voip for dummies
TRANSCRIPT
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VoIP for Dummies
Gregory MortonSr. Programmer Analyst - xwave
October 12, 2006
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Agenda
Introduction & Caveats The Why and What of VoIP Background Information
Digital vs. Analog PSTN Internet Crash Course
VoIP Architecture Overview VoIP and 911
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Caveats
This discussion is intended for non-technical people. It blatantly “glosses over” some details to save time
and confusion. It should give you enough information that you can
learn more on your own. Neither I, nor the presentation, are affiliated with the
IDG series of books in any way although there is one with the same title.
The information and opinions in this presentation are provided by me, and may not reflect those of my employer, who is a VoIP solutions provider.
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Why use VoIP?
It’s Cheaper! Unlimited long distance Bundled services (Call display, Call
forwarding, Voice mail, etc.)
Neat Features! Video teleconferencing Pick your Area code and/or exchange “Nomadic” phone service.
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What is VoIP, Simply
Voice over IP is an easy way to make phone calls using the internet.
Voip uses the same principles that web browsers and email servers do.
Voip service providers have “gateways” that patch the internet to the phone network, and the gateway translates your internet address to a phone number and back.
Voip is constantly evolving. There are several different competing standards but the two major players are H.323 and SIP
Voip could be bigger than cellular. Huge 911 impact.
Voip + WiFi = Free “wireless” calls.
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Voice over IP is a method for taking analog signals and turning them into digital signals that can be transmitted over traditional packet-switched IP networks.
Technically that is true, but what does it mean?
VoIP is full of technical jargon, and that jargon is in turn sometimes dependant on knowing other technical jargon!
The purpose of this presentation is to give a brief overview of the underlying technologies so it all makes sense.
What is VoIP, Really
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Why VoIP can be intimidating
In order to get to the top, you need to have an understanding of the technologies that it is built on or compared to.
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Background Information
Analog vs. Digital POTS and the PSTN Why “PSTN is to Analog what VoIP is to
Digital” is not really correct. Internet Crash Course
Protocols Comparing TCP vs UDP to pizza delivery
guys, really.
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Analog vs. Digital
The red line represents an analog sound. The Green bars show a digital representation of that sound.
The digital signal can be improved by increasing the number of samples. This makes the bars more narrow, and more accurate, but makes the amount of data larger.
© howstuffworks.com
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POTS and the PSTNPOTS – Plain Old Telephone Service
PSTN – Public Switched Telephone Network
Local calls go through your central office (CO) on an analog line.
When you call someone far away, the CO connects to their CO via the PSTN on a digital trunk.
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Why Digital?
So why is the network digital in the middle?
Long reason:The problem with a circuit switched network is that the circuit stays active for the length of a call, and cannot be used or shared, even if there is no dialog.
To be more efficient the call is transformed from an analog signal to a digital one. This allows some resources to be shared.
Short reason:It’s cheaper.
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Digital PSTN
PSTN digitization is a method for taking analog signals and turning them into digital signals that can be transmitted over circuit-switched networks… Sound familiar?
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Protocol – The P in VoIP
A protocol is a set of rules used to initiate and terminate communication.
The SS7 protocol suite is used to route a call through the PSTN.
The TCP/IP protocol suite is used to route internet traffic, including VoIP.
Analogous to meeting someone, there is even something called ‘handshaking’.
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The IP in VoIP
Internet Protocol Used with TCP or UDP to deliver packets.
What’s a Packet? A piece of information. Like taking a puzzle
and a box of envelopes, numbering each envelope, and mailing the individual pieces.
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Protocols within protocols
Called “packet encapsulation” Think of the Russian dolls inside each other. Each
doll has it’s own job to do to make sure the data gets to its destination.
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Sending packets
Routers move packets from one destination to another. They use IP tables to know which routers are closer to destination, know how long it takes to transmit from one router to another, and will route based on shortest path.
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Internet Pizza Delivery
TCP – Tank’s delivery service It’ll get there no matter what. The pizza
might be cold though.
UDP – Formula 1 delivery service We might not get there, but if we do the
pizza will be fresh & hot right out of the oven.
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VoIP Architecture
Phone Codec VoIP Protocols (H.323, SIP, etc.) IP Address to Telephone Number (TN)
Conversion IP to PSTN Gateway
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VoIP “Phones”
ATA (Analog Telephone Adapter) Plug your regular POTS phone into it.
IP phone. Less like a traditional phone than a computer.
Softphone (software phone) on your PC, like Skype
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Codecs
Codec = COmpression and DECompression Used to compress the size of voice data, yet preserve
the sound quality. There are four parts to balancing a codec:
Bitrate – a higher bitrate gives higher quality, but more data to transmit.
Complexity – a more complex codec, generally gives better compression and less data, but requires more cpu power and time to compress and decompress.
Voice quality – effected by bitrate, echo, and jitter. Delay – Caused by network latency, dropped packets, and
codec processing. Causes echo and makes jitter worse.
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VoIP Protocols
“The nice thing about standards is that you have so many to choose from; furthermore, if you do not like any of them, you can just wait for next year’s model.”
- Andrew S. Tanenbaum (Vrije Universiteit, Amsterdam)
H.323 versions 1-4 SIP Megaco MGCP etc.
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TN to IP Conversion
Call is initiated by a VoIP proxy server Uses lookup tables to convert TN to IP Contacts phone at IP address, and tells the
phone to communicate with the other party.
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IP to PSTN Gateway
This is the network bridge between the IP network and the PSTN.
It is composed of three main parts Voice segment Fax relay Call signalling (build up and tear down)
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VoIP and 911
Issues and Opportunities Immediate solution for VoIP (i1) Interim solution for VoIP (i2) IP based full e911 solution for VoIP (i3)
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VoIP 911 Issues
Dependant on electrical service. Recommend having UPS.
Global Traveller Issue Nomadic service everywhere, but “911”
isn’t everywhere. Privacy vs. Safety
Put a GPS chip in every IP phone? Still not a huge help within some
structures.
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Potential E911 Opportunities
Multimedia nature of IP Webcam device could allow PSAP or
responders to see inside the complex. Speech to text/Internet messaging client
for the deaf. “Medic-alert” type information sent to
PSAP.
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Immediate VoIP 911 (i1)
Route VoIP calls to correct PSAP outside of current 911 system, preferably with Caller ID (CLID)
This gives service equivalent to basic 911, and has the same problems. (if caller does not know location or is unable to communicate.)
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Interim VoIP E911 (i2)
Route VoIP calls to correct PSAP into the current 911 system, with CLID and location information (ALI).
Works for both stationary and nomadic VoIP (but not for Mobile VoIP).
Provides MSAG validated location information.
Nomadic phone must update its information on reconnection to the network
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i2 e911 callflow
Taken from NENA 08-001v1 p30
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IP Based e911 (i3)
PSAPs will be 100% IP based. Like phase 2, only better!
Gateways will be used to convert incoming PSTN calls.
IP calls will use SIP and ENUM to give a unique ID to each phone.
Caller location will be attached to the DHCP request, when the handset connects to the network.
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Bonus Slide
© CTC 2005
This diagram shows the potpourri of data packets that could flow through a home network.