3Com MSR 50 Series, Руководство по настройке

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2234 C
HAPTER
129: V
OICE
O
VERVIEW
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The VoIP signal processing module generates a dial tone.
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The user hears the dial tone played by the session application and begins dialing
before the dial tone expires.
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The session application collects the digits dialed by the user.
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The session application compares the collected digits with the match template in
real time during digit collection.
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After finding a match template for the called number, the originating VoIP
gateway maps the number to the terminating VoIP gateway.
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The originating VoIP gateway initiates a VoIP call to the terminating VoIP gateway
over the IP network and establishes a logical channel for the call to send and
receive voice data.
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The terminating VoIP gateway receives the call from the IP network and seeks the
destination telephone according to the match template. If the call is to be
processed by a private branch exchange (PBX), the terminating VoIP gateway
passes the call via PSTN signaling to the PBX for processing until the destination
telephone is connected. When the calling party or the called party hangs up, the
conversation ends.
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During call connection, the calling party and called party negotiate the
encoding/decoding method for the call and voice data is transferred through
real time protocol (RTP)
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The RTP voice channel is used to transfer prompt signals during call connection
and other signals suitable for in-band transmission across the IP network.
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When either party hangs up, the session application will end the conversation.
VoIP Features
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Silence compression
The voice traffic to be transmitted can be reduced by automatically detecting the
time ranges of silence in a conversation and stopping generating voice traffic
within these time ranges.
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Comfortable noise
Silent gaps during a call can be filled by comfortable background noise.
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QoS
As the voice service is highly time-sensitive, the priority transmission of voice
packets must be guaranteed. Some measures, such as priority queuing (PQ),
custom queuing (CQ), weighted fair queuing (WFQ), class-based queuing (CBQ),
and real time protocol (RTP) can be adopted on the sender side for this purpose. To
ensure an adequate bandwidth for voice transmission, you can adopt the
committed access rate (CAR) mechanism to implement traffic classification and
policing.
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Fax over IP
On basis of VoIP, the fax over IP (FoIP) system is responsible for setup of fax
channels and the receiving and sending of fax data. FoIP implementation involves