3Com CoreBuilder 7000, Руководство по эксплуатации

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5
E
STABLISHING
ATM C
HANNELS
ATM is a connection-oriented transport service, much like a telephone.
Unlike Ethernet, where data is sent out on a common bus, ATM requires
that a path or
virtual channel be established to carry the call from the
source station to the destination station before data transmission can
begin. A virtual channel may be established either manually through
management or automatically through the processes of
signaling and
routing .
This chapter provides basic concepts and information about:
Virtual Channels
VP Tunneling
Signaling — External Links
Signaling AAL
Call Admission Control
UNI Signaling 4.0 Features
Routing — Internal Links
Physical-Link Failure Indicator
Virtual Channels
A virtual channel
is a communications path that can carry a single call
from the source station to the destination station. The term virtual is used
because the channel does not necessarily correspond to a single physical
line and, in fact, usually passes through many different network devices
and cables before reaching its destination.
Local Links and
Connections
A virtual channel is built from a series of local links of two types:
External links between ports of adjacent ATM devices
Internal links between input and output ports of an ATM device