Therefore, the links are not required to participate in any way and can be
any bit rate or format, utilizing copper or fiber. Skew compensation is included so the
individual channels are not required to travel the same path through the network.
Historically, different types of payloads are not combined by transport systems into
a single channel. The ability to adapt payloads of any type is a differentiating factor for
this new technology. Each payload in the channel may be a different format and have
different performance and bandwidth requirements. Supporting requirements ranging
from fixed bit rate (TDM) to burst data payloads are accomplished by mapping all
clients into a common structure call a Payload Data Unit (PDU). Once in this common
structure, the differences in the payloads are reflected in the amount of bandwidth and
the priority assigned to each payload.
Another basic feature provided by circuit bonding is channel protection. Failures in
the individual channels are recognized quickly and inoperable channels are removed
280 Chapter 10
from service. The payloads continue to be supported using the bandwidth available in
the remaining operational channels.
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