Basic Telecom Training

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Basic Telecom Training
2011-09-13 11:38:55
T1 telecom

Common T1 Technical Training
Show Answers:

  1. What is the Speed of a T1?
    1.544 Mbps
  2. How many channelsare on a T1?
  3. What is the transmission rate per channel on a T1?
  4. If the data channel is 64kbs why is the maximum throughput per channel only 56kbps?
    In order to trasmit one of the 8 bits on the channel must be 'robbed' to signal the far and near end. This means the maximum can only be 56kbps per channel.
  5. What is the lowest channel of the T1?
    The Ds0, commonly sold as a Frac T1, or as a single voice line.
  6. How many channels can you get on a fractional T1?
    2-23 channels, or .128-1.472mbps
  7. How many channels are in a T1\Ds1.
    24 channels (1.544)
  8. How many Channels are in a DS2?
    96 Channels 6.312 Mbps.
  9. How many Channels on a Ds3? How many T1's?
    96 Channels, and 4 T1's.
  10. TDM stands for ?
    Time Domain Multiplexing.
  11. What is the most common type of T1?
    The T1-ESF, or Extended Super Frame.
  12. What is a CRC?
    Cyclical Redundancy Check
  13. How does CRC work?
    Netowork equipment sends a 6 bit word. The customer/z side equipment catches that word and calculates what it should see next. If the next word matches, then the system assumes there are no errors. If the word or bit positions of the word are off, it creates a CRC error.
  14. AMI?
    Alternate Mark Inversion the original standard on T1 line encodnig. Requiring a 12.5% average density of 1's. With a maximum of 15 consecutive 0's. This standard was dropped because of the widespread use of T1's for carrying Data.
  15. B8ZS
    Bi Polar 8 Bit Zero Insertion: Data\voice is always a series of 0/1's. If this system sees 8 zeros strung together in a data stream. It inserts a BPV or BiPolar Violation into the data stream. Then recieving or monitoring gear can see that BPV and report it.
  16. Voice T1 timing comes across to a customer as?
    Clicking or popping, or dropped calls.
  17. Timing is critical for Phone. What is the heirarchy for clock?
    Stratum there are 5 levels of stratum.
  18. What is the highest level of timing accuracy available?
    Stratum 1, 2.5 slips per year.
  19. In reference to timing what is SMC?
    Sonet Minimum Clocking, it is between stratum 3/4. It offers a very poor 10 timing slips per minute.
  20. SONET?
    Synchronous Optical Network
  21. OC-1
    The OC-1 or STS synchronous Transport signal 1 has a speed of 51.84 mb per second. This equals a 28 Ds1's or 1 DS3.
  22. OC-12
    Equal to STS-12, 622 mbps, and 12 Sts-1, or 336 Ds1's
  23. 0C-48
    Equal to an STS-48, transporting 2488mbps it is equal to 48 STS-1's or 1344 Ds'1s or 48 DS3's.
  24. What are he characteristics of Circuit Switching?
    Common PSTN or Public Switched Telephone Network, this is how most analog voice is transmitted.

    • -Connection Oriented -requires call setup prior to exchange
    • -Dedicated Bandwidth
    • -Transmitted at full wirespeed to reduce jitter
    • -There is no error recovery (buffers are too small)
    • -Cost is from start to finish of the circuit, regardless of the passed traffic.
  25. What are the characteristics of a packet switched network.
    Packet switching segments traffic into smaller packets.

    -It is connection oriented, doesnt need call setup but must have a sender and start and destination.

    -Dynamically routed, known as a virtual circuit or virtual channel.

    -Packet switches use a store-and-forward. This temporary forward allows for error correction in the packet send/receive. It also allows for prioritization.
  26. CAS (pronounced Caz) often heard in Cas Group.
    • Channel Associated Signaling
    • Also known as Call Associated Signaling. This is an in bad transmition that transmits signaling bits along with digitized voice and data.

    • Cas is also known as robbed bit signaling.
    • each channel in robbed bit signalling is 56kbps instead of the normal 64 because 8kbps is reserved for the signaling (hence robbed bit).

    Good for voice, it is often limited to that use as it has little flexibility for other transmisisons.
  27. What is the most common example of a CCS (common Channel Signal)?
    The Primary Rate Interface is the most commonly used type of CCS.
  28. What is Common Channel Signaling?
    Unlike the inefficient Robbed bit signaling. This takes one whole channel to use for signaling. Leaving 23 other channels for voice traffic. That signaling channel is most commenly referred to as a Data Channel.
  29. Gr303, SS7, Q.931, Electronic Tandem Network, Qsig are all potential components of what signaling method?
    CCS, Common Channel Signaling
  30. What is a DSX?
    • There are 4 parts to a DSX.
    • -The in/Out terminal
    • -The Cross connect terminal (also called xconn terminal).
    • -Jacks:in and out switching jackes allow access to test adn patching. Commonly attached to he out Jack is a monitor for non-intrusive testing.
    • -Led's to show the active xconn.
  31. What are the types of line tests, not the patterns but what they actually send.
    • low density -Just eough transitions to test timing
    • High Density- Forces repeaters to work at maximum Power
    • Pseudorandom Patterns to simulate customer Traffic Stresses automatic LBO (line build out) and equalization circuitry.
    • Line Code just to test for mis-matched line code.
  32. What is the alternate name of the blue alarm?
    AIS, or Alarm indication signal
  33. What is a far end alarm?
    • A yellow alarm is a far end alarm. It indicates a loss of signal at the end of the circuit.
    • It is also known as the RAI alarm., or Remote Alarm Indication.
  34. What PRBS test pattern is used most often in testing?
    QRSS or Quasi. This test is stress timing, Automatic Line Build Out ALBO, and it simulates cusotmer traffic.
  35. Describe Bit Errors.
    Bit Errors are logical errors in the bit stream.

    • Because of this performance evaluator we can:
    • Test on Out of Service
    • Stress test the circuit
    • Truest measure of point to point circuit performance
    • Live Traffic Must be removed from the circuit
  36. BPV errors are?
    • Bi Polar Violations: They provide an approximate value of Bit error rate.
    • --They provide a good indications of Circuit or repeater problems
    • Will often be corrected by Mux/DCS and some CSU.

    Multiplexer/Digital Cross connect System and Channel service unit.
  37. Frame errors are?
    The number of tims an incorrect value appears in a framing bit location.

    • Only analyzes every 193rd bit.
    • May be corrected by DCS or Mux.
  38. CRC errors
    Errors in a block of data (cyclical redundancy check).

    Only available on Extended Superframe Circuits.

    98.4% accurate in detecting in service bit errors.
  39. What is the key to troubleshooting Transport?
    Sectionalize. You must start in segmetns. It wont matter what side you start from if you test all the way through.
  40. What are the components of a CSU?
    T1, Monitoring and loopback jacks, Line build out (either physical or logical), Status/alarm lights.
  41. If the technician is connected to the port in the blue box, pictured, what the cross connect.
  42. What is a line Loopback?
    A complete loopback in which the signal is returned to the source that generated the loop back. Think of it as someone stepping in the middle of a hula hoop and shoving a shower curtain ring from one point. The infromation and data simply makes the circle with no changes to the information passed on the circuit.
  43. What is a BERT?
    Bit Error Test Rate
  44. What must a customer and telco have to complete a circuit?
    CSU/DSUs are like bridges. They have one interface in telco territory and oneinterface in data-communications territory. Both are serial interfaces that make use of tight timing tolerances. Appropriate configuration of the CSU/DSU to work within the timing straitjacket is essential.
  45. What are DID Trunks?
    • Direct-Inward-Dial Trunks
    • One way incoming wto the PBX
    • Serving centroal office forward the extension number of the incoming calls so a PBX can immediately route the call to destination

    DID trunks provide the battery voltage so the CO can signal an incoming call bly merely closing the loop to draw current. After the PBX reverses the battery momentarily "winks" to signify it is ready to receive digits. The Central office Generates the DTMF tones to send the extension number. After the designation station answers, the PBX, reverses the batter again to signify the connected state and holds that state for the duration of the call. Variations in signaling protocol depend on the type of central office.
  46. What is like an IP address but for telephony?
    Point Codes

    Point codes serve a function similar to IP addresses, providing an orginating address and destination address for messages sent across the network.

    In an SS7 their is 3 layers to a point code.

    • Member -Signalling point within a cluster
    • Cluster -A collection of signaling points
    • Network - Each cluster is defined as being part of a network.
  47. What is the key point of LNP (Line Number Portability)?
    -Gives telephone subsribers the ability to change local service providers without changing their phone number.
  48. What is TNS?
    That is the Caller ID database.
  49. What does LRN stand for and why does it exist?
    • Location Routign Number
    • -LRN supports LNP
    • -It works because each switch is assigned a unique ten-digit LRN (also known as telephone number)
    • -The first six digits are refered to as NPA/NXX
    • NPA is often refered to as the Area code.
  50. A standard PRI has 23b and 1 d channel, what is a b channel and why is it broken down this way?
    B channel is a bearer channel and carries voice or data traffic.

    All signaling is sent down the D channel.
  51. What is a bridge tap?
    Multiple connections of a single cable to more than one location. Think of it as a tree branch with multiple tree limbs. This is a bad situation for HDSL as it increases the loop distance and ultimately speed and quality.
  52. What does a cross connect consist of?
    2 sides of a DACS pronounced (Dax) or Digital Access and Cross-connect System. Also called a DCS.

    DCS hardware is essentially aswitch. All the lines coming into a CO are connected to the DCS so the incomingdigital streams can be logically connected to outgoing streams. DCSs also performmultiplexing functions, so several incoming T1s can be combined and mappedonto a single higher-speed output stream.
  53. Why do we use Dacs?
    DCS hardware is essentially aswitch. All the lines coming into a CO are connected to the DCS so the incomingdigital streams can be logically connected to outgoing streams. DCSs also performmultiplexing functions, so several incoming T1s can be combined and mappedonto a single higher-speed output stream.
  54. What is a TDM (time division multiplexing) Network?
    It is a Digital network.

    TDM divides the resources into time slots and transmits the time slots in turn, using the full capacity of the channel. Increasedcapacity was a major motivation for migrating the phone system to digital transmission.Each analog trunk could handle 12 calls, but digitized trunks, which usedthe same transmission facilities (wires), could handle 24 calls. Adding trunk linestook time and money—and lots of both. To add a trunk line, AT&T needed toevaluate potential routes, survey the chosen route, and acquire the right of way.
  55. What is a Frame Slip?
    Slips are divided into two categories. Controlledslips replicate or delete a complete 192-bit frame of data, but do not causeany problems with the T1 path. Uncontrolled slips, which are also called change offrame alignment (COFA) events, are much more severe because they disrupt theframing pattern. Controlled slips are the more benign of the two because the pathremains available. Uncontrolled slips indicate more severe problems with the circuit.
  56. What is ARP?

    It is used within a network to locate the physical Media access control (MAC) address of the network interface card NIC.

    In troubleshooting knowing that you have arp means you can see the NIC card on the far side and it is talking to the netowork. Without 'good ARP' you cannot have connectivity.
  57. What is port 80 used for?
    HTTP Traffic (web browsing)
  58. What is port 25 used for?
    SMTP (outbound email)
  59. What is port 110 used for?
    POP3 (incoming email)
  60. What is port 20 used for?
    FTP (file transfer protocol)
  61. What is SNMP?
    Simple Network Mangement Protocol: Allows for the remote mangement of a computer network by polling and setting terminal values and monitoring network events.
  62. How many PDU (or Protocol Data Units) are there in SNMP?
    • Five.
    • GetRequest
    • GetNextRequest
    • GetResponse
    • SetRequest
    • Trap
  63. What is a DTE?
    The data terminal equipment (DTE) is the device where data is generated or consumed by users. The canonical example of a DTE is a dumb terminal, which displays data it receives and sends data in the form of user keypresses.
  64. What is a DCE?
    data communications equipment (DCEs), which areresponsible for sending the bitstream to another location. In the dumb terminalsetup, the DCE is a modem or terminal server. Routers often use high-speed seriallinks to connect to devices, which interface with the telephone network. On T1links, a serial link is used between the router and the CSU/DSU. The router is theserial DTE, and the CSU/DSU is the serial DCE.
  65. What is the Demarc?
    The Jack where the Telco Terminates the line from the Central Office.
  66. What is an Extended Demarc?
    Where the customer will extend the Demarc to a location that is more convinient than the Telco's installation.
  67. Symptom is No incoming signal (LOS).

    What is the cause?
    Generally there is a cable issue, try reseating, rebooting and verifying the cable connection.

    If that failes the cable should be replaced to confirm that it has not failed.

    Loopback test to verify the circuit has continuity.
  68. What is the most significant thing about a Yellow alarm?
    • The most significant thing about a yellow alarm is that framing is received correctly,so the remote transmit to local receive path is good.
    • A yellow alarm is sentby the remote end to indicate that it is not receiving a signal.
    • The problem exists somewhere in the local transmit to remote receive path.
  69. If you have a problem with line build out, what type of alarm could you see?
    Yellow alarm
  70. Bipolar violations (line code violations)
    Excessive bipolar violations are the result of one of two problems.

    An AMI line receiving B8ZS code words will record bipolar violations, and a high bipolar count can indicate that a device that should be set for AMI is instead set for B8ZS.
  71. ANI
    Automatic Number Identification. A similar service to CLID, which transmitsthe number of the calling party.
  72. asynchronous
    Data transmission that relies on the endpoints to send explicit stop and startinstructions. While easier to do than synchronous transmission, the overheadof start and stop messages makes it impractical for high-speed links.

    Think CB radio..over
  73. B8ZS
    Bipolar with 8 Zero Substitution. An encoding scheme that replaces eightzeros with intentional bipolar violations. Eight zeros are replaced with a code that has two intentional bipolar violations.

    The substitution takes the form 000V10V1, where V is a pulse of the same polarity as the previous pulse. B8ZS enables clear channel transmission because it ensures adequate pulse density even when long strings of zeros must be transmitted.
  74. DS0
    Digital Stream, level zero. A single 64-kbps channel that can be used to transmit a sequence of pulses across the telephone network.
  75. NFAS
    Network Facilities Associated Signaling. A means of sharing a single ISDN PRID channel among several PRI lines. NFAS also allows for a backup D channelin case of the failure of the primary D channel.
  76. Out of Fram
    • Out of frame.
    • When frame synchronization is lost, an OOF event is recorded.If OOF persists, LOF is declared.

    Some T1 CSU/DSUs may have a light that blinks briefly on OOF events.

    OOF is cleared when frame synchronization is regained.
  77. PBX
    Private branch exchange. A customer-owned switch that creates a private telephonenetwork at the customer location.
  78. PSTN
    Public switched telephone network. A fancy name for the telephone network,used frequently in job interviews.
  79. SEF
    Severely errored framing. Refers to a certain density of frame bit errors, whichalmost always causes an out of frame defect.
  80. SES
    Severely errored second. One-second interval that is likely to have garbage ondata links because framing was lost, AIS was detected, or 320 or more framesfailed the CRC check.
  81. T1
    DS1 delivered over a 4-wire copper interface.
  82. UAS
    Unavailable second. Used in measuring the performance of T1 lines; carrierswill often guarantee a certain uptime. Uptime is the number of seconds in themeasuring period minus the number of unavailable seconds. Different monitoringspecifications define this quantity in different ways.
  83. What is a Biscuit?
    Terminating end of an extended Demarc used to connect to a CSU/DSU.

    They are called biscuits because they are small squarish and have an off-white color.
  84. What is required to connect a data network to the telephone network?
    To connect a data network to the telephone network, you need a device called aCSU/DSU. CSU/DSU stands for Channel Service Unit/Data Service Unit.* As the name implies, the CSU/DSU includes two separate functions.

    The DSU is responsiblefor handling the V.35 interface with the router.

    The CSU handles connection to the telco network.
  85. What is a V.35?
    V.35 is commonly used as a medium-speed serial interface between routersand CSU/DSUs.
  86. What is the first layer?
    The first layer is a layer of the OSI Model. It is often used in a 'we have a layer 1 issue. It just means physical problem.