Link Fragmentation and Interleaving (LFI)
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
OVERVIEW OF LFI IN FRAME RELAY
LFI is supported for FR and FR sub-interfaces.
LFI in FR is implemented through End-to-End Fragmentation technique as per the
FRF.12 Frame Relay Forum Standard. End-to-End fragmentation is limited to
fragmenting frames on selected PVCs. Since DLCI 0 is never carried end-to-end,
it is never fragmented using End-to-End fragmentation.
Fragments are created on the FR link based on the fragment size configured on
FR interface. The fragment size is fixed irrespective of the underlying link speed.
To decrease the serialization delay, interleaving functionality must be performed.
Interleaving functionality is implemented through QoS configured on the FR
interface.
END-TO-END FRAGMENTATION
End-to-End fragmentation is used between two end devices and is restricted to
use on PVCs only. It is useful when the PVC is configured through slower trunk
interfaces.
PACKET FORMATS
End-to-End Fragmentation Format
For End-to-End fragmentation, a two-octet fragmentation header follows the
FRF.3.1 multiprotocol encapsulation header. The Network Layer Protocol ID
(NLPID) 0xB1 has been assigned to identify this fragmentation header format.
Figure 46: End-to-End Fragmentation Format
The (C)ontrol bit is set to 0 in all fragments. It is reserved for future control
functions. There is a separate sequence number maintained for each fragmented
PVC between DTE peers.
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