© 2004, NexTone Communications. All rights reserved. Introduction to H.323

© 2005, NexTone Communications. All rights reserved. Elements of an H.323 System  Terminals  Multipoint Control Units (MCUs)  Gateways  Gatekeeper  Border Elements Referred to as “endpoints”

© 2005, NexTone Communications. All rights reserved. Terminals  Telephones  Video phones  IVR devices  Voic Systems  “Soft phones”

© 2005, NexTone Communications. All rights reserved. Multipoint Control Units (MCUs)  Responsible for managing multipoint conferences (two or more endpoints engaged in a conference)  The MCU contains a Multipoint Controller (MC) that manages the call signaling and may optionally have Multipoint Processors (MPs) to handle media mixing, switching, or other media processing

© 2005, NexTone Communications. All rights reserved. Gateways  The Gateway is composed of a “Media Gateway Controller” (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

© 2005, NexTone Communications. All rights reserved. Gatekeeper  The Gatekeeper is an optional component in the H.323 system which is used for admission control and address resolution  The gatekeeper may allow calls to be placed directly between endpoints (Direct Endpoint Model) or it may route the call signaling through itself (Gatekeeper Routed Model).

© 2005, NexTone Communications. All rights reserved. GK Signaling

© 2005, NexTone Communications. All rights reserved.  Border Elements, which are often co-located with a Gatekeeper, exchange addressing information and participate in call authorization between administrative domains  Border Elements may aggregate address information to reduce the volume of routing information passed through the network  Border elements may assist in call authorization/authentication directly between two administrative domains or via a clearinghouse Border Elements

© 2005, NexTone Communications. All rights reserved. The Protocols

© 2005, NexTone Communications. All rights reserved. The Protocols  H.323 is a “framework” document that describes how the various pieces fit together  H defines the call signaling and communication between endpoints (Call Signaling) and the Gatekeeper (RAS), RAS happens first  H.245 is the conference control protocol which handles post-connect signaling (e.g. T.38 Fax & out-of-band DTMF)

© 2005, NexTone Communications. All rights reserved. The Protocols (cont)  RTP/RTCP is used for audio and video  H.450.x is a series of supplementary service protocols (IP Centrix)  T.120 specifies how to do data conferencing  H.235 defines security within H.323 systems

© 2005, NexTone Communications. All rights reserved. Registration, Admission, and Status - RAS  Allows an endpoint to request authorization to place or accept a call  Allows the Gatekeeper to communicate the address of other endpoints (See RAS COMMAND LIST)

© 2005, NexTone Communications. All rights reserved. Registration, Admission, and Status - RAS  GateKeeper Discovery  GK Request (GRQ)To GK  GK Confirm (GCF)From GK with GK RAS channel transport channel  GK Reject (GRJ)From GK (possible config error)  Gateway Registration  Registration Request (RRQ)To GK  Registration Confirm (RCF)From GK  Registration Reject (RRJ)From GK  Gateway Unregistration  Unregistration Request (URQ)Both To or From GK  Unregistration Confirm (UCF)Both To or From GK  Unregistration Reject (URJ)From GK (maybe GW wasn’t registered)  Resource Availability  Resource Availability Indicator (RAI)To GK  Resource Availability Confirm (RAC)From GK  Bandwidth Change  Bandwidth Change Request (BRQ)To GK  Bandwidth Change Confirm (BCF)From GK  Bandwidth Change Reject (BRJ)From GK  Location Request  Location Request (LRQ)Between GKs  Location Confirm (LCF)Between GKs (sends RAS channel for itself (GK Routed) or destination GW (Direct call)  Location Reject (LRJ)Between GKs (GW not registered or has no resources)  Call Admission  Admission Request (ARQ)To GK  Admission Confirm (ACF)From GK (sends GW the destination IP Address (terminating GW or GK))  Admission Reject (ARJ)From GK  Disengage  Disengage Request (DRQ)To GK  Disengage Confirm (DCF)From GK  Disengage Reject (DRJ)From GK  Request in Progress  Request in Progress (RIP)From GK  Info Requests  Info Request (IRQ)From GK  Info Request Response (IRR)To GK  Info Request Acknowledgement (IACK)From GK  Info Request Negative Acknowledgement (INAK) From GK.

© 2005, NexTone Communications. All rights reserved. Registration, Admission, and Status – RAS (cont) TGK RRQ ARQ RCF (endpoint is registered) ACF (endpoint may place call) DRQ DCF (call has terminated) or RRJ (endpoint is rejected) or ARJ (call is rejected)

© 2005, NexTone Communications. All rights reserved. H Call Signaling  Allows an endpoint to initiate and terminate a call with another endpoint GWMSW Setup Alerting/Progress Connect (call is established) Release Complete (call is terminated) Call Proceeding

© 2005, NexTone Communications. All rights reserved. H.245 Signaling  H.245 is used to negotiate capabilities and to control aspects of the conference between two or more endpoints GW TCS M/S Determination M/S Determination Ack OLC OLC Confirm Open a channel TCS M/S Determination

© 2005, NexTone Communications. All rights reserved. An H.323 Stack RAS RTP / RTCP H Call Signaling H.245 Packet Network H.323 Application

© 2005, NexTone Communications. All rights reserved. FastStart (Fast Connect)  Fast Connect is a procedure introduced to speed up connections by proposing channels in the setup, rather than going through the H.245 procedures  For most point to point calls that use Fast Connect, H.245 is only necessary for DTMF relay or T.38 FAX

© 2005, NexTone Communications. All rights reserved. Fast Connect (cont) GW Setup* Alerting** Connect (call is established) Release Complete (call is terminated)  The Setup message will contain channel proposals (OLCs) with CODEC(S)  The Call Proceeding, Alerting, Connect or other messages from called endpoint will contain accepted proposals with a CODEC

© 2005, NexTone Communications. All rights reserved. Using LRQs (GK Peering) T GK LRQ ARQ LRQ  A Gatekeeper may send an LRQ to one or more Gatekeepers  It may accept any LCF response and utilize that information to satisfy the original ARQ RIP T RRQ LCF ACF

© 2005, NexTone Communications. All rights reserved. Using LRQs with Hierarchical GKs  A Gatekeeper may forward an LRQ received on to another Gatekeeper in order to resolve the address  The response may be directed back to the originating Gatekeeper or the intermediate Gatekeeper T GK LRQ ARQ GK LRQ RIP LCF RIPACF LCF

© 2005, NexTone Communications. All rights reserved.

Alternate Gatekeepers  By using Alternate Gatekeepers, endpoints are able to continue functioning in the face of one or more failures  Never Lose a Call! T GK X X

© 2005, NexTone Communications. All rights reserved. Acronyms  ARQ – H Admission Request message  BE – Border Element  GK – Gatekeeper  GW – Gateway  IETF – Internet Engineering Task Force  IP – Internet Protocol  IVR – Interactive Voice Response  LAN – Local Area Network

© 2005, NexTone Communications. All rights reserved. Acronyms  LRQ – H Location Request message  MCU – Multipoint Control Unit  MC – Multipoint Controller  MG – Media Gateway  MGC – Media Gateway Controller  MP – Multipoint Processor  M/S – Master/Slave  MSW – Multi-protocol Signaling Switch

© 2005, NexTone Communications. All rights reserved. Acronyms  OLC – H.245 Open Logical Channel message  PSTN – Public Switched Telephone Network  RFC – Request for Comments  RTP – Real-Time Transport Protocol  T – Terminal  TCS – H.245 Terminal Capability Set message  UDP – User Datagram Protocol  VoIP – Voice over IP

© 2005, NexTone Communications. All rights reserved.