3 1 Understanding VoIP

8/4/2019 3 1 Understanding VoIP

1/34

August 4, 20101

SPECTRA2

VoIP


2/34

August 4, 20102

Objectives of VoIP

WHAT is VoIP

VoIP Network Architecture

The VoIP Protocols & Call Flows

VoIP and PSTN Interworking


3/34

August 4, 20103

VoIP Terminal VoIP Terminal

Voice over Internet Protocol

Also called IP Telephony or Internet Telephony

What Is VoIP?

Nowadays, not only Voice but also Video

Calls are broken down into IP packets using CODECs,and transmitted over networks as data

Packets are re-assembled at the receiving end and theCODEC returns the call to analog form

Signaling

Media (Packet)

Break &

Re-assemble

Break &

Re-assemble

Analog AnalogCODEC CODEC

Microphone/Speaker

Microphone/Speaker


4/34

August 4, 20104

What Do VoIP Terminals Look Like?

VoIP calls can be placed on any devicewhich can run a CODEC:

Cell phones: digital cell phones already

transmit packetized voice and are movingto more popular VoIP CODECs to supportwireless roaming to WiFi networks (VoIPClient on Mobile )

A dedicated IP-phone(CISCO, AVAYA)

PCs (using a softphone - Skype, YahooMessenger, Vonage, PC-based PBX)


5/34

August 4, 20105

VoIP TechnologyMaking a Phone Call Means

1 Calling someone Call setup or session initiation

Also known as Signaling

Uses the network control plane (layer 4) Key protocols: SIP, H.323

Requires a Signaling Gateway /Proxy Server

Signaling

2 Having a conversation Real-Timedata Streaming: layer 3 packets

Uses UDP (packets not resent if lost)

Key protocol: RTP

Common CODECs: G.711, G.723.1, AMR

Requires a Media Gateway

Media

There are VoIP Families: SIP Family and H.323 Family


6/34

August 4, 20106

How does VoIP Work?

1. Compression voice is compressed typically with one of the followingcodecs, G7.11 64k, G7.29AB 8k, G723.1 6.3k

These steps happen in reverse at the other end

2. Encapsulation the digitized voice is wrapped in an IP packet

3. Routing the voice packet is routed thru the network to its final destination

The 1-2-3s of VoIP


7/34

August 4, 20107

VoIP SIP Network Architecture

Proxy: receive SIP client message and forward it;, Network Access Control, Routing, reliablerequest retransmission, and security;

MGW (Media Gateway): Perform media conversion between VoIP RTP & TDM.

SGW (Signaling Gateway): conversion at transport level between the SS7 based and the IP based,does not interpret the application layer (e.g. MAP, CAP, BICC, ISUP);

MGC (Media Gateway Controller): also called softswitch/call agent; Responsible for Call routing,signaling, call services, billing, address translation;

Registrar: Registration, Session Control, Authentication, Authorization;

Redirect Server: Alternate Routing for users, provides next hop(s) information;

Application Server (ASP): ????????????????????

SIP Nodes

Interworking Nodes

TE TERTP

Proxy Proxy

RedirectServer

RedirectServer

Registrar

SI

P

SI

P

SIP

SIP

SIP

SIP

SIP-SIP Call

Domain

SIP-ASP

SGW

MGW MGW

MGC

H.24

8

Megaco/M

GCP

RTP

ISUP/SIGTRAN

SIP-T/SIP-I/BICCSGWMGC

H.248

Megaco/MGCP

ISUP/SIGTRAN

SIPSIP

SignalingMedia

RTPRTP

ISUP/Legacy SS7

ISUP/Legacy SS7

TDM TDM


8/34

August 4, 20108

RTP

SIP

SIP

SIP

SIP

SIP

SIP

SIPSIPSIPSIP----SIP CallSIP CallSIP CallSIP Call

DomainDomainDomainDomain

RTP RTPTETETETE

TETETETE

ProxyProxyProxyProxy Proxy ProxyProxyProxy

RedirectRedirectRedirectRedirect Redirect RedirectRedirectRedirect

RegistrarRegistrarRegistrarRegistrar

ASASASAS

ISUPISUP

How To Understand the SIP Architecture

Once upon a time, there was a village of people called the SIPPERs. They made a very special drink called Spectra2.Spectra2 was so good, that the SIPPERs had to put a quota on how much the people could have.So they elected a chief who lived in the Registrar and controlled the quotas of Spectra2 using the AS (Allocation System).To get Spectra2, SIPPERs needed to get permission by Proxy, then had to be guided by Redirect, & granted access by the Chief.The SIPPERs rightly imagined that other villages might like to purchase Spectra2.So they made arrangements with the neighboring villages called ISUPs to trade in Spectra2.They stored the Spectra2 in MGWs (Metal Guarded Warehouses). And extended the road to transport Spectra2 from MGW to MGW.

They called the road RTP (Road To Profitability).

MGWMGWMGWMGW MGW MGWMGWMGW

ISUPs did not speak SIPPER language so the SIPPERs had to build translation stations so the chief could receive and fill the orders.

MGCMGCMGCMGC MGC MGCMGCMGC

SGWSGWSGWSGW SGW SGWSGWSGW

ISUP ISUPISUP

SIGTRANISUP

SIGTRAN

SIPSIP

Mega

co/MGC

P Megaco/MGC

P

Spectra2 became a global industry. SIPPERs became very rich. However, problems did arise as pirates tried to steal the Spectra2.This required the building of castles, gateways, and controllers to ensure the revenue stream and keep the Spectra2 services running.



9/34

August 4, 20109

VoIP SIP Protocol Family

Signaling: SIP, Defined by IETF, adopted by 3GPP, 3GPP2, OMA, MSF for IMSA text based protocol that provides call signaling, registration, status, & control

Transport-independent, over UDP, TCP, & SCTP

SDP (Session Description Protocol) is embedded in order to share endpoint media

Commonly used in xDSL, FTTx, broadband VoIP and enterprise cable VoIP offerings

Lots of Extensions based on the SIP basic protocolTLS

TCP

IPsec

L1SIP

IP

SIP

UDP SCTP

DL

TE TERTP

Proxy Proxy

RedirectServer

RedirectServer

Registrar

SI

P

SI

P

SIP

SIP

SIP

SIP

SIP-SIP Call

Domain

SIP-ASP

SGW

MGW MGW

MGC

H.24

8

Megaco/M

GCP

RTP

ISUP/SIGTRAN


H.248

Megaco/M

GCP

ISUP/SIGTRAN

SIPSIP SignalingMedia

RTPRTP

ISUP/Legacy SS7

ISUP/Legacy SS7

TDM TDM


10/34

August 4, 201010

VoIP H.323 Network Architecture

H.323 Gatekeeper:Virtual switch, translating network address;Admissions control, bandwidth control; Call authorization, bandwidthmanagement; Supplementary services, directory services, call

management services

TE TE

H.323

Gatekeeper

MGW MGW

MCUH.323

GatekeeperRTP

H.323H.323

H.323 H.323

H.32

3

RTPRTP

RTP

RTP

RTP

RTPRTP

H.323H.323

H.323

Signaling

Media

MGW (Media Gateway):Perform media conversion between TDM & VoIP RTP;

MCU (Multi-point Control Unit):Bridge conferencing connections.


11/34

August 4, 201011

VoIP H.323 Protocol Family

Signaling: H.323, Defined by ITU-TA suite of protocols that is based on Q.931 and provides call control, media control,and RAS (Registration, Admission, and Status)

Binary protocol

Deployed by many early adopters of VoIP H.225.0: Describe Call Signaling, Media (Audio & Video), streaming; H.245: Control protocol for multimedia for opening & closing channels; H.450: Supplementary Services; H.235: Security; H.261, H.263, H.264: Video encoding.

UDP

H.225.0RAS

H.225.0

Call

Signaling

H.245

Control

Signaling

TCP

IPData Link

L1

H.323

TE TE

H.323

Gatekeeper

MGW MGW

MCUH.323

GatekeeperRTP

H.323H.323

H.323 H.323

H.32

3

RTPRTP

RTP

RTP

RTP RTPRTP

H.323H.323

H.323

Signaling

Media


12/34

August 4, 201012

VoIP Common Protocols

H.248/MEGACO (MEdia GAteway COntrol protocol) A device control protocol that grew out of MGC

Available as a binary or text implementation Instructs MGs to setup and teardown voice calls and manages media resources

(available circuits and IP ports) Signals endpoint events to the MG (e.g. off-hook, on-hook)

UDP SCTP

IP IP

DL DL

L1 L1

H.248/MEGACO

H.248/MEGACO

MGCP (Media Gateway Control Protocol) Commonly used in residential cable VoIP networks

Text-based protocol that is used to establish sessions on a MG

Instructs MGs to setup and teardown voice calls and manages media resources(available circuits and IP ports)

Signals endpoint events to the MG (e.g. off-hook, on-hook) UDP SCTPIP IP

DL DL

L1 L1

MGCP

MGCP


13/34

August 4, 201013

VoIP Common Protocols

L1RTP/RTCP

RTP/RTCP

UDP

IP

DL

Media: RTP, Defined by IETFRTP (Real time Transport Protocol):

Designed to carrier media over IP Built to be more reliable than TCP and used in place of TCP

RTCP (Real time Transport Control Protocol): Adjunct protocol to RTP

Provide out of band control information for RTP Provides statistics on an RTP session and sends reports on the session

Sender reports provides information on packets sent, delay, jitter, timestamps

Receiver reports respond back with jitter, delay, and lost packets

SDP (Session Description Protocol) Embedded in SIP, H.323, Megaco, and MGCP

Provides information on the the capabilities of the endpoints in a session, suchas supported codecs


14/34

August 4, 201014

Protocol Comparisons

H.323 SIP

Designed to support voice and video

communications

Contains a service framework (SIMPLE)

for presence, messaging, and video

ISDN-based signaling facilitates SS7

interworking

SIP-T/SIP-I provides SS7 interworking

Deployed in the first and secondgeneration VoIP solutions

Gaining global popularity as the VoIP

protocol of choice

Binary Based on Q.931

Text Parameters can be added easily

MGCP MEGACO/H.248

More common in fixed line VoIPnetworks

Used in fixed and wireless VoIP

Networks

Adopted by cable operators for devicecontrol

NCS / TGCP

Adopted by 3GPP standards fordevice control

Text Text and binary implementations


15/34

August 4, 201015

Voice is receivedover traditional

T1/E1 circuit

1. Registration All VoIPimplementations require adevice or user to register withthe network for security

44

4. Calls to the PSTN are madethrough the MGC and mediais converted through the MG

Call Basics

MGC

MG

IP Network

RegisterFunction

11

44

22

3333

44

44

SSP

PSTN

This is called RAS

in H.323 and theregistrar in SIP

2. Calls can be made direct toanother IP phone.

3. Or calls can be routed to asoftswitch, then to the called party

Voice is sentover RTP


16/34

August 4, 201016

SIP Server:RegistrarProxyRedirect

SIP Call Flow

Invite

180 Ringing200 OK

Bye

ACK

Register

200 OK

Invite

RTP

Bye

200 OK200 OK

200 OK

ACK

User Agent1 User Agent2

TLS

TCP

DL

L1

SIP

SIP

UDP SCTP

IP


17/34

August 4, 201017

MGC MG

Megaco Call Flow

RTP stream isinitiated fromthe endpoint

Add

AddReply

Modify

ModifyReply

Subtract

SubtractReply

RTP

UDP SCTP

IP IP

DL DL

L1 L1

H.248/MEGACO

H.248/MEGACO


18/34

August 4, 201018

MGC MG

MGCP Call Flow

CRCX Create Connection

200 OK

MDCX Modify Connection

200 OK

DLCX Delete Connection

250 OK

RTPRTP stream isinitiated fromthe endpoint

UDP SCTPIP IP

DL DL

L1 L1

MGCP

MGCP


19/34

August 4, 201019

A Simple Voice Call in a VoIP Environment

Invite IAMCRCX

SIP signaling providescall control in the

IP domain

SS7 ISUP providescall signaling andmedia control with

device controlembedded in theclass 5 switch

MGCP provides devicecontrol for setup andtear down on voice

session and resourcemanagement

RTP provides the transport and delivery ofpacketized real-time media.

SDP (embedded in SIP and MGCP) defines mediaset capabilities and codec selection for the

RTP session

RTCP monitors quality and reports informationabout participants in an open RTP session.

MGCSSP/LE

MG

SIP MGCP Media

SS7


20/34

August 4, 201020

VoIP and PSTN Interworking

VoIP can interworking with different networks

VoIP SIP PSTN VoIP H.323 VoIP PSTN

VoIP SIP VoIP SIP

VoIP SIP VoIP H.323

VoIP Mobile CS Network

VoIP IMS (IP Multimedia Subsystem)


21/34

August 4, 201021

How to Understand the PSTN & VoIP Interworking?

RTP

SIP

SIP

SIP

SIP

SIP

SIP

SIPSIPSIPSIP----SIP CallSIP CallSIP CallSIP Call

DomainDomainDomainDomainRTP RTP

TETETETE

TETETETE

ProxyProxyProxyProxy Proxy ProxyProxyProxy

RedirectRedirectRedirectRedirect Redirect RedirectRedirectRedirectRegistrarRegistrarRegistrarRegistrar

ASASASAS


SGWSGWSGWSGW SGW SGWSGWSGW

MGCMGCMGCMGC MGC MGCMGCMGCSIP

SIP

ISUPISUP

ISUP ISUP

SIPSIPISUPISUP

ISUP/

SIGTRAN

ISUP/

SIGTRAN

H.248

Megaco/M

GCP

H.248

Megaco/M

GCP

MGWMGWMGWMGW MGW MGWMGWMGW

TDM TDM

SGW MGC

MGW

SS7/PSTN VoIP

ISUPLegacy

ISUPSIGTRAN

SIP-T/SIP-IBICC

TDM RTP

H.248

Media Convergence

Signaling ConvergenceTransport Convergence


22/34

August 4, 201022

SIP VoIP and PSTN Interworking There are 3 signaling protocols for SIP VoIP and PSTN Interworking:

Bearer Independence Call Control(BICC)

SIP Interworking

(SIP-I)

SIP for Telephony

(SIP-T)

Defined by IETF Transport ISUP Message

across IP network as

attachment of SIP message

Define by ITU-T Mapping between SIPand ISUP messages

Define by ITU-T, ISUP extension Separate Call Control and Bearer

Connection Control

- BICC Capability Set 1 for control ATM

- BICC Capability Set 2 for control IP

TE TERTP

Proxy Proxy

RedirectServer

RedirectServer

Registrar

SI

P

SI

P

SIP

SIP

SIP

SIP

SIP-SIP Call

Domain

SIP-ASP

SGW

MGW MGW

MGC

H.24

8

Megaco/M

GCP

RTP

ISUP/SIGTRAN


H.248

Megaco/M

GCP

ISUP/SIGTRAN

SIPSIP

SignalingMedia

RTPRTP

ISUP/Legacy SS7

ISUP/Legacy SS7

TDM TDM


23/34

August 4, 201023

TE TERTP

Proxy Proxy

RedirectServer

RedirectServer

Registrar

SI

P

SI

P

SIP

SIP

SIP

SIP

SIP-SIP Call

Domain

SIP-ASP

SGW

MGW MGW

MGC

H.24

8

Megaco/M

GCP

RTP

ISUP/SIGTRAN

SIP-T/SIP-ISGWMGC

H.248

Megaco/M

GCP

ISUP/SIGTRAN

SIPSIP

SignalingMedia

RTPRTP

ISUP/Legacy SS7

ISUP/Legacy SS7

TDM TDM

Network Elements For PSTN & VoIP Interworking Signaling Gateway:

Provides interworking of signaling between PSTN & IP,

ISUP/Legacy ISUP/SIGTRAN.

Often deployed in groups of two or more to ensure high availability.

Media Gateway: Converge (Compress/Decompress and Packetize/Depacketize) the voice databetween PSTN and the IP network.

Media Gateway Controller: Handles the registration & management of resources at the Media Gateway(s).

Converge ISUP and SIP Signaling Protocols

Also called a Softswitch.


24/34

August 4, 201024

SIGTRAN SIGnaling TRANsport

Defined by IETF SIGTRAN Working Group

Reliable Transport SS7 over IP networks.

ISUP over SIGTRAN ISUP over Legacy SS7SGW

Functions:

Transfer Signaling over IP Flow Control, Congestion Control,

In-sequence delivery of signaling messages

Identification of the originating and terminating signaling points & voice circuits

Error Detection, Retransmission, Outages Recovery and other error correction

Detection of the status of peer entities (e.g., in service, out-of-service, etc.) Security mechanisms to protect the integrity of the signaling information

The Architecture identifies two components:

A common Transport Protocol for the SS7 protocol layer being carried

An Adaptation Module to emulate lower layers of the protocol.


25/34

August 4, 201025

How To Understand SIGTRAN?

ISUPUpper layer No Change

M3UAChange to M3UA

Change to MTP3

Change to SCTP/IP

IP

SCTP

Change to MTP2/MTP1

SUA

Change to SUA

Change to SCCP

IP

SCTP

Change to SCTP/IP

Change to

MTP3/MTP2/MTP1

SUA: Change at SCCP Layer

MTP1

MTP2

MTP3SCCP

TCAP

APP.

TCAPUpper layers No Change

APP.

Step1: Determine which Layer tobe Change to xUA

Any layers except MTP1

Note: One exception: M2PA is not xUA

Step2: Change the selectedLayer to the corresponding xUA

MTP2 -> M2UA or M2PA

MTP3 -> M3UA

SCCP -> SUA

TCAP -> TUA

MTP1

MTP2

MTP3

ISUP

M3UA: Change at MTP3 LayerFrom Legacy SS7 to SIGTRAN

Step3: The upper layer(s) of the selected

layer remain no change The lower layers of the selected

layer are changed to SCTP/IP;

From SIGTRAN to Legacy SS7

Reverse the procedures


26/34

August 4, 201026

SS7 Family and SITRAN

SS7 Family

SS7 Over E1/T1 SS7 Over ATMSS7 Over IP

MTP1

SS7 over E1/T1

Applications

ISUP TUP

MTP3

MTP2

TCAP

SCCP

L1

BISUP

SSCF

SSCOP

AAL5

AT M

BISUP

MTP-3b

TCAP TCAP

TCAP

TUA IUA DUA ISUA V5UA

SCTP SCTP SCTP SCTP SCTP

IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


DPNSS

/DASSISUP

SS7 Apps

SUAM3UA

DL

SCTP SCTP

TUPTUPISUP

SS7 Apps

ISUP TUP

IP IP IP

TCAPV5ISUP

MTP3MTP3

DL DL

SS7 Apps

M3UA SUA M2PA

SS7 Apps

L1 L1 L1

SIGTRAN

SCCP

SCCP

M2PA

SCTP

TCAPISDN/

QSIGSCCP

L1

M2UA

M2UA

SCTP

IP

DL

SIGTRAN

TCAP TUA

ISUP ISUA SCCP SUA ISDN IUA DUA V5 V5UA

MTP3 M3UA

M2UA MTP2 M2PA

DPNSS

/DASS


27/34

August 4, 201027

SCTP Stream Control Transmission Protocol

Glue SIGTRAN Adaptation protocol and IP together

Acknowledged error-free non-duplicated transfer of signaling info.

In-sequence delivery of messages within multiple streams Optional bundling of multiple messages into a single SCTP packet

TCAP TCAP

TCAP



IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


SS7 Apps

SCCP

M3UA

SCTP

DL

M3UA

ISUP TUP

SS7 Apps SS7 AppsISUP TUP

SS7 AppsISUP TUP

TCAPISDN/

QSIG

DPNSS

/DASSISUP V5

TCAP SCCP SCCP

SUAMTP3 MTP3

M2PA M2UA

SCTP SCTP SCTP

IP IP IP IP

DL DL DL

L1 L1 L1 L1

SUA M2PA M2UA

SIGTRAN


28/34

August 4, 201028

M2UA MTP2 User Adaptation Layer

Transporting SS7 MTP2 user (i.e. MTP3) signaling messages over IP

Using SCTP

Provides the equivalent set of services to its users as MTP Level 2

provides to MTP Level 3.

Used between the Signaling Gateway and Media Gateway Controller

TCAP TCAP

TCAP



IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


SS7 Apps

SCCP

M3UA

SCTP

DL

M3UA

ISUP TUP

SS7 AppsSS7 Apps

ISUP TUP

SS7 Apps

ISUP TUPTCAP

ISDN/

QSIG

DPNSS

/DASSISUP V5

TCAP SCCP SCCP

SUAMTP3 MTP3

M2PA M2UA

SCTP SCTP SCTP

IP IP IP IP

DL DL DL

L1 L1 L1 L1

SUA M2PA M2UA

SIGTRAN


29/34

August 4, 201029

M2PA MTP2 User Peer-to-Peer Adaptation Layer

A Sigtran protocol for transporting SS7 MTP2 user part signaling messages(i.e. MTP3) over IP using SCTP.

Used to support full MTP3 message handling and network managementbetween any two SS7 nodes communicating over an IP network. .

M2PA can be used between a signaling gateway and a media gateway controller,

between a signaling gateway and an IP signaling point,

between two IP signaling points..

TCAP TCAP

TCAP



IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


SS7 Apps

SCCP

M3UA

SCTP

DL

M3UA

ISUP TUP

SS7 AppsSS7 Apps

ISUP TUP

SS7 Apps

ISUP TUPTCAP

ISDN/

QSIG

DPNSS

/DASSISUP V5

TCAP SCCP SCCP

SUAMTP3 MTP3

M2PA M2UA

SCTP SCTP SCTP

IP IP IP IP

DL DL DL

L1 L1 L1 L1

SUA M2PA M2UA

SIGTRAN


30/34

August 4, 201030

M3UA MTP Level 3 User Adaptation Layer

Defined by the IETF sigtran Working Group

For transporting MTP3 user part signaling messages (e.g.,

ISUP, TUP, SCCP) over IP using SCTP. M3UA is used:

between a signaling gateway and a media gateway controller orIP telephony database.

The signaling gateway receives SS7 signaling using MTP astransport over a standard SS7 link.

TCAP TCAP

TCAP



IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


SS7 Apps

SCCP

M3UA

SCTP

DL

M3UA

ISUP TUP

SS7 AppsSS7 Apps

ISUP TUP

SS7 Apps

ISUP TUPTCAP

ISDN/

QSIG

DPNSS

/DASSISUP V5

TCAP SCCP SCCP

SUAMTP3 MTP3

M2PA M2UA

SCTP SCTP SCTP

IP IP IP IP

DL DL DL

L1 L1 L1 L1

SUA M2PA M2UA

SIGTRAN


31/34

August 4, 201031

SUA SCCP User Adaptation Layer

Defined by the IETF SIGTRAN Working Group

For transporting SS7 SCCP (Signaling Connection Control Part) userpart signaling messages (e.g., TCAP) over IP using the SCTP

SUA is used between a signaling gateway and an IP signaling endpoint

between IP signaling endpoints.

SUA supports

SCCP unordered and in-sequence connectionless services;

Bi-directional connection-oriented services with/without flow control

TCAP TCAP

TCAP



IP IP IP IP IP

DL DL DL DL DL

L1 L1 L1 L1 L1


SS7 Apps

SCCP

M3UA

SCTP

DL

M3UA

ISUP TUP

SS7 AppsSS7 Apps

ISUP TUP

SS7 Apps

ISUP TUPTCAP

ISDN/

QSIG

DPNSS

/DASSISUP V5

TCAP SCCP SCCP

SUAMTP3 MTP3

M2PA M2UA

SCTP SCTP SCTP

IP IP IP IP

DL DL DL

L1 L1 L1 L1

SUA M2PA M2UA

SIGTRAN


32/34

August 4, 201032

Thank You


33/34

August 4, 201033

SIP Exercise Origination for Tester


34/34

August 4, 201034

SIP Exercise Termination for Tester

Documents

3 1 Understanding VoIP