are less than or equal to 768 Kbps, the delay through the SP network could introduce packet loss due to
jitter buffer over and under runs. In most cable environments, LFI is not needed. However, there is no
method in this environment of informing the QoS-enabled router of changes in the load present on the
cable segment. For QoS to be effective in this case you must shape to a worst-case rate to protect VoIP
bearer and control traffic from congestion in the cable segment. The QoS provided in this environment
may not be sufficient to guarantee voice quality as the QoS- enabled router does not have vision into the
state of the cable network.
environment that supports IP telephony.
wireless or DSL with ISDN as the Layer 2 transport (IDSL), you can provide scheduling services via
LLQ/CBWFQ for the traffic that has been tagged with the appropriate DSCP PHB labels by the IP
phone. You can also shape the traffic to the speeds guaranteed to by the SP. You cannot, however,
provide LFI for these types of connections. This means that on links where either the link serialization
rate or virtual circuit speeds are equal to or less than 768 Kbps, you cannot provide sufficient QoS
services to guarantee voice quality.
end