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IP Telephony Standards and Protocols D-15

Appendix D - Voice Over the Internet Protocol

IP Telephony Standards and Protocols

The Discovery VoIP card uses the H.323 Revision standard for call processing. This is an

updated version of the H.323 standard. It provides a set of standards defining real-time

multimedia communications and conferencing over packet-based networks. These

standards define how components that are built in compliance with H.323 set up calls,

exchange compressed audio and video, participate in multi-unit conferences, and operate

with non-H.323 endpoints.

The IP telephony standards/protocols shown in Table D-4 are adhered to by the Discovery

VoIP card.

Table D-4: IP Telephony Standards/Protocols

Standard Description

H.323 Revision 2 Supports H.323 terminals and is the basis for all IP telephony.

H.225 Media Packetization Provides media packetization and synchronization for video/

audio telephony on non-guaranteed quality of service LANs.

H.245 DTMF Signaling

Close Logic Signaling

Round Trip Signal

Arbitration of GSM compression -- provides the new audio

capabilities and supports the signaling entities required for call

control functions for multimedia communications, while it

specifies the in-band signaling protocol necessary to establish a

call, determine capabilities, and issue the commands necessary

to open/close the media channels.

Supports signaling of a pair of associated unidirectional channels

which allows for the establishment of a T.120 data channel.

Allows determination of the round trip delay between two

communicating channels.

G.165 Echo Cancellation When echo is present, a preprogrammed button is available to

increase or decrease the latency of that call. Upon termination of

each call, the unit restores the default setting.

G.711 Pulse Code Modulation of

Voice Frequencies

TransmitsandreceivesA-lawandU-lawPCMvoiceatdigitalbitrates

of 48, 56, and 64 Kbps. It is used for digital telephone sets on digital

PBX and ISDN channels. Support for this algorithm is required for

ITU-T compliant videoconferencing. (slowest protocol)

G.723.1 5.3 Kbps compression for

dual rate speech coders

for multimedia

communications

Runs at 6.3 or 5.4 Kbps a compression and uses linear predictive

coding directory for an open architecture to ensure connectivity

with other switches. Moreover, this compression helps provide

smoothness. (Default)

G.729 Speech encoding 8 Kbps Encodes/decodes speech at the rate of 8 Kbps using conjugate-

structure, algebraic-code excited linear predictive methods.

Q.931 Messages:

-Progress

- Setup

- Acknowledgment

Creates a unique global identifier that allows all messages

associated with a call to be interoperable between the

registration, administration and status protocol used in IP

networks utilizing the Q.931 signaling protocol used in

circuit-switched telephony networks.

Supports messages that are used for call signaling, including all

mandatory and conditionally mandatory messages, some

optional messages and information elements, and the facility

message defined in Q.931 and Q.932.

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