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Cisco IP Telephony Network Design Guide
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Chapter 8 Quality of Service
WAN QoS Model
Traffic Shaping
Traffic shaping is required for multiple access, non-broadcast media such as ATM
and Frame Relay, where the physical access speed varies between two endpoints.
Traffic shaping technology accommodates mismatched access speeds. In the case
of Frame Relay with FRF.12, traffic shaping also allows delay variation, or jitter,
to be bounded appropriately. For ATM, data rates are such that fragmentation is
typically not required. Figure 8-5 demonstrates traffic shaping with Frame Relay
and ATM.
Figure 8-5 Traffic Shaping with Frame Relay and ATM
T1
T1
768 kbps
512 kbps
256 kbps
128 kbps
Frame Relay / ATM
Central site
Remote sites
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