Transcript
IP Telephony DigiPoints, Volume 2
Page 9.1 Student Workbook
DigiPoints Volume 2 Student Workbook Module 9 – IP Telephony Summary In this module, students will learn engineering theory and operational information about IP Telephony.
Module Objectives Upon successful completion of this module, the student will be able to: • • • • • • • • •
Explain the differences between IP telephony and switched-circuit telephony. List the steps in preparing a voice signal for transmission over an IP network. Explain which steps in preparing a voice signal are common to all analog-to-digital conversions. Describe the most common cause of poor quality transmission in an IP telephony call and indicate why this happens. Compare and contrast the quality of IP telephony over an intranet vs. the Internet. List the four components of IP telephony as specified by H.323. Outline the main functions of an H.323 gatekeeper. Name the four components of MGCP, as specified in PacketCable TM NCS 1.0. Discuss the practical benefits of IP telephony in a cable system.
Prerequisites Read DigiPoints, Volume 2, Chapter 9. As you complete this module, you should be filling in answers and definitions for the items found on the following pages.
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Module 9 – IP Telephony Take notes on the following pages as your instructor covers the topics in this session. For some topics, key points are identified. You should add to them with supplementary information from the class discussions. For other topics, you will need to fill in key points as requested in the workbook. Constructing meaningful notes in this way helps you to understand the subject and can serve as a valuable future reference.
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How IP Telephony Works What is IP telephony?
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Workbook Exercise 1 Show the relationship of the Internet Protocol to the OSI model by labeling the IP layer in the DOD Protocol stack:
OSI
DOD
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
Extra Notes on IP protocol in the context of the OSI model.
List the main points of the following concepts that help move packets across a network. Lifetime 1.
2.
3.
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4.
5.
Segmentation 1.
2.
Routing 1.
2.
3.
4.
Addressing 1.
2.
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3.
4.
5.
6.
7.
Other notes
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Voice Packetization What is Waveform Coding?
What is Vocoding?
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Group Exercise #1 In your group, list as many points as possible about the steps of analog-to-digital conversion that you have been assigned. If there is a question under your topic, please complete the answer. Sampling
1.
2.
3.
Quantizing
What is done by quantizing?
How does quantizing differ between waveform coding and vocoding?
Encoding
What is encoding?
How does encoding differ between waveform coding and vocoding?
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Page 9.9 Student Workbook
Compression
What is compression?
Some main points about compression are: 1.
2.
3.
Packetizing
What is packetizing?
Some main points about packetizing are: 1.
2.
3.
4.
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5.
6.
7.
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Table 9-1 VoIP CODEC’s
Complexity
G.711 PCM
Compressed Voiced Digitizing Rate (kbps) 64
G.726 ADPCM
40/32/24
Low (8 MIPS)
G.729 CS-ACELP
8
High (30 MIPS)
G.729A CA-ACELP
8
Moderate
G.723 MP-MLQ
6.4/5.3
Moderate-High (20 MIPS)
G.723.1 MP-MLQ
6.4/5.3
G.728 LD-CELP
16
N/A
Very High
Other Notes
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Page 9.12 Student Workbook
Packet Header and Payload
1
1
1
0
......... Header
0 1
0
0
.... Payload
Other Notes
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Page 9.13 Student Workbook
Workbook Exercise #2 Label the IP/UPD header, Voice Header, and Voice Information parts of the following diagram:
28 bytes
6 bytes
40 bytes
Other Notes
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Technical Issues Surrounding IP Telephony What are some of the differences between analog and digital technology? Analog
Digital
What is latency?
Causes of latency can include high traffic on one or more of the networks that comprise the Internet.
Once both data and voice move as packets on the same network, both will contribute to the total traffic.
Ensuring latency does not exceed acceptable levels requires managing both data and voice traffic.
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Internet vs. Intranet List 8 main points of the Internet as discussed in class.
Other Notes
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Group Activity #2 With a partner, list as many points as possible about either intranets or extranets (whichever you have been assigned). Add to your notes anything extra that is brought out in class discussion. Intranet
Extranet
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IP Telephony vs. VoIP Telephony What are two main differences between VoIP and IP telephony?
Standards
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H.323: ITU Takes a First Step Toward Packet Voice Standardization What are five main points of H.323 as discussed in class? 1.
2.
3.
4.
5.
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Group Exercise #3 Based on the H.323 component that you have been assigned (Terminals, Gateways, Gatekeepers, and Multi Control Units), answer any questions listed for that component and discuss and list the main points of that component with your group. If there is a question under the component that you have been assigned, find the answer to that question and list it with your information. Terminals
1.
2.
3.
4.
Gateways
1.
2.
3.
4.
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5.
6.
7.
Gatekeepers
What functions can be provided by the gatekeeper?
Main Points 1.
2.
Multipoint Control Units
1.
2.
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The Alphabet Soup of Telephony Feature Delivery What are some facts about the Session Initiation Protocol?
What are some facts about the Simple Gateway Control Protocol (SGCP) and the Media Gateway Control Protocol (MGCP)?
What are some facts about the Distributed Open Signaling Architecture (DOSA)?
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PacketCable™ What are five points of PacketCable as discussed in class? 1.
2.
3.
4.
5.
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Workbook Exercise #3 Label the PacketCable protocol layers in the diagram below, and list the functions that are performed by each of them.
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Group Exercise #4 In your group, list the main points of the NCS 1.0 component that you have been given (endpoints, gateways, embedded client, or call agents). Endpoints
1.
2.
3.
Other Notes
Gateways
1.
2.
3.
Other Notes
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Embedded Client
1.
2.
3.
4.
Other Notes
Call Agents
1.
2.
Other Notes
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PacketCable™ Quality of Service Upon what does PacketCable base its Quality of Service?
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VoIP and Telephony Architectures Workbook Exercise #4 Label the major components (CMTS, Internet, Router, Cable Modem, and Microphone) in this diagram of VoIP using a computer as the Terminal.
VoIP Using a Computer as the Terminal
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Workbook Exercise #5 Label the major components (PSTN, Gateway, CMTS, Internet, Router, Cable Modem, and Microphone) in this diagram of VoIP with a gateway to the PSTN using a computer as the terminal.
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Workbook Exercise #6 Label the major components (PSTN, Gateway, CMTS, Internet, Router, Cable Modem, Telephone Adapter, and Microphone) in this diagram of VoIP with a Gateway to the PSTN using a phone adapter.
What is the difference between this diagram and the diagram of VoIP with a gateway to the PSTN using a computer as the terminal?
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Workbook Exercise #7 Label the major components (Public Switched Telephone Network, Local Telephony Switch, Access Gateway, Managed IP Network, CMTS, Managed IP Network, Packet NIU with Embedded MTA and DOCSIS Cable Modem) in this diagram of full feature telephony via IP access to a circuit switch.
Fully Featured Telephony Via IP Access to a Circuit Switch
TR-303
What is the source of telephony features in this diagram?
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Workbook Exercise #8 Label the following components on the diagram of end-to-end IP telephony below. (SS7 Gateway, Trunk Gateway, Feature Server, Policy Server, Layer Three Switch/Router, CMTS, HFC Plant, DOCSIS 1.1, Cable Modem)
Full Service IP Backbone Network
IP
IP
Packet NIU With Embedded MTA and DOCSIS Cable Modem
What is the source of telephony features in this diagram?
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Workbook Exercise #9 Add the missing labels in this diagram of cable telephony migration.
Public Switched Telephone Network
HFC Plant TR303
NIU
Backbone Network Evolution
HFC Plant
NIU
Full Service IP Backbone Network
IP
DOCSIS 1.1
IP
Cable Modem
HFC Plant Packet NIU With Embedded MTA and DOCSIS Cable Modem
What is important about any migration plan from constant bit rate circuit switched telephony to IP telephony?
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Testing Your Knowledge 1. What is the fundamental difference between IP telephony and switched circuit telephony?
2. What are the steps in preparing a voice signal for transmission over an IP network? Which of these steps are common to all analog-to-digital conversions?
3. What is the most common cause of poor quality transmission in an IP telephony call? Why does it happen?
4. Why is it easier to provide good quality IP telephony on an intranet than on the Internet?
5. What are the four components of IP telephony as specified by H.323?
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6. What are the main functions of an H.323 gatekeeper?
7. What are the four components of MGCP, as specified in PacketCable NCS 1.0?
8. Your boss says, ”Telephony in a cable system is just too risky a business no w. We can’t commit to circuit switched HFC telephony with all this talk about IP telephony being the future technology for telecommunications. We need to wait until IP telephony matures before we get into the telephony business.”" How would you try to convince him that there are ways to get into telephony now that may make sense?
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