Intro to VoIP

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Introduction to VoIPIntroduction to VoIP


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2004, NexTone Communications. All rights reserved.

1

VoIP Defined

Routing of voice traffic over internet protocols

Based on packet switching vs. traditional circuit

switching (PSTN)

VoIP is NOT: IP Telephony: refers to any "telephone" type service

carried over IP, which could include faxing, or text

messaging (VoIP is voice over IP only).

True data convergence: refers to sending both voiceand data (such as LAN traffic) over any data network

(typically an IPnetwork, frame relay network or ATM

network)


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Circuit Switching

Based on T1 or E1 circuits (SS7 and ISDN)

Maintains connection path

Bandwidth reserved through circuit life

Dedicated channel

PBXPBX


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Packet Switching

Payload broken up & sent individually as packets

Each Packet individually addressed

Connection path different for each packet

Packets only sent when there is payload

Call

Server

Call

Server


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4

Why is VoIP an attractive solution?

Real-time application of voice / video

Cost

Low-cost infrastructure

Scalability / routing flexibility Control of policy routing based on non-deterministic

parameters (e.g.: cost, least number of hops)

Simultaneous multimedia transmission

Efficient use of bandwidth Discreet states (on / off) vs. dedicated circuits (always

on)


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Circuit Switch vs Packet Switched

Circuit Switched Packet Switched

Bandwidth Fixed 56K or 64Kbps Variable up to Gbps

Addressing Required (phone number) Required per packet

Latency Minimal Minimal to high

Payload during

silence

Yes No

Intelligence In Network In CPE


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VoIP Elements: Codecs

Note: Customer quality calls normally

need a MOS in the range 3.5 to 4.2

Device / program that converts sampled analog

signals into digital signals for transmission

(compression), then converts the digital signals

back to analog for playing (decompression)

Operate on a set standardized algorithms designed to

yield specific bandwidth


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Bandwidth Consumption: Codecs

Compression Bit Rate (kbps) MOS Score Compression Delay (ms)

G.711 PCM 64 4.1 0.75

G.726 ADPCM 32 3.85 1

G.728 LD-C

ELP 16 3.61 3 to 5

G.729 CS-ACELP 8 3.92 10

G.729 x 2 Encodings 8 3.27 10

G.729 x 3 Encodings 8 2.68 10

G.729a CS-ACELP 8 3.7 10

G.723.1 MP-MLQ 6.3 3.9 30

G.723.1 ACELP 5.3 3.65 30

T38 Fax Transmission


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VoIP Elements: Quality Factors

Latency The amount of time from the source sending a packet to the source

receiving a response

Jitter (Delay Variation) The difference in packet arrival from origination to termination

Packet Loss Lost packets of information from origination to termination


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VoIP Elements: Signaling

Main signaling protocols:

H323

SIP


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VoIP Elements: Media

Media and Signaling paths can be separate

Utilizes established IP technology

Resilient to packet loss

Delay intolerant Uses RTP

Application Layer

Transport Layer

Internet Layer

Network Access Layer

SMTP, TELNET, ICMPHTTP, FTTP, RTP etc.

TCP and UDP

IP addressing, routingand masking

Ethernet, Token Ring,FDDI etc


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VoIP Elements IP Phones

IP Phones really need no introduction or little

explanation. They are simple devices we are

familiar with but have a VoIP signaling capability

that enables them to interact directly with other

VoIP devices


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VoIP Elements Analog Terminal Adapter

(ATA)

Adaptors that interface legacy analog telephones, fax machines, analog conference

telephones and other analog devices to IP based telephony networks therebyallowing companies to protect their investments in analog phones, fax machines,and speakerphones, and migrate to IP at their own pace. These products addressthe needs of enterprises, small-office environments, and the emerging VoIPmanaged voice services and local services market by helping companies cost-

effectively turn their analog devices into IP devices.


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VoIP Elements Session BorderController

New breed of networking technology thatprovides layer 5 routing and control to managereal-time traffic flows in IP networks.

Technology addresses issues of:

Session routing Signaling interoperability

Network security

Call admission control

Service quality


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Market Requiremnts

As VoIP is on IP, it is therefore inherently non-

deterministic.

VoIP signaling has to be reliably handled

The two protocols for signaling the VoIPcommunity uses mainly are H.323 and SIP for

end-points.

Session Controllers contend with several issues

that impede the progress ofVoIP networks forcarriers


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VoIP Elements Session BorderController

Used at the edge of the network (border) to route

signaling and/or media between endpointsIntegrates signaling / media streams seamlessly

Can act as:Peering agent

Border Element from network core

Interoperates with various VoIP protocolsH323 / SIPRTP


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Session BorderController Benefits

For Private IPs:

Enable calls securely to and from a protected enterprise

network

Used with firewall (networksecurity)

For Public IPs:

NAT

Interoperability (H

323 / SIP)

Without an SBC, the media traffic travels directly between the

VoIP phones, which consumes bandwidth unnecessarily


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Call Flow Example 1: Basic Network

A

100.1.1.1

B

200.2.2.2

Media can be established to each other

IP Header:

Source IP: 100.1.1.1

Dest. IP: 200.2.2.2

Signaling From IP 100.1.1.1 To IP 200.2.2.2

IP Header:

Source IP 200.2.2.2

Dest. IP 100.1.1.1



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Call Flow Example 2: Basic Network with Firewall

B

200.2.2.2

A

10.10.1.1

FW

100.1.1.1

Media cannot be established to each other

X

IP Header:

Source IP 100.1.1.1

Dest. IP 200.2.2.2


IP Header:

Source IP 200.2.2.2

Dest. IP 10.10.1.1



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Call Flow Example 3: Proxy Network

Media cannot be established to each other

B

200.2.2.2

IP Header:

Source IP 200.2.2.2

Dest. IP 100.1.1.1Signaling From IP 200.2.2.2 To IP 100.1.1.1

IP Header:

Source IP 100.1.1.1

Dest. IP 200.2.2.2


A

10.10.1.1

Signaling only

Proxy

100.1.1.1

IP Header:

Source IP 200.2.2.2

Dest. IP 100.10.1.1


IP Header:Source IP 10.10.1.1

Dest. IP 200.2.2.2


X


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Call Flow Example 4: SBCNetwork

Media can be established to each other

B

200.2.2.2

IP Header:

Source IP 200.2.2.2

Dest. IP 100.1.1.1Signaling From IP 200.2.2.2 To IP 100.1.1.1

IP Header:

Source IP 100.1.1.1

Dest. IP 200.2.2.2


A

10.10.1.1

SBC

100.1.1.1IP Header:

Source IP 200.2.2.2

Dest. IP 100.10.1.1


IP Header:Source IP 10.10.1.1

Dest. IP 200.2.2.2



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Session Controller

Follow the packets - Packet

1 (before the firewall)

SA: 10.1.1.3

DA: 190.18.18.100

SIP Info Based on 10.1.1.3

190.18.18.100


2 (after the firewall)

SA: 200.200.200.200

DA: 190.18.18.100


190.18.18.100


3 (coming back)SA: 190.18.18.100

DA: 10.1.1.3


190.18.18.100


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Challenges of VoIP

Call Quality (QoS)

Is network transmission / routing reliable between

endpoints?

Interoperability

How does VoIP work between various telecom

vendors? (ex: Cisco, Clarent, Broadsoft)


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Challenges of VoIP

Interworking Function (IWF)

Are existing IP / VoIP-specific protocols compatible?

Network Security How does VoIP protect customers and businesses

within public and private IP space?

Session Border Controllers: do they help orhurt in

terms of efficient call routing / security?

KUMAR

Date post:	09-Apr-2018
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Intro to VoIP

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