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Chapter 11 Voice and Data Delivery Networks. Introduction. Basic Telephone Systems Dial-up Modem ISDN DSL Cable Modem T1 Leased Line Services Frame Relay ATM CTI & UC. Basic Telephone Systems (I). POTS is the ‘plain old telephone system’ Transmit voice at bandwidth less than 4000 Hz

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Chapter 11 Voice and Data Delivery Networks

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chapter 11 voice and data delivery networks
Chapter 11

Voice and Data Delivery Networks

  • Basic Telephone Systems
  • Dial-up Modem
  • ISDN
  • DSL
  • Cable Modem
  • T1 Leased Line Services
  • Frame Relay
  • ATM
  • CTI & UC
basic telephone systems i
Basic Telephone Systems (I)
  • POTS is the ‘plain old telephone system’
  • Transmit voice at bandwidth less than 4000 Hz
  • Two 4000 Hz channels required for telephone conversation
  • A 4000 Hz analog signal can only carry 33,600 bps, while a 4000 Hz digital signal can carry about 56,000 bps
  • Higher frequency needed for faster transmission.
  • POTS cannot deliver faster signals
basic telephone systems ii
Basic Telephone Systems (II)
  • Local loop runs from the central office to your home or business
    • Central office houses the switching equipment and provides a local dial tone on your telephone
    • Central office passes your long distance call off to a long distance provider
  • The country is divided into a few hundred local access transport areas (LATAs)
    • long distance call goes from one LATA to another, handled by a long distance telephone company
    • Local call stays within a LATA, handled by a local telephone company
basic telephone systems iii
Basic Telephone Systems (III)
  • Trunk runs between central offices and other telephone company switching centers
    • Trunk is usually digital, high speed, and carries multiple telephone circuits
    • Trunk is typically a 4-wire circuit, while a telephone line is a 2-wire circuit
    • Trunk is not associated with a single telephone number like a line is
  • A telephone number consists of an area code, an exchange, and a subscriber extension
  • The area code and exchange must start with the digits 2-9 to separate them from long distance and operator services
  • Modified Final Judgment of 1984 made AT&T split off the local telephone companies from the long distance company
    • Regional Bells (baby bells) service local phone.
    • Started with 7, only 3 remained (AT&T, CenturyLink, Verizon)
  • Telecommunications Act of 1996 opened up the local telephone market to competitors
    • Cable TV companies (cable telephony), long distance telephone companies, or anyone that wanted to start a local telephone company could offer local telephone service
  • 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, special prefixes for WATS, FX, etc. (private dialing plans)
    • PBX collects dialed digits and intelligently decides how to route this call for lowest cost
  • Additional advanced 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
automated attendant
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
automatic call distributor
Automatic Call Distributor
  • Automatic Call Distributor: perhaps you’ve experienced this when you call a business, 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 calling 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!)
  • 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
interactive voice response
Interactive Voice Response
  • IVR is similar to AA 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
  • Common examples of IVR include:
    • Calling 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
key telephone system
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)
basic telephone systems services
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
  • 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
other players in the market
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
    • ARDIS and RAM Mobile Data two good examples
the 56k dial up modem
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
  • 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
dsl i
  • 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
  • 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
dsl ii
  • 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
  • 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
  • A leased service that provides a digital telephone or data connection into a home or business
  • Can have a digital telephone line and a 64 Kbps data line, or one 128 Kbps data line
  • Basic rate interface (BRI) for homes and small businesses
    • Consists of two B channels and one D channel
    • One B channel carry 64 Kbps of data or PCM-encoded voice.
    • D channel is 16 Kbps and carries signaling information
    • The B channels are dialable, and the D channel can be always on
    • The 2 B channels can be combined for a 128 Kbps data channel
  • Primary rate interface (PRI) for larger businesses
    • Used by larger businesses and contains 23 B channels and one 64 Kbps D channel
    • Essentially equivalent to a T-1, but with ISDN the 23 channels are dialable!
    • Appropriate ISDN modems / multiplexors are necessary to support this service
cable modems
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
t 1 leased line
T-1 Leased Line
  • A digital, synchronous TDM stream used by businesses and telephone companies
  • To support a T-1 service, a channel service unit / data service unit (CSU/DSU) is required at the end of the connection
  • Always on and always transmitting
  • Support up to 24 simultaneous channels. These channels can be either voice or data (PBX support)
  • Can be provisioned as a single channel delivering 1.544 Mbps of data (LAN to ISP connection)
  • Can order a ¼ T-1 or a ½ T-1
    • T-1 constantly transmits 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)
frame relay i
Frame Relay (I)
  • High-speed (45 Mbps) connection for data transfer between two points either locally or over long distances
  • A business connect itself to the local frame relay port through a high-speed line
  • The frame relay network transmits the data to the other side
  • Permanent virtual circuit (PVC) is a connection between two endpoints
    • PVCs are created by the provider of the frame relay service
  • The high-speed line, the port, and the PVC should all be chosen to support a desired transmission speed
  • The user and frame relay service 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
frame relay ii
Frame Relay (II)
  • Frame Relay vs. the Internet
    • Frame relay has many advantages over the Internet, including guaranteed throughput and minimum delay as well as better security
    • Internet has the advantage of being practically everywhere
      • Cheaper and simpler to create connections (no PVCs necessary)
      • Internet tunnels (VPNs) are also attractive
  • Voice over Frame Relay (VoFR)
    • Frame relay is also capable of supporting voice communications
      • High transfer speeds adequately support the needs of interactive voice
    • If a company requires multiple voice circuits, frame relay is an interesting solution
  • Frame Relay Switched Virtual Circuits
    • Frame relay can also provide switched virtual circuits (SVC)
    • An SVC can be created dynamically by the customer
    • Good for short-term connections, but more expensive
  • Very high-speed packet delivery service, capable of speeds up to 622 Mbps (in 53-byte cells)
  • Able to offer various classes of service (QoS)
    • constant bit rate service for a high-speed, continuous connection
    • A less demanding service is variable bit rate (VBR)
      • VBR can also support real time applications, as well as non-real time applications, 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
mpls and vpns
  • Frame relay and ATM are declining in popularity due to more people using the Internet
  • But you can’t just send potentially important data over the Internet without doing something first
  • One thing businesses are doing is applying MPLS labels to the IP packets
  • The use of MPLS routes data packets quickly through the Internet
  • And as we have also seen, VPNs (virtual private networks) create secure tunnels
  • 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
  • Combines traditional voice networks with modern computer networks.
  • Can also integrate voice cabling with data cabling.
  • 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
    • Third party call control
    • PBX Graphic User Interface
    • Call filtering
    • Customized menuing systems
unified communications
Unified Communications
  • Just as CTI is a convergence of multiple technologies and applications, unified communications is the convergence of real-time and non-real-time communications
  • For example, convergence of telephony, instant messaging, video conferencing, voice mail, e-mail, and presence information into one or more applications