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Telephony, VoIP - USALearning _v401/course/... · PDF fileTelephony / VOIP . 191....

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  • Telephony, VoIP

    Table of Contents

    Telephony / VOIP ............................................................................................................................ 2

    Voice over Internet Protocol (VoIP) Architectures ......................................................................... 3

    Parts of a VoIP Implementation -1.................................................................................................. 5

    Parts of a VoIP Implementation -2.................................................................................................. 6

    Parts of a VoIP Implementation -3.................................................................................................. 8

    Parts of a VoIP Implementation -4................................................................................................ 10

    VoIP Protocols ............................................................................................................................... 11

    VoIP Protocol H.323 ................................................................................................................... 12

    Diagram of an H.323 Implementation .......................................................................................... 13

    SIP Session Initiation Protocol ................................................................................................... 14

    VoIP Protocol H.323 ................................................................................................................... 15

    SIP Session Initiation Protocol ................................................................................................... 16

    SIP Network Servers ...................................................................................................................... 17

    SIP Network Servers in Action ...................................................................................................... 18

    VoIP Protocol Types -1 .................................................................................................................. 19

    VoIP Protocol Types -2 .................................................................................................................. 21

    VoIP Security Considerations -1 .................................................................................................... 22

    VoIP Security Considerations -2 .................................................................................................... 25

    Notices .......................................................................................................................................... 26

    Page 1 of 26

  • Telephony / VOIP

    191

    Telephony / VOIP

    **191 Instructor: I'd like to talk to you about telephony. In particular, we're going to focus our attention on VOIP. And the reason why we should talk about telephony and how it works is because well, quite frankly, as security people, and as network security people, we've inherited a lot of telephony by it being changed over to voice over IP.

    Page 2 of 26

  • Voice over Internet Protocol (VoIP) Architectures

    193

    Voice over Internet Protocol (VoIP) Architectures

    IP centric System is entirely IP-based with a dedicated trunk to the PSTN

    IP enabled End-user phones are IP-based, switching and trunks are traditional

    **193 So, when we talk about voice over IP, the architectures, they are IP centric. In other words, our call communication is done IP address to IP address. It's no longer done telephone number to telephone number. But what we have to do is we have to create a dedicated trunking system that will allow us to keep that idea in our mind. Now, where we truly see voice over IP really kicking in is-- I don't know if you've seen this lately, but a lot of the websites that you pop on to say, "Would you like to chat with a representative right now?" And then there's another button that's popping

    Page 3 of 26

  • up more and more often, "Would you like to have a voice communication with this person right now?" So, you've got both options. The chat is a lot more automated, a lot more cost effective for them because they can put robots in place up until the point where you ask a question that's I don't know to the robot. And then a real person can step in so they can set up those calls and get those people ready, and optimize all those people that are in that call center. When you click the voice button and you actually get somebody ringing and picking up the phone, that is very costly to the organization. So, what they say is, "Okay, we'll pay for that cost, but we won't pay for the cost of the dime to actually make the call."

    Page 4 of 26

  • Parts of a VoIP Implementation -1

    194

    Parts of a VoIP Implementation -1

    IP network Provide underlying connectivity Should prioritize voice and data latency in voice communication is

    more noticeable than in data communication Quality of service (QoS) specifies a priority Class of service (CoS) marks packets for compliance with QoS

    **194 When we look at VoIP implementations out there, you have to know who's providing the underlying connectivity. This is your Internet service provider, which Internet service providers are really-- well, they were telephone providers for a long time. Do you, when you set up this communication, prioritize the voice and data in a way that is different than other customers? Remember, one of the problems that we run into with voice that we expect is we want nice clean communication from me to you. We want that quality of service. We want that high level communication

    Page 5 of 26

  • that we've come to expect from a hundred years of communication over regular telephones. And we expect it on a cellular network. Or we expect it on our computer.

    Parts of a VoIP Implementation -2

    195

    Parts of a VoIP Implementation -2

    Call processor / controller

    Aka, softswitch, call agent, call manager, gatekeeper Setup and monitoring of calls Authorization of users Provides phone features like voicemail, caller-ID Controls bandwidth for each call

    **195 One of the pieces that we have to understand here is that there now needs to be that was replaced from old Ma Bell a call processor and a controller. Somebody has to set up or connection to the phone system from our computer. That needs to be automated. And that needs to be sent out over the wire. And then the call connection on the other side needs to be made. This used to be

    Page 6 of 26

  • made by somebody actually plugging in a switch and connecting the circuit from one source to the destination. Well, that stuff's gone, but we still have to do that function because it's not immediate like it is with a lot of other technologies. Then we have to set up and monitor calls and see if that's reasonable. Are we allowed to monitor because that's a security issue depending on the country that you're in. So, we need a call agent, a call manager, and a gatekeeper. And all these functions go together to make up what is our telephony today. So, all of those concepts have now been abstracted into certain protocols and services that are being offered by the voice over IP providers. We also need to do the things that we thought we had before with the auto-attendant locally are things like voicemail and caller ID. All of that-- all of those tools need to be in place. And all that data needs to be passed up the channel on something that is a multi-use computer rather than a single use phone. We also need to check the bandwidth on this and whether we actually have enough bandwidth to support all the calls that are happening simultaneously.

    Page 7 of 26

  • Parts of a VoIP Implementation -3

    196

    Parts of a VoIP Implementation -3

    Media / signaling gateway Interface VoIP network with public switched telephone network Call origination and detection Analog to digital conversion voice packets from analog signal

    Three kinds Media gateway data / voice conversion, interface with PSTN Signaling gateway call signaling conversion Media gateway controllers call origination and tear down

    **196 Now, when we're dealing with this, we also have this media signaling issue. So, what is our interface from the VOIP network to the public switched telephone network because there are still people that still have phones at this point? How do we communicate with them? There are still people that are connecting from their cellular phones down to a physical landline. We have to have call origination and call detection. And that could be the reverse. If you've got a physical phone, and you actually pick it up and you call me, and it's actually a real phone and not washed away

    Page 8 of 26

  • VOIP underneath it, if you actually can pick up that phone and call me on a rotary dial phone, at that moment in time, now we have to have that origination and detection popping back toward my side of the digital conversation. Now, there are three kinds of VOIP that are out there. Or not three kinds of VOIP, but three overall media signaling gateways that are there. It's the media gateway itself. That's where we do data and voice conversion. The signaling gateway, which is making the phone ring is what it boils down to. And the media gateway controllers, and that's call origination where it comes from, but also tearing down the circuit after we're finished because we could sit on the phone and be quiet for a real

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