Alcatel-Lucent OmniAccess 5740 - LFI Overview; Alcatel-Lucent Specific Overview on LFI Features; LFI Scenario

Link Fragmentation and Interleaving (LFI)
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
LFI OVERVIEW
Link Fragmentation and Interleaving (LFI) is a Layer 2 technique in which all the
Layer 2 frames are broken into small, equal-size fragments, and transmitted over
the link in an interleaved fashion.
Link Fragmentation and interleaving feature for MLPPP and FR supports the
transport of real-time (voice) and other (data) traffic on lower-speed PPP and FR
links without causing excessive delay to the real-time traffic. The feature enables
delay-sensitive real-time packets and packets that are not real-time data, to share
the same link by fragmenting the long data packets into a sequence of smaller
data packets (fragments). The fragments are interleaved with the real-time
packets. On the receiving side of the link, the fragments are reassembled and the
packet reconstructed. This method of fragmenting and interleaving helps
guarantee the appropriate Quality of Service (QoS) for the real-time traffic.
Consider a 1500 byte data frame that is being sent out of a 64 Kbps serial
interface. The interface, in this case, needs 187ms just to place that data frame on
the wire. If a smaller packet (for example, a voice frame) were sitting behind that
data frame, that frame might have already experienced excessive "serialization"
delay before it was ever placed on the wire. LFI mechanisms fragment larger
payloads to specified fragment sizes and then interleave the smaller payloads
among the fragments, greatly reducing the serialization delay that is experienced
by the smaller payloads.
Figure 42: LFI Scenario
ALCATEL-LUCENT SPECIFIC OVERVIEW ON LFI FEATURES
The following features are available with the current release:
• The OmniAccess 5740 USG supports RFC 1990 (MLPPP) without necessarily
conforming to all the optional items mentioned in the specification.
• Multilink PPP with interleaving
• FRF.12 LFI is used with Frame Relay data connections.