Transcript
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
.pu
lve
r
pu
lve
r@v
on
1
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
Je
ff.p
ulv
er
pu
lve
r@v
on
1
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
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