Voice over IP (VOIP)

1. Eng:AhmedAymanFahmy

2. Introduction
Whatis VoIP
Howdoes VoIPwork?
VoIPAdvantages
Typesof Codecs
 Signaling Protocols
Securityin VOIP
references
OUTLINE

3.  PSTN (public switching telephone network)
• It is traditional telephone system.
• Voice network use circuit switching.
• Dedicated path between calling and Called party.
• Bandwidth is reserved in advance Each line is 64kbps.
Central
office
Trunk
Introduction
UserA
UserB

4. Introduction
 PBX (private branch exchange)
• PBX is a private telephone network used in a company.
• Users of the PBX phone system share a number of outside
lines for making external phone calls.

5. Whatis VOIP
VoIPis a technology that enables one to make and receive phone
calls through IP (Internet protocol) network.

6. TCP/IPProtocol
Transport Control Protocol
It allows packet
retransmission, packet order
management, and receipt
acknowledgement.
TCP carries additional information
that adds weight to the packet. That is
why it is not recommended for real
time applications like voice & video.

7. UDPProtocol
User Datagram Protocol
It divides information into packets called datagrams.
This protocol doesn't care if the data arrives with errors or if it
doesn´t arrive at all. That is the main difference with TCP.
This is why it introduces little extra weight to the IP packet which
makes it ideal for real-time applications like voice.

8. RTPprotocol
Real-time Transport Protocol
Includes sequence numbering, time stamping,
payloadtype.

9. Howdoes VoIP work?
VOIP use packet switching.
No dedicated path between sender and receiver.
It acquires and releases bandwidth, as it is needed.
Upgrades usually requires only bandwidth.
We can also make video call.

10. TheseCount as Phones?

11. Converged network

12. VoIPAdvantages
Highly secured and Low cost communication.
Easy to use.
Easy to establish the network.
Communication Possible through laptop.
Unlimited user can beAdd.
Multipoint conferencing.

13. Codecs
Are used to convert analog signal into digital data.
codec Bandwidth (kbps)
G.711(PCM) 64
G.726 (ADPCM) 32
iLBC 15.2
GSM 13
G.723 6.3 /5.3
G.729a 8
G.723 and G.729a have built in VAD (voice activity detection)

14. Signaling Protocols
Why we need signaling in
VOIP?
numbers must be communicated.
phones have to ring.
routes have to be set up
Set up, manage client sessions
Types of signaling protocols
H.323
SIP
Skinny

15. H.323protocol
H.323, invented by ITUin 1996, defines four
elements that comprising a signaling system:
 Terminal:IPphone
 Gateway :connect different signal protocols
 Gatekeeper :handles billing, control session,
bandwidth allocation, etc.
 MCU (multipointcontrol unit):multipoint
conferencing

16. H.323messages

17. SIPprotocol
Session Initiation Protocol.
Developed by IETFsince1999.
SIP isthe core protocol for initiating,
managing and terminating communication
sessions (i.e audio & video call) over the
Internet
SIP sessions involve one or more participants and
can use unicast or multicast communication.

18. SIPnetwork
A SIPnetworkconsists of:
UserAgents (clients,phones)
SIPservers(SIPproxy server,redirect server,registrarserver,location server)
SIP Servers and services
Proxy
SIP Server
Registrar Redirect Location
Register
I am here
Redirect
Here is the address
Locate
Where this name is
or tel. number…
INVITE
I want to speak
with another agent.
Proxy INVITES
I will call it
for you.
SIP User
Agents
GW SIP
SIP User
Agents

19. SIPmessages

20. Securityin VOIP
As VoIP uses the Internet, for example, it is vulnerable to the same
type as security risks
Hacking
Denial of service
Eavesdropping
SRTP (secure real time protocol) It was first published be IETF in March 2014.
If SRTP is used you can make encryption andauthentication.
It is used to encrypt the payloadonly.
SRTP useAES ( advanced encryption standard) algorithm.
The default encryption key length 128bit.

21. references
“packet guide tovoice over IP”by Bruce hartpence February 2013.
“VOIPfordummies”TimothyV. killy
“securing VOIPnetworks”Peter Thermos

22. Any questions