The document discusses Voice over IP (VoIP) and its description and operation. It defines VoIP as using private networks for IP telephony and Internet telephony as using public networks. It describes how audio is digitized, compressed, and transported via IP packets. Common VoIP deployments like IP phone to IP phone are also outlined. The differences between SIP and H.323 protocols are highlighted. Typical call flows for SIP, H.323, and interworking between SIP and H.323 are illustrated. Implementing VoIP requires IP-IP gateways or Asterisk servers to connect IP and PSTN networks. Using VoIP eliminates traditional time-based telephony charges and distinctions between local and long distance calls.

1. Applied Networking-IV (2231114)
Lecture Week-9
VOIP Description & Operation
Lecture by: Djadja.Sardjana, S.T., M.M.
Djadja.Sardjana,
www.slideshare.net/djadja
Djadja.sardjana@widyatama.ac.id
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2. VOIP Description & Operation
VOIP
2m00
Description
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3. What is Voice over IP (VoIP)?
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Internet/
Private IP Network
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IP Packet
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4. What is IP Telephony ?
ITU Definitions
VoIP : Use of Private Networks
Internet Telephony : Use of Public Network
IP Telephony : VoIP + Internet Telephony
Alternatives
This deployment is VoIP
(end points are PSTN)
End points are IP
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5. Audio Packet Transfer
…
Digitization (e.g., sampling at 8kHz, 16 bits per sample,
i.e, 128 kb/s or 320 bytes per 20 ms)
i.e,
Real-
Real-time compression/encoding (e.g., G.729A at 8 kb/s)
compression/encoding G.729A
Transport to remote IP address and port number over
UDP (Why not TCP?)
Processing on receiver side is the reverse
Introduction to VoIP 5

6. Sampling, Quantization,
Encoding
+127
10101111…01101101
Encode each quantized
sample into 8 bit code word
+0 PCM: 8000 x 8 bits = 64 kb/s
Other techniques (differential
coding, linear prediction)
2.4 kb/s to 64 kb/s
-127
Sample at twice the Round off samples to one
highest voice frequency of 256 levels (introduces
2 x 4000=8000 Hz noise)
(interval of 125 µsec)
Introduction to VoIP 6

7. VoIP Deployments
Phone to Phone
1998 is mainly provided by
Service Provider or
Private Network
(E.g. Singtel’s 019)
1999 PC(Web) to Phone
is mainly provided
by Service Provider
(E.g. Web2Phone)
IP Phone to IP Phone
2002 is mainly provided by
Service Provider or
self Managed
(E.g. Free World Dial)
post Wireless IP Phone
2003 to Wireless IP Phone
will be provided by whom?
New Comer:
Skype, Vonage etc.
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8. IP-to-IP Calls
IP-to-
Internet
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9. IP-to-PSTN Calls
IP-to-
Internet
PSTN
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10. The Internet Multimedia Protocol Stack
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11. SIP and H.323 comparisons
H.323
SIP H.323
Minimal delay - simplified Possibilities of delay (up to 7 or
signalling scheme makes it 8 seconds!)
A simple toolkit relative of
"New World" - aupon which
faster H.323 specifies everything
"Old World" - complex,
smart clients and - simple, open
Internet protocols applications including the codec for the
deterministic and vertical
Slimbe built. It re-uses Net
can and Pragmatic
and horizontal The suite ishow cumbersome to
media and too you carry the
elements (URLs, MIME and deploy easily
packets in RTP
IETF ITU
DNS)
Seamless interaction with other
Leaves issues of reliability to Services are nailed-down and-
Assumes fallibility of network
media - services are only limited
underlying network constricted
an unnecessary overhead
Carrier-class solution addressing
by the developers imagination Borne of the LAN - focusing on
the wide area enterprise conferencing priorities
Many vendors developing
SIP messages are formatted as The majority of existing IP
H.323 messages are ASN.1
products
text. telephony products rely on the
binary encoded, adding
H.323 suite www.sipcenter.com
complexity
Taken from
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12. SIP Protocol Flow
SIP UA
INVITE
(with SDP)
100 Trying
407 Auth Req
ACK
INVITE
With auth
100 Trying
180 Ringing
200 OK
(with SDP)
ACK
RTP
BYE
200 OK

13. H.323 protocol flow
H.323 Endpoint H.323 Endpoint
Open logical channel inc
TCS
Call Proceeding
Open logical channel
Alerting Connecting
RTP
Close logical
channel
Close logical channel ACK

14. SIP to H.323 Protocol Flow
SIP UA IP-IP Gateway H.323
INVITE
(with sdp)
100 Trying
Open logical channel
inc TCS
Call Proceeding
Open logical
channel
Alerting
180 Ringing Connecting
200 OK (with
SDP)
ACK
RTP
Close logical
BYE channel
Close logical channel
ACK ACK

15. Cisco
SIP-H.323 and H.323-SIP support was introduced in IOS
SIP- H.323-
release 12.3(11)T
Supports Voice calls. Video is supported for some calls
Not a big performance impact, as no media transcoding is
involved. At worst case, just copy the media stream from input
buffer to output buffer
Costs money (2 cisco routers, 1or 2 ‘expensive’ software
license)

16. SIP-H.323 Gateway Network
SIP-
Architecture (Cisco IP-IP Gateway)
IP-

17. SIP-H.323 Gateway Network
SIP-H.323
Architecture (Asterisk Server)

18. IP-IP International
IP-
Gateway/Gatekeeper GDS
peering configuration

19. VOIP Description & Operation
Operation
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20. Implications
No more time-based
telephony charges
No concept of local call, long-
distance call or IDD call
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21. Change in Business Paradigm
Traditional Telecom Model New Telecom Model
Value-Added
Voice
Service
Data Service Value-Added Service
Voice Service Data Service
Infrastructure Infrastructure
“The most powerful paradigm shift is the fact that applications are not woven into the
platforms. Now to be a phone company, you don't have to weave tightly the voice service
into the infrastructure. They (Vonage) turn voice into a application and shoot it across one
of these platforms. And, suddenly, you're in your business.”
– Michael Powell, Chairman of FCC
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22. Technical Issues
Technical Architecture
To achieve interoperability between different IP Telephony services,
What should be the technical common platform?
What are the technical specifications to adopt?
Quality of Service
What is the acceptable QoS for IP Telephony?
How to ensure QoS?
Security and Privacy
How secure is IP Telephony?
What about wiretapping requirements?
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23. Business Issues
Interconnection
Who can interconnect to PSTN?
What is the pricing model?
Market Studies
What is the economic impact?
How would it change the telco landscape?
(cost to setup IP Telephony service ~= cost to setup Email service)
Numberings
What’s is the numbering plans for IP Telephony?
How are numbers assigned for IP Telephony services?
What if there is no service provider?
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24. Regulatory Issues
Classification
How do we classify all the different IP Telephony services?
Are they subjected to similar “regulation”?
Licensing
Who needs to apply for license?
What if there is no service provider?
Universal Access
Is it applicable to IP Telephony?
How about emergency numbers?
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25. Future
Convergence
5m00
Conclusion & Final Words
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