Chapter Twelve

1
Chapter Twelve

• Voice and Data Delivery Networks
• Data Communications and Computer Networks A
  Business Users Approach, Fourth Edition

2
Topics

• The basic elements of a telephone system
• The 1984 Modified Final Judgment and it effects
  on the telephone industry
• Local and inter-exchange carriers and services
• The Telecommunications Act of 1996
• Basic characteristics of a modem
• Characteristics of leased lines, DSL, and cable
• Frame relay permanent and switched virtual
  circuits and committed information rate
• Asynchronous Transfer Mode virtual path and
  channel connections and classes of service
• Convergence in the networking industry

3
Introduction

• The fields of data and voice communications are
  merging
• Voice systems can transfer computer data
• Data networks support voice transfers
• An understanding of basic telecommunications is
  critical for anyone studying networks and data
  communications

4
Telephone Lines, Trunks, and Numbers

• The local loop runs from a phone companys
  central office to a home or business
• The central office houses switching equipment and
  provides a dial tone
• For long-distance calls the central office passes
  the call to a long-distance provider

5
Central Office Local Loop

6
Local Access Transport Areas (LATAs)

• The United States is divided into roughly 300
  LATAs
• Long-distance calls travel from one LATA to
  another, and are handled by long-distance phone
  companies
• Local calls stay within a LATA and are handled by
  a local phone company

7
Trunks

• Special telephone lines that run between central
  offices and telephone switching centers
• Usually digital, high-speed lines comprised of
  multiple circuits
• Trunks are typically a 4-wire circuit, while a
  telephone line is a 2-wire circuit
• Not associated with a single phone number like a
  telephone line is

8
Telephone Numbers

• Consist of
• an area code
• an exchange, and
• a subscriber extension
• The area code and exchange begin with the digits
  2-9 to separate them from long distance and
  operator services

9
Composition of a Telephone Number

10
Interfaces

• Telephone company can install lines no further
  than 12 inches into the building
• This point is called the demarcation point, or
  demarc
• Modular RJ-11 connectors are commonly used to
  interconnect lines and the telephone handset to
  its base
• When handset is lifted off its base an off-hook
  signal is sent to the central office

11
Making a Call

• When an off-hook signal is received by a central
  office, a dial tone is generated and returned to
  callers telephone
• The dial tone is the users signal to dial a
  phone number
• Central office equipment processes the dialed
  digits and places a call (creates a circuit) to
  the destination dialed

12
Private Branch Exchange (PBX)

• An internal phone switching system designed for
  medium to large businesses
• Provides advanced features to users, such as
• 4-digit internal dialing
• Special prefixes for private dialing plans such
  as WATS, FX, etc
• Intelligently decides how to route a call for
  lowest cost

13
PBX Components

• CPU, memory, telephone lines, trunks
• Switching network
• Supporting logic cards
• Main distribution frame
• Console or switchboard
• Battery back-up system

14
PBX Features

• Voice mail
• Automated attendant
• Automatic call distribution
• Interactive voice response
• VoIP

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

16
Automatic Call Distributor

• Answers with a message when operators are busy
  and distributes callers on hold to first
  available operator
• 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 available
  human operator

17
Advanced Features

• Modern ACD systems perform the following advanced
  functions
• Call prioritization
• Route calls based on the skill set of the agent
• Place calls in a waiting queue and play an
  appropriate message (how long callers must wait
  when) when agents are busy
• Forward calls to another call center, or perform
  automatic return call

18
Interactive Voice Response (IVR)

• Similar to automated attendant except, IVR
• incorporates a connection to a database (on a
  mainframe or server)
• allows caller to access and/or modify database
  information
• can also perform fax on demand

19
Interactive Voice Response Examples

• Calling a 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

20
Key Telephone System

• A on-premises resource-sharing device similar to
  a PBX
• Used by a small or branch offices
• Distributes a given number of internal telephones
  over a lesser number of external phone lines
• Outside lines selected by pressing a special key
  on the telephone

21
Basic Telephone Services

• Foreign exchange service (FX) - A local number is
  used to call a remote site over a leased line
• 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

22
Other Players in the Market

• Alternate operator services
• Pay phones, hotel phones
• Aggregator
• Pools small companies together to get phone
  discounts
• Reseller
• Resells a variety of leased lines from phone
  companies to customers
• Specialized mobile radio carriers
• Provides mobile communication services to
  businesses and individuals, including dispatch,
  paging, and data services
• Examples - ARDIS and RAM Mobile Data

23
The Telephone Network Before and After 1984

• In 1984, U.S. government broke up ATT
• Before then, ATT owned almost all local phone
  circuits and all the long-distance service
• The Modified Final Judgment of 1984 required that
  ATT split off local phone companies from the
  long-distance company
• Seven Regional Bell Operating Companies were
  formed
• Today there are 4 companies BellSouth, SBC,
  Qwest (US West), and Verizon (Bell Atlantic)

24
The Original Bell Companies

25
Exchange Carriers

• Another result of the Modified Judgment was
  creation of LATAs (local access and transport
  areas)
• Local telephone companies became known as local
  exchange carriers (LECs), and long distance
  telephone companies became known as
  inter-exchange carriers (IEC, or IXC)
• Calls that remain within LATA are intra-LATA, or
  local calls
• Calls that pass from one LATA to another are
  inter-LATA, or long distance

26
Office Classes

• Before 1984, telephone networks in the U.S.
  resembled a large hierarchical tree, with Class 5
  offices at the bottom and Class 1 offices at the
  top
• Users were connected to Class 5 offices
• The greater the distance between caller and
  receiver, the further up the tree the call
  progressed
• Todays telephone structure is a collection of
  LECs, POPs, and IECs

27
Telephone Networks After 1996

• The Telecommunications Act of 1996 is another
  landmark ruling affecting the telephone industry
• This legislation opened up the local telephone
  market to competition
• Cable TV companies, long-distance telephone
  companies, or anyone that wants to start a local
  telephone company can offer local telephone
  service
• Local phone companies that existed before the Act
  are known as incumbent local exchange carriers
  (ILEC) while the new companies are competitive
  local exchange carriers (CLEC)

28
LECs vs CLECs

• LECs are supposed to allow CLECs access to all
  local loops and switching centers / central
  offices
• If a local loop is damaged, the LEC is
  responsible for repair
• The LEC is also supposed to provide the CLEC with
  a dial tone discount (17-20)
• LECs can also provide long-distance service if
  they can show there is sufficient competition at
  the local service level

29
Limitations of Telephone Signals

• POTS lines were designed to transmit the human
  voice over 4000 Hz channels
• A telephone conversation requires two channels,
  each occupying 4000 Hz

30
Telephone Channels

31
Bandwidth Limitations

• A 4000 Hz analog signal can only carry about
  33,600 bps of information
• To send more information per second, a higher
  frequency signal or more advanced modulation
  techniques are required

32
56k Modems

• 56 kbps modems are rated at 56,000 bps because
  digital signaling as opposed to analog signaling
  is used
• Could achieve 64k except
• Local loop is still analog
• Analog to digital conversion at the local modem
  introduces noise/error
• In reality 56k cannot be attained because
• FCC restricts power levels so only 53k can be
  attained
• 53k is not possible if an additional analog to
  digital conversion exists between sender and
  receiver, or if there is significant noise on the
  line

33
Analog Local Loop

34
Analog and Digital Connections

35
56k Modem Standards

• V.90
• Maximum upstream speed is 33,600 bps
• V.92
• Newer standard
• Allows maximum upstream speed of 48 kbps (under
  ideal conditions)
• Can place a data connection on hold when a voice
  telephone call arrives if call waiting is
  available

36
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
• Approximately half of the telephone lines in the
  U.S. are not capable of supporting DSL
• DSL providers are limited or non-existent in
  certain parts of the US

37
DSL Basics

• Depending on the type of service, DSL is capable
  of transmission speeds from 100,000s of bits per
  second to single-digit megabits per second
• Because DSL is highly dependent upon noise
  levels, a subscriber cannot be any more than 5.5
  kilometers (about 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

38
DSL Service

• Often connects a user to the Internet
• Can also provide 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 splitter separates the POTS from DSL, and a DSL
  modem converts the DSL signals into a form
  recognized by the computer

39
DSL Components

40
DSL Formats

• 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

41
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 rates between 500 kbps
  and 25 Mbps

42
Cable Modems Illustrated

43
T-1 Leased Line Service

• Digital service offered by the telephone
  companies that can transfer both voice and
  computer data as fast as 1.544 Mbps
• Requires a channel service unit / data service
  unit (CSU/DSU) as an interface

44
T-1 Features

• A digital, synchronous TDM stream used by
  businesses and telephone companies
• 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)

45
T-1 Features (continued)

• Requires 4 wires, as opposed to a 2-wire
  telephone line
• Intra-LATA (local) which costs roughly 350-400
  per month
• inter-LATA (long distance) which can cost
  thousands of dollars per month (usually based on
  distance)
• Fractional T-1 (1/4 T-1 or a 1/2 T-1) also
  available

46
T-1 Frames

• Constantly transmits at a rate of 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)
• At 8000 frames per second 193 bits per frame
  1.544 Mbps
• On voice channels each byte is one byte of
  PCM-encoded voice
• On data channels, each byte contains 7 bits of
  data and 1 bit of control information (7 8000
  56 kbps)

47
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

48
A Simple Frame Relay Connection

49
Permanent virtual circuit (PVC)

• Connection between two Frame Relay endpoints
• Created by the provider of the frame relay
  service
• A high-speed telephone line connects subscribers
  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

50
Frame Relay Ports and PVC

51
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

52
Leased Line Connections Between Locations

53
Frame Relay PVCs Between Locations

54
Committed Information Rate (CIR)

• A service-level agreement between user and
  carrier
• 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

55
Committed Information Rate (CIR) Example

• A company agrees to a CIR of 512 kbps with a
  burst rate of 256 kbps. Transmissions must lt 512
  kbps, with an occasional burst up to 768 kbps,
  that lasts no longer than than 2 seconds
• If the company maintains their end of the
  agreement, the carrier will provide roughly
  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 customers frames may be
  discarded

56
Frame Relay vs. the Internet

• Frame relay has many advantages over the
  Internet, including
• guaranteed throughput
• minimum delay
• better security
• Internet has the advantage of being practically
  everywhere, cheaper, and simpler to create
  connections (no PVCs necessary)
• VPNs are attractively priced

57
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 a viable solution

58
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

59
Asynchronous Transfer Mode (ATM)

• A very high-speed packet-switched service,
  similar 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 relays maximum is typically 45 Mbps

60
ATM Virtual Channel Connections

• ATM data travel over virtual channel connections
  (VCCs)
• To better manage VCCs, virtual path connection
  (VPC) is required
• One of ATMs strengths is its ability to offer
  various classes of service

61
ATM Classes of Service

• Constant bit rate service supports high-speed,
  continuous real-time connections
• Variable bit rate (VBR) supports
• real-time applications (rt-VBR)
• non-real-time applications (nrt-VBR)
• Available bit rate (ABR) is used for bursty
  traffic non-real time traffic
• 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

62
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

63
Comparison of DSL, Cable Modems, Frame Relay, and
ATM

64
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

65
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 customers telephone number appears on the
  customer support reps terminal and immediately
  pulls up the customers 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

66
Computer-Telephony Integration (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
  users computer
• The telephones may still be connected to the PBX
  or they may be connected to the LAN via the LAN
  wiring

67
Computer-Telephony Integration Applications

• Unified messaging
• Interactive voice response
• Integrated voice recognition and response
• Fax processing and fax-back
• Text-to-speech and speech-to-text conversions
• Third-party call control
• PBX graphic user interface
• Call filtering
• Customized menu systems

68
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

69
Telecommunication Systems In Action A Company
Makes a Service Choice (continued)

• What could Better Box use for communications?
• 56kbps dial-up?
• DSL?
• Cable modem?
• T-1?
• Frame relay?
• ATM?

70
Telecommunication Systems In Action A Company
Makes a Service Choice (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

71
Telecommunication Systems In Action A Company
Makes a Service Choice (continued)

72
Telecommunication Systems In Action A Company
Makes a Service Choice (continued)

73
Telecommunication Systems In Action
Hypothetical Prices

74
Telecommunication Systems In Action A Company
Makes a Service Choice (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

75
Telecommunication Systems In Action A Company
Makes a Service Choice (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

76
Telecommunication Systems In Action A Company
Makes a Service Choice (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

77
Summary

• The basic telephone system that covers the U.S.
  is called plain old telephone service (POTS) and
  is a mix of analog and digital circuits
• Divestiture of ATT in 1984 opened the
  long-distance telephone market to other
  long-distance providers, forced ATT to sell off
  its local telephone companies, and divided the
  country into local access transport areas (LATAs)
• A PBX is an on-premise computerized telephone
  switch that handles all internal and outgoing
  telephone calls and offers a number of telephone
  services

78
Summary (continued)

• A Centrex offers same services as PBX, but
  equipment resides on telephone companys
  property, and business leases the service
• Telecommunications Act of 1996 opened local
  telephone service to new competitors and required
  existing local telephone companies to provide
  these competitors with access to local telephone
  lines
• Data rate of standard modems using voice-grade
  telephone lines has peaked at 33,600 bits per
  second.
• Newer digital modems are capable of speeds near
  56,000 bits per second, depending on line
  conditions
• Leased lines are established by communications
  service provider and serve as permanent, private
  connections between two locations

79
Summary (continued)

• New technologies such as digital subscriber line
  (DSL) and cable modems have improved data
  transfer rates available between homes and
  businesses and Internet service providers
• Frame relay is service that provides digital data
  transfer over long distances and at high data
  transfer rates
• Asynchronous Transfer Mode (ATM) is also a
  packet-switched service, but it supports all
  types of traffic and operates over LANs as well
  as WANs and MANs
• Computer-telephony integration is convergence of
  data communications networks and voice systems