1. Network+ Guide to Networks 6th Edition
Chapter 12
Voice and Video Over IP

2. Objectives Use terminology specific to converged networks
Explain VoIP (Voice over IP) services, PBXs, and their user interfaces
Explain video-over-IP services and their user interfaces
Describe VoIP and video-over-IP signaling and transport protocols, including SIP, H.323, and RTP
Understand QoS (quality of service) assurance methods critical to converged networks, including RSVP and DiffServ
Network+ Guide to Networks, 6th Edition

3. Terminology IP telephony (VoIP)
Any network carrying voice signals using TCP/IP
Public or private
Runs over any packet-switched network
Virtually any data connection type can carry VoIP signals, including:
T-carriers, ISDN, DSL, broadband cable, satellite connections, WiFi, WiMAX, HSPA+, LTE, cellular telephone networks
Network+ Guide to Networks, 6th Edition

4. Terminology (cont’d.) Internet telephony
VoIP calls carried over Internet
Network+ Guide to Networks, 6th Edition

5. Terminology (cont’d.) Nondata applications on converged networks
IPTV (IP television)
Videoconferencing
Multiple participants communicate and collaborate via audiovisual means
Streaming video
Compressed video delivered in continuous stream
Webcasts
Streaming videos supplied via the Web
Network+ Guide to Networks, 6th Edition

6. Terminology (cont’d.) Multicasting Video over IP Services:
One node transmits same content to every client in group
Video over IP Services:
IPTV, videoconferencing, streaming video, & IP multicasting
Unified communications (unified messaging) service
Several communication forms available from single user interface
Users can access the Web, send & receive faxes, messages, instant messages, or telephone calls, and participate in videoconference calls—all from one console
Network+ Guide to Networks, 6th Edition

7. VoIP Applications and Interfaces
Reasons for implementing VoIP
Lower voice call cost (toll bypass)
New, enhanced features and applications
Centralize voice and data network management
Voice & data can be combined on a network in several configurations:
Use traditional telephone (sends, receives analog signals)
Use telephone specially designed for TCP/IP transmission
Use a computer with microphone, speaker, VoIP client software
Mixture of these types
Network+ Guide to Networks, 6th Edition

8. Analog Telephones Traditional telephone used for VoIP
Signals converted to digital form
Codec (coder/decoder)
Method of compressing, encoding, analog signals into bits
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9. Analog Telephones, cont.
Analog VoIP clients may connect to IP networks in one of four ways:
First analog-to-digital conversion method:
ATA (analog telephone adapter)
Card within computer workstation
Or externally attached device
Telephone line connects to RJ-11 adapter port
Converts analog voice signals to IP packets
Network+ Guide to Networks, 6th Edition

10. Figure 12-1 ATA (analog telephone adapter)
Courtesy of Grandstream Networks, Inc.
Network+ Guide to Networks, 6th Edition

11. Analog Telephones (cont’d.)
Second analog-to-digital conversion method:
Connecting an analog telephone line to VoIP-enabled device (switch, router, gateway)
Convert analog voice signals into packets and then issuing the packets to a data network—and vice versa
Network+ Guide to Networks, 6th Edition

12. Figure 12-2 VoIP router
Photo of SmartNode™4520 Analog VoIP router from Patton Electronics , Co.
Network+ Guide to Networks, 6th Edition

13. Analog Telephones (cont’d.)
Third analog-to-digital conversion method:
Digital PBX (a.k.a IP-PBX)
PBX (private branch exchange): telephone switch connecting calls within private organization
IP-PBX
Is a private switch
Accepts, interprets both analog & digital voice signals
Connects with traditional PSTN lines, data networks
Transmits, receives IP-based voice signals to and from other network connectivity devices
Most are packaged with sophisticated software used to configure and maintain an organization’s phone system
Network+ Guide to Networks, 6th Edition

14. Figure 12-3 IP-PBX Courtesy of Epygi Technologies, Ltd.
Network+ Guide to Networks, 6th Edition

15. Analog Telephones (cont’d.)
Hosted PBX
Exists on the Internet
Separate provider for call management services
May also be called virtual PBXs
Trademark of VirtualPBX company
Advantage of Hosted PBXs
No installation or maintenance of hardware and software for call completion and management
VoIP Trunk
ONSIP example of a VoIP trunk provider
Network+ Guide to Networks, 6th Edition

16. Analog Telephones (cont’d.)
Fourth analog-to-digital conversion method:
Traditional telephone connects to analog PBX
Then connects to voice-data gateway
Gateway connects traditional telephone circuits with TCP/IP network
Internet or private WAN
The Gateway
Digitizes incoming analog voice signal
Compresses data
Assembles data into packets
Issues packets to packet-switched network
Network+ Guide to Networks, 6th Edition

17. Figure 12-4 Integrating VoIP networks and analog telephones
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

18. IP Telephones IP telephones (IP phones)
Transmit, receive only digital signals
Voice immediately digitized, issued to network in packet form
Requires unique IP address
Looks like traditional touch-tone phone
Connects to RJ-45 wall jack
Connection may pass through connectivity device before reaching IP-PBX
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19. Figure 12-5 Accessing a VoIP network from IP phones
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

20. IP Telephones (cont’d.)
IP telephone features
Speed-dialing
Call hold
Transfer, forward
Conference calling
Voic access
Speakers, microphones, LCD screen
Mobile and wired styles
Some can act as Web browsers
Easily moved from office to office
Network+ Guide to Networks, 6th Edition

21. IP Telephones (cont’d.)
Conventional analog telephone
Obtains current from local loop
Current used for signaling (ring, dial tone)
IP telephones
Need electric current
Not directly connected to local loop
Most use separate power supply
Susceptible to power outages
Requires assured backup power sources
Some use PoE (power over Ethernet)
Network+ Guide to Networks, 6th Edition

22. Figure 12-6 An IP phone Courtesy of Grandstream Networks, Inc.
Network+ Guide to Networks, 6th Edition

23. Softphones Computer programmed to act like IP telephone Prerequisites
Provide same calling functions
Connect to network; deliver services differently
Prerequisites
Computer minimum hardware requirements
IP telephony client installed
Digital telephone switch communication
Full-duplex sound card
Microphone, speakers
Softphone example: Skype is a popular Internet proprietary telephony software and is a type of softphone
Network+ Guide to Networks, 6th Edition

24. Softphones (cont’d.) Graphical interface Versatile connectivity
Presented after user starts softphone client software
Customizable
Versatile connectivity
VoIP solution for traveling employees and telecommuters
Convenient, localized call management
Call tracking
Date, time, duration, originating number, caller names
Simplifies recordkeeping and billing
Network+ Guide to Networks, 6th Edition

25. Figure 12-7 Softphone interface
Courtesy of CounterPath Corporation
Network+ Guide to Networks, 6th Edition

26. Figure 12-8 Connecting softphones to a converged network
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

27. Video-over-IP Applications and Interfaces
Cisco Systems estimate
By 2015, over two-thirds of Internet traffic will be video traffic
Factors fueling growth
Large quantity of video content available (Netflix & Hulu)
Increasing number of devices accessing Internet
Decreasing cost of bandwidth, equipment
Video-over-IP services categories
Streaming video, IPTV, videoconferencing
Network+ Guide to Networks, 6th Edition

28. Streaming Video Is a video-over-IP application
Basic computer appropriate audiovisual hardware and software to view the encoded video
One method is Video-on-demand:
Files stored on video streaming server
Popular
Viewer chooses video when convenient: Web browser
Another method is Streaming video:
Video issued live
Directly: source to user
Network+ Guide to Networks, 6th Edition

29. Streaming Video (cont’d.)
Drawbacks of live stream
Content may not be edited before distribution
Viewers must connect with stream when issued
Video-on-demand benefits
Content viewed at user’s convenience
Viewers control viewing experience
Pause, rewind, fast-forward capabilities
Network+ Guide to Networks, 6th Edition

30. Figure 12-9 Video-on-demand and live streaming video
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

31. Streaming Video (cont’d.)
Most streaming video
Takes place over public networks
Network+ Guide to Networks, 6th Edition

32. IPTV (IP Television)
Telecommunications carrier and cable company networks
Offer high-bandwidth Internet connections to deliver digital television signals using IPTV
Elements of delivering digital video to consumers
Telco accepts video content at a head end
Telco’s CO (central office) servers provide management services
Video channel assigned to multicast group
When an IPTV user changes the channel they are opting out of one IP multicast group and opting into another
Network+ Guide to Networks, 6th Edition

33. Figure 12-10 A telecommunications carrier’s IPTV network
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

34. Videoconferencing Videoconferencing Full-duplex connections Real time
Participants send and receive audiovisual signals
Real time
Benefits
Cost savings, convenience
Replace face-to-face business meetings
Allow collaboration
Network+ Guide to Networks, 6th Edition

35. Videoconferencing (cont’d.)
Videoconferencing uses
Telemedicine
Tele-education
Judicial proceedings
Surveillance
Hardware, software requirements
Means to generate, send, receive audiovisual signals
Computer workstation with cameras, microphones, software
Video terminal or video phone
Network+ Guide to Networks, 6th Edition

36. Figure 12-12 Videophone Courtesy of Grandstream Networks
Network+ Guide to Networks, 6th Edition

37. Videoconferencing (cont’d.)
Video bridge
Manages multiple audiovisual sessions so that participants can see and hear each other
May exist as a piece of Hardware or software, in the form of a conference server
Internet-accessible video bridging services can be leased
Well suited for occasional videoconference use
Some organizations might maintain their own conference servers
Network+ Guide to Networks, 6th Edition

38. Signaling Protocols Signaling protocols:
Set up and manage sessions between clients
Early VoIP: used proprietary signaling protocols
Today: standardized signaling protocols are usually used which are discussed next
SS7 (Signaling System 7): typically handles call signaling on the PSTN
May come up when trying to interconnect the PSTN with VoIP
Network+ Guide to Networks, 6th Edition

39. H.323 Describes architecture & a group of protocols for:
Establishing and managing packet-switched network multimedia sessions
Supports voice and video-over-IP services
Terms:
H.323 terminal (IP phone)
H.323 gateway (connects to other signaling protocols)
H.323 gatekeeper (authenticates terminals, manages bandwidth, and oversees call routing, accounting, and billing
MCU (multipoint control unit) provides support for multiple H.323 terminals
H.323 zone (collection of H.323 terminals, gateways, and MCUs are managed by a single H.323 gatekeeper)
Network+ Guide to Networks, 6th Edition

40. Figure An H.323 zone
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

41. H.323 (cont’d.) In sum, H.323 is the call control signaling protocol
H.225 and H.245 signaling protocols
Specified in H.323 standard
Operate at Session layer of OSI
H.225 handles call or videoconference signaling
IP telephone requests a call setup via H.225
H.245 ensures correct information type formatting—whether voice or video issued so that the H.323 terminal can interpret the data
H.323 remains a popular signaling protocol on large voice and video networks
In sum, H.323 is the call control signaling protocol
Used to setup, maintain, teardown, and redirect calls
Network+ Guide to Networks, 6th Edition

42. SIP (Session Initiation Protocol)
Performs similar functions as H.323
Application layer signaling and control protocol that was modeled after HTTP
VoIP call is formatted like an HTTP request and rely on URL style addresses
Limited capabilities compared to H.323
SIP does not have features such as caller ID and instead it depends on other protocols and services to supply them
Network+ Guide to Networks, 6th Edition

43. SIP (cont’d.) SIP network components (pg. 574): User agent
User agent client
User agent server
Registrar server
Proxy server
Redirect server
Network+ Guide to Networks, 6th Edition

44. Figure An H.323 zone
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

45. SIP (cont’d.) Some VoIP vendors prefer SIP over H.323 SIP and H.323
Simplicity—easier to setup
Fewer instructions to control call
Consumes fewer processing resources than H.323
SIP and H.323
Regulate call signaling and control for VoIP or video-over-IP clients and servers
Do not account for communication between media gateways
MGCP or MEGACO protocols are used for communication between media gateways
Network+ Guide to Networks, 6th Edition

46. MGCP (Media Gateway Control Protocol) and MEGACO (H.248)
Media Gateway: A gateway capable of accepting connections from multiple devices, such as IP telephones, traditional telephones, IP fax machines, traditional fax machines, and translating analog signals into packets and vice versa
Accepts PSTN lines, converts signals into VoIP format, and translates between signaling protocols
Gateways still need to exchange and translate signaling and control information with each other so that voice and video packets are properly routed through the network
They rely on the MGC (media gateway controller) device, which can manage multiple media gateways
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47. MGCP and MEGACO (cont’d.)
MGC (media gateway controller)
Used by media gateways to make sure that voice and video packets are properly routed through the network
Enables multiple media gateways to communicate
Computer managing multiple media gateways
Also called a softswitch (software performs the call switching)
Network+ Guide to Networks, 6th Edition

48. MGC (media gateway controller)
Example:
When a media gateway receives a call, rather than attempting to determine how to handle the call, the gateway contacts the MGC with a message that says, “I received a signal. You figure out what to do with it next.”
The MGC then determines which of the network’s media gateways should translate the information carried by the signal. It also figures out which physical media the call should be routed over
Media gateways simply follow orders from the MGC
Network+ Guide to Networks, 5th Edition

49. MGCP and MEGACO (cont’d.)
MGC communicate with media gateways according to several protocols (MGCP or MEGACO)
MGCP (Media Gateway Control Protocol)
Commonly used on networks that support a number of media gateways
Can operate with both H.323 or SIP call signaling and control protocols
Older protocol
Newer gateway control protocol is MEGACO
Network+ Guide to Networks, 5th Edition

50. MGCP and MEGACO (cont’d.)
MGC gateway communicate protocols (cont’d.)
MEGACO (H.248)
Is a newer gateway control protocol
Performs same functions as MGCP
Different commands and processes
Operates with H.323 or SIP
Superior to MGCP
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51. Figure 12-15 Use of an MGC (media gateway controller)
Courtesy of Course Technology/Cengage Learning
Network+ Guide to Networks, 6th Edition

52. Transport Protocols
Session Protocols: only communicate information about a voice or video session
Transport layer Protocols: are a set of protocols used to actually deliver the voice or video payload—the bits of encoded voice that together make up words spoken into an IP telephone
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53. Transport Protocols, cont.
UDP and TCP operate at the Transport layer
TCP: connection oriented and provides some measure of delivery guarantees
UDP: connectionless
The preferred protocol for telephone conversations and videoconferences—requires less overhead and therefore can transport packets more quickly
Packet loss tolerable if additional protocols overcome UDP shortcomings
Real-time Transport Protocol (RTP)
Real-time Transport Control Protocol (RTCP)
Network+ Guide to Networks, 5th Edition

54. RTP (Real-time Transport Protocol)
A Transport layer protocol used with voice and video transmission
RTP operates on top of UDP and provides information about packet sequence to help receiving nodes detect delay and packet loss
RTP also assigns packets a timestamp that corresponds to when the data in the packet was sampled from the voice or video stream
Timestamp helps the receiving node synchronize incoming data
Has no mechanism to detect whether or not it is successful
For that, it relies on RTCP
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55. RTCP (Real-time Transport Control Protocol)
A companion protocol to RTP that provides feedback on the quality of a call or videoconference to its participants
Packets transmitted periodically to all session endpoints
Recipients of RTP data use RTCP to issue information about the number and percentage of packets lost and delay suffered between the sender and receiver
Not mandatory on RTP networks and some network admins may prefer not to use it
RTP and RTCP
Provide information about packet order, loss, delay
Cannot correct transmission flaws that is handled by QoS protocols
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56. QoS (Quality of Service) Assurance
QoS: is a measure of how well a network service matches its expected performance
Despite all the advantages of using VoIP and video-over-IP, it is more difficult to transmit these types of signals over a packet-switched network than it is to transmit data signals
Network+ Guide to Networks, 6th Edition

57. Techniques to overcome QoS Challenges
QoS techniques:
RSVP (Resource Reservation Protocol)
DiffServ (Differentitated Service)
MPLS (Multiprotocol Label Switching)
Help to eliminate call and video delays
Network+ Guide to Networks, 5th Edition

58. RSVP (Resource Reservation Protocol)
Transport layer protocol
Before transmission
Attempts to reserves network resources (bandwidth) for a transmission so the signal will hopefully arrive without suffering delays
Creates path between sender & receiver
Provides sufficient bandwidth so the signal arrives without delay
Sending node issues PATH statement via RSVP to receiving node
Indicates required bandwidth and expected service level it expects
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59. RSVP (cont’d.) Two service types:
Guaranteed service: assures the transmission will not suffer packet losses and will experience minimal delay
Controlled-load service: provides the type of QoS a transmission would experience if the network carried little traffic
Each router that the PATH message traverses marks the transmission’s path by noting which router the PATH message came from
After the destination node receives the PATH message, it responds with a Reservation Request (RESV) message
Follows same path in reverse
Routers between destination and sending nodes allocate the requested bandwidth
Sending node transmits data
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60. RSVP (cont’d.) Specifies and manages unidirectional transmission
For two users to participate in a VoIP or videoconference, the resource reservation process takes place in both directions
RSVP Emulates circuit-switched path
Which provides excellent QoS
Drawback: high overhead
Acceptable on small networks
Larger networks use DiffServ
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61. DiffServ (Differentiated Service)
Differentiated Service (DiffServ)—another way to prioritize network traffic
Places information in the DiffServ field in an IPv4 datagram. In IPv6 datagrams, it uses a similar field known as the Traffic Class field
This information indicates to the network routers how the data stream should be forwarded
Because of its simplicity and relatively low overhead, DiffServ is better suited to large, heavily trafficked networks than RSVP
Network+ Guide to Networks, 6th Edition

62. DiffServ (cont’d.) Two forwarding types: EF (Expedited Forwarding)
Data stream assigned minimum departure rate
Circumvents delays
AF (Assured Forwarding)
Data streams assigned different router resource levels
Prioritizes data handling, but does not guarantee that on a busy network packets will arrive on time and in sequence
A deeper discussion of these prioritization techniques is beyond the scope the textbook and class
Network+ Guide to Networks, 6th Edition

63. MPLS (Multiprotocol Label Switching)
Modifies data streams at Network layer
To indicate where data should be forwarded, MPLS replaces the IP datagram header with a label at the first router a data stream encounters
The MPLS label contains information about where the router should forward the packet next
Router’s in the data stream’s path revises label
To indicate next hop to the receiving router
Routers only need to read the MPLS (shim)
Routers do not have a perform a route lookup to determine where to forward the packet next
With MPLS, data streams are more likely to arrive without delay
Networks can and often do combine multiple QoS techniques
Network+ Guide to Networks, 6th Edition

64. Summary VoIP services carry voice signals over TCP/IP protocol
Four ways to connect VoIP clients to IP networks
Streaming video can be delivered live or on-demand
IPTV television signals travel over packet-switched connections
Video bridges manage communication for videoconferences
H.323 standard
Describes architecture and protocols for managing multimedia sessions on a packet-switched network
Network+ Guide to Networks, 6th Edition