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

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1 Network+ Guide to Networks 6 th 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, 6 th Edition2

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, 6 th Edition3

4 Terminology (contd.) Internet telephony –VoIP calls carried over Internet Network+ Guide to Networks, 6 th Edition4

5 Terminology (contd.) 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, 6 th Edition5

6 Terminology (contd.) Multicasting –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, email messages, instant messages, or telephone calls, and participate in videoconference callsall from one console Network+ Guide to Networks, 6 th Edition6

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, 6 th Edition7

8 Analog Telephones Traditional telephone used for VoIP –Signals converted to digital form Codec (coder/decoder) –Method of compressing, encoding, analog signals into bits Network+ Guide to Networks, 6 th Edition8

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, 6 th Edition9

10 10 Figure 12-1 ATA (analog telephone adapter) Courtesy of Grandstream Networks, Inc.

11 Analog Telephones (contd.) 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 networkand vice versa Network+ Guide to Networks, 6 th Edition11

12 Network+ Guide to Networks, 6 th Edition12 Figure 12-2 VoIP router Photo of SmartNode4520 Analog VoIP router from Patton Electronics, Co.

13 Analog Telephones (contd.) 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 organizations phone system Network+ Guide to Networks, 6 th Edition13

14 Network+ Guide to Networks, 6 th Edition14 Figure 12-3 IP-PBX Courtesy of Epygi Technologies, Ltd.

15 Analog Telephones (contd.) 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, 6 th Edition15

16 Analog Telephones (contd.) 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, 6 th Edition16

17 Network+ Guide to Networks, 6 th Edition17 Figure 12-4 Integrating VoIP networks and analog telephones Courtesy of Course Technology/Cengage Learning

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 Network+ Guide to Networks, 6 th Edition18

19 Network+ Guide to Networks, 6 th Edition19 Figure 12-5 Accessing a VoIP network from IP phones Courtesy of Course Technology/Cengage Learning

20 IP Telephones (contd.) IP telephone features –Speed-dialing –Call hold –Transfer, forward –Conference calling –Voice-mail 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, 6 th Edition20

21 IP Telephones (contd.) 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, 6 th Edition21

22 Network+ Guide to Networks, 6 th Edition22 Figure 12-6 An IP phone Courtesy of Grandstream Networks, Inc.

23 Softphones Computer programmed to act like IP telephone –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, 6 th Edition23

24 Softphones (contd.) Graphical interface –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, 6 th Edition24

25 Network+ Guide to Networks, 6 th Edition25 Figure 12-7 Softphone interface Courtesy of CounterPath Corporation

26 Network+ Guide to Networks, 6 th Edition26 Figure 12-8 Connecting softphones to a converged network Courtesy of Course Technology/Cengage Learning

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, 6 th Edition27

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, 6 th Edition28

29 Streaming Video (contd.) 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 users convenience –Viewers control viewing experience Pause, rewind, fast-forward capabilities Network+ Guide to Networks, 6 th Edition29

30 Network+ Guide to Networks, 6 th Edition30 Figure 12-9 Video-on-demand and live streaming video Courtesy of Course Technology/Cengage Learning

31 Streaming Video (contd.) Most streaming video –Takes place over public networks Network+ Guide to Networks, 6 th Edition31

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 –Telcos 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, 6 th Edition32

33 Network+ Guide to Networks, 6 th Edition33 Figure 12-10 A telecommunications carriers IPTV network Courtesy of Course Technology/Cengage Learning

34 Videoconferencing –Full-duplex connections Participants send and receive audiovisual signals –Real time –Benefits Cost savings, convenience Replace face-to-face business meetings Allow collaboration Network+ Guide to Networks, 6 th Edition34

35 Videoconferencing (contd.) 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, 6 th Edition35

36 Network+ Guide to Networks, 6 th Edition36 Figure 12-12 Videophone Courtesy of Grandstream Networks

37 Videoconferencing (contd.) 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, 6 th Edition37

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, 6 th Edition38

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, 6 th Edition39

40 Network+ Guide to Networks, 6 th Edition40 Figure 12-13 An H.323 zone Courtesy of Course Technology/Cengage Learning

41 H.323 (contd.) 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, 6 th Edition41

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, 6 th Edition42

43 SIP (contd.) SIP network components (pg. 574): –User agent –User agent client –User agent server –Registrar server –Proxy server –Redirect server Network+ Guide to Networks, 6 th Edition43

44 Network+ Guide to Networks, 6 th Edition44 Figure 12-14 An H.323 zone Courtesy of Course Technology/Cengage Learning

45 SIP (contd.) Some VoIP vendors prefer SIP over H.323 –Simplicityeasier 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, 6 th Edition45

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 Network+ Guide to Networks, 6 th Edition 46

47 MGCP and MEGACO (contd.) 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, 6 th Edition47

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 networks 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, 5 th Edition48

49 MGCP and MEGACO (contd.) 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, 5 th Edition49

50 MGCP and MEGACO (contd.) MGC gateway communicate protocols (contd.) –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 Network+ Guide to Networks, 6 th Edition50

51 Network+ Guide to Networks, 6 th Edition51 Figure 12-15 Use of an MGC (media gateway controller) Courtesy of Course Technology/Cengage Learning

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 Network+ Guide to Networks, 5 th Edition52

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 videoconferencesrequires 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, 5 th Edition53

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 Network+ Guide to Networks, 6 th Edition54

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 Network+ Guide to Networks, 6 th Edition55

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, 6 th Edition56

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, 5 th Edition57

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 Network+ Guide to Networks, 6 th Edition58

59 RSVP (contd.) 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 transmissions 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 Network+ Guide to Networks, 6 th Edition59

60 RSVP (contd.) 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 Network+ Guide to Networks, 6 th Edition60

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, 6 th Edition61

62 DiffServ (contd.) 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, 6 th Edition62

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 –Routers in the data streams 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, 6 th Edition63

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, 6 th Edition64


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