VOIP

ENGR 475 – TelecommunicationsHarding University

November 16, 2006

Jonathan White

Outline

• Functionality• What it runs over• Benefits

– 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

• 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• 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.