3), which includes a
sequence number and frame markers. This header is used by the receiver to resequence
the fragments and to reassemble them into complete frames.
To allow vendor differentiation, the algorithm for partitioning the frames over the
loops is not specified. However, the partitioning algorithm must obey certain rules in
that fragments must obey size constraints and that loops in an aggregate must obey
rate and differential delay constraints. As long as the loop aggregation algorithms obey
these constraints and restrictions, any fragmentation algorithm can be handled by the
reassembly process, yielding a very flexible and interoperable solution.
Figure 5.3 Multipair aggregation in IEEE 802.3ah
Loop aggregation ??“ fragmentation
Frame
Frag-1 FH Frag-1 FH Frag-1 FH
Loop aggregation ??“ reassembly
FH = fragment header
SeqNum SOP
SOP = start of packet flag
EOP = end of packet flag
SeqNum = sequence number
Frame
EOP
136 Chapter 5
Not Link Aggregation Although they may look similar, loop aggregation as defined in
802.3ah is very different than link aggregation as defined in 802.3ad. Loop aggregation
fragments individual frames into variable-sized segments in order to minimize latency
and maximize utilization of disparate speed links.
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