Packetizer - cpham.perso.univ-pau.frcpham.perso.univ-pau.fr/ENSEIGNEMENT/PAU-UPPA/RHD/07-H323.pdf · A resource for packet-switched conversational protocols 8 Packetizer TM Gatekeeper

www.packetizer.com

A resource for packet-switchedconversational protocols

PacketizerTM

Copyright © 2004

Overview of H.323http://www.packetizer.com/voip/h323/papers/

Paul E. JonesRapporteur, ITU-T Q2/SG16

[email protected] 2004

www.packetizer.com

A resource for packet-switched conversational protocols

1

PacketizerTM

Executive Summary• H.323 was first approved in February 1996, the same

month that the first SIP draft was published• Designed to operate over complex networks, such as the

Internet• Although base-level functionality required only voice,

video dominated early implementations remains a majorstrength of H.323

• First standards-based “Voice over IP”• Today, H.323 is the most widely deployed standards-based

voice and videoconferencing standard for packet-switchednetworks, with literally billions of minutes of billabletraffic every month

• ITU-T now considering work on H.323v6

www.packetizer.com


2

PacketizerTM

The Basics of H.323

www.packetizer.com


3

PacketizerTM

What is H.323?

• H.323* is a multimedia conferencingprotocol, which includes voice, video, anddata conferencing, for use over packet-switched networks

* H.323 is “ITU-T Recommendation H.323: Packet-based multimediacommunications systems”

www.packetizer.com


4

PacketizerTM

Elements of an H.323 System

• Terminals• Multipoint Control Units (MCUs)• Gateways• Gatekeeper• Border Elements

Referred to as“endpoints”

www.packetizer.com


5

PacketizerTM

Terminals

• Telephones• Video phones• IVR devices• Voicemail Systems• “Soft phones” (e.g., NetMeeting®)

www.packetizer.com


6

PacketizerTM

MCUs

• Responsible for managing multipointconferences (two or more endpointsengaged in a conference)

• The MCU contains a Multipoint Controller(MC) that manages the call signaling andmay optionally have Multipoint Processors(MPs) to handle media mixing, switching,or other media processing

www.packetizer.com


7

PacketizerTM

Gateways

• The Gateway is composed of a “Media GatewayController” (MGC) and a “Media Gateway”(MG), which may co-exist or exist separately

• The MGC handles call signaling and other non-media-related functions

• The MG handles the media• Gateways interface H.323 to other networks,

including the PSTN, H.320 systems, and otherH.323 networks (proxy)

www.packetizer.com


8

PacketizerTM

Gatekeeper

• The Gatekeeper is an optional component inthe H.323 system which is primarily usedfor admission control and address resolution

• The gatekeeper may allow calls to be placeddirectly between endpoints or it may routethe call signaling through itself to performfunctions such as follow-me/find-me andforward on busy

www.packetizer.com


9

PacketizerTM

Border Elementsand Peer Elements

• Peer Elements, which are often co-located with aGatekeeper, exchange addressing information andparticipate in call authorization within and betweenadministrative domains

• Peer Elements may aggregate address information toreduce the volume of routing information passed throughthe network

• Border Elements are a special type of Peer Element thatexists between two administrative domains

• Border Elements may assist in callauthorization/authentication directly between twoadministrative domains or via a clearinghouse

www.packetizer.com


10

PacketizerTM

The Protocols

www.packetizer.com


11

PacketizerTM

The Protocols (cont)• H.323 is a “framework” document that describes how the

various pieces fit together• H.225.0 defines the call signaling between endpoints and

the Gatekeeper• RTP/RTCP (RFC 3550) is used to transmit media such as

audio and video over IP networks• H.225.0 Annex G and H.501 define the procedures and

protocol for communication within and between PeerElements

• H.245 is the protocol used to control establishment andclosure of media channels within the context of a call andto perform conference control

www.packetizer.com


12

PacketizerTM

The Protocols (cont)• H.450.x is a series of supplementary service protocols• H.460.x is a series of version-independent extensions to

the base H.323 protocol• T.120 specifies how to do data conferencing• T.38 defines how to relay fax signals• V.150.1 defines how to relay modem signals• H.235 defines security within H.323 systems• X.680 defines the ASN.1 syntax used by the

Recommendations• X.691 defines the Packed Encoding Rules (PER) used to

encode messages for transmission on the network

www.packetizer.com


13

PacketizerTM

Typical H.323 StackH.323

IP

UDP

RTP

RTCP

TCP/UDP TCP UDPUDP TCP

Audio

Codecs

G.711

G.723.1

G.729

..

Video

Codecs

H.261

H.263

H.264

..V.150 T.120

TCP/UDP

T.38

H.225.0

Call

Signaling

H.245H.225.0

RAS

Terminal Control and ManagementDataApplications Media Control

Multimedia Applications, User Interface

Slide added by C. Pham for educational purposes

H323 Physical entities


H323 & ISO model


www.packetizer.com


17

PacketizerTM

Registration, Admission, andStatus - RAS

• Defined in H.225.0• Allows an endpoint to request authorization to

place or accept a call• Allows a Gatekeeper to control access to and from

devices under its control• Allows a Gatekeeper to communicate the address

of other endpoints• Allows two Gatekeepers to easily exchange

addressing information

www.packetizer.com


18

PacketizerTM

Registration, Admission, andStatus – RAS (cont)

T GKRRQRCF

ARQ

(endpoint is registered)

ACF(endpoint may place call)

DRQ

DCF(call has terminated) T Terminal

GK Gatekeeper

GW Gateway

Symbol Key:

www.packetizer.com


19

PacketizerTM

H.225.0 Call Signaling

• Allows an endpoint to initiate and terminatea call with another endpoint

GW GWSetupAlerting

Connect(call is established)

Release Complete(call is terminated)

H.245Signalingmay takeplace atany point

www.packetizer.com


20

PacketizerTM

Open achannel in

eachdirection

H.245 Signaling

• H.245 is used to negotiate capabilities andto control aspects of the conference betweentwo or more endpoints

GW GWTCS + MSDTCS + TCS Ack + MSD Ack

TCS Ack + MSD Ack + OLCOLC Ack + OLC

OLC Ack

www.packetizer.com


21

PacketizerTM

Fast Connect and H.245

• Some H.323 calls do not utilize the richcapabilities offered by H.245 and simplymedia channels using the “Fast Connect”procedures

• In this mode, a call may be established withas few as two messages (Setup / Connect)

GW GWSetup

Connect

www.packetizer.com


22

PacketizerTM

An H.323 Stack

RAS RTP / RTCP

Packet Network

H.323 Application

H.245

H.225.0Call Signaling

www.packetizer.com


23

PacketizerTM

Resolving Addresses• A Gatekeeper may resolve addresses in a number of ways

– Sending a Location Request (LRQ) message to another Gatekeeper– Accessing a Peer Element– Accessing a back-end database (e.g., LDAP)

• Gatekeepers and Peer Elements may query otherGatekeepers and Peer Elements and may exchange addressinformation outside the context of a call

• Since a Gatekeeper is not required, endpoints may resolveaddresses themselves using, for example, DNS, LDAP, ora local “phonebook” containing static IP addresses

www.packetizer.com


24

PacketizerTM

Using LRQs

TGK

LRQ

GK

GK

ARQLRQ

• A Gatekeeper may send anLRQ to one ore moreGatekeepers

• It may accept any LCFresponse and utilize thatinformation to satisfy theoriginal ARQ

www.packetizer.com


25

PacketizerTM

Using LRQs with HierarchicalGatekeepers (cont)

• A Gatekeeper mayforward an LRQ receivedon to another Gatekeeperin order to resolve theaddress

• The response may bedirected back to theoriginating Gatekeeper orthe intermediateGatekeeper

TGK

LRQ

GK

ARQ

GK

LRQ

www.packetizer.com


26

PacketizerTM

Using a Border Element• As with hierarchical

Gatekeepers, BorderElements may sendAccessRequestmessages to otherBorder Elements andindicate where to send areply

• Border Elements mayalso reply directly to arequest by utilizingaddress informationcached from previousexchanges with otherBorder Elements

TGK

LRQ

GK/BE

ARQ

GK/BE

AccessRequest

www.packetizer.com


27

PacketizerTM

H.323 Features

www.packetizer.com


28

PacketizerTM

Advanced Videoconferencing

• Supports advanced videoconferencingfeatures, including– Cascading MCUs– MCU control over audio and video mixing– Chair control– Far-end camera control

www.packetizer.com


29

PacketizerTM

Supplementary Services• Standard mechanisms to provide a variety of services,

including– Call transfer– Call forward– Call park/pick-up– Call Hold– Call Waiting– Message Waiting Indication– Call Completion on Busy / No-Answer– Call Intrusion

• Support for HTTP-based service control (H.323 Annex K)

www.packetizer.com


30

PacketizerTM

Dynamic Routing and Re-Routing

• Gatekeeper may provide multiple “routes”to a destination, including information suchas:– Multiple destination addresses– Alternate “source” alias information– Source and destination circuit information

• H.460.8 allows an endpoint to re-query thegatekeeper for an alternate route in theevent that the primary route is unavailable

www.packetizer.com


31

PacketizerTM

Addressing

• Supports URLs, including the “h323” URLand “tel” URLs

• Supports dialed digits from a traditionaltelephone

• Supports various numbering types used inthe PSTN

www.packetizer.com


32

PacketizerTM

QoS

• H.460.9 allows an endpoint to reportQuality of Service information to theGatekeeper, aiding in determine how toroute calls

• H.323 devices may utilize IETF standardsfor providing quality of service, includingDiffServ and RSVP

www.packetizer.com


33

PacketizerTM

Miscellaneous Capabilities

• Device Diagnostics: H.323 allows testingequipment to place “test calls” to a device andestablish “media loops” in order to measure packetloss and delay

• Emergency Services– H.323 devices may indicate the priority of a call– Emergency call centers have the wherewithal to control

how and when a call is released• Support for user, terminal, and service mobility

(H.510)• Ability to tunnel any legacy protocol

www.packetizer.com


34

PacketizerTM

On to Next Generation Network

www.packetizer.com


35

PacketizerTM

Scalability

• H.323 allows calls to be routed directlybetween endpoints without the need for anintermediate entity that maintains call state

• Ability to utilize network services foraddress resolution, including ENUM,LDAP, and DNS

www.packetizer.com


36

PacketizerTM

Gateway Decomposition

• H.248.1 defines how to decompose anH.323 gateway into a Media GatewayController and one or more MediaGateways MGC

MGMGMGMGMG

MGMGMGMGMG

MGMGMGMGMG

www.packetizer.com


37

PacketizerTM

Robustness

• Alternate gatekeepers• Mechanisms for “failing over” to an

alternate softswitch or other routing entity(H.323 Annex R)

www.packetizer.com


38

PacketizerTM

Re-Routing Active Calls (H.460.15)

• Useful to allow “session bordercontrollers” to participate in initial callsetup (e.g., manipulate source or destinationaddresses) and then exit the call signalingpath

• Allows devices to participate in signalingonly when there is a need to exchangemessages during a call (often only thebeginning and the end of a call)

www.packetizer.com


39

PacketizerTM

Flexibility

• Voice over IP (or any packet-basednetwork)

• Videoconferencing• Support for T.120 data conferencing• Support for real-time text communication• Support for fax and modem relay

www.packetizer.com


40

PacketizerTM

Multimedia

• The most important aspect of the Next GenerationNetwork is the ability to communicate in newways

• Video will be a very important component• H.323 has very strong support for video• H.323 and T.120 allow users to work side by side

on a document using voice, video, text, andapplication sharing technologies

• H.323 is “multimedia over IP”, ushering in theNext Generation Network that users are seeking

www.packetizer.com


41

PacketizerTM

Documents

Packetizer - cpham.perso.univ-pau.frcpham.perso.univ-pau.fr/ENSEIGNEMENT/PAU-UPPA/RHD/07-H323.pdf · A resource for packet-switched conversational protocols 8 Packetizer TM Gatekeeper