Cisco Cisco IOS Software Release 12.2(14)S
Frame Relay Queueing and Fragmentation at the Interface
Feature Overview
2
Cisco IOS Release 12.2(14)S
the largest high-priority frames. This configuration will prevent priority traffic from being fragmented
and queued behind non-priority fragmented frames. If the size of a priority frame is larger than the
configured fragment size, the priority frame will be fragmented. Local Management Interface (LMI)
traffic will not be fragmented and is guaranteed its required bandwidth.
and queued behind non-priority fragmented frames. If the size of a priority frame is larger than the
configured fragment size, the priority frame will be fragmented. Local Management Interface (LMI)
traffic will not be fragmented and is guaranteed its required bandwidth.
When a low-latency queueing policy map is applied to the interface, traffic through the interface is
identified using class maps and is directed to the appropriate queue. Time-sensitive traffic such as voice
should be classified as high priority and will be queued on the priority queue. Traffic that does not fall
into one of the defined classes will be queued on the class-default queue. Frames from the priority queue
and class queues are subject to fragmentation and interleaving. As long as the configured fragment size
is larger than the high-priority frames, the priority queue traffic will not be fragmented and will be
interleaved with fragmented frames from other class queues. This approach provides the highest QoS
transmission for priority queue traffic.
identified using class maps and is directed to the appropriate queue. Time-sensitive traffic such as voice
should be classified as high priority and will be queued on the priority queue. Traffic that does not fall
into one of the defined classes will be queued on the class-default queue. Frames from the priority queue
and class queues are subject to fragmentation and interleaving. As long as the configured fragment size
is larger than the high-priority frames, the priority queue traffic will not be fragmented and will be
interleaved with fragmented frames from other class queues. This approach provides the highest QoS
transmission for priority queue traffic.
illustrates the interface queueing and fragmentation
process.
Figure 1
Frame Relay Queueing and Fragmentation at the Interface
Subrate shaping can also be applied to the interface, but interleaving of priority frames will not work
when shaping is configured. If shaping is not configured, each PVC will be allowed to send bursts of
traffic up to the physical line rate.
when shaping is configured. If shaping is not configured, each PVC will be allowed to send bursts of
traffic up to the physical line rate.
When shaping is configured and traffic exceeds the rate at which the shaper can send frames, the traffic
is queued at the shaping layer using fair queueing. After a frame passes through the shaper, the frame is
queued at the interface using whatever queueing method is configured. If shaping is not configured, then
queueing occurs only at the interface.
is queued at the shaping layer using fair queueing. After a frame passes through the shaper, the frame is
queued at the interface using whatever queueing method is configured. If shaping is not configured, then
queueing occurs only at the interface.
Note
For interleaving to work, both fragmentation and the low-latency queueing policy must be configured
with shaping disabled.
with shaping disabled.
The Frame Relay Queueing and Fragmentation at the Interface feature supports the following
functionality:
functionality:
•
Voice over Frame Relay
•
Weighted Random Early Detection
•
Frame Relay payload compression
•
IP header compression
Incoming packets
Voice
packets
Data
packets
Priority queue
Priority queue and
class queues
Transmitted packets
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Classify
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