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14 Cards in this Set

  • Front
  • Back
- The local loop consist of a pair of twisted wires; Explain;


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- In the pair of twisted wires – one is called Tip, the other is called ring
- The ring wire ties to the negative side of the power source called battery
- The Tip wire connects the ground.


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- Name 3 types of local loop signalling; (It’s used to prompt the subscriber and the switch into a certain action)

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- Supervisory signalling; (on hook, off hook, ringing)
- Address signalling (DTMF or pulse)
- Informational signalling (by the use of call progress indicators used to notify subscriber of call status.)


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- What is local loop signalling;

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- It’s when a subscriber and telephone company notify each other of the call status through audible tones and an exchange of electrical current.

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- Name 3 common trunk types;

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- Private trunk lines; or Tie-trunk line are used to connect multiple PBX
- [Tie trunk have bidirectional supervisory signalling that allows either end to initiate a trunk seizure. ]
- CO trunks; direct connection between a PBX and the local CO; One example is the connection from a private office network to the public switched telephone network (PSTN)
- Interoffice trunks; connects two local telephone company CO


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- What is an FXO interface?

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- An FXO interface connects a PBX to another switch or Cisco devices
- The purpose of and FXO is to extend the Telephony connection to a remote site.
- For instance is a corporate PBX wanted a telephone installed at home, then an FXO (remember “off premises” extension) would be sued


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- What is and FXS interface?

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- An FXS interface connects directly to station equipment; telephones, fax machines and modems. A telephone connected directly to a switch or Cisco device requires an FXS interface.

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- What are the 5 types of trunk signalling (each applies to different kinds of interfaces)?

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- Loop start; allow a user or a telephone company to size a line or trunk when subscriber is initiating a call. – primarily used on local loop siganling
- Ground start – not common on VoIP networks. It’s a modification of loop-start signalling that correct the probability of glare. Especially used on high-volume trunks.
- E&M Wink Start
- E&M immediate Start
- E&M delay start
- Note: E&M signalling supports tie-line facilities or signal between voice switches.


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- Describe briefly the 5 types of E&M signalling;

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- Type 1; Common in North America.- 4 wire partially looped – United States
- Type 2; 8 wire interfaces - used where common ground is not possible; PBX in one building and Cisco equipment in another.
- Type 3; 8 wire interfaces – used in environment where M- lead is likely to experience electrical interference and falsely signal its attached equipment.
- Type 4; 8 wire interfaces –cisco equipment does not support type 4
- Type 5; Most common form outside North America – 4 wire looped, Nonsymmetrical – Europe


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- Name 3 trunk signal types used by E&M

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- Wink Start; most common E&M trunk seizure signal type
- Immediate Start; used when timing of returned wink is too short or impossible to detect.
- Delay Start; used when all of the equipment is mechanical and requires time to process request.


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- A telephone connection exists in 3 states;

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- Idle (on hook); the telephone or PBX opens the two-wire loop.
- Telephone seizure (off hook) – closes the loop
- CO seizure (ringing) – when CO or FXS detect and incoming call, it applies AC ring voltage superimposed over the -48 VDC battery.


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- What is Glare?

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- Simultaneous seizure of the trunk from both ends.

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- Telephone networks can experience two types of echo;

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- Acoustic echo ; when the received voice on the speaker excites the microphone and travel back to the speaker
- Electrical echo; occurs when there is electrical inconsistency in the telephony circuits


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- What are the 2 components of echo?

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- Loudness
- Delay (Echo delay over 50 ms is generally problematic)
- Note: reducing either component reduces overall echo.


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- What are the 2 methods used to solve echo problem?

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- Echo suppression; works by sending transmitting speech in the forward direction and prohibiting audio in the return direction. – not good for full duplex modem it prevent communication
- Echo cancellation; uses a special circuit to build a mathematical model of the transmitted speech pattern and subtract it from the return path ( filter)


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