Transcript Lecture 15: VOIP - Harding University

VOIP
ENGR 475 – Telecommunications
Harding University
November 16, 2006
Jonathan White
Outline
• Functionality
• What it runs over
• Benefits
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Cost
Flexibility
Quality
Security
Drawbacks
Hurdles that need to be overcome
Adoption rates
Legal issues
VOIP
• VOIP: Voice over Internet Protocol.
– A method for routing voice calls across the
Internet, instead of the PSTN.
– Your voice is packetized and sent across the
Internet.
• No longer circuit switched.
• Main benefit:
– You have a telephone wherever you have an
Internet connection
• You can bypass the PSTN, and its charges.
VOIP Access Methods
• Computer to Computer:
– Skype, free, closed source, security by obscurity,
potential bandwidth issues.
– Requirements:
• Software, microphone, speakers/headphones, soundcard,
connection to the Internet.
– No charges ever involved.
• Does it matter how far away a website is?
– Easiest method.
• But, who wants to be on a computer all the time
to make a phone call?
VOIP Access Methods
• ATA: Analog Telephone Adapter.
– Your analog telephone is connected
to a special device that connects your phone to
the Internet.
• Just looks like a DSL router.
– This is typically what Vonage sends you when
you buy service from them.
• $20 a month for Vonage service, with deals similar
to cell phone plans.
• Inexpensive, typically $50 for the Adapter.
VOIP Access Methods
• IP Phones
– Look like normal phones, except they use an
RJ-45 (Ethernet) jack instead of an RJ-11.
– Connects to your router or switch.
– All the necessary hardware and software is on
the phone when you buy it.
– Phones cost $150 and up
• Combination of the
ATA and analog phone.
Packet Switching
• Most PSTN network trunks are becoming packet
switched.
– Why?
• Voice providers are carrying more data than they are voice.
• Most calls today get sent across a packet
switched network at some point already.
– However, there can be a large lag time:
• 600 ms for a call in China from the US
• As time goes on, many predict that voice will just
be another application on the Internet.
– This is already true to some extent.
Nokia E61
• Dual Mode with WiFi and 3G CDMA support:
– At home or where ever there is a wireless Internet
connection, the phone uses VOIP to communicate for
free.
– Where there isn’t an Internet connection, it accesses
the cellular network.
• Both have high data transfer rates.
• Is this the future of telephony?
– Is this the future of computing?
Benefits of VOIP
• Free or nearly free calls to other VOIP
users.
– No long distance
• Every feature imaginable is free or nearly
free: Call waiting, ring tones, call
forwarding, etc, etc, etc.
• Quality can actually be quite good.
– Better than cellular calls.
– On par with landlines.
Benefits of VOIP
• Large installed base of packet switched networks
get to be used more fully.
• Voice data gets compressed from the beginning.
– When no one is talking, no packets are sent.
• Voice is encrypted from the beginning.
• You can get a phone number for free.
• You can receive calls anywhere where there is an
Internet connection.
– Your landline phone is no longer stuck on land.
How a VOIP call works
• You have an IP address and probably a
telephone number on your ATA or IP phone.
– Dial who you want to talk to.
– The phone number is sent to your VOIP provider’s call
processor.
• Large database that maps IP address to phone numbers and
back and forth.
– A session using a protocol called SIP ( or H.323) is
used to essentially connect the 2 computers.
• Much like the HTTP protocol.
– You then can talk with your voice being carried on the
Internet.
• The data network can’t tell the difference between your voice
and a webpage.
VOIP Drawbacks
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Can’t send a fax with VOIP.
Dependent on wall power.
Dependent on an Internet connection.
Added one more database dip to the
telephone system.
• Latency and Jitter.
– Must use voice buffers on both end.
– Packet delay can be a maximum of 600 ms if
using a satellite link.
VOIP Drawbacks
• Packet loss.
– Your data network must be non-congested.
– UDP is used in some implementations, which doesn’t
guarantee delivery of packets.
• Reliability of your Internet connection
– Especially compared to your landline phone.
• 911 doesn’t work at all or it works poorly.
• In 2005, the government made VOIP providers:
– Support CALEA (wiretapping)
– LNP
– Payment of Universal Service Fees
VOIP Drawbacks
• In developing countries, cellular phones have
nearly complete market penetration.
– Is there a need for a VOIP phone?
• VOIP numbering schemes and protocols are not
interoperable.
– VOIP is still a developing technology.
• Some devices depend on having a telephone
grade connection.
– TIVO, home security systems, some digital TV services
• Operating systems of VOIP users.
– Has your computer ever had a virus?
– Has your landline ever had a virus?
VOIP Codec
• Called G.723.1 and it is a descendant of
PCM.
– Samples at 8000 times a second.
– Uses LPC (like a cell phone), so it doesn’t
send the actual samples.
• The look ahead is 7.5 ms.
• Packages voice in samples of 30 ms.
• The codec only takes up 2.2 Kbytes of
RAM in execution.
VOIP Protocols
• 2 Main protocols:
– H.323
• Primary protocol for backbone networks.
• Doesn’t handle firewalls well.
– SIP
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Session Initiation Protocol.
Used by end nodes.
Text based protocol, similar to HTTP
Uses TCP and UDP over port 5060 to connect to
SIP servers.
• Highly centralized, like the telephone network.