VoIP{ Voice Over IP }

What is VoIP?

The transportation of packets containing voice data over a network (LAN, WAN or internet).

Why is it Important?

• Voice over IP does not just mean “voice.”– Video, data conferencing

• Cost• Convergence

– Using high-speed internet connection for all voice, video, and data communications.

• Reduce maintenance costs• Reduce deployments costs

• Home has more options in service choices• Increased functionality

Better Use of Resources{ Beating a Dead Horse }

How Does it Work?• Sound heard by computer at rate of 8,000 times per

second or more• Uses CODEC (ulaw, alaw, gsm, ILBC, and others)

– Speech CODECs are optimized to improve spoken words at the expense of sounds outside the frequency range of human speech

• Placed into data packets – a single packet will contain 10 or more milliseconds (20 or 30 is more common)

• PLC (Packet Loss Concealment) compensated for by CODEC– Redundancy– FEC (Forward Error Correction)

• Delay – Jitter

How Does it Work?

The Wireless Version

VOWi-Fi

PSTN = Public Switched Telephone Networks

IMS = IP Multimedia Subsystem

A Blip about SIP{I’m so clever}

SIP

• Simple – SIP has only six methods

• Transport-independent (application-layer):– Can be used with UDP, TCP, and more.

• Readable – text based

{ Session Initiation Protocol }

SIP{ Session Initiation Protocol }

Provides necessary protocol mechanisms so that end systems and proxy servers can provide services

• call forwarding, including• equivalent to 700, 800, and 900 type calls• address-translation services

• number delivery, where numbers can have naming scheme• personal mobility

• the ability to reach a party under a single, location-independent address when the user changes terminals

• negotiation• caller can be given choice how to reach the party

• Internet telephony, mobile phone, answering service• caller and called authentication• invitations to multicast conferences

pulver.com

Proxy server

nortel.com

user@nortel.com

1. INVITE sip:jeff.pulver@pulver.com SIP/2.0 From: sip:user@nortel.com

Location Server

jeff

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2. INVITE sip:pulver@von1 SIP/2.0 From: sip:user@nortel.com3. SIP/2.0 200 ok From: sip:pulver@von1

pulver@von1

4. SIP/2.0 100 OK From: sip:jeff.pulver@pulver.com

5. ACK sip:jeff.pulver@pulver.com SIP/2.0 From: sip:user@nortel.com

6. ACK sip:pulver@von1 SIP/2.0 From: sip:user@nortel.com

SIP Proxy Mode

1. INVITE sip:jeff.pulver@pulver.com From: sip:user@nortel.com

2. SIP/2.0 320 Moved temporarily Contact: sip:pulver@von1.pulver.com

nortel.com

user@nortel.com

pulver.com

Redirect Server

Location Server

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ulv

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4. INVITE sip:pulver@von1.pulver.com From: user@nortel.com

3. ACK sip:jeff.pulver@pulverr.com From: sip:user@nortel.com

5. SIP/2.0 200 OK To: user@nortel.com

6. ACK sip:pulver@von1.pulver.com From: sip:user@nortel.com

Pulver@von1

SIP Redirect Mode

• Can be stateful or stateless

Hybrid Proxy Is Best Alternative

Proxy Server Redirect

Stateful Proxy Servers

• Maintains call context • Replicates User Agent Server/User Agent Client to

process requests/responses• Call state and transaction state can be maintained

• Forking proxies require state • TCP proxies must be stateful for reliability• Enhanced services require state for execution• Can populate billing information

Services Dictate Statefulness of Proxy

Stateless Proxy Servers

• No call context • Response is not based on User Agent replication• Provides client anonymity • Restricted gateway access • High processing capacity • Allows for easier replication than stateful proxy• Can have semi-stateful proxy for ultimate benefits

Stateless Proxies Geared for Capacity

• Can be stateful or stateless• Flexible, network service

implemenations

• Reliability achieved through replication

• Scalability achieved through partitioning

• Overload potential if not properly scaled

• Hybrid (semi-stateful) model provides maximum benefits

• High capacity

• Minimal state overhead

• Service execution pushed to client

Hybrid Proxy Is Best Alternative

Proxy Server Redirect

H.323

• Complex• Easier to look at H.323 and SIP

comparisons than to try to understand ‘how it works’ in a brief period of time– (big debate)

What does that mean?!

• Scalability: SIP• Reliability: H.323• Speed: SIP• Standardized: H.323• Most Flexibility with Services: SIP• Low Complexity: SIP• Features (as of right now): H.323

Everyone is biased!

Commercial Break{please stay tuned for your regularly scheduled broadcasting

Some Problems

• Reliability• Quality

– Example: NATs prove to be big problem

STUN{ Simple Traversal of UDP through NAT }

• Used in residential NATs

• allows for P2P connection through the NAT

• Not 100% reliable

• Does not work with Enterprise NATs (Symmetric)

STUN

TURN

• Uses relay server to connect to single peer behind the NAT

• 100% Reliable• Comes at great cost

– Access bandwidth– Delay

{ Traversal Using Relay NAT }

ICE

• Basically says to use STUN if at all possible, only using TURN as a last resort.

{ Interactive Connectivity Establishment }

one smart decision amongmany many stupid ones

Please stay tuned for the conclusion of your program, just after this

Problems with VoIP• Bandwidth Dependency

– No internet = no phone– Poor connection = hate– Shared connection = unpredictable

• Power Dependency– No power = no router/modem/ATA = no phone– No power = no 911

• Voice Quality– Delays, noise, echoes, strange sounds– Less robust than PSTN

• Milliseconds mean everything

Security Problems

• Phreaking– Encryption is not common in SIP

• Eavesdropping

• Viruses and Malware– Soft-phones

• DOS (Denial of Service)• SPIT (Spamming over Internet Telephony)

– Easy to send to thousands of IP addresses (leads to phishing)

• Call Tampering• Man-In-the-Middle Attacks

– Particularly vulnerable

Recent Legal News

• Patents– Verizon won $58 million patent suit against Vonage– Web Telephony filed patent lawsuit with Verizon,

Vonage, AT&T, EarthLink, and SunRocket

• DoT clamp down in India– unlicensed foreign service providers

In Conclusion, why use VoIP?

Because even Jack Bauer Needs it

The End