CPT 245 Telephony Worksheets

Since the book does not have "Chapter Review Questions," think of these as replacing those questions.  For each question, write out a complete answer (that means your answer should include enough of the question that I can tell what the question is).

For example:  
Question:  What does "Carrier-grade" mean?
Answer:  Carrier-grade means extremely high availabliltiy and high capacity.

Chapter 1

  1. Define VoIP.
  2. Does IP provide delivery guarantee?
  3. Why is TCP not appropriate for the delivery of voice traffic?
  4. List the five (5) bullet items from page seven (7) explaining why IP is an attractive choice for voice transport.
  5. Is the "IP world" proprietary?
  6. Why is it good that IP systems tend to use a distributed client-server architecture?  (there are two parts to this answer)
  7. What are two examples of advantages to combining voice with data transactions?
  8. How much bandwidth is needed for a standard telephone call?
  9. Which ITU Recommendation is the standard for traditional telephony?
  10. Why are Voice over Frame Relay and Voice over ATM less advantageous than VoIP?
  11. What is the most important issue in VoIP?
  12. What (specifically) is VoIP tolerant of?
  13. What (specifically) is VoIP intolerant of?
  14. What two things cause jitter?
  15. Why can traditional retransmission mechanisms used in the case of lost data packets not be applied to real-time communications?
  16. What is the first network requirement for a voice call?
  17. Why is it necessary to prioritize certain types of traffic?
  18. What does "scalable" mean?

Chapter 2

  1. What provides the connectivity between various networks and form the backbone of the Internet?
  2. Considering the OSI stack, at what layer does IP reside?
  3. Compare TCP to UDP.
  4. For each of the following groups of people, in one sentence tell me what the group does.
  1. An Internet standard begins its life as an Internet draft; what happens when it is considered sufficiently complete?
  2. Briefly (one sentence per step) outline the steps taking a proposed standard to a standard.
  3. What is IP?
  4. Is IP a guaranteed service?
  5. What is the main function of IP?
  6. How does a router determine the next hop?
  7. What is the “main issue” with routing tables?
  8. OSPF (Open Shortest Path First) is a “link state protocol.”  In a few sentences, define what this means.
  9. Considering the OSI stack, at what layer does TCP reside?
  10. What is the primary function of TCP?
  11. Is a TCP port number a physical location (hardware-based) or a logical location (software-based)?
  12. What comprises a socket address?

    FYI:  Page 43, Figure 2-9, Establishing a TCP connection.
         This is also called a three-way handshake

  13. Considering the OSI stack, at what layer does UDP reside?
  14. IP is unreliable, and so is UDP; why would anyone want to use UDP?
  15. How does UDP handle lost packets?
  16. How does UDP handle duplicate packets?
  17. Why is UDP a better choice for voice transmission than TCP?
  18. For voice, what amount of packet loss is acceptable?
  19. Considering the OSI stack, at what layer do RTP/RTCP reside?
  20. Briefly, how does RTP help to avoid packet loss or ensuring delivery of packets?
  21. The payload type identifier in the RTP header is used to do what?
  22. Today, what protocols are used to agree in advance of a transmission on the type of coding scheme to be used to encode and decode?
  23. Why is the use of dynamic payload types useful?
  24. What does RED do about lost voice packets?
  25. Which header carries the actual encoded voice?
  26. Which part of the RTP Header enables to receiver to detect packet loss and/or packets out of sequence?
  27. What is a mixer?
  28. How does a mixer handle a video conference where every participant except one has a high-speed connection?
  29. What is a translator?
  30. What is the advantage of a mixer over a translator?
  31. What is the disadvantage of a mixer over a translator?
  32. Although there are five RTCP packet types, they are never sent individually from session participant to another; explain.
  33. What is the default encryption algorithm for RTCP?
  34. What does an RR block do (from page 60)?
  35. What is the SDES packet?
  36. Which SDES item is mandatory?
  37. What is CNAME?
  38. How is the BYE packet used?
  39. What is jitter?
  40. If RTCP reports are so useful, why not send them all of the time?
  41. What is the suggested bandwidth consumption of RTCP?
  42. What is multicasting?
  43. Why is multicasting more efficient than sending separate copies of the same packet to all participants?
  44. How is IGMP used?
  45. What are the five listed enhancements of IPv6 over IPv4?
  46. How is the Traffic Class field of the IPv6 header used?
  47. How do you think the Traffic Class header of IPv6 is going to affect future VoIP?
  48. How does IPv6 significatnly change upper-layer protocols?
  49. How/when is the IPv6 address with embedded IPv4 address (type1) used?
  50. How/when is the IPv6 address with embedded IPv4 address (type2) used?
  51. Why is the Hop-by-Hop Extension located immediately following the IP header?
  52. What does the Routing Extension enable?
  53. Based on Figure 2-29 on page 77, how is interworking accomplished when both IPv4 and IPv6 networks are along a given path?

  

Chapter 3

  1. On page 80, what is one of the reasons for implementing VoIP?
  2. While bandwidth is easily quantified, what is meant by voice quality is subjective, rather than objective?
  3. What is the MOS (Mean Opinion Score), and what are the five levels?
  4. What is toll quality's MOS?
  5. What are the three classifications of speech sounds?  Use one or two sentence to describe each.
  6. What is the Nyquist sampling theorem?
  7. What is quantization noise?
  8. What is the easiest way to minize the effect of quantization noise?  
  9. What are the two effects of applying uniform quantization levels?
  10. There are three types of codecs.  Create the table below, filling in the blank cells:

    Type of Codec

    How does it work?

    Advantage

    Disadvantage

         		  

    		 

    		 

     

    		 

    		 

    		 

     

    		 

    		 

    		 

  11. What is G.711?
  12. What is the main drawback of G.711?
  13. What is a major advantage of DPCM?
  14. What kind of a codec are PCM/ADPCM?
  15. With CELP coders, what is transmitted?
  16. How much bandwidth is saved by the G.728 codec compared to regular PCM codecs?
  17. If the G.728 is so good, why is it not used more?
  18. What is the advantage of how G.723 handles periods of silence?
  19. What is the transmitted bit rate of G.729?
  20. What is VAD?
  21. How long is a SID frame compared to a voice frame?
  22. What is comfort noise?
  23. Create a table comparing CDMA, GSM and AMR, filling in the blank cells: 

    Bit Rate

    Bandwidth

    Uniqueness

    CDEMA QCELP IS-733

     

     

     

    GSM EFT 06.60

     

     

     

    AMR GSM 06.90

     

     

     
  24. Why is the MOS value not expected to be experienced in particular network implementation?
  25. Why do we want to minimize the number of times that a speech segment is coded and decoded?
  26. What is DTMF?
  27. How/why does a VoIP system use a gateway?
  28. How should a gateway handle DTMF signals (give two methods)?
  29. When are DTMF digits found in the middle of a call?
  30. What does RFC 2833 do?

Chapter 4

  1. How does one party indicate to another a desire to set up a call?
  2. How does the second party indicate a willingness to accept a call?
  3. In traditional telephony networks, what do specific signaling protocols communicate?
  4. Why was it a problem that the first VoIP systems used proprietary signaling protocols?
  5. What is the most widely deployed standard in VoIP networks today?
  6. What is the most recent version of H.323?
  7. What is the overall objective of H.323?
  8. What is an H.323 terminal?
  9. What is an H.323 gateway?
  10. What is an H.323 MCU?
  11. What are the functions of the two sides of an H.323 gateway?
  12. What are some of the services of a gatekeeper?
  13. What is a zone?
  14. Do all entities in a zone need to be contiguous?
  15. What does an MC manage?
  16. What does an MP manage?
  17. Are MC multipoint conferences centralized or decentralized?
  18. In an MC multipoint conference, do all participants have to be the same (centralized or decentralized?
  19. What four protocols in the H.323 protocol stack have already been discussed in this book?
  20. H.225:  Give a one sentence description of each part of this protocol.
  21. Is RAS signaling carried over TCP or UDP?
  22. In H.323 version 4, is call signaling carried over TCP or UDP?
  23. Why might you want to use both TCP and UDP for call signaling?
  24. What is the main purpose of H.245?
  25. Which H.323 messages are sent on which types of channels?
  26. In an IP environment, what is a channel?
  27. What is the default port number of RAS?.
  28. What is a TSAP in IP terms?
  29. How are port numbers assigned for signaling transactions or media exchanges (and what are some of the default port numbers)?
  30. How many aliases can an endpoint have?
  31. What is the only restriction to an endpoint’s alias?
  32. When video is supported, what must an H.323 endpoint minimally support?
  33. Why is G.711 specified as mandatory in an H.323 endpoint?
  34. What is RAS (what does it do)?
  35. Where is RAS signaling defined?
  36. How does an endpoint register with a gatekeeper, if configuration has not been previously defined?
  37. What is an advantage of advanced registration?
  38. What is a disadvantage of advanced registration?
  39. Why might you want to have several gatekeepers in a zone?
  40. What is a gateway-request message?
  41. What is the port for a gatekeeper discovery multicast address?
  42. What is a gatekeeper-confirmation message?
  43. What is a gatekeeper-reject message?
  44. Can a gatekeeper suggest other gatekeepers to be used?
  45. How many gatekeepers can control one endpoint at a given time?
  46. What are a few things that an endpoint includes in an RRQ?
  47. Why might a gatekeeper send a RegistrationReject message?
  48. What is a RegistrationConfirmation message?
  49. How long can Registration live?  Can this time be altered?
  50. What is an UnregistrationRequest message?
  51. Why might a gatekeeper send an UnregistrationReject message?
  52. What is a LocationRequest message?
  53. What is a LocationConfirm message?
  54. What is Admission?
  55. What is one of the most important mandatory parameters in the ARQ?
  56. How much bandwidth should an endpoint request?
  57. Why is it important to set up bandwidth requirements at the beginning?
  58. What happens if the endpoint requests more bandwidth than the gatekeeper imposes?
  59. How is the callModel parameter used?
  60. What is the first message in call establishment?
  61. How can a gatekeeper minimize call setup delay?
  62. When can an endpoint change the bit rate of a given channel without approval from the gatekeeper?
  63. What can an endpoint do if it wants more bandwidth than the gatekeeper has established?
  64. What is the endpoint’s request for more bandwidth is denied?
  65. What is the InformationRequestResponse message?
  66. In what two ways can a gatekeeper stimulate an endpoint to send an IRR?
  67. What is a DisengageRequest (include some of the contents)?
  68. When might a gatekeeper send a DRQ to an endpoint?
  69. What two H.225.0 messages relate to resource availability?
  70. What are the H.323 ServiceControlIndication and ServiceControlResponse message?
  71. What is the RequestInProgress message?
  72. Why does the Bearer Capability information element not map very well to an IP network?
  73. What are some of the parameters included within the mandatory User-to-User information element?
  74. What is the Connect message?
  75. What is the Release Complete message?
  76. What is the Facility message (when might it be used)?
  77. For a straightforward two-party voice cal, what does H.245 ensure?
  78. Does H.245 carry the actual media?
  79. What four groups of messages make up H.245 message groupings?
  80. What is a logical channel?
  81. How many channels exist in a two-party conversation?
  82. How is channel 0 used?
  83. What is the H.245 CapabilitiesExchange?
  84. What do receive capabilities indicate?
  85. What do transmit capabilities indicate?
  86. What two options are part of the SendTerminalCapabilitySet?
  87. What two pieces of information is needed at each entity in a master-slave procedure?
  88. Which entity begins the master-slave determination?
  89. What does the entity beginning the master-slave determination send?
  90. How is a logical channel opened?
  91. What is an OpenLogicalChannelAck message?
  92. What is an OpenLogicalChannelReject message?
  93. How is a logical channel closed?
  94. Generally, who can close a logical channel?
  95. How can a receiving endpoint close a channel?
  96. What is the Fast-Connect procedure?
  97. Is there a separate H.245 control channel when using Fast-Connect?
  98. How is the conclusion of a Fast-Connect call faster?
  99. In what two ways can a conference call be established?
  100. What is used in the event that a two-party call needs to be expanded to three or more parties?
  101. Is a gateway a single entity?
  102. Where are the functions of an MGC performed?

Chapter 5

Due to my delay of getting these two worksheets ready for you, chapters 5 and 6 will be due October 20th.  Chapter 6 is very short.
 

  1. Why do many consider SIP a powerful alternative to H.323?
  2. What is SIP?
  3. What transport protocol is commonly used with SIP?
  4. Is SIP similar to, or different from, H.323 when it comes to handling signals and media?
  5. What is a SIP server?
  6. What is a SIP client?
  7. List the four types of SIP servers, with a one-sentence description of what each does.
  8. What are the three steps to a SIP call establishment?
  9. Does SIP care what type of media is to be exchanged?
  10. List two custom services and features available with SIP (due to its flexibility).
  11. SIP syntax has a similar look and feel to what?
  12. How is this similarity an advantage?
  13. How is this similarity a disadvantage?
  14. What does the request-line specify?
  15. What are the six different types of requests defined by RFC 3261?
  16. What are three extensions?
  17. How is the SIP INFO method used?
  18. What are the six status codes for SIP responses?
  19. Which of the response codes are final?
  20. Which of the response codes should be acknowledged with an ACK message?
  21. What is the form of a SIP address?  (give an example)
  22. How can a SIP address refer to a telephone number?  (give an example)
  23. How are SIP message headers used?
  24. What are the six SIP message headers?
  25. Briefly describe (from page 189) how the redirect server works in the Daniel to Boss call, but Boss is out of the office.
  26. How many proxy servers are most commonly involved?
  27. When does a proxy server change a Request-URI?
  28. How is the proxy server Via: header field used?
  29. How does a proxy server know that there is a potential for a loop condition?
  30. What is a spiral condition?
  31. What does stateless mean?
  32. What does stateful mean?
  33. When is “forking” used?
  34. What does SDP do?
  35. Can SDP work alone?
  36. Since SDP is text-based, how does it counteract bandwidth inefficiency?
  37. List the mandatory SDP fields (no description is required).
  38. What is the correct order of SDP field?
  39. What kind of media type is used for voice?
  40. If several types of media are offered by both the sender and receiver, how is a media type chosen?
  41. What happens if the sender and receiver cannot agree on a media type (because of a lack of support at one end or the other)?
  42. How/when is the OPTIONS method used?
  43. What are three uses of the SIP INFO method?
  44. How/when are the SUBSCRIBE and NOTIFY methods used?
  45. How/when is the REFER method used?
  46. How/when is a re-INVITE method used?
  47. How/when is the UPDATE method used?
  48. How does the bandwidth requirement for signaling compare to the bandwidth requirement for media transfer?
  49. Why does the successful transfer of a signaling message not automatically lead to a successful transfer of media?
  50. If sufficient bandwidth cannot be reserved, what are the options?
  51. What does a policy server hold?
  52. What is required for interworking with the PSTN?
  53. Why is seamless interworking between two different protocols not often easy?
  54. What is SIP for Telephony (SIP-T)?
  55. Why is interworking with H.323 a major consideration?
  56. When interworking with H.323, how does a gateway look to the H.323 side?
  57. When interworking with H.323, how does a gateway look to the SIP side?

Chapter 6

MGCP/MEGACO have been mostly discontinued in the VoIP field, so I have only one question for you:

  1. What is meant by “softswitch architecture?”


Chapter 7

  1. What is Common Channel Signaling (CCS)?
  2. What is the standard for CCS today?
  3. What are some of the services enabled by SS7?
  4. Why is it important to VoIP providers to know the services enabled by SS7?
  5. What are the two aspects of interworking that need to be provided to support interworking between VoIP and SS7?
  6. What are the three lower levels of the SS7 stack?  (include each name, what it does, and what OSI level is most closely maps to)
  7. Above MTP, what two main alternatives exist?
  8. What is ISUP (how is it used)?
  9. What does SCCP provide?
  10. Describe SCCP addressing.
  11. What does TCP do?
  12. Is TCAP designed for connection-oriented or connectionless signaling?
  13. Why are STPs typically arranged in a quad?
  14. What is the function of an STP?
  15. What is the function of an SCP?
  16. Briefly describe how SSP/SCP handle a call to an 800 number.
  17. What is an MSU?
  18. How do SS7 entities in different countries communicate (given different formats and addressing schemes)?
  19. What is the function of ISUP?
  20. What are the two purposes of an Answer Message (ANM)?
  21. What happens after a conversation is over?
  22. How does the ISUP signaling differentiate between calls?
  23. What is Sigtran?
  24. Describe using TCP vs. using UDP as the transport protocol for an ISUP message.
  25. What does the adaptation layer (of the Sigtran Architecture) provide?
  26. Why was SCTP developed?
  27. What is an SCTP endpoint?
  28. What is an SCTP association?
  29. What is an SCTP stream?
  30. What are the four categories of SCTP chunks?
  31. What happens if the processing endpoint does not recognize the chunk type?
  32. What is the INIT chunk used for?
  33. What is the INIT ACK chunk used for?
  34. What is the SACK chunk used for?
  35. What is the HEARTBEAT chunk used for?
  36. What is the ABORT chunk used for?
  37. What is the SHUTDOWN chunk used for?
  38. What is the SHUTDOWN ACK chunk used for?
  39. What is the SHUTDOWN COMPLETE chunk used for?
  40. What is the ERROR chunk used for?
  41. What is the COOKIE ECHO chunk used for?
  42. What is the COOKIE ACK chunk used for?
  43. What is the DATA chunk used for?
  44. The reliable transfer of user data is achieved by which two SCTP chunks?
  45. What does “robustness” mean?
  46. How does SCTP ensure that an endpoint is aware of the reachability of another endpoint?
  47. What are the four terms that apply to M3UA (include one sentence to describe each)?
  48. What is required to ensure carrier-grade service?
  49. Describe how M3UA uses a client-server model.
  50. How is the MTP-Pause indication primitive used?
  51. When is M2UA used?
  52. What three main types of SS7 messages are used in a traditional SS7 network?
  53. Why does M2PA need no FISU equivalent?
  54. How is the Link Status message used?
  55. What is link alignment?
  56. When interworking H.323 and SS7, how can the gateway terminate SS7 links directly?

Chapter 8

  1. What is Quality of Service (QoS)?
  2. How is QoS characterized? 
  3. In an IP network, how can QoS be measured?
  4. Why is retransmission of voice not an option?
  5. Why/how does circuit switching have a distinct advantage over packet switching?
  6. What is meant by “QoS must be end-to-end?
  7. What are SLAs?
  8. Why are SLAs not necessarily effective over the Internet?
  9. Besides technical solutions within a network, how is QoS provided?
  10. What are the three approaches to QoS solutions?
  11. What does Moore’s Law state?
  12. What is RSVP?
  13. What two levels of service are provided by RSVP?
  14. Using RSVP, who makes the reservations?  Why?
  15. What is DiffServ?
  16. What does DiffServ ensure?
  17. What is the primary function of MPLS?
  18. How does the MPLS FEC label provide higher QoS?
  19. What is traffic engineering?
  20. What is COPS?
  21. What is RSVP service number 2?
  22. What is RSVP service number 5?
  23. What is RSVP service number 1?
  24. Does RSVP work with unidirectional, multidirectional, or broadcast data transfer:
  25. What does TSpec describe?
  26. What is the “token bucket” approach?
  27. What does a filter spec define?
  28. Where is the filter spec included?
  29. How is ADSpec used?
  30. What is the RSVP message STYLE Class?
  31. When is PattErr used?
  32. When is ResvErr used?
  33. What does RFC 2212 define?
  34. What are the two parts of RFC 2212?
  35. What is controlled-load service?
  36. How can reservations be removed?
  37. Who uses PathTear?
  38. Who uses ResvTear?
  39. What is meant by “RSVP uses a soft state approach…?”
  40. RSVP works by reserving a set bandwidth for a particular data stream; what happens once all the bandwidth is consumed?
  41. What is meant by “DiffServ scales extremely well?”
  42. What/why is a disadvantage of DiffServ?
  43. What should be included in an SLA?
  44. How does an SLA handled traffic outside the traffic profile?
  45. What is the objective of Expedited Forwarding?
  46. What is the objective of Assured Forwarding?
  47. Within a DiffServ network, how does AF handle long-term congestion?
  48. How is MPLS similar to ATM?
  49. Why is label stacking important?
  50. What is the difference between traffic-oriented and resource-oriented traffic engineering?
  51. What are the two primary causes of congestion?
  52. What is the advantage of directing traffic over a trunk?
  53. Which of the three mappings that need to tape place is “at the heart of ensuring…?”
  54. What is LDP?
  55. What are the four categories of LDP messages?  (add one sentence about each message)
  56. What is CR-LDP?
  57. What is an explicit route?
  58. What is preemption?
  59. How does RSVP-TE enable RSVP to be used?
  60. Why would we want to combine QoS solutions?

 

Chapter 9

  1. What are the three requirements in the design of any network?
  2. A 99.999 percent availability corresponds to how much down time?
  3. What are the five aspects of the overall design approach?
  4. What are the two purposes of a build-ahead?
  5. Which architecture is being applied to the example network?  Why?
  6. Which signaling solution is being applied to the example network?  Why?
  7. What if the vendor you choose cannot supply the exact functionality you want right away?
  8. If a secondary MGC normally carries traffic, and the primary MGC fails, how do you determine the amount of bandwidth required at the secondary MGC?
  9. How does your choice of redundancy depend on the capabilities of the vendor?
  10. What are the three decisions to be made regarding voice coding?
  11. What is blocking probability?
  12. Which QoS is being used in the example network?
  13. Which Wide Area Network (Layer 2) is being used in the example network?
  14. What does an RFI/RFP address?
  15. What is non-level redundancy?
  16. What is meant by node availability?
  17. What are alarms and statistics?
  18. What is the typical interface between the network elements and the EMS?
  19. What is typically used above the EMS?
  20. How are traffic projections made in a brand new network (in a given market)?
  21. How are traffic projections made in a network already being covered by your company’s competition?
  22. Who is typically responsible for determining the subscriber forecast?
  23. Define Erland; what is its equivalent?
  24. What is the MHT?
  25. What is traffic distribution?
  26. What does the network topology specify?
  27. Where are MGs located in the example network? (which cities)
  28. Where are MGCs located in the example network? (which cities)
  29. What is the function of each MGC?
  30. Where are SGs located in the example network? (which cities)
  31. What three factors determine the bandwidth requirement for a single call?
  32. How can approximately 60% of the bandwidth (for each call) be saved?
  33. Why does the author keep suggesting use of a spreadsheet program to do the required calculations?
  34. What is the formula for per-call bandwidth for a VoIP network?
  35. What four additional factors (besides the actual voice call) cause traffic in the network?
  36. If a fully mesh network is too expensive, how do you design connectivity so that each city has fault tolerance?

 


And that's everything!