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Collaboration, Voice & AV · Advanced

Link Fragmentation and Interleaving (LFI)

A QoS tool that fragments large data packets on slow links so small voice packets can be interleaved between fragments.

Definition

LFI reduces serialization delay on low-speed links by limiting the size of data fragments, typically targeting 10 ms of serialization. It is implemented with Multilink PPP (MLP LFI) or FRF.12 for Frame Relay. On links faster than about 768 kbps the serialization delay of a full-size packet is already small, so LFI is generally unnecessary.

Example

ppp multilink fragment delay 10 and ppp multilink interleave enable LFI on a 512 kbps branch link.

Exam tip

LFI is only recommended for links slower than 768 kbps; on fast links it adds overhead with no benefit.

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