Voice over IP

by Rahul varikuti

course instructor:

Vicky Hsu

Outline

□Introduction□How VoIP works and its reliability □Explanations of VoIP protocols and

its security □Compare VOIP with PSTN□VoIP Packet capture and explanation□Conclusion

Introduction

□More than 30 years ago Internet didn't exist. Interactive communications were only made by telephone at PSTN line

□VOIP, It offers multiple opportunities such as lower call fees, convergence of voice and data networks, simplification of deployment, and greater integration with multiple applications

Cont’

□Voice over IP (VOIP) uses the internet Protocol (IP) to transmit voice as packets over an IP network. VOIP works like that using an ADC (analog to digital converter) digitalizing voice in data packets, sending them and then using DAC (digital to analog converter) to reconvert them in voice at destination.

How does VoIP work?

VoIP components:

□ Codecs (coder or decoder)

□  TCP/IP and VoIP protocols

□  IP telephony servers and PBXs

□ VoIP gateways and routers(ATA’s)

Call setupHere is what happens when a VoIP call is

made:1. The caller picks up the telephone

headset and waits for a dial tone.2. The caller dials a telephone

number, which is mapped to the IP address of the callee.

3. Call setup protocols are invoked to locate the callee and send a signal to produce a ring.

4. The destination phone rings, indicating to the callee that a call has arrived.

5. The callee picks up the telephone handset and begins a two-way conversation. The audio transmission is encoded using a codec and travels over the IP network using a voice streaming protocol.

6. The conversation ends, call teardown occurs, and billing is performed.

Call sequence:

Signaling protocol: SIP

Media transport protocol:RTP

Networking protocol : IP

Three ways of calling the destination:

□ATA’s

□IP phones

□Computer to computer calling

Making pc to phone call Receiving calls

Explanations of VoIP protocols and their relationship to the OSI model and its security

□Media Transport protocols for transmission of packetized audio/video

□Supporting protocols include gateway location, QoS, address translation, IP, etc.

□Signaling protocol to establish presence, locate users, set up, modify and tear down sesssions

Con’t

□ SIP (Session Initiation Protocol) is an application-layer control protocol that can establish, modify, and terminate multimedia sessions such as Internet telephony calls (VOIP). SIP is the first protocol to enable multi-user sessions regardless of media content.

□ H.323 is representative of an old-world ethos: complex, deterministic and vertical. It is not well suited for controlling the voice over IP systems. SIP, on the other hand, is simple, open and horizontal. Because of SIP’s internet heritage it is ideal for integrating telephony with the IP world.

Cont’

□ Media Gateway Control Protocol (MGCP) is used to define communication between call control elements (Call Agents) and telephony gateways. MGCP is a master/slave protocol.

□ RTP stand for Real-Time Transport Protocol, it supports the transfer of real-time media (audio and video) over packet switched networks.

□ The RTP control protocol (RTCP) works with RTP. In a RTP session, participants periodically send RTCP packets to obtain useful in formations.

IP

UDPTCP

Signaling

H.255.0 H.245 RAS SIP SGCP PDC H.GCP RTP RTCP RTSP

H.450.x H.235 MGCP

Audio Codecs

Video Codecs

Gateway Control

Media

Network layer

H.323

Transport layer

Session layer

Presentation layer

VoIP Security - Threats

□Attackers hijacking the calls and destroying operating systems

□Signaling Server Setup and manage calls List of incoming and outgoing calls Duration and parameters of the callsWith the above information the attackers

can map all the calls on the network.

Cont’

□Attackers can even replay all the conversations occurring on the network

□Attackers can also modify the call parameters

□Some of the treats are Identity theft Call redirection □Attackers use computers with software

which has different types of bugs that results in exploitation of all operating systems.

VoIP Security – Defense

□Encryption a) Adds overhead b) Eliminates Bandwidth reduction

from tradition voice calls (throughput and performance)

□Types of encryption:a) VPN setupsb) IPSec protocolsc) SRTP(secure RTP)

□A fast and efficient algorithm helps in improving the performance features.

VoIP - QoS

□Requirements in QOS ensure a) Voice begin present in a timely

manner b) Reducing the chance of

degraded quality c) Prolonged redundancy options

in case of power failure.

VoIP Security - Firewall

□ Security acts as a firewall which accepts

□ the outgoing voice and rejects the in coming voice

□ which tends to have malicious information

Advantages :

□Probability□scalability□Reduce scalability cost□Low maintenance cost

Disadvantages:

□Cost of installation

□Emergency calls cannot be traced

□Low reliability

VoIP vs. PSTN

□Establishing and releasing a connection

□Telephony service provided by PSTN –POTS

a) Circuit switched connections b) Quality and reliability in the

connection c) Level of reliability – 99.999% of

time

Telephony Standards

□ITU plays a major role in standardizing the technology of PSTN

□ITU-T standards are grouped into similar functional areas, called recommendations

G-Transmission Systems and Media, digital systems and networks.

H-Audio Visual and Multi-media Systems P-Telephone Transmission

quality,Installation and local time network. Standards - G.711 and H.323

HOW DOES PSTN WORK?

SIX STEPS IN TYPICAL TELEPHONE CALL

PSTN Components

□Voice encoding□PSTN Switches□Private Branch Exchange(PBX)□Signaling□Telephones

Demo Setup

RTP Header Format

RTCP Header Format

Conclusion

□The right time to switch to VoIP□Future of VoIP