VOIP CH 11
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is considered the latest version as ratified by ITU. H.323
H.323v5 (version 5)
created by ITU-T for transmitting audio and video and data
for Integrated Services Digital Network (ISDN)
for plain old telephone service (POTS)
Also called endpoints, terminals provide point-to-point and multipoint conferencing for audio and, optionally, video and data
(end points at a work station)
from ip based network to interconnect to Public
Switched Telephone Network (PSTN) or ISDN networks for H.323 endpoint internetworking
(ip based to PSTN or ISDN)
provide admission control and address translation services for terminals or gateways.
(call control between device)
Devices that allow two or more terminals or gateways to conference with either audio and/or video sessions
Multipoint control units (MCU)
from analog to digital
Encodes the signal from the audio equipment for transmission and decodes the incoming audio code
Formats or recieves the transmitted audio, video, data, control streams, and messages onto network interface.
Provides H.225 and H.245 call control, capability exchange, messaging, and signaling of commands for proper operation of the terminal.
system control unit
Optional, but if provided, must be capable of encoding and decoding video according to H.261/H.263 standards.
call setup and teardown on both the IP network and pbx
acts as an H.323 terminal or MCU on the network and an SCN (Switched Circuit Network )terminal or MCU on the SCN
translates between audio,
video, and data transmission formats as well as communication systems and protocols.
it does conversion and transcoding between the ip network(H.323 terminal) and the PBX network(SCN)
provides pre-call and call-level control services to H.323 endpoints.
do have more then one so it can be redundent
logically separated from the other network elements in H.323 environments.
who preforms the following
Address Translation-Provides endpoint IP addresses
(such as <email@example.com>) or E.164 addresses (standard phone numbers).
Admissions Control- Provides authorized access, (ARQ/ACF/ARJ) messages
Bandwidth Control- managing endpoint bandwidth requirements, BRQ/BCF/BRJ) messages
Zone Management- Provided for registered terminals, gateways, and MCUs
is an endpoint that supports multipoint conferences
it supports centralized multipoint conferences
consists of MC and MP
MCU( multipoint control unit)
supports conferences between three or more endpoints in a multipoint conference.
can be resident in a terminal, gateway, gatekeeper, or MCU
transmit the capability set to each endpoint
multipoint controller (MC)
receives audio, video, and/or data streams
distributes them to endpoints participating in a multipoint conference
multipoint processor (MP)
protocols are supported by both reliable(TCP) and unreliable(UDP) packet delivery mechanisms over data networks
supports call admissions, setup, status, teardown, media streams, and messages
Most H.323 implementations today use what protocol
Provides pre-call control in H.323 gatekeeper-based networks.
Registration, Admissions and Status (RAS) Signaling
Used to connect, maintain, and disconnect calls between endpoints.
Call control signaling
Provides the reliable H.245 channel that carries media control messages. The transport occurs with an unreliable UDP stream.
Media control and transport
a device that is between call set up and and a zone that is authenticated
is established between endpoints and gatekeepers
unreliable UDP connection
independent of the call control signaling and media transport channels
The gatekeeper discovery multicast address is
the gatekeeper UDP discovery port is
the gatekeeper UDP registration and status port is
A multicast message sent by an endpoint looking for the gatekeeper.
Gatekeeper Request (GRQ)
The reply to an endpoint GRQ indicating the transport address of the gatekeeper’s RAS channel.
Gatekeeper Confirm (GCF)
Advises the endpoint that the gatekeeper does not want to accept its registration. This is usually due to a configuration on the gateway or gatekeeper.
Gatekeeper Reject (GRJ)
Enables gateways, endpoints, and MCUs to join a zone and inform the gatekeeper of their IP and alias addresses.
Occurs after the discovery process, but before you can attempt any calls.
To obtain contact information when only alias information is available.
messages between endpoints and gatekeepers provide the basis for call admissions and bandwidth control
by confirming or rejecting an request.
gatekeeper can obtain status information from an endpoint
to monitor whether the endpoint is online and offline due to a failure condition.
is initially managed through the admissions exchange between an endpoint and the gatekeeper within the ARQ/ACF/ARJ
looks only at its static bandwidth table to determine whether to accept or reject the bandwidth request.
In H.323 networks, call control procedures are based on International Telecommunication Union (ITU)
which specifies the use and support of Q.931 signaling messages.
A reliable call control channel is created across an IP network on TCP port
1720 (the well-known port for H.323).
no gatekeeper involved but only to see requests and conformations (ARQ and ACF)
Call signaling messages are sent directly between two endpoints
Direct Endpoint Call Signaling
Call signaling messages are routed through a gatekeeper
q.931 goes between the end point and the gatekeeper
alerting and connecting go through gatekeeper
GKRCS (Gatekeeper Routed Call Signaling)
Proxy designed for H.323 and its at what level
application layer (Layer 7)
Can manage QoS for a terminal that doesn’t support
a hybrid system constructed of centralized intelligent gatekeepers, MCUs, and less intelligent endpoints (terminals)
When high-density gateways are needed for PSTN interconnection, alternatives such as
Media Gateway Control Protocol (MGCP) and H.248 (MEGACO)
cisco prioperty end point is
sip is more common in an
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