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© 2004, NexTone Communications. All rights reserved. Introduction to H.323
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© 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”
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© 2005, NexTone Communications. All rights reserved. Terminals Telephones Video phones IVR devices Voicemail Systems “Soft phones”
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© 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
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© 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
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© 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).
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© 2005, NexTone Communications. All rights reserved. GK Signaling
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© 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
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© 2005, NexTone Communications. All rights reserved. The Protocols
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© 2005, NexTone Communications. All rights reserved. The Protocols H.323 is a “framework” document that describes how the various pieces fit together H.225.0 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)
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© 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
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© 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)
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© 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.
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© 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)
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© 2005, NexTone Communications. All rights reserved. H.225.0 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
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© 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
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© 2005, NexTone Communications. All rights reserved. An H.323 Stack RAS RTP / RTCP H.225.0 Call Signaling H.245 Packet Network H.323 Application
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© 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
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© 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
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© 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
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© 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
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© 2005, NexTone Communications. All rights reserved.
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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
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© 2005, NexTone Communications. All rights reserved. Acronyms ARQ – H.225.0 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
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© 2005, NexTone Communications. All rights reserved. Acronyms LRQ – H.225.0 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
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© 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
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© 2005, NexTone Communications. All rights reserved.
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