Port Features
Page 60 7750 SR Interface Configuration Guide
Link Fragmentation and Interleaving Support
Link Fragmentation and Interleaving (LFI) provides the ability to interleave high priority traffic
within a stream of fragmented lower priority traffic. This feature helps avoid excessive delays to
high priority, delay-sensitive traffic over a low-speed link. This can occur if this traffic type shares
a link with lower priority traffic that utilizes much larger frames. Without this ability, higher
priority traffic must wait for the entire packet to be transmitted before being transmitted, which
could result in a delay that is too large for the application to function properly
For example, if VoIP traffic is being sent over a DS-1 or fractional DS-1 which is also used for
Best Effort Internet traffic, LFI could be used so the small (usually 64-128B) VoIP packets can be
transmitted between the transmission of fragments from the lower priority traffic.
Figure 6 shows the sequence of events as low priority and high priority frames arrive and are
handled by LFI.
Figure 6: Frame Sequence of Events
1. A low priority frame arrives in the low priority queue. At this particular instant, there are
no packets in the high priority queue so low priority frame is de-queued and passed to the
fragmentation mechanism for MLPPP.
2. The original packet is divided into ānā fragments based on the size of the packet and the
fragment threshold configuration.
3. The fragments are then transmitted out the egress port.
4. After the transmission of the fragments has begun, high priority frames arrive in the high
priority queue.
5. The transmission of the remaining fragments stops and the high priority packets are
transmitted out the egress interface. Note that high priority packets are not fragmented.
6. When the high priority traffic is transmitted, the remaining lower priority fragments are
then transmitted.
Fig_2
MLPPP
Fragmentation
High Priority Queue
Egress
Low Priority Queue
4
1 2 6 5 3
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