Traditionally, Ethernet technologies (and the
IP layers above them) have been built upon an architecture where false packet acceptance
cannot statistically occur. To achieve FPA performance acceptable for Ethernet
and IP delivery, the 64/65-octet layer appends every frame (or fragment) with a CRC
in addition to the Ethernet FCS. The combination of these two error-checking codes
practically eliminates the possibility of FPA, thus maintaining the historically high
reliability of Ethernet.
These changes result in a more efficient and more reliable access network. For example,
carrying Ethernet over ATM results in 20??“50 percent overhead, and carrying
Ethernet natively via Mid-Band Ethernet results in less than 5 percent overhead. This
allows carriers to squeeze more bandwidth (and more revenue) out of their existing
infrastructure.
Multipair Aggregation
The loop aggregation techniques of IEE 802.3ah are simple and powerful. Frames are
passed to the loop aggregation layer from the higher layer, where they are fragmented
and distributed across the loops within the aggregate. When transmitted across the individual
loops, a fragmentation header is prepended (see Figure 5.
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