# A H.323 Support and Compliance

Purpose

This Appendix briefly describes the H.323 Version 2 support and compliance including:

Offer Overview

H.323 Version 2 Compliance

H.323 offer in relation to IMTC Testing and iNOW! Profile criteria.

Restrictions and Limitations

Supported Standards MIBs and RFCs

Related Documents

H.323 Offer Overview

The CSP H.323 implementation enhances the CSP software to comply with the mandatory requirements of the H.323 Version 2 specification. This feature enhances the existing Voice over IP offering of the VDAC-ONE card for RTP bearer channels.

General Information

Conforms to the H.323 ITU Protocol Version 2

H.225 Call Signaling Protocol

H.245 Control Protocol

Registration, Admission & Status (RAS)

Real-time Transport Protocol/Real-time Transport Control Protocol (RTP/RTCP)

Q.931

Gateway functionality only: Not a Gatekeeper Implementation

Supports Fast Connect

Supports H.323-to-SIP Interworking

Provides well defined EXS API messages for ease of development

Interoperability

Backward compatible with the ITU H.323 Version 1 Protocol

Interoperates with leading PC Clients

Interoperates leading VoIP Gateways at the RTP level.

Media Processing Features Supported

G.711 CODEC (A-law and ΅-law) - 64 Kbps

G.729/G.729A/B CODEC - 8 Kbps

G.723.1 CODEC - 5.3 Kbps and 6.3 Kbps

Voice Activity Detection (VAD)

Comfort Noise Generation (CNG)

Jitter Buffer Management

Echo Cancellation

DTMF generation/detection: Supported by the DSP
Card. (G.711 CODEC only)

H.323 Version 2 Compliance

The CSP H.323 implementation enables the CSP to send and receive all the REQUIRED or mandatory fields in the H.323 Version 2 messages.

Lightweight Registration

The CSP H.323 implementation enhances the CSP software to comply with the mandatory requirements of the H.323 Version 2 specification. This includes the Lightweight Registration Feature. H.323 Version 2 defines a lightweight registration procedure that still requires the full registration, but uses an abbreviated renewal procedure to update the gatekeeper and subsequently reduces overhead.

Lightweight registration requires each endpoint to specify a Time-to-Live (TTL) value in its Registration Request (RRQ) message. When a gatekeeper receives an RRQ message from the CSP with a TTL value, it returns an updated TTL timer value in a Registration Confirmation (RCF) message to the endpoint. Prior to the TTL timer expiring, the endpoint sends an RRQ message with the KeepAlive field set to "Yes", which refreshes the existing registration.

An H.323 Version 2 endpoint is not required to indicate a time-to-live in its registration request. If the endpoint does not indicate a time-to-live, the gatekeeper assigns one and sends it to the gateway in the RCF message. No configuration changes are permitted during a lightweight registration.

DTMF Support

Dual-Tone Multi-Frequency (DTMF) is the tone generated on a touch-tone phone when you press keypad digits. During a call you might enter the DTMF to access Interactive Voice Response (IVR) systems such as voicemail, calling card services, and so on. DTMF is transported the same way as voice in the PSTN.

There are two methods of providing this DTMF capability in an IP network:

Out-of-band:

H.323 provides the DTMF digit support using the User Input Indication (UII) H.245 message.

In-band:

Media gateways or the VDAC-ONE card can provide DTMF digits in separate RTP packet formats.

Media streams can accurately transmit DTMF digits "in-band" using high bit-rate CODECS. Media gateways or the VDAC-ONE card with high bit-rate CODECS can reproduce DTMF digits in the same manner as it creates voice packets.

Converged networks contain media gateways and other devices with high bit-rate and/or low bit-rate CODECS. High bit-rate CODECS, such as G.711, G.726, and G.727, reproduce DTMF digits accurately. However, low bit-rate CODECS, such as G.729, and G.723.1 require DTMF tones to be put in a separate RTP payload format because they cannot reproduce DTMF tone signals accurately enough for automatic recognition. Using separate RTP payload formats for both high and low bit-rate CODECS is one way to address DTMF tone reproduction in a standard way in the IP media stream.

The CSP is capable of supporting all methods of handling DTMF digits for ultimate partner flexibility. The current plan for DTMF digit support in this version of the CSP system is as follows:

Out-of-band DTMF digit support:

H.323 signaling support with the H.245 message set

In-band DTMF digit support with VDAC-ONE for high bit-rate CODECS such as G.711, G.726, and G.727:

VDAC-ONE RTP payload formats (all CODECS)

Hookflash Relay

A 'hookflash" indication is a brief on-hook condition that occurs during a call. For example during a call, a phone user quickly depresses and then releases the hook switch on their telephone. It is not long enough to be interpreted as a signal to disconnect the call, but telephone switches and PBXs are frequently programmed to intercept hookflash indications and use them as a way to allow a user to invoke supplemental services. For example, your local service provider may allow you to enter a hookflash as a means of switching between calls if you subscribe to a call waiting service.

In the traditional telephone network, a hookflash results in a voltage change on the telephone line. Since there is no equivalent of this voltage change in an IP network, the ITU H.245 standard defines a message representing a hookflash. To send a hookflash indication using this message, an H.323 endpoint sends an H.245 User Input Indication message containing a "signal" structure with a value of "!". The value represents a hookflash indication.

The CSP H.323 implementation includes support for relaying hookflash indications using the H.245 User Input Indication message.

CODEC Negotiation

CODEC negotiation allows the gateway to offer several CODECS during the H.245 capability exchange phase and ultimately settle upon a single common CODEC during the call setup. This increases the probability of establishing a connection because there is a greater chance of overlapping audio capabilities between endpoints. During the call setup phase, the gateway uses the highest priority CODEC selected from the list that it has in common with the remote endpoint. It also adjusts to the CODEC selected by the remote endpoint so that a common CODEC is established for the receive and transmit audio directions.

H.323 Offer in Relation to IMTC Testing and iNOW! Profile Criteria

IMTC stands for the International Multimedia Telecommunications Consortium, Inc., a non-profit corporation comprising more than 120 organizations around the globe. The IMTC's mission is to promote and facilitate the development and implementation of interoperable, multimedia, conferencing solutions based on open international standards -- particularly the multimedia conferencing standards adopted by the International Telecommunication Union (ITU), as well as other standards organizations.

Table A-1 IMTC VoIP H.323 Scoresheet - CSP as a Gateway Entity

Elements | Supported | Notes
--- | --- | ---
Call Direction: (O)riginate/(R)ecieve | Yes |
GRQ/GCF RRQ/RCF URQ/UCF | Yes |
BRQ/BCF | Yes |
IRQ/IRR/IACK/INAK | Yes |
GK Routed Call | Yes |
Gateway Resource Availability | No |
PreGranted ARQ | Yes |
Q.931 Connection | Yes |
Fast Start | Yes |
Overlapped Sending | No |
H.245 Tunneling | No |
Q.931 Multiplexing | No |
H.245 Connection Establishment | Yes |
Empty Term Cap Set | Yes |
MC Cascading | No |
Supplementary Services H.450 | No |
ReplacementFor | No |
Request Mode | No | Future Release
CommunicationModeCommand | No |
H.235 | No |
T.38 FoIP | No | Future Release
IP Addressing | Yes |
E.164 Alias Addressing | Yes |
H.323 ID Alias Addressing | Yes |
UniCast RTP/RTCP | Yes |
MultiCast RTP/RTCP | No |
G.711 | Yes |
G.726 | No |
G.723.1 | Yes |
G.722/G.722.1 | No |
G.728 | No |
G.729 (A, B) | Yes | G.729C is not supported
H.261 | No |
H.263 | No |
Data Channel (T.120) | No |

IMTC iNOW!

IMTC iNOW! stands for "interoperability NOW!". IMTC iNOW! is an industry initiative to achieve interoperability as soon as possible between different vendor's IP telephony equipment platforms. IMTC iNOW! is not a standard and it is not proprietary.

IMTC iNOW! is an initiative that is supported by the major players in IP telephony including Dialogic, with new supporters being added all the time. Supporters of this initiative have committed to building or buying equipment that follows the IMTC iNOW! Profiles, publicly available documents that draw upon existing standards such as H.323. Any vendor that follows these Profiles will have the blueprint to build or operate IMTC iNOW! compliant equipment.

Table A-2 IMTC iNOW! Profile Testing Criteria

Elements | Supported | Notes
--- | --- | ---
SRV Discovery | No | Future Release
TXT Discovery | No | Future Release
A Record Discover | No | Future Release
Pre-Configured ID Discovery | Yes |
GRQ Discover | Yes |
GRQ/GCF RRQ/RCF URQ/UCF | Yes |
GK Routed Call | Yes |
Pre-Granted ARQ | Yes |
Q.931 Connection | Yes |
Fast Start | Yes |
H.245 Tunneling | No |
Lightweight RRQ(Keep Alive) | Yes |
H.323 Annex J Authentication | No |
H.323 Annex J Integrity | No |
E.164 Addressing | Yes |
E-mail Addressing | Yes |
Keypad entries (Q.931 Info Msg.) | No |
Alternate GK | Yes |
Status Inquiry/Status | Yes |
Unicast RTP/RTCP | Yes |
G.711 | Yes |
G.723.1 | Yes |
G.729 (A, B) | Yes | G.729C is not supported
H.245v4 | No | Future Release
H.245v6 syntax for Fax | No | Future Release
Interoperability with Simple Endpoint Type (SET) devices implementing the minimum requirements as defined by H.323 Annex F | No | Future Release

Restrictions

The CSP H.323 Version 2 offering does not operate on Release 5.x. If you are planning to use an CSP H.323 Version 2 Platform, your software requires Release 8.0 or later and the following hardware:

CSP Matrix Series 3 Card

IP Signaling Series 3 card

VDAC card or IP Network Interface card for relaying RTP streams

DSP-ONE or DSP Series 2 card for detecting/generating DTMF Tones

Feature Limitations:

Gatekeeper Functionality NOT supported

Voice Only - Video is NOT supported

No redundancy in the IP Signaling Series 3 card in this release.

Supported Standard MIBs and RFCs

No MIBs are supported by this feature release.

This feature provides support for the ITU H.323 V2 teleconferencing standard.

ITU-T standard defines a set of call control, channel setup, and codec specifications for transmitting real-time voice and video over networks that do not offer guaranteed service or quality of service.
Internet Protocol. Part of the TCP/IP family of protocols used to route messages and tracks the addresses of nodes.
Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.
International Telecommunications Union (UN)
The Registration, Admission, and Status messages communicated between two H.323 entities for example between an Endpoint and a Gatekeeper.
Real-Time Transport Control Protocol.
Call signaling protocol for setup and termination of calls.
A device that translates calls between an IP network and another network, typically the PSTN.
An H.323 entity on the network that provides address translation and controls access to the network for H.323 terminals and other end points. The gatekeeper may also provide other services to the endpoints such as bandwidth management and locating gateways.
Session-Initiation Protocol. A signaling protocol used for establishing sessions in an IP network. A session could be a simple, two-way telephone call, or it could be a collaborative multi-media conference session.
Interworking is a software feature within the Excel platform call control layer that enables protocol conversion by analyzing and converting Network Signaling (NS) Layer 3 information.
Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).
Coder/Decoder. A CODEC converts voice signals from their analog form to digital signal acceptable to modern digital transmission systems.
Digital Signal Processor
DTMF. Method by which the digits (0-9) and symbols (* and #) are generated from a handset, represented by two tones, one high and one low frequency (touchtone dialing).
See Integrated Voice Response.
Public Switched Telephone Network
Admission Request
Address format for ISDN networks. The international public telecom-munications numbering plan. A standard set by ITU-T for addressing telephone numbers. See ITU Recommendation E.164 (1991).
An H.323 terminal or gateway, or MCU. An endpoint can call and be called. It generates and/or terminates the information stream.