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Telecommunications > VoIP > Flashcards

VoIP Flashcards

1
Q

What is a Voice over IP Telephone

A

a Voice over IP telephone is more of a computer than a telephone. It has to be a LAN device, it has to be an IP device, it has to have a codec for digitizing the speech and compressing it, it has to run protocols like SIP to set up phone calls, it might have to do authentication to register with a Soft Switch, there are a lot of pieces of software that is running inside of that telephone.

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2
Q

What “computer” functions must a VoIP phone perform?

A

Since it is VoIP, this computer that looks like a telephone also has to have a IP protocol stack. It also has to have a DHCP client (Dynamic Host Configuration Protocol). This is a little software program that lets the phone go off over the LAN to a DHCP Server and get an IP address assigned to it. It also has to support protocols like UDP.

Short answer: IP, DHCP and LAN functions

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3
Q

Which of the following are the minimum requirements on a VoIP telephone?

A

The G.711 Codec & SIP Client

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4
Q

What component produces coded digitized speech?

A

Codec

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5
Q

How are IP packets moved from one router to another?

A

Carried in Ethernet MAC frames (Media Access Control)

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6
Q

How much speech is typically contained in an IP packet?

A

20 Milliseconds

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7
Q

What is the difference between SIP and a softswitch?

A

SIP is a Protocol. A softswitch is a call management system

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8
Q

What is the main purpose of a SIP?

A

To communicate the IP address of telephones to each other

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9
Q

What is a key attribute of a video server?

A

Movies stored in Random Access Memory so multiple people can watch at different start times

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10
Q

What protocol is between RTP (Real-Time Transport Protocol) and IP (Internet Protocol)?

A

UDP (User Datagram Protocol)

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11
Q

What does RTP (Real-Time Transport Protocol) do?

A

Adds a time stamp

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12
Q

What does “IP dial tone” mean?

A

A service that allows you to send an IP packet to any destination on the network, like telephone calls.
The telephone network and the internet being the same thing.
Telephone service becomes a helper application to set up a Voice over IP phone call.

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13
Q

Once there is IP dial tone, what happens to the World Wide Web?

A

It is simply a helper application DNS (Domain Name Server) to look up web server addresses

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14
Q

What technique is first used to represent speech inside a telephone?

A

Analog

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15
Q

What is a LAN (Local Area Network)?

A

Connects IP telephones to a router in-building

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16
Q

Which of the following is a function of a gateway?

A

Convert between DS0 (Digital Service Level 0) and RTP/IP

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17
Q

What is a media server?

A

Video server, Web server, Email server

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18
Q

what is a WAN (Wide Area Network)?

A

Connects to buildings

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19
Q

Which of the following does computer-computer VoIP over the internet provide?

A

Free calling

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20
Q

What performs the voice digitization and reconstruction function when doing computer to computer VoIP over the internet?

A

The sound card in the computer

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21
Q

What part of the network from calling party to called party does the VSP (Voice over IP Service Provider) provide?

A

Internet to LEC (Local Exchange Carrier)

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22
Q

What two essential functions does the VSP provide for internet to phone VoIP?

A

Gateway and softswitch

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23
Q

Why is phone to phone over the internet service cheaper than POTS?

A

Avoids switched access charges at the originating end
Avoids fees and taxes leveled on POTS
Service provider is not providing the long-distance network

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24
Q

What is a managed IP network?

A

An IP packet communication service with Service Level Agreements backing it up, i.e. guaranteed network quality

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25
Q

What part of the network from calling party to called party with POTS does a managed-IP telephony service provider provide?

A

Calling party to LEC

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26
Q

What is most of SIP trunking traffic?

A

VoIP

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27
Q

What does “native” communication mean?

A

The data is not reformatted

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28
Q

What functions does a VoIP-enabled PBX provide?

A

Softswitch and gateway

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29
Q

What would be a primary reason to use on a VoIP-enabled PBX?

A

Existing investment

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30
Q

Which of the following is an advantage of a softswitch (non-PBX) system for PBX replacement?

A

Leverage investment in PBX operations
Possibility of geographic diversity
Possibility of standards-based interfaces

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31
Q

What is necessary as part of the design using a softswitch product in a medium or large business?

A

Two softswitches, call-state-mirroring and automatic redirection when a failure occurs

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32
Q

Which of the following is an advantage of a Hosted PBX solution?

A

Scalability and flexibility
Professional implementation, security, reliability
Backup and redundancy

33
Q

What is communicated from the VoIP phones to the Hosted PBX?

A

Formatted text messages coded into ASCII (American Standard Code for Information Interchange)

34
Q

How can a VoIP system use existing PBX trunks?

A

Put a gateway between the two

35
Q

What are the five facets of communications supported by SIP?

A

Locating the called party
Determine and report availability of called party
Call progress “tones”
Enable call type negotiation
Manage calls

36
Q

What would be part of a call type negotiation?

A

Media type

37
Q

Which of the following is associated with Personal Communication Services?

A

Separation of wires and services

38
Q

Which protocol carries the SIP message as a payload?

A

UDP (User Datagram Protocol)

39
Q

Which protocol’s data is carried as a payload in a SIP message?

A

SDP (Session Description Protocol)

40
Q

What is an “address of record”?

A

Your public SIP address

41
Q

What does URI stand for?

A

Uniform Resource Identifier

42
Q

What is a proxy?

A

A thing that acts for something else

43
Q

What does REGISTER do?

A

Updates your contact URIs

44
Q

Which of the following functions does an outbound SIP proxy perform?

A

Returns call progress messages
Sends INVITE messages
Resolves URIs

45
Q

How does the outbound proxy determine what IP address to send the INVITE message to?

A

Looks up the server portion of the address of record in the DNS (Domain Name Server)

46
Q

Which message does the caller send to complete call setup?

A

ACK (Acknowledgment)

47
Q

What message does the called party’s terminal return to indicate it accepts a call INVITE?

A

180 RINGING

48
Q

Which message carries the IP address or contact URI of the called party?

A

180 RINGING

49
Q

The correct sequence of messages is?

A

INVITE, TRYING, RINGING, OK, ACK

50
Q

Which are learned during a SIP message exchange?

A

The IP addresses of phones and media port number

51
Q

What is the difference between a softswitch and a SIP server?

A

A SIP server is part of a softswitch

52
Q

What function does a softswitch do that SIP does not?

A

AAA (Authentication, Authorization, and Accounting)

53
Q

What is “call disposition”?

A

What happens to an incoming phone call

54
Q

What is “media” in a VoIP phone call?

A

Voice
Video
Music

55
Q

The location database associates what?

A

Address of Record and URIs

56
Q

Analog-Digital conversation is performed by?

A

An integrated circuit

57
Q

Coding is performed by?

A

A software program
An integrated circuit

58
Q

What is a hard constraint on voice quality for POTS?

A

The voiceband frequency restrictions

59
Q

Which are factors affecting voice quality?

A

Coding
Delay
Jitter
Packet Loss

60
Q

Which codec provides near toll quality with moderate delay?

A

G.729

61
Q

Why is buffering used in network elements?

A

Allows temporary storage of data waiting to be processed

62
Q

What is the maximum recommended delay on VoIP systems?

A

150 Milliseconds

63
Q

What does a jitter buffer do?

A

Increases delay

64
Q

What does jitter mean?

A

Variable delay

65
Q

What is the principal purpose of RTP (Real-Time Transport Protocol)?

A

Time stamp

66
Q

What protocol carries the RTP Protocol Data Units?

A

Transport Protocol

67
Q

What does TCP (Transmission Control Protocol) do that UDP (User Datagram Protocol) does not do?

A

Retransmission

68
Q

Which protocol is used to carry RTP (Real-Time Transport Protocol) Protocol Data Units?

A

UDP (User Datagram Protocol)

69
Q

What causes packets to be lost?

A

Buffer overwriting

70
Q

What causes buffer overwriting?

A

Transient faster input than output

71
Q

What creates the analog of the voice that is digitized and packetized?

A

A microphone

72
Q

What is segmentation?

A

Creating fixed-sized blocks of bits from the codec output

73
Q

What are buffers?

A

Memory like RAM

74
Q

What device is currently required to connect to a LEC?

A

Gateway

75
Q

What is the essential function that VSPs (VoIP Server Providers) like Vonage perform?

A

Connect to the internet to the PSTN

76
Q

How is a phone call communicated with carrier-carrier IP interconnect?

A

Digitized voice in IP packets

77
Q

What is a function of a Session Border Controller?

A

Controlling outbound calls
Address resolution
Network security

78
Q

What is a SBC?

A

A device that connects a carrier and a LEC for VoIP

Telecommunications (1 decks)

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