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Feature Overview
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In general, fax/modem cards are not supported over VoIP links.
Contact your network management, provisioning, or operations team to determine what your
network supports.
Voice Handling
The Cisco uBR924 cable access router supports the following compression and decompression
algorithms (CODECs):
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G.711 A Law 64000 bps
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G.711 u Law 64000 bps
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G.723.1 5300 bps
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G.723.1 6300 bps
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G.726 16000 bps
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G.726 24000 bps
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G.726 32000 bps
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G.728 16000 bps
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G.729 Annex-A 8000 bps
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G.729 8000 bps — Default CODEC for telephone calls
Caution
your network to adequately support VoIP typically involves a series of protocols and features geared to
support Quality of Service (QoS).
To achieve acceptable voice quality and reduce network bandwidth usage, several voice processing
techniques and services are employed, including echo cancellation, voice compression, Voice
Activity Detection (VAD) or silence compression, and Dual Tone Multi- Frequency (DTMF) tone
detection and generation.
The Cisco uBR924 cable access router supports multiple QoS service IDs (SIDs), enabling multiple
classes of service on the cable interface. This enables VoIP and data traffic to be treated separately,
with all data assigned to a default class of service, while VoIP traffic is assigned to a different class
of service. Thus, voice traffic from the Cisco uBR924's telephone ports can take precedence over the
data traffic coming from the Ethernet interfaces.
Note
connected to a CMTS that supports multiple classes of service per router. In addition, the router's
configuration file must specify the use of multiple classes of service.
If the Cisco uBR924 interoperates with a DOCSIS 1.0 CMTS that does not support multiple CoS per
router, voice traffic will be transmitted on a "best effort" basis along with data traffic. This may cause
poorer voice quality and lower data throughput when calls are being made from the router's
telephone ports.
12
Cisco IOS Release 12.0(7)T
Because voice transmission is delay-sensitive, a well-engineered network is critical. Fine-tuning
Separate class of service (CoS) streams are only available when the Cisco uBR924 is
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