In the beginning by liaoqinmei


									Telco Basics, Convergence and
Total Network Connectivity
            Lesson 3
Some interesting numbers from CNN

What are our goals in Security?
 The “CIA” of security
Computer Security Operational Model

 Protection = Prevention + (Detection + Response)

              Access Controls      Intrusion Detection
                Encryption          Incident Handling

  Textbook uses Prevention, Detection and Remediation
Is an ROI from Security Possible?
  Security as an ROI

  Improved Security ROI

  Security that provides savings in the budget

  Security that provides additional revenue
    Switching Systems - Manual
 Early telephone switchboards used flexible lines with plugs
  on each end to connect two jacks.
 To make a connection:
       The operator picked up a cord and plugged it into the jack for the
       person making the call
       The operator obtained the name or number from the caller for who
       they wanted to connect to
       The operator then plugged the other end of the cord into the
       correct jack to complete the connection.
   The plug had a couple parts referred to as the “tip” and
    “ring”, terms later used to denote the different wires in a pair
    of phone wires (the “tip” wire was connected to the tip of the
    plug, the “ring” to the ring)
Early Switchboard
1884 Central Office
Early Telephone Switchboard
Early phone lines
A Toll Switchboard
Information Operators
    Why are no men/young men working the
   From “Information Warfare and Security” by Dorothy Denning, pg. 44:
       “In 1878 – long before the invention of digital computers – AT&T hired teenage
       boys to answer switchboards and handle office chores. It did not take long,
       however, before the company realized that putting boys in charge of the phone
       system was like putting a rabbit in charge of the lettuce. Bell‟s chief engineer
       characterized them as „Wild Indians.‟ In addition to being rude to customers
       and taking time off without permission, the boys played pranks with switchboard
       plugs. They disconnected calls and crossed lines so that people found
       themselves talking to strangers. A similar phenomenon took place in the United
       Kingdom. A British commentator remarked, „No doubt boys in their teens found
       the work not a little irksome, and it is also highly probable that under the early
       conditions of employment the adventurous and inquisitive spirits of which the
       average healthy boy of that age is possessed, were not always conducive to the
       best attention being given to the wants of the telephone subscribers.‟”
Tip and Ring
Newton’s Telecom Dictionary

 Telephone terminology
 Old fashioned way of saying “plus” and “minus” or
  ground and positive in electrical circuits
 Derive their names from the operator‟s cordboard plug
        The tip wire was connected to the tip of the plug
        The ring wire was connected to the slip ring around the jack
   Today, tip refers to the first wire in a pair of phone
    wires, ring is the second wire. Together they constitute
    the circuit that carries speech or data.
Tip and Ring
Switching Systems – Step-by-step

 The Step-by-step (or Strowger, the name of the
  undertaker who invented the switch) switch
  connects pairs of telephone wires by progressive
  step-by-step operation of a series of switches.
 Replaced the manual switchboard
 Required frequent maintenance and generated
  large amounts of electrical and mechanical noise
    Almon B. Strowger – the legend
   Strowger moved into telephony from the undertaking
    business because, as the near-legend has it, he was convinced
    that some local telephone operators, their power over him
    having gone to their heads, were deliberately giving wrong
    numbers and busy signal reports to his customers in order to
    drive him out of business. Strowger determined to find a way
    to rid the world of those pesky operators, once and for all.
    The first Strowger office could serve only 99 telephones, used
    buttons instead of a dial and each telephone needed a strong
    battery and five wires to connect it to the central office.
    During the next few years, however, these and other problems
    were solved. In 1896 the first system, this time using a dial,
    was built by the Automatic Electric Company of Chicago,
    based on Strowger's patents. It went into operation at the
    City Hall in Milwaukee, Wisconsin.
Strowger sounds
Switching Systems – Crossbar
   Works on principle of Common Control
       A method of switching in which the control equipment is
       responsible for routing calls through the network (as opposed
       to step device responsible only for the next step in the
   Depends on a crossing or intersection of two points to
    make a connection. The switching matrix, or crosspoint
    array, depends on energizing a vertical line and a
    horizontal line and the point where they intersect
    represents the connection made.
Crossbar sound
    Switching - Electronic
 The next evolutionary step in switching technology was the
  electronic switching system (ESS).
 Early electronic switches were still analog (the “reed
  switch”), now replaced with digital switches.
 Use stored program control as the next step to common
  control. Systems are much more fault tolerant.
 Tremendous increase in speed of switching with the new
  digital switches.
Private Branch Exchange (PBX)
   A privately owned (usually scaled-down) switching
    system for a company.
       A phone company central office was originally referred to as
       a public exchange thus a PBX is just a small version of the
       phone company‟s larger central switching office.
   May also be called a Private Automatic Branch
    Exchange (PABX)
       Original PBX‟s were manual, then systems introduced without
       the need for an operator – you would simply dial a „9‟ for an
       outside line. Thus the term automatic was added to PBX.
       Today this distinction is obsolete.
   Two broad categories of transmission media:
        – Copper wire, coax, fiber optic
        – Microwave, satellite
   Numerous considerations when discussing transmission
      Distance a signal will travel on a media, speed, requirement
      of line of sight, delay, susceptibility to interference/noise,
      cost, reliability, and of course, security
Transmission Media (cont.)
 Conducted Media
    Copper Wire
    Twisted pair
    Coaxial Cable
    Fiber Optics
 Radiated Media
    Encoding and Decoding
 Since voice is inherently analog, there is a conversion
  process that must take place to change the signal from
  analog to digital (and back).
 Pulse Code Modulation (PCM) is the most common method
  of encoding an analog voice signal into a digital bit stream.
     The amplitude is first sampled and then coded (quantized), and
     then converted into a binary number.
     Based on Nyquist theorem, sampling should be at a rate twice the
     highest frequency on the channel to be effective.
       – Thus, since highest frequency on voice channel is 4kHz, sampling should be
         done 8,000 times per second.
Encoding and Decoding
 Sampling – records the voltage level in time intervals
  along an analog wave.
 Quantizing – rounding to the nearest discrete value
 Encoding – Converting the numeric amplitude voltage
  levels into binary 8-bit code

 Decoding – Converting the 8-bit code into the voltage
 Reconstruction – reproduces the original analog wave
  from the voltage levels
 Filtering – strips noise out.
 The process of combining many signals into one
  composite signal – thus several calls can be
  transmitted at once over a single line.
 Three types of multiplexing in use
     Frequency Division Multiplexing (FDM)
     Time Division Multiplexing (TDM)
     Statistical Time Division Multiplexing (STDM)
 Frequency Division Multiplexing
 The oldest method of multiplexing
 Limited to analog transmissions
 Possible when useful bandwidth exceeds the required
  bandwidth of signals to be transmitted
 Splits bandwidth into multiple smaller pieces of
     e.g. 14,400 Hz can be divided into 6 channels of 2,400 HZ
 Time Division Multiplexing
 Can be used to transmit digital signals
 Uses time not frequency to achieve greater
  utilization of line
 Allocates a time slot for each device on the line
     Similar to timesharing in an operating system
FDM –vs- TDM
Data and Computer Communications by Stallings, p. 186
   Statistical Time division multiplexing
       Also known as asynchronous TDM and intelligent TDM
 Variation of TDM
 In TDM, if time slot not used, it is idle and wasted
 STDM assigns time slots dynamically, if time slot for
  one device is idle it can be used for another
       Requires address information to assure proper delivery
Some other ”phun phone sounds”
  Call Trace

  Please Deposit…

  Quarter tone

  2600 tone
    2600 Hz tone
   “Until the late 1960‟s, America‟s telephone network was run
    100% by AT&T and used 100% in-band signaling, whereby
    the circuit you talked over was the circuit used for signaling.
    For in-band signaling to work there needs to be a way to
    figure when a channel is NOT being used. You can‟t have
    nothing on the line, because that “nothing” might be a pause
    in the conversation. So, in the old days, AT&T put a tone on
    its vacant long distance lines, those between its switching
    offices. That tone was 2600 Hertz. If its switching offices
    heard a 2600 Hz, it knew that that line was not being used.”
                                    From Newton’s Telecom Dictionary, 15th ed
    Blue Boxes
   “Blue boxes are nothing more then a device to generate pairs
    of tones, and a single 2600 Hz tone. They had 12 keys, plus a
    single button (or a key). Each key was numbered 0 - 9, and
    had a "KP" key and "ST"key. The button emitted a pure
    2600 Hz tone. A toll free number is dialed, and just as the
    number is ringing, the 2600 Hz tone is sent to clear or "Blow
    off" the call. A "Ker-chink" sound is heard, which is the
    switch signaling back indicating its ready to receive the tones.
    A "KP" is sent, followed by the 10 digit number, and ending
    with an "ST" tone. Call goes through, and the only indication
    was that an 800 number was dialed. This was how it was done
    more than 15 years ago. Since then, all of the American and
    Canadian phone companies have all but ditched this older
    "in-band" signaling equipment.”
Voice Over Network
Newton’s Telecom Dictionary

   Several potential benefits to moving voice over a data
        You may save some money
        You may achieve some benefits of managing a voice and data
        network as one network
        If you have IP phones, moves, adds, and changes will be
        easier and cheaper
        Added, and integrated, new services including
          – Integrated messaging
          – Bandwidth on demand
          – Voice emails
   IP Telephony Overview
                              H.323 Architecture


Gatekeeper                               Packet-switched
                 H.323                     IP Network
                Terminal             intranet, Internet, VPNs
 Ethernet                                                              Ethernet Phone
  Phone                                                                                            H.323

     Gateway                    Router                              Gateway

 Phone           PBX                                                                                Standard
                                         Circuit-switched                                            Phone
                                         PSTN, ISDN, wireless

                                            From: “Security Requirements and Constraints of VoIP” by Mika Marjalaakso
H.323 Components
   Terminal – a terminal, or a client, is an endpoint where H.323
    data streams and signaling originate and terminate. It may be a
    multimedia PC with a H.323 compliant stack or a standalone
    device such as a USB (universal serial bus) IP telephone. A
    terminal must support audio communication; video and data
    communication support is optional.
   Gateway – a gateway is an optional component in a H.323-
    enabled network. When communication is required between
    different networks a gateway is needed at the interface. It
    provides data format translation, control signaling translation,
    audio and video codec translation, and call setup and termination
    functionality on both sides of the network.
H.323 Components (cont.)
   Gatekeeper – a gatekeeper is a very useful, but
    optional, component of an H.323-enabled network.
    Gatekeepers are needed to ensure reliable,
    commercially feasible communications. When a
    gatekeeper exists all endpoints (terminals, gateways,
    and MCUs) must be registered with it.
       A gatekeeper provides several services to all endpoints in its
       zone. These services include:
        –   Address translation
        –   Admission and access control of endpoints
        –   Bandwidth management
        –   Routing capability
H.323 Components (cont.)
   MCU – a multipoint control unit (MCU) enables
    conferencing between three or more endpoints.
    Although the MCU is a separate logical unit it may be
    combined into a terminal, gateway, or gatekeeper. The
    MCU is an optional component of an H.323-enabled

    The multipoint controller provides a centralized location
    for multipoint call setup. Call and control signaling are
    routed through the MC so that endpoints capabilities
    can be determined and communication parameters
 Standards for IP Telephony

          H.323 for IP Telephony

 Video          Audio                      Control                                 Data

H.261            G.711                                         H.245
                             H.225         H.225                               T.120
H.263            G.722
                 G.723                                                         (Multipoint
(video                       Terminal to   Call                                data transfer)
Coding)          G.728
                             gatekeeper    signaling


      Unreliable Transport (UDP)                   Reliable Transport (TCP)

                                                       From: IP Telephony, by Goralski & Kolon
H.225 and H.245
   H.225 performs the signaling for call control
       uses H.245 to establish and terminate individual logical channels
       for communication
   Five phases of signaling process
       Call setup
       Initial communications and capability exchange
       Establishment of audiovisual communication
       Call services
       Call termination
       Convergence & VoIP
April 03, 2000, Issue: 807,
Cisco Pushes VoIP To The Fore –
Merrill Lynch, TI seek cost savings in new convergence products

Cisco last week beefed up its voice and data convergence arsenal with new enterprise-oriented voice-over-IP products.

The new hardware and software, bundled under Cisco's Architecture for Voice, Video and Integrated Data (AVVID)
nameplate, is an outgrowth of Cisco's plans to mesh its voice and data products under a single architecture.

Both Merrill Lynch and Texas Instruments Inc. have been testing various components of AVVID for the past several

"There are clear advantages to be gained in deploying this platform," said Don McFarlane, system architect at Merrill

 "We expect costs to be reduced as we deploy unified messaging and have a uniform troubleshooting capability" for
administering a single voice and data conduit, he said.

 Texas Instruments is using VoIP to link its overseas offices to trim telecommunications costs. The company is also using
Cisco VoIP products as part of a trial with Expand Networks Inc. to push VoIP traffic over connections linking TI offices
in Texas with remote facilities maintained by the company in Mexico.
       VoIP (cont.)
Among the products rolled out by Cisco were enhanced call processing management software, second-generation IP
phones, more advanced support of VoIP in its Catalyst 6000 line of switches, as well as a new media server
supporting converged voice/data networks.

The products will be available later this spring. Among the new products: the 7910 and 7960 IP phones are priced from
$145 to $495; the Cisco MCS server, an NT platform that supports transmission of voice, video and data across Cisco
switches and routers, is priced at $14,995.

CallManager software, which runs on the server, is offered free to existing customers and is preinstalled on the MCS
server. The latest version of the software, compatible with Windows 2000, is capable of handling up to 100,000
users in a cluster made up of up to five media servers.

"Cisco's move is a further endorsement of IP telephony within the enterprise,“ said analyst Tere Bracco of Current

"With a player like Cisco aiming products at large companies, it's telling IT managers that VoIP isn't a toy anymore; it's an
inducement for businesses to take a look at this technology.

What Will Drive VoIP?

Still, Bracco said convergence isn't necessarily what will drive enterprises to sample VoIP.

"It's the management that will drive deployment," she said. "Managing these IP devices is much simpler and can help a
company save a lot of money for moves, adds and changes."
Convergence & VoIP   (April 2000)
Why Converge?
   $ Savings
      Eliminate long distance toll charges
      Eliminate duplicate infrastructures
      Increased competition in the industry
 Enhancement of current applications and development
  of new applications
 Collaborative tools
 The industry has been heading there for a while now
    Communication Networks
   Switched Networks – data transferred through series of
    intermediate nodes
       Circuit-switched networks
       Packet-switched networks
   Broadcast networks – no intermediate switching nodes, each
    station communicates over a shared medium
       Packet radio networks
       Satellite networks
       Local networks
        – E.g. bus or ring
Circuit Switching
   Basic premise is that an uninterrupted connection exists
    between the endpoints
       Constant bandwidth dedicated to this session
       Resources for this session reserved for the entire duration of
       the call
       Blocking is possible as a circuit may not be available
       Initial connection requires considerable work but once
       established, minimal to maintain it
       The PSTN is a circuit switched network
   “Addressing” is geographically based
     Packet Switching
   Data network is a packet switched network
        Designed for “bursty” traffic
         – Normal data traffic not as sensitive to delays
         – Voice highly sensitive to delays
   In packet switched network, data is fragmented into discrete units
   Each packet contains information about its source and destination
   A complete message may consist of 1000‟s of packets
   Packets may actually take different routes and may arrive out of order, or
    not at all
   Packet switched networks do not reserve bandwidth for each connection
   Addressing is organizationally based
     Circuit –vs– Packet Switching
Call request signal                                            Pkt 1

                                                               Pkt 2 Pkt 1

                                                 Time spent    Pkt 3 Pkt 2 Pkt 1
                                                 Hunting for
                      Time                       An outgoing           Pkt 3 Pkt 2
                                                                             Pkt 3


                              AB BC CD
                             trunk trunk trunk

                             A B C           D                 A B C             D
    Circuit –vs– Packet Switching

                           Circuit Switching   Packet Switching
Dedicated Bandwidth        Yes                 No

Quality of Service
         Voice Quality     Toll-quality        Non-toll-quality
         Delay Latency     Minimal             Variable

Utilization Level          Poor                High

Economics of Utilization   Low                 High

Call management features   Numerous            Few
    Analog –vs– Digital Signaling
   At one point, the entire voice session utilized analog signaling,
    today it is only analog at the endpoints.
       Analog voice signal now converted to digital for transmission
   Digital transmissions preferred over Analog
       Digital equipment cheaper to produce
       Digital signals provide higher quality communication
        – Digital less susceptible to „noise‟
       Digital signals easy to compress to reduce required bandwidth
   Thus – digital transmission facilities developed for PSTN to
    take advantage of these benefits: The
    T-Carrier system is born!!
Voice Energy Frequency
Multiplexing Frequency Signals
 The T1-Carrier
      CH 1
      8 bits
               CH 2   CH 3   CH 4   CH 5   CH 6   CH 7   ..........   CH 24

 The U.S. T1-Carrier system can handle 24 digitized voice
  channels multiplexed together.
 A voice channel of 4-kHz must be sampled at an 8-kHz
  rate to render clear representation with one sample thus
  taken every 125 microseconds.
 With 193 bits (8*24channels plus 1 framing bit) taken
  every 125 microseconds, the data rate is 1,544,000
  bits/second, or 1.544 megabits/second.
 This can be used for voice, or…
    Integrated Services Digital Network
   Telephone industry has gathered statistics for years on average length of call,
    average number of calls, etc. to be able to design a network that can handle the
   With the introduction of calls made for computer connections, their statistics went
    out the window – avg. length, for example, no longer applied.
   In an attempt to provide large-scale digital services, ISDN was introduced but with
    the 64Kbps rates, which at first seemed impressive, the need to use ISDN instead of
    the normal PSTN diminished. Instead an even higher speed method was desired.
   Digital Subscriber Lines (DSL) was an answer.
        Uses the same twisted-pair telephone wires that currently exist but utilizes the higher
        frequencies not used in voice band thus enabling both voice and data on the same
        Asymmetric DSL (ADSL) takes advantage of the fact that the majority of traffic is
        downstream not upstream and provides greater downstream data rates.
 While all of the digital fun was going on in the PSTN, a new
  element was introduced to the picture, Community Antenna
  Television (CATV)
 Originally designed to carry one-way video signals, with the
  addition of an upstream return channel voice and data
  communication was possible.
       Analog head-ends replaced with digital devices
       Coax trunks replaced with fiber
   While voice is not generally available (a connection to the
    PSTN is necessary), data communication across cable has
    become an increasingly popular option.
Computer Telephony Integration
   The SW and HW elements that allow a computer to manage
    telephone calls and integrate additional features beyond
    those offered by the PBX, is known as CTI.
      Popular in the SOHO environment
      One of the earliest applications was hotel-motel hospitality
      package (toll charge tracking, voice mail, housekeeping functions)
      Unified messaging (a single GUI for fax, voice mail, and e-mail)
      Additional and more sophisticated applications constantly being
 So, what factors have facilitated the move toward
  converged networks?
    Digitization of PSTN
    Rise of digital networks
    Competition from other industries such as CATV
    Increased integration of computers and telephony
    Technology advances which make things such as VoIP
    economically feasible.
Sample network and Security



  A Better Picture of the network
  and the potential threats
   Back Door                              Internet
    Attack                                 Attack

PSTN                                          Internet

                     User Connected
  And what else could possibly
  happen next?
    Back Door
     Attack                                         Internet

PSTN                                                   Internet

                           User Connected
 What is the Importance and Significance of this

 How does this topic fit into the subject of “Voice
  and Data Security”?

To top