Which of the following terms describes LFI?

A.
a QoS model

B.
a queuing method

C.
a link efficiency mechanism

D.
a resource reservation method

E.
a congestion avoidance mechanism

Explanation:
Link fragmentation and interleaving (LFI) is a link efficiency mechanism. Without LFI, small packets, such as
voice packets, can become stuck behind large packets as the large packets are transmitted through an
interface, thereby causing delay and jitter. LFI breaks up large data packets into small pieces and then
interleaves the small packets among the fragments of the large packet. Another link efficiency mechanism used
by Voice over IP (VoIP) is Compressed Real-time Transport Protocol (cRTP), which compresses the Layer 3
and Layer 4 headers of voice packets to a fraction of their original size.
LFI is a Quality of Service (QoS) feature, not a QoS model. QoS enables a network to treat a specific type of
traffic with a different priority than other types of traffic. For example, QoS can ensure that voice traffic gets
higher priority on a network than data traffic. QoS models include the best-effort model, the Integrated Services
(IntServ) model, and the Differentiated Services (DiffServ) model. Each QoS model handles packet flows in a
different manner. For example, IntServ requires that applications reserve their end-to-end bandwidth
requirements, and DiffServ prioritizes packets by traffic class. Because of some inherent shortcomings in the
IntServ model, Cisco recommends using DiffServ when delivering voice traffic.
LFI is not a resource reservation method. When IntServ is used, bandwidth resources must be reserved for
each traffic flow. These resources are reserved from the source to the destination by Resource Reservation
Protocol (RSVP).
LFI is not a queuing method. Queuing methods deal with congestion management. Each queuing method
handles network congestion in a different manner. Queuing methods employed by Cisco routers include first-infirst-out (FIFO) queuing, priority queuing (PQ), custom queuing (CQ), round robin (RR), weighted RR (WRR),
weighted fair queuing (WFQ), class-based WFQ (CBWFQ), and low latency queuing (LLQ). By default, Cisco
devices use FIFO queuing for interfaces faster than 2.048 Mbps and use WFQ for serial interfaces at 2.048
Mbps or lower.
LFI is not a congestion avoidance mechanism. Congestion avoidance mechanisms mitigate tail drop, which
occurs when a router drops new packets because its queues are too full to accept them. Congestion avoidance
mechanisms employed by Cisco routers include random early detection (RED), weighted RED (WRED), and
class-based WRED (CBWRED).

Cisco: Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2: Chapter: Link Efficiency
Mechanisms Overview