services

• DSL can provide very high data transfer rates over standard telephone lines

• Unfortunately, less than half the telephone lines in the U.S. are incapable of supporting DSL– And there has to be a DSL provider in your region

(to p38)

38

DSL Basics

• DSL, depending on the type of service, is capable of transmission speeds from 100s of kilobits into single-digit megabits

• Because DSL is highly dependent upon noise levels, a subscriber cannot be any more than 5.5 kilometers (2-3 miles) from the DSL central office

• DSL service can be:– Symmetric – downstream and upstream speeds are

identical– Asymmetric – downstream speed is faster than the

upstream speed(to p39)

39

DSL Basics (continued)

• DSL service – Often connects a user to the Internet– Can also provide a regular telephone service (POTS)

• The DSL provider uses a DSL access multiplexer (DSLAM) to split off the individual DSL lines into homes and businesses– A user then needs a splitter to separate the POTS line

from the DSL line, and then a DSL modem to convert the DSL signals into a form recognized by the computer

(to p40)

40

DSL Basics (continued)

(to p41)

41

DSL Formats

• A DSL service comes in many different forms:– ADSL (Asymmetric DSL)– CDSL (Consumer DSL)

• Trademarked version by Rockwell– DSL Lite

• Slower form than ADSL– HDSL (High bit-rate DSL)– RADSL (Rate-adaptive DSL)

• Speed varies depending on noise level

(to p36)

42

Cable Modems

• Allow high-speed access to wide area networks such as the Internet

• Most are external devices that connect to the personal computer through a common Ethernet card

• Can provide data transfer speeds between 500 kbps and 25 Mbps

(to p43)

43

Cable Modems (continued)

(to p36)

44

T-1 Leased Line Service

• T-1 – digital service offered by the telephone companies that can transfer data as fast as 1.544 Mbps (both voice and computer data)

• To support a T-1 service, a channel service unit / data service unit (CSU/DSU) is required at the end of the connection

(to p45)

45

T-1 Leased Line Service (continued)

• A T-1 service – Is a digital, synchronous TDM stream used by

businesses and telephone companies

– Is always on and always transmitting

– Can support up to 24 simultaneous channels• These channels can be either voice or data (PBX

support)

– Can also be provisioned as a single channel delivering 1.544 Mbps of data (LAN to ISP connection)

(to p46)

46


• A T-1 service (continued)– Requires 4 wires, as opposed to a 2-wire

telephone line

– Can be either intra-LATA (local) which costs roughly $350-$400 per month, or inter-LATA (long distance) which can cost thousands of dollars per month (usually based on distance)

• A customer may also be able to order a 1/4 T-1 or a 1/2 T-1

(to p47)

47


• Constantly transmits frames (8000 frames per second)– Each frame consists of one byte from each of the 24

channels, plus 1 sync bit (8 * 24 + 1 = 193 bits)• 8000 frames per second * 193 bits per frame = 1.544

Mbps

– If a channel is used for voice, each byte is one byte of PCM-encoded voice

– If a channel is used for data, each byte contains 7 bits of data and 1 bit of control information (7 * 8000 = 56 kbps)

(to p36)

48

Frame Relay

• Leased service that can provide a high-speed connection for data transfer between two points either locally or over long distances

• A business only has to connect itself to local frame relay port– Hopefully this connection is a local telephone call

– Once data reaches local frame relay port, the frame relay network, or cloud, transmits the data to the other side

(to p49)

49

Frame Relay (continued)

(to p50)

50


• Permanent virtual circuit (PVC) – connection between two endpoints – Created by the provider of the frame relay service

• The user uses a high-speed telephone line to connect its company to a port, which is the entryway to the frame relay network

• The high-speed line, the port, and the PVC should all be chosen to support a desired transmission speed

(to p51)

51


(to p52)

52

Frame Relay Setup

• Consider a company that has four office locations and currently has six leased lines interconnecting the four locations– To install frame relay, the company would ask for

six PVCs in place of the six leased lines

– The company would also need four high-speed telephone lines and four ports connecting the four locations to the frame relay cloud

(to p53)

53

Frame Relay Setup (continued)

(to p54)

54

Frame Relay Setup (continued)

Service agreement/ Committed Information Rate (CIR) (to p55)

55

Committed Information Rate (CIR)

• The user and frame relay service would agree upon a committed information rate (CIR)

• The CIR states that if the customer stays within a specified data rate (standard rate plus a burst rate) the frame relay provider will guarantee delivery of 99.99% of the frames

• The burst rate cannot be exceeded for longer than 2 seconds

(to p56)

56

Committed Information Rate (CIR) (continued)

• Example – if a company agrees to a CIR of 512 kbps with a burst rate of 256 kbps, the company must stay at or below 512 kbps, with an occasional burst up to 768 kbps, as long as the burst does not last longer than 2 seconds– If the company maintains their end of the agreement,

the carrier will provide something like 99.99% throughput and a network delay of no longer than 20 ms

– If the customer exceeds its CIR, and the network becomes congested, the customer’s frames may be discarded

(to p57)

57

Frame Relay vs. the Internet

• Frame relay has many advantages over the Internet, including guaranteed throughput and minimum delay, and better security

• Internet has the advantage of being practically everywhere, cheaper, and simpler to create connections (no PVCs necessary) – And Internet tunnels (VPNs) are attractive

(to p58)

58

Voice over Frame Relay (VoFR)

• Frame relay is also capable of supporting voice communications

• The high transfer speeds of frame relay adequately support the needs of interactive voice

• If a company requires multiple voice circuits, frame relay is an interesting solution

(to p59)

59

Frame Relay Switched Virtual Circuits

• Frame relay can also provide switched virtual circuits (SVC)– A SVC can be created dynamically by the

customer

– Good for short-term connections, but more expensive

(to p60)

60

Asynchronous Transfer Mode (ATM)

• Asynchronous Transfer Mode (ATM) – very high-speed packet-switched service, similar in a number of ways to frame relay

• Both send packets of data over high-speed lines• Both require a user to create a circuit with a

provider• One noticeable difference between ATM and

frame relay is speed – ATM is capable of speeds up to 622 Mbps while

frame relay’s maximum is typically 45 Mbps

(to p61)

61

Asynchronous Transfer Mode (ATM) (continued)

• Similar to frame relay, data travels over a connection called a virtual channel connection (VCC)

• To better manage VCCs, a VCC must travel over a virtual path connection (VPC)

• One of ATM’s strengths (besides its high speeds) is its ability to offer various classes of service

• If a company requires a high-speed, continuous connection, they might consider a constant bit rate service

(to p62)

62

ATM Classes of Service

• A less demanding service is variable bit rate (VBR)– VBR can also support real-time applications (rt-VBR),

as well as non-real-time applications (nrt-VBR), but do not demand a constant bit stream

• Available bit rate (ABR) is used for bursty traffic that does not need to be transmitted immediately– ABR traffic may be held up until a transmission

opening is available• Unspecified bit rate (UBR) is for lower rate traffic

that may get held up, and may even be discarded part way through transmission if congestion occurs

(to p63)

63

Advantages and Disadvantages of ATM

• Advantages of ATM include very high speeds and the different classes of service

• Disadvantages include potentially higher costs (both equipment and support) and a higher level of complexity

(to p36)

64

Comparison of DSL, Cable Modems, Frame Relay, and ATM

(to p36)

65

Convergence

• Big issue in the voice and data delivery industry

• Phone companies are buying other phone companies

• Older technologies are falling by the wayside as newer technologies take over a larger share of the market

• Newer devices are incorporating multiple applications

• Computer telephony integration is one large example of convergence

(to p66)

66

Computer-Telephony Integration (CTI)

• Emerging field that combines more traditional voice networks with modern computer networks

• Consider a system in which a customer calls a customer support number– The customer’s telephone number appears on the

customer support rep’s terminal and immediately pulls up the customer’s data

– The rep answers the phone by clicking on an icon on the screen and helps the customer

– The rep transfers the call by clicking on another icon on the computer screen

(to p67)

67

Computer-Telephony Integration (CTI) (continued)

• CTI can also integrate voice cabling with data cabling

• The company PBX talks directly to the LAN server– The PBX can direct the LAN server to provide a

telephone operation to the user through the user’s computer

• The telephones may still be connected to the PBX or they may be connected to the LAN via the LAN wiring

(to p68)

68


• CTI applications could include the following:– Unified messaging

– Interactive voice response

– Integrated voice recognition and response

– Fax processing and fax-back

– Text-to-speech and speech-to-text conversions

(to p69)

69


• CTI applications could include the following: (continued)– Third-party call control

– PBX graphic user interface

– Call filtering

– Customized menuing systems

70

Telecommunication Systems In Action: A Company Makes a Service Choice

• Better Box Corporation has offices in Seattle, San Francisco, and Dallas, with headquarters in Chicago

• Better Box wants to connect Chicago to each of the other three offices

• Better Box needs to download 400k byte files in 20 seconds– This requires a transmission speed of 160,000

bps

71


(continued)• What could Better Box use for communications?

– 56kbps dial-up?

– DSL?

– Cable modem?

– T-1?

– Frame relay?

– ATM?

72


(continued)• 56 kbps lines are too slow for our application• DSL and cable modems connect users to the

Internet, not user-to-user as needed in our application

• T-1s, frame relay, and ATM appear to be viable choices

73


(continued)

74


(continued)

75


(continued)• Typical various prices for these services are

shown on the next table

76


(continued)

77


(continued)• To provide T-1 service to all four offices:

– Seattle to Chicago: $6325 ($1200 + $2.50 per mile)

– San Francisco to Chicago: $6625

– Dallas to Chicago: $3500

– Total interLATA T-1 costs = $16,450 / month

78


(continued)• To provide frame relay service:

– Three ports at 256K = 3 x $495

– One port at 768K = $1240

– Three 256K PVCs = 3 x $230

– Four intraLATA T-1s = 4 x $350

– Total charge = $4815 / month

79


(continued)• To provide asynchronous transfer mode service:

– Four ports at 1.544 Mbps ABR = 4 x $1750

– Three channels = 3 x $250

– Three paths = $2 per mile x 5140 miles = $10,280

– Four intraLATA T-1s = 4 x $350

– Total ATM charges = $19,430 / month

Chapter Twelve Voice and Data Delivery Networks. 2 Introduction General, we used to go into either – data communications or voice communications Today,

Documents

telephone systemline

telephone handset

telephone lines

local telephone company

residential telephone

nationwide telephone

multiple telephone circuits

central office equipment